| The damage of drought to crop is the most serious in all non-biological stress. Besides selecting the variety of drought-resistance to improve the drought-resistance of seeds, Seed soaking is one of the most common methods to improve drought resistance. In the practice of farming cultivation of crops of soaking seed, people often give consideration to the regulating function of the nutriment, such as plant hormone, chemicals and manure. People find soaking seed with KH2PO4 solution can promote seed to sprout and grow under drought condition. In addition, the previous research showed that seed-soaking treatment with the mixture of calcium chloride (CaCl2) and gibberellins (GA) can gain the complementation on physiology and metabolism of the two different effect, which strengthen the ability of drought resistance of the seed. The author treated the seed of winter wheat (Triticum aestivum L. yumai wheat 49) with H2O, potassium dihydrophaphate, potassium chloride and the mixture of calcium chloride (CaCl2) and gibberellins (GA) to find the mechanism of enhanced drought-resistance of this seed-soaking treatment under PEG condition (moderate water stress, osmotic potential –0.63Mpa) and pot ed-plant condition, which also offer the theoretical foundation for the fact that the applied chemistry method improves the drought-resistance of crops. The present experiment showed that through dealing with the wheat with different concentration Na2HPO4,NaH2PO4, KH2PO4, K2HPO4 and KCl, the length of bud and root and fresh weight of the wheat which is soaked with KH2PO4 that concentration is 1mM is the highest.Under indoor PEG condition which simulates moderate drought condition the wheat which is soaked with chemicals can prolong the length of root and bud, increase fresh weigh and the ratio of root and shoot, improve activity of α-amylase, lengthen the span of germination. The result of wheat of which is soaked the mixture of CaCl2 (0. 5%)+GA (50|ìg/mL) deal and KH2PO4 (1mM ) is remarkable, but the wheat which is soaked with the mixture of CaCl2(0. 5%) +GA (50|ìg/mL) +KH2PO4 (1mM ) is not obvious. With the decline of the soil moisture, with contrasting comparing, the wheat which is soaked with chemicals can alleviate the decline of the relative water content of the laminae effectively (except 1mMKCl ), improve the ratio of root and shoot(dry weight),thus increase the ability of keeping water and absorbing water. By soaked with chemicals the fluorescence parameter of seedling wheat Fm , Fv , Fv/Fm , Fm/Fo , Fv/Fo and qP reduce slowly compared with wheat that is not soaked ,thus alleviate the prohibition of activity of photochemistry of PSⅡ which is caused by water stress , especially the result of the wheat that is soaked with CaCl2 +GA and KH2PO4 is remarkable. Experimental result verify Fv/Fm and Fv/Fo can be as an index of drought resistance of wheat, but the idea that qP and NPQ can can be as an index of drought resistance of wheat is still to be proved. Under moderate stress of soil moisture, the decrease of Pn of the laminae of wheat is mainly caused by the limitations of stoma. The decline of Pn is mainly caused by decline of activity of wheat mesophyll. The wheat that is soaked with CaCl2 +GA and KH2PO4 can improve activity of wheat mesophyll especially in severe stress of soil moisture and increase speed of photosynthesis of laminae. Under severe stress of soil moisture the results of wheat soaked with different chemicals are different. The wheat that soaked with CaCl2 +GA and KH2PO4 keeps the relatively higher content of soluble protein, GSH content, AsA content and level of protective enzyme (SOD, POD, CAT and AP), the wheat that soaked with KCl keeps higher Pro content and the wheat treated with water keeps higher MDA content. The index of wheat soak with CaCl2 +GA +KH2PO4 is in the middle. Compared with other treatments, the wheat soaked with CaCl2 +GA and KH2PO4 can improve remarkably its ability of drought resistance. The treatment of CaCl2 +GA combines the ability of Ca2+ that could mak...
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