Effect Of Cadmium On Nodulation Process Of Pea

Cadmium is one of the heavy metals which will pollute the soil. The existence of cadmium is harm to not only people's health but also the growth of plants. In this study , 604 sweet pea has been used as the experimental material to study the effect of cadmium on nodulation process, and the results showed that:1. Cadmium stress inhibited growth of pea roots and also decreased the biomass of pea plantsB y treating for 24 h in 0.6 mg·L^-1 cadmium solution, the elongation of pea primary roots was inhibited significantly and the inhibition reached the utmost significant level after treated for 48 h. The lateral roots elongation was inhibited in an utmost significant way when it was treated with 0.3 mg·L^-1 cadmium for 24 h. After planted the pea plants in perlite for 40 days which have been treated with 1.5, 3.0, 4.5 mg·L^-1 cadmium , the fre-sh weight of pea plants decreased by 15.83%, 16.38%, 28.87%. respectively comparing to the control. All the data showed aboveindicates that cadmium inhibits the growth of roots of pea plants ,especially the inhibition of lateral roots elongation , meanwhile , it also decreases the biomass of pea plants .2. Cadmium stress postponed growth of Rhizobium Leguminosarum and changed morphology of rhizobium cellIn the cadmium concentration range of 0³.0 mg · L"1, the higher cadmium concentration the more obvious inhibition on the growth of rhizobium was produced within the initial 24 hours ; but, as the time goes by , the rhizobium was still growing and reached their growth peaks . Observing the rhizobium morphology which has been treated by different concentration cadmium for 24 hours by electronic transmission microscopy showed that the cadmium stress thickened the rhizobium cell wall and the cell wall was even brokened when the cadmium concentration increased to 3.0 mg · L"1.3. Existence of cadmium stress decreased the amount of rhizobium which infected plant roots successfullyPlants treated with 0.3, 0.6, 0.9, 1.2 mg · L"1 cadmium were inoculated with rhizobium and the results showed that the roots hair deformation rate decreased by 8.8%, 29.2%, 63.9%, 74.3% respectively. It also indicates that with the increasing of cadmium concentration , the amount of rhizobium which successfully infected plant roots decreased and the interference of cadmium on the interaction between rhizobiumand plants improved.4. Cadmium stress destroyed construction of nodules and bacteroidsThe construction of pea nodules and bacteroids peri-membrane have been destroyed after the plants treated with 1.2 mg ? L"1 cadmium for 10 days , but the PHB granules still can been seen clearly; while the whole bacteroids turned to black and can not differentiate the construction of nodules and PHB granules when the plants were treated with 1.5 mg ? L'1 for 10 days .