Plant hormones ethylene (ET), and brassinosteroids (BRs) also have positive effect on seed germination by controlling the inhibitory effects of ABA on germination and rupturing testa and endosperm. ABA promotes seed dormancy and inhibits germination of seed, whereas GAs release dormancy and stimulate germination. Germination has been found to be under strict regulation of plant hormones, especially GA and ABA. ROS damage the macromolecules including proteins, carbohydrates, nucleic acids, and lipids, or cellular structures like membranes, resulting with inhibition of seed germination. Dynamic balance between the generation and scavenging of reactive oxygen species (ROS) such as hydroxyl radicals, superoxide, and hydrogen peroxide could be disturbed by high salinity stress. As a result, high salinity level causes a delay in germination, even inhibition of seed germination depending on salt tolerance of plants. Salinity also damages the nutrient and hormone balances, especially gibberellin (GA)/abscisic acid (ABA), during germination. Besides, the absorption of excess Na + and Cl − ions from soils creates ionic stress and cause toxicity which contributing to disruption in biochemical processes including nucleic and protein metabolism, energy production, and respiration. High salinity leads a decrease in osmotic potential of ambient soil water, resulting with a decrease in water uptake by dry seeds (imbibition). There have been high yield losses in these crops under moderate salinity (EC 4–8 dS m −1, approximately 40–80 mM NaCl). At present, around 30 crop plants provide 90% of plant-based human food and the majority of these crops are not salt tolerant, even salt-sensitive, called glycophytes. Salinity is a major stress responsible for the inhibition of seed germination or reduction in germination percentage and a delay in germination time in crops. This number could be increased in the future due to increased land salinization as a consequence of contaminated artificial irrigation, climate change, and unsuitable land management. It is estimated that about approximately 7% of world land is affected by salinity and approximately 20% of 230 million ha irrigated land is salt-affected. Seed germination is affected by adverse environmental conditions including salinity, high temperature, and drought. Seed germination begins with the water uptake of dry seed (imbibition) and ends with radicle protrusion. Seed dormancy and germination are distinct physiological processes, and the transition from dormancy to germination is not only a critical developmental step in the life cycle of higher plants but also determines the failure or success of the subsequent seedling establishment and plant growth. Seed priming is a simple, low cost, and powerful biotechnological tool used to overcome the salinity problem in agricultural lands. In seed priming, seeds are exposed to an eliciting solution for a certain period that allows partial hydration without radicle protrusion. Seed priming is one of the useful physiological approaches for adaptation of glycophyte species to saline conditions during germination and subsequent seedling establishment. Rapid seed germination and subsequent seedling establishment are important factors affecting crop production under salinity conditions. Salinity may adversely influence seed germination by decreasing the amounts of seed germination stimulants such as GAs, enhancing ABA amounts, and altering membrane permeability and water behavior in the seed. Salt stress affects the seed germination and seedling establishment through osmotic stress, ion toxicity, and oxidative stress. Because most of the cultivated plants are salt-sensitive glycophytes. Salt negatively effects the crop production worldwide. Salinity is the major environmental stress source that restricts on agricultural productivity and sustainability in arid and semiarid regions by a reduction in the germination rate and a delay in the initiation of germination and subsequent seedling establishment.
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