Abstract
3-weeks old Commelina was transferred to and grown in Hoagland solution ($\pm$ 100 $\mu{M}$ $Cd^{2+}$, 100 $\mu{M}$ $Cd^{2+}$ ＋ 100$\mu{M}$ $Ca^{2+}$, 100 $\mu{M}$ $Cd^{2+}$ ＋ 200 $\mu{M}$ EGTA) for two weeks and then a number of physiological activities was investigated. $Cd^{2+}$ reduced total chlorophyll content up to 29% at a week and 75% at two weeks. In the treatment of $Cd^{2+}$ ＋ $Ca^{2+}$, the total chlorophyll content was reduced to 29% at a week and 80% at two weeks. $Cd^{2+}$ reduced 24% of Fv/Fm after two weeks. In case of $Cd^{2+}$ ＋ $Ca^{2+}$, Fv/Fm was reduced 55% at a week, but after two weeks, the plants were almost dead and Fv/Fm could not be measured. When EGTA was treated with $Cd^{2+}$, the value of Fv/Fm was not affected. There were no differences of water potential between the control and the treatment of $Cd^{2+}$+EGTA toy a week, but in other treatments. water potential was reduced. $Cd^{2+}$ reduced about 21% of water potential and $Cd^{2+}$ ＋ $Ca^{2+}$ reduced 43% of water potential after two weeks. $Cd^{2+}$ inhibited 21% of photosynthetic activity at a week and 32% at two weeks. In case of photosynthetic activity, $Cd^{2+}$ ＋ $Ca^{2+}$ inhibited 58% at a week and 73% at two weeks. $Cd^{2+}$+EGTA inhibited 15% of photosynthetic activity at a week and 21% at two weeks. Similar results were found in stomatal conductance. From the above results, it was observed that the treatment of $Ca^{2+}$ with $Cd^{2+}$ induced more reduction of a series of physiological responses than those of the treatment of $Cd^{2+}$ alone. Therefore, it could be concluded that $Ca^{2+}$ did not reduce the toxicity of $Cd^{2+}$, but enhanced $Cd^{2+}$ -induced physiological toxicities, but EGTA induced an decrease of $Cd^{2+}$ -induced physiological toxicities.