Control of Enzyme Activities in Cotton Cotyledons during Maturation and Germination: I. Nitrate Reductase and Isocitrate Lyase 1

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Actinomycin D at 10 μg/ml strongly inhibited the increase in isocitrate lyase activity during germination of seeds and 40-day-old embryos of cotton (Gossypium hirsutum L.) when the germination period was preceded by 3 hours of soaking in the inhibitor solution. No inhibition was observed without the presoaking. Induction of nitrate reductase activity by nitrate was never inhibited by actinomycin D under the same conditions, and was frequently stimulated about 50%. Thus, the method of applying actinomycin D to the seeds and ovules could affect interpretation of its action. Abscisic acid at 5 μg/ml blocked production of isocitrate lyase activity in both pregermination treatments, but did not inhibit induction of nitrate reductase activity. Induction of nitrate reductase activity became insensitive to the two inhibitors during ovule maturation, at about 32 days after anthesis. The results indicate that isocitrate lyase, a germination enzyme, is not synthesized on performed mRNA. In this respect, the appearance of activity in cotton resembles that in other species of fatty seeds. In contrast, induction of nitrate reductase activity, which is unnecessary for germination, apparently is not regulated at the level of transcription except in young ovules.

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