Influence of Foliar Application of Osmoprotectants to Ameliorate Salt Stress in Sunflower (Helianthus annuus L.)

Osmoprotectants are highly soluble, neutral and non-toxic chemical compounds which have low molecular weight. These molecules help the plants to regulate osmotic adjustment and to enhance abiotic stress tolerance in plants. This study was aimed to examine mitigation effects of different osmoprotectants (salicylic acid, ascorbic acid, proline and their admixture) @ 200 mgL^-1 on sunflower (Helianthus annuus L.) grown under saline environment (150 mM NaCl). The results showed that salinity stress (150 mM) resulted into significant decrease in biomass accumulation of sunflower up to 50%, while it was improved by 80% in control by the foliar application of osmoprotectants. Chlorophyll (Chl^-a, chl b and total chlorophyll) contents were also decreased significantly due to saline environment; however, there was improvement of 288.5%, 162.5% and 141.0% by 200 mgL^-1 spray of proline. The amount of hydrogen peroxide and Malondialdehyde were elevated by 170.3% and 68.7%, respectively while enhanced by 54% and 47.4% by spray of proline under salinity. Significant reduction in K^+ uptake with concurrent increase in Na^+ content was observed under NaCl salt stress, while the foliar application of proline increased the amount of K^+ at vegetative growth under stress and non-stress conditions. The biological yield, physiological, and oxidative activity of sunflower crop could be enhanced by aerial spray of proline at the rate of 200 mgL^-1 under saline environment.