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.     

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.     

The Comparative Effects of Blue and Red Light on the Stomata of Allium cepa L. and Xanthium pennsylvanicum

Stomatal responses to blue and red light were compared in leavesof Xanthium pennsylvanicum (which contain starch in their guardcells) and in onion leaves (which are devoid of starch). Bluelight was found to be more effective than red in opening stomatain both species. However, a significant difference in the ratiosof blue to red light required to produce equal stomatal openingwas found between Xanthium pennsylvanicum and onion. It is concludedthat blue light may promote stomatal opening by its effect onenzymes controlling the starch and soluble polysaccharide contentof guard cells.     

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.     

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     

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     

Stomatal Responses to High Temperature in Darkness

The effect of a temperature increase from 25 to 35°C onstomatal opening in darkness (‘night opening’) onexcised, turgid leaves of Stachytarpheta indica was investigatedby microscopic examination of a baxial epidermis fixed in absoluteethanol. An appreciable degree of opening occurred towards theend of a 14-h night at 25°C, and this was substantiallyenhanced by the temperature increase to 35°C in the dark,which also promoted a marked increase in starch hydrolysis andaccumulation of potassium in the guard cells. The degree oftemperature-induced night opening was somewhat smaller thanthat of light-induced opening, and was higher in CO₂-free airthan in normal air. 2,4-dinitrophenol (DNP) was effective inarresting stomatal opening and suppressing starch hydrolysisand increase in stomatal potassium. The temperature-inducednight opening is related, to a great extent, to the enhancementby high temperature of starch hydrolysis and potassium accumulationin the guard cells, and the inhibitory effect of DNP on stomatalopening is attributed largely to its suppression of these twometabolic processes. The importance of oxidative phosphorylationas a possible source of energy for stomatal opening is brieflydiscussed.     

Suppression of Stomatal Opening in Leaves Treated with Abscisic Acid

Small doses of abscisic acid (approximately 0.02 µg cm^-2of leaf) applied to the leaf surface as a 10^-4 M solution causedmarked stomatal closure in Xanthium pennsylvanicum, and theeffect persisted for up to 9 days after application. Similareffects were found when 10^-4 M abscisic acid was supplied todetached tobacco leaves via their petioles. CO²-free air didnot cause a reversal of the closure, and it was therefore concludedthat the effect was not due simply to an increase in the intercellularCO²concentration; a more direct effect on the stomatal apparatusis suggested. It is considered that abscisic acid could playan endogenous role in the control of stomatal aperture, andthat this, and/or related substances, might be more useful as‘anti-transpirants’ than the phytotoxic substancescurrently employed for this purpose.     

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     

The Effects of Red, Far-red, and Blue Light on the Geotropic Response of Coleoptiles of Zea mays

The effects of red, far-red, and blue light on the geotropicresponse of excised coleoptiles of Zea mays have been investigated.Seedlings were grown in darkness for 5 or 6 days, exposed tovarious light treatments, and then returned to darkness fordetermination of the geotropic response. The rate of response of the coleoptiles is decreased after theyhave been exposed to red light (620–700 mµ, 560ergs cm^–2sec^–1 for the 24 hrs, but not for the 4hrs, preceding stimulation by gravity. Furthermore, their rateof response is greatly reduced if they are exposed to red lightfor 10 min and then returned to darkness for 20 hrs before geotropicstimulation. At 25° C an interval of 6 to 8 hrs elapses between a 10-minexposure to red light and the first detectable decrease in thegeotropic response of the coleoptile. This interval can be lengthenedby exposing the seedlings to low temperatures (0° to 2°C) after the light treatment but cannot be greatly shortenedby increasing the duration of exposure to red light. Using a standard procedure of exposing 5-day-old etiolated seedlingsto light for various times, replacing them in darkness for 20hrs and then determining the response of the coleoptiles to4 hrs geotropic stimulation, it has been found that: (a) Exposureto red light for 15 sec significantly decreases the geotropiccurvature of the coleoptiles and that further reduction occurson increasing the length of the light treatment to 2 and 5 min.(b) Far-red light has no effect on the geotropic response ofthe coleoptiles but it can completely reverse the effect ofred light. After repeated alternate exposure to red and far-redlight the geotropic response of the coleoptile is determinedby the nature of the last exposure, (c) Complete reversal ofthe effect of red light by far-red radiation only occurs whenexposure to far-red follows immediately after exposure to red.The reversing effect of far-red radiation is reduced if a periodof darkness intervenes between the red and far-red light treatments,and is lost after a dark interval of approximately 2 hrs. The effect of red light on the rate of geotropic response ofthe coleoptiles is independent of their age and length at thetime of excision. Blue light acts in a similar way to red light, but the seedlingsare less sensitive to blue than to red light. Coleoptiles grown throughout in a mixture of continuous, weak,red, and far-red light have a lower rate of geotropic responsethan etiolated coleoptiles.     

Light dependency of the mating process in Closterium acerosum

Sexual cell division and activation of gametangial cells forconjugation in Closterium acerosum were induced by light. L₂₀₀cells conjugated at maximum level under the following conditions;(i) a light intensity higher than 1,000 lux in a 16-hr lightand 8-hr dark regime and (ii) an illumination time longer than12 hr at 3,000 lux. L₂₀₀ cells also conjugated under continuousillumination at 3,000 lux. The action spectrum for the activation of gametangial cellshad peaks around 450, 611 and 665 nm. 3-(4'-Chlorophenyl)-l,l-dimethylurea (CMU) inhibited the accumulationof carbohydrates and sexual cell division at 10^–5 M andthe activation of gametangial cells for conjugation at 10^–4M. (Received August 15, 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.     

Light and Spore Discharge in Ascobolus

Spore discharge in Ascobolus crenulatus occurs both in the lightand in the dark. In a 12 h light: 12 h dark daily regime discharge-ratehas peaks in the dark periods, due apparently to light stimulationwith about half a day's interval between stimulus and response. Using a ‘spore clock’ the course of discharge hasbeen followed for a single apothecium on changing from darknessto light. Exposure to light (500 lux) of wave-lengths around400, 440 and 460 mµ immediately causes ’puffing‘,whilst light of longer wave-length (504 and 580 mµ) hasno effect. Change from darkness to white light has no immediateeffect, but there is a delayed stimulation with a marked increasein discharge-rate 10–14 h later. Simultaneous illuminationof an apothecium, which has been in darkness, by blue light(420 mµ, or 440 mµ, 500lux) and yellow light (580mµ, 500 lux) does not result in puffing. The yellow appearsto prevent the blue light from exerting its effects.     

Light-induced formation of fruit-bodies in a basidiomycete, Favolus arcularius (FR.) AMES

fruit-bodies in Favolus arcularius. The effect of light lastedfor about one day after transfer to darkness. The mycelium became sensitive to light about 2.5 days afterinoculation; i.e., at the beginning of the rapid growth phase.The site of fruiting was 2–5 mm inside the edge of colony(actively dividing zone) at the start of illumination. Whenone half of the plate culture was illuminated, fruiting wasrestricted to the illuminated half of the colony ; i.e., theeffect of light was localized. These results suggest that thecells sensitive to light are the actively dividing cells. Under a fixed light intensity, the total irradiation time requiredfor the initiation of fruiting was nearly constant, irrespectiveof the durations of pre-incubation in darkness and the dailyillumination period. With increasing light intensities, up toabout 500 lux, fruiting was promoted, however, a further increasein light intensity was inhibitory. (Received March 27, 1968; )     

Persistence of the Potassium Uptake Rhythm in the Presence of Exogenous Sucrose in Lemna gibba G3

The potassium uptake rhythm in a flow medium culture of Lemnagibba G3 persisted in darkness for 3 days, when the flow mediumcontained sucrose (1%). The rhythm was damped out after thatin darkness but it persisted longer when the plants were keptunder continuous weak light (80 lux). The rhythm was not dampedout when a daily light pulse (4,200 lux for 15 min) was applied.A single light pulse (4,200 lux for 15 min) at hour 48 of theprolonged dark period caused the rhythm to start again. DCMU(1 µM) slightly reduced the amplitude of the rhythm butdid not nullify the effect of the inserted light pulse. (Received September 16, 1981; Accepted February 2, 1982)     

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     

Floral Induction of Xanthium strumarium in Long Days

An efficient method of inducing flowering in the normally strictshort-day plant, Xanthium strumarium L., in long days is described.Plants were grown in 16-h long days and subjected to two thermocycleswith a root application of gibberellic acid at the 8th h ofthe light period. A thermocycle was defined as follows. Forthe first 8 h of the 24-h cycle, the temperature was 4 °C;for the remaining 16 h, it was 23 °C. The light was on forthe first 16 h and off for the remaining 8 h. Xanthium strumarium L., floral induction, thermoperiod, gibberellic acid     

Environmental Factors Controlling Capitulum Opening and Closing of Dandelion, Taraxacum albidum

The capitula of Taraxacum albidum kept in darkness opened whenthe temperature rose. The higher the temperature before thechange and greater the temperature rise, the larger the openingresponse was. The opening was promoted by light. The capitulakept in darkness at 20?1?C opened after exposure to light withoutthe temperature rise. The capitula closed 8–10 h afterthe beginning of the opening under constant light and temperatureconditions. (Received November 8, 1986; Accepted March 13, 1987)     

Some effects of light and heat on the feeding and resting behaviour of tsetse flies,Glossina morsitans Westwood

A laboratory investigation was carried out into the effects of light and heat on the feeding and resting behaviour of Glossina morsitans morsitans Westwood. Flies placed in small cages on the ears of rabbits were tested for feeding responsiveness at light intensities of 0, 10, 100, 1000 and 25 000 lux. Feeding occurred at the same rate in darkness as it did in light at up to 1000 lux, but at 25 000 lux was largely inhibited. At 26° C, flies flew to and settled in the light end of a 1.2 m-long choice chamber. As the temperature was raised (by 10° C/hour) they eventually took off and flew directly to the dark end. The temperature at which this skototaxis occurred was strongly negatively correlated with the light intensity: each log unit increase in light intensity (in lux) caused a 2.2° C fall in take-off temperature. Skototaxis occurred at higher temperatures in recently fed female flies than in starved ones.     

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; )