The response of terpenoids to exogenous gibberellic acid in <Emphasis Type="Italic">Cannabis sativa</Emphasis> L. at vegetative stage

In this study the influence of gibberellic acid (GA₃) 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 GA₃ 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 GA₃ in a concentration dependent manner. The α-tocopherol content of cannabis plants decreased in 50 μM GA₃ treatment and increased in 100 μM GA₃ treatment. Exogenous GA₃ caused an increase in HMGR activity. Concomitant with this result, the amount of squalene and phytosterols increased with GA₃ treatment. The amount of THC and CBD did not change at 50 μM GA₃ treatment, but applying of 100 μM GA₃ increased THC and CBD content in leaf plant in comparison with control plants. GA₃ treatment declined number and percentage of monoterpenes in treated plants. Also the number of sesquiterpenes decreased in response to GA₃ treatment but among the remainder of them, the amount of some sesquiterpenes decreased and some sesquiterpenes increased with GA₃ treatment. Our results showed that GA₃ 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 GA₃ treatment probably due to interference of two biosynthetic pathways in their formation.