The effect of common bean (Phaseolus vulgaris L.) seed pretreatment with proline and glycine betaine on tolerance to lead stress

  With increasing population and the intensification of industrial, urban and agricultural activities, the concentration of heavy metals in agricultural soils is also increasing. Lead (Pb) is one of the most toxic heavy metals that severely limit the crops growth and productivity. Exogenous application of some compatible solutes such as proline and glycine betaine is one of the effective methods for improving plants tolerance to abiotic stresses. Although much research has been done on the effect of proline and glycine betaine application on increasing the tolerance of different plants to abiotic stresses, including heavy metals, however, there is very limited information about the comparison of the application of these compatible solutes on improving common bean tolerance to Pb toxicity, therefore, the present experiment was designed and carried out. In order to comparison study the effect of proline and glycine betaine application on Pb stress tolerance of common bean plant, a pot experiment was done at the spring and summer of 2015 in south of Tehran. This research was conducted as a completely randomized design with 6 treatments and 4 replications. The treatments included the following levels: Control (no Pb, proline and glycine betaine); Pb stress (500 mg lead nitrate kg-1 soil); Pb stress + seed priming with 25 mM proline; Pb stress + seed priming with 50 mM proline; Pb stress + seed priming with 25 mM glycine betaine; and Pb stress + seed priming with 50 mM glycine betaine. The results of this study showed that Pb stress increased root Pb concentration and oxidative damage to common bean plants. Pb toxicity also reduced the chlorophyll value, relative water content (RWC), plant height, leaf area and root and shoot biomass. However, under Pb stress conditions, seed treatment with proline or glycine betaine reduced Pb uptake, increased activity of antioxidant enzymes and declined oxidative damage, which improved the chlorophyll value, RWC, plant height, leaf area and root and shoot biomass. There were no significant differences between proline and glycine betaine treatments. According to the findings of this study, seed priming with proline or glycine betaine by reducing Pb uptake, increasing the activity of antioxidant enzymes, chlorophyll value, and plant water status, can be used as a beneficial method for improving tolerance of common bean to Pb stress.