Abstract
Measured by GC—MS2—SIR3, endogenous ABA4 in embryonic axes of seeds of Malus pumila L. cv. Golden Delicious decreased 8-fold and cotyledon ABA by only 60%, during 10–50 d of stratification at 5 °C, after ABA leaching during an initial 24 h soaking. During stratification, the percentage germination of embryos transferred to 17°C showed a significant linear dependence on loge of ABA levels in the axes at transfer. Between 50 and 70 d, ABA levels increased markedly in axes and testa both of stratified seeds and seeds allowed to re-dry at 17 °C after initial soaking. The ability of fully stratified axes with elevated endogenous ABA to germinate indicated that stratification had decreased their ABA sensitivity. Changes in cotyledon ABA could not account for the promotory effect of cotyledons on germination during the first 30 d of stratification. Loss of testa inhibition of germination during stratification was not linked with changes in testa ABA. Stratification markedly increased the sequestration in the axes of exogenous ABA supplied via the cotyledons. Changes both in axis ABA levels and sensitivity were thus correlated with dormancy release, but subject to modifying control by the cotyledons and testa not involving ABA. Rehydration of dried seeds affected axis ABA later during storage via mechanisms unconnected with dormancy.
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