Abstract
Soil salinity is a crucial environmental constraint which limits biomass production at many sites on a global scale. Saline growth conditions cause osmotic and ionic imbalances, oxidative stress and perturb metabolism, e.g., the photosynthetic electron flow. The plant ability to tolerate salinity is determined by multiple biochemical and physiological mechanisms protecting cell functions, in particular by regulating proper water relations and maintaining ion homeostasis. Redox homeostasis is a fundamental cell property. Its regulation includes control of reactive oxygen species (ROS) generation, sensing deviation from and readjustment of the cellular redox state. All these redox related functions have been recognized as decisive factors in salinity acclimation and adaptation. This review focuses on the core response of plants to overcome the challenges of salinity stress through regulation of ROS generation and detoxification systems and to maintain redox homeostasis. Emphasis is given to the role of NADH oxidase (RBOH), alternative oxidase (AOX), the plastid terminal oxidase (PTOX) and the malate valve with the malate dehydrogenase isoforms under salt stress. Overwhelming evidence assigns an essential auxiliary function of ROS and redox homeostasis to salinity acclimation of plants.
Highlights
Soil salinity is a major environmental stress that strongly impairs crop productivity and harvest quality in the world (Horie and Schroeder, 2004)
Salinity interferes with metabolism by ionic and osmotic effects and alters the redox and reactive oxygen species (ROS) state of the cell (Figure 4)
The central mechanisms realizing salt acclimation within the given tolerance range is selective short and long distance ion transport, safe ion compartmentation, synthesis of compatible solutes, and adjustment of osmotic homeostasis. As long as these mechanisms realize effective ion detoxification, deregulation of redox and ROS homeostasis is a minor component in stress acclimation
Summary
Soil salinity is a major environmental stress that strongly impairs crop productivity and harvest quality in the world (Horie and Schroeder, 2004). The quality of approximately 20% of the world’s cultivated area and about 50% of the world’s irrigated lands is affected by salinization (Sairam and Tyagi, 2004). Plant responses and tolerance mechanisms to salt stress are a major topic of plant research (Munns and Tester, 2008). Glycophytic plants under salt stress conditions exhibit slow growth, wilting and eventually death (Parida et al, 2004). To survive under stress condition, plants respond and adapt with complex mechanisms that include developmental, morphological, physiological and biochemical strategies (Taji et al, 2004; AcostaMotos et al, 2015) addressing ion homeostasis, osmolyte biosynthesis, compartmentation of toxic ions, and reactive oxygen species (ROS) scavenging systems (Stepien and Klobus, 2005; Flowers and Colmer, 2008). Many genes involved in membrane transport, signal transduction, redox reactions
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