Plant Responses and Tolerance to Combined Salt and Drought Stress

Abstract

Agricultural production is exposed to different environmental challenges such as salinity, drought, and global warming; plants have used different physiological and biochemical responses to adapt and survive under abiotic stress conditions. Drought and salinity are the most important abiotic constraints to plant survival and to crop productivity; they furthermore have main harmful effects on the plant tissue such as the negative effects on the cellular energy supply and redox homeostasis that are stable by re-programming of plant primary metabolism and modification of cellular composition. The agricultural sector is considered the main user of freshwater resources in numerous regions of the world, with growing population and increasing water scarcity in various regions of the world, thus reducing the amount of crop production, which affects the availability of global food quantity in the near future. Drought can affect plants in various ways such as decrease in photosynthesis and growth inhibition; accumulation of abscisic acid (ABA), proline, mannitol, sorbitol; formation of radical scavenging compounds (ascorbate, glutathione, α-tocopherol etc.); and synthesis of new proteins and mRJNAs; also, water stress results in stomatal closure and reduced transpiration rates, a reduce in the water potential of plant tissues, and therefore, plants under drought stress use two processing to control the relation between photosynthetic potential and relative water content of leaves; first one through decreased stomatal conductance and reduced photosynthesis and decreased CO2 concentration inside the leaf, while the other one by elevated CO2 which decreases progressively as relative water content (RWC) declines, and reduced gas exchange; with both type there is reducing in metabolic processing in leaf tissue. Salinity stress causes changes in numerous physiological and metabolic processes in plant tissue, unfortunately, the majority of economic crop species are glycophytes, therefore, salinity inhibits crop productivity worldwide. Salinity stress causes changes in various physiological and metabolic processes, depending on severity and duration of the stress, and eventually hamper crop production; glycophytes plant have different physiological mechanisms such as ion homeostasis, compatible solute, antioxidant regulation, and polyamines production. Generally, plants could combine a range of response to avoiding drought and salinity stresses injuries by different mechanisms to be able to complete their life cycle. By using different strategies such as using maximum available resources, they store reserves in plant organs and use them for fruit production; also, plants can tolerate stress conditions by avoiding tissue dehydration.