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.