Environmental Factors Controlling Flower Opening and Closing in aPortulacaHybrid

To examine flower opening and closing of aPortulacahybrid, flowerbuds were placed in darkness for 12 h (2030–0830 h) at20 °C and then exposed to various light-temperature conditions.Flower buds exposed to light at 25, 30 or 35 °C opened within1 h, and wilted 10–14 h later. Flower buds exposed tolight at 20 °C started to open after 4 h but opened slowlyand not completely. Flower buds subjected to 25, 30 or 35 °Cin darkness also opened rapidly, but did not reach full opening.Flowers opened at 30 °C in light, and partially closed andopened repeatedly in response to cycles of a 2-h exposure to20 °C and a 2-h exposure to 30 °C at any time between1000 to 1600 h. Similar phenomena were observed when the flowersopened at 30 °C in light and then were subjected to darknessand light alternately at 30 °C, although the effect of lightwas less obvious than that of alternating temperature. Floweropening and closing were not affected by relative humidity.These results indicate that a rise in temperature is requiredfor rapid flower opening in the buds kept at 20 °C, andthat light intensifies the effect of high temperature. Exposureto light without a temperature change delayed and slowed floweropening which was never complete. The involvement of an endogenousrhythm in flower opening byPortulacais indicated. Portulacahybrid, flower opening, flower closing, temperature shift, endogenous rhythm.     

Flower opening and closing ofOxalis martiana

Flowers ofOxalis martiana open in the morning and close in the afternoon repeatedly for 3–5 days in May–July under natural conditions. Both in light and in darkness, the closed flowers opened in reponse to a rise in temperature (thermonasty), but not under the constant temperatures. Transfer from darkness to light along with temperature rise caused rapid flower opening, and at 20 C or higher temperatures, exposure to light caused flower opening even without changing temperature (photonasty). Therefore, the temperature of the night before opening is critical in determining whether the flower opening under natural conditions depends on thermonasty or photonasty. The opened flowers closed about 8–11 hr after the beginning of opening both under natural conditions and constant light-temperature conditions, which suggests that the time of flower closing is determined by endogenous factors. Length of the perianth increased greatly during opening and slightly during closing. Application of actionomycin D or cycloheximide inhibited both the flower opening and closing, probably by suppressing the perianth growth.     

Flower Opening in Asiatic Lily is a Rapid Process Controlled by Dark-light Cycling

In commerce, Asiatic lilies are picked in bud, each stem holdingseveral buds. We found flower opening was rapid, taking lessthan 4 h both on the stem and for excised buds. Opening wasalso strongly synchronous. For a 12 h day-night cycle, openingbegan late in the dark period, reaching a mid-point after 11h of darkness. This was equally true of buds that were excisedwhen nearly ready to open, and those with 3–4 d of developmentto complete. Reversing day and night reversed the time of opening,and red light was as effective as white light in providing ‘day’conditions. A 15 min light break during the night did not affectthe opening. Lengthening the night (8, 12, 16 h) and shorteningthe day delayed opening from 9, to 11, to 13 h after the startof darkness, respectively. In continuous light and continuousdark, synchronicity was lost. If opening flowers were held inextended darkness, two phases of opening could be discriminated.In a ‘dark phase’, petals opened to approx. 40°,and anthers remained intact. When such flowers were returnedto light, there was a ‘light phase’, where petalsopened further, became more pigmented and began to recurve,and the anthers dehisced, these events taking only 2–3h. The net result was that flowers became fully open and anthersdehisced approx. 2 h after dawn, regardless of daylength. Copyright2000 Annals of Botany Company Asiatic lily, Lilium hybrid, flower opening, timing, endogenous rhythm, synchronicity     

Photonastic and thermonastic opening of capitulum in dandelion,Taraxacum officinale andTaraxacum japonicum

The capitula ofTaraxacum officinale andT. japonicum open in response to temperature rise at lower temperatures (thermonasty), and in response to light at higher temperatures (photonasty), as was the case inT. albidum. The capitula ofT. officinale could respond to the same temperature rise more sensitively than those ofT. albidum orT. japonicum. The minimum temperature for photonastic opening is as low as 13 C forT. officinale, while that forT. albidum andT. japonicum is about 18 C. That is why the capitula ofT. officinale opened earlier than those ofT. albidum andT. japonicum in the morning in April under natural conditions. The capitulum continued to be open for about 13–14 hr inT. officinale and about 8–11 hr inT. japonicum and inT. albidum both under natural conditions in April and even under constant light-temperature conditions, suggesting that the time of capitula-closing in these three species is not controlled by changes in environmental factors (light and/or temperature).     

Studies in Stomatal Behaviour: XII. OPENING IN HIGH TEMPERATURE IN DARKNESS

Xanthium pennsylvanicum exhibited a small stomatal opening (‘nightopening’) towards the end of a long night at 27? C. Experimentsare described in which a temperature increase from 27? to 36?,given during the period of night opening, caused the stomatato open widely for several hours. The degree of opening firstachieved was comparable with that observed in light of 1,000lux, but high temperature was less efficient than light formaintaining opening. Openmg was greater in mature than in youngleaves. The opening did not appear to be due to water strainunder the high temperature. It was found that temperature-induced opening was much greaterafter a long night (16 hours) than after a short night (fourhours). From this it is deduced that the opening is affectedby the endogenous rhythm which occurs in darkness (this wasstudied in previous work). The results obtained here contrastsharply with some obtained previously (and confirmed here) inwhich different temperatures were given throughout the night.The differences can probably be explained in terms of temperatureeffects on the endogenous rhythm. The stomata retained their normal responses to carbon dioxideand carbon dioxide-free air during temperature-induced opening.Thus the opening must occur in spite of any temperature stimulationof respiration. An experiment on the effect of temperature on stomatal closurein response to darkness is also described. Closure was significantlyslower at 36? than at 27? C.     

Effects of Light and Temperature on Flower-opening of Pharbitis nil

Flower buds of Pharbitis nil cut from plants growing in thefield opened rapidly when kept in darkness for 8 hr followedby continuous light at 20–25°C, but those kept indarkness for 4 hr opened promptly oniy when the temperatureduring the following light period was kept at 23°C or lower.Buds exposed to continuous light at 25°C did not open, butthose exposed to continuous light at 23°C opened slowly.At a lower temperature, the buds opened rapidly even in continuouslight. When the buds were placed in darkness at 25°C at13:30, 17:30 and 21:30 (artificial light from 17:30 to 21:30),they opened about 10 hr after the onset of darkness regardlessof the time of the onset of darkness, but when the buds werekept at 20°C in light from 13:30, 17:30 and 21:30, theyopened at 3:30–5:30 regardless of the time of transferto the lower temperature. The biological clock which controlsthe time of flower-opening is suggested to be easily reset bya light-off signal, but not by a shift from a normal to lowertemperature (20°C). At the lower temperature, the time offlower-opening probably is determined by the time of the latestpreceding light-off (or light-on) signal. ¹Dedicated to Professor Dr. Erwin Biinning on the occasion ofhis 75th birthday. (Received October 23, 1980; Accepted December 15, 1980)     

Adventitious bud formation on leaf and stem segments of Heloniopsis orientalis grown at various temperatures

The effect of different temperatures on bud formation in excisedleaf fragments and in stem segments of Heloniopsis orientalis,a monocotyledonous plant, was investigated in light and in darkness.The optimal temperature for bud formation was 21?C to 25?C.16?C pretreatment for 7 to 21 days promoted bud formation inleaf segments. 30?C pretreatment for 7 days or more reducedthe number of buds in both young etiolated and mature greenleaf segments but not in young green leaf segments. In younggreen leaf segments grown in darkness, however, 30?C pretreatmentreduced the number of buds. Inhibition of bud formation dueto high temperature could not be reversed by BA. (Received November 15, 1978; )     

Studies on the light controlling the time of flower-opening in Pharbitis nil

Flower buds of Pharbitis nil, strain Violet, open about 10 hrafter the onset of darkness at 24?C. Daylight fluorescent lightat 0.3–3 W/m² given during the first 4 hr of this darkperiod delayed the time of flower-opening, but that given laterhad only a slight effect or was ineffective. Red light was mosteffective in delaying the time of flower-opening, and a 5-minred light pulse given every 30 min also was effective. The effectof this 5-min red light was partly reversed by a subsequentfar-red light pulse which suggests that the absence of P_fr duringthe first 4 hr in the dark is necessary for normal timing offlower-opening. Five minutes of red light given 10 hr after the onset of darknessadvanced the phase of the circadian rhythm which controls thetime of flower-opening; buds opened about 7 hr earlier on thefollowing day. This effect of red light was also reversed bya subsequent exposure to far-red light, which suggests the participationof phytochrome in this reaction. (Received October 8, 1979; )     

Light and temperature control of germination in Agropyron smithii seeds

In darkness, A. smithii seeds germinated poorly at constanttemperatures but well at alternating temperatures. Prolongedperiods on the high part of the temperature cycles reduced germination;the higher the temperature the shorter was the period requiredon the high part of the temperature cycles for optimum germination.Continuous, unfiltered, incandescent illumination and intermittentfar red at 15?–25?C alternation also inhibited germination;the inhibitory effects were similar to those caused by the highintensity reaction. Far red inhibited germination when appliedafter 1 and 2 complete 15?–25?C cycles in darkness butnot after 3 cycles. Less than 20% of the seeds were under phytochromecontrol at constant 20?C. When red light was applied directlyafter far red that was applied in intermittent cycles at 15?–25?C,however, 50% of the seeds caused to germinate by the alternatingtemperature were shown to be controlled by the reversible phytochromereaction. The induced high-temperature dormancy was overcome by gibberellicacid (GA₃) plus kinetin. The hormonal treatment was much moreeffective than light for breaking dormancy. Inhibition fromprolonged illumination was alleviated or eliminated by GA₃+kinetin.The failure of red light to promote good germination at 20?Cwas also overcome with GA₃+kinetin; effects of light plus thehormone treatments were more than additive. These data suggestthat optimum alternating temperatures facilitate a proper balanceand interaction of hormones, enzymes, substrates and possiblypreexistent P_fr so that the germination of A. smithii seedscan proceed without benefit of a light treatment. (Received July 7, 1976; )     

Studies in Stomatal Behaviour: X. AN INVESTIGATION OF RESPONSES TO LOW-INTENSITY ILLUMINATION AND TEMPERATURE IN XANTHIUM PENNSYLVANICUM

Two experiments are described in which stomatal sensitivityto low-intensity white light was studied for Xanthium pennsylvanicumWall. In the first experiment a daylength extension for 7, 9, or 15hrs. was given using 10, 40, or 160 lux to shorten a basic 16-hr.night, which was also given at its full length as a tenth treatment.Measurements were made of stomatal opening ability on the morningfollowing the different treatments. With a 15-hr. extensionthere was at all intensities a significant response, shown bya reduced rate of opening in the morning. With a 9-hr. extensionusing 40 or 160 lux, opening ability was reduced, but 9 hrs.of 10 lux was insufficinet to produce a detectable effect. The7-hr. extension was ineffective at all three intensities. In the second experiment stomatal behaviour was observed during20 hrs. of either darkness or 10 lux at four temperatures (15,22, 29, and 36°C.). During 20 hrs. of darkness there wasnight opening at all temperatures, but at lower temperaturesit began sooner and lasted longer. These responses to temperaturedid not fit a simple linear relationship, there being a significantcubic term revealed by non-linear regression analysis. Thiscould be explained if the response was considered in terms ofthe magnitude of the change in temperature (from 25°C.)at the beginning of the experiment; there appeared to be sometemperature compensation over a limited range. in 10 lux, nightopening was suppressed at 29° and 36°, but at 15°it was apparently unaffected by the light; at 22° it wasnot completely suppressed by 10 lux but the time of its occurrencewas delayed. Effects of light and temperature are discussed in relation toan endogenous rhythm in darkness which was previoulsy shownto operate in Xanthium pennsylvanicum (Part IX). It is considered that to explain effects of very low intensitylight it will be necessary to recognize a ‘low intensityresponse’ by stomata, which does not operate via changesin guard-cell carbon dioxide.     

Tentoxin Suppresses Stomatal Opening by Inhibiting Photophosphorylation

Tentoxin and, to a lesser extent, dihydrotentoxin (both at 10mmol m^–3) reduce stomatal opening in epidermal stripsof Commelina communis in the light but not in darkness. Thiseffect was significantly greater in normal air than in CO₂-freeair. Fusicoccin overcame the tentoxin effect. However, tentoxindid not inhibit stomatal opening in the light in epidermal stripsof Paphiopedilum harrisianum, a species which lacks guard cellchloroplasts. It is concluded that tentoxin exerts its actionon stomata not by an ionophorous effect in the plasmalemma ofguard cells but by the inhibition of photophosphorylation intheir chloroplasts. The effects of DCMU and tentoxin on guardcells are discussed in terms of their effects on chloroplastsand the extent to which energy is supplied from this organelleduring stomatal opening in the light. The results indicate thatneither photophosphorylation nor non-cyclic electron transportin guard cell chloroplasts are essential for stomatal opening. Key words: Commelina, epidermal strips, Paphiopedilum, photophosphorylation, stomata, tentoxin     

Phase Shifts of Potassium Uptake Rhythm in Lemna gibba G3 Due to Light, Dark or Temperature Pulses

Phase shifts in potassium uptake rhythm during continuous lightin flow medium (FMC) and static (STC) culture of Lemna gibbaG3, produced by various light and temperature pulses were examined.The phase responses were very similar to those known for a varietyof circadian rhythms: A pulse of high temperature (39°C)shifted the phase in the same way as a light pulse insertedduring darkness. A pulse of darkness, or of low temperature(5 or 10°C), however, caused a phase shift that was theinverse of that caused by a light pulse. A temperature pulseof definite timing erased the rhythm. Although the rhythms inthe STC and FMC had essentially the same phase response, a highintensitylight pulse was more effective in FMC and dark and temperaturepulses in STC. (Received December 18, 1982; Accepted March 8, 1983)     

Effects of Light, pH, Temperature, and Crowding on Megaspore Germination and Sporophyte Formation in Marsilea

Megaspore germination and sporophyte formation of Marsilea vestitaH. and G. was studied under different light, pH, temperature,and crowding conditions during a 6 d experimental period. Maximumgermination and sporophyte development occurs under relativelylow light intensity. Darkness and high light intensity inhibitsporophyte development. Selected wavelengths of light (red,far-red, green, blue) and darkness reduce both megaspore germinationand sporophyte development as compared to white light. Megasporesand sporophytes show maximum development at 25 ?C in light,whereas their development is reduced at all temperatures indarkness. The optimum pH range for megaspore germination ispH 7–8 and that for sporophyte development is pH 7. Sporocarpcontents alter the pH of unbuffered acidic and basic media towarda more optimal growth condition (pH 6–8) for megasporegermination. Megaspore germination and sporophyte developmentvary inversely with conditions of crowding. Root and leaf growthon developed sporophytes is very similar in most treatments.     

CO2 fixation in leaves of a CAM plant without lower epidermis and the effect of CO2 on their deacidification

The effects of peeling the epidermis off Bryophyllum daigremontianumleaves on CO₂ uptake in light and darkness were investigated.Light-induced CO₂ uptake in the daytime was markedly enhancedin the peeled leaves, but dark fixation of CO₂ carried out atmidnight was not. The difference in promotion of CO₂ uptakein light and darkness was due to stomatal closing in the dayand opening at night. Also, deacidification was strikingly inhibitedby CO₂ in peeled leaves. (Received February 3, 1977; )     

Stomatal Opening in Light of Different Wavelengths: Effects of Blue Light Independent of Carbon Dioxide Concentration

Stomatal opening in Xanthium pennsylvanicum was found to besignificantly greater in blue light than in red. Experimentsin which leaves were placed in a closed system and allowed toestablish their own steady-state carbon dioxide concentrationshowed that when the CO₂ concentration was about the same asthat in red, opening was much greater in blue light. Blue lightof low intensity could cause as great an opening as red of higherintensity, even though the CO₂ concentration was much higherin blue. Stomatal opening in light is considered as involvingat least two reactions: (1) a response to the removal of CO₂by photosynthesis; (2) a response to blue light not dependenton the removal of CO₂. Blue light became increasingly effective, relative to red, asthe length of night was increased over the range 2 to 14 hours.This might, in part, explain previously observed effects ofnight length on rate of opening in light. The initial very rapid phase of closure in darkness appearedto be independent of CO₂ accumulation, for it was not preventedby flushing the intercellular spaces with air free of CO₂. Itis suggested that closure in darkness, like opening in light,should be considered as involving components both dependentupon, and independent of, CO₂ concentration.     

Effect of the Mesophyll on Stomatal Opening in Commelina communis

The effect of a number of factors on the opening of stomatain the intact leaf and in the isolated leaf epidermis of Commelinacommunishas been investigated. Stomata in the intact leaf opened widein the light and closed rapidly on transfer to the dark. Theywere also sensitive to CO₂. In contrast, stomata in isolatedepidermis floated on an incubation solution containing 100 molm^–3KCl responded neither to light nor CO₂. They opened as widelyas those in the intact leaf when treated with fusicoccin. Stomata in isolated epidermis opened almost as wide as thosein the intact leaf when they were incubated with isolatedmesophyllcells in the light. The solution in which the mesophyll cellswere incubated was separated by centrifugation. Themedium fromcells previously incubated in the light caused the stomata inisolated epidermis to open but that from cells kept inthe darkhad no effect. A similar effect was observed when isolated chloroplastswere incubated with the isolated epidermis.However, the supernatantfrom the chloroplast suspension had no significant effect onstomatal opening. These results indicate that the mesophyll plays an importantrole in stomatal opening in the light. The mesophyll appearstoproduce in the light, but not in the dark, a soluble compoundwhich moves to the guard cells to bring about stomatal opening.Theexperiments with isolated chloroplasts suggest that this substanceis a product of photosynthesis. Key words: Commelina communis, stomata, light, mesophyll     

Effect of Photoperiod on Stomatal Opening in Vicia faba

Stomatal apertures in darkness and subsequent average opening rates in light were measured in Vicia faba leaf discs throughout the nyctoperiods for plants grown on three light:dark cycles (8:16, 12:12, and 16:8). The time course of opening in darkness depended on the specific light:dark cycle with the maximum aperture always occurring at the time the lights normally went on. The light-induced opening rate was also maximum at the end of the nyctoperiod.     

SUCCESSIVE PROCESSES INVOLVED IN THE GERMINATION RESPONSE OF NASTURTIUM SEEDS

1. The seeds ofNasturtium palustreDC. do not germinate, eitherin the light or darkness, at various constant temperatures,but require for their full germination a certain period of alow temperature (5°) applied immediately after light irradiation.These results indicate the existance of at least two processes,a light-dependent process and a low temperature-requiring process,in the initiation of germination ofNasturtiumseeds. Experimentalevidence indicated further that the light exposure causes twodifferent processes in the seed germination. 2. When a dark period at 23° was inserted between the lightirradiation and the low temperature treatment the germinationwas suppressed. The inhibitory effect of the inserted dark periodat 23° was eliminated by a short irradiation during thedarkness (light-break). 3. Prolonged exposure ofNasturtium seeds to any concentrationof gibberellin brought about no germination when exposure wasgiven in complete darkness. The germination was promoted onlywhen light irradiation was applied to the seeds. A short applicationof gibberellin at a fairly high concentration was, however,remarkably effective for the germination even in the darkness,and the germination was inhibited as the gibberellin applicationwas lengthened. It was considered that gibberellin could substitutefor the combined effect of light irradiation and low temperaturetreatment to induce the germination of Nasturtium seeds, andthat gibberellin was inhibitive toward the reactions followingthe above treatments which induced the germination (Received October 31, 1996; )     

Light- and Auxin-Induced Leaflet Opening in Detached Pinnae of Mimosa pudica

Leaflet pairs from detached pinnae of Mimosa pudica opened afterthe pinnae had been irradiated with light (2 W·m^–2)of 726 or 403 nm, whereas they remained almost closed with lightof 585 or 656 nm. Light-induced leaflet opening was observedonly in the daytime, from 6:00 to 16:00. Application of IAAat more than 30 µg/ml to the cut end of the pinna rachisesmade the leaflets open even in darkness with almost constantlag times of about 100 min which were independent of the concentration.NAA and 2,4-D also made the leaflet open at lower concentrationsthan IAA. Auxin-induced leaflet opening showed diurnal variation.Application of IAA for 2 to 6 min, depending on the concentration,was enough to open the leaflets. Autoradiography showed thatIAA was transferred from the cut end of a rachis throughouta pinna within 4 min. ¹Present address: Biological Institute, Faculty of Science,Kobe University, Kobe 657, Japan. (Received September 24, 1982; Accepted March 4, 1983)     

Studies in Stomatal Behaviour: IX. PHOTOPERIODIC EFFECTS ON RHYTHMIC PHENOMENA IN XANTHIUM PENNSYLVANICUM

An investigation of the effects of different day-length treatmentson stomatal behaviour in Xanthium pennsylvanicum Wall. has shownthat there are differences in long-and short-day treatmentssimilar to those first reported by Schwabe (1952) for Chrysanthemumand Kalanchoe, viz. stomatal opening towards the end of thenight in short days, but not in long days (short night precededby a period of low intensity illumination). In Xanthium therewere in addition very marked differences in rates of stomatalopening in the morning after different lengths of night. Theseeffects were not persistent, there being an immediate reversalupon a change from long- to shrot-day treatment, or vice versa. Further investigation showed that there was an endogenous rhythmaffecting the stomata in continuous darkness; rate of openingwas slow after very short nights, but became greater with extensionof the night to 14–16 hrs., this being the first ‘peak’of an ‘opening ability’ rhythm. The rhythm diedout rapidly and the second cycle was much reduced in amplitude.The period of the rhythm appeared to be approximately 24 hrs.The phase was set mainly by the time of onset of darkness, butthe duration of the pretreatment with low intensity illuminationwas also important—prolonging this was found to reudcethe time in darkness before the first peak. Each hour of lightof 1,500 lux given before darkness was found to be equivalentot approximately 0.3 hr. to darkness. The predominant effect of the length of the preceding nightwas on the slope of the opening curves rather than on the timeof onset of opening following illumination. The first peak of the opening ability rhythm was often manifestedeven in continuous darkness by a period of ‘night opening’of the stomata. The results are discussed and compared with those of other authorsand attempts are made to relate them to theories of the stomatalmechanism.