MECHANISM OF PLANT SALINITY STRESS TOLERANCE

Halophytes grown in some saline areas in Iraq and other countries could be propagated to be grown as green areas, green belts and for fodder. Field crops still suffer from low number of released cultivars tolerant to salinity stress. This could be attributed to difficulties in their breeding techniques and to low handling of such cultivars in the markets. Soil and water salinity cause osmosis to the plants, nutrient imbalance and cell toxicity. Halophytes are characterizing by morphological, histological, chemical and physiological traits different from those in cultivated crop cultivars. Accordingly, the mechanism of salt tolerance between these two groups of plants will be different. Some of these mechanisms is prevention of some ions to be absorbed by plant and/or translated, compartmentation of ions in the cell vacule on apoplast, and the ability of plants to survive well under salinity stress due to high ability of osmotic adjustment. The latter is considered as the best trait. However, the mentioned traits of plant salt tolerance are directly related to one or more of mechanisms; proteomic, metabolomics, genomic and/or transcriptomic. Plasma membrane, aquaporins, proteins and sugars are playing prime roles in salt tolerance. Meanwhile, DNA-methylation, histone modificated and RNAi have another dimension beside genotype genetic background. Low reactive oxygen spices (ROS), and/or ROS damage repair are importance in many crop species to be salt tolerant. Results of molecular analyses revealed that epigenetics plays an important role in salt stress tolerance. It was found in oats cultivars tested under salt stress that grain weight, number of tillers/m(2) and longer time for maturity were positively correlated with plant salt tolerance. These traits could be used in selecting tolerant plants to salt stress.