PHOTOCONTROL AND TEMPERATURE DEPENDENCE OF GERMINATION OF RUMEX SEEDS

1. Light is not obligatory for the germination of the seed ofRumex obtusifolius L. subsp.agrestis DANSER, which has beenregarded as being a typical light sensitive seed. Even in continuousdarkness, a short period of high (30°) or low temperature(5°) treatment evokes germination very readily. 2. Germination is markedly promoted by 1 min exposure to a redlight and this red light effect is completely removed by 1-hrexposure to a far-red light. Alternations of the red and far-redradiation bring about an alternate promotion and inhihibitionof germination. 3. When a dark interval is inserted between the red and thefar-red treatments, inhibition of germination becomes less distinctas the duration of darkness increases. When the seeds are irradiatedwith far-red prior to red, with an inserted darkness, germinationpromotion due to the red light also decreases with the durationof inserted darkness. 4. Complicated interdependence between the light and temperatureeffects are demonstrated. This suggests a participation of somereactants besides pigments in the photoreaction. 5. The observed interdependence between the light and temperatureeffects on the germination of Rumex seeds implies that, if,as BORTHWICK has assumed, two forms of pigment, viz., a far-red-absorbingform and a red-absorbing one, are participating in the photoreaction,they should be presumed to coexist from the start of imbibition. (Received September 27, 1960; )     

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     

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     

Rate of Change in Dormancy Level and Light Requirement in Weed Seeds During Stratification

The rate of change in dormancy level and light requirement,induced during stratification at 3.2 °C, was investigatedin seeds ofStellaria media, Cerastium fontanum, Veronica agrestisandTaraxacumofficinale.Two stratification environments, soil and wet filterpaper in petri-dishes, were used. On nine occasions during a6 week stratification period, germination was tested under threelight conditions at 3.5/18.5 °C: (1) darkness; (2) light;and (3) short-term light exposure followed by darkness. Priorto stratification, germination in all species was 89% in lightand 53% in darkness. Within 2 weeks of stratification, germinabilityinV. agrestisandS. mediaseeds decreased in all treatments. InC.fontanumandT. officinaleseeds, germinability also decreasedafter 2 weeks but only in the dark treatment, indicating inductionof a light requirement. After two more weeks of stratification,the induced dormancy inS. mediaseeds stratified in soil becameweaker and the light requirement inT. officinaleseeds was lost.Differences between the two stratification environments and/orinteractions between light conditions, stratification environmentsand time were found for all species. These results suggest that:(1) the dormancy level and the light requirement of seeds maychange dramatically over relatively short-time periods duringstratification; and (2) germinability depends on the stratificationenvironment experienced by the seeds. Predicting the dormancylevel or light requirement in a seed batch is difficult andrequires a thorough knowledge of the effect of the stratificationconditions used.Copyright 1997 Annals of Botany Company Burial; Cerastium fontanumBaumg.; chickweed; cold stratification; common mouse-ear; dandelion; dormancy; light requirement; seed; Stellaria media(L.) Vill.; speedwell; Taraxacum officinalegroup; Veronica agrestisL.; weed     

Effects of Photoperiod on Germination of Seeds of Talinum triangulare (Jacq.) Willd

Seed germination in Talinum triangulare as affected by photoperiod,with or without previous incubation in the dark in water at25 or 4 °C, was studied. The time course and quantity ofseed germination in photoperiods of 1 h and above were similarwith or without dark pretreatment, but the time to half maximumgermination was reduced from 12 days in non-dark pretreatedseeds to 4 days in seeds given 20 days in the dark at 25°C.A photoperiod of 0·25 h gave a lower rate and total germinationthan photoperiods of 1 h and above. Un-pretreated seeds required17 cycles of 24 h photoperiod for maximum germination as comparedwith 7 or less cycles if the seeds received more than 10 daysdark pretreatment at 25 °C. Both the rate and total germinationin light increased as the length of dark pretreatment at 25°C was increased from zero to 30 days. Incubation of theseeds in water in the dark at 4 °C for 5 to 30 days priorto illumination at 21 °C, reduced both the rate and quantityof seed germination in light as compared with those similarlyincubated in the dark at 25 °C. However, previous incubationin the dark for 30 days at 4 °C partially substituted forthe light requirement. The possible mechanism of breakage ofseed dormancy in Talinumis discussed in relation to these andother findings. Talinum triangulare (Jacq.), Willd, light, photoperiod, 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     

Seed Germination and Seedling Development in Cyclamen persicum

Cyclamen persicum Mill, seeds germinate in a narrow range oftemperature and germination is strongly inhibited by continuousirradiation with white light. The thermal optimum is approx.15 °C in both darkness and light. Seed germination is alsovery sensitive to oxygen deprivation and this sensitivity ismore pronounced at 20 °C than at the optimum 15 °C.Very immature seeds cannot germinate at any temperature, butgerminability increases during seed maturation Seedling development is unusual since seed reserves are usedimmediately for tuber formation. Tuberization is optimal at15–20 °C in light and in darkness. Supra-optimal temperatures(25–30 °C) or hypoxia inhibit tuber formation andlead to very elongated tubers These results allow the producers to improve the productionof homogeneous populations of cyclamen seedlings Wheat seeds, Triticum aestwum L., acetylcholinesterase, electrophoresis, germination, assay     

A Comparative Study of Germination Responses to High Irradiance Light

Seeds of 19 native British herbaceous species (14 grasses andfive forbs) were exposed to white light at three photon fluencerates: high (19–2 mol m^–2 d^–1), medium (9·6mol m^–1 d^–1) and low (2·3 mol m^–2 d^–2) These photon doses have been found by previous workers to inhibitgermination in several species. High and low photon doses wereapplied only as continuous light, but the medium dose was appliedas both continuous light and as a 12 h light/12 h dark photoperiod.All four treatments, plus a dark control, were carried out at15 °C; the high and low doses were also applied with a dailyalternation of 10/20 °C. The majority of species (15) fell into one of two groups. Inseven species germination was relatively high and consistentacross all treatments, including darkness; in the other eightspp germination was inhibited only in darkness. Mostly thesedata confirmed published results for the same species In contrast in Agrostis capillaris and A. stolonifera germinationwas high only at alternating temperatures, irrespective of photondose, but was also slightly promoted by a constant temperaturecombined with light/dark alternations. Only in Bromus sterilisand B. ereclus was germination inhibited by light, in B. erectusat all photon doses and in B. sterilis only at the highest photondose These results suggest that inhibition of germination by highirradiance light is not widespread among native British species Aira caryophyllea, Arrenatherum elatius, Festuca ovina, F. rubra, Hordeum murinum, Milhim effusum, Silene dioica, Achillea millefolium, Brachypodium syhaticum, Digitalis purpurea, Holcus lanatus, Leucanlhemum vulgare, Phleum pratense, Poa trivialis, Taraxacum officinale, Agrostis capillaris, A. stolonifera, Bromus erectus, B. sterilis, seed, dormancy, germination, light, High irradiance reaction, alternating temperatures, photoperiod     

Effects of long-term storage on phytochrome-mediated germination in lettuce seeds

The effects of long-term seed storage on the physiological properties of phytochrome-mediated germination including water uptake, the temperature and light flunnce dependencies of germination and dark germination were studied. The fluenceresponse relationships of the brief irradiation with monochromatic red (660 nm, 7.5 W m⁻²) and far-red (750 nm, 6.6 W m⁻²) light at various times after sowing were also studied. The samples used consisted of three lots of seeds ofLactuca sativa L. cv. MSU-16, which had been harvested in 1976, 1979 and 1985 and stored dry for 9, 6 and 0 years, respectively, in darkness at 23±2 C until the experiments were carried out in July–August, 1985. Seeds with the longer storage periods showed the higher ability to germinate in both continuous darkness and continuous white fluorescent light at 20–30 C. In the seeds stored for 6 or 9 years, red light irradiation for 20 sec given at 15 min or more after sowing at 25 C induced as high a percent germination (85–95%) as those under continuous white fluorescent light. In the freshly harvested seeds, however, germination under continuous white fluorescent light (46%) was considerably lower than the germination induced by the red pulse (97%). Germination of the seeds decreased when the intervals between sowing and a far-red irradiation for 20 sec increased up to 100 min (or 30 min in the freshly harvested seeds). The far-red pulse given later than 100 min (or 6 hr in the freshly harvested seeds) after sowing resulted in an increased germination up to the dark-germination levels with increasing intervals between sowing and the pulse irradiation. Before or at 3 min after sowing, the seeds stored for 6 or 9 years were responsive to the far-red pulse although they were not or hardly responsive to the red pulse, while the freshly harvested seeds were responsive to both the far-red and the red pulses. These data indicate that normal functions of phytochrome completely survived in the dry seeds during storage at 25 C for as long as 6 or 9 years and that these functions are restored into full operation by means of imbibition. The differences in the dependence of germination on the time and fluence of a single pulse of red or far-red light seems to be related to the smaller water content throughout the imbibition in the seeds with the longer storage periods. The greater ability to germinate in the dark indicates the greater amounts of P_FR or the greater responsivity to P_FR, in the seeds with the longer storage periods.     

Changes in Ultrastructure and Abscisic Acid Level, and Response to Applied Gibberellins inTaxus maireiSeeds Treated With Warm and Cold Stratification

Seeds ofTaxus maireiare known for their deep dormancy whichcan only be broken by a procedure involving warm stratificationfollowed by cold stratification. Treatments with alternatingtemperatures of 25/15 or 23/11 °C (12 h light) for 6 monthsfollowed by 5 °C for 3 months were successful in overcomingseed dormancy. After 6 months of warm stratification, cytologicalchanges observed included: enlargement of the embryo; a decreasein the number of lipid bodies; appearance of ER; and increasesin mitochondria, plastids, dictyosomes, vacuoles and microbodiesin the shoot apical meristem. Cold stratification followingthe warm treatment induced cell division, and one or two distinctnucleoli in the shoot apical meristem cells were observed. Bothwarm and cold stratification reduced endogenous ABA concentrationsfrom the original 8888 pg per freshly harvested seed to 392and 536 pg, respectively. Treatment with exogenous gibberellinsafter seeds had been warm-stratified showed that GA₄and GA₇wereeffective at promoting seed germination, but GA₃was not. Theseresults suggest that the strong seed dormancy ofT. maireicouldbe caused by a high ABA content and underdevelopment of theembryos in freshly shed seeds. We conclude that warm stratificationwith alternating temperatures increases the growth of embryosby cell expansion and enlargement and decreases ABA content,but seeds still remain ungerminated. Cold stratification mayinduce the response to GAs and initiate cell division resultingin release from physiological dormancy and subsequent germinationofT. maireiseeds.Copyright 1998 Annals of Botany Company Taxus mairei; ultrastructure; abscisic acid; gibberellin; seed dormancy; stratification; germination.     

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.     

Nitrate Reductase Independent Stimulation of Seed Germination in Sisymbrium officinale L. (Hedge Mustard) by Light and Nitrate

After a 72 h preincubation in darkness at 15 °C seed germinationof Sisymbrium officinale L. (hedge mustard) at 24 °C wasstimulated by a combination of red light and nitrate. In thepresence of nitrate the seeds escaped from the inhibiting effectof far-red irradiation with an escape time of approx. 8 h. Afterred light, the exposure of seeds to nitrate could be delayedfor 3 h without affecting maximal germination. Prolonged delayresulted in a decrease of the germination response. The possibilitythat nitrate reduction was involved in the stimulation of germinationwas studied by pre-incubating seeds for 72 h in nitrate andsubsequently transferring them to water and irradiating withred light. During the first 8 h period after the red irradiationin which induction of germination occurred, total nitrate levels(endogenous + leachate) remained constant, indicating an absenceof nitrate reductase activity. During the next 8 h visible germinationstarted and total nitrate levels declined, suggesting inductionof nitrate reduction. It is concluded that nitrate reductiondocs not play a role in the induction of germination. The conclusionwas supported by the lack of inhibition of seed germinationby sodium chlorate and sodium tungstate in spite of an inhibitionof nitrate reduction of 80 and 100%, respectively. The contrastsbetween our results and hypotheses concerning the mechanismof action of nitrate in seed germination are discussed Sisymbrium officinale L., hedge mustard, germination, light, nitrate, nitrate reductase     

PHOTOMORPHOGENESIS IN PTERIS VITTATA: I. PHYTOCHROME-MEDIATED SPORE GERMINATION AND BLUE LIGHT INTERACTION

1. Spores of the fern Pteris vittata did not germinate under totaldark conditions, while an exposure of the spores to continuouswhite light brought about germination. The germination was mosteffectively induced by red light and somewhat by green and far-red,but not at all by blue light. The sensitivity of spores to redlight increased and leveled off about 4 days after sowing at27–28. The promoting effect of red light could be broughtabout by a single exposure of low intensity. Far-red light givenimmediately after red light almost completely reversed the redlight effect, and the photoresponse to red and far-red lightwas repeatedly reversible. The photoreversibility was lost duringan intervening darkness between red and far-red irradiations,and 50% of the initial reversibility was lost after about 6hr of darkness at 27–28. These observations suggest thatthe phytochrome system controls the germination of the fernspore.
2. When the imbibed spores were briefly exposed to a low-energyblue light immediately before or after red irradiation, theirgermination was completely inhibited. The blue light-inducedinhibition was never reversed by brief red irradiation givenimmediately after the blue light. The escape reaction of redlight-induced germination as indicated by blue light given aftervarious periods of intervening darkness was also observed, andits rate was very similar to that determined by using far-redlight. Spores exposed to blue light required 3 days' incubationin darkness at 27–28 to recover their sensitivity tored light. The recovery in darkness of this red sensitivitywas temperature-dependent. It is thus suggested that an unknownbluelight absorbing pigment may be involved in the inhibitionof phytochrome-mediated spore germination.

(Received August 21, 1967; )     

Germination of seeds in Jussiaea suffruticosa

Seeds of Jussiaea suffruticosa reach high germination percentagesonly when exposed to long periods of continuous illumination.The light reaction may be repeatedly reversed by short exposuresto red and far red light, thus being mediated by the phytochromesystem. Seeds also germinate at high percentages if exposedto various cycles of 1 hr light and 24 hr of darkness at 20°C.If the temperature in the periods of darkness is raised up to30°C or lowered to 10°C the promotive effect of lightis inhibited. High temperatures (35°C) during imbibitionhave a promotive effect, whereas a pure O₂ atmosphere decreasesthe response to light. KNO₃ and kinetin enhance the responseto light but do not provoke germination in the dark. Only ifseed coats are punctured or removed does germination in thedark occur. (Received January 14, 1969; )     

Nitrate,abscisic acid and gibberellin interactions on the thermoinhibition of lettuce seed germination

Germination of lettuce seeds has obvious thermoinhibition, but the mechanism for thermoinhibition of seed germination is poorly understood. Here, we investigated the interactions of nitrate, abscisic acid (ABA) and gibberellin on seed germination at high temperatures to understand further the mechanism for thermoinhibition of seed germination. Our results showed that lettuce (Lactuca sativa L. ‘Jianye Xianfeng No. 1’) seeds exhibited notable thermoinhibiton of germination at ≥17°C in darkness, and at ≥23°C in light, but the thermoinhibited seeds did not exhibit secondary dormancy. Thermoinhibition of seed germination at 23 or 25°C in light was notably decreased by 5 and 10 mM nitrate, and the stimulatory effects were markedly prevented by nitric oxide (NO) scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. The sensitivity of seed germination to exogenous ABA increased with increasing temperature. Thermoinhibition of seed germination was markedly decreased by fluridone (an inhibitor of ABA biosynthesis) and GA₃, and was increased by diniconazole (an inhibitor of the ABA-catabolizing enzyme ABA 8′-hydroxylase) and paclobutrazol (an inhibitor of GA biosynthetic pathway). The effect of fluridone in decreasing thermoinhibition of seed germination was obviously antagonized by paclobutrazol, and that of GA₃ was notably added to by fluridone, and that of nitrate was antagonized by paclobutrazol, diniconazole and ABA and was added to by GA₃ and fluridone. Our data show that thermoinhibition of lettuce seed germination is decreased by nitrate in a NO-dependent manner, which is antagonized by ABA, diniconazole and paclobutrazol and added by fluridone.     

Germination and Dormancy in Immature and Fresh-mature Lettuce Seeds

The effects of red light, far-red light, Gibberellin A₃, andethephon were studied on the germination of lettuce seeds cv.Grand Rapids harvested at different stages of development. Seeds did not become capable of germination until 8 days afteranthesis. Red light promoted seed germination from the age of8–9 days following anthesis up to the newly mature stage.Ten or 11 days following anthesis, a large percentage of seedsbecame capable of germination in the dark and therefore couldbe considered not dormant. They were affected by far-red light,but less so than the mature seeds. The effect of light on the germination of developing seeds appearedto be similar to the known light effect on mature lettuce seedgermination. Gibberellin A₃ and ethephon had no effect on immatureand fresh seed germination. Lactuca sativa L., Lettuce, germination, dormancy, red light, far-red light, gibberellin A₃, ethephon     

Germination of Tagetes minuta L. I. Temperature Effects

Initial studies have indicated that Tagetes minuta achenes haveboth a temperature and a light requirement for germination.Temperatures tested were 10, 20, 25, 30 and 35 °C. Germinationwas optimal at 25 °C under white light conditions. Underthese conditions 100 per cent of achenes germinated within 7days of imbibition. There was no germination at 10 or 35 °Ceither in the light or in the dark. Achenes imbibed and incubatedat 35 °C for 4 days showed no visible signs of germinationbut on transfer to 25 °C, 100 per cent of these achenesgerminated within 24 h. Furthermore, achenes given this hightemperature (35 °C) treatment could be dried at 25 °C,re-imbibed at 25 °C and again 100 per cent of achenes germinatedwithin 24 h of re-imbibition. This rapid germination responsefollowing removal from the high temperature regime could alsobe induced by transfer to temperatures of 20 °C or 20 °C(16 h) alternating with 10 °C (8 h). Tagetes minuta L., weed seeds, germination, temperature, light     

Photoinhibition of Seed Germination in the Maritime Plant Matthiola tricuspidata

The three-horned stock, Matthiola tricuspidata (L.) R. Br. isa widespread annual plant of the Mediterranean sandy shores.Its seeds are dark germinating and negatively photosensitive,in accordance with our previous findings for a number of othermaritime plants. Full germination was obtained at a wide rangeof temperatures (5-25 °C) in the dark. Inhibition of germinationunder light of various spectral qualities could be generallycorrelated, negatively and positively, respectively, with phytochromephotostationary state (ø) and relative cycling rate ofphytochrome (H). The inhibition of germination by white (fluorescent),blue and far-red light, applied either continuously or intermittently,consistently showed a linear dependence upon the logarithm ofthe flux density of the irradiation. The resulting photoinhibitioncurves had parallel slopes and, compared to those of other maritimeplants, they were shifted to higher flux densities, Continuousblue or far-red irradiations, both establishing a similar øvalue (0·26), resulted in statistically similar regressioncurves, thus favouring the hypothesis that phytochrome is thesingle photoreceptor in the photoinhibition of seed germination.Copyright1994, 1999 Academic Press Matthiola tricuspidata (L.) R. Br., three-horned stock, seed germination, light, photoinhibition, phytochrome     

An unusual effect of the far-red absorbing form of phytochrome: Photoinhibition of seed germination inBromus sterilis L.

Seeds ofBromus sterilis L. germinated between 80–100% in darkness at 15° C but were inhibited by exposure to white or red light for 8 h per day. Exposure to far-red light resulted in germination similar to, or less than, that of seeds maintained in darkness. Germination is not permanently inhibited by light as seeds attain maximal germination when transferred back to darkness. Germination can be markedly delayed by exposure to a single pulse of red light following 4 h inhibition in darkness. The effect of the red light can be reversed by a single pulse of far-red light indicating that the photoreversible pigment phytochrome is involved in the response. The response ofB. sterilis seeds to light appears to be unique; the far-red-absorbing form of phytochrome (Pfr) actually inhibiting germination.Abbreviations Pr red absorbing form of phytochrome - Pfr far-red absorbing form of phytochrome     

Growth and Dormancy in Lunularia cruciata (L.) Dum.: IV. LIGHT AND TEMPERATURE CONTROL OF RHIZOID FORMATION IN GEMMAE

The first sign of initiation of growth in dormant gemmae ofL. cruciata is the formation of rhizoids. Gemmae in the cupcannot ‘germinate‘ until exposed to substrate conditionsallowing the outward diffusion of a growth inhibitor. Rhizoidproduction depends on temperature and light. With long lightperiods rhizoids are formed over a wide range of temperatures.Transference to darkness after 2 h white light causes about50 per cent of gemmae to produce rhizoids, and these are formedonly between 20 and 25 °C. Outside these temperature limitsthe percentage of gemmae with rhizoids soon drops to zero. Althoughrhizoid production is prevented in total darkness, gemmae remainalive for well over 6 months. Red light for as little as 5 spromoted, and far-red light inhibited, rhizoid formation inthe dark. Coumarin and indol-3yl-acetic acid can substitutefor light and partly reverse the effect of far-red irradiation.