Independent mode of action of cyanide and light on lettuce seed germination

Gaseous hydrogen cyanide stimulated subsequent lettuce seed ( Lactuca sativa L. cv. Grand Rapids) germination in darkness when applied for 1 or 22 h. Optimum concentrations were 5 × 10-5 M and 10-6 M, respectively. However, seeds did not germinate in the presence of HCN even at 10-8 M. The effects of unsaturating red light (R) and HCN (1 μM) showed a slight synergism. On the other hand, there was no difference between the effects of the sequences HCN – R and R – HCN. Stimulation of lettuce germination by an HCN pulse was practically not affected by far-red illumination, independently of the sequence of treatments. It was concluded that the primary stimulatory effect of HCN is of a regulatory character. Cyanide controls a regulatory point different from that affected by activated phytochrome.     

Dependence of gibberellic acid-induced dark germination of lettuce seed on RNA synthesis

Summary Gibberellicacid-induced dark germination of Grand Rapids lettude seed was completely inhibited by 6-azauracil and partly by 2-thiouracil. Other inhibitors of nucleic acid and protein synthesis used were without effect. Inhibition of gibberellic acid-induced dark germination was reversed by uracil but not by thymine, deoxycytidine and orotic acid. The results suggest that gibberellic acid-induced dark germination is dependent on RNA synthesis and not on DNA synthesis.Gibberellic acid-induced lettuce hypocotyl growth was inhibited by all the inhibiters of nucleic acid and protein synthesis used, including actinomycin D, puromycin, chloramphenicol and p-fluorophenylalanine.Approved by the Director of the New York State Agricultural Experiment Station for publication as Journal Paper No. 1507.     

Actions of gibberellic Acid and phytochrome on the germination of grand rapids lettuce seeds

Red light and gibberellic acid were about equally effective in promoting germination of Grand Rapids lettuce (Lactuca sativa L.) seeds. With initial far red light treatment more than 80% remained dormant in subsequent dark storage. After 2 days of dark storage, red light effectively promoted germination, while gibberellic acid action was weak. With between 2 and 10 days of dark storage, gibberellic acid had little effect, while promotion by red light decreased slowly and finally disappeared. After 10 days of dark storage, both gibberellic acid and red light were required for germination. The dark storage treatment interferes with phytochrome-independent germination processes and cannot be overcome by added gibberellic acid. However, storage may also decrease the effectiveness of endogenous gibberellins. Phytochrome-dependent germination seems to require only low levels of endogenous gibberellin activity or the addition of gibberellic acid. Gibberellins and red light appear to act on germination by regulation of sequential sites of a branched-looped pathway.     

An action spectrum in the blue for inhibition of germination of lettuce seed

Summary Using a 2-h irradiation period at constant quantum irradiance, a complete action spectrum for inhibition of germination of lettuce seed has been obtained. Action maxima were near 470 and 720 nm, the latter being the most active wavelength. It was also shown, under conditions where light inhibition cannot occur, that phytochrome potentiation of germination is maximal at all wavelengths below 700 nm, including the highly active blue region. Evidence was presented for promotion of germination by a 2-h irradiation in the red which cannot be explained on the basis of conversion of phytochrome to the active form.Abbreviations Bl blue - FR far-red, P_FR far-red-absorbing form of phytochrome - R red Supported in part by funds provided for biological and medical research by the State of Washington Initiative Measure No. 171 and the Graduate School Research Funds.     

Stimulation of lettuce seed germination by ethylene

Ethylene increased the germination of freshly imbibed lettuce (Lactuca sativa L. var. Grand Rapids) seeds. Seeds receiving either red or far-red light or darkness all showed a positive response to the gas. However, ethylene was apparently without effect on dormant seeds, those which failed to germinate after an initial red or far-red treatment. Carbon dioxide, which often acts as a competitive inhibitor of ethylene, failed to clearly reverse ethylene-enhanced seed germination. While light doubled ethylene production from the lettuce seeds, its effect was not mediated by the phytochrome system since both red and far-red light had a similar effect.     

Lettuce seed germination: modulation of pregermination protein synthesis by gibberellic Acid, abscisic Acid, and cytokinin

Protein synthesis in gibberellin-treated lettuce (Lactuca sativa) seeds has been studied during the lag phase between the beginning of imbibition and the first signs of radicle protrusion. When compared to the water-imbibed controls, both polyribosome populations and radioactive leucine incorporation into protein increase in the embryos of GA₃- induced seeds early in the imbibition period. Since these results are contradictory to previously published studies, the reasons for the differences are outlined and various alternative possibilities eliminated. The protocol for protein extraction, particularly the speed at which the supernatant from the seed homogenate is cleared, is important for demonstrating the GA₃-mediated changes. Embryos maintained in the dormant state by abscisic acid still conduct considerable amounts of protein synthesis, and this is enhanced by concentrations of 6-benzylaminopurine which also promote germination. Therefore, the actions of GA₃, abscisic acid, and cytokinin on lettuce seed germination are mediated, directly or indirectly, via protein synthesis.     

Morphactin-kinetin interaction in lettuce seed germination and seedling growth

Summary Butylester of morphactin (n-butyl-9-hydroxy-fluorence-(9)-carboxylate) greatly inhibited seed germination and seedling growth of two strains of lettuce, Attraktion and Hohlblättriger Butter. The inhibitory effect of morphactin on seed germination was completely overcome by kinetin but the latter chemical was ineffective in reversing the morphactin induced inhibition of seedling growth. Thus it appears probable that the two substances effect seedling growth independently.     

The effect of growth retardants on phytochrome-induced lettuce seed germination

Experiments were carried out to explore the involvement of the plant hormone gibberellin (GA) in the light-induced germination of lettuce seeds. Three growth retardants known to be inhibitors of GA biosynthesis were tested for their effect on red-light-induced germination. Chlormequat chloride (CCC) and AMO-1618 had no effect, but ancymidol was strongly inhibitory. Moreover, the inhibition caused by ancymidol was completely overcome by GA₃. CCC and AMO-1618 inhibit the formation ofent-kaurene, while ancymidol blocks the oxidation ofent-kaurene toent-kaurenoic acid. Ancymidol also was found to inhibit GA-induced dark germination of lettuce seeds, and this inhibition was partially reversed by higher levels of GA. Therefore, the results suggest two possibilities for the relationship between phytochrome and GA in this system: first, the rate-limiting step in the germination of light-sensitive lettuce seeds, that which is regulated by phytochrome, is the oxidation ofent-kaurene toent-kaurenoic acid. Alternatively, red-light treatment may result in the release of active GAlike substances which, in turn, induce germination. In either case the results presented here support the view that phytochrome exerts its effect on lettuce seed germination by means of GA rather than via an independent pathway.     

Morphactin-gibberellin interaction in lettuce seed germination and seedling growth

Morphactin-butylester (a flourene-9-carboxylic acid derivative) inhibited seed germination of two strains of lettuce. Morphactin induced inhibition of germination could be partially or wholly reversed by simultaneous addition of gibberellic acid. However, gibberellic acid played very little part in reversing the inhibitory effect of morphactin on seedling growth. It is concluded that gibberellin can not reverse all the growth effects induced by morphactin.     

Effect of light and temperature on the germination of lettuce seeds

A short period (15–30 min) at 30° C promotes germination of seeds of Lactuca sativa L. cv. Repolhuda in darkness. Far-red light reverses this stimulation, and the escape curves for phytochrome and high-temperature action are quite similar, indicating that the two factors act at a common point in the chain of events leading to germination. It is suggested that high temperature acts by decreasing the threshold of the active, far-red absorbing, form of phytochrome (Pfr) needed to promote germination.Abbreviations FR far-red light - Pfr far-red-absorbing form of phytochrome - R red light     

Inhibition of lettuce seed germination and seedling growth by antimetabolites of nucleic acids,and reversal by nucleic acid precursors and gibberellic acid

Summary Germination of White Paris lettuce seeds is inhibited by 2-thiouracil up to 24 hours. This inhibition is reversed by RNA precursors only. Seedling growth of lettuce is inhibited by 2-thiouracil and 5-fluorouracil; and white the effect of 2-thiouracil is counteracted by RNA precursors, inhibition due to 5-fluorouracil is not reversed significantly by any nucleic acid precursors. Possibly 2-thiouracil controls germination and seedling growth by interfering with RNA synthesis, while the effect of 5-fluorouracil is non-specific.In the presence of gibberellic acid, 5-fluorouracil and 2-thiouracil are relatively ineffective in causing inhibition of hypocotyl growth. Mechanism of gibberellic acid action remains obscure.     

Activity and metabolism of 9-substituted cytokinins during lettuce seed germination

The activities of N⁶-benzyladenine (BA) and its 9-substituted methyl, methoxymethyl, tetrahydropyranyl, cyclopentyl, and cyclohexyl analogs were determined for the promotion of lettuce seed (Lactuca sativa L. cv. Grand Rapids) germination. Cytokinin concentrations used were 10^?4, 10^?5, 10^?6 and 10^?7M. All seeds were incubated under total dark conditions at 28 ± 1°C. After 48 h the percentage of germination was recorded. A comparison of means based on Duncan's Multiple Range Test allowed for a ranking of cytokinin activities for the promotion of lettuce seed germination. The activities were: BA = 9-tetrahydropyranyl BA > 9-methyl BA > 9-methoxymethyl BA > 9-cyclopentyl BA > 9-cyclohexyl BA. The results were significant at the 95% confidence level as determined by analysis of variance. In order to study the metabolism of a cytokinin, lettuce seeds were incubated with 9-methyl-BA-methylene-¹⁴C. The labeled cytokinin was prepared by refluxing benzylamine hydrochloride (methylene-¹⁴C) with an equal molar ratio of 6-chloro-9-methylpurine. Final cytokinin concentration was 10^?5M. Incubation periods were 2, 4, 8, 12, 16 and 20 h at 28 ± 1°C under total dark conditions. At the end of the various time periods the seeds were extracted with 70 percent methanol. The resulting extracts were purified and radioactive metabolites identified by solvent fractionation, Sephadex LH-20 column chromatography, and paper chromatography. Co-chromatography with authentic standards in the appropriate solvent system revealed that the metabolites were 9-methyl BA, N⁶-benzyladenosine-5′-monophosphate, and N⁶-benzyladenosine. The results lend support to the theory that the cytokinin ribonucleotide serves as a storage form which is converted to the active ribonucleoside as needed during lettuce seed germination.     

Mediation of phytochrome in the inductive action of low temperature on dark germination of lettuce seed at supra-optimal temperature

The induction of dark germination in light-requiring lettuce (Lactuca sativa) seed at supraoptimal temperatures by cold treatment (in darkness) was partly reversed by a brief far-red irradiation made at time of transfer, and even more so when the irradiation was made at the beginning of the cold pretreatment. When the inhibitory far-red irradiation was followed by additional cold treatment, the promotion was greatly restored. The promotive effects of brief irradiations with red light were further enhanced by a following cold period, before transfer to the supraoptimal temperature. These results are interpreted as indicating that the active (far-red absorbing) form of phytochrome is pre-existing in the dry seed, and interacts with a co-factor which is built-up during imbibition. The rate of build-up of this co-factor, as well as of the dark inactivation of active phytochrome increase with temperature. The products of the interaction pass through a photo-labile thermo-stable phase, before becoming photo-stable as well.     

Effects of gibberellic Acid and gold light on germination, enzyme activities, and amino Acid pool size in a dwarf strain of watermelon

Gibberellic acid (GA₃) promotes and continuous gold light inhibits germination of seeds of a dwarf strain (WB-2) of watermelon [Citrullus lanatus (Thunb.) Matsu. and Nakai]. Osmotic inhibition of germination with mannitol in light-grown seeds of WB-2 was only slightly reversed by GA₃ at the concentrations used, whereas, GA₃ substantially relieved osmotic inhibition in dark-grown seeds.

The effects of GA₃ and gold light on development of catalase and invertase activities and on levels of free amino acids in germinating seeds of WB-2 were examined. Light depressed development of catalase and invertase activity. Levels of free amino acids increased more slowly in embryonic axes of light- than dark-incubated seeds, but in cotyledons higher levels of amino acids were maintained in light-grown seeds. GA₃ accelerated the development of catalase activity in whole embryos and invertase activity in embryonic axes, but did not significantly affect invertase activity in cotyledons during germination. GA₃ had little effect on amino acid pools in cotyledons and embryonic axes.

     

Regulation of phenylalanine ammonia-lyase activity and growth in lettuce by light and gibberellic acid

Abstract The effects of light and gibberellic acid (GA3) on growth and phenylalanine ammonia-lyase (PAL) activity were studied in seedlings of lettuce (Lactuca sativa L.). Using an in vivo assay for PAL it was shown that wounding caused by excising hypocotyls results in an increase in PAL activity with time that can mask the effect of light on the activity of this enzyme. When hypocotyl sections were excised from light-treated seedlings immediately prior to the in vivo assay of PAL, light was shown to cause a marked increase in PAL activity. Experiments with an inhibitor of PAL activity, α-aminooxy-β-phenylpropionic acid (AOPP), confirmed that the volatile radioactive products measured in the in vivo assay resulted from the activity of PAL. Gibberellic acid suppresses the light-induced increase in PAL activity and there is an inverse relationship between GA₃-induced growth and the activity of PAL. Over a wide range of GA₃ concentrations, the activity of PAL is also inversely correlated with growth rate along the length of the hypocotyl section; the upper halves of sections elongate more rapidly and have lower levels of PAL than the lower halves. Despite the strong correlation between growth and PAL activity, experiments with AOPP and t-cinnamic acid show that it is unlikely that elongation is regulated directly by products of PAL activity.     

Effects of after-ripening and gibberellic acid on the thermoinduction of seed germination in Solarium melongena

Daily alternating temperatures or a short exposure to low orhigh temperatures were necessary for the germination of eggplantseeds at the initial stage of after-ripening. But requirementsbecame less strict with the progress of after-ripening, andafter 4 to 8 months of afterripening, germination occurred easilyboth at constant (20 and 25) and daily alternating temperatures(30 for 16hrs and then 20 for 8hrs). With further progress in after-ripening, however, daily alternatingtemperatures or a short exposure to low or high temperaturesbecame again indispensable for attaining a high percentage ofgermination. The progress of after-ripening was greatly influencedby the degree of seed ripening, that is, by the period beforethe seeds were sampled from fruits after anthesis (ripening). The effect of GA on the germination of egg plant seeds varieddepending on the concentration of GA, temperature and the degreeof maturity (ripening and after-ripening) of the seeds. (Received March 8, 1968; )     

Mode of phytochrome B action in the photoregulation of seed germination in Arabidopsis thaliana

Arabidopsis thaliana seeds imbibed for a short duration show phytochrome B (PhyB)-specific photo-induction of germination. Using this system, the relationship was determined between the amount of PhyB in seeds and photon energy required for PhyB-specific germination in two transgenic Arabidopsis lines transformed with either the Arabidopsis PhyB cDNA (ABO) or the rice PhyB cDNA (RBO). Immunochemical detection of PhyB apoprotein (PHYB) showed that the expression level of PHYB in ABO seeds was at least two times higher than that in the wild-type seeds, but in RBO seeds the PHYB level was indistinguishable from that in wild-type seeds. The photon fluence required for induction and photoreversible inhibition of germination was examined using the Okazaki large spectrograph. At the wavelengths of 400–710 nm, the ABO seeds required significantly less photon fluence than wild-type seeds for induction of germination, whereas the RBO seeds required similar fluence to wild-type seeds. A critical threshold wavelength for either induction or inhibition of germination of ABO seeds shifted towards the longer wavelengths relative to wild-type seeds. By assuming that PhyA and PhyB are similar in their photochemical parameters, amounts of P_fr at each wavelength were calculated. The photon fluence required for 50% germination was equivalent to the fluence generating a P_fr/P_tot ratio of 0.21–0.43 in wild-type seeds, and of 0.035–0.056 in ABO seeds. These results indicate that PhyB-specific seed germination is not strictly a function of the P_fr/P_tot ratio, but is probably a function of the absolute P_fr concentration.