Growth and Dormancy in Lunularia cruciata (L.) Dum.: III. THE WAVELENGTHS OF LIGHT EFFECTIVE IN PHOTOPERIODIC CONTROL

Growth and dormancy in Lunularia are controlled by daylength,short-day promoting active growth, long-day or light-break treatmentinducing dormancy. Light-breaks of red light are highly effectivein inducing dormancy, while irradiation with other wavebandsis much less inhibitory to growth. Far-red light given afterred irradiation causes substantial reversal of the red-lighteffect, suggesting strongly that phytochrome is involved inthe photoperiodic response mechanism of Lunularia. However,even short(15 sec.) exposures to far-red light alone cause significantgrowth inhibition, and it is considered possible that far-redirradiation also leads to the formation of some of the P 730form of phytochrome.     

Growth and Dormancy in Lunularia cruciata (L.) Dum.: I. RESUMPTION OF GROWTH AND ITS CONTINUATION

Lunularia cruciata may become dormant at three stages in itslife history: mature thallus, gemma, and spore. The resumptionof growth and its continuation in various conditions have beenstudied in thalli and gemmae. Air-dry, mature thalli of theIsrael strain, planted on a suitable medium, produce adventitiousbranches ventrally from the region immediately posterior tothe existing meristem, which itself fails to resume growth.When dormant gemmae are taken from the gemma-cup, however, theexisting apical cells and meristems simply recommence growing,so that the new growth is continuous with the old. Except inthe case of mature thalli aroused from dormancy, apical dominanceis pronounced, and branching occurs only by bifurcation. Thisdominance can be broken by applying sucrose solution to thegrowing tips—possibly a plasmolytic effect. The growth in area of freshly planted gemmae accelerates forabout 25 days before its relative rate slows to any great extent.During the first half of this period, growth is due exclusivelyto the expansion of existing cells, but subsequently cell numbersincrease rapidly from the 8–10,000 present in the dormantgemma. Cell numbers were estimated by using a modified macerationtechnique, in which chelation followed prolonged fixation. Lunularia grows successfully at quite low light intensities.Of the mineral nutrient deficienccs investigated, lack of Plimits growth most severely, although N-deficiency also restrictsit to a very low level. Gemma-cup production appears to be unaffected by light intensity,at least within levels permitting growth. There is, however,a large temperature effect, cup production decreasing markedlyabove 12° C.     

Dormancy and Flowering in Anemone coronaria L. as Affected by Photoperiod and Temperature

The effects of day-length and temperature on flowering and dormancyinduction were studied in Anemone coronaria L., with plantsraised either from corms or achenes. An Israeli hybrid sourcewas used (de Caen cv. Hollandia x Israeli wild type). Dormancy onset is characterized by the cessation of foliageleaf production, the appearance of leaf scales protecting theperennating bud, and leaf senescence. Dormancy was induced byhigh temperature and long days but increasing temperatures (from17/12 °C to 32/12 °C) induced earlier dormancy thanprolonging the photoperiod (range 8–16 h). A significant(P = 0.01) interaction was found between these factors, withsmaller photoperiodic effects the higher the temperature. At22/17 °C the critical day-length for dormancy inductionwas between 11 and 12 h. The transition from the vegetative to the reproductive stageappears to be an autonomous process that occurs with developmentin plants raised from either corms or achenes and does not requireenvironmental induction. Photo- and thermoperiodic effects onflowering were indirect, being mediated through their influenceon dormancy induction. Anemone coronaria L., dormancy, flowering, photoperiod, thermoperiod     

Photoperiod Responses of Corchorus olitorius L. in Controlled Environments

Controlled environments were used to establish the base-linegrowth and to evaluate the photoperiodic response of two Tossajute (Corchorus olitorius) cultivars. Fresh and dry weightsof shoots and roots, leaf areas and stem lengths were much greaterat long day (LD) 12·5, 11·5 than LD 11·5,12·5 photoperiods for both cultivars. Root lengths weregreater at LD 12·5, 11·5 initially but were longestat LD 11·5, 12·5 at 35 days from emergence. Meanrelative growth rates (MRGR) were similar irrespective of photoperiodor cultivar but declined with plant age. The superior growthof cultivar ‘Yaya’ at LD 12·5, 11·5was due to more growth in the first 7 days, while, for cultivar‘Angbadu’ it was a combination of growth for 7 days,and higher MRGR up to 21 days. Stomatal density was greaterat LD 12·5, 11·5 than LD 11·5, 12·5. Corchorus olitorius L., Tossa jute, photoperiodism, relative growth rate     

Apple Fruit Bud Development and Growth; Analysis and an Empirical Model

Analysis of the information available on apple bud developmentand growth after dormancy leads to an empirical model of growthto full bloom. The analysis and model are set in the frameworkof the physiological mechanisms considered to be responsiblefor dormancy and subsequent bud growth. It is necessary to introducean arbitrary ‘growth unit’ scale to describe theseprocesses quantitatively, which is done by the equation G = A/(I+be^–k(I).P) where G and A are in growth units, the value of k is controlledby a dormancy index I and P is a temperature summation. Themodel fulfils the main requirements laid down for it and thevalues of P at full bloom, derived from controlled environmentwork and field observations, are very similar.     

Effects of Abscisic Acid on the Growth Pattern of the Shoot Apical Meristem and on Flowering in Chenopodium rubrum L.

Abscisic acid (ABA) at 1 x 10^–4 M or 3 x 10^–4 Mwas applied to the apical buds of Chenopodium rubrum plantsexposed to different photoperiodic treatments and showing differentpatterns of floral differentiation. Stimulation of growth inwidth of the apical meristem of the shoot and/or inhibitionof growth in length was obtained under all photoperiodic treatments.This change of growth pattern was followed by different effectson flowering. In non-induced plants grown under continuous light ABA stimulatedpericlinal divisions in the peripheral zone and the initiationof leaves as well as the growth in width of bud primordia. Inplants induced by two short days reduced growth of the meristemcoincided with ABA application. Longitudinal growth of the meristemwas inhibited in this case and only a temporary stimulationof inflorescence formation took place. In plants induced ata very early stage, ABA exerted a strong inhibitory effect onflowering. A permanent and reproducible stimulatory effect onflowering was obtained in plants induced by three sub-criticalphotoperiodic cycles if ABA was applied to apices released fromapical dominance. In this case formation of lateral organs andinternodes was promoted by ABA and was followed by stimulatedinflorescence formation. Gibberellic acid (GA2) at 1x 10^–4M or 3 x 10^–4 M brought about a similar effect on floweringas ABA, although the primary growth effect was different, i.e.GA₂ stimulated longitudinal growth. The effects of ABA and GA₂ on floral differentiation have beencompared with earlier results obtained from auxin and kinetinapplications. These growth hormones are believed to regulateflowering by changing cellular growth within the shoot apex.Depending on the actual state of the meristem identical growthresponses may result in different patterns of organogenesisand even in opposite effects on flowering. Shoot apex, flowering, photoperiodic induction, abscisic acid, gibberellic acid, Chenopodium rubrum L.     

Different actions of red and blue or far-red lights in the photoperiodic tuberization of Begonia evansiana

The spectral dependence of Begonia evansiana in supplementarylight periods of photoperiodic tuberization and sprouting wasinvestigated. Supplementary application of red light inhibitedtuber development, thereby stimulating vegetative growth. Supplementaryblue or far-red light also suppressed tuber development, butbarely stimulated vegetative growth. However, both red and blue light, given at 6°C during themain light period or the supplementary light period, permittedthe tuberization under the subsequently given conditions ofeither long-days or darkness at 23°C. Blue light appliedafter 5-days of irradiation with white light at 10°C, showedalmost the same action as far-red light, which suppressed tuberizationin darkness. The nature and function of the pigments concernedin the photoperiodic responses are discussed. (Received October 11, 1968; )     

Photoperiod and Reproduction in Lobsters (Homarus)

SYNOPSIS. Photoperiodic control of lobster (Homarus) ovipositionranges from none in the European species (H. gammarus) to atwo-phase requirement in some populations of H. americanus.In the inshore population from Massachusetts two to three monthsof shortday photoperiod appear necessary to condition the ovaryfor final vitellogenesis following long-day onset (LDO). Thestimulus of LDO is only effective near the time of molt. Ifmolt follows LDO within 120 days, egg extrusion follows themolt in about 80 days. If LDO follows the molt, extrusion occursin about 125 days. Extrusion delayed in this way delays thefollowing molt, which is also delayed by the retention of eggson the pleopods. In lobsters from Prince Edward Island the photoperiodic responseseen at laboratory temperatures (ca. 14°C) appears to besubordinated to a response to other cues, probably temperature,when females are held on a near-natural temperature regime withwinter minimum of 2°C characteristic of inshore environments.H. americanus from the migratory outer continental shelf populationexperience winter temperatures rarely lower than 8°C andprobably require photoperiodic control to initiate migrationas well as vitellogenesis. The photoperiodic response may haveoriginated in offshore populations during the Pleistocene andspread to more northerly inshore areas as habitat opened afterthe retreat of the continental ice sheet.     

Interaction of vernalization, photoperiod and high temperature in flowering of Arabidopsis thaliana (L.) HEYNH.

Flowering of Arabidopsis thaliana (L.) HEYNH., var. "Stockholm",plants, raised from vernalized seeds, may be modified by thephotoperiodic conditions or a short (1 week) exposure to hightemperature (32°C) following vernalization, depending onthe duration of the cold treatment. When vernalization is partial(1 to 4 weeks at 4°C), both short days (8hr light) and hightemperature have a devernalizing effect, but when the cold requirementhas been fully satisfied, after 5 to 6 weeks at 4°C, devernalizationis no longer possible. There is no interaction between photoperiodand high temperature. Fully vernalized plant flower in bothlong and short days, although flowering is delayed in shortdays. This delay is not a photoperiodic effect, however, butmay be ascribed to the decreased radiant energy available inan 8-hr photoperiod. Thus, fully vernalized Arabidopsis plantsare day-neutral. (Received November 5, 1969; )     

LIGHT- AND DARK-GROWTH IN LONG-DAY DUCKWEED, LEMNA GIBBA G3, AS AFFECTED BY KINETIN

Under short-day conditions the growth or the production of fronds in Lemna gibba G3 was stimulated by KIN (10^–5 M);the longer the nyctoperiod, the greater the stimulation was.Under long-day conditions KIN was slightly inhibitory for thefirst 2 days, but promotive thereafter. IAA (10^–5 M) reversedthe growth inhibition by KIN in long-days, and DCA (10^–4to 10^–6 M) and also CA (10^–4 to 10^–6 M), althoughless effectively, cancelled the growth promotion by KIN in short-days.DCA (10^–5 M) little altered the KIN inhibition in thefirst 2 days of light culture, nevertheless it alleviated strikinglythe KIN promotion in the subsequent illuminated days. These and relevant findings explained the above-described promotionand inhibition by KIN of the duckweed growth in terms of invivo level of a cofactor (probably auxin) which may be underthe regulative influence of photoperiodic conditions given.Moreover, some bearing of the above conclusion on floweringmechanism in this long-day duck-weed was suggested. (Received September 12, 1966; )     

Infection of the diatom Asterionella by a chytrid. I. Effects of light on reproduction and infectivity of the parasite

The influence of hight limitation of the diatom Asterionellaformosa Hass, on the growth-determining parameters of its fungalparasiteRhizophydium planktonicum Canter emend, was measured,using laboratory cultures of both organisms. The experimentswere earned out at 6°C under a 15:9 h light-dark cycle.At saturating light conditions, the mean zoospore productionof the parasite was 23.4 zoospores sporangium^–1, and themean development time of the sporangia was 7 9 days. Light limitationof the host caused a substantial decrease of the zoospore production,while the development time was only slightly reduced. The improvedzoospore production at high light intensities was mainly theresult of incorporation of photosynthetic products generatedby the host after infection. Under limiting light conditions,Asterionella cells were less susceptible to infection withfungal zoospores. No infection at all occurred below 2 µEm^–2 s^–1, a light intensity that still supportedsome algal growth The maximum infection rate indicated thatchemotactic attraction of the parasite's zoospores by extracellularproducts of the host is involved. The infective lifetime ofthe zoospores of the parasite did not depend on light conditions,and was estimated at 8 days. The measured zoospore productionrates, both under limiting and saturating light conditions,enable the parasite to exceed the specific growth rate of thehost, and thus become epidemic, at sufficiently high host densities.     

Effects of Environmental Change on Wood Production and Wood Structure in Picea sitchensis Seedlings

Changes in environment that would be expected to reduce substrateavailability, decrease the rate of xylem increment, tracheiddiameter and wall thickness, in seedlings of Picea sitchensis.But after reaching a minimum about 10 days to 3 weeks afterenvironmental change, xylem increment, tracheid wall thickness,and in some instances tracheid diameter, increase again up toabout 4 to 6 weeks after transfer. This recovery parallels arecovery in net assimilation rate, and is associated with anincrease in photosynthetic efficiency. Although the light intensity and temperature treatments imposedwere more drastic than those that would normally be expectedin the field, they had remarkably little net effect on tracheiddimensions. On the other hand change in photoperiod producedgreater changes in tracheid dimensions, photoperiodic effectsbeing superimposed on effects of change in substrate availability.It is suggested that adaptation to reduced substrate will bufferthe plant against climatic fluctuations during the growing season,while the photoperiodic response will ensure preparation forwinter dormancy. It is concluded that the major seasonal changes in tracheiddimensions are unlikely to be caused by variation in substrateavailability. Changes in light intensity and temperature haveminor effects on wood production and structure through effectson substrate availability, but the major seasonal trends aremore likely to be associated with changes in growth regulationproduction.     

Bud Dormancy in the Kiwi Fruit, Actinidia chinensis Planch

A study of lateral bud dormancy in Actinidia chinensis has shownthat true dormancy can be induced, especially in short daysat warm and constant temperatures This dormancy can be brokenquantitatively by chilling but temperatures as high as 10 °Care effective The dormancy appears to be due to an inhibitor(possibly ABA), apparently stored in the special bud cover aspecial structure in Kiwi fruit which may represent fused stipulesRemoval of the cover also admits oxygen and light, both of whichhave promoting effects on bud break Application of ABA enhancesdormancy (as do crude extracts tentatively identified as ABA)while GA₃ application enhances dormancy before chilling andpromotes bud break only after chilling Actinidia chinensis, Kiwi fruit, dormancy, abscissic acid, gibberellic acid, chilling     

Studies on the Role of Photosynthesis in the Photoperiodic Induction of Flowering in the Short-Day Plants Kalanchoe blossfeldiana Poellniz and Xanthium pensylvanicum Wallr: I. THE REQUIREMENT FOR CO2 DURING PHOTOPERIODIC INDUCTION

It has been established that Kalanchoe blossfeldiana and Xanthiumpensylvanicum require CO₂ during the light period of short daysfor successful photoperiodic induction of flowering, even ifall but the induced leaf are held in normal air. In X. pensylvanicumfloral induction in normal air was independent of the starchstatus of the leaves but when reserves were reduced, lack ofCO₂ in the light suppressed floral induction to an even greaterextent. Injection into the induced leaf (Kalanchoe) or leaftip feeding (Xanthium) of carbohydrates, organic and amino acidsor several other metabolites failed to substitute for the CO₂requirement for induction. A small response was produced by10 mg ml^–1 sucrose in X. pensylvanicum while in normalair 25 parts 10^–6 ATP reduced the time to flowering inK. blossfeldiana and 10^–4 M proline was inhibitory. Anexperiment on the light requirement established a need for redlight ( max 660 nm) during photoperiods but red light alonedid not facilitate maximal induction. It is concluded that someearly, possibly labile, product of photosynthetic CO₂ fixationis essential to floral induction in these species.     

Bulbing in Long-day Onion (Allium cepa L.) Cultured In Vitro: Comparison Between Sugar Feeding and Light Induction

Bulbs were obtained on onion plants cultured in vitro. No bulbinghappened under long days with fluorescent light and 30–40g l^–1 sucrose. Bulb formation was mainly dependent eitheron sucrose concentration in the culture medium, or on lightspectral composition. Raising the sucrose concentration from40 to 120 g l^–1 increased plant basal swelling and stoppedfurther vegetative development. These plants were not dormant.When fluorescent light was enriched in incandescence duringa long day period, bulbs were obtained in two months and underwenta consecutive dormancy. Bulb, dormancy, light spectral quality, photoperiod, R: FR ratio, sugar, tissue culture     

Long-Day Induced Bud Break in Salix pentandra Is Associated with Transiently Elevated Levels of GA1 and Gradual Increase in Indole-3-Acetic Acid

Initiation of dormancy in woody species is induced by a shortphotoperiod. In the early stages of dormancy development, growthcan be initiated by long days. To study the possible involvementof gibberellins and indole-3-acetic acid in bud break in Salixpentandra, effects on levels of these plant hormones of transferof seedlings in an early stage of dormancy to a growth-inductivelong photoperiod was investigated. The bud break and initiationof growth correlated with a rapid transient increase in GA₁in defined zones of shoot tips to levels twice of that in continuouslyelongating long day-grown control seedlings, followed by a rapiddecrease to levels similar to in these control plants. Also,the contents of GA₅₃, GA₁₉, GA₂₀, GA₈ increased upon transferfrom short to long days. Levels of indole-3-acetic acid showeda gradual decline under short days, and increased graduallyupon transfer to long days up to a level of continuously elongatingplants. The present data suggest an interaction between gibberellinand indole-3-acetic acid in the photoperiodic control of dormancydevelopment and bud break in S. pentandra. (Received October 14, 1996; Accepted February 18, 1997)     

The relation between light and temperature effects in the induction and release of dormancy in the aerial tuber of Begonia evansiana

The effect of light quality on the induction and release ofbud dormancy in aerial tubers of Begonia evansiana ANDR. andthe relation in controlling the mechanism of dormancy betweenlight and temperature were investigated using aerial tubersin different dormant states; immature tubers which were sproutedby irradiation and mature ones which were sprouted only afterchilling. Blue or far-red light induced photo-sprouting in immature tubersat higher temperatures and also promoted release of dormancyin mature tubers caused by chilling (2–5°C). Blueor far-red light, however, failed to break mature tuber dormancyat room temperature. The induction of dormancy in immature tubers was advanced atlow temperatures (15–17°C) which were inoperativefor photo-sprouting. Lower temperatures showed conflicting dualeffects of inducing and breaking dormancy. Red light inhibitednot only photo-sprouting in immature tubers but also dormancyrelease in mature tubers at low temperatures. These light- and temperature-dependent reactions are independentlyinvolved in dormancy regulation, the former is overcome by thelatter with dormancy development. (Received December 3, 1968; )     

Abscisic Acid Metabolism and Stomatal Physiology in Betula lutea Following Alteration in Photoperiod

Birch seedlings ceased extension growth when transferred fromlong days (LD) to short days (SD). The cessation of growth underSD was associated with enhanced rates of photosynthesis, probablydue to a lowered diffusive resistance to gas exchange. Endogenouslevels of ABA were lowered under SD but the degradation of 2-¹⁴C(±)ABAwas not disturbed. It is concluded that the photoperiodic controlof extension growth in Betula lutea is not mediated by ABA,although hormonal changes following transfer to SD may findsome expression in an altered stomatal physiology.     

Influence of Genotype and Environment on Growth of Barley Embryos in vitro

Isolated embryos of three contrasting barley genotypes werecultured in vitro on a range of media comprising 16 combinationsof sucrose (3–12 per cent) and 2, 4-D (0–8 mg 1^–1)concentration. Cultures were incubated at a range of temperaturesfrom 5 to 25°C and were examined after 21 days when shootlengths as well as fresh and dry weights were recorded. Therelative influence on growth of increasing concentrations ofsucrose and 2, 4-D was investigated, as was their interactionwith the incubation temperature. The genotypes were found todiffer markedly in their response to these two media components,with each parameter of growth differentially affected. Resultsare discussed in relation to the known dormancy characteristicsof these genotypes. Hordeum vulgare L., barley, embryo, dormancy, 2, 4-dichlorophenoxy acetic acid, sucrose