不同生长调节物质对水稻生长及镉积累的影响

比较脱落酸(ABA)、乙烯利(ETH)、水杨酸(SA)和茉莉酸甲酯(MeJ A)4种植物生长调节物质(PGR)对水稻生长及籽粒镉(Cd)积累的影响差异。试验采用重金属污染土种植水稻,于分蘖期、灌浆期各进行1次PGR叶面喷施处理,分析灌浆期叶片光合指标,丙二醛(MDA)含量以及收获期各部位生物量和Cd含量。结果表明:(1)低浓度ABA(5mg/L)可维持水稻正常产量;高浓度ABA(15mg/L)则导致产量下降。ETH对水稻地上部生长和单株产量有显著抑制作用,SA和MeJ A(0.56mg/L)均可保证地上部正常生长,维持正常产量。(2)外施4种PGR均抑制灌浆期叶片气孔开放,降低蒸腾速率和光合速率,抑制效果最明显的是高浓度MeJ A(0.56mg/L)。(3)在供试浓度范围内SA、低浓度ABA(5mg/L)以及高浓度MeJ A均可降低灌浆期叶片MDA含量,减少质膜过氧化水平。(4)4种PGR均可降低水稻籽粒Cd含量,其中低浓度ABA(5mg/L)抑制籽粒Cd积累的效应最佳。相关性分析结果表明,PGR抑制籽粒积累Cd的效应与地上部向籽粒转运Cd的调控机制有关,与蒸腾速率无显著相关关系。(5)综上所述,低浓度ABA(5mg/L)处理对水稻产量无影响,且籽粒Cd含量降低程度最大。适当浓度的PGR可降低水稻籽粒Cd含量,在中低度重金属污染农田生态修复实践中具有一定的应用前景,但必须精确控制PGR的处理时间和处理浓度,避免出现抑制生长和降低产量的负效应。

Effects of four plant growth regulators on growth and cadmium accumulation in rice

Cadmium (Cd) pollution has become a serious problem following rapid industrial development. The increasing amounts of Cd in farmlands are the result of increased discharge of industrial waste, abuse of chemical fertilizers, and other man-made sources. Cd likely causes damage to crop physiology when its concentration in soil exceeds the maximum tolerable limit, resulting in growth inhibition and grain yield reduction. Continuous intake of Cd causes human health problems. Therefore, reducing Cd concentration in rice grain, a staple food for half of the world''s population, is extremely important and urgent. Plant growth regulators (PGRs) are chemicals-plant endogenous hormones and artificially synthetic growth regulators-that affect and regulate plant growth and/or development at trace levels. Some PGRs play important roles in inducing plant tolerance to drought, salt, low temperature, high temperature, and heavy metals. In this study, the roles of four PGRs, abscisic acid (ABA), ethylene (ETH), salicylic acid (SA), and methyl jasmonate (MeJA), were investigated during stress responses to Cd treatments in rice. Rice seedlings, grown in heavy metal-contaminated soil, were sprayed with the four PGRs on leaves twice, one time each during tillering and filling stages. On the second day after the PGR treatments during the filling stage, the photosynthesis indices and malondialdehyde (MDA) contents of the upper leaves were analyzed. After harvesting, the roots, shoots, and grains were collected to investigate Cd content, biomass, and yield. The results were as follows: (1) The ABA treatment at 5 mg/L maintained normal rice growth and yield, while the ABA treatment at 15 mg/L showed the opposite effects. Treatment with two different levels of ETH significantly decreased the grain yield compared to that of the control. However, SA and MeJA high-level treatments maintained normal yields. (2) The exogenous application of the four PGRs inhibited stomatal opening and reduced the transpiration and photosynthetic rates. Interestingly, the most obvious inhibitory action was observed following the treatment with 0.56 mg/L MeJA. (3) Both the SA treatments, 5 mg/L ABA and 0.56 mg/L MeJA treatments, reduced MDA production and prevented plasma membrane peroxidation of leaves at the tillering stage. (4) Decreases in the Cd concentrations were observed in rice grain treated with the four PGRs at their appropriate levels, and the ABA treatment at 5 mg/L showed the strongest inhibitory effect. The grain Cd content showed positive and highly significant (P<0.01) correlation with the Cd translocation factor from shoot to grain, but it did not show a significant correlation with the transpiration rate. PGRs may inhibit the accumulation of Cd in the grain by regulating Cd transport from shoots to grain. (5) In summary, ABA treatment at 5 mg/L had no effect on grain yield but induced the maximum decline in grain Cd content compared to the treatments with other PGRs. Proper application of PGRs can reduce the Cd content in rice grain and can be used in bioremediation of heavy metal polluted farmland. For a practical application of PGRs, appropriate timing, and accurate concentrations are the critical factors to avoid negative effects of inhibited growth and reduced rice yields.