Light‐controlled Cycocel Reversal of Coumarin Inhibition of Lettuce Seed Germination and Root Growth

Lettuce seed germination or lettuce root elongation after germination in water was inhibited by coumarin and these inhibitions were reversed by Cycocel. 2.53 × 10 3 M Cycocel reversed the inhibition of seed germination by 6.8 × 10 4 M coumarin. and 6.32 × lO −4 M Cycocel reversed the inhibition of root elongation by 3.4 × 10 3 M coumarin. No other analogs of Cycocel reversed these coumarin induced inhibitions of growth. Cycocel reversal of coumarin inhibition of lettuce seed germination occurred in red light but not in far‐red light or darkness. The red‐far‐red system was photoreversible. Cycocel and kinetin appear to act similarly in reversing coumarin inhibition of germination. Gibberellin A 3 and IAA were unable to reverse these coumarin induced inhibitions. A common mechanism is suggested for Cycocel reversal of coumarin and lAA inhibition of growth.