苹果酸-天冬氨酸代谢对水稻镉吸收转运特性的影响

为了探讨苹果酸-天冬氨酸代谢在水稻镉吸收转运过程中的作用，本研究采用根系添加和叶面喷施两种手段，在镉胁迫环境中外源施加不同浓度的苹果酸，对水稻各器官镉分布特征以及天冬氨酸和谷氨酸含量的变化进行分析。结果表明：添加0.5~1.5 mmol·L^-1的苹果酸能显著抑制镉在水稻幼苗根系及地上部的积累，与不添加苹果酸处理相比，根系和地上部细胞液组分中的镉含量分别下降23.8%~39.6%和29.5%~39.7%。同时，水稻根系及地上部谷胱甘肽、天冬氨酸和谷氨酸含量显著增加，而植物螯合肽（PC₂、PC₃和PC₄）的含量显著下降。水稻开花期叶面喷施5.0 mmol·L^-1的苹果酸3次后，灌浆期间发育籽粒中苹果酸脱氢酶和天冬氨酸氨基转移酶的活性分别提高63.0%~96.8%和14.6%~22.6%，营养器官和稻米中的天冬氨酸和谷氨酸含量显著增加，镉从茎基部向顶部营养器官以及稻米转运的效率大幅度下降，致使稻米镉含量下降37.5%~55.4%。研究表明，促进细胞内苹果酸向天冬氨酸以及谷氨酸的转化能有效抑制水稻植株对镉的吸收转运，显著降低顶部营养器官和稻米中镉的含量。

Effects of malate-aspartic acid metabolism on cadmium uptake and transport in rice

To explore the roles of malate-aspartic acid metabolism in the processes of cadmium uptake and transport in rice plant, the distribution characteristics of cadmium and the change of aspartic acid and glutamate in different rice organs were examined by adding or spraying different concentrations of malic acid under cadmium stress. The results revealed that adding 0.5-1.5 mmol·L^-1 MA significantly inhibited cadmium accumulation in the roots and shoots of rice seedlings. The cadmium content in the soluble fraction of root and shoot cells decreased by 23.8%-39.6% and 29.5%-39.7%, respectively. Simultaneously, the content of glutathione, aspartic acid, and glutamate in roots and shoots increased significantly, while the content of PC₂, PC₃ and PC₄ decreased significantly. During the grain-filling period, the activities of malate dehydrogenase and aspartate transaminase in developing grains increased by 63.0% -96.8% and 14.6% -22.6%, respectively. After foliar application of 5 mmol·L^-1 malic acid three times at anthesis, the content of aspartic acid and glutamate in both vegetative organs and rice grains increased significantly. The transport efficiency of cadmium from the stem base to the top vegetative organs and rice grains decreased significantly, resulting in a 37.5%-55.4% decrease in rice cadmium. These results indicate that promoting the transformation between malate and aspartic acid or glutamate in cells can efficiently inhibit the uptake and transport of cadmium in the rice plants and significantly reduce the cadmium content in top vegetative organs and rice grains.