Changes in Chloroplast Lipids during the Development of Photosynthetic Activity in Barley Etio‐Chloroplasts

Changes in acyl lipids and pigments during leaf development in a virescens barley mutant (M) and the normal (N) were studied. Apical 3-cm leaf segments were extracted with chloroform-methanol, the extracts were purified on Sephadex G-25 columns, and the polar Upids were separated on two-dimensional-thin layer chromatography silica gel plates. The pigment reining on the Sephadex column was identified as flavonoids and a zone on the TLC plates which did not correspond to the usual standards was identified as gramine. Quantification of acyl lipids by either polar head group analysis or fatty acid analysis using heptadecanoate as an internal standard gave similar results. The per cent of the total lipid extract quanted for the M between 4 and 8 days ranged from 46 to 65% and that for the N ranged from 60 to 68%. Of these, acyl lipids represented 37 to 48% in the M and 43 to 50% in the N. By 8 days, mono-and digalactosyldiglyceride (MG and DG) accounted for 45 and 25% of the total acyl lipid of both the M and N. For the period of study here, this represented a 4-fold increase in MG and a 2.5-fold increase in DG in the M but only a 1.8-fold increase for MG and DG in the N. These increases were closely correlated with the increases in chlorophyll. Chlorophyli increased sharply between 4 and 6 days for the N, whereas, in the M, it rose from 7 to 50% relative to the normal by 8 days. The proportions of the various fatty acids were unique for the lipld classes. The only major quantitative change for a fatty acid was for hexadecanoate in phosphatidylglycerol which increased from 5% at 4 days to 25 to 30% by 8 days. Relative to the N, the carotenoid content of the M increased from 14 to 50% between 4 and 8 days. In both the M and N, the increase in a8-carotene and chlorophyll were closely correlated.Chloroplast thylakoid membranes contain a unique lipid composition which is ubiquitous to higher plants and differs considerably from that of other cellular membranes. an unique fatty acid, trans-3-hexadecanoic acid, which is found specifically in photosynthetic tissue and is esterified primarily to PG (20). This specialized acyl lipid composition has led to the suggestion that lipids play a vital role in photosynthesis.The chloroplast is very active in cellular lipid biosynthesis; the complete biosynthetic pathway from 5-ALA to Chl (8) and the synthesis of carotenoids occur within the plastid (18). Also, the plastid has been suggested to be the major, if not the sole, site of cellular de novo fatty acid biosynthesis (36). The full assembly of the complex chloroplast acyl lipids, however, appears to require enzyme systems associated with both the plastid and the cytoplasm (17,46). Studies using inhibitors specific for cytoplasmic ribosomes indicated the formation of 5-ALA (26) and the fatty acid desaturase enzyme activity (35) are dependent upon protein synthesis by the cytoplasmic ribosomes. Nuclear mutations controlling the steps between protophorphyrin IX and protochlorophyllide (51) and the desaturation and cyclizati...

Section: Discussionsupporting

confidence: 81%

Section: Discussionmentioning

confidence: 52%

See 1 more Smart Citation

Acyl Lipids, Pigments, and Gramine in Developing Leaves of Barley and Its Virescens Mutant

Thomson¹,

Zalik²

1981

“…Evidence cited in support of this suggestion included a decrease in PSII activity following treatment with phospholipase A2 (5), and a positive correlation during plastid greening between diuron-sensitive electron transport and the concentration of PG (23). In addition, the increase in 16:1 concentration found in PG from resistant Brassica biotypes could be associated with triazine resistance.…”

Section: Methodsmentioning

confidence: 97%

Characterization of Chloroplasts Isolated from Triazine-Susceptible and Triazine-Resistant Biotypes of Brassica campestris L.

Burke¹,

Wilson²,

Swafford³

1982

Chloroplasts isolated from triazine-susceptible and triazine-resistant biotypes of Brassica campestris L. were analyzed for Upid composition, ultrastructure, and relative quantum requirements of photosynthesis. In general, phospholipids, but not glycolipids in chloroplasts from the triazineresistant biotype had a higher linolenic acid concentration and lower levels of oleic and linoleic fatty acids, than chloroplasts from triazine-susceptible plants. Chloroplasts from the triazine-resistant biotype had a 1.6-fold higher concentration of t-A-hexadecenoic acid with a concomitantly lower palmitic acid concentration in phosphatidylglycerol. Phosphatidylglycerol previously has been hypothesized to be a boundary lipid for photosystem 11. Chloroplasts from the triazine-resistant biotype had a lower chlorophyll a/b ratio and exhibited increased grana stacking. light-saturation curves revealed that the relative quantum requirement for whole chain electron transport at limiting light intensities was lower for the susceptible biotype than for the triazine-resistant biotype. Althougb the level of the chlorophyll a/b light-harvesting complex associated with photosystem II was greater in resistant biotypes, the increased levels of the light-harvesting complex did not increase the photosynthetic efficiency enough to overcome the rate limitation that is inherited concomitantly with the modification of the Striazine binding site.Variability in the sensitivity of photosynthesis to S-triazine herbicides has been demonstrated in 10 different weed species (14). The mechanism for resistance to triazine has resulted from specific genetic mutations or subtle modifications of the biochemistry in the photosynthetic apparatus.Radosevich and Appleby (19) have shown that the differences in resistance found in common groundsel (Senecio vulgaris L.) biotypes were not attributed to variation in germination time, rooting depth, or morphology resulting in differences in exposure to the herbicide. They also demonstrated that uptake and eventual metabolism of the triazines was identical for the susceptible and resistant groundsel biotypes (18) (14,15). In those studies, [4C]azido-atrazine was shown to bind to a 32 kd polypeptide of susceptible, but not herbicideresistant, chloroplast membranes. Analysis of the atrazine-binding protein by SDS-polyacrylamide gel electrophoresis, however, has failed to demonstrate any protein modifications between biotypes that might account for the mechanism of this type of triazine resistance.The 32 kd polypeptide is an integral component of the PSII structural complex within the membrane. Hence, the environment provided by neighboring polypeptides and lipids surrounding the binding site on the 32 kd protein could affect the binding of triazine molecules. In an attempt to explore these possibilities, we have analyzed the lipid composition, ultrastructure, and photosynthetic efficiency of chloroplasts from triazine-susceptible and resistant Brassica biotypes to determine both the nature of the lipoidal compl...

“…Previous work has shown that PG serves as a fixed-boundary lipid in thylakoids (13) and has established a positive correlation between DCMU-sensitive electron transport and PG concentration (3,7,18). Therefore it is believed that loss of PG may affect the structural orientation of PSII in thylakoid membranes.…”

Section: Studies On Male-sterile Soybeansmentioning

confidence: 99%

Studies on Genetic Male-Sterile Soybeans

Burke¹,

Kalt-Torres²,

Burton³

et al. 1987

Soybean (Glycine max L. Meff.) germplasm, isogenic except for loci controlling male sterility (ms,), was utilized to study the effects of reproductive development on certain aspects of photosynthesis. Plants were sampled at various times between flowering (77 days after transplanting) and maturity (147 days after transplanting). During that period photosynthetic rates declined more rapidly in the male-sterile genotypes than male-fertile genotypes; and after 105 days, the sterile genotypes maintained low but relatively constant carbon exchange rates. The decline of leaf photosynthesis in the male-sterile genotype occurred concomitantly with an inhibition of the photosynthetic electron transport chain associated with photosystem II. Changes in photosystem I activities, cytochromef levels, and chlorophyll a/b ratiosperse were not responsible for the decline in whole leaf photosynthesis. These conditions were independent of the source of nitrogen nutrition. Lipid analyses of the thylakoids revealed that a loss of phosphatidylglycerol was highly correlated with the inhibition of photosystem II activity. These results suggested a relation between the decline in leaf carbon exchange and the decline in photosynthetic electron transport activity.