Comparative studies on the effect of a protein-synthesis inhibitor on aluminium-induced secretion of organic acids from Fagopyrum esculentum Moench and Cassia tora L. roots

Aluminium (Al)-induced secretion of organic acids from plant roots is considered a mechanism of Al resistance, but the processes leading to the secretion of organic acids are still unknown. In the present study, a protein-synthesis inhibitor, cycloheximide (CHM), was used to investigate its effect on Al-induced organic acid secretion in a pattern I (rapid exudation of organic acids under Al stress)plant buckwheat ( Fagopyrum esculentum Moench)and a pattern II (exudation of organic acids was delayed by several hours under Al stress)plant Cassia tora L. A dose-response experiment showed that the secretion of oxalate by buckwheat roots was not affected by CHM when added in the range from 0 to 50 ì M , with or without exposure to 100 ì M Al, but the secretion of citrate was completely inhibited by 30 ì M CHM in C. tora . A time-course xperiment showed that even prolonged exposure to 20 ì M CHM did not affect oxalate secretion in buckwheat, but significantly inhibited citrate secretion in C. tora . However, citrate synthase (CS)activity in C. tora was not affected during 12 h exposure to 100 ì M Al when compared with that in control roots, although CHM can inhibit CS activity effectively. These results indicated that CS activity was not related to Alregulated citrate efflux in C. tora . The total protein was decreased by 14.0