Planta
Planta (1992)187:261-265
9 Springer-Verlag1992
Glycerolipid-fatty-acid desaturase deficiencies in chloroplasts from fruits of Capsicum annuum L. B.D. Whitaker
U.S. Department of Agriculture, Agricultural Research Service, Horticultural Crops Quality Laboratory, Beltsville Agricultural Research Center-West, Beltsville,MD 20705-2350, USA Received 19 August; accepted 6 December 1991 Abstract. Chloroplasts from fruits and leaves of Capsicum annuum cv. 'Bell Tower' were purified on sucrose gradients, and the lipids were separated by column and thin-layer chromatography. The glycerolipids monoand digalactosyldiacylglycerol (MGDG, DGDG), sulfoquinovosyldiacylglycerol (SQDG), and phosphatidylglycerol (PG) were quantified, and the fatty-acid composition at the 1 and 2 positions of the glycerol moiety (sn-1 and sn-2) was determined after hydrolysis with positionspecific lipases. In fruit chloroplasts, A3-trans hexadecenoate (trans-3-16:1) was absent and replaced by palmitate (16: 0) at sn-2 of PG, and Av, 10.13_hexadecatrien_ oate (16:3) at sn-2 of M G D G was greatly reduced and largely replaced by linoleate (18:2). The ratio of 18:2 to linolenate (18 : 3) was consistently greater in glycerolipids from fruit compared with leaf chloroplasts. The lower percentage of C-16 fatty acids at sn-2 indicated that " p r o k a r y o t i c " molecular species were reduced by _ 50% conversion to the unusual fatty acid A 3-trans-16:1 during maturation of the chloroplast (Roughan 1985), In a previous study (Whitaker 1986) the total fattyacid composition of M G D G , D G D G and PG from crude chloroplast preparations was compared in fruits and leaves from five Solanaceous species, including Capsicum annuum. The amount of 16:3 in M G D G was greatly diminished, and loss of this prokaryotic fatty acid was largely offset by an increase in 18:2 in fruit chloroplasts from all five species. Also, A3-trans-16:l was virtually absent and replaced by 16:0 in PG from the fruit chloroplasts. These findings indicated apparent deficiencies in fatty-acyi desaturase activity in the fruit chloroplasts as well as decreased synthesis of glycerolipids via the prokaryotic pathway. In the present study, M G D G , D G D G , SQDG and PG isolated from purified fruit and leaf chloroplasts of C. annuum were quantified and analyzed for the positional distribution of fatty 1 For asymmetricallysubstituted glycerolderivatives, the stereospecific numbering (sn) system of nomenclature is used to distinguish between the two primary carbinol groups at C-1 and C-3. In glycerolipids, fatty acids esterified to the hydroxyl groups on C-1 and C-2 are designated sn-I and sn-2, respectively, whereas the polar head group linked to the hydroxyl on C-3 is designated sn-3.
262
B.D. Whitaker: Fatty-acid desaturase deficiencies in fruit chloroplasts of Capsicum
acids. T h e results s u p p o r t the c o n c l u s i o n t h a t Capsicum fruit c h l o r o p l a s t s are deficient in three f a t t y - a c y l desat u r a s e activities a n d , f u r t h e r m o r e , t h a t one o f these deficiencies alters the r a t i o o f p r o k a r y o t i c d i a c y l g l y c e r o l species a m o n g M G D G , D G D G a n d S Q D G .
Material and methods 2
Bell pepper plants (Capsicum annuum L. cv. 'Bell Tower'; seed obtained from Northrup King, Minneapolis, Minn., USA) were grown in cultivar trial plots at the Beltsville Agricultural Research Center using standard horticultural practices (Whitaker and Lusby 1989). Mature-green fruits and young, fully-expanded leaves were harvested during the first two weeks of September, 1990, when the plants were approx. 14 weeks old. The tissues were homogenized in cold (4~ C) Tricine-sorbitol buffer (0.1 M N-[2-hydroxy1,1-bis(hydroxymethyl)ethylglycine-KOH, pH 7.8, containing 0.33 M o-sorbitol, 1 mM EDTA and 1 mM fl-mercaptoethanol) and crude fruit and leaf chloroplast fractions were obtained by differential centrifugation as previously described (Whitaker 1986). The crude chloroplasts were purified by centrifugation on discontinuous sucrose gradients as described in Whitaker (1991) with the exceptions that the gradients consisted of 16 ml of 1.0 M buffered sucrose solution layered over 10 ml of 2.0 M sucrose, and the duration of centrifugation (at 62000.g) was 15 rnin. The band of largely intact chloroplasts at the 1.0-M/2.0-M interface was collected from each of six centrifuge tubes with a Pasteur pipet. The pooled, purified plastid suspension was then diluted with an equal volume of 50 mM Tricine (pH 7.8 with KOH), followed by centrifugation for 5 min at 4000.g to precipitate the plastids before lipid extraction. Chloroplast pellets were first extracted with 16 ml of boiling isopropanol containing 10~tg.ml -a butylated hydroxytoluene, then with 18 ml of chloroform-methanol, 2:1 (v/v). The isopropanol was evaporated from the first extract under a stream of N2 and the two extracts were combined and washed (Whitaker 1991). After addition of 10 lag of lathosterol (cholest-7-en-3/%ol) as an internal free sterol (FS) standard, lipid extracts were stored at - 8 0 ~ C, sealed under N2 in 2 ml of chloroform. A 20-I-tlaliquot was withdrawn from each of the chloroplast-lipid extracts for determination of total chlorophyll and the chlorophyll a:b ratio (Chl a:b) (Inskeep and Bloom 1985). Total chloroplast lipids were separated into neutral lipid, glycolipid and phospholipid (PL) fractions by silicic-acid column chromatography (Whitaker 1991). Carotenes and FS in the neutral-lipid fraction were separated by elution from silica Sep-Paks (Waters Assoc., Milford, Mass., USA), and FS were recovered and quantified by capillary gas chromatography with flame-ionization detection (FID-GLC) as previously described (Whitaker and Lusby 1989). Galactolipids (MGDG, DGDG), acylated steryl glycosides and free steryl glycosides were isolated from the glycolipid fraction, and SQDG, PG, phosphatidylcholine, phosphatidylethanolamine (PE) phosphatidylinositol and phosphatidic acid were isolated from the PL fraction by one-dimensional TLC (Whitaker 1991). Phospholipids, MGDG, DGDG and SQDG were quantified by spectrophotometric assays as reported in Whitaker (1991). Acylated and free steryl glycosides were quantified as described in Whitaker et al. (1990). Chemicals and lipid standards were obtained from Sigma Chemical Co., St. Louis, Mo., USA or from Matreya, Pleasant Gap, Penn., USA. All solvents used were high-performance liquid chromatography grade. Determination of the positional distribution of fatty acids in MGDG, DGDG, SQDG and PG was performed as described by Norman and St. John (1986). The glycoglycerolipids (MGDG, DGDG, and SQDG) were dissolved in 1 ml of diethyl ether and 2 Use of a company or product name does not imply approval or recommendation of the product by the U.S. Department of Agriculture to the exclusion of others which may also be suitable.
fatty acids were hydrolyzed from the sn-1 position by incubating for 1 h at 37~ with lipase from Rhizopus arrhizus (Boehringer Mannheim Biochemicals, Indianapolis, Ind., USA). Samples of PG dissolved in 50 lal of N,N-dimethylformamide were suspended in 1 ml of diethyl ether and fatty acids were hydrolyzed from the sn-2 position by incubating for 1 h at 37~ C with phospholipase Az from Crotalus adamanteus (Sigma). Free-fatty-acid and lysolipid products of the enzymatic hydrolyses were separated by elution from silica Sep-Pak cartridges with chloroform (free fatty acids) followed by methanol (lysolipids). Lysolipid products were further separated from any unhydrolyzed glycerolipid substrate by TLC (Norman and St. John 1986). Fatty acids on the lysolipids and free fatty acids were derivatized to fatty-acid methyl esters with 14% boron trifluoride in methanol (Sigma) (20 min at 70~ C under N J . Fatty-acid methyl esters were analyzed by FID-GLC on a Perk• 8320 gas chromatograph fitted with a 15-m SP2330 fused silica capillary column (0.25 mm internal diameter, 0.20 ~m film thickness; Supelco, Bellefonte, Penn., USA). The column oven temperature was increased from 145~ to 170~ C over 9 rain. Injector and detector temperatures were 200 ~ and 225~ C, respectively, and the carrier gas (He2) head pressure was 41 kPa.
Results
C o m p a r i s o n o f the c a r o t e n e , g l y c e r o l i p i d a n d steryl lipid c o n t e n t s (per 1 m g C h l ; Table 1) s h o w e d the levels o f PL, D G D G , S Q D G a n d F S to be higher in fruit c h l o r o plasts, w h e r e a s the levels o f c a r o t e n e s a n d M G D G were higher in l e a f c h l o r o p l a s t s o f C. annuum. T h e P L c o m p o sition was quite similar in fruit a n d leaf c h l o r o p l a s t s ; P G a n d p h o s p h a t i d y l c h o l i n e were the p r e d o m i n a n t P L in a r a t i o o f > 2 P G to I p h o s p h a t i d y l c h o l i n e (Table 2). P h o s p h a t i d y l e t h a n o l a m i n e is v i r t u a l l y a b s e n t f r o m chlor o p l a s t m e m b r a n e s (in leaves) ( K i r k a n d T i l n e y - B a s s e t t 1978, p. 56) a n d hence the m o l % o f P E in the c h l o r o p l a s t P L f r a c t i o n is indicative o f the extent o f c o n t a m i n a t i o n b y o t h e r cell m e m b r a n e s . By this criterion, the fruit chlor o p l a s t p r e p a r a t i o n s were slightly p u r e r t h a n those f r o m the leaves (Table 2 a n d P E : P G in Table 3). In a g r e e m e n t with o t h e r studies o f c h l o r o p l a s t lipids ( P o i n c e l o t 1976; K i r k a n d T i l n e y - B a s s e t t 1978, p. 60), small a m o u n t s o f F S , a c y l a t e d steryl glycoside a n d free steryl glycoside were p r e s e n t in fruit a n d l e a f c h l o r o -
Table 1. Lipid content in chloroplasts from fruits and leaves of C. annuum. Values are expressed in lamol.(mg Chl) I + S D , with
the exception of those for carotenes which are in lag. (mg Chl)-1 • SD (n = 4) Lipid Carotenes Phospholipid Monogalactosyldiacylglycerol Digalactosyldiacylglycerol Sulfoquinovosyldiacylglycerol Free sterol Acylated steryl glycoside Steryl glycoside
Fruit chloroplasts
Leaf chloroplasts
27.0 • 0.423 • 0.041 1.161 +0.121
35.1 • 0.320 • 0.033 1.323+0.028
1.015 _+0.107
0.608 _+0.035
0.266 + 0.019
0.183 + 0.008
0.037• 0.015 • 0.004
0.014_+0.002 0.012 _+0.003
0.006 • 0.002
0.007 _+0.002
B.D. Whitaker: Fatty-acid desaturase deficiencies in fruit chloroplasts of Capsicum TaMe 2, Phospholipid composition of chloroplasts from fruits and leaves of C. annuum. Values are expressed as the tool% of total phospholipids_+ SD (n =4) Phospholipid Phosphatidic acid Phosphatidylethanolamine Phosphatidylglycerol Phosphatidylcholine Phosphatidylinositol
Fruit chloroplasts
Leaf chloroplasts
1.8 • 0.6
1.3 • 0.6
7.5 • 2.1
9.5 • 2.0
57.0 _+3.7
54.9 • 4.1
25.1 • 2.7
26.7 • 3.3
8.6_+ 1.5
7.6 • t .6
Table 3. Lipid ratios in chloroplasts from fruits and leaves of C. annuurn. All values are expressed as molar ratios+SD (n=4). TSL = FS + acylated and free steryl glycosides Lipid ratio
Fruit chloroplasts
Leaf chloroplasts
FS : PL TSL:PL PE:PG GL: PL MGDG:DGDG MGDG: SQDG MGDG: PG
0.09_ 0.02 0.14__+0.03 0.13-t-0.04 5.77 • 0.20 1.15• 4.40 • 0.35 4.85 • 0.37
0.05 • 0.01 0.10+0.01 0.17+0.05 6.69 • 0.43 2.18_+0.09 7.24 • 0.21 7.68 _+0.41
263
Table 4. Positional distribution of fatty acids in glycerolipids from fruit and leaf chloroplasts of C. annuurn. Values are expressed as the weight-% of total fatty acids in either the intact lipid (Total) or at the sn-i or sn-2 position of the glycerol moiety, and represent the mean of four determinations from four chloroplast preparations Fatty acids
Fruit chloroplasts Total
Leaf chloroplasts sn-2
Total
sn-1
sn-2
2
Planta (1992)187:261-265
9 Springer-Verlag1992
Glycerolipid-fatty-acid desaturase deficiencies in chloroplasts from fruits of Capsicum annuum L. B.D. Whitaker
U.S. Department of Agriculture, Agricultural Research Service, Horticultural Crops Quality Laboratory, Beltsville Agricultural Research Center-West, Beltsville,MD 20705-2350, USA Received 19 August; accepted 6 December 1991 Abstract. Chloroplasts from fruits and leaves of Capsicum annuum cv. 'Bell Tower' were purified on sucrose gradients, and the lipids were separated by column and thin-layer chromatography. The glycerolipids monoand digalactosyldiacylglycerol (MGDG, DGDG), sulfoquinovosyldiacylglycerol (SQDG), and phosphatidylglycerol (PG) were quantified, and the fatty-acid composition at the 1 and 2 positions of the glycerol moiety (sn-1 and sn-2) was determined after hydrolysis with positionspecific lipases. In fruit chloroplasts, A3-trans hexadecenoate (trans-3-16:1) was absent and replaced by palmitate (16: 0) at sn-2 of PG, and Av, 10.13_hexadecatrien_ oate (16:3) at sn-2 of M G D G was greatly reduced and largely replaced by linoleate (18:2). The ratio of 18:2 to linolenate (18 : 3) was consistently greater in glycerolipids from fruit compared with leaf chloroplasts. The lower percentage of C-16 fatty acids at sn-2 indicated that " p r o k a r y o t i c " molecular species were reduced by _ 50% conversion to the unusual fatty acid A 3-trans-16:1 during maturation of the chloroplast (Roughan 1985), In a previous study (Whitaker 1986) the total fattyacid composition of M G D G , D G D G and PG from crude chloroplast preparations was compared in fruits and leaves from five Solanaceous species, including Capsicum annuum. The amount of 16:3 in M G D G was greatly diminished, and loss of this prokaryotic fatty acid was largely offset by an increase in 18:2 in fruit chloroplasts from all five species. Also, A3-trans-16:l was virtually absent and replaced by 16:0 in PG from the fruit chloroplasts. These findings indicated apparent deficiencies in fatty-acyi desaturase activity in the fruit chloroplasts as well as decreased synthesis of glycerolipids via the prokaryotic pathway. In the present study, M G D G , D G D G , SQDG and PG isolated from purified fruit and leaf chloroplasts of C. annuum were quantified and analyzed for the positional distribution of fatty 1 For asymmetricallysubstituted glycerolderivatives, the stereospecific numbering (sn) system of nomenclature is used to distinguish between the two primary carbinol groups at C-1 and C-3. In glycerolipids, fatty acids esterified to the hydroxyl groups on C-1 and C-2 are designated sn-I and sn-2, respectively, whereas the polar head group linked to the hydroxyl on C-3 is designated sn-3.
262
B.D. Whitaker: Fatty-acid desaturase deficiencies in fruit chloroplasts of Capsicum
acids. T h e results s u p p o r t the c o n c l u s i o n t h a t Capsicum fruit c h l o r o p l a s t s are deficient in three f a t t y - a c y l desat u r a s e activities a n d , f u r t h e r m o r e , t h a t one o f these deficiencies alters the r a t i o o f p r o k a r y o t i c d i a c y l g l y c e r o l species a m o n g M G D G , D G D G a n d S Q D G .
Material and methods 2
Bell pepper plants (Capsicum annuum L. cv. 'Bell Tower'; seed obtained from Northrup King, Minneapolis, Minn., USA) were grown in cultivar trial plots at the Beltsville Agricultural Research Center using standard horticultural practices (Whitaker and Lusby 1989). Mature-green fruits and young, fully-expanded leaves were harvested during the first two weeks of September, 1990, when the plants were approx. 14 weeks old. The tissues were homogenized in cold (4~ C) Tricine-sorbitol buffer (0.1 M N-[2-hydroxy1,1-bis(hydroxymethyl)ethylglycine-KOH, pH 7.8, containing 0.33 M o-sorbitol, 1 mM EDTA and 1 mM fl-mercaptoethanol) and crude fruit and leaf chloroplast fractions were obtained by differential centrifugation as previously described (Whitaker 1986). The crude chloroplasts were purified by centrifugation on discontinuous sucrose gradients as described in Whitaker (1991) with the exceptions that the gradients consisted of 16 ml of 1.0 M buffered sucrose solution layered over 10 ml of 2.0 M sucrose, and the duration of centrifugation (at 62000.g) was 15 rnin. The band of largely intact chloroplasts at the 1.0-M/2.0-M interface was collected from each of six centrifuge tubes with a Pasteur pipet. The pooled, purified plastid suspension was then diluted with an equal volume of 50 mM Tricine (pH 7.8 with KOH), followed by centrifugation for 5 min at 4000.g to precipitate the plastids before lipid extraction. Chloroplast pellets were first extracted with 16 ml of boiling isopropanol containing 10~tg.ml -a butylated hydroxytoluene, then with 18 ml of chloroform-methanol, 2:1 (v/v). The isopropanol was evaporated from the first extract under a stream of N2 and the two extracts were combined and washed (Whitaker 1991). After addition of 10 lag of lathosterol (cholest-7-en-3/%ol) as an internal free sterol (FS) standard, lipid extracts were stored at - 8 0 ~ C, sealed under N2 in 2 ml of chloroform. A 20-I-tlaliquot was withdrawn from each of the chloroplast-lipid extracts for determination of total chlorophyll and the chlorophyll a:b ratio (Chl a:b) (Inskeep and Bloom 1985). Total chloroplast lipids were separated into neutral lipid, glycolipid and phospholipid (PL) fractions by silicic-acid column chromatography (Whitaker 1991). Carotenes and FS in the neutral-lipid fraction were separated by elution from silica Sep-Paks (Waters Assoc., Milford, Mass., USA), and FS were recovered and quantified by capillary gas chromatography with flame-ionization detection (FID-GLC) as previously described (Whitaker and Lusby 1989). Galactolipids (MGDG, DGDG), acylated steryl glycosides and free steryl glycosides were isolated from the glycolipid fraction, and SQDG, PG, phosphatidylcholine, phosphatidylethanolamine (PE) phosphatidylinositol and phosphatidic acid were isolated from the PL fraction by one-dimensional TLC (Whitaker 1991). Phospholipids, MGDG, DGDG and SQDG were quantified by spectrophotometric assays as reported in Whitaker (1991). Acylated and free steryl glycosides were quantified as described in Whitaker et al. (1990). Chemicals and lipid standards were obtained from Sigma Chemical Co., St. Louis, Mo., USA or from Matreya, Pleasant Gap, Penn., USA. All solvents used were high-performance liquid chromatography grade. Determination of the positional distribution of fatty acids in MGDG, DGDG, SQDG and PG was performed as described by Norman and St. John (1986). The glycoglycerolipids (MGDG, DGDG, and SQDG) were dissolved in 1 ml of diethyl ether and 2 Use of a company or product name does not imply approval or recommendation of the product by the U.S. Department of Agriculture to the exclusion of others which may also be suitable.
fatty acids were hydrolyzed from the sn-1 position by incubating for 1 h at 37~ with lipase from Rhizopus arrhizus (Boehringer Mannheim Biochemicals, Indianapolis, Ind., USA). Samples of PG dissolved in 50 lal of N,N-dimethylformamide were suspended in 1 ml of diethyl ether and fatty acids were hydrolyzed from the sn-2 position by incubating for 1 h at 37~ C with phospholipase Az from Crotalus adamanteus (Sigma). Free-fatty-acid and lysolipid products of the enzymatic hydrolyses were separated by elution from silica Sep-Pak cartridges with chloroform (free fatty acids) followed by methanol (lysolipids). Lysolipid products were further separated from any unhydrolyzed glycerolipid substrate by TLC (Norman and St. John 1986). Fatty acids on the lysolipids and free fatty acids were derivatized to fatty-acid methyl esters with 14% boron trifluoride in methanol (Sigma) (20 min at 70~ C under N J . Fatty-acid methyl esters were analyzed by FID-GLC on a Perk• 8320 gas chromatograph fitted with a 15-m SP2330 fused silica capillary column (0.25 mm internal diameter, 0.20 ~m film thickness; Supelco, Bellefonte, Penn., USA). The column oven temperature was increased from 145~ to 170~ C over 9 rain. Injector and detector temperatures were 200 ~ and 225~ C, respectively, and the carrier gas (He2) head pressure was 41 kPa.
Results
C o m p a r i s o n o f the c a r o t e n e , g l y c e r o l i p i d a n d steryl lipid c o n t e n t s (per 1 m g C h l ; Table 1) s h o w e d the levels o f PL, D G D G , S Q D G a n d F S to be higher in fruit c h l o r o plasts, w h e r e a s the levels o f c a r o t e n e s a n d M G D G were higher in l e a f c h l o r o p l a s t s o f C. annuum. T h e P L c o m p o sition was quite similar in fruit a n d leaf c h l o r o p l a s t s ; P G a n d p h o s p h a t i d y l c h o l i n e were the p r e d o m i n a n t P L in a r a t i o o f > 2 P G to I p h o s p h a t i d y l c h o l i n e (Table 2). P h o s p h a t i d y l e t h a n o l a m i n e is v i r t u a l l y a b s e n t f r o m chlor o p l a s t m e m b r a n e s (in leaves) ( K i r k a n d T i l n e y - B a s s e t t 1978, p. 56) a n d hence the m o l % o f P E in the c h l o r o p l a s t P L f r a c t i o n is indicative o f the extent o f c o n t a m i n a t i o n b y o t h e r cell m e m b r a n e s . By this criterion, the fruit chlor o p l a s t p r e p a r a t i o n s were slightly p u r e r t h a n those f r o m the leaves (Table 2 a n d P E : P G in Table 3). In a g r e e m e n t with o t h e r studies o f c h l o r o p l a s t lipids ( P o i n c e l o t 1976; K i r k a n d T i l n e y - B a s s e t t 1978, p. 60), small a m o u n t s o f F S , a c y l a t e d steryl glycoside a n d free steryl glycoside were p r e s e n t in fruit a n d l e a f c h l o r o -
Table 1. Lipid content in chloroplasts from fruits and leaves of C. annuum. Values are expressed in lamol.(mg Chl) I + S D , with
the exception of those for carotenes which are in lag. (mg Chl)-1 • SD (n = 4) Lipid Carotenes Phospholipid Monogalactosyldiacylglycerol Digalactosyldiacylglycerol Sulfoquinovosyldiacylglycerol Free sterol Acylated steryl glycoside Steryl glycoside
Fruit chloroplasts
Leaf chloroplasts
27.0 • 0.423 • 0.041 1.161 +0.121
35.1 • 0.320 • 0.033 1.323+0.028
1.015 _+0.107
0.608 _+0.035
0.266 + 0.019
0.183 + 0.008
0.037• 0.015 • 0.004
0.014_+0.002 0.012 _+0.003
0.006 • 0.002
0.007 _+0.002
B.D. Whitaker: Fatty-acid desaturase deficiencies in fruit chloroplasts of Capsicum TaMe 2, Phospholipid composition of chloroplasts from fruits and leaves of C. annuum. Values are expressed as the tool% of total phospholipids_+ SD (n =4) Phospholipid Phosphatidic acid Phosphatidylethanolamine Phosphatidylglycerol Phosphatidylcholine Phosphatidylinositol
Fruit chloroplasts
Leaf chloroplasts
1.8 • 0.6
1.3 • 0.6
7.5 • 2.1
9.5 • 2.0
57.0 _+3.7
54.9 • 4.1
25.1 • 2.7
26.7 • 3.3
8.6_+ 1.5
7.6 • t .6
Table 3. Lipid ratios in chloroplasts from fruits and leaves of C. annuurn. All values are expressed as molar ratios+SD (n=4). TSL = FS + acylated and free steryl glycosides Lipid ratio
Fruit chloroplasts
Leaf chloroplasts
FS : PL TSL:PL PE:PG GL: PL MGDG:DGDG MGDG: SQDG MGDG: PG
0.09_ 0.02 0.14__+0.03 0.13-t-0.04 5.77 • 0.20 1.15• 4.40 • 0.35 4.85 • 0.37
0.05 • 0.01 0.10+0.01 0.17+0.05 6.69 • 0.43 2.18_+0.09 7.24 • 0.21 7.68 _+0.41
263
Table 4. Positional distribution of fatty acids in glycerolipids from fruit and leaf chloroplasts of C. annuurn. Values are expressed as the weight-% of total fatty acids in either the intact lipid (Total) or at the sn-i or sn-2 position of the glycerol moiety, and represent the mean of four determinations from four chloroplast preparations Fatty acids
Fruit chloroplasts Total
Leaf chloroplasts sn-2
Total
sn-1
sn-2
2
