Effect of the Kinetin-Naphthaleneacetic Acid Interaction Upon Total RNA and Protein in Senescing Detached Leaves

The interaction between kinetin and naphthaleneacetic acid in the regulation of senescence of excised tissue of mature broccoli leaves has been used to examine the extent of synchrony between changes in chlorophyll, RNA, and protein. Kinetin increased the net uptake of 14 C-labeled orotic acid and leucine. Naphthaleneacetic acid decreased the effect of kinetin on net uptake after long treatment, but in short-time treatments the auxin increased the effect of kinetin on net uptake. Results of long (24 hr) treatments indicated a general synchrony between the loss of RNA, protein, and chlorophyll. Naphthaleneacetic acid reduced the stabilizing effect of kinetin upon chlorophyll content and upon the content and synthesis of RNA. In short-time experiments, however, RNA content and synthesis were transiently increased by kinetin, and further increased by kinetin plus naphthaleneacetic acid, while chlorophyll content decreased in the presence of kinetin and decreased further in the presence of kinetin plus naphthaleneacetic acid. Actinomycin-D accelerated the loss of chlorophyll, RNA and protein and strongly depressed the rate of RNA synthesis. In the presence of actinomycin-D the stabilizing effect of kinetin upon RNA was substantially reduced. In contrast, the chlorophyll and protein contents remained higher than in the control. Actinomycin-D did not nullify the basal incorporation of orotic acid into RNA, nor did it negate the effect of kinetin upon incorporation. The failure of synchrony between changes in chlorophyll and RNA does not substantiate the proposal that kinetin regulates senescence by a direct effect upon DNA-dependent RNA synthesis.