Effect of an As(V)-Resistant Plant Growth Promoting Bacterial Consortium on Growth, Antioxidant Content and Arsenic Accumulation in Azolla microphylla Kaulf. Under As(V) Stress

Aquatic fern Azolla microphylla Kaulf. was exposed to arsenic (As(V)) stress at 7 mg/L in its natural cultivation environment, in the presence or absence of an As(V)-resistant bacterial consortium. The bacterial strains used show plant growth promoting traits such as phosphate solubilisation, siderophore production and indole acetic acid production. In absence of the bacterial consortium, the effects of As(V)-induced toxicity on the fern are manifested in the form of reduced biomass production, with decline in chlorophyll, carotenoids, flavonoids and phenolics contents, and increase in anthocyanin content, endogenous H2O2 concentration, lipid peroxidation, with respect to the control set. However, in presence of the bacterial consortium, these effects are alleviated, with the fern plant showing significant improvement in growth and non-enzymatic antioxidant concentrations. The extent of As accumulation in the fronds of fern also show marked differences: in presence of the bacterial consortium, A. microphylla accumulates 51.8% lesser As in its fronds. The abundant presence of bacterial cells on the root surface of the fern, as seen in scanning electron micrograph, along with a heightened As peak in the energy dispersive X-ray spectra indicates that the bacterial cells uptake major fraction of the As from the cultivation environment, thereby reducing As(V)-induced toxicity in the plant.