Title : Potential role of exogenous protectants and rhizobacteria in alleviating heavy metal-induced toxicity in lentil (Lens culinaris medikus)
Abstract:
Accumulation of heavy metals (HMs) particularly arsenic (As) and chromium (Cr) in various plant tissues and subsequent plant growth inhibition, is a serious concern for agricultural crops including legumes. Lentil is one of the major protein providing sources among leguminous crops to human diet. It greatly contributes to the economic growth of low-income agricultural countries like Pakistan. High concentration of HMs in soil are continuously damaging and reducing lentil production every year. There is a need of an hour to identify the HM stress and design the strategies to reduce it. In this study we successfully tested plant growth promoting rhizobacteria (PGPR) and melatonin (MLT) in Petri plate as well as pot experiment against As and Cr stress in lentil. After selecting the best As and Cr-resistant PGPR (Bacillus paralicheniformis) and MLT (10 μM) concentration, we conducted a pot experiment to further check their in-planta efficacy under single and interacted As and Cr stress conditions. Single and interactive As and Cr stress conditions significantly reduced lentil growth indices, protein and water content (RWC) and increased oxidative stress by lipid peroxidation (H2O2, MDA) and, osmotic stress indicators (proline, total soluble sugar (TSS). The severity of toxic effects of concomitant stress conditions was more prominent on growth and biochemical parameters in lentil plants compared to individual stresses. However, inoculation of lentil plants with B. paralicheniformis significantly improved plant growth attributes including plant height, fresh and dry biomass and, photosynthetic pigments under As and Cr stresses. We detected that the MLT and B. paralicheniformis pre-treated plants significantly detoxified the adverse effects of osmotic and oxidative stress caused by HM stress by accumulating and adjusting proline, TSS, MDA and H2O2 contents. We further observed that pre-treatments particularly B. paralicheniformis inoculations significantly accumulated tolerance related antioxidant enzyme activities involving catalase (CAT), superoxide-dismutase (SOD), peroxidase (POD), ascorbate (APX), polyphenol oxidase (PPO), and phenylalanine ammonia lyase (PAL) and, mitigated the As-and Cr-toxicity in lentil. We clearly demonstrated that MLT and B. paralicheniformis-assisted remediation is a promising technique for the alleviation of HM-induced toxicity in legumes, which may further enhance the phytoremediation potential and improve the quality of soil.
