Senescence of rice leaves IV. Influence of benzyladenine on chlorophyll degradation

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Abstract
Why benzyladenine (BA) retards chlorophyll degradation of rice leaf segments, but does not prevent it was investigated. When BA solutions bathing segments of rice leaves were replaced daily, the effect of BA was not enhanced. Solutions of BA kept at 27°C in the dark for 4 days were as active as fresh solutions. It seems unlikely, therefore, that the decrease in the chlorophyll content with increased incubation time in BA-treated leaf segments is caused by inactivation of BA either in the leaves or in solution. Of 25 L-amino acids at 50 mM added singly with BA, 19 were antagonistic to the effect of BA on chlorophyll content, but four, L-arginine, L-histidine, L-lysine and L-methionine, significantly enhanced the effect of BA. The effects of amino acids decreased with a decrease in the amino acid concentration or an increase in BA concentration. When concentrations were decreased to 5 mM, only L-lysine slightly increased the chlorophyll content in BA-treated leaf segments. L-Proline and L-tryptophan did not modify the effect of BA on chlorophyll content. Effects of amino acids on chlorophyll content in leaf segments without BA treatment are similar to those with BA. Furthermore, cycloheximide (50 μg/ml), which decreased the soluble amino acid content, increased the chlorophyll content in BA-treated leaf segments. Since an accumulation of soluble amino acids precedes the degradation of chlorphyll in BA-treated leaf segments, probably antagonisms caused by the amino acids accumulated in the tissue, prevent the added BA from being fully effective in stopping chlorophyll loss.

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