Rehydration induces rapid onset of lipid biosynthesis in desiccated Nostoc commune (Cyanobacteria)

Abstract

Water, which contained [1,3- 3H]glycerol, [ 35S]sodium sulfate, or [ 32P]sodium orthophosphate, was used to rehydrate air-dried cells of the desiccation-tolerant filamentous cyanobacterium Nostoc commune. The cells retained their capacities for the uptake and transport of all three compounds and, in response to rewetting, they mobilized the radiolabels into lipid precursors and initiated complex lipid biosynthesis. The onset of these events, measured in short-term, long-term and pulse-chase labeling experiments, was judged to be very rapid. The radiolabeled pool sizes of the major membrane species phosphatidylglycerol (PG) and sulfoquinovosyl diacylglycerol (SQDG) reached steady-state within several minutes, while those of the two abundant membrane glycolipids, mono- and di-glycosyldiacylglycerol (MGDG, DGDG), achieved uniform labeling within 2 h. The pattern of sulfolipid synthesis was generally more complex than the other lipid species. Analysis of the maturation of SQDG through differential labeling provided the only example of a lag in lipid maturation during the early stages (minutes) of cell rehydration. In this instance, the lag appeared to be associated specifically with the incorporation of 35SO 3 − by the sulfoquinovose. During the initial 2 h of rewetting there was complete turnover of 3H-label in the pools of the principal lipid precursors 1,2- sn-diacylglycerol and 1,3-diacylglycerol. In contrast, the accumulation of label by the major lipid of the heterocyst cell-wall, a non-saponifiable glycolipid, became detectable only after 24 h of rewetting. The present data are discussed in relation to the basis for desiccation tolerance in N. Commune.