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Articles

The Development of Isocitric Lyase Activity in Germinating Cotton Seed ¹

^a Department of Plant Sciences, Texas A&M University, College Station, Texas 77843

In cotyledons of germinating cotton (Gossypium hirsutum L. var. Stoneville 213) seedlings, in the dark, isocitric lyase (EC 4.1.3.1) activity peaks after 2 days and thereafter slowly declines to a negligible value after 8 days. The maximum activity of this enzyme in cotyledons of 2-day-old seedlings was 16.2 µmoles of glyoxylate formed/15 min·10 cotyledon pairs. Actinomycin D at a concentration of 10 µg/ml, if added to the imbibing solution, completely prevents the development of isocitric lyase activity in these germinating seed. In cotyledons of germinating cotton seedlings, in the light, isocitric lyase activity peaks after 2 to 3 days and sharply declines to a negligible value after 4 days. The maximum activity of this enzyme in cotyledons of 2- to 3-day-old seedlings was 13.2 µmoles of glyoxylate formed/15 min·10 cotyledon pairs. Actinomycin D at a concentration of 10 µg/ml, if added to the imbibing solution, severely inhibits the development of enzyme activity.

In germinating seed, in the light, the synthesis of chlorophyll and glyceraldehyde-3-P dehydrogenase is also limited by the addition of low concentrations of actinomycin D. The new synthesis of fructose-1, 6-diP aldolase, which is detectable after 1 to 2 days of germination, is inhibited by 10 µg/ml of actinomycin D. We, therefore, conclude that the synthetic events leading to the development of chlorophyll, some glyoxysomal and chloroplast enzymes in germinating cotton seedlings depend on newly transcribed mRNA.

¹ This work was supported by the U.S. Department of Agriculture with funds made available through Cotton Incorporated and in part by a postdoctoral fellowship to R.H.S. from the Texas A&M University Research Council.