Effects Of Foliar Application Of Sulfhydryl Compound DMSA On Cadmium Transport In Rice

Due to the increase of human industrial and agricultural production activities,the problem of Cd pollution in farmland has become increasingly prominent.Rice is the main source of dietary intake for Chinese people,and Cadmium in rice exceeds standard has seriously threatened human health.In recent years,foliar spraying of Cd-reducing technology has been widely used in controlling Cd pollution in rice.Dimercaptosuccinic acid?DMSA?is an effective antidote for many heavy metals,including Cd²⁺,Pb²⁺,Hg²⁺and Cu²⁺.In this study,hydroponics,pot and field experiments are performed to explore the mechanism of DMSA blocking the transport of heavy metal cadmium ions to shoots and grains,and pxplore how to alleviate cadmium stress in rice seedlings,which provide technical support for the development of a new foliar fertilizer to reduce cadmium content in rice.The main findings are as follows:1.Hydroponics experiments showed that foliar application of DMSA could significantly reduce the accumulation of Cd in the shoot of rice seedlings,and could also significantly alleviate Cd stress in seedlings.When the concentration of DMSA was 0.2-1.0 mmol·L^-1,the content of Cd in shoots gradually decreased with the increase of DMSA spraying concentration,and the maximum decrease can reach 43.5%compared with the control,but there is no significant effect on the content of K,Ca,Mg,Mn,Fe,Zn and Cd in the root of the seedlings.Foliar application of DMSA significantly reduced the MDA content in the shoots,increased the activity of antioxidant enzymes?SOD,CAT?and the content of antioxidant GSH,and significantly alleviated the cadmium stress in seedlings.2.Pot experiments showed that spraying DMSA for three times in succession during rice flowering period could significantly reduce cadmium content in grains and vegetative organs.When the spraying concentration is 4.0 mmol L^-1,the Cd content in grain,spikelet axis,spike neck and spike node decreased by 74.12%,34.74%,10.17%and 12.86%,respectively,while the Cd content in flag leaf increased by 25.09%.Therefore,it is speculated that spraying DMSA to reduce Cd content in grains may be related to reducing Cd transport from flag leaves to grains.3.Field tests show that foliar spraying tests are carried out in paddy fields polluted by a single heavy metal Cd,spraying DMSA only once at the flowering stage of late rice can significantly reduce Cd content in rice grains.When the spraying concentration is 2.0-5.0 mmol L^-1,the Cd content in grain,spikelet axis,spike neck and spike node were decreased by 15.84%-46.09%,10.03%?41.41%,9.13%?28.46%and 18.30%?38.32%,respectively,which has no significant effect on the Cd content in other organs.Spraying DMSA significantly reduced the transport of Cd from flag leaf to the spike node.Therefore,it is speculated that spraying DMSA to reduce Cd content in grains may be related to reducing Cd transport from flag leaves to grains.4.Field experiments also showed that the foliar spraying are carried out in rice fields polluted by compound heavy metals such as cadmium,arsenic and lead,and spraying DMSA once during the flowering period of later rice can significantly reduce the content of three heavy metals in grains.When the concentration of DMSA was 5 mmol L^-1,the contents of Cd,total As and Pb in grains were reduced by 47.87%,36.37%and 61.76%,respectively.Meanwhile,the contents of Cd,As and Pb in flag leaves increased by 20.87%,32.67%and 49.40%respectively.The contents of three heavy metals in spikelet axis,spike neck and spike node also showed a significant decreasing trend with the increase of spraying concentration,but had no significant effect on the contents of Cd,As and Pb in other organs.Field data showed that increasing DMSA spraying concentration could significantly reduce the contents of Cd,As and Pb in grains,spikelet axis,spike neck and spike node,but the contents of three heavy metals in flag leaves showed a significant increase trend.It is speculated that spraying DMSA to reduce the heavy metal content in grains,which may be related to reducing the transport of heavy metals from vegetative organs?particularly flag leaves?to grains.