Effects of Ethylene and Carbon Dioxide on the Germination of Osmotically Inhibited Lettuce Seed

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Abstract
Lettuce seeds (Lactuca sativa L.) used in this study germinated 98% at 25.degree. in light or dark. Their germination was completely inhibited by 0.20 M NaCl, 0.35 M mannitol, or polyethylene glycol 6000 (-7 bars) under continuous light when germination tests were made in Petri dishes. Approximately 50% germination occurred in sealed flasks due to endogenously produced C2H4 and CO2. Removal of either or both gases prevented germination. In the presence of endogenous CO2, addition of C2H4 (0.5-16 .mu.l/l) stimulated 95-100% germination (after 5 days) only in the light, but the rate of germination was dependent on C2H4 concentration. At 16 .mu.l/l C2H4, full germination occurred within 72 h. Addition of up to 3.2% CO2 had no adverse effect on the C2H4 action. Higher concentrations or the complete absence of CO2 reduced both rate and total germination. CO2 alone was ineffective. Under these osmotic conditions the promotive effect of C2H4 was under the control of phytochrome.