Biomedical subjects

E Maissan

Publications and source records attributed to E Maissan.

3 recordsLinked to original sources

PubMed1988

Overwintering Periwinkle (Vinca minor L.) Exhibits Increased Photosystem I Activity.

The effects of natural, overwintering conditions on photosystem I and photosystem II activity were examined in isolated thylakoids of periwinkle (Vinca minor L.), an endemic, cold-tolerant, herbaceous evergreen. DCMU-Insensitive photosystem I activity (ascorbate/dichlorophenolindophenol --> methylviologen) exhibited a twofold increase in light-saturated rates upon exposure to low temperature and freezing stress with no effect on the apparent quantum yield of this reaction. DCMU-Sensitive photosystem II activity (H(2)O --> dichlorlophenolindophenol) exhibited only minor fluctuations in light-saturated rates but a 50% decrease in the apparent quantum yield of this reaction upon exposure to overwintering conditions. This was correlated with a decrease in the 77 degrees K fluorescence emission at 694 nanometers. These functional changes occurred with no detectable changes in the relative chlorophyll contents of the chlorophyll-protein complexes or the chlorophyll-thylakoid protein. The chlorophyll a/b varied less than 10% during any single growth year. Analyses of total leaf extracts indicated that all lipid classes exhibited increased levels of linoleic and linolenic acid. Neither the trans-Delta(3)-hexadecenoic acid level nor the ratio of oligomeric:monomeric light harvesting of photosystem II was affected by exposure to winter stress. The content of the major chloroplast lipids monogalactosyldiacylglycerol, digalactosyldiacylglycerol, phosphatidyl-diacyl-glycerol, and sulfoquinovosyldiacylglycerol exhibited minor fluctuations, whereas phosphatidylcholine and phosphatidylethanolamine content doubled on a mole percent or chlorophyll basis. We conclude that the previously reported increase in photosystem I activity during controlled, low temperature growth is observed during exposure to natural overwintering conditions. This appears to occur with minimal changes in the structure and composition of the photosynthetic apparatus of periwinkle.

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PubMed1987

Low Temperature Development Induces a Specific Decrease in trans-Delta-Hexadecenoic Acid Content which Influences LHCII Organization.

Lipid and fatty acid analyses were performed on whole leaf extracts and isolated thylakoids from winter rye (Secale cereale L. cv Puma) grown at 5 degrees C cold-hardened rye (RH) and 20 degrees C nonhardened rye (RNH). Although no significant change in total lipid content was observed, growth at low, cold-hardening temperature resulted in a specific 67% (thylakoids) to 74% (whole leaves) decrease in the trans-Delta(3)-hexadecenoic acid (trans-16:1) level associated with phosphatidyldiacylglycerol (PG). Electron spin resonance and differential scanning calorimetry (DSC) indicated no significant difference in the fluidity of RH and RNH thylakoids. Separation of chlorophyll-protein complexes by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that the ratio of oligomeric light harvesting complex:monomeric light harvesting complex (LHCII(1):LHCII(3)) was 2-fold higher in RNH than RH thylakoids. The ratio of CP1a:CP1 was also 1.5-fold higher in RNH than RH thylakoids. Analyses of winter rye grown at 20, 15, 10, and 5 degrees C indicated that both, the trans-16:1 acid levels in PG and the LHCII(1):LHCII(3) decreased concomitantly with a decrease in growth temperature. Above 40 degrees C, differential scanning calorimetry of RNH thylakoids indicated the presence of five major endotherms (47, 60, 67, 73, and 86 degrees C). Although the general features of the temperature transitions observed above 40 degrees C in RH thylakoids were similar to those observed for RNH thylakoids, the transitions at 60 and 73 degrees C were resolved as inflections only and RH thylakoids exhibited transitions at 45 and 84 degrees C which were 2 degrees C lower than those observed in RNH thylakoids. Since polypeptide and lipid compositions of RH and RNH thylakoids were very similar, we suggest that these differences reflect alterations in thylakoid membrane organization. Specifically, it is suggested that low developmental temperature modulates LHCII organization such that oligomeric LHCII predominates in RNH thylakoids whereas a monomeric or an intermediate form of LHCII predominates in RH thylakoids. Furthermore, we conclude that low developmental temperature modulates LHCII organization by specifically altering the fatty composition of thylakoid PG.

Journal Article↗

PubMed1987

Development at Cold-Hardening Temperatures : The Structure and Composition of Purified Rye Light Harvesting Complex II.

Light harvesting complex II (LHCII) was purified from cold-hardened (RH) and nonhardened winter rye (RNH) (Secale cereale L. cv Puma) employing a modified procedure of JJ Burke, CL Ditto, CJ Arntzen (Arch Biochem Biophys 187: 252-263). Triton X-100 solubilization of thylakoid membranes followed by three successive precipitations with 100 mm KCl and 10 mm MgCl(2) resulted in yields of up to 25% on a chlorophyll (Chl) basis and a purity of 90 to 95%, based on polypeptide analysis within 4 hours. Polypeptide and pigment analyses, 77 K fluorescence emission and room temperature absorption spectra indicate the LHCII obtained by this modified method is comparable to LHCII obtained by other published methods. Comparison of purified RH and RNH LHCII indicated no significant differences with respect to polypeptide, amino acid, Chl, and carotenoid compositions as well as no differences in lipid content. However, RH LHCII differed from RNH LHCII specifically with respect to the fatty acid composition of phosphatidyldiacylglycerol only. RH LHCII exhibited a 54% lower trans-Delta(3)-hexadecenoic acid level associated with PG and a 60% lower oligomeric LHCII:monomeric LHCII (LHCII(1):LHCII(3)) than RNH LHCII. Both RH and RNH LHCII exhibited a 5-fold enrichment in PG specifically. Complete removal of PG by enzymic hydrolysis resulted in a significant reduction in the oligomeric content of both RH and RNH LHCII such that LHCII(1):LHCII(3) of RH and RNH LHCII preparations were the same. This confirms that this specific compositional change accounts for the structural differences between RH and RNH LCHII observed in situ and in vitro.

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