Effect of seed priming on drought and salinity tolerance of wheat: An overview

Wheat is one of the most important crops in north of China. Wheat suffers from various unfavorable conditions, especially drought and high soil salinity, leading to unpredictable loss in crop production in agriculture. Seed priming is a simple and efficient technology which is the induction of a particular physiological reaction in plants by application of natural or synthetic compounds to incubate the seeds before germination. Wheat seeds treated with priming agents can reduce emergence time, enhance seeding vigor and metabolism, and improve yields and seed quality under high soil salinity or water deficit conditions. This review illustrated the mechanisms and effects of various priming agents, such as water, organics, hormones, bioactive substances, organisms, oxides, inorganic signal substance and so on. We summarized the main mechanism of seed priming. Seed priming reduced absorption of Na+ and increased absorption of K⁺ and Ca²⁺ to reducing the toxicity of single saline ion in plant. Seed priming also improved synthesizing and accumulating of osmotic regulatory substances, such as soluble protein and soluble sugar, which maintaining osmotic pressure of intracellular at a high level to benefit root uptaking water. Seed priming induced synthesis of antioxidant enzymes, such as superoxide dismutase, peroxidase, catalase, ascorbate peroxidase and so on, and enhanced the activities of those enzymes under stress conditions. The high activity of antioxidant enzymes reduced the content of reactive oxygen species effectively and maintained the oxygen balance in cells. Furthermore, seed priming also improved endogenous hormones synthesis and transportation under stressed conditions, which was important for adaptations to environmental change. We further discuss the connections of mutual complement and promotion between seed priming and adversity resistant physiology of crops. Finally, we expectate the prospect of the application and the development for seed priming in agriculture.