Benzimidazole delays the senescence of detached leaves 1-4 . Nickel ions have also a preservative effect on the green pigment of detached leaves 5-7 . The effect of nickel in regulating senescence has not yet been adequately studied. Since both benzimidazole and Nickel chloride delay the senescence of detached leaves, a study was undertaken to measure the drifts in chlorophyll, protein, RNA and ribonuclease activity of leaves treated with these compounds during senescence. Healthy and uniform

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... aves (ca. 5 cm length) of rice (Oryza sativa variety IR-8) were floated on 30 ml test solutions in 10 cm petridishes. The test solutions were: Water (control), Benzimidazole (10 -3 M), Nickel chloride (10 -3 M) and the combination of benzimidazole and Nickel chloride at a final concentration of 10 -3 M. To prevent contamination, chloramphenicol (20 /ug) and penicillin (120 units) were added to each of the petridishes. The leaves were floated on the test solutions for 120 hours in complete darkness at room temperature (30 °C), after which the samples were analysed for chlorophyll 8 , protein 9 , RNA 10 and ribonuclease 11 activity. All the values are expressed as percent of the initial value, i. e. in terms of the contents present in the leaves before floatation. The experiment was repeated thrice and the values presented in Table I are the mean of three separate experiments. Preliminary experiments established that more than 50% of the leaves showed visible sign of senescence within 120 hours of detachment. Hence the effect of these chemicals on the retention of chlorophyll, protein and RNA was measured at 120 hours after treatment. Benzimidazole reduced the loss of chlorophyll, protein and RNA (Table I ).