Characterization of Osmotic Restraints on Lettuce Fruit Germination

Germination responses of fruits of lettuce (Lactuca sativa L.cv. Arctic King) to solutions of mannitol or potassium chlorideof different osmotic potentials were examined over a range oftemperatures in both light and dark. The upper temperature limit(‘cut-off’) for germination was progressively loweredby solutions of increasingly negative osmotic potential. Thisobservation explained inhibition of germination by solutionsof low osmotic potential at single experimental temperatures,found in previous investigations. Solutions of the two compoundshaving equal calculated osmotic potentials produced an equalinhibitory effect. No evidence for solute absorption was seen.Solutions of lower osmotic potential were needed to producethe same inhibition of germination in light against total darknessand also at lower temperatures.