Studies on the Chemical Induction of a Light Requirement for Germination in Seeds of Lettuce,Lactuca sativaL., cv. ‘Great Lakes’

Abstract

Detailed time courses of germination were recorded for three seed batches of lettuce, cv. 'Great Lakes The germination of this variety is usually considered to be insensitive to light, but considerable variability was noted between seed batches with respect to the effect of light. Previous reports on the chemical induction of a light requirement for germination in lettuce seeds were not substantiated for this variety. Naringenin was found to be relatively ineffective, and although coumarin, ABA, and IAA all delayed germination with increasing concentration, this delay was not diminished by continuous light. The inhibitions of germina tion by sucrose, mannitol, Carbowax, sodium chloride, potassium chloride, and potassium nitrate were also similar in light and darkness ; these inhibitions appeared to relate to the osmotic pressures of the solutions. It is postulated that previous reports of chemical induction of a light requirement may be the result of presenting germination figures at one point in time. Analysis of germination by detailed time courses showed that while prolonged light irradiation slightly accelerated germination, perhaps by raising seed temperature, it in no way overcame chemical inhibition.