|
The response observed for biomass accumulation in Sesamum indicum L cv PB-1 seedlings during early growth phase induced by 1.0 mM Pb2+ supply in our earlier studies was not persistent when 1.0 mM Cu2+ and Cd2+ were supplied either alone or in the various combinations of Pb2+, Cu2+ and Cd2+. Root and leaf fresh weights of the seedlings were hardly affected due to supply of 1.0 mM Pb2+, whereas Cu2+ and Cd2+ caused a drastic decrease in the tissue fresh weight which was more pronounced in the roots. The dry weight of the roots showed a similar effect, however, leaf dry weight was increased with the metal supply. In vivo nitrate reductase activity (NRA, EC 1.6.6.1) was significantly inhibited in roots in the order Pb2+>Cu2+>Cd2+. Leaf NRA was inhibited with Cu2+ supply and with the combinations of the metals. The in vitro enzyme activity, on the other hand, was increased in most of the cases due to the metal supply. Further, total organic nitrogen of the young roots and in several cases in the leaves also increased with the metal supply, possibly because of increased translocation of nitrogen from seed to growing seedlings. The results show that growth and nitrate reduction of this cultivar of sesame respond differentially to Pb2+, Cu2+ and Cd2+, and the effect was specific to the tissue examined.
|
