Effect of Cadmium-Tolerant Rhizobacteria on Growth Attributes and Chlorophyll Contents of Bitter Gourd under Cadmium Toxicity.

Cadmium (Cd) is one of the heavy metals that negatively affects the growth of plants. High solubilization in water leads Cd to enter into plants quite easily, thus decreasing seed germination, photosynthesis, and transpiration. It also shows an antagonistic effect with many of the plants' nutrients like Mn, Ca, K, Mg and Fe. Nowadays, inoculation of plants with ACC deaminase (ACCD) rhizobacteria to mitigate Cd's adverse effects has drawn the attention of environmental microbiologists. The rhizobacteria secrete organic compounds that can immobilize Cd in soil. Therefore, this study was accomplished to investigate the effect of ACCD plant growth promoting rhizobacteria (PGPR) on the bitter gourd under Cd stress. There were six treatments consisting of two ACCD PGPR (Stenotrophomonas maltophilia and Agrobacterium fabrum) strains and inorganic fertilizers at two levels of Cd, i.e., 2 (Cd2) and 5 mg kg-1 soil (Cd5). The results showed A. fabrum with the recommended NPK fertilizer (RNPKF) significantly increased the vine length (48 and 55%), fresh weight (24 and 22%), and contents of chlorophyll a (79 and 50%), chlorophyll b (30 and 33%) and total chlorophyll (61 and 36%), over control at the two Cd levels i.e., Cd2 and Cd5, respectively. In conclusion, the recommended NPK fertilizer + A. fabrum combination is a very effective treatment with which to immobilize Cd in soil for the improvement of bitter gourd growth.

Mechanisms of Cr(VI) resistance by endophytic Sphingomonas sp. LK11 and its Cr(VI) phytotoxic mitigating effects in soybean (Glycine max L.).

Chromium Cr(VI) is highly toxic and leads to impaired phenotypic plasticity of economically important crops. The current study assessed an endophytic-bacteria assisted metal bio-remediation strategy to understand stress-alleviating mechanisms in Glycine max L (soybean) plants inoculated with Sphingomonas sp. LK11 under severe Cr(VI) toxicity. The screening analysis showed that high Cr concentrations (5.0 mM) slightly suppressed LK11 growth and metal uptake by LK11 cells, while significantly enhancing indole-3-acetic acid (IAA) production. Endophytic LK11 significantly upregulated its antioxidant system compared to control by enhancing reduced glutathione (GSH), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activities to counteract Cr-induced oxidative stress. Cr toxicity induced cell morphological alteration, as shown by SEM-EDX analysis and triggered significant lipid peroxidation. The interaction between LK11 and soybean in Cr-contaminated soil significantly increased plant growth attributes and down-regulated the synthesis of endogenous defense-related phytohormones, salicylic acid and abscisic acid, by 20% and 37%, respectively, and reduced Cr translocation to the roots, shoot, and leaves. Additionally, Cr-induced oxidative stress was significantly reduced in LK11-inoculated soybean, regulating metal responsive reduced GSH and enzymatic antioxidant CAT. Current findings indicate that LK11 may be a suitable candidate for the bioremediation of Cr-contaminated soil and stimulation of host physiological homeostasis.

Alleviation of lead-induced physiological, metabolic, and ultramorphological changes in leaves of upland cotton through glutathione.

Plants face changes in leaves under lead (Pb) toxicity. Reduced glutathione (GSH) has several functions in plant metabolism, but its role in alleviating Pb toxicity in cotton leaves is still unknown. In the present study, cotton seedlings (28 days old) were exposed to 500 µM Pb and 50 µM GSH, both alone and in combination, for a period of 10 days, in the Hoagland solution under controlled growth conditions. Results revealed Pb-induced changes in cotton's leaf morphology, photosynthesis, and oxidative metabolism. However, exogenous application of GSH restored leaf growth. GSH triggered build up of chlorophyll a, chlorophyll b, and carotenoid contents and boosted fluorescence ratios (F v/F m and F v/F 0). Moreover, GSH reduced the malondialdehyde (MDA), hydrogen peroxide (H2O2), and Pb contents in cotton leaves. Results further revealed that total soluble protein contents were decreased under Pb toxicity; however, exogenously applied GSH improved these contents in cotton leaves. Activities of antioxidant enzymes (catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), glutathione reductase (GR), and ascorbate peroxidase (APX)) were also increased by GSH application under Pb toxicity. Microscopic analysis showed that excess Pb shattered thylakoid membranes in chloroplasts. However, GSH stabilized ultrastructure of Pb-stressed cotton leaves. These findings suggested that exogenously applied GSH lessened the adverse effects of Pb and improved cotton's tolerance to oxidative stress.