THE TRANSPORT OF CARBON IN WHEAT PLANTS

Radioactive tracer experiments indicate that acetate, injected into the top internode of wheat plants, is metabolized during a 24-h period and that it is utilized before translocation from the stem. Movement of tracer was largely toward the head of the plant, the kernel constituents becoming especially radioactive. Free glutamic acid was an early metabolic product of acetate, but protein-bound glutamic acid did not reach a maximum specific activity until between the 1st and 3rd days after injection of the tracer. The maximum specific activity of kernel-protein glutamic acid occurred at about the same time as it exceeded the specific activity of the free glutamic in the kernels. However, the relationship between the specific activities of free and protein-bound glutamic acid of other plant parts was not consistent with the view that the protein glutamic acid was derived solely from a uniform pool of free glutamic acid in the particular plant part being considered. 14 C incorporated by exposing the head of the wheat plant to 14 CO 2 was effectively retained in the head, but extensive transport of 14 C from the chaff to the kernel was observed. When the leaf of the plant was exposed to 14 CO 2 there was extensive respiration of 14 C Appreciable amounts of 14 C appeared in the head of the plant and some translocation of tracer to lower stem parts was observed.