Promotion of Mineral Contents and Antioxidant Compounds in Water Spinach Using Foliar Paclobutrazol and Salt Elicitors

Green vegetables are important food resources to feed the world population. Water spinach ( Ipomoea aquatica Forsk; Convolvulaceae) is one such food resource that can grow rapidly in a short-cultivation period and by simple cultivation practices. The objective of this study was to stimulate antioxidant compounds, mineral nutrients, physiological adaptation, and overall growth performances in two cultivars of water spinach (wild type, WT; Chia Tai, CT) using paclobutrazol (PBZ) and NaCl salt elicitors. Six-week-old seedlings of WT and CT water spinach were foliar-sprayed with 0 (control), 17, and 51 M PBZ for 1 week, followed by 0 (control) and 100 mM NaCl (salt elicitor) for 7 days. The growth characteristics and physiological and biochemical changes were measured for all scenarios during the period of application. Plant height in WT was found to be sensitive to PBZ (decline by 16.5% under 17 M PBZ and 46.6% under 51 M PBZ as compared to the control scenario). This in turn led to a 50% shorter shoot length when compared to the control scenario, and the 100-mM NaCl salt treatment significantly inhibited shoot length, whereas it was not affected in CT. The number of leaves and shoot fresh weight were maximal in WT with 51 M PBZ and 0 mM NaCl at 14.7 leaves plant −1 and 9.97 g plant −1 , respectively. On the contrary, these parameters in the 0-µM PBZ and 100-mM NaCl scenarios decreased by 40.9% and 57.4%, respectively, over the control scenario. A significant reduction in Na + and Ca 2+ was found in PBZ-pretreated plants exposed to NaCl elicitor. Interestingly, Na + enrichment in the leaf tissues of 51- µM PBZ-treated plants under salt stress decreased by 40% over 0 M PBZ, leading to sustained chlorophyll pigments, photon yield of PSII (Φ PSII ), net photosynthetic rate ( P n ), and plant biomass. Moreover, total soluble sugar (TSS), ascorbic acid (AsA), and tocopherol contents in the leaf tissues were enhanced in the NaCl-treated cultivar CT as compared to certain degrees of PBZ foliar applications. In summary, reduced plant height and NaCl toxicity in water spinach using PBZ were observed. In addition, osmotic adjustment compounds and non-enzymatic antioxidants were regulated as major defense responses to retain the photosynthetic abilities and growth performances. Accumulation of AsA and tocopherol in the green leaf vegetable of water spinach was found to be regulated by a combination of PBZ pretreatment and NaCl elicitor.