Zinc-induced anti-oxidative defense and osmotic adjustments to enhance drought stress tolerance in sunflower (Helianthus annuus L.)

Zinc (Zn) is an essential micronutrient for plant growth and development and plays a vital role in drought stress tolerance. To explore the physiological mechanisms of drought stress tolerance improved by exogenous application of Zn in sunflower, a hydroponic experiment was conducted. The present study comprised of two factors i. e. PEG-6000 induced drought stress for 0, 7, and 14 days and Zn treatments (0, 1, and 3 mu M ZnSO4), arranged in a completely randomized factorial design. Exogenous application of Zn significantly boosted the photosynthetic pigments i.e. chlorophyll a (31.2 %), chlorophyll b (35.9 %), photosynthetic rate (41.7 %), and shoot (44.0 %) and root dry matter (38.7 %) of sunflower under PEG-6000 induced drought stress compared to the control without any Zn treatment. In comparison to control, antioxidant enzymes activities, i.e. ascorbate peroxidase, superoxide dismutase and catalase and non-enzymatic antioxidant i.e. ascorbic acid were significantly enhanced by 57.1, 26.6, 62.3, and 38.3 %, respectively while the malondialdehyde (MDA) contents reduced by 83.5 % with exogenous application 3 mu M ZnSO4 under PEG-6000 induced drought stress. The same treatment enhanced osmoregulatory substances such as soluble proteins (79.5 %) and free proline contents (70.5 %) under PEG-6000 induced drought stress as compared to control. Relative water contents showed highly significant positive correlation with free proline (R-2 = 0.95), soluble proteins (R-2 = 0.98), superoxide dismutase (R-2 = 0.91) and negative correlation with MDA contents (R-2 = 0.91). It is concluded that exogenous application Zn enhanced anti-oxidative defense and osmotic adjustment and ultimately drought stress tolerance in sunflower (Helianthus annuus L.).

Automated summary

Exogenous application of zinc significantly enhances the antioxidant defense and osmotic adjustment in sunflower under drought stress, ultimately improving drought stress tolerance.