Root-knot nematodes (RKN), Meloidogyne sp. hinders functioning of crops and causes global losses in terms of productivity and yield. Meloidogyne sp. are microscopic, obligatory endoparasites with ubiquitous distribution in different parts of the world. Taking into consideration these aspects, the present study was conducted to explore nematicidal activity of the Streptomyces hydrogenans strain DH-16 against M. incognita to regulate its pathogenicity in plants. In-vitro experimentation revealed that pretreated seeds with solvent and culture supernatant lowered root galls in infested plants and promoted growth of Solanum lycopersicum seedlings, revealed through the morphological analysis. Additionally, antioxidative defense responses were induced with microbes. However, oxidative stress markers were considerably reduced after microbial inoculations. Apart from this, secondary metabolites were assessed and modulated in RKN infested plants on microbial supplementations. Confocal studies evaluated glutathione accumulation within root apices and its enhancement was directly proportional to defense responses. Therefore, the current study concluded the role of S. hydrogenans in stimulating antioxidant potential against RKN along with growth promoting aids. Thus, the outcome of the current study endorses that metabolites produced by S. hydrogenans can be used as safe biocontrol agents against M. incognita and also as plant growth promoting agents.

Hydrogen sulfide (H₂S) is predominantly considered as a gaseous transmitter or signaling molecule in plants. It has been known as a crucial player during various plant cellular and physiological processes and has been gaining unprecedented attention from researchers since decades. They regulate growth and plethora of plant developmental processes such as germination, senescence, defense, and maturation in plants. Owing to its gaseous state, they are effectively diffused towards different parts of the cell to counterbalance the antioxidant pools as well as providing sulfur to cells. H₂S participates actively during abiotic stresses and enhances plant tolerance towards adverse conditions by regulation of the antioxidative defense system, oxidative stress signaling, metal transport, Na⁺/K⁺ homeostasis, etc. They also maintain H₂S-Cys-cycle during abiotic stressed conditions followed by post-translational modifications of cysteine residues. Besides their role during abiotic stresses, crosstalk of H₂S with other biomolecules such as NO and phytohormones (abscisic acid, salicylic acid, melatonin, ethylene, etc.) have also been explored in plant signaling. These processes also mediate protein post-translational modifications of cysteine residues. We have mainly highlighted all these biological functions along with proposing novel relevant issues that are required to be addressed further in the near future. Moreover, we have also proposed the possible mechanisms of H₂S actions in mediating redox-dependent mechanisms in plant physiology.

Abiotic stresses including heavy metal toxicity, drought, salt and temperature extremes disrupt the plant growth and development and lowers crop output. Presence of environmental pollutants further causes plants suffering and restrict their ability to thrive. Overuse of chemical fertilizers to reduce the negative impact of these stresses is deteriorating the environment and induces various secondary stresses to plants. Therefore, an environmentally friendly strategy like utilizing plant growth-promoting rhizobacteria (PGPR) is a promising way to lessen the negative effects of stressors and to boost plant growth in stressful conditions. These are naturally occurring inhabitants of various environments, an essential component of the natural ecosystem and have remarkable abilities to promote plant growth. Furthermore, multifarious role of PGPR has recently been widely exploited to restore natural soil against a range of contaminants and to mitigate abiotic stress. For instance, PGPR may mitigate metal phytotoxicity by boosting metal translocation inside the plant and changing the metal bioavailability in the soil. PGPR have been also reported to mitigate other abiotic stress and to degrade environmental contaminants remarkably. Nevertheless, despite the substantial quantity of information that has been produced in the meantime, there has not been much advancement in either the knowledge of the processes behind the alleged positive benefits or in effective yield improvements by PGPR inoculation. This review focuses on addressing the progress accomplished in understanding various mechanisms behind the protective benefits of PGPR against a variety of abiotic stressors and in environmental cleanups and identifying the cause of the restricted applicability in real-world.