In this study, the effects of sublethal heat application before lethal heat treatment on thermotolerance mechanisms of tetraploid two wild wheats (Aegilops biuncialis and Aegilops cylindrica), and two durum wheats (Triticum turgidum L. cv. Kiziltan-91 and Harran-95) have been investigated. Eight-day-old seedlings were exposed sublethal heat pretreatment followed by lethal heat treatment [39 +/- 1 degrees C for 24h afterwards 50 +/- 1 degrees C for 1 h (T1)] and lethal heat treatment [50 +/- degrees C for 1 h (T2)]. When plants exposed to direct lethal temperature (T2), seedling lengths were significantly reduced in all genotypes. The sub-lethal treatment enabled the seedlings to tolerate the lethal effects of heat stress with respect to seedling length but this effect was not observed in Kiziltan-91 cultivar. T1 and T2 applications caused a decrease in relative water content in leaves of all genotypes. Total chlorophyll and carotenoid contents of tetraploid wild species were significantly decreased after all heat treatments. The sub-lethal heat pretreatment caused an accumulation of total chlorophyll and carotenoid contents in only Kiziltan-91 cultivar. Ae. cylindrica was found to be sensitive to heat but its degree of protection was higher than other genotypes. This tetraploid wild genotype probably withstands heat with better upregulating protective mechanisms.