Significant promotion in dark germination was observed when Grand Rapids lettuce (Lactuca sativa L.) seeds were soaked in acetone or dichloromethane, vacuum-dried, and imbibed at 25 C. Permeation of kinetin via these organic solvents further enhanced the dark germination. Those seeds that were affected by acetone and acetone-kinetin treatments and germinated in the dark escaped red-far red photocontrol of germination. Although abscisic acid was not detected in the organic solvent leachates, they did contain other inhibitory substances affecting lettuce seedling growth. In the light, acetone and acetone-kinetin treatments also enhanced the rate of germination and the increased germination by acetone-kinetin treatment was correlated with increased polynbosome formation. The possible mechanisms involved in promotion of lettuce seed germination by organic solvents and kinetin are discussed.A number of hormones and other chemicals have been used to promote dark germination of light-sensitive lettuce seeds. Whereas GA3 was shown to substitute for the light requirement in these seeds (12), kinetin was only partially effective in causing germination in the dark (20,26).Acetone and DCM4 have been successfully used as organic solvents to introduce hormones and other chemicals into dry seeds (16,18,29) in spite of claims to the contrary (1, 7). The kinetics of penetration of hormones dissolved in acetone into dry seeds show that the amount of chemical penetrating depends on the seed type, penetration time, and the concentration of solution (29). The amounts of chemicals reaching the embryo have been shown to be physiologically active (16,29).Treatment of seeds with organic solvent alone increases germination to some extent. Wheat, tomato, and sugar beet seeds germinated better after acetone washing (19). Treatment of Grand Rapids lettuce seeds with DCM resulted in 70% dark germination compared to 50% for untreated seeds after a 5-min exposure to red light following 1 min of imbibition (27). Preliminary studies from this laboratory showed that germination of acetone-treated Grand Rapids lettuce seeds was significantly increased in darkness, and further promotion was observed when kinetin was permeated via acetone (22). Acetone GA3 for dark germination 10-to 20-fold (17)! The studies reported here were undertaken to examine further the effects which organic solvents and kinetin, alone and in combination, would have on the dark germination and red-far red photomechanism of Grand Rapids lettuce seeds.
MATERIALS AND METHODSSeeds of lettuce (Lactuca sativa L., cvs. Grand Rapids and Parris Island) were stored in airtight containers at 4 C. Three hundred Grand Rapids lettuce seeds were soaked in the dark in 5 ml of redistilled organic solvent (acetone or DMC) or the solvent containing 500 uM kinetin for various periods. The solutions (leachates) were poured off, and the seeds were vacuum-dried for 90 min and used for germination tests. One hundred seeds in each of the three replications were placed on Whatman No. 1 filte...