| Aluminum(Al)is the most abundant metal element in soil,which is mainly present in the form of minerals in neutral and alkaline soils,and the form of aluminum is not easily absorbed by plants.However,a large amount of the insoluble aluminum compounds can be converted to the free toxic aluminum ions which are harmful to plants in acidic soils.Aluminum ions can inhibit root growth,chang the shape of the root tip cells,destroy the cells integrity,affect the composition of cell wall,which is one of the most important factors limiting crop growth.Iron plaque is a ferromanganese oxide plaque,and that can absorb a large amount of metal and non-metallic elements in the soil.Iron plaque is an important factor to study the element absorption.Phosphorus is also an essential element for plant growth,which plays vital role on the aluminum resistance of plants.The iron plaque of wetland plants has very high specific surface area and a large number of functional groups,which can absorb large amounts of phosphorus under the condition of phosphorus deficiency and waterlogging.So we need further study the influence of phosphorus adsorbted on iron plaque on uptake,translocation of Al in the micro-interfacial processes of root surface.In this study,ZheFu802 was used in hydroponic culture,iron plaque was induced by phosphorus deficiency and Fe2+,then the influence of phosphorus adsorbed on iron plaque on the absorption,tanslocation of aluminum in rice root tips,roots and shoots were studied.The results are as follows:(1)The effect of iron plaque composition on the aluminum tolerance of rice was studied by hydroponic method,which was induced by phosphorus deficiency and Fe2+.The results showed that the thickness of iron plaqueinduced by-P,20mg/L and 30mg/L Fe2+ increased gradually with the prolongation of culture time.The thickness of iron plaque induced by phosphorus deficiency and Fe2+ was very close at 48h.The root elongation of-P,20mg/L Fe2+ and 30mg/L Fe2+ was reduced by 66.08%,43.75%and 51.25%.The Al content of root tip was increased by 1005.58%,710.12%and 242.79%,respectively,compared with the CK.The The P content in the iron plaque induced byphosphorus deficiency was significantly lower than that of 20 mg/L and 30 mg/L Fe2+,which was only 21.43%and 12.48%to the Fe20 and Fe30 group.The content of P in Fe30 was significantly different from Fe20 and-P group.The content of aluminum in-P root tip was also higher than that in Fe20 and Fe30 groups,and the relative elongation of rice root was lower than Fe20 and Fe30.Iron ions can reduce the distribution of aluminum in the root tip,but would increase the content of aluminum in the cell wall.Indicating that the phosphorus can reduce the aluminum content of the apical aluminum to alleviate the aluminum toxicity.The effect of the iron plaque on the aluminum toxicity was the result of the combined effect of the iron plaque thickness and the surface phosphorusunder iron supplied.(2)Iron plaque on the root surface was induced by phosphorus deficiency(-P)and Fe2+ supply(+Fe).Rice,Zhefu 802,was used to investigate the effect of aluminum(Al)toxicity on root growth,Al content in root tips and root cell wall composition.Relative root length in the-P and +Fe treatment was decreased by66.6%and 51.25%when treated with 100 μmol/L Al3+,and it was significantly lower in-P treatment than in +Fe treatment.Al content and malonaldehyde(MDA)content in root tips was increased by 1105.6%and 322.5%,82.45%and 51.61%in-P and Fe treatment than CK.Furthermore,Al supply significantly increased pectin,hemicellulose 1 and hemicellulose 2 content,and the increase degree in roots treated with-P is higher than that +Fe pretreatment,indicating rice with-P induced iron plaque was more sensitive to Al toxicity.Although iron content was higher in the iron plaque treated by-P than by +Fe,the phosphorus content adsorbed on iron plaque on the root surface was significantly lower in the former than the latter.These results suggested that phosphorus adsorbed on iron plaque played a major role in Al tolerance.(3)The phosphorus plaque was induced by phosphorus deficiency,after that phosphorus was adsorbed on the iron plaqueby adding exogenous phosphorus,and the effect of iron plaque on the aluminum uptake was studied with or without phosphorus.The results showed that aluminum can decrease the root relative elongation.Compared with-P,theroot elongation of-P+P roots increased by 91.6%.Compared with CK,the root apex aluminum content increased 33%and 207.2%in-P and-P+P group,respectively,and the cell wall A1 content increased by 96.6%and 218.9%.The P content in the iron plaque of the root surface was 442.5%and 851.4%higher than that of the CK and-P,respectively.Al treatment significantly increased the content of Al in the iron plaque,root and shoot of A1 in the roots of rice,and 78%of the total Al content in the iron plaque.Indicating that the phosphorus in the iron plaque under the condition of phosphorus deficiency can increase the content of aluminum in the iron plaque and root tip cell wall component and alleviate the toxicity of aluminum to rice by reducing the root tip Al content.(4)The effect of phosphorus and iron plaque on the A1 absorption was studied by the formation of iron plaque induced by phosphorus deficiency and iron.The results showed that no matter CK or the iron group,the root absorption of aluminum is in accordance with the Michaelis-Menten equation.Under the condition of phosphorus deficiency,the adsorption of Al can reach the saturation at the lower concentration.P can reduce the Vmax in the roots and reduce the affinity of the roots to Al.The iron plaque induced by 20mg/L Fe2+ can reduce the affinity of root to aluminum and make Vmax smaller than that of iron plaque induced by 30mg/LFe2 +.The indicated that the P on iron plaque can hinder the root of the absorption of Al,The greater amount of iron plaquehad the strong ability to alleviate aluminumtoxicity. |
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