EFFECTS OF PROTEIN-SYNTHESIS INHIBITORS ON UPTAKE OF ALUMINUM IN ALUMINUM-RESISTANT AND ALUMINUM-SENSITIVE CULTIVARS OF WHEAT

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 i nvestigated. Treatment of intact roots of the Al-sensitive cultivar, N eepawa, with cycloheximide (0 to 5 mM) showed that this inhibitor was more effective in reducing incorporation of S-35 into microsomal membr ane proteins than into total proteins. Cycloheximide at 0.25 mM reduce d incorporation of S-35 into microsomal membrane proteins by 68%, whil e a 21% reduction into total proteins was observed. Cycloheximide at 1 .0 mM was sufficient to induce maximal inhibition of S-35 incorporatio n into both microsomal membrane (72%) and total (40%) proteins. At thi s concentration, cycloheximide caused quantitative differences in shor t-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 obs erved in the Al-resistant cultivars. These results are in contrast to previous results from long-term experiments (6 and 12 h), where cycloh eximide stimulated Al uptake in an Al-resistant cultivar, Atlas 66 (An iol, 1984; Rincon and Gonzales, 1992). In experiments where Al uptake was measured after a 4-h pretreatment with 1.0 mM cycloheximide (7 h t otal exposure), a stimulation of uptake (45%) was observed in the Al-s ensitive cultivar, Neepawa. Thus, time of exposure is an important exp erimental variable that can account for contradicting results in the l iterature. In both resistant and sensitive cultivars, treatment with c hloramphenicol, an inhibitor of prokaryotic protein synthesis, had no effect on the kinetics of Al uptake. Possible mechanisms whereby prote in synthesis might affect Al uptake in Al-resistant and Al-sensitive g enotypes are discussed.