Effect of the Kinetin - Naphthaleneacetic Acid Interaction Upon Total RNA and Protein in Senescing Detached Leaves 1

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). It is not known how the regulation is accomplished. Kinetin retards the loss of chlorophyll, RNA, and protein, and enhances synthesis of RNA and protein in detached leaves and leaf tissue of several species. Inhibition of the effect of kinetin by actinomvcin-D has led to the proposal that the hormone influences the rate of senescence by regulating DNA-dependent RNA synthesis (13, 28). Changes in permeability and free space are associated with senescence and have been shown to be susceptible to hormone regulation in the fleshy leaves of Rhoeo. A substantial loss of protein occurred prior to detectable increase in free space (15). However, even the most subtle alteration of an interface might well be the predominant event in the control of senescence. Attempts to correlate the function of kinetin in the regulation of senescence with the induction of specific enzymes have been 1 This investigation was supported in part by a research grant (UI-00102) from the National Center for Urban and Industrial Health, United States Public Health Service. 12'71 inconclusive ( 1). A\lothes has shown that kinetin is able to cause directed transport and localized accumulation of amino acids. From the results of a series of investigations, he has concluded that this is the primary function of kinetin in the regulation of leaf senescence (10). There is evidence w-hiclh is inconsistent with this proposal ( 12, 23, 27), but none by whiclh it is conclusively contradicted. WN e have previously reported that a-naphthaleneacetic acid (NAA) strongly depresses the effect of kinetin, but does not by itself influence the senescence of detached leaves of broccoli or Xanthliim (22). This being so, the regulation of senescence by kinetin may be experimentally altered by the presence or absence of NAA. and the degree of synchrony among the effects of kinetin on the various parameters of senescence may be observed. The interaction between kinetin and NAA was used subsequently to examine the relationship between the regulation of senescence and the directed transport and accumnulation of substrate (23). The auxin by itself had little effect, but when present with kinetin it simultaneously reduced the effect of kinetin upon senescence and increased directed transport and accumulation in the treated locus. In the present report we describe experiments in which the kinetin-NAA interaction was used to examine the relationship between changes in chlorowww.plantphysiol.org on October 30, 2017 Published by Downloaded from Copyright © 1968 American Society of Plant Biologists. All rights reserved.