C AND N MOBILIZATION FROM STALK AND LEAVES DURING KERNEL FILLING BY C-13 AND N-15 TRACING IN ZEA-MAYS L

The sink capacity of the stalk in Zea mays L. (cv DEA) during the elongation period was previously investigated with C-13 and N-15 tracing. The chase experiment described here demonstrates the different behavior of intermediary reserves for C and N remobilization until full maturity of the kernels. Carbon incorporated during stalk elongation participated mainly in cellulose formation in vegetative organs appearing after the labeling period; the remobilization to kernels was low (0.5%). Soluble carbohydrates and proteins were the main intermediary sink compounds, starch being little remobilized. N first incorporated in roots, sheaths, stalk, blades was translocated to the kernel; 42% of the labeled N were recovered in kernels where they represented 8% of the total N. Cob, husk, and shank acted first as N sinks and then as N sources during ear development. It appeared that amino acids used for synthesis of kernel proteins have a common origin, except for glutelin G3.