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Hydrogen sulfide (H₂S) is considered as plant growth promoter under heavy metal stress, though its specific effects on photosynthesis are rarely explored. This study investigates the protective effects of exogenous H 2 S donor sodium hydrosulfide (NaHS) on chlorophyll metabolism and photosystem II (PSII) function in 24-day-old bean plants exposed to 10 μM chromium (Cr) stress. Sodium hydrosulfide (100 μM) reduced Cr accumulation in both roots and leaves, leading to restored plant growth. Concomitantly, H₂S mitigated Cr-induced oxidative damages by decreasing reactive oxygen species levels and further enhancing antioxidant scavenging activities. This resulted in significant reductions in Cr-elevated leaf pheophytin and chlorophyllide levels by 59% and 67%, respectively. Furthermore, NaHS application increased levels of porphyrin and its precursor, 5-aminolevulinic acid (5-ALA), in Cr-stressed bean. The up-regulation in chlorophyll biosynthesis was associated with enhanced activities of glutamine synthetase and glutamate synthase, essential for glutamate (precursor of 5-ALA) production, as well as nitrate and nitrite reductase, leading to increased nitric oxide generation. Under Cr stress, H₂S significantly improved the electron transport rate, effective quantum yield of PSII, and photochemical quenching by 112%, 53%, and 38%, respectively, while reducing non-photochemical quenching by 50%. Furthermore, H₂S promoted net CO₂ assimilation and photosynthesis at saturating light, respectively, while reducing stomatal conductance and transpiration to maintain water balance. Exogenous H₂S restored respiration, as indicated by increased light saturation and compensation points in Cr-treated plants. Overall, these findings indicate that H₂S regulates photosynthesis in Cr-stressed bean by modulating nitrogen and chlorophyll metabolism, thereby optimizing PSII efficiency and gas exchange., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Masson SAS. All rights reserved.)

The reuse of water using effluents containing antibiotics from anthropogenic activities has been mainly linked to the development of antibiotic resistance. However, we report that the development of bacterial tolerance promotes plant growth. In the present study, we aimed to evaluate the efficiency of inoculation of a new antibiotic-degrading bacterium, Erwinia strain S9, in augmenting the tolerance of pea (Pisum sativum L.) plants to tetracycline (TET) (10 and 20 mg/L). Physiological parameters such as tissue elongation and biomass, as well as relative water content, were remarkably lower in plants exposed to TET than in the control. The inhibitory effects of TET were associated with reduced CO 2 assimilation, stomatal conductance, transpiration, dark respiration, and light saturation point (LSP). High concentrations of TET-induced oxidative stress are attested by the overproduction of superoxide radicals (O 2 •- ), hydrogen peroxide (H 2 O 2 ), and hydroxyl radicals (HO • ), resulting in increased malondialdehyde content and cell death. The high activity of antioxidant enzymes such as catalase, ascorbate peroxidase, and guaiacol peroxidase validated the proposed mechanism. Under TET stress conditions, supplementation with Erwinia strain S9 was beneficial to pea plants through osmotic adjustment, increased nutrient uptake, gas exchange optimization, and increased antioxidant activities. Its presence not only ensures plant survival and growth during antibiotic stress but also degrades TET via significant antibiotrophy. This strategy is a cost-effective environmental chemical engineering tool that can be used to depollute wastewater or to improve crop resistance in rhizofiltration treatment when treated wastewater is reused for irrigation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Masson SAS. All rights reserved.)

Nitric oxide (NO) is a signaling molecule controlling several steps of plant development and defense process under stress conditions. NO-induced alleviation of manganese (Mn) toxicity was investigated on bean plants submitted for 28 days to 500 µM MnCl 2 . Manganese excess decreased plant dry weight and elongation and increased levels of reactive oxygen species and lipid peroxidation leading to up-regulation of superoxide dismutase, catalase, and ascorbate peroxidase activities. The inhibitory effects of Mn on plant growth were associated to reduction of light-saturated carbon assimilation (A max ), stomatal conductance (g s ), and transpiration (E). By contrast, Mn induced significant increase in the apparent quantum yield (ɸ) and light compensation point (LCP). Interestingly, intracellular CO 2 (Ci) remains stable under Mn stress. Concomitantly, leaf membrane lipids have drastically reduced under high Mn concentration. After Mn exposition, leaf fatty acids exhibited a significant loss of linolenic acid, accompanied by an accumulation of palmitoleic, stearic, and linoleic acids leading to alteration of lipid desaturation. NO supply reversed Mn toxicity as evidenced by enhancement of growth biomass and recovery of A max , E, ɸ, and LCP. Similarly, NO addition has positive effects on leaf lipid content and composition leading to restoration of lipid unsaturation. The modulation of fatty acid composition can be a way to reduce leaf membrane damages and maintain optimal photosynthesis and plant growth. Despite the absence of enough evidences in how NO is involved in lipid and photosynthesis recovery under Mn stress conditions, it is assumed that NO beneficial effects are attributable to NO/Mn cross-talk., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)