ABSTRACT
172Enterobacter sp. C1D is a multi-metal tolerant plant growth promoting bacterium. The aim of the present work was to understand the effect of Cd induced morphological changes on the roots of Vigna radiata and the influence of Enterobacter sp. C1D on root development. The experiments were conducted under hydroponics in which germinated seedlings of Vigna radiata were exposed to a range of different Cd concentrations to determine 50% inhibitory concentration (IC50), Cd accumulation, and cell death. Hematoxylin staining revealed that Cd accumulation was deceased by 90% using bacterial treatment. A novel dual agar plate method has been developed in which one side of the germinated seedling was exposed to Cd containing medium, while the other side was without Cd. This method allows the visualization of the effect of Cd on the overall growth of the plant as well as on the tissues directly exposed to Cd as compared with the unexposed tissues of the same plant. In this method, bacterial effect can be studied by incorporating the culture in the medium. Cadmium was found to inhibit the overall root elongation and it negatively influences root anatomy and lateral root development. Some clear morphological responses observed were: (i) the roots were quite sensitive with the root apex tending to turn toward the no Cd zone, (ii) higher numbers of lateral roots were seen on the side of the Cd free medium, (iii) microscopic images of the transverse section of the root showed Cd mediated damages on one side of the root, (iv) phloroglucinol staining of the section showed high lignin formation only one side of the root. On the other hand, coinoculation with bacterium Enterobacter sp. C1D alleviated Cd stress. The number and the length of the lateral roots were much higher as compared with the uninoculated control.
