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 duri ng and after desiccation stress was investigated by in vivo P-31 NMR, The effect of desiccation was simulated by addition of the nonionic os moticum PEG 200 (polyethylene glycol). Photosynthesis and respiration were effectively inhibited under these conditions. The most notable ch anges in the in vivo P-31 NMR spectra were an increase in the cytoplas mic inorganic phosphate signal after PEG stress, a decrease in the pol yphosphates and a low-field shift of the core polyphosphate signal fol lowed by an appearance of extracellular inorganic phosphate. Cytoplasm ic pH remained almost constant during stress. After a return to contro l conditions, photosynthesis and respiration recovered within 4 h as w ell as the concentrations of the phosphorus metabolites, An as yet una ssigned phosphate signal increased in the phosphodiester region of the NMR spectra. Simultaneously, the polyphosphate signal recovered in in tensity and chemical shift. It is suggested that phosphate metabolism and complexation of cations to polyphosphates may play an important ro le in the distinct desiccation tolerance of P. crispa.