Plants synthesize an astonishing diversity of isoprenoids, some of which play essential roles in photosynthesis, respiration, and the regulation of growth and development. Two independent pathways for the biosynthesis of isoprenoid precursors coexist within the plant cell: the cytosolic mevalonic acid (MVA) pathway and the plastidialmethylerythritol phosphate (MEP) pathway. However, little is known about the effects of plant hormones on the regulation of these pathways. In the present study we investigated the effect of gibberellic acid GA3) on changes in the amounts of many produced terpenoids and the activity of the key enzymes, 1-deoxy-D-xylulose 5-phosphate synthase (DXS) and 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), in these pathways. Our results showed GA3 caused a decrease in DXS activity in both sexes that it was accompanied by a decrease in chlorophylls, carotenoids and Δ9 tetrahydrocannabinol (THC) contents and an increase in α-tocopherol content. The treated plants with GA3 showed an increase in HMGR activity. This increase in HMGR activity was followed by accumulation of stigmasterol and β-sitosterol in male and female plants and campestrol in male plants. The pattern of the changes in the amounts of sterols was exactly similar to the changes in the HMGR activity. These data suggest that GA3 can probably influence the MEP and MVA pathways oppositely, with stimulatory and inhibitory effects on the produced primary terpenoids in MVA and DXS pathways, respectively.
Mansouri H, Asrar Z, Mehrabani M (2009). Effects of gibberellic acid on primary terpenoids and Δ9-tetrahydrocannabinol in Cannabis sativa at flowering stage. J. Integr. Plant Biol. 51(6), 553-561.