叶面喷施褪黑素调控水稻幼苗耐盐性的浓度效应研究

Concentration-Dependent Effect of Foliar Spraying of Melatonin on Salt Tolerance of Rice

为了探讨褪黑素(MT)对植物耐盐性的调控,以水稻"盐稻12号"为试验材料,研究了外源MT对75 mmol L-1 Na Cl胁迫下水稻幼苗株高、干重(DW)、根冠比(R/S)、氮磷钾(NPK)及钠(Na)含量的影响,并计算不同处理下各器官的K/Na和K、Na的选择性比率(SK,N a)。结果表明:盐胁迫下,外源喷施25~400μmol L-1 MT能够有效提高水稻植株的株高、DW,降低R/S;且随着MT浓度的升高,该效应越发显著,在MT施用浓度为200μmol L-1时,植株株高和DW均达到最大值。MT浓度为200和400μmol L-1时,植株生长指标差异均不显著。盐胁迫下,喷施MT明显提高植株的NPK含量,降低Na含量,显著增加氮转运系数(N-TF)、磷转运系数(P-TF)和钾转运系数(KTF),显著提高植株根吸收SK,Na(ASK,N a),而叶片运输SK,Na(TSK,Na)随着MT浓度增加逐渐降低。综上所述,盐胁迫下,喷施25~400μmol L-1 MT可明显提高水稻幼苗的NPK吸收,降低植株Na的积累,显著提高了水稻幼苗对K的选择性吸收,维持体内的离子稳态,增加植株地上部和根部生物量积累,从而显著提高水稻的耐盐性,其中,提高水稻耐盐的最适MT浓度为200μmol L-1。

【Objective】 Soil salinization is a soil problem getting more and more serious nowadays, reducing plant growth and affecting agricultural production. The area of salinized rice fields is expanding, what is more, rice（Oryza sativa L.）, a main staple food crop of the country is quite sensitive to salt stress. More and more attention has been paid to the study on how to regulate salt tolerance of rice. Melatonin（MT） is an important class of indole compounds widely found in most organisms. More and more studies have found that though very low in content in plants, MT plays a very important role in physiological regulation and enhancement of plants. However, little has been found in literature on application of melatonin to rice. It is, therefore, of great significance to explore concentration-dependent effects of MT on salt tolerance of rice and its physiological mechanism. 【Method】A hydroponics experiment was carried out on effects of foliage spraying of MT to rice on plant height, biomass, root/shoot ratio, absorption and transportation of N, P, K and Na, K/Na ratio and SK,Na（K/Na selectivity ratio）. In this study, pass boxes were used for hydroponic cultivation of rice and extraneous MT sprayed. The experiment was designed to have 7 treatments, i.e.（1） Nutrient solution ＋ spraying deionized water（Control）;（2） Nutrient solution ＋ 75 mmol L^-1 Na Cl ＋ spraying deionized water（S75）;（3） Nutrient solution ＋ 75 mmol L^-1 Na Cl ＋ spraying 25 μmol L^-1 MT（S75 ＋ MT1）;（4） Nutrient solution ＋ 75 mmol L^-1 Na Cl ＋ spraying 50 μmol L^-1 MT（S75 ＋ MT2）;（5） Nutrient solution ＋ 75 mmol L^-1 Na Cl ＋ spraying 100 μmol L^-1 MT（S75 ＋ MT3）;（6） Nutrient solution ＋75 mmol L^-1 Na Cl ＋ spraying 200 μmol L^-1 MT（S75 ＋ MT4）;（7） Nutrient solution ＋75 mmol L^-1 Na Cl ＋ spraying 400 μmol L^-1 MT（S75 ＋ MT5）. Each treatment had six boxes as duplicate, and solutions in the boxes were replaced every other day during the whole culture period; foliar spraying of deionized water or MT varying in concentrations in line with the treatments, in late afternoon every other day; and samples of plants collected for analysis on D15. 【Result】Results show as follows.（1） MT efficiently increased plant height and biomass（dry weight） of the plants under salt stress and reduced their root/shoot ratio. The effects intensified with rising MT concentration, and peaked in the treatment 200 μmol L^-1 MT in spraying rate, which was, 51% and 130%higher than the treatment 75 mmol L^-1 in MT spraying rate, respectively, in plant height and biomass.（2） In plants under salt stress, extraneous MT significantly increased N, P and K contents in shoot and root of the seedlings. The effects also peaked in the treatment, 200 μmol L^-1 MT in spraying rate. Compared with control, the treatment 75 mmol L^-1 Na Cl in salt stress was lower in N translocation factor（N-TF）, unchanged in P-TF, and higher in K-TF, however, foliar spraying of MT significantly increased all the three indices in plants under salt stress. But with MT spraying rate rising up to 200 and 400 μmol L^-1, N-TF increased, P-TF remained almost unchanged, and K-TF decreased significantly.（3） With rising MT spraying rate, Na content in the plants decreased significantly. Under salt stress, seedlings were high in Na-TF, which was not affected by spraying of MT, no matter how much.（4） Spraying of MT significantly increased K/Na in both shoot and root of the seedlings under stress, and the value peaked in the treatment 200 μmol L^-1 in MT spraying rate. Spraying of MT increased absorptive SK,Na（ASK,Na） of the plants under salt stress. ASK,Nacontinued to increase with rising MT spraying rate, and also peaked at 200 μmol L^-1 MT. Spraying of MT decreased transport SK,Na（TSK,Na） of the plants under salt stress, especially when the rate reached 200 and 400 μmol L^-1. 【Conclusion】 To sum up, foliage spraying of 25～400 μmol L^-1 MT significantly increases NPK uptake, decreases Na accumulation, improves ion homeostasis in rice seedlings under salt stress, and promotes salt tolerance of the rice plants. All the findings demonstrate that foliar spraying of MT at 200 μmol L^-1 is the most appropriate practice to improve salt tolerance of rice.