Sensitivity of photosystem 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 I1 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 I1 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 sen- sitive. The NaC1-induced changes in Chl a fluorescence characteristics of intact thylakoids were sub- stantially reversed by addition of hydroxylamine, indicating that the water-oxidizing site of photosystem I1 is sensitive to the NaCl concentration. These results are consistent with NaC1-induced depletion of the 23 and 17 kDa proteins from photosystem 11-enriched membrane sheets. While the inhibition of oxygen-evolving activity by 500 mol m-' NaCl was substantially reversed in thylakoids kept in the dark, 500 mol m-3 NaCl induced marked photoinhibitory damage in illuminated thylakoids. Thus, accumu- lation of ions in the chloroplasts of either salt-tolerant or salt-sensitive species would probably result in rapid damage to photosystem 11, particularly in the light.