A possible requirement for RNA and protein synthesis during cell elongation of intact seedling tissue was studied using the soybean seedling foot with the elongating zone being delineated by India ink marks at 2 and 7 mm back of the root tip. In contrast to most excised plant tissues, there was marked net synthesis of RNA and protein during cell elongation of the intact root. AD and CH were potent inhibitors of cell elongation in the soybean root. CH essentially eliminated protein synthesis, whether measured by net accumulation of protein or by14C-leiicine incorporation, while completely inhibiting cell elongation after a short lag. AD, on the other hand, only partially inhibited protein synthesis while causing almost total inhibition of cell elongation after a lag. The capacity of the tissue to synthesize protein in the presence of AD was correlated with the maintenance of functional polyribosomes, thus suggestive that m-RNA associated with the regulation of cell elongation is more unstable (i.e., a shorter mean life) than total root m-RNA. FU did not inhibit cell elongation, protein synthesis or the level of functional polyribosomes. The requirement for RNA synthesis during cell elongation of the seedling root, as in excised plant tissues, appears to be restricted to the AMPrich species of RNA presumed to be m-RNA.
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