Reactive oxygen species (ROS) and nitric oxide (NO) are produced in all aerobic life forms under both physiological and adverse conditions. Unregulated ROS/NO generation causes nitro-oxidative damage, which has a detrimental impact on the function of essential macromolecules. ROS/NO production is also involved in signaling processes as secondary messengers in plant cells under physiological conditions. ROS/NO generation takes place in different subcellular compartments including chloroplasts, mitochondria, peroxisomes, vacuoles, and a diverse range of plant membranes. This compartmentalization has been identified as an additional cellular strategy for regulating these molecules. This assessment of subcellular ROS/NO metabolisms includes the following processes: ROS/NO generation in different plant cell sites; ROS interactions with other signaling molecules, such as mitogen-activated protein kinases (MAPKs), phosphatase, calcium (Ca²⁺), and activator proteins; redox-sensitive genes regulated by the iron-responsive element/iron regulatory protein (IRE-IRP) system and iron regulatory transporter 1(IRT1); and ROS/NO crosstalk during signal transduction. All these processes highlight the complex relationship between ROS and NO metabolism which needs to be evaluated from a broad perspective.

Plant growth promoting rhizobacteria (PGPRs) are very effective in immobilization of heavy metals and reducing their translocation in plants via precipitation, complex formation and adsorption. The present study was therefore designed to understand the role of Pseudomonas aeruginosa and Burkholderia gladioli in mitigation of Cd stress (0.4 mM) in 10-days old L. esculentum seedlings. The present work investigated growth characteristics, photosynthetic pigments, metal tolerance index, metal uptake and the contents of metal chelating compounds (protein bound and non-protein bound thiols, total thiols) in microbes inoculated Cd treated L. esculentum seedlings. The gene expression profiling of different metal transporters was conducted in order to investigate the quantitative analysis. Our results revealed Cd generated toxicity in seedlings in terms of reduced growth (root length, shoot length and fresh weight) and photosynthetic pigments (chlorophyll, carotenoid and xanthophyll) which enhanced upon inoculations of P. aeruginosa and B. gladioli. Further, the metal uptake along with levels of protein and non-protein bound thiols was also enhanced in Cd-treated seedlings. Gene expression studies suggested enhanced expression in the metal transporter genes which were further declined in the microbe supplemented seedlings. Therefore, micro-organisms possess growth promoting traits that enable them to reduce metal toxicity in plants.