Non-enzymatic anti-oxidants potential in enhancing hibiscus sabdariffa L. Tolerance to oxidative stress

Abstract

Background and Objectives: In scope of roselle plant salinity tolerance, saline water irrigation is a principle cause of reduction in biomass and productivity. This study aimed to investigate the influence of three different non-enzymatic anti-oxidant protectants, i.e., ascorbic acid (AsA), citric acid and thiamin, applied as foliar spray, in ameliorating the adverse effects of salinity on Hibiscus sabdariffa L. var. Dark Red Calyces exposed to 0 and 75 mM NaCl. Materials and Methods: Pot experiment was conducted at the open field of the Experimental Farm of Agricultural Botany Department, Faculty of Agriculture, Ain Shams University, Qalyubia, Egypt, during the two successive seasons of 2016 and 2017. Growth parameters, yield components, leaf relative water content, membrane stability index and malondialdehyde and the activities of some anti-oxidants were determined. Results: Salt stress markedly decreased plant fresh and dry biomasses, leaf area, leaf fresh biomass, number of fruits, fruits dry biomass and calyces dry biomass/plant beside the loss of color in dry calyces while shoot length, root length and number of leaves relatively unaffected by exposure to salinity. Salinity also alleviated the anti-oxidant defense system in term of total soluble phenols, flavonoids, reduced glutathione (GSH) concentrations, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and phenyl alanine ammonia lyase (PAL) activities and proline as osmoregulator. Exogenously applied AsA, citric acid and thiamin improved both growth and production in roselle plants under the two different concentrations of salinity; 0 and 75 mM NaCl. This improvement was found to be associated with increasing leaf relative water content, membrane stability index, total soluble phenols, flavonoids, proline, GSH concentrations in leaves and anthocyanins in dry calyces. On contrast, significant reduction was showed in malondialdehyde concentration when plants treated with foliar applications in compared with unsprayed plants and altered the activities of SOD, CAT, POD and PAL anti-oxidant enzymes due to balancing of the cell homeostasis under salt oxidative stress. Conclusion: The results of this study proved that AsA, citric acid and thiamin had antioxidant potential to improve roselle plant tolerance against salt stress.