| Soil salinization and alkalization causes serious lesses in agricultural productivity and is one of ecological crisis that faces humans. In order to improve and use the degeneration and saline-alkalization grassland, it is important to study the physiological responses characteristics of plant to salt and alkali stresses, and to improve the salt and alkali tolerance, seed production of plant. Plant hormones are one of main signal transduction components of plant responding to environmental stresses. The hormones contents will change when plant growed in stress conditions. Application of exogenous hormones can alleviate the damage of environmental stress on plant. In addition, plant hormones are key factors in controlling the flower formation and reproductive growth of plants. In this paper, we used wheat and Leymus chinensis as the experiments materials, conducted the experiment to study the effects of salt and alkali stresses on wheat and L. chinensis seedlings; and alleviated function of ABA on both stresses; and application of plant hormones on improvement of sexual reproduction of L. chinensis. We got the conclusions as follows:(1)Salt and alkali stresses both inhibited the growth of wheat seedlings, and the adverse effects of alkali stress were higher than that of salt stress. Wheat had the different physiological responses mechanisms between salt and alkali stresses. Under salt stress, wheat significantly accumulated Na+ and simultaneously accumulated Cl-, soluble sugars and proline to keep osmotic and ionic balance. Under alkali stress, high pH enhanced Na+ accumulation and affected absorption of inorganic anions. To maintain ionic and osmotic balance, wheat greatly accumulated organic acids, soluble sugars and proline. The accumulation of Cl- and organic acids was the main difference of wheat in the physiological responses and adaptive mechanisms to salt and alkali stresses, respectively.Organic acids were the special components of wheat responding to alkali stress. We concluded that malate and citrate were the main OAs components of wheat seedling by determining the contents of organic acids components (OAs) in wheat shoots and roots, but the contents and increments of OAs between shoots and roots were different. All OAs components contents in shoots were higher than that in roots, but the increment in roots was higher than that in shoots. With increasing alkalinity, malate and citrate increased in shoots, but in roots they increased first then decreased after. It indicated that the injuries of alkali stress on roots were higher than that on shoots. Organic acids components played different roles in responding to alkali stress. Malate and citrate were the special OAs components of wheat responding to alkali stress.(2) Foliar application of ABA could alleviate the adverse effect of salt and alkali stresses on wheat seedlings. Because of the different responding mechanisms of wheat seedlings to salt and alkali stresses, the alleviation mechanisms of ABA on salt and alkali stresses were also different. ABA could decrease the accumulation of Na+ that caused by salt stress, and increase the ratio of K+/Na+ and Ca2+/Na+ to improve the salt resistance of wheat. Under alkali stress, application of ABA could increase the synthesis of organic solutes, such as soluble sugars, organic acids components contents in shoots to decrease the adverse effect of alkali stress on wheat. The lower concentration of ABA had the better mitigation effects than the higher one.(3) With certain concentration of salt and alkali stresses, the root growth of L. chinensis was not inhibited, and the inhibition of rhizome growth was higher than that of other organs. Both stresses decreased the buds number that produced from tillerings nodes and rhizomes, and the inhibition of the latter was higher. There was a significant inhibited effect of higher concentration of alkali stress on biomass of above- and under- ground and buds number, comparing with other stress concentration. L. chinensis indicated the different physiological responses mechanisms between salt and alkali stresses. Under salt stress, the inorganic ions such as Na+ and Cl- were the main osmotic ajustment substances of L. chinensis, the osmotic regulation of organic solutes such as soluble sugars, prolines and organic acids was little. Na+ and Cl- accumulated in L. chinensis distributed mainly in rhizome, and NO3- contents were the lowest in rhizome. The capacity of containing toxic ions in rhizomes protected the normal growth of other organs, and avoided adverse effect of salt stress on them. Under alkali stress, L. chinensis accumulated Na+, soluble sugars, proline, and organic acids to involve in the osmotic ajustment. The role of rhizome was similar to that of salt resistance. When the alkaline concentration increased, the contents of Na+, soluble sugar, proline, and organic acids in stems and leaves were increased sharply, which indicated that this concentration caused serious damage on L. chinensis, the metabolism of organic solutes was destroyed, the synthesis of which was the product of damage.(4) Exogenous GA3 significantly increased the number of apical rhizome buds, axillary rhizome buds and daughter shoots of apical rhizome at the end of growth season, and decreased endogenesis IAA and ABA contents, then significantly increased the heading number and heading percentage of unit area next year. We concluded that the apical rhizome buds and daughter shoots of apical rhizome were the main components of heading shoots next year. The decreases of endogenesis IAA and ABA were the foundation of inducing differentiation on reproductive buds. Although exogenous IAA and KT can increase the daughter shoots comed from apical rhizome and axillary rhizome, neither of them increased the heading number and heading percentage of L. chinensis population next year. The reason was that exogenous IAA and KT induced the increament of ABA contents, and decreased IAA/ABA, and had no significantly active effect on reproductive buds differentiation.(5) The regulation of plant hormone on growth and reproduction, was correlated with the treatment time, concentration and action mechanisms of plant hormone. There was no significant effect of GA3, IAA and KT on heading number and heading percentage when they were sprayed at the three stages. This was related to the process of spikelets differentiation. According to study of Zhang et al, L. chinensis had finished the spikelets differentiation in this time. On period of seedling establishment, GA3 treatment not only increased seed number, seeding percentage, weight of spikes and seeds, but also decreased CV of seed percentage, which optimized the heading, flower, pollination. But there was no significant effect of GA3 treatment on tillering stage. On jointing stage, GA3 could increasing the number of florets and seeds per spike significantly, and then increasing the weight of spike and seeds per spike and seed yield. So we concluded that GA3 accelerated the florets differentiation of L. chinensis. There was no positive effect of IAA on the traits of sexual reproduction number characters when it sprayed on period of seedling establishment, tillering stage and jointing stage. The effect of KT that sprayed on period of seedling establishment on seeding of L. chinensis was similar to that on tillering stage. They didn't change the seeding percentage, but increased the seed numbers and spike weights, which played active function on seed filling and development. On jointing stage, KT could increase the number of florets and seeds per spike significantly, and then increase the weight of spike and seeds per spike and seed yield. But there was no difference between different concentration.
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