Effects of aluminum on NAD kinase activity in chloroplast fraction from leaves of rice seedlings

The effect of aluminum on NAD kinase in vivo and in vitro was studied. The concentration of alu- minum and exposure time are the main factors determining aluminum toxicity.Al can accumulate in the chloroplast of rice seedlings and affect calmodulin-dependent NAD kinase activity,however,calmodulin-in- dependent NAD kinase was insensitive to Al application. Calmedulin can reverse the inhibition of Al at low Al concentrations(0.001mmol/L -O. 5mmol/L),but the relaxing ability decreases at higher Al(2mmol/L).It is suggested that,aside from impairing calmedulin, Al may also affect calmedulin-dependent NAD kinase activ- ity by changing the enzyme structure.