Effects Of Foliar Application Of Iron Fertilizer On Cadmium Uptake And Accumulation And Related Gene Expression In Rice

Cadmium（Cd）is one of the heavy metal elements that has strong toxic to plants and humans.There are interactions between iron and cadmium,which shows that the deficiency of iron may increase cadmium absorption and cadmium transfer to the aboveground part of rice.During the time before conventional intermittent irrigation and after the rice is in the ear,the release of accumulated water can lead to soil oxidation,which can further result in the dissolution of cadmium,while the iron not.Therefore,iron deficiency exists in the rice paddy field,promoting cadmium absorption by rice.In this study,we have simulated iron deficiency in paddy fields by hydroponics and field experiments using iron deficiency nutrient solution.We focused on determining the contents of iron and cadmium in different parts of rice,and studied whether the foliar application of iron fertilizer can reduce cadmium content in rice or not.In order to further study the mechanisms of iron-cadmium interaction,we also carried out differential expression analysis of genes related to cadmium uptake and enrichment.Results are as follows:1. Among treatments with three different nutrient solutions,the elongation of plant height that are treated with cadmium are significantly lower than those without cadmium,which means that cadmium has obvious toxic effect on rice.Under the total Fe nutrient solution,the elongation of plant height that are treated with ferrous fulvic acid plus cadmium are significantly higher than the control treatment,which means that iron can alleviate toxicity of cadmium to rice plant height elongation.2. Under the cadmium stress with 1/4 Fe and 1/2 Fe nutrient solution treatments,foliar spraying with EDTA-FeNa₂ and ferrous fulvic acid can increase iron content in aboveground part of rice,promoting iron uptake and transport.Under the total Fe nutrient solution plus the cadmium stress treatments,iron content under both two different Fe nutrient solution treatments significantly lower than the treatment without cadmium stress,which means that foliar spraying with Fe can restrain of iron uptake and transport in aboveground part of rice.Treatments with EDTA-FeNa₂ and Ferrous fulvic acid plus the cadmium stress have higher iron content than the treatment without cadmium stress,which means that cadmium stress has remarkable promotion effect on iron content of rice.The total Fe nutrient solution with cadmium stress plus adding ferrous fulvic acid treatment can significantly restrain of iron uptake in root.3. After seven days of 1/4 Fe nutrient solution treatments,there are the lowest cadmium content when adding ferrous fulvic acid,which is significantly lower than the control treatment,and this treatment has the best effect to reduce cadmium content.While under the 1/2 Fe nutrient solution treatments,adding EDTA-FeNa₂can get the lowest cadmium content both in the roots or the aboveground part of rice.Under the total Fe nutrient solution treatments,adding ferrous fulvic acid can get the lowest cadmium content both in the roots or the aboveground part of rice.4. Under the 1/4Fe and 1/2Fe nutrient solution with cadmium stress treatments,adding ferrous fulvic acid can significantly down-regulated the gene of OsIRT1 and OsIRT2 in the root,which means that when the iron deficiency exists in root system,foliar application of ferrous fulvic acid can inhibit the expression of related genes associated with cadmium absorption.Under the total Fe nutrient solution with cadmium stress treatments,adding ferrous fulvic acid can significantly up-regulated the gene of OsIRT1 and OsIRT2 in the root,which means that when the iron deficiency is absent in root system,foliar application of ferrous fulvic acid can promote the expression of related genes associated with cadmium absorption.Under the total Fe nutrient solution with cadmium stress treatments,the gene of OsMT3A and OsMT21A are significantly down-regulated compared with the control treatment,indicating that when the root system are absent with iron deficiency,foliar application offerrous fulvic acid will inhibit the detoxification of cadmium.Under the 1/2Fe nutrient solution treatments,adding ferrous fulvic acid can significantly up-regulated the gene of OsMT3A,OsMT1B,OsMT3B,OsMT4C,OsCAX1C and OsCAX1B in the leaf,which indicate that foliar application of ferrous fulvic acid will promote the detoxification of cadmium in rice.The significantly up-regulated the gene of OsNRAMP1 and OsIRT2 means that under the 1/2 Fe nutrient solution treatments,foliar application of ferrous fulvic acid might promote the absorption of iron in the leaf of rice.Under the total Fe nutrient solution treatments,foliar application of ferrous fulvic acid significantly up-regulated the gene of OsMT3A,OsMT1B and OsMT3B,which indicating that when the root system are absent with iron deficiency,foliar application offerrous fulvic acid can inhibit the detoxification of cadmium for rice leaf,while the significantly down-regulated the gene of OsNRAMP1,OsIRT1and OsIRT2 indicating that foliar application of ferrous fulvic acid inhibit the absorption of iron for rice leaf.5. When adding EDTA-FeNa₂,there are the lowest cadmium content in the stem, which is significantly lower than the control treatment.The maximum cadmium content in rice grains is 0.95 mg·kg^-1 under the control treatment,while the treatment of both adding ferrous fulvic acid and EDTA-FeNa₂ have significantly lower content,which might reduce cadmium content by 21.0%-24.2%.These results show that both treatments of adding different iron fertilizer can all reduce cadmium content in the rice grain.