Metabolic changes of the Antarctic green alga Prasiola crispa subjected to water stress investigated by in vivo P-31 NMR

The energy status and the phosphate metabolism of Prasiola crispa during and after desiccation stress was investigated by in vivo P-31 NMR, The effect of desiccation was simulated by addition of the nonionic osmoticum PEG 200 (polyethylene glycol). Photosynthesis and respiration were effectively inhibited under these conditions. The most notable changes in the in vivo P-31 NMR spectra were an increase in the cytoplasmic inorganic phosphate signal after PEG stress, a decrease in the polyphosphates and a low-field shift of the core polyphosphate signal followed by an appearance of extracellular inorganic phosphate. Cytoplasmic pH remained almost constant during stress. After a return to control conditions, photosynthesis and respiration recovered within 4 h as well as the concentrations of the phosphorus metabolites, An as yet unassigned phosphate signal increased in the phosphodiester region of the NMR spectra. Simultaneously, the polyphosphate signal recovered in intensity and chemical shift. It is suggested that phosphate metabolism and complexation of cations to polyphosphates may play an important role in the distinct desiccation tolerance of P. crispa.