Responses to Salt Stress in Terms of Morpho-Physiological, Leaf, Mineral Composition .L Zea Mays: A Review

Abstract

Salinization is spreading in soil, and on current estimates, about half of the world's arable land could be salt-affected by 2050. Maize (Zea mays L.) is one of the crops that is among the most heavily liable to lose. It sustains widespread populations in arid and semi-arid areas, for example in the Middle East and North Africa, and as a moderately salt-sensitive C4 cereal, it occupies an uneasy middle path not collapsing immediately like a glycophyte, but losing yield relatively steadily as EC is increased. This review synthesizes what is known about how yellow maize responds to salt stress, from morphology down to ion and redox biochemistry. The morphological picture is the same for all studies. Germination appears to be retarded and reduced. Plant height, leaf area, root and shoot biomass also decrease, with the amount of drop depending on genotype, salt concentration, and growth stage. There are two things happening physiologically in parallel, as well. Stomata close, decreasing CO₂ supply, and PSII suffers non-stomatal injury, so chlorophyll declines, and net photosynthesis decreases more rapidly than stomatal conductance would lead one to expect. Tolerance is largely determined in ion relations. Na⁺ and Cl⁻ accumulate to toxic concentrations and compete with K⁺, Ca²⁺, and Mg²⁺ on membrane and tissue levels. Most screening work relies on the shoot K⁺/Na⁺ ratio, not Na⁺, as it is the ability to keep K⁺ in the cytosol whilst excluding or compartmentalizing Na⁺ that separates the tolerant lines from those that are sensitive. The ionic and osmotic disturbance contributes to a secondary issue, ROS accumulation, which maize counterbalances with the usual enzymatic defences (SOD, POD and CAT) and with osmolytes and antioxidant metabolites, including proline and phenolic compounds. Tolerant genotypes also typically have anatomical features that contribute: greater root cortical aerenchyma and a tighter regulation of Na⁺ loading into the xylem. Research on mitigation has broadened well beyond gypsum-and-leaching. Measurable improvements in ion homeostasis and antioxidant activity in maize under salt have been proven in plant growth-promoting microbes, exogenous phytohormones, and diverse organic and inorganic amendments to soil. The catch is that most of that evidence relies on short pot trials with NaCl alone, usually at the seedling stage. When field salinity does exist, it is seldom a single salt, so the stress is not typically for a very short period of time and seedling tolerance often does not relate to yield at the grain level. For Iraqi and regional farming in particular, the gap that matters is that between a healthy-looking 21-day seedling grown in the greenhouse and an ear of maize grown at harvest in a saline field.