Comparative Studies of Seed Germination of two Newly Isolated Lines of Grand Rapids Lettuce

Two lines of Grand Rapids lettuce were isolated by self-pollinationof single plants. Seeds of one line, designated ‘A’,germinate in the dark at 25 °C. Seeds of the second line,designated ‘B’ germinate in a manner typical oftheir variety. The lines differ in sensitivity to red (R) andfar-red (FR) light, in the ability of their seeds to overcomeresistance of an external osmotically active medium, in theresponse of mature seeds to abscisic acid, and in the responseof young seeds to gibberellin and benzyl adenine. ‘A’seeds germinate faster than ‘B’ seeds in the darkor after R or FR irradiation.     

Low Pressure and Ethylene in Lettuce Seed Germination

The extent and manner of ethylene involvement in germination of lettuce (Lactuca Sativa L. cv. Mesa 659) seed at a moderate temperature (20°C) were investigated. Inhibition of germination at low pressure of 150 mmHg in an oxygen flow-through system was alleviated to a marked extent by ethylene. Carbon dioxide was ineffective by itself but caused further alleviation of inhibition in presence of ethylene and oxygen. Other seed treatments which partially alleviated the inhibition caused by low pressure included soaking in 10μM of fusicoccin and a prior treatment with acetone. Of the two ethylene adsorbents used, Purafil was more effective in inhibiting germination in a closed container. Although the ethylene biosynthesis inhibitor, 8-hydroxyquinoline (1.0 mM). showed no effect on ethylene production, it markedly inhibited germination and the effect was partially reversed by ethylene and GA₃. An ethoxy analog of rhizobitoxine, on the other hand, had little or no effect on germination but strongly inhibited the ethylene production. Although no causal relation of ethylene to germination was established, the evidence presented here implicates ethylene, together with other gases, in the regulation of germination.     

Growth Retardants and the Germination of Light Sensitive Lettuce Seed

The effect of the dwarfing compounds chlormequat, B995, and Phosphon D on the germination of lettuce seed in darkness was found to be a depression which could be overcome in part by red light, GA, and kinetin. There was a marked statistical interaction between the growth retardants and all the mitigating treatments except B995 and GA, and light, at 30°C and GA and Phosphon D at 20°C and this implies a biological interaction at the site of action of the growth retardant. It is suggested that the action of the compounds considered is in the establishment of an ordered system since it is unlikely that there would be a common binding site for kinetin and GA.     

Salicylhydroxamic Acid Potentiates Germination of `Waldmann''s Green'' Lettuce Seed

A combination of salicylhydroxamic acid (SHAM) + cyanide (CN) is known to stimulate dark germination of Lactuca sativa L. seeds. Further studies were done to characterize SHAM and CN action in stimulating dark germination of lettuce seed. Germination was stimulated slightly by either SHAM or CN, whereas when SHAM and CN were combined germination was greatly enhanced. Treatment of seeds with SHAM + CN only during the first 8 hours of hydration stimulated germination as much as did treatment for 72 hours. During the first 8 hours of incubation in SHAM + CN, potentiation (i.e. dormancy-breaking) of germination occurs. SHAM alone stimulated potentiation nearly to the level of SHAM + CN but inhibited subsequent radicle elongation, thereby decreasing germination when present for 72 hours. Oxygen must be present for SHAM or SHAM + CN to potentiate dark germination. The ability of SHAM and SHAM + CN to potentiate germination is influenced by O₂ concentration and the timing of chemical treatment.     

Changes in Endogenous Cytokinins of Lettuce Seed during Germination

Using the soybean callus bioassay it has been shown that dormant lettuce seeds (Lactuca sativa L. cv. Grand Rapids) contain large amounts of water soluble cytokinins and small amounts of butanol soluble ones. When the seeds are irradiated with red light, or imbibed with 5 mg/1 gibberellic acid in the dark, the total cytokinin content of the seeds decreases, the level of water soluble cytokinins decreases, and the level of the butanol soluble cytokinins increases. Far-red light does not reverse this effect completely although cytokinin activity in the butanol extracts decreases following such irradiation. It is proposed that the interconversion of cytokinins initiated by red light, or gibberellic acid in the dark, is one of the primary events leading to radicle elongation in light-sensitive lettuce seed.     

Short-Term Metabolism of Radioactive Kinetin during Lettuce Seed Germination

Exogenously applied 8-¹⁴C-kinetin is rapidly taken up by seeds of lettuce (Lactuca sativa L. cv. Grand Rapids). Radioactive metabolites were extracted and purified by solvent fractionation, column and paper chromatography. The primary metabolite was identified as the 9-riboside-5′-monophosphate. As germination proceeds, some kinetin is released from this bound storage form, giving a maximum level of free kinetin at 12 hours after imbibition. After this time the concentration of ribotide increases while the concentration of free base decreases. Other metabolites are the 9-riboside, AMP and IMP. It is suggested that a required amount of free base cytokinin is necessary by 12 hours after imbibition. This concentration of free cytokinin may act as a physiological trigger for later events during germination.     

Investigations on the Control of Lettuce Seed Germination at High Temperatures

The activity of sodium hypochlorite solution in relieving thermo-inhibitionof germination of lettuce seed is shown to be due to its chlorinecontent. Results of experiments in which the pericarp, and pericarpand endosperm were removed, together with direct measurementsof penetration forces, suggest that the relief of thermo-inhibitionresults from weakening of the pericarp by the hypochlorite.Differences between the cultivars ‘Cobham Green’and ‘Grand Rapids’ in the contributions made bypericarp and endosperm to germination control at 35 °C aredemonstrated. Key words: Lactuca sativa L, Chlorine, Thermo-inhibition     

Dependence of Lettuce Seed Germination on Actinomycin D-resistant RNA Synthesis

The response of Grand Rapids lettuce half seed and intact seed to different nucleic acid and protein synthesis inhibitors was studied. 6-azauracil, 2-thiouracil and cycloheximide were strong inhibitors of germination of intact seed as well as of radicle elongation of half seed. Inhibition by 6-azauracil and 2-thiouracil was reversed by uracil but not by orotic acid, thymine or deoxycytidine. Actinomycin D and puromycin were ineffective suggesting that actinomycin D-resistant RNA synthesis possibly controls both germination of intact seed and radicle elongation of half seed. The requirements of RNA synthesis for the elongation of radicle in half seed in light and in the presence of gibberellic acid was the same. Such was not the case in the germination of intact seed which had different requirements of RNA synthesis in light and in presence of gibberellic acid. It is concluded that the mechanism of gibberellic acid and light in the intact seed germination, in so far as it involves the regulation of RNA synthesis, depends on the integrity of the seed coats.     

The Interaction of Coumarin and Temperature in the Germination of Lettuce Seed

Dormancy was induced in lettuce seed by exposing to coumarin during imbibition. The level of dormancy which is imposed is dependent on the temperature during germination, coumarin being ineffective below 20°C. At 25°C there is marked interaction between coumarin and this temperature, and the response of the seed. It was shown by exposing treated seeds to temperature regimes involving periods at 25°C and 10°C. that the action of coumarin can be explained more readily by concluding that the events which are affected are cell elongation and division. There is also evidence that the coumarin is metabolised more rapidly at 25°C, and that the effectiveness of the coumarin in the experiments cited depends on its presence at the time when embryo growth is initiated. The mode of action of coumarin is unknown.     

Interaction of Moisture Stress and Three Phenolic Compounds on Lettuce Seed Germination

No interactions between water stress and three phenolic acids(p-coumaric, caffeic and ferulic acids) on lettuce (Lactucasativa L. var. Grand Rapids) seed germination were found. Probitanalysis indicated that mechanisms of action of water stressand the phenolic inhibitors were similar. The relative effectivenessof the compounds was p-coumaric > ferulic > caffeic. Nointeraction was found between p-coumaric and ferulic acid, whereasantagonism was found between caffeic acid and each of the othertwo phenolic acids. Lactuca sativa L., lettuce, germination, phenolic compounds, moisture stress, allelopathy, seed     

Phytochrome Action during Prechilling Induced Germination of Betula papyrifera Marsh

Seeds of paper birch (Betula papyrifera Marsh.) were induced to germinate by prechilling at 3 C or by red light. The light requirement was mediated by phytochrome and the action of phytochrome during prechilling was investigated. Red irradiation (R) prior to prechilling markedly enhanced the effectiveness of the prechilling treatment in inducing subsequent germination at 18 C. Reversal of this enhancement by far-red irradiation (FR) was more effective when FR was supplied after a 1-week prechill treatment than after a 2-week treatment. The R enhancement effect exhibited a sharp drop as prechilling temperature was increased from 5 to 7 C. This decline is consistent with a membrane phase transition at about 7 C where Pfr action is diminished by a loss in sensitivity of its receptor sites. Although phytochrome action was observed during prechilling treatments, the seeds failed to germinate at prechilling temperatures. Therefore, it was concluded that while potentiation of germination by Pfr occurred during prechilling, some other reaction(s) leading to radicle protrusion requires higher temperatures. In one seed source loss of germination potential was observed with protracted storage at 3 C. This was prevented by R supplied during the prechilling treatment. Taken collectively the data suggest that action of phytochrome during prechilling is accentuated in these seeds by two factors: (a) an increase in the sensitivity (or number) of Pfr receptor sites; and (b) preservation of Pfr by deferment of thermal reversion.     

Effect of Temperature on the Short Chain Fatty Acid-induced Inhibition of Lettuce Seed Germination

In lettuce, Lactuca sativa short chain fatty acids (C₆ - C₉) vary in their effectiveness as inhibitors of germination according to temperature; the higher the temperature, the greater the inhibition. A linear relationship exists between temperature and the dose causing half-maximal germination. Nonanoic (C₉) acid is the most effective.     

外源脱落酸抑制花生种子发芽的生理机制

花生品种'汕油523'种子用10-3mol·L-1脱落酸(ABA)浸泡12 h后,种子发芽显著受抑制,胚α-淀粉酶活性降低,内源ABA水平提高.5 mmol.L-1ABA合成抑制剂钨酸钠处理的种子发芽率和活力指数提高,胚根增长,α-淀粉酶活性提高,内源ABA含量降低.据此认为ABA对种子萌发的抑制作用可能与α-淀粉酶活性和ABA含量有关.