Control of Enzyme Activities in Cotton Cotyledons during Maturation and Germination

Abstract

The sequence of glyoxysomal enzyme development was investigated in cotyledons of cotton (Gossypium hirsutum L. cv. Deltapine 16) embryos from 16-70 days after anthesis (DAA). Catalase, malate dehydrogenase and citrate condensing enzyme activities were barely detectable prior to 22 DAA, but showed dramatic increases from 22-50 DAA. Development of malate synthase activity, however, was delayed during this period, rising to peak activity from 45-50 DAA (just prior to desiccation) in the absence of any detectable isocitrate lyase activity. Substantial activities of all of these enzymes (except isocitrate lyase) persisted in the dry seeds. Isopycnic centrifugations on sucrose gradients demonstrated that the enzymes were compartmentalized within particles increasing in buoyant density with time of development (1.226-1.245 g per cm3 from 22-50 DAA). Of particular significance were the observations in 22 day embryos of smooth surfaced membrane dilations of rough endoplasmic reticulum having cytochemical catalase reactivity, and the demonstrations of catalase activities in microsomal fractions isolated throughout the 16-50 DAA period. The data do not allow determination of the mechanism(s) for enzyme activation and/or addition to previously existing or newly formed microbodies, but do show that development and acquisition of enzyme activities within glyoxysomes occur sequentially and thus are not regulated in concert as previously thought.