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1985. Effect of light and benzyladenine on dark-treated growing rice leaves (Oryza saiivti). I. Changes in chlorophyll content and catalase activity. -Physiol. Plant. 63: 79-86.Light-and benzyladeuine-indiiced reversal of the changes in chlorophyll content and catalase activity were studied in the attached first leaf of Oryza sativa L. cv. Bala, kept in darkness for different periods before maturation. Dark treatment caused a decrease in chlorophyll content and catalase activity at all times. Light treatment of dark-incubated seedlings at different periods before maturation reversed the dark-induced effect on chlorophyll content, catalase activity and dry weight and also caused a further rise in chlorophyll content compared to initial values. In darkness, the application of benzyladenine replaced the iight effect in maintaining catalase activity. Chlorophyll content was also maintained by initially applied benzyladenine. Benzyladenine did not promote the photoinduced maintenance and increase in chlorophyll content and catalase activity at any time. Treatment with hydrogen peroxide, glycolate and amizol resulted in an accelerated chlorophyll breakdown and had varied effects on catalase levels. Chlorophyll decrease due to peroxide accumulation was to some extent reversible by benzyladenine, but the hormone had no effect on the peroxide-induced decrease in catalase activity. Development of catalase is light dependent. Benzyladenine stabilises the enzyme but has no effect on its synthesis.

Activity of RNase was studied in attached and detached leaves of 7‐day‐old ragi (Eleusine coracana Gaertn. cv PR 202) plants during senescence using crude enzyme extracts. The RNase activity was relatively constant in attached leaves. In excised leaves incubated in the dark there was a rapid rise in enzyme activity up to 48 h, followed by a decline. No such decrease was observed in the light. Benzimidazole and gibberellic acid suppressed the activity of RNase up to 48 h in the dark and 96 h in the light. Both the growth regulators also prevented the post‐48 h decline in RNase activity of dark incubated excised leaves. Decline in the levels of chlorophyll and RNA in the illuminated excised leaves was not affected by 3‐(3,4‐dichlorophenyl)‐1,1‐dimethyIurea, but the inhibitor prevented the photo‐induced rise in RNase activity. Cycloheximide and actinomycin D could completely prevent both detachment (increase in enzyme activity after the leaf is excised) and photo‐induced rise in RNase activity. Benzimidazole and gibberellic acid prevented the rise in the activity of RNase on one hand and maintained it on the other by their influence on its biosynthesis. Photoinduction of RNase and photo‐induced retardation of senescence are concluded to be two different processes.

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