Effect of phosphorus supply on iron efficiency in rice bean(Vigna umbellata)

In low iron condition (1 μmol/L FeEDTA), hydroponic experiments were carried out to study the effects of different phosphorus supply levels: P 3, 30 and 300 μmol/L on iron efficiency in rice bean (Vigna umbellata). The results indicate that chlorophyll contents in leaves and dry weights of roots are all significantly decreased along with increase of phosphate supply amounts, and iron content of shoots by the low-P supply is also higher than that of other two treatments. The ratios of shoot total Fe to root total Fe are reduced with the increase of P supply levels, which indicates that the transportion of root Fe to shoot might be blocked, and thereby Fe deficiency is stimulated. Further analysis shows that apoplastic Fe concentration of roots is remarkable lower in the low-P treatment than that of the high P supply levels. These results indicate that the increase of P supply enhances the Fe fixtion in the apoplast of root during Fe acquisition, and consequently inhibites Fe transfer from root to shoot. This may be a mechanism that how the P antagonisticly acts on Fe, and also a reason why high P supply is disadvantageous to Fe nutrient status of plants grown in low Fe condition.