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     

Benzyladenine-induced inhibition of flowering in Chenopodium rubrum in vitro is not related to the levels of isoprenoid cytokinins

The effect of 6-benzylaminopurine (BAP) on floweringand on endogenous levels of isoprenoid cytokinins wasinvestigated in explanted terminal shoots of Chenopodium rubrum cultivated in vitro. Themother plants were grown under continuous light andexplants were cut off when the 6th leaf primordiumoriginated at the shoot apex. The explants wereexposed to one dark period of 13 hours inductive forflowering or to continuous light on medium with orwithout BAP (0.05;0.2;0.4 mg.l^-1). Undernon-inductive conditions no flowering was observedeither in the control or after BAP treatment. Afterreceiving one inductive dark period, the controlexplants flowered. However, BAP application either atthe beginning of the inductive dark period and/orduring the following light cultivation inhibitedflowering and stimulated initiation and growth of leafprimordia. In the case of the most efficient BAPconcentration (0.05 mg.l^-1) flowering wasinhibited by 80% and the number of leaf primordia wasincreased by 3. Explantation caused a significantincrease in the total amount of endogenous cytokininsin the explants within first 13 h, provided they werekept in light. When explants were kept in darkness,only a slight increase in cytokinin levels wasobserved. BAP treatment had no influence on the levelsof endogenous cytokinins either in light or indarkness. We may thus conclude, that BAP applicationinhibited flowering of photoperiodically inducedterminal shoot explants and stimulated leaf primordiaformation with no significant effect on changes inlevels of endogenous isoprenoid cytokinins. This maysuggest the direct ability of BAP to regulate morphogenesis.     

The behaviour of the shoot apical meristem inChenopodium rubrum under conditions non-inductive for flowering

The results of different photoperiodic treatments preventing flowering and representing the control vegetative treatments in the studies of floral induction and differentiation were studied inChenopodium rubrum seedlings. A fully vegetative growth pattern of the meristem was maintained only in continuous light or after a photoperiodic treatment which consisted in a 15 min light break of the 8 h dark periods which themselves are a threshold for flowering inChenopodium. Light breaks applied to 10 h and longer dark periods did not prevent the changes resembling the early events of transition to flowering. Disappearance of zonal pattern, stimulation of apical growth, precocious initiation of leaf primordia and weakening of apical dominance have been observed. Flower formation did not follow. This work was supported by a grant from the Scientific Research Fund of SR Serbia.     

毛地黄(Digitalis purpurea)叶离体培养过程中光质与培养基对器官发生的交互作用

培养基成分影响毛地黄叶外值体的生长,不含BA的培养基中芽不能发生,无NAA的培养基中无根发生。光质的效应与培养基成分有关,黄、蓝、绿光在未加有机成分(NAA为0.ling·L~(-1))的培养基中能促进芽的生长,当NAA为0.5 mg·L~(-1)时则抑制芽的生长。红光、黑暗处理与培养基成分关系不大,一般均抑制发芽;根的发生不需要光。光质和培养基之间有交互作用。     

Growth and Dry-weight Distribution in Callistephus chinensis as Influenced by Lighting Treatment

Plants of two cultivars of Callistephus chinensis (Queen ofthe Market and Johannistag) were grown in 8 h of daylight perday with one of the following treatments given during the 16h dark period: (a) darkness—‘uninterrupted night’,(b) I h of light in the middle of the dark period—a ‘nightbreak’, (c) I min of light in every hour of the dark period—‘cycliclighting’, (d) light throughout—‘continuouslight’. The plants receiving uninterrupted dark periods remained compactand rosetted in habit with small leaves, while leaf expansion,stem extension, and flower initiation were promoted in all threeillumination treatments (b, c, d). Although these three treatmentsproduced similar increases in leaf area, continuous light wasthe most effective for the promotion of both stem growth andflower initiation while cyclic lighting was generally more effectivethan a I-h night break. Continuous light also caused more dry matter to be divertedto stems at any given vegetative dry weight and it was shownthat the stem weight ratio of both varieties was correlatedwith stem length.     

Chloroplast Protein Synthesis During Barley Leaf Growth and Senescence: Effect of Leaf Excision

Chloroplast protein synthesis was measured during the expansion,maturity and senescence of the oldest leaf of barley, Hordeumvulgare L., var. Hassan. A maximum rate of protein synthesisoccurred near the end of the expansion stage 9 d after sowing.Protein synthesis increased again at the beginning of senescenceand reached a new maximum at day 14 after sowing. Detachmentand incubation of leaves in the dark stimulated chioroplastprotein synthesis by fully expanded or by senescent leaves butnot by expanding leaves. If the detached leaves were kept inthe light, chloroplast protein synthesis was stimulated in fullyexpanded but not in senescent leaves. Short treatments (18 h)of leaf segments with growth substances in either light or indarkness, significantly changed the rate of protein synthesisshown by chloroplasts. The relationship between chloroplastprotein synthesis and leaf senescence is discussed. Key words: Hormones, light, maturity     

The Role of Light in Leaf and Flower Bud Break of the Peach (Prunus persica)

The effect of light on peach leaf and flower bud break was examined. It was found that leafless dormant shoots were light-perceptive organs. Darkness, after light preconditioning during dormancy, reduced leaf bud opening; however, light was obligatory when the shoots were preconditioned in the dark. Relatively short exposures to light were sufficient to stimulate leaf bud break. Terminal buds were less inhibited by darkness than were laterals. Flower bud break was inhibited in light after dark preconditioning. The red region of the spectrum was found to be active; the phytochorome system seems to be involved in the light reactions, as the red light effect was reversible with subsequent far-red illumination. Supplementary light, producing long-day conditions, could partly compensate for insufficient chilling. A possible sequence of reactions in the plant is suggested.     

Calcium and pH patterning at the apical meristem are specifically altered by photoperiodic flower induction in Chenopodium spp.

The apical meristem of the short‐day plant Chenopodium rubrum responds to photoperiodic flower induction with specific changes of pH and Ca²⁺ patterning immediately after the inductive dark span. The red–far‐red reversibility of the pH and Ca²⁺ patterning in response to night break treatments was measured in order to distinguish between the effect of the prolonged dark span per se and the specific effect of photoperiodic flower induction. In addition, the pH and Ca²⁺ patterning in C. rubrum was compared with the long‐day plant Chenopodium murale. The pH was visualized using the fluorescent probe carboxy SNARF‐1. Calcium ion concentrations were studied using a combination of Ca²⁺‐probes Fluo‐3 and Fura Red. It was observed that the specific changes in pH and Ca²⁺ patterning at the apical meristem of C. rubrum were abolished by the red‐light break. This effect was fully reversed with a subsequent single far‐red treatment. These observations infer the influence of phytochrome on both pH and Ca²⁺ patterning. Changes in pH and Ca²⁺ patterning upon flower induction were observed in both long‐day and short‐day plants. These results support the hypothesis that changes of pH and [Ca²⁺] in cells of the apical meristem are part of the pathway in signal transduction triggering flower initiation.     

Twilight effect: initiating dark measurement in photoperiodism of xanthium

Six experiments studied the effects of low levels of red and far-red light upon the initiation of measurement of the dark period in the photoperiodic induction of flowering in Xanthium strumarium L. (cocklebur), a short-day plant, and compared effects with those of comparable light treatments applied for 2 hours during the middle of a 16-hour inductive dark period. Red light, or red plus far-red, at levels that inhibit flowering when applied during the middle of the inductive dark period, either had no effect on the initiation of dark measurement (i.e., were perceived as darkness), or they delayed the initiation of dark measurement by various times up to the full interval of exposure (2 hours). Far-red light alone had virtually no effect either at the beginning or in the middle of the dark period. These results confirm that time measurement in the photoperiodic response of short-day Xanthium plants is not simply the time required for metabolic dark conversion of phytochrome. Results also suggest that the pigment system (phytochrome?) and/or responses to it may be significantly different as they function during twilight (initiation of dark measurement), and as they function during a light break several hours later. Possible mechanisms by which cocklebur plants detect the change from light to darkness are discussed.Comparing experimental results with spectral light measurements during twilight and with measurements of light from the full moon led to two conclusions: First, light levels pass from values perceived by the plant as full light to values perceived as complete darkness in only about 5.5 to 11.5 minutes, although twilight as perceived by the human eye lasts well over 30 minutes. Second, cocklebur plants probably do not respond to light from the full moon, even when most sensitive, 7 to 9 hours after the beginning of darkness.     

Induction of anthocyanin pigments in callus cultures of <Emphasis Type="Italic">Rosa hybrida</Emphasis> L. in response to sucrose and ammonical nitrogen levels

The influence of varied concentrations of sucrose and ammonical (NH₄⁺) nitrogen on in vitro induction and expression of anthocyanin pigments from Rosa hybrida cv. ‘Pusa Ajay’ was investigated. Of two explants (petal and leaf discs) selected and cultured under two different conditions (light and dark), leaf discs were found to be most suitable for callus initiation. Profuse and early callus induction was observed when leaf discs of rose were cultured under total dark conditions on solid Murashige and Skoog (MS) medium supplemented with 4.0 mg l⁻¹ 2,4-dichlorophenoxyacetic acid (2,4-D). Early pigment initiation, enhancement and maximum anthocyanin production from calluses were recorded when leaf discs were cultured on Euphorbia millii (EM) medium supplemented with 7% sucrose compared with calluses cultured at 4% sucrose concentration under 16/8 h (light/dark) photoperiod regime. Reducing the concentration of NH₄⁺ nitrogen in the solid MS medium led to slight improvement in anthocyanin production in rose leaf calluses.     

SINGLE‐CELL PULSE AMPLITUDE MODULATION FLUORESCENCE MEASUREMENTS OF THE GIANT DIATOM ETHMODISCUS (BACILLARIOPHYCEAE)1

Diurnal changes in effective yield (ΔF:F_m′), rapid light curves (RLCs), and induction/dark recovery time series were measured on individual cells of the giant diatom Ethmodiscus Castracane using active fluorescence (pulse amplitude modulation fluorometry). Unlike the co‐occurring diatom Hemiaulus and bulk phytoplankton, there was no observable diurnal down‐regulation of yield or relative electron transport rates in Ethmodiscus. Yields were constant at or near maximum values (0.7–0.8). Increases in ΔF:F_m′ during the initial actinic levels are consistent with dark nonphotochemical quenching mechanisms. Sustained actinic illumination (660 μmol photon·m^?2·s^?1) resulted in a ΔF:F_m′ of 0.2–0.3, but rapid recovery to near‐maximum values occurred in subsequent dark periods. Such recovery occurred even after exposure to full sunlight for 28 min, but not at 60 min. Thus, the lack of diurnal down‐regulation in Ethmodiscus is apparent, not real, and is an artifact of the time scale of sample extraction from net tows. These positively buoyant cells showed no evidence of routine photodamage, probably due to mixing and reduction in the average light exposure. The general patterns seen in RLCs from light‐and dark‐adapted higher plants are significantly different from those observed in Ethmodiscus. These results suggest that active fluorescence characteristics require careful examination to differentiate habitat‐ and taxon‐specific characteristics from light‐history effects. It is unclear whether the rapid recovery seen in Ethmodiscus is unique. The differences seen between Hemiaulus and Ethmodiscus from the same samples suggest that changes in community yield values measured in countertop systems could be the result of species replacement in addition to experimental or environmental perturbations.     

The influence of atmospheric humidity on leaf expansion in Beta vulgaris L.

Humidity effects on leaf expansion in sugar beets (Beta vulgaris L.) were explored using linear variable differential transducers. In continuous light, an increase in relative humidity (RH) from 35 to 61 or 75% resulted in a rapid increase in leaf extension which was maintained for 10–15 min before slowing down. Increasing RH from 35 to 85% increased leaf-extension rate (LER) in light and in dark and substantially diminished the ratio of dark LER to light LER, showing that high humidity can offset the reduction in LER which occurs on illumination. Episodes of irradiance with visible or infrared radiation resulted in diminished LER, indicating that increases in transpiration may reduce the flux of water available for leaf cell expansion. The hypothesis that leaf area expansion in sugarbeet may be controlled by the expansion of the leaf epidermis is discussed.Abbreviations IR infrared - LER leaf extension rate - LVDT linear variable differential transformer - RH relative humidity     

EFFECTS OF CANOPY POSITION AND IRRADIANCE ON THE LEAF PHYSIOLOGY AND MORPHOLOGY OF PENTACLETHRA MACROLOBA (MIMOSACEAE)

Pentaclethra macroloba (Willd.) Kuntze (Mimosaceae) is a dominant late-successional tree species in the Atlantic lowland forests of Costa Rica. Leaves of P. macroloba from three heights in the forest canopy were compared with leaves of seedlings grown in controlled environment chambers under four different irradiance levels. Changes in leaf characteristics along the canopy gradient paralleled changes resulting from the light gradient under controlled conditions. The effect of light or canopy position on light-saturated photosynthesis was small, with maximum photosynthesis increasing from 5 to 6.5 μmol m^−-2 s^−-1 from understory to canopy. Both chamber grown and field leaves showed large adjustments in photosynthetic efficiency at low light via reductions in dark respiration rates and increases in apparent quantum yields. Light saturation of all leaves occurred at or below 500 μmol m^−-2 s^−-1. Leaf thickness, specific leaf weight, and stomatal density increased to a greater extent than saturated photosynthesis with higher irradiance during growth or height in the canopy. As a result, there was a poor correspondence between leaf thickness and light-saturated photosynthesis on an area basis. It is concluded that Pentaclethra macroloba possesses the characteristics of a typical shade-tolerant species.     

ENDOGENOUS LEVELS OF INDOLE-3-ACETIC ACID IN SYNCHRONOUS CULTURES OF CHLORELLA PYRENOIDOSA12

Endogenous levels of indole-3-acetic acid were mesaured in synchronous cultures of Chlorella pyrenoidosa (TX-7-11-05). The cultures were synchronized by alternating light:dark periods of 15:9 hr at a temperature of 40 ± 1 C. After 2 synchronous cycles the cultures were exposed to a low light treatment of 350 ± 100 ft-c. The time to incipient cell division under these conditions was 6 hr and 15 min. Samples were taken at 3 sampling periods during the low light treatment period:low light 0 hr (LL0); low light 3 hr (LL3); and low light 6:15 hr (LL6:15). The algal extracts were analyzed by a fluorometric procedure which measured the indole-α-pyrone product formed by the action of the trifluoracetic acid-acetic anhydride reagent with IAA. The IAA levels increased gradually from the autospore stage (5.19 μg × 10^?4/mg dry wt) to the adolescent stage (7.13 μg × 10^?4/mg dry wt) and more rapidly when approaching the ripened adult stage (14.55 μg × 10^?4/mg dry wt). The mean percentage increase from autospore to adolescent was 36.9%, and from adolescent to ripened adult 104.6%. The total percentage increase from autospore to adult was 180.3%. Levels of IAA were 2 times higher just prior to division than in the autospore stage.     

Light,leaf age,and leaf nitrogen concentration in a tropical vine

Summary Tropical vines in the Araceae family commonly exhibit alternating periods of upward and downward growth, decoupling the usual relationship between decreasing light environment with increasing age among the leaves on a shoot. In this study I examined patterns of light, leaf specific mass, and leaf nitrogen concentration in relation to leaf position, a measure of developmental age, in field collected shoots of Syngonium podophyllum. These data were analyzed to test the hypothesis that nitrogen allocation parallels within-shoot gradients of light availability, regardless of the relationship between light and leaf age. I found that leaf nitrogen concentration, on a mass basis, was weakly correlated with leaf level light environment. However, leaf specific mass, and consequently nitrogen per unit leaf area, were positively correlated with gradients of light within the shoot, and either increased or decreased with leaf age, providing support for the hypothesis that nitrogen allocation parallels gradients of light availability.     

THE INDUCTION OF LEAF TUMORS BY AGROBACTERIUM TUMEFACIENS

Using carborundum as an abrasive and light rubbing with a culture of Agrobacterium tumefaciens, leaves of various species of bean and tobacco develop tumors on the leaf lamina. The induction of these tumors requires wounding, the presence of a virulent strain of the bacterium and is due to the bacterium, not substances released into the bacterial culture medium during growth. Observations of the histology and cytology of these tumors on the primary leaves of pinto bean show no significant differences from the more commonly studied stem tumors. The tumors on pinto beans first appear as chlorotic nests of dividing cells which gradually accumulate chlorophyll, eventually becoming dark green in color as opposed to the surrounding leaf tissue which is completely chlorotic at this stage. Tumor development is enhanced by a dark period following inoculation while growth of the leaf is essentially stopped. The tumors thus exhibit a pattern of growth and development independent of that of the normal leaf. The number of tumors obtained on pinto bean leaves was found to depend on the concentration of bacteria in the inoculum and on the age of the plants. A sharp peak in response was observed at about 7 days from planting. Best results were obtained by adding the bacterium at the time of wounding. The tumors were shown to differ from IAA-induced leaf proliferations with respect to their point of origin on the leaf, morphology, physiology and development.     

Leaf expansion in Rhamnus alaternus L. by leaf morphological, anatomical and physiological analysis

Morphological, anatomical and physiological traits of Rhamnus alaternus during leaf expansion were analysed. Bud break occurred when mean air temperature was 14.1 ± 1.2°C, and it was immediately followed by the increase of leaf area and leaf dry mass. The highest leaf expansion rates happened during the first 22 days of the process. Leaf area and leaf dry mass reached the steady-state value 46 and 62 days after bud break, respectively. Net photosynthesis increased from bud break to full leaf expansion, and total chlorophyll content had the same trend, confirmed by the correlation between the two variables. Leaf dark respiration peaked during the first 11 days of leaf expansion, then decreased and reached a steady-state value 34 days after bud break. R. alaternus completed cell division and cell enlargement of the epidermal tissue 28 days after bud break, and the ones of the mesophyll tissue at full leaf expansion. The results underline that morphological, anatomical and physiological leaf traits in R. alaternus are indicative of a less sclerophyllous species (i.e. higher specific leaf area) compared with other Mediterranean evergreen species. Moreover, the higher fraction of mesophyll volume occupied by the intercellular air spaces, and the ability to end the leaf expansion process before air temperature might be a limiting factor, makes R. alaternus closer to the mesophyte species.     

CELL DIVISION STUDIES OF THE SHOOT APEX OF DATURA STRAMONIUM DURING TRANSITION TO FLOWERING

Seedlings of Datura stramonium L., although not photoperiodically sensitive, are useful for floral transition studies when raised in a growth chamber at a constant temperature of 25 C with a photoperiod of 8 hr of light (1,600-2,000 ft-c) and 16 hr of darkness. A terminal flower is formed after the seventh or eighth leaf primordium is produced. A constant rate of leaf initiation up to the time of flowering enables specific apical stages to be obtained and studied. Changes in the mitotic index, substantiated with calculated rates of cell division (measured by the accumulation of metaphases following treatment with colchicine) were studied in shoot apical zones during transition to flowering. Fluctuations in the mitotic index of each zone in the vegetative and transition apex with respect to apical stage as well as time of day were not statistically significant. The mitotic index of the summit zone of the vegetative apex was significantly lower than in the other zones whose mitotic indices were not significantly different from one another. During floral transition the mitotic index of the summit zone as well as the central zone (just below the summit zone) significantly increased while no significant changes were detected in the flank zones. It was shown that the mitotic index could be considered representative of the rates of cell division in Datura.     

Light Breaks and Fruit-Body Maturation in Coprinus congregatus: Dark Inhibitory and Dark Recovery Process

Experiments were conducted to better understand the inhibitoryeffect of lightduring the dark-induced process of fruit-bodysporulation of Coprinus congregatus Bull, ex Fr. Light-initiatedfruit-body primordia were subjected to different dark periodsinterrupted by a short blue light break at different times.The sporulating response depended on the duration of the darkperiod following the light break. For any inductive dark periodlonger than 3.5 h, a period of darkness lasting half as longas the inductive night completely inhibited fruit-body maturationwhen given after the light break (dark inhibitory process).Longer dark periods after the light break causedrecovery ofthe maximal sporulating response (dark recovery process). Theeffects of the dark inhibitory and the dark recovery processwere alternately reversible, the sporulating response dependingon the duration of darkness after the last light break. Studyof the time course of sporulation showed that a new dark-inducedprocess of fruit-body sporulation was initiated by the beginningof the dark period after the light break. (Received August 2, 1982; Accepted May 6, 1983)