Does salt stress lead to increased susceptibility of photosystem II to photoinhibition and changes in photosynthetic pigment composition in halophyte Suaeda salsa grown outdoors?

The effects of salt stress (0-400 mM NaCl) on PSII photochemistry, photoinhibition and photosynthetic pigment composition were investigated in the halophyte Suaeda salsa grown under outdoor conditions and exposed to full sunlight. Salt stress resulted in a growth stimulation which was optimal at 200 mM NaCl. With increasing salt concentration, leaf water potential and evaporation rate decreased significantly while there were no changes in leaf relative water content. Salt stress also resulted in a significant accumulation of sodium and chloride in leaves. Salt stress induced neither effects on the maximal efficiency of PSII photochemistry measured either at predawn or at midday nor effects on the actual PSII efficiency (phi(PSU)), the efficiency of excitation energy capture by open PSII reaction centres, photochemical quenching, and non-photochemical quenching (NPQ) at midday. No significant changes were observed in the contents of neoxanthin, lutein, beta-carotene, violaxnthin, antheraxthin, zeaxanthin, chlorophyll a and b in salt-stressed plants. Our results suggest that S. salsa showed high resistance not only to salinity stress but also to photoinhibition even when treated with high salinity as high as 400 mM NaCl and exposed to full sunlight. The results indicate that tolerance of PSII to high salinity stress and high light stress can be viewed as an important strategy for S. salsa to grow in very high saline soil. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.