| Summary: | Systematic analysis of the composition of the heterocyst specific glycolipid fraction, labelled from either sodium [l-14] acetate or Na H 14CO3 in the filamentous heterocystous Cyanobacterium Anabaena cylindrica, showed that the glycose ester fraction normally contained 10-16% of the heterocyst glycolipid radioactivity, while the glycosidic fraction contained the remainder of the heterocyst glycolipid radioactivity. In time course studies, using batch cultures grown for between 36 to 252 h., the major labelled acyl component of the glycose ester fraction was a C16-C18 fatty acid fraction. Acyl components tentatively identified as very long chain (C26-C28) hydroxy and dihydroxy fatty acids contained 15-22% and 20-25%, respectively, of the glycose ester fraction radioactivity in cells of 36-84 h., whereas in cells from older cultures these components normally contained much lower amounts of radioactivity. Fractionation of the fatty alcohols from the heterocyst glycolipid glycoside fraction gave four labelled components. A major component at all times examined was hexacosane-1,3,25-triol, the major quantitative component of the glycolipid fraction. A fraction tentatively identified as containing very long chain 1,3- and 1,25-diol was also identified. The remaining two fractions were incompletely identified. The distribution of radioactivity within the fatty alcohol fractions varied significantly with the age of culture; the triol fraction being most heavily labelled in 36-84 h. cells. Whereas trichloroacetic acid, sodium fluoride, and dichlorallyl-di-isopropyl thiocarbamate which each inhibit fatty acid elongation in higher plants, did not inhibit incorporation of sodium [1-14C] acetate into the very long chain components of the heterocyst glycolipid fraction in whole cells of A.cylindrica. Sodium arsenite, which inhibits elongation of palmitic acid to stearic acid in higher plants caused a specific inhibition of incorporation of label into the major very long chain component of the heterocyst glycolipid, which was accompanied by an accumulation of radioactivity in C16 fatty acids specifically in the monogalactosyl diglyceride fraction.
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