Study On Phosphate And Abscisic Acid In Alleviating Iron Deficiency In Apple(Malus × Hupenensis)

Iron(Fe)is an essential micronutrient in plants and plays an important role in many cellular processes.Although the Fe content in the earth's crust is very rich,it mainly exists in the form of peroxides,which is difficult to be absorbed and utilized.Therefore,Fe deficiency generally exists in the process of plant growth and development.As the main fruit in China,apples(Malus domestica)often use a large amount of fertilizer during the cultivation process,which causes soil compaction and salinization,which will hinder the absorption and utilization of apple Fe nutrients over time.Therefore,studying the relationship between the nutrient environment of fruit trees and the absorption and utilization of Fe has a crucial role in improving fruit yield and quality.The antagonistic effects of Fe and phosphate(Pi)have largely affected the effective use of Fe.Although the lack of Pi helps to increase the effectiveness of Fe in Fe-sufficient conditions,the underlying physiological mechanisms controlling this phenomenon remain unclear.In addition,hormone regulation,as a key factor in plant growth and development,is widely involved in various stress responses of plants,including Fe deficiency responses.Previous studies have shown that the accumulation of ferritin is parallel to the accumulation of abscisic acid(ABA).ABA is involved in Fe transport and reuse in Arabidopsis,but the mechanism of action in apples is unclear.In this study,Malus hupenensis was used as the experimental material,and different concentrations of Pi and ABA were used to treat the apple rhizosphere.The following results have been achieved in exploring the physiological mechanisms of hormones and nutrients in apples in response to Fe deficiency:1.Phosphate regulates malate and citrate mediated Fe uptake and utilizationIn this study,we found that low Pi treatment reduced the Fe deficiency phenotype in apples.In addition,low Pi(0,0.125 and 0.5 mM Pi)treatment increased Fe chelate reductase(FCR)activity in the rhizosphere,promoted proton exocytosis,increased Fe content in roots and shoots,and increased the effective use of Fe.In contrast,the high Pi(5 mM Pi)treatment inhibited the above process.Under low Pi conditions,exudation of malate and citrate in apple roots occurs regardless of whether Fe is sufficient or lacking.In addition,treatment with 0.5 mM malate and citrate can effectively alleviate Fe and Pi deficiency.In summary,appropriately reducing the supply of Pi helps to reduce the antagonistic effect of Fe and Pi and promote the exudation of organic acids to enhance Fe absorption.2.ABA promotes iron transportUnder Fe deficiency conditions,endogenous ABA accumulates rapidly in apple roots.External application of low concentrations(5 ?M)of ABA can increase the Fe content in the shoots,but there is no significant change in the roots.Subsequent experiments showed that ABA increased the Fe content in xylem,proving that ABA was involved in Fe transport.Interestingly,under Fe deficiency conditions,exogenous ABA not only significantly reduced the chlorosis of new leaves,but also relieved the stress of root growth under Fe deficiency conditions.In summary,our research shows that applying low concentrations of exogenous ABA can effectively regulate the distribution of Fe in apple roots and shoots.