Histochemical and physicochemical studies reveal improved defense in tomato under Cd stress with rhizobacterial supplementation

Abstract

Environmental fluctuations due to anthropogenic activities show negative effects on plant growth and crop production. Among the heavy metals, cadmium (Cd) pollution is most dangerous and is devastating most of the cultivable land. The current study evaluated the Cd induced toxicity in Lycopersicon esculentum plants and the mitigating role of rhizobacteria. Different parameters such as metal uptake, metal chelators, oxidative stress markers, antioxidative defense expression, secondary metabolites, H2O2 tagging, MDA localization and cell viability has been assessed. Cd accumulation enhanced by 64.7% in roots and 267.1% in shoots, which resulted in generating oxidative burst measured in the terms of superoxide content (54.5%), H2O2 (255.1%), and MDA (202.2%) content. Moreover, the Cd stress also modulated the activities of enzymatic antioxidants and non-enzymatic antioxidants. In addition, organic acids and metal chelators were also enhanced in plants under the influence of Cd. Inoculation of rhizobacterial strains reduced the Cd uptake in plant parts (roots and shoots), increased heavy metal tolerance index (HMTI) and reduced oxidative stress markers. Also, enzymatic antioxidants such as, SOD, POD, PPO were increased in microbe inoculated plants whereas CAT, GPOX, APOX, GST, DHAR and GR were reduced. In situ immobilization studies were also conducted in root sections of L. esculentum in which Cd localization, H2O2 accumulation, cell viability and MDA accumulation were observed using confocal and visible microscopy. Reduction in the levels of H2O2, MDA and Cd accumulation along with improved cell viability was observed in the rhizobacterial inoculated plants.