Effects of Protein Synthesis Inhibitors on Uptake of Aluminium in Aluminium-Resistant and Aluminium-Sensitive Cultivars of Wheat

Abstract

Summary The effects of two inhibitors of protein synthesis on the kinetics of Al uptake by excised roots of Al-resistant cultivars (Atlas 66 and PT 741) and Al-sensitive cultivars (Neepawa and Scout 66) of wheat were investigated. Treatment of intact roots of the Al-sensitive cultivar, Neepawa, with cycloheximide (0 to 5 mM) showed that this inhibitor was more effective in reducing incorporation of 35 S into microsomal membrane proteins than into total proteins. Cycloheximide at 0.25 mM reduced incorporation of 35 S into microsomal membrane proteins by 68 %, while a 21 % reduction into total proteins was observed. Cycloheximide at 1.0 mM was sufficient to induce maximal inhibition of 35 S incorporation into both microsomal membrane (72 %) and total (40 %) proteins. At this concentration, cycloheximide caused quantitative differences in short-term (3 h) Al uptake between Al-resistant and Al-sensitive genotypes. A significant decrease in rates of Al uptake was observed in both Al-sensitive cultivars (24 and 29 %), while no significant effect was observed in the Al-resistant cultivars. These results are in contrast to previous results from long-term experiments (6 and 12 h), where cycloheximide stimulated Al uptake in an Al-resistant cultivar, Atlas 66 (Aniol, 1984; Rincon and Gonzales, 1992). In experiments where Al uptake was measured after a 4-h pretreatment with 1.0 mM cycloheximide (7 h total exposure), a stimulation of uptake (45 %) was observed in the Al-sensitive cultivar, Neepawa. Thus, time of exposure is an important experimental variable that can account for contradicting results in the literature. In both resistant and sensitive cultivars, treatment with chloramphenicol, an inhibitor of prokaryotic protein synthesis, had no effect on the kinetics of Al uptake. Posible mechanisms whereby protein synthesis might affect Al uptake in Al-resistant and Al-sensitive genotypes are discused.