[14C]Ethylene Metabolism during Leaf Abscission in Cotton

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Abstract
Changes in 14C2H4 metabolism in the abscission zone were monitored during cotton (cv. Deltapine 16) leaf abscission. Rates of 14C2H4 oxidation to 14CO2 and tissue incorporation in abscission zone segments cut from the second true leaf of nonabscising leaves of intact plants were similar (about 200 disintegrations per minute per 0.1 gram dry weight per 5.5 hours) and relatively constant over a 5-day period. Deblading to induce abscission caused a dramatic rise in 14C2H4 oxidation, but tissue incorporation was not markedly affected. This rise occurred well before abscission, reaching a peak of 1,375 disintegrations per minute per 0.1 gram dry weight per 5.5 hours 2 days after deblading when abscission was 40%. The rate then gradually declined, but on day 5 when abscission reached completion, it was still nearly three times higher than in segments from nonabscising leaves. Application of 0.1 millimolar abscisic acid in lanolin to the debladed petiole ends increased the per cent abscission slightly and initially stimulated 14C2H4 oxidation. In contrast, naphthaleneacetic acid applied in a similar manner delayed and markedly inhibited both abscission and 14C2H4 oxidation.