ACTIONS OF ACID IMMERSION, RED-LIGHT AND GIBBERELLIN-A(3) TREATMENTS ON GERMINATION OF THERMODORMANT LETTUCE SEEDS

Lactuca sativa cv. Grand Rapids seeds not exposed to dark storage at 3 0-degrees-C (DS) germinated completely at 20-degrees-C with red light (R) or 0.5 mM gibberellin A3 (GA3) regardless of pretreatment of R, fa r-red light (FR) or 1-hr acid immersion (pH 0.1) plus water rinse (H+) . H+ treatment alone increased germination of FR-treated seeds from 16 to 50%. GA3 had little effect on FR-treated seeds held in DS for betw een 18 hr and 10 days. Promotion of germination by R decreased slowly increased DS time and finally disappeared, indicating the induction of thermodormancy. Seeds rendered thermodormant by 10-30-day DS did not germinate with water alone, but germinated 8% or less following R, GA3 or H+ treatment. These thermodormant seeds germinated 85% or more if H+ was given before R or GA3. Thermodormant seeds, which received R on days 0, 10 or 20 of DS, germinated 83-90% if given only H+ treatment. GA3 caused higher germination at 20-degrees-C in R-pretreated thermod ormant seeds than R, indicating synergism between GA3 and R. The R pre treatment reduced the degree of thermodormancy and also dark reversion of P(fr) (FR-absorbing form of phytochrome). It is suggested that P(f r) cannot induce germination in thermodormant seeds although some P(fr ) persists for up to 30 days DS. P(fr) can function in these thermodor mant seeds only when they are given an H+ treatment. It is concluded t hat thermodormant seeds incubated in darkness at 30-degrees-C are simi lar to skotodormant seeds incubated in darkness at 20-degrees-C, but t he depth of secondary dormancy in the former is deeper. Presumably P(f r) loss is accelerated at higher temperature.