Effects of red light and ethylene on growth of etiolated lettuce seedlings.

Low concentrations of ethylene inhibit hypocotyl elongation of etiolated lettuce seedlings (Lactuca sativa cv. Grand Rapids), whereas red light does not inhibit it. The plumular hook tightens in response to either ethylene or red light. A combination of these two factors gives an additive response. Red light has no effect on ethylene production and red light will cause hook closure even under hypobaric pressure which removes endogenous ethylene. This suggests that ethylene and red light act independently in causing hook closure.These findings differ from those about etiolated beans where red light causes a decrease in ethylene production and a straightening of the plumular hook.