Prevention of Action of Far-Red-Absorbing Phytochrome in Rumex crispus L. Seeds by Ethanol

Phytochrome-enhanced germination of curled dock (Rumex crispus L.) seeds is further stimulated by pretreatments in solutions of 0.5 to 2 molar methanol and 0.03 to >/= 0.3 molar 2-propanol during a 2-day 20 degrees C imbibition. Similar pretreatments in 0.1 molar ethanol, acetaldehyde, and n-propanol inhibit phytochrome-enhanced germination. If exposure to ethanol is delayed until 16 hours after a red irradiation, seeds escape the ethanol inhibition indicating a mechanism other than toxicity. The rate of escape from ethanol inhibition roughly parallels the escape from phytochrome control in seeds held in water only, indicating possible ethanol effects on phytochrome. It was found that ethanol pretreatment prevents the far-red absorbing form of phytochrome (Pfr) from acting but does not accelerate dark decay or prevent transformation. Ethanol inhibition may be prevented if ethanol pretreatment is at 10 degrees C instead of 20 degrees C, or may be overcome by transferring ethanol-pretreated seeds to 10 degrees C in water. Similarly, ethanol inhibition can be overcome by a 2-hour 40 degrees C temperature shift concluding the pretreatment. It is proposed that the ethanol causes perturbations at a membrane which prevent Pfr from acting.