PHYSIOLOGICAL RESPONSES OF CITRUS ROOTS TO Fe DEFICIENCY

An experiment was conducted to study the root secretions and Fe3+ reduction of citrus grown in nutrient solution with and without Fe supply. The results showed that H+ efflux and Fe3+ reduction by the roots of citrus increased in the case of Fe deficiency. The higher the rate of H+ efflux and Fe3+ reduction, the stronger the abilities of Fe absorption by citrus species. H+ efflux and Fe3+ reduced substances release by the roots were inhibited by removing chlorotic leaves and buds caused by Fe deficiency, and progressively increased as they sprouted again. It suggested that H+ efflux and Fe3+ reduced substances release were regulated by Fe- deficient leaves and buds. The inhibition of H+ efflux was elimilated by adding 0.1nmol/L IAA into nutrient solutions. Moreover, it was observed that the root tips of tangerine, the species with strong ability to absorbe iron from soils, were swollen, which is beneficial to uptake iron by contact between roots and soil particles.