PHOSPHATE DEFICIENCY IN MAIZE .5. MOBILIZATION OF NITROGEN AND PHOSPHORUS WITHIN SHOOTS OF YOUNG PLANTS AND ITS RELATIONSHIP TO SENESCENCE

The effects of phosphorus (P) deprivation on the changes in the conten ts of reduced nitrogen (N) and P in the shoots of young maize plants ( Zea mays L.) were investigated for up to 30 days after planting (DAP). P deprivation decreased the fresh weight and the contents of Chi, tot al P, esterified P, acid-soluble P-i, total reduced N, soluble protein N, and insoluble protein N in the entire shoot. Thirty DAP, in the fi fth leaf blade, which was expanding, P deprivation greatly decreased t he concentration of acid-soluble P-i but had a smaller effect on the c oncentration of esterified P and little or no effect on the concentrat ions of Chi, total reduced N, soluble protein N, and insoluble protein N. By contrast, in the fully expanded second leaf blade, P deprivatio n greatly decreased the contents of acid-soluble P-i, esterified P, Ch i, total reduced N, soluble protein N, and insoluble protein N at 30 D AP. It is concluded that P deprivation induced the early initiation an d accelerated remobilization of N from old leaf blades. Since this phe nomenon is a critical feature of leaf senescence, it is suggested that the P status of leaves is involved in the regulation of leaf senescen ce in maize.