Non-stomatal limitation of photosynthesis by soil salinity

Soil salinity is a major threat to agricultural sustainability and a global food security. Until now, most research has concentrated around stomatal limitation to photosynthesis, while non-stomatal limitations receiving much less attention. This work summarizes the current knowledge of impact of salinity on chloroplast metabolism and operation and finding viable solutions to minimize it. The major topics covered are: (1) the key targets of the photosynthetic apparatus under salt stress; (2) a tolerance of PSII to salt stress and its repair; (3) salinity effects on biochemistry of CO₂ fixation and its regulation; (4) ionic requirements for optimal operation of chloroplasts; and (5) ion transport systems in chloroplasts that optimize chloroplast performance under hostile saline conditions. We show that enhancing plant capacity for protection by modifying PSI cyclic electron transport, redistribution of electron transport between photosystems, thylakoid membrane composition and photosynthetic antioxidant enzymes activity may be a promising way to improve tolerance to salt stress under real-field condition. It is concluded that revealing the molecular nature of chloroplast ion transporters and understanding the modes of their operation will ensure the future sustainability of the world agriculture and the prospects of biological phytoremediation of salinized land via using salt-tolerant crop germplasm.