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

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.