Planta (Berl.) 97, 50--61 (1971) 9 by Springer-Verlag 1971
Influence of IAA upon the Longitudinal and Tangential Movement of Labelled Sugars in the Phloem of Willow N. W . L~PP a n d A. J. :PEEL Department of Botany, University, Hull, England Received October 17, 1970
Summary. Using a bark abrasion technique, the influence of IAA upon patterns of sugar translocation in isolated stem segments of Willow (Salix viminalis L.) has been studied. IAA was found to exert a considerable influence over translocation in both a longidutinal and tangential direction. Studies on longitudinal movement have led to the postulation of two possible effects of IAA on this system. Firstly a stimulation of sugar loading from the storage parenchyma into the sieve elements as described by Lepp and Peel (1970), and secondly a direct effect upon the longitudinal transport process. The situation with regard to the tangential transport system is not as clear in all its aspects, though once again it is postulated that IAA may have a direct effect upon the movement of sugars in the tangential transport system. Introduction Since t h e d i s c o v e r y t h a t I n d o l y l - 3 - a c t e t i c a c i d (IAA) could m o d i f y t h e d i s t r i b u t i o n p a t t e r n of 14C labelled sugars w i t h i n t h e p l a n t (Booth et al, 1962), t h e role of p l a n t h o r m o n e s in t h e r e g u l a t i o n of assimilate d i s t r i b u t i o n has been f i r m l y e s t a b l i s h e d (reviews of Moorby, 1968; M i l t h o r p e a n d Moorby, 1969).
It is clear that two possibilities exist which could explain the effects of growth substances on the phloem transport system; they could either affect the unloading of solutes at sinks or they could directly affect the longitudinal transport system within the sieve tubes. The work of Davies and Wareing (1965), Seth and Wareing (1967) and Morris and Thomas (1968) could all be explained in terms of the effect of growth substances on the rate of unloading of solutes at sinks. These workers applied growth substances to the end of stems from which the growing a p e x h a d been excised, a n d i t is therefore n o t u n r e a s o n a b l e to a s s u m e t h a t t h e m e t a b o l i c a c t i v i t y , a n d hence t h e sink c a p a c i t y , of t h e c u t s t e m m a y h a v e been e n h a n c e d b y t h e a p p l i e d g r o w t h substances. C e r t a i n l y I A A can affect t h e r a t e of loading of sugars into sieve elements as d e m o n s t r a t e d b y the w o r k of L e p p a n d Peel (1970) on willow. T h e r e a p p e a r s to be little, if any, i n c o n t r o v e r t i b l e evidence t h a t growth~substances can d i r e c t l y affect t h e l o n g i t u d i n a l t r a n s p o r t mechan i s m in sieve tubes. D a v i e s a n d W a r e i n g (1965) a p p l i e d T I B A to t h e s t e m
Movement of Labelled Sugars
51
a t a p o i n t between t h e sites of g r o w t h substance a n d r a d i o t r a e e r application, a n d f o u n d t h a t this r e d u c e d the effect of I A A u p o n t h e accum u l a t i o n of t h e tracer. T h e y i n t e r p r e t e d these results as i n d i c a t i n g t h a t I A A could exert a n influence u p o n t r a n s l o c a t i o n processes a t a d i s t a n c e from t h e p o i n t of its application. However, recent w o r k b y Mullins (1967-1969) has cast some d o u b t u p o n this i n t e r p r e t a t i o n . H e w et al. (1967) h a v e also p r o d u c e d evidence to suggest t h a t I A A m a y a c t a t a distance from t h e site of its application, a n d their w o r k is n o t complic a t e d b y t h e use of T I B A . I t has r e c e n t l y been suggested t h a t I A A , when a p p l i e d t h r o u g h a b a r k abrasion, m a y move in a p o l a r m a n n e r in the sieve t u b e s of isolated stem segments of willow (Lepp a n d Peel, in t h e press). I t is also k n o w t h a t laC labelled sugars can e x h i b i t a polar d i s t r i b u t i o n in certain tissues. H a r t t a n d K o r t s c h a k (1964) showed t h a t labelled sugars m o v e with a p o l a r d i s t r i b u t i o n in d e t a c h e d leaf blades of sugar cane when t h e apical end of t h e leaf was held u p p e r m o s t . W h e n t h e leaf blade was i n v e r t e d from its n o r m a l position, i.e. when t h e basal end was u p p e r m o s t , no p o l a r distrib u t i o n was found, a s i t u a t i o n v e r y similar to t h a t d e m o n s t a t e d b y L e p p a n d Peel (in t h e press). S h i r o y a (1968) has p r o d u c e d evidence from exp e r i m e n t s with sunflower seedlings t h a t a difference m a y exist between t h e chemical species bearing t h e laC label which are t r a n s l o c a t e d apically as o p p o s e d to those t r a n s l o c a t e d b a s a l l y from a leaf fed w i t h labelled sugars. I t is n o t impossible t h a t t h e p o l a r m o v e m e n t of 14C-labelled sugars in d e t a c h e d sugar cane leaf blades is due to t h e effects of endogenous g r o w t h substances u p o n t h e t r a n s p o r t system. Therefore in view of t h e possibility t h a t g r o w t h substances m a y affect t h e d i s t r i b u t i o n of solutes b y acting d i r e c t l y u p o n t h e l o n g i t u d i n a l transp o r t system, i t was decided to f u r t h e r i n v e s t i g a t e this p r o b l e m using the isolated s e g m e n t s y s t e m described b y L e p p a n d Peel (in t h e press). Investigations were also e x t e n d e d to t h e t a n g e n t i a l t r a n s p o r t s y s t e m of t h e p h l o e m of willow (Peel, 1964) which m a y involve l a t e r a l m o v e m e n t of solutes b e t w e e n sieve elements a n d p h l o e m p a r e n c h y m a cells. Materials and Methods 2-4 year old stems of Salix viminalis L. were collected in the field. These stems were then cut into segments, the length of which varied with the type of experiment. The segments used in the experiments on longitudinal movement were 10 cm in length and 1.5 cm in diameter, whilst those used in the studies on tangential movement were 8 cm in length and had a diameter of 2-3 cms. The tracers used in this investigation were applied on filter paper via a bark abrasion, the technique being essentially the same as that employed by Lepp and Peel (in the press). 0.1 ml of a solution of IAA 2-1~C (specific activity 27.8 mCi/mM), witch a radioactive concentration of 5 ~xCi/mlwas spotted onto the piece of filter paper. In the case of sugar, this was applied as 0.01 ml of a solution of glucose-6-aIt (specific activity 4.9 Ci/rnM) also at a radioactive concentration of 5 ~xCi/ml. 4*
52
N. W. Lepp and A. J. Peel:
At the termination of an experiment radioactivity was extracted from the bark using the techniques described by Lepp and Peel (in the press). The activities of 14C and 3tI in the extracts were determined by liquid scintillation spectroscopy.
Results and Discussion
1. E//ect o / I A A upon Patterns o/Movement o/aH Sugars in a Longitudinal Direction when the Sites o/ A pplication are Spatially Separated P r e v i o u s w o r k (Lepp a n d Peel, 1970) has shown t h a t I A A can ex er t a n influence on t h e d i s t r i b u t i o n p a t t e r n of labelled sugars in tile longit u d i n a l t r a n s p o r t s y s t e m w h e n t h e sites of a p p l i c a t i o n of I A A an d sugars
Table 1. E//ect o] I A A (unlabelled) on the distribution o] 3H-sugars in a longitu-
dinal direction when the sites o[ application are spatially separated
x
A. IAA at apex, 8H glucose in centre
B. IAA at base, ~H glucose in centre
apical
basal
apical
basal
106.5 70.4 370.5 177.1 472.3 38.1 80 176.3 101.5 156
183.5 307.5 394.9 476.2 635 276.8 128.7 340.5 714.8 390.2
121.9 559.4 319.8 58.6 235.5 112.9 327.8 120.7 141.2 172
27.6 20.7 33.9 20.6 29.6 74.3 80.3 81.8 124.2 107.8
174.8~94.5
384.8:t=111.2
x 216.8•
60.0•
All segments horizontal. Results expressed as C. P. M • 10-1. Fidueial limits given at P = 0.05. All samples counted at the same efficiency. IAA employed at a concentration of 10-sM.
are s p at i al l y separated. This effect was observed using a bark strip system, a n d it was decided to see w h e t h e r a similar effect could be produced in isolated s t e m segments. T h e e x p e r i m e n t s were set up as shown in Fig. 1, an d t h e results of one e x p e r i m e n t are p r e s e n t e d in T a b l e l. F r o m these it can be seen t h a t t h e I A A exerts essentially t h e same effect on labelled sugar m o v e m e n t in segments as it does in b a r k strips; the labelled sugar m o v e s a w a y f r o m t h e site of I A A application.
Movement of Labelled Sugars
53
lOcm
lcm 2cm lcm 2cm lcm
2
h
1
5
3
Fig. 1. Experimental technique for studying the effect of IAA applied at a distance from aH glucose upon the pattern of distribution of the latter. 1 Site of application of 3tt glucose. 2 Site of application of unlabelled IAA (10-5M). 3 Site of application of distilled water. 4, 5 Experimental sections
2. E//ect o/ I A A on the Movement o/ aH Sugars in a Longitudinal Direction when Both are Applied at the ~ame Site Segments e m p l o y e d in these e x p e r i m e n t s were p r e p a r e d in a similar m a n n e r to t h a t described b y L e p p a n d Peel (in t h e press). H o w e v e r , in the p r e s e n t e x p e r i m e n t s , t h e b a r k was d i v i d e d l o n g i t u d i n a l l y into two halves b y m e a n s of slits cut into the b a r k on d i a m e t r i c a l l y opposite sites of the stem. A b a r k a b r a s i o n was t h e n p r e p a r e d in t h e centre of each half of the segment. I n these e x p e r i m e n t s , as opposed to those described in section (1), laC labelled I A A was used as well as aH labelled glucose, in order t h a t t h e m o v e m e n t of b o t h labels could be followed. B o t h substances were a p p l i e d to t h e b a r k a b r a s i o n on one side of t h e s t e m (experimental) whilst all-glucose only was a p p l i e d to t h e a b r a s i o n on t h e other side of t h e s t e m to act as a control. The segments were t h e n o r i e n t a t e d in either a h o r i z o n t a l or v e r t i c a l p o s i t i o n for a period of 6 hours. The results from these e x p e r i m e n t s are p r e s e n t e d in Table 2. F r o m these it can be seen t h a t t h e p e r c e n t a g e d i s t r i b u t i o n of a c t i v i t y from t h e ~It glucose is virt u a l l y identical to t h a t of the 14C a c t i v i t y from t h e I A A , a l t h o u g h t h e absolute a c t i v i t y of b o t h tracers in t h e samples varies due to differences in t h e u p t a k e of t h e a p p l i e d c o m p o u n d s b y different segments. W h e n t h e 3H glucose is a p p l i e d b y itself, however, t h e s u b s e q u e n t dist r i b u t i o n of t h e aI-I a c t i v i t y is quite different from when i t is a p p l i e d with I A A . I t m u s t therefore be concluded t h a t t h e I A A is e x e r t i n g considerable influence over t h e m o v e m e n t of labelled sugars. H o w t h e n can we e x p l a i n this effect of I A A ? As m e n t i o n e d in t h e I n t r o d u c t i o n , I A A enhances t h e r a t e of loading of sugars from t h e storage
54
N. W. Lepp and A. J. Peel:
Table 2. Movement o] 14C-labelled I A A and 3H-labelled sugar8 in a longitudinal direction when both are applied at the same site A. Segments vertical, apex uppermost Experimental 14C apex
236 202 477 70 310 90 455 226 384 147
Control 8It
base
apex
3H base
apex
(i) Distribution of total activity recovered (C. P . M ) 573 426 1030 307 288 373 516 417 884 869 1612 451 463 129 838 242 800 569 1473 204 172 167 309 233 804 848 1493 302 415 404 741 211 587 698 1061 460 271 523 956 368
x
259.7 101
x
29.9
551 -r 162
475 • 189
999.3 :L 303
319.5 • 83
base
298 176 486 61 330 456 432 268 308 257 307.2 ~: 104
(ii) Mean % distribution of total activity recovered 70.1 29.9 70.I 52.5 47.5 B. Segments horizontal
Experimental 140 apex
279 672 528 511 324 410 227 476 346 146 x
432.8 4- 94
x
47.5
Control 3H
base
apex
3H base
apex
(i) Distribution of total activity recovered (C. P.M.) 422 308 467 204 516 744 570 183 461 583 509 394 507 564 558 243 445 357 491 227 511 451 560 222 354 251 389 331 297 527 328 353 325 382 358 218 263 161 292 324 391.9 -r 123
452.2 ~_ 75
410.1 • 83
269.9 • 108
base
255 638 175 323 370 376 266 267 318 307 329.5 • 78
(ii) Mean % distribution of total activity recovered 52.5 47.5 52.5 45.7 54.3
All samples counted at the same efficiency. Fiducial limits given at P ) 0 . 0 5 .
Movement of Labelled Sugars IAA
LabelLed sugar
T2o, I
55
o
,
I
"
v
I
Sievetube
j i i
A B Fig. 2. Diagrammatic representation of the possible dual effect of IAA on phloem transport systems. 1 IAA enhances the rate of sugar loading into sieve elements, and thus sets up a gradient of sugar potential from A to B. 2 Labelled sugars loaded into sieve element. 3 IAA stimulates the longitudinal transport system. Labelled sugars entering the system therefore move towards B along a gradient of sugar potential, this movement being enhanced by IAA stimulation of the longidutinal transport system
parenchyma into sieve elements of willow (Lepp and Peel, 1970), but the data presented in Table 2 cannot be explained in these terms; an enhancement of sugar loading would merely lead to more aH sugars being moved, it would not affect their relative distribution apieally and basally from the application point. Is it then not possible that the IAA, if it moves along the sieve tubes, creates sinks in the storage parenchyma cells which then produce a concomitant movement of the labelled sugar ? This possibility seems unlikely, unless IAA has a different effect upon the storage parenchyma when it is present in the sieve tube as opposed to when it is merely applied to the exterior of the phloem. The situation is clearly complicated, but it could well be that once the IAA is present within the sieve tubes, then it exerts a direct effect upon the longitudinal sieve tube transport system. If we now consider the results of the experiments presented in Section l, and also the triple-chambered bark strip experiments described by Lepp and Peel (1970), it becomes apparent that there are two possible effects of IAA which could have produced the observed results. These are (i) an increase in the rate of sugar loading from the storage parenehyma into the sieve elements at the IAA-treated end of the bark, the explanation given by Lepp and Peel (1970), and (ii) an enhancement of longitudinal transport in the sieve tubes once the IAA has entered the transport conduits. These possibilities are illustrated diagramatically in Fig. 2. If IAA does have both these effects upon the phloem transport system, then the data presented in Tables 1 and 2 could be adequately explained. A further point which emerges from the foregoing results concerns their relevance to the suggestion put forward by Lepp and Peel (in the press), that applied IAA moves in a polar manner through the sieve tubes of isolated stem segments. I t must be apparent that the data presented
56
N. W. Lepp and A. J. Peel:
ff% t__scm
!m
l
Fig. 3. Experimental technique for studying the effect of IAA applied at a distance from aH glucose upon the pattern of distribution of the latter in a tangential manner. A Transverse view of the experimental segment. B Longitudinal view of the experimental segment. X Point where the bark was divided into upper and lower sections in experiments employing laC IAA. I Site of application of aH glucose. 2 Site of application of IAA (inactive or 14Clabelled). 3 Site of application of distilled water. 4 Longitudinal girdle below application sites. 5 Lateral girdle separating the experimental bark from the remainder of the segment
here strongly s u p p o r t the suggestion t h a t I A A moves in the sieve tubes. Certainly there can be little d o u b t t h a t the labelled sugars move i n the sieve tubes, therefore it seems reasonable to assume t h a t since the I A A has a n effect on their m o v e m e n t t h e n this m u s t also be t r a n s p o r t e d i n the same system. I t seems inconceivable t h a t I A A could produce the effects d e m o n s t r a t e d b y the e x p e r i m e n t s presented in Section 2 if the I A A were m o v i n g i n a system outside the sieve tubes. I f this l a t t e r s i t u a t i o n existed, t h e n the I A A would surely have a quite different effect on the labelled sugar m o v e m e n t , for if it were present outside the sieve t u b e s t h e n it would affect sugar loading into these cells. Hence we would expect t h a t t h e labelled sugars would move a w a y from the highest c o n c e n t r a t i o n of IAA, n o t towards it.
3. E//ect o / I A A upon Patterns o/Movement o/3H Sugars in a Tangential Direction when the Sites o/Application are Spatially Separated These experiments were essentially similar to those described in Section 1, except t h a t here, the effects of I A A u p o n labelled sugar movem e n t i n a t a n g e n t i a l direction were investigated. Fig. 3 shows the design
Movement of Labelled Sugars
57
of the experiments. The segments were held in a horizontal position. aH glucose was applied t h r o u g h a bark abrasion on the u p p e r m o s t side of the segment, whilst unlabelled I A A was applied t h r o u g h a n abrasion at one side of the stem (1), distilled water as a control being applied to the other (2). Table 3. E]/ect o[ I A A (unlabelled) on the distribution o/8H sugars in a tangential direction when the application sites are spatially separated Experimental Control
Average
424.4 331.2 363.4 360.1 248.3 298.7 52.7 80.1 196 134.6
168.7 90.1 131.8 149.2 209.3 25.5 18.8 59.9 29 51.2
248.9-[- 91.8
93.7 ~ 47.7
Results expressed as C. P. M. • 10-2. Fiducial limits given at P -- 0.05. IAA employed at a concentration of 10-sM.
The results are presented in Table 3. I t can be seen from these t h a t the I A A has a n a p p a r e n t l y quite different effect on the t a n g e n t i a l t r a n s p o r t of sugars when compared with the results from experiments in the longit u d i n a l t r a n s p o r t system (Section 1).
4. E]]eet o] I A A upon Patterns o / M o v e m e n t o] ~H Sugars in a Tangential Direction when Both are Applied at the Same Site These experiments were essentially similar to those described in Section 2, where l o n g i t u d i n a l m o v e m e n t was investigated. The arrang e m e n t of the experiments reported in the present section is shown in Fig. 4, a n d the d a t a from one of these is presented i n Table 4. The results show a p a t t e r n which is very similar to t h a t f o u n d i n the l o n g i t u d i n a l m o v e m e n t e x p e r i m e n t s ; I A A moved from its site of application into one side of a segment in m u c h greater quantities t h a n m o v e d into the other side, a n d the ~H sugars also m o v e d in the same direction. I n the control experiments where 3H glucose only was appJied a n d which were carried out on the same segment, the p a t t e r n s of m o v e m e n t were n o t i n the same sense. W e do n o t know w h y i n e q u a l i t y of m o v e m e n t of I A A occurs be-
58
N.W. Lepp and A. J. Peel:
Table 4. Movement o/l~C-labelled I A A and ~H-labelled sugars in a tangential direction when both are applied at the same site
Experimental 14C
Control ~H
side 1
side 2
side 1
aH side 2
side 1
side 2
A. Distribution of total activity recovered (C. P.M. • 10-1) 1280 29 191 4 154 374 54 1386 8 205 80 298 2249 51 348 7 30 787 1447 175 221 27 93 234 771 73 116 l0 266 51 5264 93 805 13 1132 48 2941 172 431 24 1157 140 925 625 137 90 391 91 60 179 9 26 3 28 3112 262 471 38 2065 256 x
1810 •
x
75.1
304.5 :t: 296
273.7 ~176
444 •
537.1 :E397
230.7 •
B. Mean % distribution of total activity recovered 24.9 75.1 24.9 54.1 45.9
All samples counted at the same efficiency. Fidueial limits given at P = 0.05.
t w e e n t wo sides of a stem, since b o t h sides of the s t e m would a p p e a r to be e q u a l l y suitable for t r a n s p o r t . C e r t a i n l y no p a t t e r n has e m e r g e d f r o m the p r es en t e x p e r i m e n t s which suggests t h a t I A A m o v e s in a polar m a n n e r w h e n applied to t h e s t e m in t h e position shown in Fig. 4, as it does in a l o n g i t u d i n a l direction with respect to t h e morphological a p e x an d base of a segment. H o w e v e r , it is clear from these e x p e r i m e n t s t h a t I A A would a p p e a r to h a v e a direct effect u p o n t h e t a n g e n t i a l t r a n s p o r t s y s t e m which m o v e s atI sugars, in m u c h th e same w a y as it m a y h a v e a direct effect u p o n t h e l o n g i t u d i n a l t r a n s p o r t system. T h e only d a t a in this p a p e r for which we can offer no r e a d y explanat i o n are those p r e s e n t e d in Section 3; if I A A s t i m u l a t e s t h e m o v e m e n t of sugars in t h e same direction as which it is itself t r a n s p o r t e d (Section 4), t h e n surely t h e d a t a p r e s e n t e d in Tab l e 3 should show t h e labelled sugars m o v i n g a w a y f r o m t h e site of I A A a p p l i c a t i o n an d not t o w a r d s this site. Of course, since th e e x p e r i m e n t s described in Section 3 were p e r f o r m e d using unlabelled I A A , th e m o v e m e n t of this substance could n o t be r e a d i l y followed. Could it n o t be therefore t h a t in t h e exp e r i m e n t s p r e s e n t e d in Section 3, t h e I A A h ad m o v e d only to a small
Movement of Labelled Sugars
59
]cm
1cm
1cm
V1
t
I Loc
|
lOcm
Fig. 4. Experimental technique for studying the effect of 14C labelled IAA applied at the same site as 3It glucose upon the distribution of the latter in a tangential manner. A Transverse view of the experimental segment. B Longitudinal view of the experimental segment. E 14C IAA and ~H glucose applied together (experimental). C 3H glucose only applied (control). 1 Site of isotope application. 2 Longitudinal girdles to delimit experimental portions. 3 Lateral girdles to separate experimental and control portions of the segment
extent. To t e s t this possibility, f u r t h e r e x p e r i m e n t s were performed, identical with those described in Section 3, b u t in which 14C-labelled I A A was a p p l i e d to the b a r k in t h e position shown in Fig. 3, a n d in which the b a r k of Side 1 of t h e stem was cut in half l o n g i t u d i n a l l y a t t h e t e r m i n a t i o n of the experiment. The results of such a n e x p e r i m e n t are p r e s e n t e d in Table 5. C e r t a i n l y I A A has m o v e d a w a y from its site of a p p l i c a t i o n t o w a r d s t h e ~H-glucose a p p l i c a t i o n area. H o w e v e r , the p e r c e n t a g e of t h e t o t a l 14C a c t i v i t y , a p p l i e d to t h e stem, which is t r a n s p o r t e d is small (0.3 % ), when c o m p a r e d to t h e p r o p o r t i o n m o v e d a w a y from t h e a p p l i c a t i o n site in the e x p e r i m e n t s r e p o r t e d in Section 4 (4.7 % ). W e t h e n h a v e t h e s i t u a t i o n in which t h e I A A a p p l i e d in t h e position shown in Fig. 3 moves o n l y to a small e x t e n t from the a p p l i c a t i o n site (it c a n n o t move l o n g i t u d i n a l l y due to t h e design of the experiments). W e would n o t therefore e x p e c t a c o m p a r a b l e effect to t h a t f o u n d in the e x p e r i m e n t s described in Section 4. I t could well be t h a t t h e m o v e m e n t of labelled sugars in a t a n g e n t i a l direction t o w a r d s t h e site of I A A a p p l i c a t i o n m i g h t be caused b y the i m m o b i l e I A A p r o d u c i n g a sink, for
60
N . W . Lepp and A. J. Peel:
Table 5. Patterns o/distribution o/14C labelled I A A and their subsequent e//ect upon the distribution o] aH sugars in a tangential direction when the application sites are spatially separated Experimental 14C upper
Control aH
3H lower
upper
lower
A. Distribution of total activity recovered 32 138 197 0 6 164 1847.2 944 10 154 731 0 16 218 4170 0 22 242 168 0 14 22 472 5 28 22 25 43 22 144 2293 0 22 181 1762 0 44 112 1446 196 x
21.6
139.7
1311.1
118.8
(C.P.M.) 926 199 729 59 409 341 254 42 52 938 408.9
B. Mean distribution of total aH activity recovered 1430 • 780 410 =~ 190 Experimental results consist of upper and lower sections. Fiducial limits expressed a t P = 0.10. x = Means of values.
i n s t a n c e b y s t i m u l a t i o n of r e s p i r a t o r y a c t i v i t y . A t t h e m o m e n t h o w e v e r t h i s s u g g e s t i o n is m e r e l y t e n t a t i v e a n d t h e c l a r i f i c a t i o n of t h i s e f f e c t m u s t await further experimentation. References Booth, A., Moorby, J., Davies, C. R., Jones, H., Wareing, P. F. : Effects of indolyl3-acetic acid on the m o v e m e n t of nutrients within plants. Nature (Lond.) 194~ 204-205 (1962). Davies, C. R., Wareing, P. F. : Auxin-directed t r a n s p o r t of radiophosphorns in lalant stems. P l a n t a (Berl.) 65, 139-156 (1965). H a r t t C. E., Kortschak, H . P . : Sugar gradients a n d translocation of sucrose in detached blades of sugar can. P l a n t Physiol. 39, 4 6 0 4 7 4 (1964). Hew, C. S., Nelson, C. D., Krotkov, G. : Hormonal control of translocation of photosynthetically assimilated ltC in young soybean plants. Amer, J., Bot., 54, 252256 (1967). Lepp, N. W., Peel, A. J. : Some effects of IAA and kinetin on the movement of sugars in the phloem of willow. P l a n t a (Berl.) 90, 230-235 (1970). - - - - P a t t e r n s of translocation and metabolism of 14C IAA in the phloem of willow. P l a n t a (Berl.) (in press). Milthorpe, F. L., Moorby, J. : Vascular t r a n s p o r t and its significance in plant growth. Arm. Rev. P l a n t Physiol. 20~ 117-138 (1969).
Movement of Labelled Sugars
61
Moorby, J. : The effects of growth substances on transport in plants. In: The Transport of Plant Hormones, p. 192-206. Amsterdam 1968. Morris, D. A., Thomas, E. E: Distribution of 14C labelled sucrose in seedlings of Pisum salivium (L). treated with IAA and Kinetin. Planta (Berl.) 88, 276-281 (1968). Mullins, M. G.: Mechanism of hormone-directed transport of metabolites.--In C. S. I. R. 0 Division of Hort. Research report 32-33 (1967-69). Peel, A. J. : Tangential movement of 14C-labelled assimilates in stems of willow. J. ex. Bot. 15, 104 113 (1964). Seth, A., Wareing, P . F . : Hormone directed transport of metabolites and their possible role in plant senescence. J. exp. Bot. 18~ 67-77 (1967). Shiroya, M. : Comparison of upward and downward translocation of ~4Cfrom a single leaf of sunflower. Plant Physiol. 43, 1605-1610 (1968). Dr. A. J. Peel Department of Botany University of Hull Hull, England
Influence of IAA upon the Longitudinal and Tangential Movement of Labelled Sugars in the Phloem of Willow N. W . L~PP a n d A. J. :PEEL Department of Botany, University, Hull, England Received October 17, 1970
Summary. Using a bark abrasion technique, the influence of IAA upon patterns of sugar translocation in isolated stem segments of Willow (Salix viminalis L.) has been studied. IAA was found to exert a considerable influence over translocation in both a longidutinal and tangential direction. Studies on longitudinal movement have led to the postulation of two possible effects of IAA on this system. Firstly a stimulation of sugar loading from the storage parenchyma into the sieve elements as described by Lepp and Peel (1970), and secondly a direct effect upon the longitudinal transport process. The situation with regard to the tangential transport system is not as clear in all its aspects, though once again it is postulated that IAA may have a direct effect upon the movement of sugars in the tangential transport system. Introduction Since t h e d i s c o v e r y t h a t I n d o l y l - 3 - a c t e t i c a c i d (IAA) could m o d i f y t h e d i s t r i b u t i o n p a t t e r n of 14C labelled sugars w i t h i n t h e p l a n t (Booth et al, 1962), t h e role of p l a n t h o r m o n e s in t h e r e g u l a t i o n of assimilate d i s t r i b u t i o n has been f i r m l y e s t a b l i s h e d (reviews of Moorby, 1968; M i l t h o r p e a n d Moorby, 1969).
It is clear that two possibilities exist which could explain the effects of growth substances on the phloem transport system; they could either affect the unloading of solutes at sinks or they could directly affect the longitudinal transport system within the sieve tubes. The work of Davies and Wareing (1965), Seth and Wareing (1967) and Morris and Thomas (1968) could all be explained in terms of the effect of growth substances on the rate of unloading of solutes at sinks. These workers applied growth substances to the end of stems from which the growing a p e x h a d been excised, a n d i t is therefore n o t u n r e a s o n a b l e to a s s u m e t h a t t h e m e t a b o l i c a c t i v i t y , a n d hence t h e sink c a p a c i t y , of t h e c u t s t e m m a y h a v e been e n h a n c e d b y t h e a p p l i e d g r o w t h substances. C e r t a i n l y I A A can affect t h e r a t e of loading of sugars into sieve elements as d e m o n s t r a t e d b y the w o r k of L e p p a n d Peel (1970) on willow. T h e r e a p p e a r s to be little, if any, i n c o n t r o v e r t i b l e evidence t h a t growth~substances can d i r e c t l y affect t h e l o n g i t u d i n a l t r a n s p o r t mechan i s m in sieve tubes. D a v i e s a n d W a r e i n g (1965) a p p l i e d T I B A to t h e s t e m
Movement of Labelled Sugars
51
a t a p o i n t between t h e sites of g r o w t h substance a n d r a d i o t r a e e r application, a n d f o u n d t h a t this r e d u c e d the effect of I A A u p o n t h e accum u l a t i o n of t h e tracer. T h e y i n t e r p r e t e d these results as i n d i c a t i n g t h a t I A A could exert a n influence u p o n t r a n s l o c a t i o n processes a t a d i s t a n c e from t h e p o i n t of its application. However, recent w o r k b y Mullins (1967-1969) has cast some d o u b t u p o n this i n t e r p r e t a t i o n . H e w et al. (1967) h a v e also p r o d u c e d evidence to suggest t h a t I A A m a y a c t a t a distance from t h e site of its application, a n d their w o r k is n o t complic a t e d b y t h e use of T I B A . I t has r e c e n t l y been suggested t h a t I A A , when a p p l i e d t h r o u g h a b a r k abrasion, m a y move in a p o l a r m a n n e r in the sieve t u b e s of isolated stem segments of willow (Lepp a n d Peel, in t h e press). I t is also k n o w t h a t laC labelled sugars can e x h i b i t a polar d i s t r i b u t i o n in certain tissues. H a r t t a n d K o r t s c h a k (1964) showed t h a t labelled sugars m o v e with a p o l a r d i s t r i b u t i o n in d e t a c h e d leaf blades of sugar cane when t h e apical end of t h e leaf was held u p p e r m o s t . W h e n t h e leaf blade was i n v e r t e d from its n o r m a l position, i.e. when t h e basal end was u p p e r m o s t , no p o l a r distrib u t i o n was found, a s i t u a t i o n v e r y similar to t h a t d e m o n s t a t e d b y L e p p a n d Peel (in t h e press). S h i r o y a (1968) has p r o d u c e d evidence from exp e r i m e n t s with sunflower seedlings t h a t a difference m a y exist between t h e chemical species bearing t h e laC label which are t r a n s l o c a t e d apically as o p p o s e d to those t r a n s l o c a t e d b a s a l l y from a leaf fed w i t h labelled sugars. I t is n o t impossible t h a t t h e p o l a r m o v e m e n t of 14C-labelled sugars in d e t a c h e d sugar cane leaf blades is due to t h e effects of endogenous g r o w t h substances u p o n t h e t r a n s p o r t system. Therefore in view of t h e possibility t h a t g r o w t h substances m a y affect t h e d i s t r i b u t i o n of solutes b y acting d i r e c t l y u p o n t h e l o n g i t u d i n a l transp o r t system, i t was decided to f u r t h e r i n v e s t i g a t e this p r o b l e m using the isolated s e g m e n t s y s t e m described b y L e p p a n d Peel (in t h e press). Investigations were also e x t e n d e d to t h e t a n g e n t i a l t r a n s p o r t s y s t e m of t h e p h l o e m of willow (Peel, 1964) which m a y involve l a t e r a l m o v e m e n t of solutes b e t w e e n sieve elements a n d p h l o e m p a r e n c h y m a cells. Materials and Methods 2-4 year old stems of Salix viminalis L. were collected in the field. These stems were then cut into segments, the length of which varied with the type of experiment. The segments used in the experiments on longitudinal movement were 10 cm in length and 1.5 cm in diameter, whilst those used in the studies on tangential movement were 8 cm in length and had a diameter of 2-3 cms. The tracers used in this investigation were applied on filter paper via a bark abrasion, the technique being essentially the same as that employed by Lepp and Peel (in the press). 0.1 ml of a solution of IAA 2-1~C (specific activity 27.8 mCi/mM), witch a radioactive concentration of 5 ~xCi/mlwas spotted onto the piece of filter paper. In the case of sugar, this was applied as 0.01 ml of a solution of glucose-6-aIt (specific activity 4.9 Ci/rnM) also at a radioactive concentration of 5 ~xCi/ml. 4*
52
N. W. Lepp and A. J. Peel:
At the termination of an experiment radioactivity was extracted from the bark using the techniques described by Lepp and Peel (in the press). The activities of 14C and 3tI in the extracts were determined by liquid scintillation spectroscopy.
Results and Discussion
1. E//ect o / I A A upon Patterns o/Movement o/aH Sugars in a Longitudinal Direction when the Sites o/ A pplication are Spatially Separated P r e v i o u s w o r k (Lepp a n d Peel, 1970) has shown t h a t I A A can ex er t a n influence on t h e d i s t r i b u t i o n p a t t e r n of labelled sugars in tile longit u d i n a l t r a n s p o r t s y s t e m w h e n t h e sites of a p p l i c a t i o n of I A A an d sugars
Table 1. E//ect o] I A A (unlabelled) on the distribution o] 3H-sugars in a longitu-
dinal direction when the sites o[ application are spatially separated
x
A. IAA at apex, 8H glucose in centre
B. IAA at base, ~H glucose in centre
apical
basal
apical
basal
106.5 70.4 370.5 177.1 472.3 38.1 80 176.3 101.5 156
183.5 307.5 394.9 476.2 635 276.8 128.7 340.5 714.8 390.2
121.9 559.4 319.8 58.6 235.5 112.9 327.8 120.7 141.2 172
27.6 20.7 33.9 20.6 29.6 74.3 80.3 81.8 124.2 107.8
174.8~94.5
384.8:t=111.2
x 216.8•
60.0•
All segments horizontal. Results expressed as C. P. M • 10-1. Fidueial limits given at P = 0.05. All samples counted at the same efficiency. IAA employed at a concentration of 10-sM.
are s p at i al l y separated. This effect was observed using a bark strip system, a n d it was decided to see w h e t h e r a similar effect could be produced in isolated s t e m segments. T h e e x p e r i m e n t s were set up as shown in Fig. 1, an d t h e results of one e x p e r i m e n t are p r e s e n t e d in T a b l e l. F r o m these it can be seen t h a t t h e I A A exerts essentially t h e same effect on labelled sugar m o v e m e n t in segments as it does in b a r k strips; the labelled sugar m o v e s a w a y f r o m t h e site of I A A application.
Movement of Labelled Sugars
53
lOcm
lcm 2cm lcm 2cm lcm
2
h
1
5
3
Fig. 1. Experimental technique for studying the effect of IAA applied at a distance from aH glucose upon the pattern of distribution of the latter. 1 Site of application of 3tt glucose. 2 Site of application of unlabelled IAA (10-5M). 3 Site of application of distilled water. 4, 5 Experimental sections
2. E//ect o/ I A A on the Movement o/ aH Sugars in a Longitudinal Direction when Both are Applied at the ~ame Site Segments e m p l o y e d in these e x p e r i m e n t s were p r e p a r e d in a similar m a n n e r to t h a t described b y L e p p a n d Peel (in t h e press). H o w e v e r , in the p r e s e n t e x p e r i m e n t s , t h e b a r k was d i v i d e d l o n g i t u d i n a l l y into two halves b y m e a n s of slits cut into the b a r k on d i a m e t r i c a l l y opposite sites of the stem. A b a r k a b r a s i o n was t h e n p r e p a r e d in t h e centre of each half of the segment. I n these e x p e r i m e n t s , as opposed to those described in section (1), laC labelled I A A was used as well as aH labelled glucose, in order t h a t t h e m o v e m e n t of b o t h labels could be followed. B o t h substances were a p p l i e d to t h e b a r k a b r a s i o n on one side of t h e s t e m (experimental) whilst all-glucose only was a p p l i e d to t h e a b r a s i o n on t h e other side of t h e s t e m to act as a control. The segments were t h e n o r i e n t a t e d in either a h o r i z o n t a l or v e r t i c a l p o s i t i o n for a period of 6 hours. The results from these e x p e r i m e n t s are p r e s e n t e d in Table 2. F r o m these it can be seen t h a t t h e p e r c e n t a g e d i s t r i b u t i o n of a c t i v i t y from t h e ~It glucose is virt u a l l y identical to t h a t of the 14C a c t i v i t y from t h e I A A , a l t h o u g h t h e absolute a c t i v i t y of b o t h tracers in t h e samples varies due to differences in t h e u p t a k e of t h e a p p l i e d c o m p o u n d s b y different segments. W h e n t h e 3H glucose is a p p l i e d b y itself, however, t h e s u b s e q u e n t dist r i b u t i o n of t h e aI-I a c t i v i t y is quite different from when i t is a p p l i e d with I A A . I t m u s t therefore be concluded t h a t t h e I A A is e x e r t i n g considerable influence over t h e m o v e m e n t of labelled sugars. H o w t h e n can we e x p l a i n this effect of I A A ? As m e n t i o n e d in t h e I n t r o d u c t i o n , I A A enhances t h e r a t e of loading of sugars from t h e storage
54
N. W. Lepp and A. J. Peel:
Table 2. Movement o] 14C-labelled I A A and 3H-labelled sugar8 in a longitudinal direction when both are applied at the same site A. Segments vertical, apex uppermost Experimental 14C apex
236 202 477 70 310 90 455 226 384 147
Control 8It
base
apex
3H base
apex
(i) Distribution of total activity recovered (C. P . M ) 573 426 1030 307 288 373 516 417 884 869 1612 451 463 129 838 242 800 569 1473 204 172 167 309 233 804 848 1493 302 415 404 741 211 587 698 1061 460 271 523 956 368
x
259.7 101
x
29.9
551 -r 162
475 • 189
999.3 :L 303
319.5 • 83
base
298 176 486 61 330 456 432 268 308 257 307.2 ~: 104
(ii) Mean % distribution of total activity recovered 70.1 29.9 70.I 52.5 47.5 B. Segments horizontal
Experimental 140 apex
279 672 528 511 324 410 227 476 346 146 x
432.8 4- 94
x
47.5
Control 3H
base
apex
3H base
apex
(i) Distribution of total activity recovered (C. P.M.) 422 308 467 204 516 744 570 183 461 583 509 394 507 564 558 243 445 357 491 227 511 451 560 222 354 251 389 331 297 527 328 353 325 382 358 218 263 161 292 324 391.9 -r 123
452.2 ~_ 75
410.1 • 83
269.9 • 108
base
255 638 175 323 370 376 266 267 318 307 329.5 • 78
(ii) Mean % distribution of total activity recovered 52.5 47.5 52.5 45.7 54.3
All samples counted at the same efficiency. Fiducial limits given at P ) 0 . 0 5 .
Movement of Labelled Sugars IAA
LabelLed sugar
T2o, I
55
o
,
I
"
v
I
Sievetube
j i i
A B Fig. 2. Diagrammatic representation of the possible dual effect of IAA on phloem transport systems. 1 IAA enhances the rate of sugar loading into sieve elements, and thus sets up a gradient of sugar potential from A to B. 2 Labelled sugars loaded into sieve element. 3 IAA stimulates the longitudinal transport system. Labelled sugars entering the system therefore move towards B along a gradient of sugar potential, this movement being enhanced by IAA stimulation of the longidutinal transport system
parenchyma into sieve elements of willow (Lepp and Peel, 1970), but the data presented in Table 2 cannot be explained in these terms; an enhancement of sugar loading would merely lead to more aH sugars being moved, it would not affect their relative distribution apieally and basally from the application point. Is it then not possible that the IAA, if it moves along the sieve tubes, creates sinks in the storage parenchyma cells which then produce a concomitant movement of the labelled sugar ? This possibility seems unlikely, unless IAA has a different effect upon the storage parenchyma when it is present in the sieve tube as opposed to when it is merely applied to the exterior of the phloem. The situation is clearly complicated, but it could well be that once the IAA is present within the sieve tubes, then it exerts a direct effect upon the longitudinal sieve tube transport system. If we now consider the results of the experiments presented in Section l, and also the triple-chambered bark strip experiments described by Lepp and Peel (1970), it becomes apparent that there are two possible effects of IAA which could have produced the observed results. These are (i) an increase in the rate of sugar loading from the storage parenehyma into the sieve elements at the IAA-treated end of the bark, the explanation given by Lepp and Peel (1970), and (ii) an enhancement of longitudinal transport in the sieve tubes once the IAA has entered the transport conduits. These possibilities are illustrated diagramatically in Fig. 2. If IAA does have both these effects upon the phloem transport system, then the data presented in Tables 1 and 2 could be adequately explained. A further point which emerges from the foregoing results concerns their relevance to the suggestion put forward by Lepp and Peel (in the press), that applied IAA moves in a polar manner through the sieve tubes of isolated stem segments. I t must be apparent that the data presented
56
N. W. Lepp and A. J. Peel:
ff% t__scm
!m
l
Fig. 3. Experimental technique for studying the effect of IAA applied at a distance from aH glucose upon the pattern of distribution of the latter in a tangential manner. A Transverse view of the experimental segment. B Longitudinal view of the experimental segment. X Point where the bark was divided into upper and lower sections in experiments employing laC IAA. I Site of application of aH glucose. 2 Site of application of IAA (inactive or 14Clabelled). 3 Site of application of distilled water. 4 Longitudinal girdle below application sites. 5 Lateral girdle separating the experimental bark from the remainder of the segment
here strongly s u p p o r t the suggestion t h a t I A A moves in the sieve tubes. Certainly there can be little d o u b t t h a t the labelled sugars move i n the sieve tubes, therefore it seems reasonable to assume t h a t since the I A A has a n effect on their m o v e m e n t t h e n this m u s t also be t r a n s p o r t e d i n the same system. I t seems inconceivable t h a t I A A could produce the effects d e m o n s t r a t e d b y the e x p e r i m e n t s presented in Section 2 if the I A A were m o v i n g i n a system outside the sieve tubes. I f this l a t t e r s i t u a t i o n existed, t h e n the I A A would surely have a quite different effect on the labelled sugar m o v e m e n t , for if it were present outside the sieve t u b e s t h e n it would affect sugar loading into these cells. Hence we would expect t h a t t h e labelled sugars would move a w a y from the highest c o n c e n t r a t i o n of IAA, n o t towards it.
3. E//ect o / I A A upon Patterns o/Movement o/3H Sugars in a Tangential Direction when the Sites o/Application are Spatially Separated These experiments were essentially similar to those described in Section 1, except t h a t here, the effects of I A A u p o n labelled sugar movem e n t i n a t a n g e n t i a l direction were investigated. Fig. 3 shows the design
Movement of Labelled Sugars
57
of the experiments. The segments were held in a horizontal position. aH glucose was applied t h r o u g h a bark abrasion on the u p p e r m o s t side of the segment, whilst unlabelled I A A was applied t h r o u g h a n abrasion at one side of the stem (1), distilled water as a control being applied to the other (2). Table 3. E]/ect o[ I A A (unlabelled) on the distribution o/8H sugars in a tangential direction when the application sites are spatially separated Experimental Control
Average
424.4 331.2 363.4 360.1 248.3 298.7 52.7 80.1 196 134.6
168.7 90.1 131.8 149.2 209.3 25.5 18.8 59.9 29 51.2
248.9-[- 91.8
93.7 ~ 47.7
Results expressed as C. P. M. • 10-2. Fiducial limits given at P -- 0.05. IAA employed at a concentration of 10-sM.
The results are presented in Table 3. I t can be seen from these t h a t the I A A has a n a p p a r e n t l y quite different effect on the t a n g e n t i a l t r a n s p o r t of sugars when compared with the results from experiments in the longit u d i n a l t r a n s p o r t system (Section 1).
4. E]]eet o] I A A upon Patterns o / M o v e m e n t o] ~H Sugars in a Tangential Direction when Both are Applied at the Same Site These experiments were essentially similar to those described in Section 2, where l o n g i t u d i n a l m o v e m e n t was investigated. The arrang e m e n t of the experiments reported in the present section is shown in Fig. 4, a n d the d a t a from one of these is presented i n Table 4. The results show a p a t t e r n which is very similar to t h a t f o u n d i n the l o n g i t u d i n a l m o v e m e n t e x p e r i m e n t s ; I A A moved from its site of application into one side of a segment in m u c h greater quantities t h a n m o v e d into the other side, a n d the ~H sugars also m o v e d in the same direction. I n the control experiments where 3H glucose only was appJied a n d which were carried out on the same segment, the p a t t e r n s of m o v e m e n t were n o t i n the same sense. W e do n o t know w h y i n e q u a l i t y of m o v e m e n t of I A A occurs be-
58
N.W. Lepp and A. J. Peel:
Table 4. Movement o/l~C-labelled I A A and ~H-labelled sugars in a tangential direction when both are applied at the same site
Experimental 14C
Control ~H
side 1
side 2
side 1
aH side 2
side 1
side 2
A. Distribution of total activity recovered (C. P.M. • 10-1) 1280 29 191 4 154 374 54 1386 8 205 80 298 2249 51 348 7 30 787 1447 175 221 27 93 234 771 73 116 l0 266 51 5264 93 805 13 1132 48 2941 172 431 24 1157 140 925 625 137 90 391 91 60 179 9 26 3 28 3112 262 471 38 2065 256 x
1810 •
x
75.1
304.5 :t: 296
273.7 ~176
444 •
537.1 :E397
230.7 •
B. Mean % distribution of total activity recovered 24.9 75.1 24.9 54.1 45.9
All samples counted at the same efficiency. Fidueial limits given at P = 0.05.
t w e e n t wo sides of a stem, since b o t h sides of the s t e m would a p p e a r to be e q u a l l y suitable for t r a n s p o r t . C e r t a i n l y no p a t t e r n has e m e r g e d f r o m the p r es en t e x p e r i m e n t s which suggests t h a t I A A m o v e s in a polar m a n n e r w h e n applied to t h e s t e m in t h e position shown in Fig. 4, as it does in a l o n g i t u d i n a l direction with respect to t h e morphological a p e x an d base of a segment. H o w e v e r , it is clear from these e x p e r i m e n t s t h a t I A A would a p p e a r to h a v e a direct effect u p o n t h e t a n g e n t i a l t r a n s p o r t s y s t e m which m o v e s atI sugars, in m u c h th e same w a y as it m a y h a v e a direct effect u p o n t h e l o n g i t u d i n a l t r a n s p o r t system. T h e only d a t a in this p a p e r for which we can offer no r e a d y explanat i o n are those p r e s e n t e d in Section 3; if I A A s t i m u l a t e s t h e m o v e m e n t of sugars in t h e same direction as which it is itself t r a n s p o r t e d (Section 4), t h e n surely t h e d a t a p r e s e n t e d in Tab l e 3 should show t h e labelled sugars m o v i n g a w a y f r o m t h e site of I A A a p p l i c a t i o n an d not t o w a r d s this site. Of course, since th e e x p e r i m e n t s described in Section 3 were p e r f o r m e d using unlabelled I A A , th e m o v e m e n t of this substance could n o t be r e a d i l y followed. Could it n o t be therefore t h a t in t h e exp e r i m e n t s p r e s e n t e d in Section 3, t h e I A A h ad m o v e d only to a small
Movement of Labelled Sugars
59
]cm
1cm
1cm
V1
t
I Loc
|
lOcm
Fig. 4. Experimental technique for studying the effect of 14C labelled IAA applied at the same site as 3It glucose upon the distribution of the latter in a tangential manner. A Transverse view of the experimental segment. B Longitudinal view of the experimental segment. E 14C IAA and ~H glucose applied together (experimental). C 3H glucose only applied (control). 1 Site of isotope application. 2 Longitudinal girdles to delimit experimental portions. 3 Lateral girdles to separate experimental and control portions of the segment
extent. To t e s t this possibility, f u r t h e r e x p e r i m e n t s were performed, identical with those described in Section 3, b u t in which 14C-labelled I A A was a p p l i e d to the b a r k in t h e position shown in Fig. 3, a n d in which the b a r k of Side 1 of t h e stem was cut in half l o n g i t u d i n a l l y a t t h e t e r m i n a t i o n of the experiment. The results of such a n e x p e r i m e n t are p r e s e n t e d in Table 5. C e r t a i n l y I A A has m o v e d a w a y from its site of a p p l i c a t i o n t o w a r d s t h e ~H-glucose a p p l i c a t i o n area. H o w e v e r , the p e r c e n t a g e of t h e t o t a l 14C a c t i v i t y , a p p l i e d to t h e stem, which is t r a n s p o r t e d is small (0.3 % ), when c o m p a r e d to t h e p r o p o r t i o n m o v e d a w a y from t h e a p p l i c a t i o n site in the e x p e r i m e n t s r e p o r t e d in Section 4 (4.7 % ). W e t h e n h a v e t h e s i t u a t i o n in which t h e I A A a p p l i e d in t h e position shown in Fig. 3 moves o n l y to a small e x t e n t from the a p p l i c a t i o n site (it c a n n o t move l o n g i t u d i n a l l y due to t h e design of the experiments). W e would n o t therefore e x p e c t a c o m p a r a b l e effect to t h a t f o u n d in the e x p e r i m e n t s described in Section 4. I t could well be t h a t t h e m o v e m e n t of labelled sugars in a t a n g e n t i a l direction t o w a r d s t h e site of I A A a p p l i c a t i o n m i g h t be caused b y the i m m o b i l e I A A p r o d u c i n g a sink, for
60
N . W . Lepp and A. J. Peel:
Table 5. Patterns o/distribution o/14C labelled I A A and their subsequent e//ect upon the distribution o] aH sugars in a tangential direction when the application sites are spatially separated Experimental 14C upper
Control aH
3H lower
upper
lower
A. Distribution of total activity recovered 32 138 197 0 6 164 1847.2 944 10 154 731 0 16 218 4170 0 22 242 168 0 14 22 472 5 28 22 25 43 22 144 2293 0 22 181 1762 0 44 112 1446 196 x
21.6
139.7
1311.1
118.8
(C.P.M.) 926 199 729 59 409 341 254 42 52 938 408.9
B. Mean distribution of total aH activity recovered 1430 • 780 410 =~ 190 Experimental results consist of upper and lower sections. Fiducial limits expressed a t P = 0.10. x = Means of values.
i n s t a n c e b y s t i m u l a t i o n of r e s p i r a t o r y a c t i v i t y . A t t h e m o m e n t h o w e v e r t h i s s u g g e s t i o n is m e r e l y t e n t a t i v e a n d t h e c l a r i f i c a t i o n of t h i s e f f e c t m u s t await further experimentation. References Booth, A., Moorby, J., Davies, C. R., Jones, H., Wareing, P. F. : Effects of indolyl3-acetic acid on the m o v e m e n t of nutrients within plants. Nature (Lond.) 194~ 204-205 (1962). Davies, C. R., Wareing, P. F. : Auxin-directed t r a n s p o r t of radiophosphorns in lalant stems. P l a n t a (Berl.) 65, 139-156 (1965). H a r t t C. E., Kortschak, H . P . : Sugar gradients a n d translocation of sucrose in detached blades of sugar can. P l a n t Physiol. 39, 4 6 0 4 7 4 (1964). Hew, C. S., Nelson, C. D., Krotkov, G. : Hormonal control of translocation of photosynthetically assimilated ltC in young soybean plants. Amer, J., Bot., 54, 252256 (1967). Lepp, N. W., Peel, A. J. : Some effects of IAA and kinetin on the movement of sugars in the phloem of willow. P l a n t a (Berl.) 90, 230-235 (1970). - - - - P a t t e r n s of translocation and metabolism of 14C IAA in the phloem of willow. P l a n t a (Berl.) (in press). Milthorpe, F. L., Moorby, J. : Vascular t r a n s p o r t and its significance in plant growth. Arm. Rev. P l a n t Physiol. 20~ 117-138 (1969).
Movement of Labelled Sugars
61
Moorby, J. : The effects of growth substances on transport in plants. In: The Transport of Plant Hormones, p. 192-206. Amsterdam 1968. Morris, D. A., Thomas, E. E: Distribution of 14C labelled sucrose in seedlings of Pisum salivium (L). treated with IAA and Kinetin. Planta (Berl.) 88, 276-281 (1968). Mullins, M. G.: Mechanism of hormone-directed transport of metabolites.--In C. S. I. R. 0 Division of Hort. Research report 32-33 (1967-69). Peel, A. J. : Tangential movement of 14C-labelled assimilates in stems of willow. J. ex. Bot. 15, 104 113 (1964). Seth, A., Wareing, P . F . : Hormone directed transport of metabolites and their possible role in plant senescence. J. exp. Bot. 18~ 67-77 (1967). Shiroya, M. : Comparison of upward and downward translocation of ~4Cfrom a single leaf of sunflower. Plant Physiol. 43, 1605-1610 (1968). Dr. A. J. Peel Department of Botany University of Hull Hull, England
