The effects of seed priming with sodium hydrosulphide on drought tolerance of sunflower (Helianthus annuus L.) in germination and early growth

Sunflower seeds (hybrid Luka) were primed with water (hydropriming) or sodium hydrosulphide (NaHS) solutions (0.1, 0.5, 1.0 and 1.5 mM NaHS) and subsequently dried to initial moisture content. Unprimed (control) and primed seeds were germinated in a growth chamber on paper towels moistened with water or polyethylene glycol (PEG) 6000 solutions (2.5, 5.0 and 10%), mimicking different drought stress levels. To evaluate the response of the primed seeds to drought in the germination stage, the germination energy (GE), germination rate (SG), seedling fresh mass (SW), hydrogen peroxide and free proline content (PRO), as well as lipid peroxidation rate (malondialdehyde; MDA) were established. The results show strong effects of the imposed drought stress and the metabolic response to oxidative stress through lower germinability and proline accumulation in seedlings. NaHS priming showed some positive effects on seed germination depending on stress level and the concentration of NaHS. Sunflower seeds were also germinated in pots filled with soil, at optimal (70% of field water capacity [FWC 70%]) and drought conditions (FWC 30%), in natural outdoors conditions. When plantlets developed the first pair of leaves, the number of plants (emergence rate [ER]), shoot mass (SM) and leaves mass (LM) were determined, as well as the total activities of catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR) and dehydroascorbate reductase (DHAR). There was a significant influence of an interaction between drought stress and priming, whereas drought stress inhibited plant emergence and early growth (SW and LW), and strong antioxidative enzymatic response to drought stress was clearly established in the leaves. Although seed priming showed some influence on enzyme activities, it was mostly related to seed hydropriming effects, while NaHS seed priming was less effective, influencing only DHAR. Altogether, the results imply that sunflower seed priming with NaHS may not have a prolonged impact on the antioxidative defence mechanism based on CAT and ascorbate/glutathione cycle during sunflower early growth in drought conditions.