Patterns of translocation, respiratory loss, and redistribution in 14c in maize labelled after flowering

growing in the field was labeled with 14(CO2) at four leaf positions 15 to 18 days after flowering. On four occasions after labeling, entire plants were harvested and 14(C) in several plant fractions was analyzed by liquid scintillation spectroscopy to reveal patterns of translocation within the plants" losses of 14(C) by respiration, and patterns of mobilization and redistribution of 14(C) among and within organs. The first and third leaf blades above the ear (+1 and +3, respectively), and the first blade below the ear (-1), exported 14(C) mainly to kernels of the developing ear. Among these three leaf blades, the extent of export of 14(C) was more rapid from upper positions than from lower ones. Movement of 14(C) from the fifth leaf blade (-5) below the ear was much slower than that from the upper three blades, but kernels of the developing ear ultimately became the principle sink for 14(C) exported by this blade. Compared with the upper three leaf blade positions, however, appreciable label from -5 accumulated in the lower stem and roots. Labeling plants bearing partly-fertilized ears caused a large accumulation of 14(C) in the stem, roots and, to a lesser extent, husks, compared with completely-fertilized controls. About 20% of the 14(C) assimilated by the +1, +3, and -1 blades was lost by respiration in the 5 weeks following labeling. During the same interval, nearly 70% of the 14(C) assimilated by the -5 blade was lost by respiration. Approximately half of the carbon assimilated by +3, +1, and -1 blades was translocated directly to kernels within 24 hr after assimilation. A similar quantity of label assimilated by +3, +1, and -1 blades was deposited on cobs and husks within 24 hr after assimilation. Estimates of redistribution of label within the plants suggest that 60 to 80% of the 14(C) accumulated in kernels between days 1 and 35 following labeling was derived from 14(C) originating in upper leaves and deposited in the cob and husk within 24 hr.