Plant growth and productivity are limited by the severe impact of salt stress on the fundamental physiological processes. Silicon (Si) supplementation is one of the promising techniques to improve the resilience of plants under salt stress. This study deals with the response of exogenous Si applications (0, 2, 4, and 6 mM) on growth, gaseous exchange, ion homeostasis and antioxidant enzyme activities in spinach grown under saline conditions (150 mM NaCl). Salinity stress markedly reduced the growth, physiological, biochemical, water availability, photosynthesis, enzymatic antioxidants, and ionic status in spinach leaves. Salt stress significantly enhanced leaf Na+ contents in spinach plants. Supplementary foliar application of Si (4 mM) alleviated salt toxicity, by modulating the physiological and photosynthetic attributes and decreasing electrolyte leakage, and activities of SOD, POD and CAT. Moreover, Si-induced mitigation of salt stress was due to the depreciation in Na+/K+ ratio, Na+ ion uptake at the surface of spinach roots, and translocation in plant tissues, thereby reducing the Na+ ion accumulation. Foliar applied Si (4 mM) ameliorates ionic toxicity by decreasing Na+ uptake. Overall, the results illustrate that foliar applied Si induced resistance against salinity stress in spinach by regulating the physiology, antioxidant metabolism, and ionic homeostasis. We advocate that exogenous Si supplementation is a practical approach that will allow spinach plants to recover from salt toxicity.

Context. Defensive action of plants against biotic and abiotic stresses has been augmented by silicon (Si). Spinach (Spinacia oleracea L.) is a nutritious leafy vegetable that is a cold-tolerant but heat-sensitive crop. Aims and methods. The ability of exogenous application of Si (0, 2, 4 and 6 mmol L −1 in the form of K 2 SiO 3 ) to alleviate heat stress in spinach cv. Desi Palak was investigated. After an acclimatisation period, plants were grown with or without heat stress for 15 days, followed by Si treatment for 25 days. Plant growth and physiology were assessed at 65 days after sowing. Key results. Heat stress significantly inhibited plant growth, water status and photosynthesis, soluble sugar and protein contents, and osmolyte status in spinach leaves, but increased electrolyte leakage, activities of antioxidant enzymes, and proline content. Application of Si alleviated heat stress by enhancing water status, photosynthetic pigments, soluble proteins and essential minerals, and by reducing damage of the plasma membrane. The accumulation of osmolytes counterbalance the osmotic stress imposed by heat. Conclusions. Silicon plays a vital role in alleviating effects of heat stress by improving water status and photosynthetic rate, and accruing osmoprotectants other than proline. Implications. Exogenous application of Si is an efficient strategy to boost tolerance of spinach plants to heat stress, having significant impact on growth and productivity of spinach at higher temperatures.