Figure 1. Arabidopsis seedlings attained low levels of acquired thermotolerance in the absence of the HsfA1s. Seedlings of the wild type (Col and Ws), aTK, bTK, dTK, eTK, QK, and Hsp101 KO mutant (hsp101 or 101) lines were subjected to HS treatments with HS regimes schematically shown inside the panel B. The 7-d-old seedlings were first acclimated at 31–39°C as indicated, allowed to recover at 22°C for 2 h, and then challenged at 44°C for 150 min (A and B) or 43°C for 25 min (C and D). The plants were allowed to grow for 7 d after the HS treatments before being photographed. The effect of acclimation temperatures on acquired thermotolerance was measured by growth performance (A and C) and survival rate (B and D). The survival rates are presented as mean values of three replicates ± SD (n ≥ 50 each).