BIOCHEMICAL
Vol. 66, No. 4, 1975
BIOCHEMICAL
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
COMPONENTS OF THE PHOTOSYNTHETIC CO2
COMPENSATION POINT OF HIGHER PLANTS D.P.
Kestler,
B.C. Mayne, T.B. Ray, L.D. R.H. Broom* and C.C. Black
Botany
Received
August
Goldstein
Department, University of Georgia Athens, Georgia 30602
27,197s SUMMARY
Barley, Poxiczm mizioides and Pmicwn maxirr.wnwere exposed to 14c02 ar their photosynthetic CO2 compensation points and their respective PZ C-products were determined. In short exposure times Panicwn maxim had 100% of its l4 whereas Panicwn milioides and and aspartaE$C in c4 organic acids. Near barley had 16 and c 3%inof ma1ate their respective the respective CO2 compensation points a linear relationship occurs in plotting the ratio of glycine, serine, and glycerate to C4 organic acids. The ratio of ribulose 1,5-bisphosphate oxygenase to phosphoenolpyruvate carboxylase is linear with their CO2 compensation points. The photosynthetic CO2 compensation point apparently is controlled by the activity of enzymes producing photorespiration metabolites and the activity of phospheonolpyruvate carboxylase. INTRODUCTION The photosynthetic pressure
of CO2 at which
CO2 uptake. until
CO2 compensation
To determine
CO2 equilibrium
groups
of higher
plants
compensate
is
plants
respiratory I,
each with
There
are
have
a variable
daily
F has been
used as a qualitative
* Agronomy
Department
r changing measurement
the partial photosynthetic
in a closed
3 major
a distinctive
is
equals
are illuminated
at 0 to 10 ppm C02, C3 plants
CAM plants
(I)**
CO2 release
plants
reached.
point
chamber
photosynthetic
range
of T values.
range
from
from 0 through of photorespiration
C4
35 to 70, and to 200 (1). and in
**Abbreviations used are: I, photosynthetic CO2 compensation concentration; C3, reductive pentose phosphate; C4, C4-dicarboxylic acid; RuDPC, ribulose 1,5-bisphosphate carboxylase; PEPC, phosphoenolpyruvate carboxylase; P, P&cum; RuDPO, ribulose 1,5-bisphosphate oxygenase; PGA, 3-phosphoglyceric acid; and CAM, Crassulacean acid metabolism.
Vol. 66, No. 4, 1975
plant
BIOCHEMICAL
breeding
selection
the underlying Brown
biochemical
and the
between
those
mediate
species
of plants
P. hiarts
unpublished those
reactions,
procedures
and P. mizioides
stant
until
were
the plants
value.
865)
reached
a steady
the chamber
55 seconds
of r.
leaves
without
used to study in
were
con-
mflioides. CO2 uptake
in air
and near
14C02 fixation
a water-sealed
near
r.
chamber of air
was measured
a stream
of N2 flowing
(4)
to a con-
by removing through
a
When the CO2 concentration barley
and 25 ppm for
10 mCi per
of barley
disturbing
plants,
and a species
Pam&m
CO2 concentration
40 ppm for activity
the discovery
Studies
maxhan,
plants,
inter-
I'.
gas analyzer.
specific
are
AND METHODS
the
into
(near
14 CO2 labeled
chamber. from
infared
state
0.1 mCi of 14C02,
it
photores-
also With
Pmricwn
CO2 concentration
30 ml of gas and injecting (Model
components
illuminated
reduced
The chamber
Beckman
were
of r,
of C3 and C4 photosynthesis
controlling
MATERIALS
at 25'C
and P. lam
observation).
a C4 plant,
parameters
However,
are intermediate
on enzymes involved in light-dependent 14 14 the C-products of CO2 fixation
and the biochemical
Barley
the value
milioides,
C3 and C4 photosynthesis
be presented
The following
that
in Pmicwn
barley,
(2).
of r are unknown.
of the biochemical
between
photorespiration
reported
between
a C3 plant,
and release r,
anatomy
F values a study
intermediate Data will
recently
(R. H. Brown,
with
with
components
(3)
leaf
to reduce
of C3 and C4 plants.
we undertook ducted
programs
and Brown
piration,
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
mmole,
was injected
and P. mizioides
the atmosphere
and fixed
immediately
in 85% ethanol
maxhun
was allowed
to approach
was impossible
to remove
P. mitioides),
were
at intervals cooled
into
removed up to
in a dry-ice
acetone
bath. Pmicwn bag (3). bag without exposures
Since
it
disturbing were
made.
the
internal
In addition,
r (2 5 ppm) inside leaf
atmosphere, when
1440
samples separate
the bags were
from timed
opened
the
a mylar the sealed 14c02 some P.
Vol. 66, No. 4, 1975
BIOCHEMICAL
leaves
maximum
were
exposed
and fixed
as described
extracted
and chromatographed
of Bassham counted
for
standards
total
(5).
enzyme
grown
eluted, for
assayed
plants
times
were
up to 70 seconds of 14 CO2 fixation
products
according
chromatogram
positive
spots
identification
phosphoglycerate
using used
standard for
were
localized,
against
known
(5,6). phosphatase,
procedures
PEPC,
(4,7,8,9).
14 CO2 fixation
both
were
to the procedures
and co-chromatographed
phosphatase,
RuDPC, and RuDPO were
for
The soluble
Radioactive
solvents
Phosphoglycolate
air
in two dimensions
activity,
in other
Greenhouse
to ambient
above.
and Calvin
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
experiments
and
assays. RESULTS AND DISCUSSION
The initial near in
l4 C-products
the CO2 compensation air
than
in Table those
I.
found
point
The initial in similar
Table
Plant Leaves
(5 to 20 seconds)
CO2 Cone.
I.
are
of labeling
contrasted
with
l4 C-products experiments
formed
at ambient
similar near
experiments experiments P were
different
CO2 concentrations
Labeled Products of Photosynthetic 14CO2 Fixation Near p and in Air.
Mal.
wm
Asp.
Products Glycine PGA +Serine
% of total
l4 C-labeled
Glycerate
Others
products
Exposure Times
Seconds
Barley
P. milioides
C -25
9
7
27
33
11
13
5 to 15
air
0
0
4
37
27
30
10
P.max7hum
1441
Vol. 66, No. 4, 1975
(= 300 ppm). was PGA.
BIOCHEMICAL
The major
However,
malate,
while
near
product
labeling
times
as early
labeled
P a significant
Glycine near
fixation
F than
products products
near
of the
label
appeared
types
of plants
the products
in C4 organic
the products
quite
it
P.
did
maximum
initially
organic
3%, was found as initial
were
composed
near
I'; in air
acids
(Table
in short did
not
appear
16% of the early
increased
6-fold
near
was in C4 organic a smaller I).
in
products
higher
C4 acids
serine
of CO2 fixation
Therefore,
it
retained
over
70 seconds turnover
(1)
detectable
leaf
that
that
is
acids
fraction
Thus in all
at r are quite
the
turnover
of the three
different
from
atmospheric
of interest
that
near
at r.
at I is
the efficiency
initial
taken
is
a result
have
in malate
clearly
The total
levels
r we also
label
these
as support
plus
C4 acids
fixation
of CO2
for
of C4 photosynthesis
photorespiration
of C4 organic
with
of a 14 CO2chase;
in leaves
time
in C4 plants
80% of its
by P. maxim
acids
hypothesis
known
@30 seconds)
even after
not
into
is well
short
of CO2 (l,lO,ll).
aspartate
plus
CO2
in air.
In addition,
observed
also
in P. maximwn
label
in experiments
of label,
C4 acids
Glycine
P.
P or at ambient
detected
levels
while
in air,
at 7 and 20 seconds total
were
near
In P. miZioides
in air.
All
is
amount
and serine
r in P. miZioides.
acids
in barley
in 300 ppm CO2 no C4 acids
of photosynthesis.
'4CO2
initial
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
our previous
and the
of PEPC serving
lack
of
as a CO2
trap. The activities are
given
in Table
relationship for
tions
The present
II.
between
14C02 fixation
barley,
of some photosynthetic
shows a decreasing with
intermediate
species
r.
near
additional
relation
will
enzyme levels
and P. mtimtlm
P. miZioides,
supplemented
discussion
P and particular experiments
and photorespiratory
A plot
against (Fig.
C4 and
C3
the same relation
1442
1A).
enzymes
concentrate in
upon the
the plants
used
of the PEPC level their
respective
When these
species
as well
remains
(Fig.
of
CO2 compensa-
PEPC data as other
1B).
A plot
are
C3-C4 of RuDPO
Vol. 66, No. 4,1975
BIOCHEMICAL
Table
Plant
II.
RuDPO
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Activities of Some Photosynthetic and Photorespiration Enzymes in Leaf Extracts.
RuDPC
PEPC
umoles
P-Glycolate Phosphatase
per mg chlorophyll
46-68
2360
108
---
P. miZioides'
16
407
123
184
P. maximum
9-14
440
1235
68
Barley
1
Average
of 5 plant
introduction
P-Glycerate Phosphatase per
RuDPO PEPC
hr ---
0.54
1000
0.13
1184
0.009
lines.
I
A
n
A I 0
10
I
1 30
AA
= = E = d
40
0
IA
0
50
10
30
Figure 1. Leaf photosynthetic CO2 compensation point versus: A. PEPC in barley, P. milioides, and P. ma.rimum leaf extracts; B. PEPC collected from the literature for a variety of leaves; C. RuDPC (-) and RuDPO (---) in the three plants; and D. 14C-malate plus aspartate in 5 to 7 seconds of 14C02 fixation near I? in the three plants.0 = P. macrhwn; l = P. m-itioides; A = barley.
1443
50
Vol. 66, No. 4,1975
BIOCHEMICAL
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
0
r , ppm
20
40
60
CO2
Figure 2. Leaf photosynthetic CO2 compensation point versus: A. the ratio of RuDPO to PEPC in leaf extracts from barley, P. milioides, and P. maxim; B. ratio of % 14C in glycine plus serine to aspartate plus ma&te in 14C02 of C in glycine fixation experiments near I in the three plants; C. ratfz CO2 fixation experiplus serine plus glycerate to aspartate plus malate in measured as CO2 ments P in the three plants; and D. leaf photorespiration release into C02-free air (3).0 = P. muzinun; l = P. milioides; A = barley.
and RuDPC activity shown
in Figure
1C.
I nor were
plots
(Table
linear.
II)
is
senting
the relation
levels ratio
via
(Fig.
lower
plots
show a linear
phosphatase
This
2A).
of CO2 release PEPC.
of PEPC, therefore, is
and P. mtimwn
consistent
via
C3 plants this with
ratio
contain ratio
the low
1444
is
against
leaf high
quite levels
high.
with
T a linear
rela-
of as repre-
photorespiration levels
T is
phosphatase
can be thought
the
against
relationship
or P-glycerate
of RuDPO to PEPC is plotted
observed
to CO2 uptake
None of these
of P-glycolate
When the ratio tionship
P. mizioides,
of barley,
system
of RuDPO and low In C,J, plants
of RuDPO and the higher
this
BIOCHEMICAL
Vol. 66, No. 4,1975
levels
of PEPC associated
RuDPO nearer (Table
that
II),
is
in
The ratio
another
near
relation
acids
to the relation
versus
near
CO2 compensation
photorespiration
(Figs. data
and glycerate
the ratios
are
via components
leaves
Acknowledgements: Foundation Grant Incorporated.
that
of gp,O;
photorespiration
in
P (Table
we propose
photorespiration
point
these
to
enzymes
in
the relative
amounts
versus
1A).
I is significant, of fixation
In addition,
(3)
relation
r in similar
from
the
relationship
A linear
and l' also
intermediates
near
obtained
show a linear
2B & 2C).
The
the ratios
+ glycerate, acids I),
plants
is
co
to
relationship observed
(Fig.
in the current
2D).
schemes of
similar
the photorespiration Cq (Fig.
2).
RuDPO and the which
of higher
linear
We conclude carboxylation
determine
relationships
exist
intermediate the
carbon
of CO2 via
the photosynthetic
between
fluxes; flux
through
PEPC are
the
CO2 compensation
plants.
This research was supported in part by National Science BMSJ4-24230 and by a cooperative agreement with Cotton
REFERENCES 1. 2. 3. 4.
2
(2).
Therefore,
biochemical
of oxygenase
lD> shows a decreasing
+ serine C4 organic
points
of
to C3 plants
between
in 5 to 7 seconds
photorespiration
serine,
and leaf
enzymes
I (Fig.
or glycine
experiments
I and:
ratio
relationships
of PEPC to F (Fig.
glycine + serine C4 organic acids
Glycine,
the
a level
(12).
of these
C4 organic
leaf
for
shows
F in C3, C4 and C3-C4 intermediate
percentage
between
of PEPC close
of other
of 14 CO2 appearing
the
and a level value
study
formed
linear
fixation
P. nrizioides
of RuDPO to PEPC must be reflected
of 14C-products this
C4 plants.
an intermediate
A discussion
developed
if
of C4 plants
thus,
carboxylase.
with
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Black, C.C. Ann. Rev. Plant Physiol. 2, 253 Tolbert, N.E. Ann. Rev. Plant Physiol. 22, 45 Brown, R.H. and Brown, W.V. Crop Science, 15: Chen, T.M., Brown, R.H. and Black, C.C. Plant (1971).
1445
(1973). (1971). In Press Physiol.
(1975). 2, 199
Vol. 66, No. 4, 1975
5. 6. 7. 8. 9. 10. 11. 12.
BIOCHEMICAL
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Bassham, J.A. and Calvin, M., The Path of Carbon in Photosynthesis, Prentice Hall, Inc., Englewood Cliffs, New Jersey, 16-27 (1957). Isherwood, F.A. and Hanes, C.S. Biochem. J. 55, 824 (1953). Randall, D.D., Tolbert, N.E., and Gremel, D. Plant Physiol. 68, 480 (1971). Chen, P.S., Toribara, T.Y., and Warner, H. Analytical Chem. 2S, 1756 (1956). Barr, J.T. and Jensen, R.G. Plant Physiol. 53, 39 (1974). C.E. and Burr, G.O. Plant Physiol. do, Kortschak, H.P., Hartt, 209 (1965). Hatch, M.D. and Slack, C.R. Biochem. J., 101, 103 (1966). Goldstein, L.D., Ray, T.B., Kestler, D.P., Mayne, B.C., Brown, R.H. and Black, C.C. Plant Physiol. In Submission. (1975)
1446
Vol. 66, No. 4, 1975
BIOCHEMICAL
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
COMPONENTS OF THE PHOTOSYNTHETIC CO2
COMPENSATION POINT OF HIGHER PLANTS D.P.
Kestler,
B.C. Mayne, T.B. Ray, L.D. R.H. Broom* and C.C. Black
Botany
Received
August
Goldstein
Department, University of Georgia Athens, Georgia 30602
27,197s SUMMARY
Barley, Poxiczm mizioides and Pmicwn maxirr.wnwere exposed to 14c02 ar their photosynthetic CO2 compensation points and their respective PZ C-products were determined. In short exposure times Panicwn maxim had 100% of its l4 whereas Panicwn milioides and and aspartaE$C in c4 organic acids. Near barley had 16 and c 3%inof ma1ate their respective the respective CO2 compensation points a linear relationship occurs in plotting the ratio of glycine, serine, and glycerate to C4 organic acids. The ratio of ribulose 1,5-bisphosphate oxygenase to phosphoenolpyruvate carboxylase is linear with their CO2 compensation points. The photosynthetic CO2 compensation point apparently is controlled by the activity of enzymes producing photorespiration metabolites and the activity of phospheonolpyruvate carboxylase. INTRODUCTION The photosynthetic pressure
of CO2 at which
CO2 uptake. until
CO2 compensation
To determine
CO2 equilibrium
groups
of higher
plants
compensate
is
plants
respiratory I,
each with
There
are
have
a variable
daily
F has been
used as a qualitative
* Agronomy
Department
r changing measurement
the partial photosynthetic
in a closed
3 major
a distinctive
is
equals
are illuminated
at 0 to 10 ppm C02, C3 plants
CAM plants
(I)**
CO2 release
plants
reached.
point
chamber
photosynthetic
range
of T values.
range
from
from 0 through of photorespiration
C4
35 to 70, and to 200 (1). and in
**Abbreviations used are: I, photosynthetic CO2 compensation concentration; C3, reductive pentose phosphate; C4, C4-dicarboxylic acid; RuDPC, ribulose 1,5-bisphosphate carboxylase; PEPC, phosphoenolpyruvate carboxylase; P, P&cum; RuDPO, ribulose 1,5-bisphosphate oxygenase; PGA, 3-phosphoglyceric acid; and CAM, Crassulacean acid metabolism.
Vol. 66, No. 4, 1975
plant
BIOCHEMICAL
breeding
selection
the underlying Brown
biochemical
and the
between
those
mediate
species
of plants
P. hiarts
unpublished those
reactions,
procedures
and P. mizioides
stant
until
were
the plants
value.
865)
reached
a steady
the chamber
55 seconds
of r.
leaves
without
used to study in
were
con-
mflioides. CO2 uptake
in air
and near
14C02 fixation
a water-sealed
near
r.
chamber of air
was measured
a stream
of N2 flowing
(4)
to a con-
by removing through
a
When the CO2 concentration barley
and 25 ppm for
10 mCi per
of barley
disturbing
plants,
and a species
Pam&m
CO2 concentration
40 ppm for activity
the discovery
Studies
maxhan,
plants,
inter-
I'.
gas analyzer.
specific
are
AND METHODS
the
into
(near
14 CO2 labeled
chamber. from
infared
state
0.1 mCi of 14C02,
it
photores-
also With
Pmricwn
CO2 concentration
30 ml of gas and injecting (Model
components
illuminated
reduced
The chamber
Beckman
were
of r,
of C3 and C4 photosynthesis
controlling
MATERIALS
at 25'C
and P. lam
observation).
a C4 plant,
parameters
However,
are intermediate
on enzymes involved in light-dependent 14 14 the C-products of CO2 fixation
and the biochemical
Barley
the value
milioides,
C3 and C4 photosynthesis
be presented
The following
that
in Pmicwn
barley,
(2).
of r are unknown.
of the biochemical
between
photorespiration
reported
between
a C3 plant,
and release r,
anatomy
F values a study
intermediate Data will
recently
(R. H. Brown,
with
with
components
(3)
leaf
to reduce
of C3 and C4 plants.
we undertook ducted
programs
and Brown
piration,
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
mmole,
was injected
and P. mizioides
the atmosphere
and fixed
immediately
in 85% ethanol
maxhun
was allowed
to approach
was impossible
to remove
P. mitioides),
were
at intervals cooled
into
removed up to
in a dry-ice
acetone
bath. Pmicwn bag (3). bag without exposures
Since
it
disturbing were
made.
the
internal
In addition,
r (2 5 ppm) inside leaf
atmosphere, when
1440
samples separate
the bags were
from timed
opened
the
a mylar the sealed 14c02 some P.
Vol. 66, No. 4, 1975
BIOCHEMICAL
leaves
maximum
were
exposed
and fixed
as described
extracted
and chromatographed
of Bassham counted
for
standards
total
(5).
enzyme
grown
eluted, for
assayed
plants
times
were
up to 70 seconds of 14 CO2 fixation
products
according
chromatogram
positive
spots
identification
phosphoglycerate
using used
standard for
were
localized,
against
known
(5,6). phosphatase,
procedures
PEPC,
(4,7,8,9).
14 CO2 fixation
both
were
to the procedures
and co-chromatographed
phosphatase,
RuDPC, and RuDPO were
for
The soluble
Radioactive
solvents
Phosphoglycolate
air
in two dimensions
activity,
in other
Greenhouse
to ambient
above.
and Calvin
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
experiments
and
assays. RESULTS AND DISCUSSION
The initial near in
l4 C-products
the CO2 compensation air
than
in Table those
I.
found
point
The initial in similar
Table
Plant Leaves
(5 to 20 seconds)
CO2 Cone.
I.
are
of labeling
contrasted
with
l4 C-products experiments
formed
at ambient
similar near
experiments experiments P were
different
CO2 concentrations
Labeled Products of Photosynthetic 14CO2 Fixation Near p and in Air.
Mal.
wm
Asp.
Products Glycine PGA +Serine
% of total
l4 C-labeled
Glycerate
Others
products
Exposure Times
Seconds
Barley
P. milioides
C -25
9
7
27
33
11
13
5 to 15
air
0
0
4
37
27
30
10
P.max7hum
1441
Vol. 66, No. 4, 1975
(= 300 ppm). was PGA.
BIOCHEMICAL
The major
However,
malate,
while
near
product
labeling
times
as early
labeled
P a significant
Glycine near
fixation
F than
products products
near
of the
label
appeared
types
of plants
the products
in C4 organic
the products
quite
it
P.
did
maximum
initially
organic
3%, was found as initial
were
composed
near
I'; in air
acids
(Table
in short did
not
appear
16% of the early
increased
6-fold
near
was in C4 organic a smaller I).
in
products
higher
C4 acids
serine
of CO2 fixation
Therefore,
it
retained
over
70 seconds turnover
(1)
detectable
leaf
that
that
is
acids
fraction
Thus in all
at r are quite
the
turnover
of the three
different
from
atmospheric
of interest
that
near
at r.
at I is
the efficiency
initial
taken
is
a result
have
in malate
clearly
The total
levels
r we also
label
these
as support
plus
C4 acids
fixation
of CO2
for
of C4 photosynthesis
photorespiration
of C4 organic
with
of a 14 CO2chase;
in leaves
time
in C4 plants
80% of its
by P. maxim
acids
hypothesis
known
@30 seconds)
even after
not
into
is well
short
of CO2 (l,lO,ll).
aspartate
plus
CO2
in air.
In addition,
observed
also
in P. maximwn
label
in experiments
of label,
C4 acids
Glycine
P.
P or at ambient
detected
levels
while
in air,
at 7 and 20 seconds total
were
near
In P. miZioides
in air.
All
is
amount
and serine
r in P. miZioides.
acids
in barley
in 300 ppm CO2 no C4 acids
of photosynthesis.
'4CO2
initial
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
our previous
and the
of PEPC serving
lack
of
as a CO2
trap. The activities are
given
in Table
relationship for
tions
The present
II.
between
14C02 fixation
barley,
of some photosynthetic
shows a decreasing with
intermediate
species
r.
near
additional
relation
will
enzyme levels
and P. mtimtlm
P. miZioides,
supplemented
discussion
P and particular experiments
and photorespiratory
A plot
against (Fig.
C4 and
C3
the same relation
1442
1A).
enzymes
concentrate in
upon the
the plants
used
of the PEPC level their
respective
When these
species
as well
remains
(Fig.
of
CO2 compensa-
PEPC data as other
1B).
A plot
are
C3-C4 of RuDPO
Vol. 66, No. 4,1975
BIOCHEMICAL
Table
Plant
II.
RuDPO
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Activities of Some Photosynthetic and Photorespiration Enzymes in Leaf Extracts.
RuDPC
PEPC
umoles
P-Glycolate Phosphatase
per mg chlorophyll
46-68
2360
108
---
P. miZioides'
16
407
123
184
P. maximum
9-14
440
1235
68
Barley
1
Average
of 5 plant
introduction
P-Glycerate Phosphatase per
RuDPO PEPC
hr ---
0.54
1000
0.13
1184
0.009
lines.
I
A
n
A I 0
10
I
1 30
AA
= = E = d
40
0
IA
0
50
10
30
Figure 1. Leaf photosynthetic CO2 compensation point versus: A. PEPC in barley, P. milioides, and P. ma.rimum leaf extracts; B. PEPC collected from the literature for a variety of leaves; C. RuDPC (-) and RuDPO (---) in the three plants; and D. 14C-malate plus aspartate in 5 to 7 seconds of 14C02 fixation near I? in the three plants.0 = P. macrhwn; l = P. m-itioides; A = barley.
1443
50
Vol. 66, No. 4,1975
BIOCHEMICAL
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
0
r , ppm
20
40
60
CO2
Figure 2. Leaf photosynthetic CO2 compensation point versus: A. the ratio of RuDPO to PEPC in leaf extracts from barley, P. milioides, and P. maxim; B. ratio of % 14C in glycine plus serine to aspartate plus ma&te in 14C02 of C in glycine fixation experiments near I in the three plants; C. ratfz CO2 fixation experiplus serine plus glycerate to aspartate plus malate in measured as CO2 ments P in the three plants; and D. leaf photorespiration release into C02-free air (3).0 = P. muzinun; l = P. milioides; A = barley.
and RuDPC activity shown
in Figure
1C.
I nor were
plots
(Table
linear.
II)
is
senting
the relation
levels ratio
via
(Fig.
lower
plots
show a linear
phosphatase
This
2A).
of CO2 release PEPC.
of PEPC, therefore, is
and P. mtimwn
consistent
via
C3 plants this with
ratio
contain ratio
the low
1444
is
against
leaf high
quite levels
high.
with
T a linear
rela-
of as repre-
photorespiration levels
T is
phosphatase
can be thought
the
against
relationship
or P-glycerate
of RuDPO to PEPC is plotted
observed
to CO2 uptake
None of these
of P-glycolate
When the ratio tionship
P. mizioides,
of barley,
system
of RuDPO and low In C,J, plants
of RuDPO and the higher
this
BIOCHEMICAL
Vol. 66, No. 4,1975
levels
of PEPC associated
RuDPO nearer (Table
that
II),
is
in
The ratio
another
near
relation
acids
to the relation
versus
near
CO2 compensation
photorespiration
(Figs. data
and glycerate
the ratios
are
via components
leaves
Acknowledgements: Foundation Grant Incorporated.
that
of gp,O;
photorespiration
in
P (Table
we propose
photorespiration
point
these
to
enzymes
in
the relative
amounts
versus
1A).
I is significant, of fixation
In addition,
(3)
relation
r in similar
from
the
relationship
A linear
and l' also
intermediates
near
obtained
show a linear
2B & 2C).
The
the ratios
+ glycerate, acids I),
plants
is
co
to
relationship observed
(Fig.
in the current
2D).
schemes of
similar
the photorespiration Cq (Fig.
2).
RuDPO and the which
of higher
linear
We conclude carboxylation
determine
relationships
exist
intermediate the
carbon
of CO2 via
the photosynthetic
between
fluxes; flux
through
PEPC are
the
CO2 compensation
plants.
This research was supported in part by National Science BMSJ4-24230 and by a cooperative agreement with Cotton
REFERENCES 1. 2. 3. 4.
2
(2).
Therefore,
biochemical
of oxygenase
lD> shows a decreasing
+ serine C4 organic
points
of
to C3 plants
between
in 5 to 7 seconds
photorespiration
serine,
and leaf
enzymes
I (Fig.
or glycine
experiments
I and:
ratio
relationships
of PEPC to F (Fig.
glycine + serine C4 organic acids
Glycine,
the
a level
(12).
of these
C4 organic
leaf
for
shows
F in C3, C4 and C3-C4 intermediate
percentage
between
of PEPC close
of other
of 14 CO2 appearing
the
and a level value
study
formed
linear
fixation
P. nrizioides
of RuDPO to PEPC must be reflected
of 14C-products this
C4 plants.
an intermediate
A discussion
developed
if
of C4 plants
thus,
carboxylase.
with
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Black, C.C. Ann. Rev. Plant Physiol. 2, 253 Tolbert, N.E. Ann. Rev. Plant Physiol. 22, 45 Brown, R.H. and Brown, W.V. Crop Science, 15: Chen, T.M., Brown, R.H. and Black, C.C. Plant (1971).
1445
(1973). (1971). In Press Physiol.
(1975). 2, 199
Vol. 66, No. 4, 1975
5. 6. 7. 8. 9. 10. 11. 12.
BIOCHEMICAL
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Bassham, J.A. and Calvin, M., The Path of Carbon in Photosynthesis, Prentice Hall, Inc., Englewood Cliffs, New Jersey, 16-27 (1957). Isherwood, F.A. and Hanes, C.S. Biochem. J. 55, 824 (1953). Randall, D.D., Tolbert, N.E., and Gremel, D. Plant Physiol. 68, 480 (1971). Chen, P.S., Toribara, T.Y., and Warner, H. Analytical Chem. 2S, 1756 (1956). Barr, J.T. and Jensen, R.G. Plant Physiol. 53, 39 (1974). C.E. and Burr, G.O. Plant Physiol. do, Kortschak, H.P., Hartt, 209 (1965). Hatch, M.D. and Slack, C.R. Biochem. J., 101, 103 (1966). Goldstein, L.D., Ray, T.B., Kestler, D.P., Mayne, B.C., Brown, R.H. and Black, C.C. Plant Physiol. In Submission. (1975)
1446
