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

Abstract

Abstract. 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 14C-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 pluis 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.The senescence of detached leaves is characterized by loss of chlorophyll, associated with declining levels of RNA and protein, and the rate of senescence may be regulated by kinetin or other exogenous growth substances (5,12,21,25 radioactivity, and the total activity was used as an estimate of the net uptake of labeled substrate by the tissue. Radioactivity was determined by drying duplicate aliquots on glass-paper circles and counting in a toluene-fluor mixture in a liquid scintillation spectrometer. Quench correction was calculated from internal standard series prepared for each fraction. In some experiments, net uptake was verified in parallel samples by a combustion method (23). A "corrected incorporation" value was calculated by dividing cpm incorporated by the ratio of the net uptake (total cpm remaining after washing) of the treated sample to the net uptake of the control sample. Sacher (14) has discussed the need for a similar correction.

Mechanism of a Synergistic Effect of Kinetin on Auxin-induced Ethylene Production

“…The biochemistry of IAA conjugation has been reviewed (15). Kinetin has been reported to promote amino acid uptake by detached leaves (16,18).…”

Kinetin Inhibition of 3H-Uracil and 14C-Leucine Incorporation by Tobacco Cells in Suspension Culture

“…Cytokinins and auxins show synergistic effects on growth and differentiation of plant tissue (13,15,20,24,26). These phenomena depend not only on the concentration of each of the growth regulators but also on the ratio of their concentrations.…”