The involvement of indole acetic acid in the thermodormancy of lettuce fruits, Lactuca sativa cv. Grand Rapids.

At 20° C and at 30° C in darkness, concentrations of indole acetic acid (IAA) greater than 10(-7) M inhibited the germination of Grand Rapids lettuce at 24 h and 48 h after the beginning of imbibition. There was no marked, readily defined period of inhibition during germination that could be associated solely with an effect of IAA on suppressing radicle extension. Gibberellin A4+7, benzyladenine and red light were capable of reversing the effects of IAA. There was no consistent pattern of change in the low endogenous levels (less than 11 μg kg(-1)) of extractable IAA during the first 30 h after imbibition.