Possible Involvement of the Alternative Respiration System in the Ethylene-stimulated Germination of Cocklebur Seeds

Respiration of nondormant upper cocklebur (Xanthium pensylvanicum Wallr.) seeds was enhanced by exogenous C₂H₄, proportionally to the concentration of C₂H₄ and the duration of presoaking of the seeds. Benzohydroxamic acid (BHM) and salicylhydroxamic acid (SHM), inhibitors of alternative respiration, inhibited both the germination of nondormant lower cocklebur seeds and the respiration of the upper seeds presoaked for periods of 12 to 30 hours. Both the growth and respiration of axial and cotyledonary tissues were also inhibited by BHM. Moreover, BHM inhibited both the C₂H₄-induced germination of the upper seeds and their C₂H₄-stimulated respiration; the inhibition occurred only with concomitant addition of C₂H₄ and BHM. The respiration of seeds with a secondary dormancy induced by presoaking for prolonged periods was markedly stimulated by C₂H₄ but not suppressed by BHM. It was suggested that the alternative respiration system may be involved in the normal germination process of cocklebur seeds, secondary dormancy may result from its inactivation, and C₂H₄ may exert its germination-promoting action by stimulating the alternative respiration. The effects of BHM and SHM can suggest but not prove the involvement of the alternative respiration in seed germination.     

Light Actions in the Germination of Cocklebur Seeds: I. DIFFERENCES IN THE LIGHT RESPONSES OF THE UPPER AND LOWER SEEDS

Germination responses to light were studied in the upper andlower seeds of cocklebur (Xanthium pennsylvanicum Wallr.). Thelower seed was dark-germinating and negatively photoblastic;the upper one had a red-light (R) requirement and was positivelyphotoblastic. Germination of the lower seeds was inhibited bya prolonged single irradiation with R, blue (B) or far-red (FR)light applied during imbibition. The maximal inhibitory effectof a single irradiation occurred 9 h and 13 h after the startof soaking at 33 °C and 23 °C, respectively. However,the inhibitory effect of R differed from that of B and FR, byonly delaying germination. A single exposure to B or FR lightcould be replaced by intermittent B or FR irradiation, and theireffects were repeatedly reversible by the following R irradiation.If the upper seeds were not exposed to R during imbibition,they failed to germinate even at 33 °C which was optimalfor germination, and the promotive effect of R increased withdelay of its application time. The photoperceptive locus incocklebur seeds was the axial tissue for all B, R and FR. Lightreceived by the cotyledonary tissue had little effect. Germinationdimorphism in response to light is discussed with respect tothe phytochrome content and the ageing of axial tissues. Key words: Blue light, Dimorphism, Far red light, Germination, Red light, Xanthium seed     

Rhythmic Behavior in Germination of Cocklebur Seeds

Non-dormant, lower seeds of cocklebur (Xanthium pensylvanicum Wallr.) germinated with unimodal flush after 20 and 36 h from the start of water imbibition at 33 and 23°C, respectively. At 28°C, however, germination occurred bimodally, the time of each peak coinciding with that at 23 and 33°C. This type of germination behavior was induced even at 33°C, when the seeds were contacted with some osmotica. Further, the application of different osmotica at 28°C caused a rhythmic multimodal germination with a period of about 16 h. It was suggested that an endogenous rhythmicity may be involved in the control of cocklebur seed germination.     

Thermoperiodism Mechanism in the Germination of Cocklebur Seeds

In thermoperiodic germination of secondarily dormant cocklebur(Xanthium pennsylvanicum Wallr.) seeds, the extent of electronflow through the CN-sensitive, cytochrome path and the CN-resistant,alternative path differred in the cool and warm phases. Thecool phase triggered active engagement of the alternative pathduring the subsequent warm phase, and this led to an increasein the ratio of the alternative path flux to the cytochromepath flux. The cool and warm phases had different functionsin adenylate metabolism. The former acted mainly in the productionand accumulation of ATP, whereas the latter supplied ADP and,especially, AMP. Thus an increasing number of sequential thermoperiodiccycles augmented the size of the adenylate pool and the energycharge, both of which may be necessary for germination to takeplace. (Received September 16, 1981; Accepted November 5, 1982)     

Light Actions in the Germination of Cocklebur Seeds: V. EFFECTS OF ETHYLENE, CARBON DIOXIDE AND OXYGEN ON GERMINATION IN RELATION TO LIGHT

Esashi, Y., Hase, S. and Kojima, K. 1987. Light actions in thegermination of cocklebur seeds. V. Effects of ethylene, carbondioxide and oxygen on germination in relation to light.–J.exp. Bot. 38: 702–710. Effects of ethylene, CO² and O² on the germination of after-ripenedupper cocklebur (Xanthium pennsylvanicum Wallr.) seeds wereexamined in relation to pre-irradiation by red (R) or far-red(FR) light In order to remove the pre-existing Pfr, seeds weresoaked in the dark for various periods prior to light irradiationand gas treatments. Regardless of light, 0.3 Pa C₂H₄ promotedgermination at 23 ?C, but it strongly inhibited germinationwhen applied at 33 ?C, the optimal temperature for the germinationof this seed. However, delayed application of C₂H₄ during 33?C incubation stimulated germination independently of lightin a similar manner to that seen at 23 ?C. It is, therefore,suggested that the germination-regulating action of C2H4 iscompletely independent of phytochrome. In contrast, the germination-promoting effect of 3–0 kPaCO₂ was pronounced only when the seeds were previously irradiatedby R, regardless of temperature, suggesting that CO₂ actionto promote germination depends upon Pfr. A synergism betweenCO₂ and C₂H₄ at 23 ?C was observed only in the germination ofseeds pre-irradiated by R, while at 33 ?C an antagonism occurredindependently of light. The stimulation of C₂H₄ production byCO₂ was most striking in the cotyledonary tissue pre-irradiatedby R. However, the R-dependent enhancement of CO₂-stimulatedC₂H₄ production was negated by the subsequent FR and it wasnot found in the presence of 1-aminocyclopropane-1-carboxylicacid (ACC). Moreover, the R dependency of the germination-promotingCO₂ effect disappeared in the presence of C₂H₄. The R-dependentC₂H₄ production enhanced by CO₂ may thus be involved, at leastpartially, in some step of conversion from methionine to ACC. The germination-promoting effect of C₂H₄, but not CO₂, was enhancedby O₂ enrichment regardless of light. However, the germination-promotingeffect of pure O₂ itself appeared to depend upon pre-irradiationwith R Key words: Carbon dioxide, cocklebur seed, ethylene, far-red light, germination, oxygen, red light, Xanthium pennsyloanicum     

Cyanide-sensitive and Cyanide-resistant Respiration in the Germination of Cocklebur Seeds

Interrelation between the CN-sensitive cytochrome path and the CN-resistant, benzohydroxamic acid (BHM)-sensitive, or n-propylgallate (nPG)-sensitive alternative path in seed respiration during germination was examined using the nondormant upper and lower seeds of Xanthium pensylvanicum Wallr. The operation of both paths was required not only for normal germination of the lower seed but also for KCN- or NaN₃-induced germination of both. From the sensitivity to BHM of the germination response, it became obvious that the alternative path exerts its physiological activity as soon as it develops during the early period of water imbibition. Pretreatments with KCN and NaN₃ for promoting germination, strikingly decreased only the engagement of the cytochrome path in the subsequent respiration without affecting that of the alternative path. Nevertheless, no germination occurred without the operation of the cytochrome path. This suggested that excess operation of the cytochrome path is detrimental to germination, being maximal following the BHM-sensitive phase.     

Light Actions in the Germination of Cocklebur Seeds: IV. DISAPPEARANCE OF RED LIGHT-REQUIREMENT FOR THE GERMINATION OF UPPER SEEDS SUBJECT TO ANOXIA, CHILLING, CYANIDE OR AZIDEPRETREATMENT

Esashi, Y., Fuwa, Nn Kojima, K. and Hase, S. 1986. Light actionsin the germination of cocklebur seeds. IV. Disappearance ofred light-requirement for the germination of upper seeds subjectto anoxia, chilling, cyanide or azide pretreatmenL—J.exp. Bot. 37: 1652–1662. The effects on the germination of positively photoblastic uppercocklebur (X anthium pennsylvanicum Wallr.) seeds by pretreatingwith anoxia, chilling, cyanide or azide, which stimulates theirdark germination, were examined in relation to light actions.Prior to experiments, seeds were pre-soaked at 23 °C inthe dark for 1 or 2 weeks to remove the pre-existing Pfr. Whenthe prctreatment conditions were suboptimal for germinationinduction, the stimulating effects of the pretreatments on germinationduring a subsequent dark period at 23 °C were manifest onlywhen seeds were irradiated with red light before or after thepretreatment Red light promotion was reversed by blue or far-redlight treatment. However, both prc-chilling for 6 d at 8 °Cand prctreatment with 1· 5 mol m ^{– 3} NaN³ for 2d could induce full germination without red light exposure.On the other hand, both pre-exposure to anoxia for 8 d and pretreatmentwith 30 mol m^–3 KCN could induce the dark germinationonly when germination occurred at 33 °C which is known toaugment the ratio of an alternative respiration flux to a cytochromeone. Moreover, the dark germination in response to these inductionswere strongly inhibited by the inhibitors of alternative respiration,propyl gallate and benzohydroxamic acid, applied during a subsequentdark period. It was thus suggested that Pfr has some relationto the operation of two respiration systems of cocklebur seeds,but it is not indispensable to germination of this positivelyphotoblastic seed. Key words: Anoxia, azide, blue light, chilling cyanide, dark germination, far-red light, red light, seed germination, X anthium pennsylvanicum     

Opposing Actions of Light in Seed Germination of Poa pratensis and Amaranthus arenicola

Action spectra were measured for suppression of germination of Poa pratensis L. and Amaranthus arenicola I. M. Johnston seed under prolonged or continuous irradiation. The action maxima for both types of seeds are near 720 nm. The maxima are unchanged in position or magnitude in the presence of radiation in the region of 600 to 670 nm adequate to maintain phytochrome predominantly in the far-red-absorbing form. A reversible potentiation of germination to change in form of phytochrome was observed for both seeds. The bearing of these findings on a high-energy regulatory light response is discussed.     

Light Actions in the Germination of Cocklebur Seeds: III. EFFECTS OF PRE-TREATMENT TEMPERATURE ON GERMINATION RESPONSES TO FAR-RED LIGHT AND ON DARK GERMINATION IN THE RED LIGHT-REQUIRING UPPER SEEDS

Esashi, Y., Oota, H., Saitoh, H. and Kodama, H. 1985. Lightactions in the germination of cocklebur seeds. III. Effectsof pre-treatment temperature on germination responses to far-redlight and on dark germination in the red light-requiring upperseeds.—J. exp. Bot. 36: 1465-1477. Red light (R) responsiveness in R-requiring upper cocklebur(Xanthium pennsylvanicum Wallr.) seeds changed in differentpatterns during a soaking period at different temperatures.At temperatures above 23°C, the responsiveness increasedand then decreased. At lower temperatures (3–18°C),however, it continued to increase throughout an experimentalperiod. The lower temperatures caused germination in the subsequentdark at 33°C, regained the R responsiveness and acquiredthe dark germinability when subsequently exposed to 8°C,to an extent proportional to the duration of the chilling. Far-red (FR) was inhibitory to germination in an earlier soakingperiod at lower temperatures, but its effect gradually decresed,and finally turned promotive. The negative FR response was repeatedlycontrolled by the following R irradiation. However, the positiveFR response was enhanced by an immediate R irradiation, andFR/R reversibility occurred after the second FR. In contrastto the R responsiveness and dark germinability, the positivegermination response to FR was not induced by soaking at 3°C,in which the growth of the axial tissue as a photoreceptivesite did not occur at all. Similarly, it was not manifestedwhen the seeds soaked at 33°C were subsequently subjectedto 8°C. Key words: Cocklebur seeds, dark germination, far-red light, low temperature, red light, seed germination, Xanthium pennsylvanicum     

Further Study on the Involvement of Cyanide-Resistant Respiration in the Germination of Cocklebur Seeds

The effect of propyl-gallate (PG) and benzohydroxamic acid (BHAM),inhibitors of cyanide-resistant, alternative respiration path(AP), on germination were examined using after-ripened upperand lower cocklebur (Xanthium pennsylvanicum Wallr.) seeds pre-soakedat 23?C for various periods. Germination was strongly suppressedby PG or BHAM at concentration above 2 mM. However, germinationwas enhanced by low concentrations of PG or BHAM (0.25 or 0.5mM) which reduced some portions of AP operation. Similarly,the high temperature-induced germination of pre-soaked upperseeds was promoted by the same low concentration range of PGor BHAM, in which PG and BHAM were effective only when appliedat the start of high temperature incubation. The inhibitionof germination by C₂H₄ at high temperature occurred only whenseeds were exposed to C₂H₄ during the earlier period of hightemperature incubation, and delayed application tended to promotetheir germination, although most of germinated seeds did notexhibit the normal germination behaviour of predominant radicleprotrusion. If the upper seeds had been subjected to a short-timepre-soaking, the inhibition of high temperature-induced germinationby C₂H₄ was prevented by the low concentrations of PG or BHAM,although the germination restored was mostly an abnormal, predominantlycotyldonary growth, suggesting that the germination inhibitionby C₂H₄ may be involved in some step of axial growth or in thegrowth of some specific axial zone. The lower concentrationsof PG or BHAM were promotive to the axial growth even at 33?C.Based on these results, the involvement of AP in cocklebur seedgerminaton is discussed in relation to the differential growthof axial and cotyledonary tissues. (Received May 2, 1986; Accepted October 27, 1986)     

Inhibitory Effects of Methyl Jasmonate on the Germination and Ethylene Production in Cocklebur Seeds

Methyl jasmonate (JA-Me) inhibited the germination of cocklebur (Xanthium pennsylvanicum Wallr.) seeds. The inhibition of the germination of cocklebur seeds treated with JA-Me at concentrations less than 300 μm was nullified by ethylene applied exogenously, although the inhibitory effect of 1,000 μm JA-Me was not recovered completely even by high concentrations of ethylene (10,000 μL/liter). JA-Me inhibited ethylene production before seed germination. The level of 1-aminocyclopropane-1-carboxylic acid (ACC) in the cotyledonary tissues treated with JA-Me decreased but not the level of 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC). JA-Me inhibited the conversion of ACC to ethylene in the tissues. These results suggested that JA-Me inhibits ethylene production by prevention of ACC oxidation in addition to ACC synthesis. We believe that the inhibition of ethylene production by JA-Me results in the retardation of the germination of cocklebur seeds. Received June 4, 1997; accepted October 23, 1997     

Phytochrome and Seed Germination. IV. Action of Light Sources With Different Spectral Energy Distribution on the Germination of Tomato Seeds

Germination of tomato seeds exposed to a single, saturating irradiation from light sources of different spectral energy distribution seems to be dependent upon the photostationary P_FR/P_R ratio established by the irradiation. Germination of tomato seeds exposed to prolonged irradiations from the same light sources does not seem to be controlled solely by the P_FR/P_R ratio induced and maintained by the irradiation.     

Germination Responses of Pinus densiflora Seeds to Temperature, Light and Interrupted Imbibition

Germination responses of Pinus densiflora Sieb. et Zucc. seedsto temperature and light were examined with a special interestin the gap-detecting mechanisms in germination, i.e., responsesto fluctuating temperature and sensitivity to leaf-canopy transmittedlight. Simple linear relationships were observed between thetemperature in the suboptimal range and the germination rates,i.e., the reciprocals of the time taken to germinate by theseed subpopulations with 10–90% germination. The ‘thermaltime’ concept could thus be used effectively to analysethe responses to varying temperatures and light. Neither shiftsnor alternations of ambient temperature affected the thermaltime required for germination; the profile of the change inpercentage germination plotted against thermal time for theseed population was almost identical among various constantand varying temperature regimes. Seed germination was completelyinhibited by simulated leaf-canopy light, thus indicating thatP. densiflora seeds have a gap-detecting mechanism in the formof canopy-light sensitivity. Moreover, 1–7 d interruptionof imbibition with dehydration had little effect on the finalpercentage and thermal time required for germination, suggestingthat the germinating seeds of this species have a great capacityto withstand the fluctuating moisture conditions of the exposedsurface of soil. Key words: Germination rate, temperature, light, moisture, gap-detecting mechanism, Pinus densiflora     

Phytochrome-mediated Germination Responses in gamma-Irradiated Lettuce Seeds

Sublethal doses of γ-radiation and far red light have some-what analogous, red light reversible, effects on the germination of lettuce seeds (Lactuca sativa L. var. Grand Rapids). However, the mechanism by which γ-radiation retards germination appears to differ from that of far red light. Compared to controls, γ-radiation retarded germination for the first 24 hours; but after 36 or 48 hours of imbibition gemination of treated seeds was higher than that of the controls, whether or not the γ-irradiated seeds received red or far red light. The effects of γ-radiation are more pronounced in seeds containing 15% water at the time of treatment than in those containing only 7% water. The promotive action of red light is operative in the presumed absence of cell division in γ-treated seeds.     

Interrelations between Carbon Dioxide and Ethylene on the Stimulation of Cocklebur Seed Germination

Interrelations between CO₂ and C₂H₄ on promotion of seed germination were examined in more detail at 23°C with presoaked upper seeds of Xanthium pennsylvanicum Wallr. The germination-promoting effect of C₂H₄ decreased gradually as its application time was delayed during a soaking period, whereas CO₂ was most promotive in application at 5 days of soaking, then its effect declined. CO₂ and C₂H₄ were additive in earlier soaking periods and synergistic in later periods. Such changes in germination behavior in response to CO₂ and/or C₂H₄ during a soaking period were closely associated with growth responsiveness of the axial tissues, but not of the cotyledonary ones. Growth responsiveness of axial tissues to CO₂ or C₂H₄ disappeared finally during a soaking period, but their extinct responsiveness to any one of these gases was almost fully restored in the simultaneous presence of the other. The extinct responsiveness to CO₂ was partially recovered by a preexposure to C₂H₄. This suggests that in the later period of soaking, unlike the case in a very early period of soaking, the C₂H₄-sensitive phase for seed germination precedes the CO₂-sensitive phase in which CO₂ potentiated axial growth. The restoration of CO₂ responsiveness in axial growth occurred not only after C₂H₄ treatment but also after exposure to 8 or 33°C or after KCN treatment. Thus, secondarily dormant Xanthium seeds could germinate in response to CO₂ alone, when they were previously exposed for shortterms not only to C₂H₄ but also 8°C, 33°C, or KCN.     

Promotion of Cocklebur Seed Germination by Allyl, Sulfur and Cyanogenic Compounds

The effects of allyl, sulfur and cyanogenic compounds on thegermination of upper cocklebur (Xanthium pennsylvanicum Wallr.)seeds were examined. Mercaptoethanol and methylmercaptan aswell as KCN, substrates for rßcyanoalanine synthase(CAS), and H₂S and thiocyanate, the products of the CAS catalyzingreaction, were effective in promoting germination, suggestingthe involvement of CAS in germination. Most of allyl compounds, especially allylthiourea, as well asethylene which activated CAS [Hasegawa et al. (1994) Physiol.Plant. 91: 141], promoted the germination in an abnormal typewhich occurred by the predominant growth of cotyledons as didC₂H₄ [Katoh and Esashi (1975) Plant Cell Physiol. 16: 687].However, they failed to activate CAS unlike ethylene, and toliberate free ethylene during an incubation period. It was thuspossible that an C₂H₄-like double bond within allyl compoundscan act to promote seed germination. (Received June 10, 1996; Accepted August 21, 1996)     

Necessity of a Balance between CN-Sensitive and CN-Resistant Respirations for Germination of Cocklebur Seeds

When applied singly, KCN or NaN3, as inhibitors of the cytochromerespiration path, and benzohydroxamic acid or n-propyl gallate,as inhibitors of the alternative respiration path, were lesseffective and ineffective, respectively, in inducing germinationof secondarily dormant, upper seeds of Xanthium pennsylvanicumWallr. When applied in combination, however, these chemicalswere very effective, producing much higher gemination. Thus,we concluded that an appropriate balance between the cytochromeand alternative path fluxes is required to induce the germinationof secondarily dormant cocklebur seeds. (Received August 30, 1980; Accepted December 2, 1980)     

西南獐芽菜种子萌发对温度、光照和外源生长调节物质的响应

研究不同温度、光照和外源生长调节物质处理种子对西南獐芽菜种子萌发特性的结果表明,西南獐芽菜种子为休眠型种子,其最适合萌发温度为20℃。光照促进种子的萌发,但影响并不显著。低浓度（10mg·L-1）6-BA促进西南獐芽菜种子萌发,而高浓度（50mg·L-1）的则抑制其萌发,不同浓度和浸种时间的赤霉素（GA）和IAA均促进种子萌发,GA的效果更好。     

经夏越冬播种水曲柳种子的萌发效应

贮藏的成熟水曲柳种子经夏越冬播种的结果表明,贮藏的成熟种子经夏越冬播种可以萌发,东北地区的播种时间宜在9月之前。用适宜的植物生长调节物质处理可以获得较好的发芽效果,其中以100mg·L^-1激动素浸种1d的效果较好。