Influence of day length and temperature on number of main stem leaves and time to flowering in lupin

A growth chamber experiment was carried out to investigate the influence of day length and temperature on the development of flowering in eight varieties of the three grain lupin species Lupinus albus (Wat and C3396), L. angustifolius (Gungurru, Polonez and W26) and L. luteus, (Juno, Radames and Teo). The plants were grown at two temperatures, 10°C and 18°C, in combination with five daylength regimes: 10, 14, 18, 24 h day at full light intensity and 10 h full light extended with 8 h low intensity light. Increased daylength decreased days from sowing to flowering in all varieties, but had little effect on thermal time to flowering in most varieties. However, C3396, W26 and Radames had a significantly longer thermal time to flowering at high, non‐vernalising temperature (18°C) at short daylengths. Low light intensity daylength extension did not significantly influence thermal time to flowering. For flower initiation, measured as number of leaves on the main stem three types of response were found. All varieties formed fewer leaves on the main stem at 10°C than at 18°C, although the two thermo‐neutral varieties of L. luteus, Juno and Teo, gave only a small response to temperature and daylength. In Polonez, Gungurru and Wat, low temperature decreased leaf number, but there was only a small response to changes in daylength. Three varieties, C3396, W26 and Radames, showed longer thermal time to flowering at 18°C with short daylengths. This could be explained by a greater number of main stem leaves formed at short daylength at non‐vernalising temperatures. Increased daylength decreased leaf number in these varieties, but never to a smaller number than for plants grown at 10°C. In these varieties, low intensity extension of the daylength had a similar (W26, Radames) or decreased (C3396) effect compared to full light extension. The hastening of time to flowering by long days could be separated into two effects: a high light energy effect hastened development by increasing the rate of leaf appearance in all varieties, while low light energy in thermo‐sensitive varieties was able to substitute for vernalisation by decreasing leaf number.     

Red light stimulates flowering and anthocyanin biosynthesis in American cranberry

Morphological responses of American cranberry (Vacciniummacrocarpon Ait, Ericaceae) to different light conditions (red,far-red, white light and sunlight) were examined. Root growth and development,stem elongation, leaf enlargement, de-etiolation of stem and leaf, flower budformation, and flowering of American cranberry were measured under each lightcondition and in the dark. It was found that red light promotes development ofroots and leaves, flowering, and de-etiolation of stem and leaf of Americancranberry. Stem elongation and etiolation of stem and leaf were shown infar-redlight and dark. Anthocyanin biosynthesis as phytochemical response in cranberryplants was most sensitive to red light. Estimation of anthocyanin levels indifferent parts of cranberry plant suggested that anthocyanins were presentonlyin red fruit skins, and not in peeled fruits, green fruits, green leaves, greenstems, roots and seeds.     

Climatic factors governing plant phenological phases along a Norwegian fjord

In the present project, the time of leaf budding and flowering, and partly also of fruit ripening, was studied over 3 years in different cultivated and native plants on a gradient along a western Norwegian fjord about 300 km long, from oceanic to relatively continental regions. In the plants investigated, flowering of the red currant was most strongly favoured by oceanic conditions in the outermost part of the fjord. On the other hand, flowering of the apple was earliest in the middle district, as were flowering of the common lilac and raspberry, while differences were small between the districts for flowering of the plum and pear. In the inner district, leaf budding of the apple was about 1.5 weeks earlier than flowering of the red currant, while these two phenophases, on average, occurred on the same day in the oceanic district. The time from 1 April to flowering was generally lengthened by increased precipitation in the pear, apple, lilac and raspberry, but not in the red currant and plum. By contrast, the period from leaf budding to flowering was significantly shortened in the plum by high precipitation. The present studies also indicated that leaf budding of the birch was favoured by the high minimum temperature and the relatively high precipitation normally found in the oceanic district. Partial correlations showed that increased precipitation delayed the flowering of both rowan and bird cherry trees; there was also a week effect on bud break in the same two species. The clear conclusion of the present study, therefore, is that various plant species react differently to various climatic factors ("phenological interception"), even in different phenophases within the same species. This means that the various species are best fitted to certain climatic regions and should preferably be planted there if other growth factors are satisfactory.     

Effect of Daylength on Phenol Metabolism in the Leaves of Salvia occidentalis

A method of phenol determination in plant leaves has been developed which is based on the in situ oxidation of these compounds in an atmosphere containing ammonia, followed by difference spectrophotometry. The development of the phenol pattern has been studied in each separate leaf of a Salvia occidentalis plant grown in short and in long days. During the light period the phenol content (mainly chlorogenic acid and isochlorogenic acids) increases in proportion to the length of this period, whereas during the subsequent dark period the phenol content decreases. This decrease does not continue during the second part of a dark period if that period is interrupted by a light break with red light. Instead a small increase is observed. This effect of red light can be reversed with far red light. It is argued that a correlation with flower induction in this short day plant can be construed if it is assumed that the continuous presence of certain o-dihydroxyphenols in the cytoplasm of leaf cells inhibits the synthesis or the transport of a flowering hormone.     

Effects of Photoperiod on the Apparent Viscosity of Leaf Cytoplasm in Kalanchoe blossfeldiana: 2. Some Long- and Short-term Effects of Daylength and Spectral Composition of Light

The effects of a range of daylength treatments upon the apparentviscosity of the mesophyll cytoplasm were tested in Kalanchoeand some other daylength-sensitive species by means of a centrifugationtechnique. In Kalanchoe, apparent viscosity increases with increasingshort-day induction, the rise being rapid initially but fallingoff subsequently in the same way as the flowering response.Since the response to light-break treatment is equivalent tolong-day conditions, the effect is truly photoperiodic. Theshort-day increase appears to be only partially reversible uponreturn to long-days. Single leaves may be treated and the effect is not translocatedto the opposite member of a leaf pair. The immediate response to change from light to dark and viceversa is oscillatory; e.g. in the dark an initial fall is succeededby a steep rise and then a more gradual fall in apparent viscosity. Light-breaks with red light are equivalent to white light, andthose with far-red light to darkness. No reversal of red effectsby far-red light has yet been demonstrated. In other species tested, apparent viscosity was significantlyhigher under short-day in Chrysanthemum and Michaelmas Daisy,and under continuous light in Epilobium, i.e. in the daylengthswhich induce flowering. The results are discussed in relationto the present theories of photoperiodism.     

A Temperature Effect on the Expression of Genotypic Differences in Flowering Induction in Antirrhinum majus

Three inbred lines of Antirrhinum majus and the F₁ generationsof crosses between them were scored for flowering time in ninegreenhouse and garden experiments. The inbreds fell into twogroups, the difference between which showed a marked interactionwith environments. The two lines (An 105, An 106) which weresimilar were earlier flowering than the third line (An 101)in those environments which produced generally early flowering,but were later than An 101 when the environmental conditionsled to late flowering. In all cases the F₁ generations wereat least as early as the earlier parent. Cabinet experiments identified temperature as the importantenvironmental factor when day length was kept constant at 16h. At 25°C, An 105 and An 106 were earlier than An 101 whileat 12°C, at which temperature the average flowering timewas much later, An 101 was earlier. The F₁ generations werelike An 105 and An 106 at 25°C but showed heterosis at 12°C. The differences in flowering time between genotypes were inall cases established by the time the first reproductive budsbecame visible (budding time). Thus a temperature differencewell outside the range of vernalizing temperatures is havinga striking effect on the phenotypic expression of genotypicdifferences determining the transition from vegetative to floweringdevelopment.     

The characteristics of light in floral induction in vitro of Cichorium intybus. The possible role of phytochrome

The action of light in the initiation of floral buds in vitro has been studied using monochromatic light qualities on root explants of a long day plant, Cichorium intybus L. cv. Witloof. Red light (660 nm, 0.30 W m^-2) promotes flowering, while far-red (730 nm, 0.31 W m^-2) and irradiation with combined red + far-red (0.20 + 0.41 W m^-2) have no effect. In short day conditions floral response can be obtained in two ways: 1) by interrupting the dark period with 5 brief irradiations of red light (0.45 W m^-2, 12 min) at regular intervals, although these are counteracted by far-red irradiations of equal intensity and duration; 2) by interrupting the long night with 5 h red light applied during the second third of the night, while at the beginning or at the end it is ineffective. Red light efficiency appears to depend on the photosynthetic activity of the tissues, so that flowering increases with increasing intensity of white light and is suppressed if no white light is supplied. The reproductive development is determined by the coordination of proper irradiation conditions with sufficient sensitivity of the perceiving meristematic cells. The period of highest sensitivity to environmental light conditions in the life cycle of a Cichorium root explant occurs between the 8th and the 16th day after the start of the culture. The data strongly suggest that phytochrome is involved in flower induction of Cichorium in vitro.     

Plasticity of crassulacean acid metabolism at subtropical latitudes: a pineapple case study

Plants with the crassulacean acid metabolism (CAM) express high‐metabolic plasticity, to adjust to environmental stresses. This article hypothesizes that irradiance and nocturnal temperatures are the major limitations for CAM at higher latitudes such as the Azores (37°45'N). Circadian CAM expression in Ananas comosus L. Merr. (pineapple) was assessed by the diurnal pattern of leaf carbon fixation into l ‐malate at the solstices and equinoxes, and confirmed by determining maximal phosphoenolpyruvate carboxylase (PEPC) activity in plant material. Metabolic adjustments to environmental conditions were confirmed by gas exchange measurements, and integrated with environmental data to determine CAM's limiting factors: light and temperature. CAM plasticity was observed at the equinoxes, under similar photoperiods, but different environmental conditions. In spring, CAM expression was similar between vegetative and flowering plants, while in autumn, flowering (before anthesis) and fructifying (with fully developed fruit before ripening) plants accumulated more l ‐malate. Below 100 µmol m^?2 s^?1, CAM phase I was extended, reducing CAM phase III during the day. Carbon fixation inhibition may occur by two major pathways: nocturnal temperature (<15°C) inhibiting PEPC activity and l ‐malate accumulation; and low irradiance influencing the interplay between CAM phase I and III, affecting carboxylation and decarboxylation. Both have important consequences for plant development in autumn and winter. Observations were confirmed by flowering time prediction using environmental data, emphasizing that CAM expression had a strong seasonal regulation due to a complex network response to light and temperature, allowing pineapple to survive in environments not suitable for high productivity.     

Photomorphogenesis, Photosynthesis, and Early Growth of Primary Leaves of Phaseolus vulgaris

The response of leaf tissue to white, blue, red, and far-redlight has been examined. Leaves on plants grown in darknessshow increased cell number, cell volume, and area when exposedto long periods (up to 48 h) of low-intensity red, blue, orfar-red radiation. This is believed to be a photomorphogenicresponse which does not involve photosynthesis. Leaves fromplants exposed to white light during germination do not usuallyrespond to red, blue, or far-red light. An exception to thiswas found for leaf discs which showed a larger increase in areathan the dark controls following exposure to far-red light for24 h. Leaf tissue from light-grown plants responds to high-intensitywhite light, probably through photosynthesis. Discs cut fromdark-grown plants and cultured in white light grow equally wellin air and CO₂-free conditions. Application of the photosyntheticinhibitor DCMU reduces growth and chlorophyll formation, however. It is concluded that light, perhaps acting through the phytochromemechanism, has initially a number of morphogenic effects includinginitiation of development of the photosynthetic apparatus. Theresponses to photomorphogenically active radiation do not persistand light effects through photosynthesis are rapidly initiatedand dominate the later stages of leaf growth.     

Inhibitory Action of Blue and Far-Red Light in the Flowering of Lemna paucicostata

In a new strain of short-day duckweed (Lemna paucicostata T-101), blue and far-red light-induced inhibition of flowering was investigated. Flowering of this strain failed to be induced under a short-day photoperiod of blue and far-red light, although it responded as a typical short-day plant in red and white light. When the short-day photoperiod of blue or far-red light was terminated by a 15 min red light pulse, flowering recovered completely. This inducing effect of red light was reversed by subsequent exposure to far-red light. Furthermore, it could be demonstrated that 30 min of blue light completely reversed the flowering inductive effect of 5 min red light and vice versa. Evidence is presented suggesting that the inhibitory action of blue and far red light may be due to the lowering of phytochrome P_fr levels below those required to start the dark reactions which lead to flowering. These results are discussed in relation to the time measurement system of photoperiodism.     

Postflowering photoperiod regulates vegetative growth and reproductive development of soybean

Soybean development is controlled by environmental factors, primarily photoperiod and temperature. To date, photoperiod effects on flowering have been well studied but the performances and mechanism of postflowering photoperiod responses have not been fully understood, especially for the photoperiod effects on vegetative growth after flowering. In the present study, the responses of vegetative growth and reproductive development in soybean to different postflowering photoperiod regimes were investigated in four separate experiments. Three varieties of different maturity groups (MG) including the early (Dongnong 36, MG 000), medium (Dandou 5, MG IV), and late (Zigongdongdou, MG IX) were exposed to two photoperiods, short (10, 12 h) and long (15, 16 or 18 h). The results showed that postflowering photoperiod not only regulated reproductive development but also affected vegetative growth. Even when flowers and pods were removed, short-day (SD) treatment promoted leaf senescence. The onset of leaf senescence among varieties tested appeared to be dependent on photoperiod sensitivity. Leaf senescence of the late-maturing variety of Zigongdongdou (sensitive to photoperiod) was delayed more significantly than that of the medium and early-maturing varieties (less sensitive to photoperiod). Long-day (LD) treatments delayed leaf senescence and seed maturation in the late-maturing variety of Zigongdongdou plants with only the SD-induced leaves produced before flowering. LD treatments imposed from the beginning bloom, beginning pod setting or beginning seed filling delayed leaf senescence and seed maturation of late-maturing soybean variety (Zigongdongdou). Results of night-break with red (R) and far-red (FR) light demonstrated that postflowering photoperiod responses of soybean were R/FR reversible reactions and the phytochromes seemed to be functional as receptors of photoperiod signals even after flowering. It was proposed that the regulation of photoperiod on development of soybean was effective from emergence through maturation, and the postflowering photoperiod signals were also mediated by phytochromes similar to those before flowering. The flowering reversion in late-MG soybean varieties under LD was a direct result of LD and was not due to secondary effect of abscission of pods and flowers. Soybean leaves not only received SD signals but also LD signals; furthermore, the LD effects reversed the SD effects and vice versa.     

Effects of Interactions between Low-temperature Treatments, Gibberellin (GA3) and Photoperiod on Flowering and Stem Height of Spring Rape (Brassica napus var. annua)

Exogenous gibberellin A₃(GA₃) reduced the number of leaf nodesat flowering and time to flowering and increased the stem heightat flowering in three genotypes of spring rape (Brassica napusvar.annua L.). The responses to GA₃were similar to those forlong days (LD) and low-temperature treatments, suggesting thatthe effect of photoperiod and the vernalization response areprobably mediated through gibberellins. The response to exogenousGA₃was greatest in non-cold-treated plants in short days (SD)suggesting that endogenous GAs are limiting in these conditions.CCC, an inhibitor of gibberellin biosynthesis, caused a smallincrease in the number of leaf nodes at flowering and time toflowering and a small decrease in the stem height at flowering,but unexpectedly, its effect was hardly influenced by the applicationof exogenous GA₃. Genotypes that showed the clearest responsesto the treatments with regard to the number of leaf nodes atflowering and time to flowering did not show the clearest responseswith regard to the stem height at flowering; the pattern ofresponses of the number of leaf nodes at flowering and timeto flowering was distinct from that of stem height at flowering.This indicates that flower formation and stem elongation areseparable developmental processes which may be controlled bydifferent endogenous gibberellins, different levels of a specificendogenous gibberellin, or different responses to gibberellin.Copyright 1999 Annals of Botany Company Brassica napus var. annua, gibberellin, photoperiod, spring rape, vernalization.     

Effects of temperature on performance and phenotypic selection on plant traits in alpine Ranunculus acris

Discovering temperature effects on the performance of tundra plants is important in the light of expected climate change. In this 4-year study on alpine Ranunculus acris, I test the hypothesis that temperature influences flowering phenology, reproductive success, growth, population dynamics, and phenotypic selection on quantitative traits, by experimental warming using open-top chambers (OTCs). Warming significantly advanced flowering phenology in only one season. Seed number and weight were significantly increased by warming during the first three seasons, but not in the fourth. Plants inside OTCs produced bigger leaves than control plants in the fourth season, but leaf number was unaffected by the OTC treatment. Despite increased seed number and weight, the density of flowering plants decreased inside OTCs compared to control plots, possibly because of a higher graminoid cover inside OTCs. Phenotypic-selection regression showed a significant selection differential and gradient in the direction of larger leaf sizes in control plants, whereas no selection on leaf size was detected on warmed plants. The direction and strength of selection on flowering time, flower number, and leaf number did not differ between control and warmed plants. The results suggest that increased reproductive output of R. acris may not be sufficient to maintain current population density under a denser vegetation cover. Received: 1 December 1998 / Accepted: 14 April 1999     

Some Effects of Photoperiod on Barley

Fourteen barley varieties originating in areas of differinglatitude were grown in controlled-environment rooms. Three treatmentswere given viz. 12, 15, and 18 hours light per day, and measurementswere made of time to flowering and leaf development. An analysisof the rate of leaf appearance and leaf size was made by themethods described. The effect of lengthening photoperiod wasto hasten flowering, reduce the leaf number before flowering,increase the rate of leaf emergence, and change the patternof leaf size up the stem, though varieties differed in the magnitudeof their response. The correlated changes found appear to conformto an hypothesis of internal competition for nutrients withinthe plant. Differences between these results and those of otherworkers are discussed in the light of this hypothesis.     

On phytochrome absorption and the phytochrome photoequilibrium in a green leaf: environmental sensitivity and photoequilibrium time

The average, corrected attenuance spectra for both spectral forms of phytochrome in a mature leaf were calculated. Optical masking by chlorophyll together with the detour effect (optical path lengthening effect) due to multiple light scattering led to large changes in both the Qy band shape and wavelength position and the effective intensity of the weak vibrational bands increases. The Pfr/Pr oscillator-strength-ratio between 400-750 nm (0.93 in vitro), becomes 1.63 in a leaf. Thus the dominant absorption form is Pfr. These two values permit calculation of the phytochrome photoequilibrium under conditions of "daylight" illumination both in vitro and in folia. These values are 0.6 and 0.38 respectively. Previous literature estimates for the situation in vitro, based on the 660/730 nm absorption ratio, yielded values close to 0.6. It is demonstrated that this large decrease in the phytochrome photoequilibrium in a leaf has the effect of translating this parameter to a position on the dose (red/far-red light ratio)-response (Pfr/Ptot) plot towards greater sensitivity to changes in the environmental red/far-red ratio. The increased sensitivity factor is almost five-fold for the "daylight" environment and is even greater for the various "shade-light" environments. The approximate time taken to attain photoequilibrium (1/e lifetime) has also been calculated for phytochrome in a leaf in different light environments. For the "daylight" environment the photoequilibration time is approximately 5 s, which increases into the 20-80 s interval under different degrees of "shade light". Thus, despite the strong optical masking by chlorophyll in a mature leaf, the phytochrome photoequilibrium is attained quite rapidly on a physiological time scale.     

Effect of Light Quality and Vernalization on Late-Flowering Mutants of Arabidopsis thaliana

We have analyzed the response to vernalization and light quality of six classes of late-flowering mutants (fb, fca, fe, fg, ft, and fy) previously isolated following mutagenesis of the early Landsberg race of Arabidopsis thaliana (L.) Heynh. When grown in continuous fluorescent illumination, four mutants (fca, fe, ft, and fy) and the Landsberg wild type exhibited a reduction in both flowering time and leaf number following 6 weeks of vernalization. A significant decrease in flowering time was also observed for all the mutants and the wild type when constant fluorescent illumination was supplemented with irradiation enriched in the red and far red regions of the spectrum. In the most extreme case, the late-flowering phenotype of the fca mutant was completely suppressed by vernalization, suggesting that this mutation has a direct effect on flowering. The fe and fy mutants also showed a more pronounced response than wild type to both vernalization and incandescent supplementation. The ft mutant showed a similar response to that of the wild type. The fb and fg mutants were substantially less sensitive to these treatments. These results are interpreted in the context of a multifactorial pathway for induction of flowering, in which the various mutations affect different steps of the pathway.     

Sucrose availability on the aerial part of the plant promotes morphogenesis and flowering of Arabidopsis in the dark

Conditions to promote dark morphogenesis and flower-ing in Arabidopsis have previously been limited to liquid cultures and to a few laboratory ecotypes. We have obtained development and flowering of Arabidopsis plants under complete darkness by growing them on vertical Petri dishes containing solid agar medium with sucrose. Under these conditions, all the ecotypes tested were able to develop, giving rise to etiolated plants that flowered after producing a certain number of leaves. Dark-grown plants showed similarities with phytochrome-deficient mutants and were different from de-etiolated or constitutive photomorphogenesis mutants such as det and cop. Late- and early-flowering ecotypes, showing large differences in flowering time and leaf number under long days, flowered with a similar number of leaves when grown in the dark. Rapid dark flowering of late-flowering ecotypes was not an effect of darkness but the result of the interaction between dark and sucrose availability at the aerial part of the plant, since sucrose also had an effect when plants were grown in the light. Gibberellin-deficient and insensitive mutants were delayed in the initiation of flowers in the dark, indicating a role for these hormones in flowering promotion in the dark. The late-flowering phenotype of mutants at different loci of the autonomous and long-day-dependent flowering induction pathways was rescued in dark growth conditions. However, the late-flowering phenotype of ft and fwa mutants was not rescued by sucrose either in the dark or in the light, suggesting a different role for these genes in flowering induction.     

A high proportion of blue light increases the photosynthesis capacity and leaf formation rate of Rosa × hybrida but does not affect time to flower opening

Alterations in light quality affect plant morphogenesis and photosynthetic responses but the effects vary significantly between species. Roses exhibit an irradiance‐dependent flowering control but knowledge on light quality responses is scarce. In this study we analyzed, the responses in morphology, photosynthesis and flowering of Rosa × hybrida to different blue (B) light proportions provided by light‐emitting diodes (LED, high B 20%) and high pressure sodium (HPS, low B 5%) lamps. There was a strong morphological and growth effect of the light sources but no significant difference in total dry matter production and flowering. HPS‐grown plants had significantly higher leaf area and plant height, yet a higher dry weight proportion was allocated to leaves than stems under LED. LED plants showed 20% higher photosynthetic capacity (A_max) and higher levels of soluble carbohydrates. The increase in A_max correlated with an increase in leaf mass per unit leaf area, higher stomata conductance and CO₂ exchange, total chlorophyll (Chl) content per area and Chl a/b ratio. LED‐grown leaves also displayed a more sun‐type leaf anatomy with more and longer palisade cells and a higher stomata frequency. Although floral initiation occurred at a higher leaf number in LED, the time to open flowers was the same under both light conditions. Thereby the study shows that a higher portion of B light is efficient in increasing photosynthesis performance per unit leaf area, enhancing growth and morphological changes in roses but does not affect the total Dry Matter (DM) production or time to open flower.     

Phylogenetic conservatism and trait correlates of spring phenological responses to climate change in northeast China

Climate change has resulted in major changes in plant phenology across the globe that includes leaf‐out date and flowering time. The ability of species to respond to climate change, in part, depends on their response to climate as a phenological cue in general. Species that are not phenologically responsive may suffer in the face of continued climate change. Comparative studies of phenology have found phylogeny to be a reliable predictor of mean leaf‐out date and flowering time at both the local and global scales. This is less true for flowering time response (i.e., the correlation between phenological timing and climate factors), while no study to date has explored whether the response of leaf‐out date to climate factors exhibits phylogenetic signal. We used a 52‐year observational phenological dataset for 52 woody species from the Forest Botanical Garden of Heilongjiang Province, China, to test phylogenetic signal in leaf‐out date and flowering time, as well as, the response of these two phenological traits to both temperature and winter precipitation. Leaf‐out date and flowering time were significantly responsive to temperature for most species, advancing, on average, 3.11 and 2.87 day/°C, respectively. Both leaf‐out and flowering, and their responses to temperature exhibited significant phylogenetic signals. The response of leaf‐out date to precipitation exhibited no phylogenetic signal, while flowering time response to precipitation did. Native species tended to have a weaker flowering response to temperature than non‐native species. Earlier leaf‐out species tended to have a greater response to winter precipitation. This study is the first to assess phylogenetic signal of leaf‐out response to climate change, which suggests, that climate change has the potential to shape the plant communities, not only through flowering sensitivity, but also through leaf‐out sensitivity.