| How to reduce the cadmium?Cd?content in rice grain is one of the hot topics and urgent problems to be solved urgently.Foliar spraying zinc?Zn?is a cost-effective agronomic regulation measure to reduce the accumulation of Cd in the edible part of crops.Therefore,exploring the effect of foliar spraying Zn on the uptake and transport of Cd in rice has great significance for reasonable application of Zn fertilizer and safe production of rice.In this paper,Cd in paddy soil was selctected as the researche object.Field and pot experiments were conducted to investigate the effects of foliar spraying Zn on uptake,transport,subcellular distribution of Cd,antioxidant enzyme activities and photosynthesis in rice.The main results of this work were as follows:?1?The effects of foliar spraying Zn on rice yield,Cd and Zn content in various organs and transport of cadmium were clarified,and indentified the suitable concentration range of foliar spraying zinc.Foliar spraying 15 g·L-1 ZnSO4 at the early stage of rice filling had no significant effect on rice yield.The contentrations of Cd decreased and the Zn concentrations increased in the various organs of rice plants sprayed with Zn.The concentrations of Cd in brown rice were decreased by 9.0%47.8%,and the concentrations of Zn increased by 31.7%55.6%.After foliar application with Zn,translocation factors?TFs?of Cd from rachises to brown rice(TFs?brown rice/rachises?),from flag leaves to the first node(TFs?first node/flag leaves?),and from root to first node(TFs?first node/root?)were decreased by 4.7%26.7%,1.0%30.3%and 5.8%43.7%,respectively.There was a significant positive correlation between Cd concentration in brown rice and TFs(first nodes/roots),TFs(brown rice/rachises),and root Cd concentrations.These results indicate that foliar applied Zn reduced Cd concentrations in brown rice by inhibiting the uptake of Cd by root and translocation of Cd from root and flag leaves to the first nodes,and from rachises to brown rice.Foliar spraying 35 g·L-1 ZnSO4significantly reduced the Cd concentrations of brown rice,which was the appropriate amount of foliar application of Zn to reduce Cd concentration in brown rice.?2?The effects of foliar application of Zn on Cd concentrations in different rice varieties were investigated.There was no significant difference in rice yield among the five rice cultivars,including Jingliangyouhuazhan,Fengyuanyou 272,Jinyou 284,Longxiangyou 130and C Liangyou 7,but the Cd and Zn concentration of each organ were significantly different.The Cd concentration in brown rice of these five varieties were significantly decreased by 20.6%32.1%with application of 4 g·L-1 ZnSO4,and the decreased degree of Cliangyou7 was the largest.The Cd concentration in brown rice of Longxiangyou 130 treated with foliar application Zn was the lowest.There was a certain differences in reducing the Cd concentration of rice among these five rice varieties with Zn spraying.?3?The effects of foliar spraying Zn on the distribution of cadmium and the activities of antioxidant enzymes in rice leaves were revealed.The Cd concentration in the cell wall,organelles and cell soluble fraction of rice leaves decreased with foliar application of 4 g·L-1 ZnSO4.The distribution ratio of Cd in the cell wall was increased.The concentrations of malondialdehyde?MDA?in leaves were decreased,and the activities of peroxidase?POD?and the concentrations of glutathione?GSH?were increased.Foliar spraying Zn can reduce the accumulation of Cd in brown rice by increasing the distribution of Cd in the cell wall of the leaves,and improve the resistance of rice by regulating the activity of antioxidant enzyme system and GSH concentration.?4?The effect of foliar spraying Zn on photosynthesis of flag leaves and Cd concentration in xylem was elucidated.There was a decrease tendency of the net photosynthetic rate?Pn?,stomatal conductance?Cond?,intercellular CO2 concentration?Ci?,and transpiration rate?Tr?of flag leaves with foliar application of ZnSO4.The Cd concentration in the xylem sap also decreased.The Cd concentration in brown rice was significantly positively correlated with Tr and Ci.Foliar spraying Zn can reduce the Cd transport from rice roots to the shoot by inhibiting the transpiration of flag leaves,thus reducing the Cd concentration of rice. |
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