Studies on the photosynthesis of the terrestrial cyanobacterium Nostoc flagelliforme subjected to desiccation and subsequent rehydration

The photosynthetic response of Nostoc flagelliforme to desiccation and rehydration was investigated. The initial, variable and maximal chlorophyll fluorescence increased from the beginning of desiccation (fully hydrated), reached maxima at a water loss of about 35% and then decreased with further water loss. The area over the fluorescence induction curve reached a maximum at a water loss of about 70%. Pigment contents of chlorophyll a, phycocyanin and allophycocyanin were constant during the photosynthetic recovery phase following rehydration. A fast initial phase of recovery was completed within half an hour after rehydration, and further changes in 77 K fluorescence emission spectra were mainly related to the fluorescence level at 695 nm. A decrease in fluorescence intensities from phycobiliproteins was not detected from 0.5 to 24 h. The initial fluorescence was high at the beginning of rehydration and decreased sharply during photosynthetic recovery. This decrease appeared to be mainly related to the activation or repair of photosystem II (PS II) rather than changes in the coupling and assembly of phycobilisomes. The change of variable fluorescence and the PS II photochemical efficiency value (F-v/F-m) correlated well with the recovery of PS II activity during rehydration. Nostoc flagelliforme required light and de novo protein synthesis to recover its photosynthetic activity fully during rehydration. In darkness, F-v/F-m recovered 3.4% of activity in dried field samples but 18.9% of activity in samples dry for 2 days. When light was provided in the presence of chloramphenicol, F-v/F-m recovered 10.1% or 39.5% of activity in dried field samples and in samples dry for 2 days, respectively.