Mechanism of phosphorus‐induced zinc deficiency in cotton. I. Zinc deficiency‐enhanced uptake rate of phosphorus

Abstract

The effect of withholding Zn on the uptake, translocation and accumulation of P was studied in cotton plants (Gossypium hirsutum L. cv. Deltapine 15/21) grown in nutrient solutions under controlled environmental conditions. The influence of P on the uptake rate, translocation and distribution of 65Zn in the plants was also examined. Increasing the P supply resulted in severe Zn deficiency symptoms (interveinal chlorosis) as well as P toxicity symptoms, which were characterized by leaf puckering and grayish‐brown marginal necrosis. Zinc deficiency markedly increased the uptake and translocation rates of P over the whole concentration range tested (5x10‐5 to 1.25x10‐3M). Uptake and translocation rates of P increased with both level of P and severity of Zn deficiency. This often caused P toxicity symptoms on Zn‐deficient leaves. In contrast to P, the concentrations of K and Mg in the leaves were not affected by Zn deficiency. Similar results were obtained for sunflower (Helianthus annuus L.) and buckwheat (Fagopyrum esculentum Moench) plants. Higher P concentrations in Zn‐deficient leaves or shoots could not be attributed wholly to reduced shoot growth. This was also evident when Zn deficiency was compared with other micronutrient (Fe, Mn, and Cu) deficiencies. Only Zn‐deficient plants showed enhanced uptake and translocation of P. In experiments with 65Zn, a high P supply did not depress uptake and translocation of Zn. From the results obtained it is concluded that the P‐induced Zn deficiency in cotton, as well as in other species, is primarily caused by enhanced P uptake and translocation and not by inhibition of Zn uptake.