Characterization of 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Activity during Maize Seed Development, Germination, and Seedling Emergence

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Abstract
Many isoprenoid compounds are necessary for growth and development of the seed and seedling. The first committed step in the biosynthesis of isoprenoid compounds is the conversion of 3-hydroxy-3-methylglutaryl coenzyme A to mevalonate. This study shows that the specific activity of the rate-limiting enzyme, 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) is developmentally regulated during Zea mays seed development and seedling emergence. The highest activities were observed in seed development during stages of rapid mitotic divisions: 10 to 12 d after pollination in the endosperm (216.1 units) and embryo (140.2 units). During stages of maturation, the endosperm HMGR activity decreases to one-fifth the maximal activity, and the embryo activity remains high at one-half the maximal activity. Both the endosperm and embryo HMGR activities decrease to a basal level (2.0 units) in the desiccated seed. At approximately 48 h after imbibition, the embryo HMGR activity significantly increases to 5.1 units. In seeds germinated under white light, root HMGR activity is 2- to 4-fold higher than shoot activity. In seeds germinated in the dark, both root and shoot HMGR activities are 1- to 5-fold higher relative to activities in light-grown seeds.

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