The present study aimed to explore the effects of exogenous gibberellins (GAs) on seed germination and subsequent seedling growth of hemp (Cannabis sativa L.) under drought stress. Seeds of two industrial hemp cultivars i.e., 'Yunma 1', (YM) and 'Bamahuoma', (BM) were treated with different concentrations of GA3 solution (0, 200, 400, 600, 800 mg/L) at 20 °C for 8 h. The effect of pre-treatment was assessed on germination characteristics and physiological indexes on subsequent exposure to drought stress using 20% (m/v) polyethylene glycol (PEG) for 7 days. The results revealed that seed germination in hemp was sensitive to drought stress, as the germination indexes (germination rate and germination potential) decreased significantly, and seedling growth (hypocotyl length and radicle length) was impeded under 20% PEG-6000 condition. GA3 pre-treatment affected germination rate, germination potential, hypocotyl length and radicle length. With increasing GA3 concentration, these indexes first increased and then decreased. For seedling physiology characteristics in hemp, GA3-pretreatment remarkedly increased the osmotic regulating substances (soluble sugar and soluble protein contents) and the activities of antioxidant enzymes (SOD, superoxide dismutase and POD, peroxidase), while sharply decreased the lipid peroxidation (malondialdehyde, MDA) in seedlings grown under PEG-6000 induced drought stress. These results suggested that seeds pre-treated with GA3 could enhance the drought tolerance of hempseeds, and the optimal effect of GA3 for seed pre-treatment of YM and BM could be obtained when the concentration of GA3 solution reached 400 mg/L and 600 mg/L, respectively.
Keywords: Cannabis sativa L.; drought stress; gibberellins; seed germination; seedling physiology.