Studies Of Heavy Metal Cd Alone And In Combination With Zn On The Growth Of Cucumber Hairy Roots

Influences of heavy metal Cd alone and in combination with Zn on the growth of cucumber hairy roots were investigated in this paper as well as changes of soluble protein content, POD and SOD activities during liquid culture of hairy roots. The results were as follows:Compared to the control(MS medium without addition of Cd),lower concentration of cadmium(Cd) could enhance the growth of and make cucumber hairy roots thicker after cultured for 5-15 days but after 20 days of culture, its multicipation coefficient of fresh weight was still lower than the control; but high concentration of Cd (≥15mg/L)inhibited the growth of cucumber hairy roots. The growth of hairy roots was inhibited and formed shorter and smaller lateral roots with the increasing the concentration Of Cd in the medium. lt was also observed that during the whole culture, the content of soluble protein in hairy roots cultured in the medium with different concentration of cadmium was decreased gradually with culture time but the activities of POD and SOD were firstly increased and then decreased with time.Compared to the control(MS medium without addition of Zn),Zn concentration at 8.6 mg/L or 25.8mg/L in the medium could stimulate the growth and made the cucumber hairy roots form more, thicker and shorter lateral roots than controls;but high concentration of Zn at 68.6mg/L and 137.6mg/L inhibited the growth of cucumber hairy roots and resulted in formation less lateral roots, which grew very slowly and with swelled root tips than controls. During the whole liquid culture, the concents of soluble proteins of cucumber hairy roots cultured with different concentrations of Zn in the medium were gradually decreased, but its POD and SOD activities were gradually increased with culture time.Except that low concentration Cd lmg/L in combination with 25 mg/L Zn could stimulate the growth of cucumber hairy roots after cultured for 5-15 days, The growth of cucumber hairy roots cultured with other concentrations of Cd in combination with 25mg/L Zn was inhibited and the growth inhibition was dependent with the increasing concentrations of Cd in the medium, lt was observed that the main roots and lateral roots of cucumber hairy roots when cultured in the medium with 25mg/L+lmg/L Cd were slightly thicker and shorter than that of control. The cucumber hairy roots formed less, shorter and smaller lateral roots with the increasing concentration of Cd in the medium. The cucumber hairy roots cultured with 25mg/L Cd+25mg/L Zn almostly had no growth and the root surface looked red and formed very tiny lateral roots. During the whole culture of 25 days, The biomass of hairy roots and its POD and SOD activities were lower than that cultured with the same concentration of Cd alone, but its soluble protein concentss were increased. Our results that 25mg/L Zn in combination with different concentrations of Cd could result in more servious Cd-induced inhibition of cucumber hairy roots.