The inhibition of germination of Grand Rapids lettuce (Lactuca sativa L.) seeds at 35 C was removed to a marked extent by kinetin and 2-chloroethylphosphonic acid (ethrel). When both compounds were used together, an additive effect was observed. A synergistic effect was, however, noted when ethrel promoted the kinetin reversal of abscisic acid inhibition of seed germination (light-as well as gibberellic acid-, induced Plant hormones appear to have designated functions in seed germination (9). For example, the GA3-induced dark germination of Grand Rapids lettuce seeds is inhibited by ABA and this inhibition is reversed by cytokinins (8). Cytokinins release the dormancy of seeds presumably by counteracting the effects of inhibitors by an as yet unknown mechanism (9). Another feature of cytokinin is its ability to overcome thermodormancy in lettuce (5,18,20). There is evidence that this effect of cytokinin may be related to a higher level of ABA in lettuce seeds imbibed at 35 C compared to those imbibed at 25 C (Braun and Khan, unpublished data).Ethylene and ethrel, an ethylene-releasing compound, also release dormancy in various seeds (3,6,7,21). It has been suggested that cytokinins act by stimulating ethylene production in seeds and other systems (7,11 Polyribosome Isolation. Following 24 hr incubation of seeds in various test solutions, 150 germinating seedlings were frozen in dry ice. The tissue was powdered along with a small piece of dry ice and homogenized in 8 ml of 0.4 M sucrose, 50 mm tris-HCl, pH 8.5, 50 mm KCI, 10 mM MgCl2, and 5 ms mercaptoethanol plus 0.5 ml of 10% Triton X-100. The homogenate was centrifuged at 20,000g for 15 min. The supernatant was layered over a 2.5-ml pad of 1.5 M sucrose solution in a buffer containing 50 mM tris-HCl, pH 7.8, 20 mm KCI, 10 mm magnesium acetate, and 5 mm mercaptoethanol and centrifuged at 139,000g (average) for 2 hr in a Spinco Model 65 fixed rotor. The ribosomal pellet was resuspended in a 1 -ml resuspension solution containing the above buffer. The ribosomal resuspension was layered over a 10 to 35% sucrose density gradient containing the buffer and centrifuged for 2 hr at 148,000g in a Spinco Model 41 Ti swinging bucket rotor. The distribution of polyribosomes was determined by recording the absorbance at 254 nm in an ISCO Model 640 density gradient fractionator. RESULTSAdditive Effect of Kinetin-Ethrel in Release of Thermodormancy.The effect of various temperatures on germination is shown in Table I. A 35 C temperature completely inhibits germination, and the optimum temperature for germination is 25 C. This thermodormancy in lettuce seeds is released to a marked extent in the presence of kinetin or ethrel (Table II). An additive effect in the release of thermodormancy was observed when the two compounds were used simultaneously. No such effect was noted when a combination of GA3 and kinetin or GA3 and ethrel was used, suggesting that kinetin-ethrel effect on germination is rather specific.

Alachlor [2-chloro-2′,6′-diethyl-N(methoxymethyl)-acetanilide], propachlor (2-chloro-N-isopropylacetanilide) and prynachlor [2-chloro-N-(1-methyl-2-propynyl)acetanilide], inhibited gibberellic acid (GA3),-induced production of protease and α-amylase in deembryonated barley (Hordeum vulgareL, ‘Schuyler’) seed. Production of protease was more sensitive to these herbicides than α-amylase. The degree of inhibition of protease and α-amylase production caused by alachlor was equivalent to that caused by cycloheximide, puromycin and actinomycin-D, known protein and nucleic acid synthesis inhibitors. Higher GA3concentrations reversed the inhibition of protease and α-amylase synthesis caused by alachlor but did not reduce the effect of alachlor on barley seed germination and growth. It is concluded that the inhibition of protease and α-amylase production by alachlor is perhaps only one of several effects on early seed germination and seedling development.

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...

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