The response of terpenoids to exogenous gibberellic acid in Cannabis sativa L. at vegetative stage

In this study the influence of gibberellic acid (GA(3)) on plastidic and cytosolic terpenoids and on two key enzymes, 1-deoxy-d-xylulose-5-phosphate synthase (DXS) and 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), for terpenoid biosynthesis was compared in vegetative cannabis plants. Treatment with GA(3) resulted in a decrease of DXS activity in comparison with the control plants. The amount of chlorophylls a, b and total carotenoids declined when plants treated by GA(3) in a concentration dependent manner. The alpha-tocopherol content of cannabis plants decreased in 50 mu M GA(3) treatment and increased in 100 mu M GA(3) treatment. Exogenous GA(3) caused an increase in HMGR activity. Concomitant with this result, the amount of squalene and phytosterols increased with GA(3) treatment. The amount of THC and CBD did not change at 50 mu M GA(3) treatment, but applying of 100 mu M GA(3) increased THC and CBD content in leaf plant in comparison with control plants. GA(3) treatment declined number and percentage of monoterpenes in treated plants. Also the number of sesquiterpenes decreased in response to GA(3) treatment but among the remainder of them, the amount of some sesquiterpenes decreased and some sesquiterpenes increased with GA(3) treatment. Our results showed that GA(3) treatment had opposite effect on primary terpenoid biosynthesis by the plastidic 2C-methyl-d-erythritol 4-phosphate (MEP) and mevalonate (MVA) pathways. But secondary terpenoids showed different response to GA(3) treatment probably due to interference of two biosynthetic pathways in their formation.