Chromium stress alleviation by salicylic acid in Malabar spinach (Basella alba)

Phytoremediation is a natural approach to use plants for decontaminating soil. A pot-culture factorial experiment in completely randomized design was conducted to evaluate the effects of four levels [0, 25, 50, and 100 mg/kg] of chromium (Cr) with three levels [0, 0.5, and 1-M solution) of plant defense inducer salicylic acid (SA) on growth, physiological processes, and biochemical responses of Malabar spinach (Basella alba). Results showed that Cr significantly decreased vine length (VL), leaf number (LN), leaf area (LA), fresh- (FBM), and dry-biomass (DBM), root length (RL), and dry-matter ratio (DMR). Cr also significantly decreased SPAD (chlorophyll contents), by 9% to 29% and net photosynthesis (Pn) rates, by 36% to 71%, but increased transpiration (E) rates, by 1.5 to 2.7 times and stomatal conductance (C), by 1.7 to 3.5 times, as compared with the control. Proline contents increased with an associated decrease in oxidative enzyme activities such as peroxidase, (POD) and catalase, (CAT) with increasing Cr levels. Cr significantly reduced the Dry Matter Ratio (DMR) (12% to 42%) and LA (10% to 35%), RL -stress (11% to 27%), and SPAD (10% to 28%) stress tolerance indices. The integrated stress tolerance index (ISTIₙdₑₓ) of Malabar spinach was reduced (by 6% to 23%) by Cr stress, as compared to the control. SA application, in contrast, partially alleviated the severity of Cr toxicity effects on VL, LN, LA, FBM, DBM, RL, and DMR and increased the SPAD (by 12%), Photosynthesis Net (Pn) (by 53% to 68%), and stomatal conductance (C) (by 35% to 50%), respectively. Furthermore, SA increased plant stress tolerance indices by increasing antioxidant enzymatic functions. SA application recovered the ISTIₙdₑₓ at all Cr levels, and the recovery effect on plants was more pronounced by 0.5-M SA than by other SA treatments. The mechanism of stress tolerance as induced by SA application may help plants to better survive and maintain growth in presence of higher Cr contents in soil. Results suggested that SA, as a plant defense inducer, can be exploited for improving Cr phytoremediation potential of Malabar spinach to decontaminate soil.