Effects of light quality on the circadian rhythm of leaf movement of a short-day-plant

Studies were made of the effects of blue, green, red and far-red (FR) light on the circadian rhythm of leaf movement of Coleus blumei × C. frederici, a short day plant. Under continuous illumination with blue light, there was a significant lengthening of the period of the rhythm to about 24.0 hr, as compared to 22.5 hr in continuous darkness. Under continuous red light, the period length was significantly shortened to 20.5 hr. Under continuous green or FR, the period length was not significantly different from the dark control. It was observed that under continuous FR illumination, the leaves tended to oscillate in a more downward position. Eight-hr red light signals were effective in advancing the phase of the rhythm as compared to a control under continuous green light. Blue light signals were effective in delaying the phase of the rhythm. FR light signals were ineffective in producing either delay or advance phase shifts. Far-red light did not reverse the effects of either red or blue light signals. On the basis of these results it is suggested, that pigments which absorb blue or red light, rather than phytochrome, mediate the effect of light on the circadian rhythm of leaf movement.     

The participation of two rhythms in the leaf movements of xanthium plants given various light-dark cycles

We have shown Xanthium strumarium exhibit two distinct leaf movement rhythms with one occurring in continuous light and presumably related to an endogenous rhythm initiated by the “light-on” signal and the other occurring in continuous dark and presumably related to an endogenous rhythm initiated by the “light-off” signal. Characteristic of the light-on rhythm is a sudden and rapid downward movement of the leaf occurring about 16 hours after the light-on signal. Characteristic of the light-off rhythm is an immediate and sudden upward movement following the light-off signal. Under certain photoperiodic treatments, the two movements seem to be in conflict.     

The Circadian Rhythm of Leaf Movement of Coleus blumei x C. frederici, a Short Day Plant. II. The Effects of Light and Temperature Signals

The phase response curve for the circadian rhythm of leaf movement of Coleus blumei x C. frederici, a short day plant, is generally similar to those reported for other organisms. An increase in the duration of the light signal caused an increase in the extreme values of the phase response curve and shortened the time for transition from maximum delays to maximum advances. Experiments with 2 light signals showed that the overt rhythm of leaf movement represents the rhythm of the light sensitive oscillator even during the transient period that followed the first light signal. A temperature decrease of 7° for 8 hr caused only a transient phase shift in the following 2 cycles but not in the steady state. The combination of such a temperature decrease and a light signal showed that only the overt rhythm of leaf movement was disturbed by the temperature decrease whereas the light sensitive oscillator was free running. A temperature decrease of 11° for 10 hr caused a steady state phase shift and affected the light sensitive oscillator as well.     

Different circadian rhythms regulate photoperiodic flowering response and leaf movement in Pharbitis nil (L.) Choisy

The phase shifting effect of red light on both the leaf movement rhythm, and on the rhythm of responsiveness of photoperiodic flower induction towards short light breaks (10 min red light), has been studied in Pharbitis nil, strain Violet, and comparisons between the two rhythms have been made. The phase angle differences between the rhythms after a phase shift with 2 or 6 h of red light given at different times during a long dark period were not constant. The results indicate the involvement of two different clocks controlling leaf movement and photoperiodic flower induction.Abbreviations DD continuous darkness - l:D x:y light/dark cycles with x hours of light and y hours of darkness - PPR rhythm of photoperiodic responsiveness towards light break     

Phase relations between the circadian leaf movement rhythm and its zeitgeber within the range of entrainment in the cotton plant,Gossypium hirsutum L.

Abstract

The leaf movement rhythm of Gossypium hirsutum L. (cv. Lakshmi) could be entrained to 24 h LD cycles with different photofractions varying from 4 to 20 h such that the night peak position of the rhythm occurred during darkness. The phase angle (ψ) of the rhythm varied in a regular manner with different photoperiods of a 24 h LD cycle. Under 24 h LD cycles with different photoperiods, the leaf movement shows probable evidences for the concurrent participation of a ‘light‐on’ and ‘light‐off rhythm.     

The response of growth and circadian rhythm to cycle length and photoperiod

Summary The growth of bean plants (Phaseolus vulgaris L., cv Red Kidney) is inhibited by cycle lengths of 36 and 48 hours. Maximal inhibition occurs when the length of the light period is equal to or shorter than 3/6 of the cycle length. The inhibition does not occur when the photofraction is 5/6 or longer. The rhythmic leaf movement in beans can be entrained to a 30-hour cycle with a photofraction of 3/6 or less. No entrainment occurs to 36-or 48-hour cycles, but such cycles with photofraction of 3/6 or less cause an irregular course of the rhythm. When the photofraction is 5/6 or greater, the leaf movement proceeds as in continuous light, independent of cycle length. In continuous light the rhythm persists for at least 12 days. The parallel response of growth and circadian rhythm to cycle length and photoperiod suggests that a circadian oscillation is involved in the growth process. It further indicates that the response of these phenomena to cycle length and photoperiod involves the same basic timing mechanism.With 4 Figures in the Text     

Endogenous rhythmic activity of photosynthesis, transpiration, dark respiration, and carbon dioxide compensation point of peanut leaves

At 14-hour day length, 25 C leaf temperature, 9 mm Hg vapor-pressure deficit, and 1.17 joules cm⁻² min⁻¹ irradiance, the diurnal change in daily photosynthesis of the cultivated peanut (Arachis hypogaea L.) is a result of an endogenously controlled circadian rhythm in net photosynthesis which peaks near noon and troughs near midnight. By resetting the day-night light regime, the rhythm rephased in continuous light. The free-running rhythm approximates 26 hours. Both transpiration and dark respiration show similar rhythmicity, with transpiration closely in phase with the rhythm in photosynthesis. The rhythm in carbon dioxide compensation point is approximately 12 hours out of phase, peaking at midnight and troughing at midday. Endogenous changes in stomatal aperture seemed to be the major control of the rhythm in photosynthesis. The activity of ribulose-1,5-diphosphate carboxylase increased during the normal photoperiod, leveling off after 12 hours; however, the activity was not correlated with the rhythmic change in photosynthesis.     

Chlorophyll a fluorescence kinetics of mung bean (Vigna radiata L.) grown under artificial continuous light

Continuous light can be used as a tool to understand the diurnal rhythm of plants and it can also be used to increase the plant production. In the present research, we aimed to investigate the photosynthetic performance of V. radiata under continuous light as compared with the plants grown under normal light duration. Chlorophyll a fluorescence transient (OJIP test) technique was used to understand the effect on various stages of photosynthesis and their consequences under continuous light condition. Various Chl a Fluorescence kinetic parameters such as Specific energy fluxes (per Q_A-reducing PSII reaction center (RC)) (ABS /RC; TR₀/RC; ET₀/RC; DI₀/RC), phenomenological fluxes, leaf model, (ABS/CSm; TR/CSm; ETo/CSm), Quantum yields and efficiencies (φPo; φEo; Ψo) and Performance index (PI_abs) was extracted and analysed in our investigation. Conclusively, our study has revealed that continuous light alters the photosynthetic performance of V. radiata at a different point but also improve plant productivity.     

Spontaneous action potentials and circumnutation in <Emphasis Type="Italic">Helianthus annuus</Emphasis>

Action potentials (APs) in plants are involved in fast leaf or trap closure as well as elongation, respiration, photosynthesis, and fertilization regulation. Here, spontaneous APs (SAPs) in relation to endogenous stem movement named circumnutation (CN) have been investigated in Helianthus annuus in different light conditions in freely circumnutating and immobilized plants. Extracellular electrical measurements and time-lapse photography were carried out simultaneously. The parameters of CN (trajectory length, period, and direction) and the number and transmission direction of SAPs were analysed. In continuous light (25–40 μmol m^?2 s^?1), all plants circumnutating vigorously in a regular elliptical manner and no SAPs were observed. In light/dark conditions, the plants circumnutated in a daily pattern, most SAPs were observed in the dark and freely circumnutated sunflowers had two times more SAPs (10 SAPs/24 h/plant) than the immobilized plants (5 SAPs/24 h/plant). In continuous very low light (5 μmol m^?2 s^?1), the plants circumnutated weakly and irregularly and SAPs appeared without the circadian pattern. 3–5 SAPs/24/plant occurred in the freely circumnutating and immobilized plants. In light/dark and continuous very low light conditions, an ultradian rhythm of SAPs was observed and the mean spacing between SAPs was approx. 121–271 min in the freely circumnutating and immobilized plants. Under all light conditions, more SAPs were transmitted basipetally than acropetally. One-hour lasting series of 3–4 min spaced SAPs locally propagated were observed as well in very low light. Basipetal and acropetal SAPs passing along the stem motor region accompany irregularity, changes in the CN trajectory direction, and stem torsion. These results demonstrate that APs and CN changes play a role in plant adaptation to light conditions and that there is an ultradian rhythm of SAPs beside ultradian CN rhythm.     

Rhythmic Nitrate Reductase Activity in Leaves of Capsicum annuum L. and the Influence of Kinetin

In the expanding leaves of Capsicum annuum L. cv. California Wonder, two of the three peaks of nitrate reductase activity associated with the light period exhibit a circadian rhythm that persists in continuous light.     

Endogenous Short Period Rhythms in the Movements of Unifoliate Leaves of Phaseolus angularis Wight

Rhythmic rotational movements with the midvein as the axis have been observed in the unifoliate leaves of Phaseolus angularis Wight grown under controlled environmental conditions with continuous light. The mean period of this movement for all leaves was 53.2 ± 4.3 minutes and remained constant as the leaf matured, except after removal of the apical meristem and emerging trifoliate leaf when the period increased by about 5 minutes. The amplitude of the movement also remained constant as the leaf matured. These rotational movements were pronounced when the leaf blade was in a horizontal position and were not evident during the downward or “sleep” movements of the leaf. This movement began 3 days after leaf unfolding and continued for at least 6 days. It was most pronounced at the time of inflection of the leaf length growth curve after the logarithmic phase of growth.     

A Persistent Daily Rhythm in Photosynthesis

The luminescent marine dinoflagellate, Gonyaulax polyedra, exhibits a diurnal rhythm in the rate of photosynthesis and photosynthetic capacity measured by incorporation of C¹⁴O₂, at different times of day. With cultures grown on alternating light and dark periods of 12 hours each, the maximum rate is at the 8th hour of the light period. Cultures transferred from day-night conditions to continuous dim light continue to show the rhythm of photosynthetic capacity (activity measured in bright light) but not of photosynthesis (activity measured in existing dim light). Cultures transferred to continuous bright light, however, do not show any rhythm. Several other properties of the photosynthetic rhythm are similar to those of previously reported rhythms of luminescence and cell division. This similarity suggests that a single mechanism regulates the various rhythms.     

Circadian rhythms in Kalanchoë: effects of irradiance and temperature on gas exchange and carbon metabolism

Gas exchange in K. blossfeldiana shows a circadian rhythm in net CO₂ uptake and transpiration when measured under low and medium irradiances. The period length varies between 21.4 h at 60 W m^-2 and 24.0 h at 10 W m^-2. In bright light (80 W m^-2) or darkness there are no rhythms. High leaf temperatures result in a fast dampening of the CO₂-uptake rhythm at moderate irradiances, but low leaf temperatures can not overcome the dampening in bright light. The rhythm in CO₂ uptake is accompanied by a less pronounced and more rapidly damped rhythm in transpiration and by oscillations in malate levels with the amplitude being highly reduced. The oscillations in starch content, usually observed to oscillate inversely to the acidification in light-dark cycles, disappear after the first cycle in continuous light. The balance between starch and malate levels depends in continuous light on the irradiance applied. Leaves show high malate and low starch content at low irradiance and high starch and low malate in bright light. During the first 12 h in continuous light replacing the usual dark period, malate synthesis decreases with the increasing irradiance. Up to 50 W m^-2 starch content decreases; at higher irradiances it increases above the values usually measured at the end of the light period of the 12:12 h light-dark cycle.Abbreviations CAM Crassulacean acid metabolism - FW fresh weight - PEP phosphoenolpyruvate     

Growth and development of cucumber Cucumis sativus L. in the prereproductive period under long photoperiods

When plants are grown in a greenhouse or in controlled environment growth rooms, prolonging the photoperiod, including towards continuous light, is one of the ways to increase plant productivity and energy savings. However, exposing some plant species to long photoperiods causes leaf injuries and growth reductions. We studied the effect of the photoperiod (8, 12, 16, 20, and 24 h) and photosynthetic photon flux density (60, 120, and 160 μmol/m² s PAR) on cucumber plants Cucumis sativus L. in a prereproductive period. It was shown that the response of the cucumber plants to a photoperiod over 20 h, including continuous light, depending on the plant age and light intensity, may include leaf movement or paraheliotropism, non-photochemical energy dissipation, and/or reversible photoinhibition of a reaction center of photosystem II, development of reversible chlorosis, reduction of a light-harvesting complex, and increase in the content of carotenoids. Reaction of immature and virginile plants to long photoperiods was different, which high-lights the need for experimental separation of the prereproductive period in terms of age states and consideration of this when developing crop production plan.     

Circadian rhythm leaf movement of Phaseolus vulgaris and the role of calcium ions

Legume plants, due to their distinctive botanical characteristics, such as leaf movements, physiological characteristics, such as nitrogen fixation, and their abilities to endure environmental stresses, have important roles in sustainable pastures development. Leaf movement of legume plants is turgor regulated and osmotically active fluxes of ions between extensor and flexor of pulvinus cause this movement. To determine the role of calcium ions in circadian leaf movements of Phaseolus vulgaris L., a radiotracer technique experiment using ⁴⁵Ca ions were employed. Measurements were taken during circadian leaf movements, and samples were taken from different parts of the leaflet. The ⁴⁵Ca β-particle activity reduced from leaflet base pulvinus to leaf tip. The pulvinus had the highest activity, while the leaf tip had the lowest. By increase of the ratio of ⁴⁵Ca β-particle activity within flexor to extensor (Fl/Ex) the midrib-petiole angle, as an indicator of leaf movement, increased linearly during circadian leaf movement (r = 0.86). The ⁴⁵Ca β-particle activity of Flex/Ext ratio reduced linearly (r = −0.88) toward midnight. In conclusion, it was found that calcium ions accumulation is opposite to the fluxes of osmatically active ions and water movement. Calcium ions accumulate at less negative water potential side of the pulivnus.Key words: pulvinus, extensor, flexor, leaf movement, rhythm, circadian, calcium, Phaseolus vulgaris, radioactive     

Rhythmic leaf movements in biloxi soybean and their relation to flowering

The rhythmic leaf movement of Biloxi soybean (Glycine max) and its relationship to the rhythmic flowering response were studied. The movements of fully expanded trifoliate leaves were recorded with kymographs and time lapse photography in growth chambers. A comparison between the leaf movement rhythm and the rhythmic flowering response indicates that a high degree of similarity exists between the two rhythms. A definite relationship was shown to exist between the direction of the leaf movement and the photophil-photophobe phases of the rhythmic flowering response.     

The effects of blue and far red light on rhythmic leaflet movements in samanea and albizzia

The opening of excised Samanea saman pulvini is promoted by prolonged blue or far-red irradiation. Far-red effects are attributed partially but not completely to lowering of the Pfr level. Two hours of continuous or pulsed blue light or pulsed far-red light (total dosage = 2.2 × 10¹⁸ quanta per square centimeter in all cases) also phase shifts the rhythm in Samanea while two hours of continuous blue light phase shifts the rhythm in the related plant Albizzia julibrissin. The same pigments appear to regulate opening and rhythmic phase shifting. The blue light-induced phase response curve has smaller advance and delay peaks and differs in shape from the curve induced by brief red light pulses absorbed by phytochrome. The blue absorbing pigment has not been identified, but it does not appear to be phytochrome acting in a photoreversible mode.     

The Damping and Reinitiation of the Circadian Rhythm of CO2 Output in Bryophyllum Leaves in Relation to their Malate Content

The circadian rhythm of CO₂ output in leaves of Bryophyllumfedtschenkoi damps out after 3–4 d in continuous darknessand a CO₂-free air stream at 15°C. The rhythm is reinitiatedafter a single exposure to white light of 2, 4, 6 or 8 h duration,damps out again after a further 3–4 d and can be reinitiatedfor a second time by a further exposure to light. During the exposure to light there is a burst of CO₂ outputconsistent with the decarboxylation of malate, and the rhythmbegins afterwards with an initial high rate of CO₂ fixation.Malate gradually accumulates in the leaves in continuous darknessto attain a maximum value (35 mol m^–3) at the time whenthe circadian rhythm disappears, and decreases to a low value(19 mol m^–3) after a 4 h exposure to light which reinitiatesrhythmicity. These results support the hypothesis that damping of the rhythmof CO₂ output in continuous darkness is due to the accumulationof malate in the leaf cells, eventually reaching such a levelthat its removal from the cytoplasm into the vacuole cannottake place, with the result that PEPc activity, upon which therhythm of CO₂ output depends, remains allosterically inhibited. Key words: CAM, circadian rhythm, Bryophyllum, CO₂-fixation, malate metabolism