Effects of compactin,a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor,on the growth of alfalfa (Medicago sativa) seedlings and the rhizogenesis of pepper (Capsicum annuum) explants

The effects of compactin, a specific inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, on the growth of alfalfa seedlings in vivo and the rhizogenesis of pepper explants in vitro were investigated. Compactin added to the agar medium inhibited the elongation of roots and hypocotyls of etiolated alfalfa seedlings. The growth inhibition was accompanied by strict inhibition of sterol synthesis. Addition of mevalonic acid, the direct product of 3-hydroxy-3-methylglutaryl coenzyme A reductase, together with compactin relieved the growth inhibition. The sterol level in the seedlings was also protected against the lowering effect of compactin. Similarly, the rhizogenetic process of cultured explants of pepper was inhibited by compactin and relieved by mevalonic acid. Several isoprenoid end products were tested in combination with compactin to determine which compounds, if any, might be limiting for growth. Exogenously supplied isoprenoids failed to relieve the growth inhibition of seedlings. In contrast, they partly relieved the growth inhibition of explants, suggesting their important role in plant growth. During the course of these experiments, it was also found that brassinolide caused remarkable growth inhibition and twisting of alfalfa seedlings.