Sensitivity of Photosystems II to NaCl in Relation to Salinity Tolerance. Comparative Studies With Thylakoids of the Salt Tolerant Mangrove, Avicennia marina, and the Salt-Sensitive Pea, Pisum sativum

The sensitivity of photosystem II to NaCl was compared in thylakoids isolated from the salt-tolerant mangrove, Avicennia marina, and the salt-sensitive pea, Pisum sativum. There were no indications of fundamental differences in photosystem II between these two species. Rates of oxygen evolution declined linearly with increase in NaCl from 10 to 500 mol m-3, with both species being equally sensitive. The NaCl-induced changes in Chl a fluorescence characteristics of intact thylakoids were substantially reversed by addition of hydroxylamine, indicating that the water-oxidizing site of photosystem II is sensitive to the NaCl concentration. These results are consistent with NaCl-induced depletion of the 23 and 17 kDa proteins from photosystem II-enriched membrane sheets. While the inhibition of oxygen-evolving activity by 500 mol m-3 NaCl was substantially reversed in thylakoids kept in the dark, 500 mol m-3 NaCl induced marked photoinhibitory damage in illuminated thylakoids. Thus, accumulation of ions in the chloroplasts of either salt-tolerant or salt-sensitive species would probably result in rapid damage to photosystem II, particularly in the light.