Assessment of salt and drought stress on the biochemical and molecular functioning of onion cultivars

Abstract

Background: Salt and drought stress are the main environmental constraints that limit onion growth and productivity. Türkiye is the fifth largest onion producer, whereas the stress conditions are increasing in the region, resulting in poor crop growth.

Methods and results: A current study was conducted under greenhouse conditions according to a completely randomized design with factorial arrangements to evaluate the performance of onion cultivars. Plants were subjected to salt stress with an application of 750 mM NaCl and drought stress was applied by depriving plants of irrigation water for 20 days to measure biochemical and transcript changes. The antioxidant activities of the cultivars were quantified by using four different methods, i.e., 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) assays, cupric reducing antioxidant capacity, 2,2-Diphenyl-1-picrylhydrazyl, and ferric reducing antioxidant power (FRAP). The damage to pigments, phenolic, osmolytes, and hydrogen peroxide (H₂O₂) accumulation was also evaluated. Results revealed that the cultivars "Elit and Hazar" had higher H₂O_2, maximum damage to pigments, and least accumulation of phenolics and osmolytes under both stress conditions. The cultivar "Şampiyon" performance was better under salt stress but exhibited a poor antioxidant defensive mechanism under drought stress conditions. The remaining cultivars suggested a resilient nature with a higher accumulation of osmolytes, antioxidants and phenolics. The change in transcript levels further strengthened the response of resilient cultivars; for instance, they showed higher transcript levels of superoxide dismutase, ascorbate oxidase and transcription factors (WRKY70, NAC29). It helped alleviate the oxidative stress in tolerant cultivars and maintained the physio-biochemical functioning of the cultivars..

Conclusion: The results of the current study will fill the gap of missing literature in onion at biochemical and molecular levels. Additionally, resilient cultivars can effectively cope with abiotic stresses to ensure future food security.

Keywords: Antioxidants; Osmolytes; Phenolics; Pigments; Transcriptomics.