【作者】 薛卫杰；

【导师】 刘仲齐；

【作者基本信息】 中国农业科学院 ， 植物营养学， 2020， 博士

【摘要】 水稻是我国重要的粮食作物,在酸性土壤中,水稻营养器官具有较强的镉(Cd)富集能力,并可将Cd转运到稻米中,因此降低稻米Cd含量、提高稻米品质对保障我国的粮食安全具有重要意义。本试验研究了水稻营养器官的Cd阻控机理以及叶面喷施柠檬酸(CA)的降Cd效应及机理,以期为水稻降Cd叶面肥的研发提供理论依据。主要结果如下:1.水稻营养器官通过改变Cd的化学形态来抑制Cd向籽粒的转运。在Cd污染程度不同的稻田中,水稻根系和穗节中的Cd含量以及难溶态Cd含量远高于其它器官;水稻的营养器官可以将75%以上的Cd转化为不溶态Cd(氯化钠提取态Cd和残余Cd)。穗下节和穗轴中可溶态Cd的积累总伴随着钙(Ca)的减少和锰(Mn)的增加,可溶态Cd从0.05到0.1 mg·kg-1的少量增加即可导致根和穗轴Ca:Mn比值的急剧下降;同时增加Ca:Mn比可能是水稻利用离子平衡机制减轻Cd毒害的一种特殊途径。2.水稻扬花期喷施柠檬酸能显著降低成熟期稻米Cd含量。在高Cd(2.04 mg·kg-1)污染农田中,水稻扬花期叶面喷施1 mM柠檬酸和5 mM柠檬酸均可显著降低稻米Cd含量,后者效果更好,5 mM柠檬酸可以使籽粒和穗轴中Cd含量分别降低52%和37%。营养器官中的Cd含量与柠檬酸含量呈负相关关系。5 mM柠檬酸可显著降低水稻营养器官中可溶态Cd含量,抑制Cd从叶片向节的转运。5 mM柠檬酸显著增加了籽粒、穗节和根系中Mn含量,并显著增加穗轴、穗节、旗叶和根系中Mn:Cd比值。3.水稻扬花期喷施柠檬酸能显著提高NRAMP家族基因的表达水平、促进氨基酸的合成、抑制Cd向籽粒的转运。采用Cd含量为0.1-2.4 mg·kg-1的污染土壤进行盆栽试验,扬花期叶面喷施5 mM柠檬酸可显著增加籽粒和穗节原生质体中的Mn含量,同时,显著降低籽粒、穗轴和穗节中的Cd含量,从而显著增加华占(HZ)和P7籽粒和穗节中的Mn:Cd比值。Cd胁迫显著抑制华占发育籽粒Os Nramp1,2,3,5基因的表达,且OsNramp5显著高于OsNramp1,2,3的表达量。叶面喷施柠檬酸可以有效提高发育籽粒OsNramp2,3,5的表达量。稻米中部分氨基酸含量与Cd含量显著负相关。叶面喷施柠檬酸可以缓解Cd对HZ和P7籽粒合成Glu、Met和Val产生的抑制作用。结果表明,叶面喷施柠檬酸可以通过提高OsNramp2,3,5的表达以及促进籽粒氨基酸的合成对Cd和Mn在水稻中的运输产生反向调节作用。4.在根际环境中提高柠檬酸浓度可显著抑制根系对Cd的吸收及向地上部的转运。水培试验表明,不同Mn条件下,0.65 mM柠檬酸可使水稻幼苗地上部和根系Cd含量显著降低35.7%-50.4%和9%-13.6%;可显著降低水稻幼苗地上部和根系可溶态Cd含量及其分配比例,进而显著抑制Cd的转运;增加水稻幼苗地上部和根系Mn:Cd的比值。柠檬酸可缓解高浓度Mn对水稻根系吸收Zn的抑制作用。当Mn浓度为80μM时,柠檬酸会降低水稻幼苗地上部和根系Mg和Fe的含量。高浓度Mn和Mn+0.65 mM柠檬酸处理均可以增加水稻幼苗地上部和根系谷胱甘肽和半胱氨酸的含量。更多还原

【Abstract】 Rice is an important food crop in China,while vegetative organs of rice have a strong ability to accumulate cadmium（Cd）in acid soil,and they can transport some Cd to rice grains.So,it is of great significance to reduce the Cd content and improve the quality of rice grains to ensure the food security of China.This experiments were performed to study the mechanism of Cd resistance in rice vegetative organs and the mechanism of foliar application with citric acid（CA）on reducing Cd in rice,in order to provide theoretical basis for the research and development of the foliar fertilizer which can reduce Cd content in rice.The main results were as follows:1.Vegetative organs of rice can prevent Cd from flowing into grains by altering Cd chemical forms.In farmland with different levels of Cd pollution,Cd content in roots and nodes was much higher than that in other organs.More than 75%Cd could be converted into insoluble fraction（Cd extracted by NaCl and residual Cd）by vegetative organs.Accumulation of soluble Cd was always companied by decrease of Ca and increase of Mn in roots,uppermost nodes and rachises.A small increase of soluble Cd from 0.05 to 0.1 mg·kg-1 caused a sharp decline of Ca:Mn ratio in roots and rachises,and increasing Ca:Mn ratio may be special way to alleviate Cd toxicity by establishing new ionic homeostasis in rice plants.2.Foliar application with citric acid at the flowering stage can significantly reduce Cd content in mature rice.In farmland with higher Cd pollution（2.04 mg·kg-1）,foliar application with 1 mM citric acid and 5 mM citric acid could significantly reduce the Cd content in rice grains,the effect of 5 mM citric acid was better.5 mM CA made Cd content in grains and rachises decreased by 53%and 37%,respectively.The content of Cd in organs was negative correlated with the content of citric acid in them.Foliar application with 5 mM citric acid resulted in a significantly reduction of soluble Cd content in vegetative organs,as well as the translocation factors（TFs）of Cd from leaves to nodes.5 mM citric acid made the content of Mn in grains,uppermost nodes and roots increased,made the ratio of Mn to Cd in rachises,uppermost nodes,falg leaves and roots significantly increased.3.Foliar application with citric acid can significantly promote the expression level of NRAMP and the synthesis of amino acids,inhibit of Cd transportion to rice grains.Pot experiments were carried out in polluted soil with Cd content of 0.1-2.4 mg·kg^-1,foliar application with citric acid efficiently raised Mn content in grains and protoplast fraction of nodes,and decreased Cd content in grains,rachises and nodes,and resulted in a great increase of Mn:Cd ratio in grains and nodes of both HZ and P7.Expression level of OsNramp5 was much higher than that of OsNramp1,2,3 in panicles of HZ and inhibited by Cd stress.Foliar application with citric acid efficiently enhanced the expression level of OsNramp2,3,5 in panicles.Quantities of some AAs were negatively and significantly correlated with content of Cd in grains.Exogenous citric acid alleviated the negative effect of Cd on the synthesis of Glu,Met and Val in grains.These results indicate that foliar application with citric acid can regulate the transport of Cd and Mn in the opposite directions by enhancing expression of OsNramp2,3,5 and promoting synthesis of amino acids in rice grains.4.Increasing the concentration of citric acid in the rhizosphere significantly reduced the uptake of Cd by roots and inhibited of Cd transportion to the shoot.The results of hydroponic experiments indicated that under different Mn content in solution,application with 0.65 mM citric acid could significantly reduce Cd content in shoots and roots of rice seedlings by 35.7%-50.4%,9%-13.6%,respectively;significantly reduce soluble Cd content and percentage in shoots and roots of rice seedlings,thus significantly inhibit the transport of Cd;increase the ratio of Mn to Cd in shoots and roots of rice seedlings.0.65 mM citric acid could alleviate the inhibition of higher Mn on Zn uptake by roots of rice seedlings.When Mn content in solution was 80μM,0.65 mM citric acid resulted in a reduction of Mg and Fe content in shoots and roots of rice seedlings.Higher Mn and Mn+0.65 mM citric acid in solution could increase glutathione and cysteine in shoots and roots of rice seedlings.更多还原