Effect of cadmium compounds on growth of rhizobium sesbani and on growth and dinitrogen fixation of sesban

ABSTRACT

The present investigation was made to study the capacity of some cadmium resistant colonies [isolated from the parent culture of R. sesbani in presence of some cadmium compounds; cadmium sulfate and cadmium chloride] on growth, total amount of chlorophyll, nodulation and nitrogen fixation in Sesbania sesban plants. Results showed that the sensitivity of the parent strain of R. sesbani to Cd was more or less the same for both CaSo4 and CdCl2. In addition, the treatment with CaSo4 or CdCl2 at dose 50 mug/ml was suitable to isolate certain cadmium resistant colonies from the parent culture, whereas the higher doses of both cadmium compounds over 50 mug/ml seemed to inhibit completely growth of the parent strain. Moreover, results indicated that all Cd resistant colonies gave significant decrease in nodulation and nitrogen fixation in Sesbania plants compared with the parent strain. On the other hand, results manifested also that most Cd resistant colonies isolated caused significant decrease in dry weight of shoots, while no appreciable change was observed in both dry weight of roots and total amount of chlorophylls in Sesbania plants inoculated with the majority of Cd resistant colonies. It can be concluded that the inhibitory effect of Cd takes place through its effect on nitrogenase enzyme of R. sesbani and photosynthetic process [reduction of shoots] in Sesbania sesban plants