Nostoc flagelliforme Born. et Flah is highly adapted to drought stress, cold and light stresses, and suitable for growing in the unfavorable areas. This paper presents the results of the analysis of the membrane (mainly thylakoid membrane) lipids from N. flagelliforme in order to investigate the relationship between membrane lipid composition and stress resistance to this cyanobacteria. The membrane lipids are composed of monogalactosyl diacylglycerol (MGDG), digalactosyl diacylglycerol (DGDG), sulfoquinovosyl diacylglycerol (SQDG) and phosphatidylglycerol (PG). The major fatty acids in these lipids are palmitic (16∶0), palmitoleic (16∶1), stearic (18∶0), oleic (18∶1), linoleic (18∶2) and linolenic (18∶3) acids. In N. flagelliforme , polyunsaturated fatty acids account for 73% of the total fatty acids, much higher than that of the other cyanobacteria reported so far. Among which 16∶1 and 18∶3 are as high as 28.9% and 34.3% respectively. The high resistance of N. flagelliforme to abnormal conditions may be associated with the extent of unsaturation of fatty acids. In addition, the wild N. flagelliforme treated with water for 30 min and cultured for 24 h and the lipid and fatty acid composition were found to be not affected by water_absorption.
Influence of high light stress on the photosynthesis of flag leaves of indica subspecies (cv. “Shanyou 63', sensitive to photoinhibition) and japonica subspecies (cv. “Wuyujing', resistant to photoinhibition) of rice ( Oryza sativa L.) was comparatively investigated. In both cultivars of rice, the excitation energy distribution between two photosystems was altered and the excitation energy transfer from light harvesting chlorophyll protein complexes to PSⅡ was inhibited by high light stress. These decreases were more pronounced in indica rice cultivar as compared to japonica one. The analysis of mild SDS_PAGE showed that in indica rice, high light stress almost disaggregated the trimer of light harvesting chlorophyll protein complexes of PSⅡ (LHC Ⅱ 1). The stress reduced the contents of internal antennae chlorophyll protein complexes of PSⅡ (CPa), light harvesting chlorophyll protein of PSⅠ (CPⅠa) and Chl a protein complex of PSⅠ reaction center (CPⅠ) as well as dimer of LHCⅡ (LHCⅡ 2) in indica rice. In japonica subspecies, however, high light stress depressed the contents of LHCⅡ 1, CPa and CPⅠa, but slightly impacted on CPⅠ content. Moreover, the increase in the contents of monomer of LHCⅡ by high light stress was found in both subspecies. In consistent with above results, analysis of polypeptide indicated that the amounts of 27 kD and 25 kD polypeptide of LHCⅡ in particular, as well as that of 21 kD polypeptide of CPⅠa were reduced by high light stress in both subspecies. It was found that, comparing with japonica rice, the stress pronouncedly diminished 43 kD and 47 kD proteins of CPa and 23 kD extrisic protein in indica rice.
