Effects of salinity on ion transport, water relations and oxidative damage

Abstract

Salinity is an important abiotic stress that limits growth and yield of many crop species. The effects of salinity on crop plants are exerted by presence of excess salts (ionic effect) and associated water deficits (osmotic effect). Plant responds to salinity in two phases: in a rapid phase, (plants exhibit osmotic effects and inhibits growth of young leaves), and in a slower ionic phase, (plants accelerates senescence of mature leaves). Salinity stress causes changes in ion homeostasis and osmotic adjustments. Some of adaptations to salinity stress in plants include (i) accumulation of osmoprotectants, (ii) sodium (Na+) or chloride (Cl-) exclusion (iii) tissue tolerance to accumulated Na+ or Cl-, and (iv) detoxification of reactive oxygen species (ROS). Salinity stress causes membrane damage, decreases photosynthetic rate, chlorophyll fluorescence traits, changes leaf water potential, relative water content, increases ROS level, and modifies antioxidant enzymes production system. Intensity of the membrane deterioration processes are proportional to ionic concentrations. Plant species and genotypes within species show differential responses to salinity stress. Various traits that govern salinity tolerance can be identified by studying physiological and biochemical mechanisms, which can lead to identification of new genetic sources of salinity tolerance. The ability of plants to accumulate osmoprotectants to maintain water status and detoxify ROS under salinity stress are some traits that can help to improve salinity tolerance in crop species. This chapter provides a brief overview of effects of soil salinity on plant growth and tolerance mechanisms that help plants to avoid or tolerate stress, with particular emphasis on ion homeostasis, osmotic and oxidative response and tissue tolerance.