Evaluation of B. mycoides NR5 on alleviation of As toxicity in Spinach (Spinacia oleracea L.)
Exposing leaf vegetables to arsenic resulted in the growth retardation. A delayed development in arsenic stressed plants compared to the control was observed, and found that As 25mg kg-1 soil significantly reduced the shoot (32.39%) as compared to control plants respectively (Table 3). Although root length was slightly increased in arsenic treatment plant. On the other hand, shoot fresh weight was reduced in metal stressed plant, but bacteria augmented metal stressed plants could lower down the arsenic toxicity and thus achieved the improved growth than stressed plant with no bacteria augmentation.
Similarly, dry weight of root and shoot also confirm the plant growth retardation in arsenic stressed plants. Apparently, the plants grown with bacteria were having bulgy roots which confer the exhibition of plant growth promoting traits in bacteria augmented plants under heavy metal stress. Physiology of spinach plant was also altered under heavy metal stress. Chlorophyll content estimation revealed the changes in amount of pigment content in expanding leaves. Chlorophyll-a concentration was significantly lower than that of chlorophyll-b in both tested plants. The pigment contents in plants showed an almost linear decrease in response to arsenic concentration increases in the soil. The total chlorophyll content of control plants at 45, 60, and 75 DAS was 82.22±3.71, 93.55±1.32, and 99.11±1.07 µgml-1respectively, which reduced on arsenic treatment i.e., 55.24±0.92, 48.59±2.17, and 77.65±5.42µgml-1 respectively (Table 4), however when plant added with arsenic and NR5 exhibited 39.1% improved growth as compared to plants with As but no NR5, and thus confirm NR5 potential in reducing metal uptake and toxicity in plants (Figure 7).