Photothermal model of plant development

The development of plants depends on the photoperiod length, light intensity, temperature, and length of light day integral. The reaction of a plant to the day length or daily light integral can depend on both the range of studied light intensities and photoperiod. Based on the data concerning the effects of light and thermal integrals on the developmental rate of plants of different photoperiodic groups, a photothermal model of plant development was proposed. The model was used to calculate the lengths of optimal photoperiods and ranges of daily temperature gradients ensuring the highest developmental rate of some plants, such as soybean, wheat, cucumber, and barley.     

The Effects of Temperature, Photoperiod and Light Integral on the Time to Flowering of Pansy cv. Universal Violet (ViolaxwittrockianaGams.)

The effects of temperature, photoperiod and light integral onthe time to first flowering of pansy (ViolaxwittrockianaGams)were investigated. Plants were grown at six temperatures (meansbetween 14.8 and 26.1 °C), combined with four photoperiods(8, 11, 14 and 17 h). The rate of progress to flowering increasedlinearly with temperature (up to an optimum of 21.7 °C)and with increase in photoperiod (r²=0.91, 19 d.f.), the latterindicating that pansies are quantitative long day plants (LDPs).In a second experiment, plants were sown on five dates betweenJuly and December 1992 and grown in glasshouse compartmentsunder natural day lengths at six temperatures (means between9.4 and 26.3 °C). The optimum temperature for time to floweringdecreased linearly (from 21.3 °C) with declining light integralfrom 3.4 MJ m^-2d^-1(total solar radiation). Data from both experimentswere used to construct a photo-thermal model of flowering inpansy. This assumed that the rate of progress to flowering increasedas an additive linear function of light integral, temperatureand photoperiod. Independent data from plants sown on threedates, and grown at five temperatures (means between 9.8 and23.6 °C) were used to validate this model which gave a goodfit to the data (r²=0.88, 15 d.f.). Possible confounding ofthe effects of photoperiod and light integral are discussed. Pansy;Violaxwittrockiana; flowering; photo-thermal model; temperature; photoperiod; light integral     

The Effects of Temperature and Light Integral on the Phases of Photoperiod Sensitivity inPetuniaxhybrida

Flowering in petunias is hastened by long days, but little isknown about when the plants are most sensitive to photoperiod,or how light integral or temperature affect such phases of sensitivity.The effects of these factors on time to flowering was investigatedusing reciprocal transfer experiments between long (16 h d^-1)and short days (8 h d^-1). The effect of light integral on thephases of photoperiod sensitivity was examined using two sowingdates and a shading treatment (53% transmission). The effectsof temperature were investigated by conducting reciprocal transferexperiments in glasshouse compartments at five temperature regimes(means of 13.7, 19.2, 22.3, 25.0 and 28.7 °C). The lengthof the photoperiod-insensitive juvenile phase of development,when flowering cannot be induced by any environmental stimulus,was sensitive to light integral; low light integrals prolongedthis phase, from 23 d at 2.6 MJ m^-2d^-1to 36 d at 1.6 MJ m^-2d^-1(totalsolar radiation). The length of this development phase was shortest(12.5 d) at 21 °C; it was longer under cooler (21 d at 13.5°C) and warmer temperatures (17.6 d at 28.3 °C). Afterthis phase, time to flowering was influenced greatly by photoperiod,with long days hastening flowering by between 28 and 137 d,compared with short days. Plants also showed some sensitivityto both temperature and light integral during this phase, butthe duration of the final phase of flower development, duringwhich plants were photoperiod-insensitive, was dependent primarilyon the temperature at which the plants were grown; at 14.5 °C,33.9 d were required to complete this phase compared with 11.4d at 25.5 °C. The experimental approach gave valuable informationon the phases of sensitivity to photothermal environment duringthe flowering process, and could provide the basis of a morephysiologically-based quantitative model of flowering than hashitherto been attempted. The information is also useful in thescheduling of lighting and temperature treatments to give optimalflowering times of high quality plants.Copyright 1999 Annalsof Botany Company Petunia,Petuniaxhybrida, juvenility, flowering, photoperiod, temperature, light integral, reciprocal transfer.     

Adventitious bud production on explants of Begonia×hiemalis depends on the developmental state of the donor plant

In vitro responses can be influenced by the developmental status of the donor plant tissue. The effects of the donor plant photoperiod and the developmental stage of the plant on organogenesis of petiole explants of Begonia × hiemalis cv. Schwabenland Pink are reported. Long day plants had progressively more branches, total stem length, leaf area, and branch and shoot mass. In short days, flowering was earlier and a greater proportion of dry weight accumulation was allocated to reproductive structures. Similar explant responses were obtained from all developmental stages until flowering was well advanced in short days and then the regenerative capacity diminished. Primary measurements of donor leaves (length, area and weight) at the time of explant removal were not well correlated with adventitious bud production. Loss of regeneration was not determined by tissue or plant age but was associated with the progressive development of flowers. Thus the donor plant photoperiod only indirectly affected bud production. Organogenesis decreased with duration of short days but increased in long days and thus both the duration of the multiplication phase and the intensity of the in vitro response was enhanced by maintaining donor plants in long days.     

Diurnal Periodicity and Plaut Growth

The experiments were carried out to investigate whether other plant species, in addition to tomato plants, show injury symptoms when grown for 2 to 4 weeks in an aperiodic environment and to obtain information about physiological mechanisms involved in the response to the absence of environmental periodicity. The growth of seedlings of pea, peanut, and soybean, exposed to different daylengths at constant temperature, increased with Increasing length of the light period up to 16 to 20 hours, defending on the species. Further lengthening of the photoperiod did not result in significant increases in dry matter accumulated. The absence of environmental periodicity did not cause injury in these three species. Tomato plants responded in an entirety different manner. The optimal photoperiod for dry matter production by tomato plants was 18 hours and photoperiods longer than 20 hours caused interveinal chlorosis. Thus, tomato plants have an absolute requirement for a daily periodicity, white the other species do not in short-term experiments. Under conditions of constant temperature development of chlorosis by tomato plants may be prevented by a daily dark period of 4 hours or longer or by a daily period of drastically lowered tight intensity. Complete darkness is not essential, however. This suggests that development of chlorosis is not mediated through a photoperiodic response system. Involvement of a circadian oscillation may also be excluded. Aperiodic environmental conditions appear to affect the physiology of the tomato plant in a direct manner, possibly by influencing chlorophyll synthesis or degradation.     

The influence of thermoperiod on cucumber growth and development

We studied the influence of gradient temperature regimes on various parameters of the formation of above-the-ground and underground organs of cucumber plants, such as rate of leaf appearance, rate of growth, duration of growth and length of leaves, and the rate of growth of above-the-ground organs and roots. The plants were grown under the controlled conditions: at different combinations of day and night temperature, illumination 100 Wt/m2, and 12 h photoperiod. The comparison of constant and fluctuating diurnal temperature regimes has shown that in the optimal area for all studied indices, the highest values were recorded at the constant daily temperature (25 degrees C for all growth indices of above-the-ground organs and 20 degrees C for growth of roots), while all gradient regimes either did not affect, or exerted inhibitory effects on the plant. The main acting fluctuating temperatures, that exerted stimulating effects, combined low hardening (15 degrees C) and optimal temperatures (25 degrees C), which was earlier described for animals. The 15/35 and 35/15 degrees C combinations were unambiguously inhibitory, since both temperatures are hardening for the cucumber. A lesser stimulating effect of the developmental rate in a plant, as compared to poikilothermic animals, could be due to a greater autonomy of plant ontogenesis because of autotrophy and, correspondingly, a greater degree of homeostasis. The mechanisms accounting for the reactions to temperature gradients are similar in different groups of ectotherms.     

Influence of Thermoperiod on Growth and Development in Cucumber

We studied the influence of gradient temperature regimes on various parameters of the formation of shoots and roots of cucumber plants, such as rate of leaf appearance, rate of growth, duration of growth and length of leaves, and the rate of growth shoots organs and roots. The plants were grown under the controlled conditions: at different combinations of day and night temperature, illumination 100 W/m², and 12 h photoperiod. The comparison of constant and fluctuating diurnal temperature regimes has shown that in the optimal area for all studied indices, the highest values were recorded at the constant daily temperature (25°C for all growth indices of shoots and 20°C for growth of roots), while all gradient regimes either did not affect, or exerted inhibitory effects on the plant. Outside the optimum area, the effects of gradient temperatures differed. The main acting fluctuating temperatures, that exerted stimulating effects, combined low hardening (15°C) and optimal temperatures (25°C), which was earlier described for animals. The 15/35 and 35/15°C combinations were unambiguously inhibitory, since both temperatures are hardening for the cucumber. A lesser stimulating effect of gradient temperatures on the developmental rate in a plant, as compared to poikilothermic animals, could be due to a greater autonomy of plant ontogenesis because of autotrophy and, correspondingly, a greater degree of homeostasis. The mechanisms accounting for the responses to temperature gradients are similar in different groups of ectotherms.     

Photoperiod and root-zone temperature: Interacting effects on growth and mineral nutrients of maize

Factorial effects of photoperiod (6, 12 and 18 h) and root-zone temperatures (9, 15 and 21°C) on the growth and mineral nutrient concentration and partitioning in maize (Zea mays L.) were investigated. Strong interactions were observed between photoperiod and root-zone temperature on the growth and concentration of numerous mineral elements in the plant tops and roots. For example, a threefold increase in photoperiod (from 6 to 18 h) did not affect the growth of tops or roots if the root-zone temperature was 9°C but increased them each by eightfold if the root-zone temperature was 21°C. On the other hand, raising the root-zone temperature from 9 to 21°C increased the growth of tops and root each by ca. threefold when plants were grown with 6 h of light. At 18 h photoperiod, however, plant growth was increased 20- to 30-fold by the same rise in the root-zone temperature. The concentrations of different mineral elements in the roots and tops were affected quite differently by the interacting effects of photoperiod and root-zone temperature. In general, increasing the photoperiod at a given root-zone temperature decreased the concentrations of elements while increasing the root-zone temperature at a given photoperiod increased the concentrations of most elements in both roots and tops. The exceptions were K and B which reacted opposite to each other: K concentration in both tops and roots was relatively insensitive to photoperiod but very sensitive to root-zone temperature and the reverse was true for boron. The relative insensitivity of plant growth to increased day length as long as the roots are subjected to suboptimal (low) soil temperatures may have survival significance and point to the predominant role of root temperature over that of day length in the early growth of maize. A possible mechanism by which photoperiod and root-zone temperature might interactively alter the nutrient uptake by the roots is discussed.     

The genetic basis of flowering responses to seasonal cues

Plants respond to the changing seasons to initiate developmental programmes precisely at particular times of year. Flowering is the best characterized of these seasonal responses, and in temperate climates it often occurs in spring. Genetic approaches in Arabidopsis thaliana have shown how the underlying responses to changes in day length (photoperiod) or winter temperature (vernalization) are conferred and how these converge to create a robust seasonal response. Recent advances in plant genome analysis have demonstrated the diversity in these regulatory systems in many plant species, including several crops and perennials, such as poplar trees. Here, we report progress in defining the diverse genetic mechanisms that enable plants to recognize winter, spring and autumn to initiate flower development.     

Effect of latitude on flavonoid biosynthesis in plants

The growth conditions in different latitudes vary markedly with season, day length, light quality and temperature. Many plant species have adapted well to the distinct environments through different strategies, one of which is the production of additional secondary metabolites. Flavonoids are a widely spread group of plant secondary metabolites that are involved in many crucial functions of plants. Our understanding of the biosynthesis, occurrence and function of flavonoids has increased rapidly in recent decades. Numerous studies have been published on the influence of environmental factors on the biosynthesis of flavonoids. However, extensive long‐term studies that examine the effect of the characteristics of northern climates on flavonoid biosynthesis are still scarce. This review focuses on the current knowledge about the effect of light intensity, photoperiod and temperature on the gene–environment interaction related to flavonoid biosynthesis in plants.     

中红侧沟茧蜂滞育诱导和滞育茧的冷藏

中红侧沟茧蜂Microplitis mediator (Haliday)是夜蛾科害虫低龄幼虫的重要寄生蜂。田间实验表明,在冀中地区秋季田间条件下,当日平均气温为21.5℃、日平均光照时间为12 h 33 min时,少数个体进入滞育;当气温降至17.9℃以下、日光照时间缩短到11 h 45 min以下时,全部个体进入滞育。室内模拟实验结果表明,在17～26℃、光照时间10～14 h范围内,随着温度的降低和光照时间的缩短,滞育率明显提高。高温能抵消短光照对滞育诱导的影响,在26℃下,短光照不能诱导滞育。因此,低温和短光照是诱导该种天敌昆虫滞育的主要因子。中红侧沟茧蜂感受滞育信号的敏感期为低龄幼虫期,以预蛹（茧）进入滞育。低龄幼虫感受滞育信号以后,需要在滞育环境中发育到老熟幼虫才能全部进入滞育。将室内诱导的滞育茧在4℃左右环境条件下冷藏240天,成蜂的羽化率和寄生能力与没有冷藏的非滞育茧差异不显著;冷藏300天,滞育茧仍有81.4%可以正常羽化。本项研究结果为中红侧沟茧蜂的规模化、标准化生产提供了科学的依据。     

The effect of short-term daily temperature drops on the processes of organogenesis in <Emphasis Type="Italic">Cucumis sativus</Emphasis> L. under different photoperiods

The effect of nightly temperature drops of different durations (2, 4, and 6 h) on the processes of apical and axillary meristem organogenesis was studied in young Cucumis sativus L. under short photoperiod (day/night, 10/14 h), long photoperiod (16/8 h), and continuous light. Nightly temperature drops for 2 h had no effect on cucumber development under all studied photoperiods; however, longer temperature drops (4–6 h) accelerated the development under long photoperiod and continuous light. Short-term exposures to low temperature under continuous light considerably increased lateral branching of cucumber plants.     

光周期影响植物花时的分子机制

日长感知是植物所具有的重要的生物学功能,光周期是决定植物开花时间的关键环境因子之一。光周期的暗期长度是决定植物成花的决定因素。通过形态学和遗传学研究,揭示了光周期敏感的一些遗传特性,并确定了光敏感指数的标准。构建了光周期性状相关的分子标记连锁图谱,是进行基因定位、克隆和分子标记辅助选择的重要基础工作,也是进行光周期机理研究的有效途径。通过模式植物拟南芥的研究,建立了一个长日促进开花的遗传途径。它的机理可以综合为:光和感光信息体系结合产生信号并传导,CO表达被激活。在每日日长循环、光体系及遗传背景的变化基础上,如果CO的表达和日长状况协调,那么CO激活FT表达,随后开花。水稻、小麦、玉米等作物在光周期机理研究方面也取得了一些进展。     

Flowering responses to light and temperature

Light and temperature signals are the most important environmental cues regulating plant growth and development. Plants have evolved various strategies to prepare for, and adapt to environmental changes. Plants integrate environmental cues with endogenous signals to regulate various physiological processes, including flowering time. There are at least five distinct pathways controlling flowering in the model plant Arabidopsis thaliana: the photoperiod pathway, the vernalization/thermosensory pathway, the autonomous floral initiation, the gibberellins pathway, and the age pathway. The photoperiod and temperature/vernalization pathways mainly perceive external signals from the environment, while the autonomous and age pathways transmit endogenous cues within plants. In many plant species, floral transition is precisely controlled by light signals(photoperiod) and temperature to optimize seed production in specific environments. The molecular mechanisms by which light and temperature control flowering responses have been revealed using forward and reverse genetic approaches. Here we focus on the recent advances in research on flowering responses to light and temperature.     

The molecular basis of photoperiodism

The rotation of our planet results in regular changes in environmental cues such as daylength and temperature, and organisms have evolved a molecular oscillator that allows them to anticipate these changes and adapt their development accordingly. In many plants, the transition from vegetative to reproductive growth is controlled by photoperiod, which synchronises flowering with favourable seasons of the year. Here, we describe the notable progress that has been made in identifying the molecular mechanisms that measure daylength and control of flowering time in Arabidopsis, a long day (LD) plant, and in rice, a short day (SD) plant. Although the components of the Arabidopsis regulatory network seem to be conserved in other species, the difference in the function of particular genes may contribute to the reverse response to daylength observed between LD and SD plants. We also highlight the recent advances in understanding the regulatory mechanisms that underlie other developmental transitions controlled by photoperiod, including tuberisation and the onset of dormancy in the buds of perennial plants.     

Daily temperature gradients and processes of organogenesis in apical meristem of Cucumis sativus L

We studied the influence of daily temperature gradients on organogenesis in apical and axil shoot meristems at different developmental stages in Cucumis sativus L. The level of organogenic activity of meristems was determined according to the number of leaf primordia on the main and lateral shoots, number of 2nd order shoots, and rudiments of flowers of different levels of development. At the studied ontogenetic stages (mesotrophic seedling or juvenile state), plants were grown under the controlled conditions: photoperiod 12 h, light intensity 100 Wt/m2, range of mean daily temperatures 20 ... 30 degrees C, and daily temperature gradients -20 ... +20 degrees C. After the temperature treatment, some plants were returned to the optimal, for growth and development, conditions for two weeks (aftereffect). Three types of organogenic activity of meristems in response to the influence of variable daily temperatures were described: stimulation, inhibition, or absence of effect. The phenomenon of stimulation includes two subtypes: optimization, when a maximum effect, observed at other constant temperatures, was attained under the influence of variable temperatures and maximization, when maximum values markedly exceeded those at constant temperatures. The patterns described are preserved on the whole in the aftereffect of daily temperatures.     

Induction of leaf senescence in Arabidopsis thaliana by long days through a light-dosage effect

Given the influence of photoperiod on reproductive development and whole-plant senescence in monocarpic plants, one would suspect that leaf senescence in these plants might be under photoperiodic control. In Arabidopsis thaliana , which is monocarpic and also a nonobligate long-day (LD) plant, LDs (16 h, 300 μmol m⁻² s⁻¹) caused leaves to die earlier than did short days (SDs, 10 h). Since leaf longevity was not paralleled by the reproductive development in the present study, the reproductive structures did not seem to be the primary controls of leaf senescence. The LD effect appeared to depend on the amount of light rather than on day length, for leaves given LDs at reduced light intensity (180 μmol m⁻² s⁻¹) lived longer than those in LDs with full light. In addition, the higher light intensity promoted chlorophyll loss and anthocyanin accumulation in LDs. Thus, senescence of these leaves seems to be governed by light dosage rather than photoperiod. Light may play a natural role in promoting the senescence of A. thaliana leaves.     

Improving quantitative flowering models through a better understanding of the phases of photoperiod sensitivity.

A quantitative understanding of the phases of sensitivity to photo-thermal environment is important if the accuracy of flowering models is to be improved and if the timing of long and short day treatments in protected cropping is to be optimized. A simple method of quantifying the duration of the phases of sensitivity to photoperiod is through the use of reciprocal transfer experiments where plants are transferred between long and short days at regular intervals throughout development. The advantages and disadvantages of different analytical approaches used to analyse such data sets are examined. Inconsistencies between the approaches are highlighted, as are differences in the way authors have interpreted data. The problem of confounding the effects of photoperiod and light integral is considered, as is the need to separate the number of inductive cycles needed for flower commitment from the length of the juvenile phase. The effects of photo-thermal environment on the duration of these phases of photoperiod sensitivity are discussed, together with topics requiring further development.     

Phenotypic Plasticity of Capitulum Morphogenesis in Microseris pygmaea (Asteraceae: Lactuceae)

Inbred populations of the annual Chilean species Microserispygmaea show phenotypic plasticity in the number of floretsper capitulum. In order to find out how this plastic variationmay arise during development, two inbred lines (A92 and C96)were grown under short day conditions. Groups of plants fromeach strain were transferred to long day conditions at about2 week intervals. In this way we introduced variation for plantsize (number of leaves per plant) at onset of flowering. Thenumber of florets per mature capitulum increased linearly withplant size. After transfer to long day conditions, plants wereharvested daily for light microscopic measurements of meristemwhole mounts. Only the first capitulum of each plant was analysed.All florets were formed after 12 d in strain C96 and after 14d in strain A92. In order to detect the effect of plant sizeon morphogenesis, we performed a multiple regression analysisof developmental parameters on time and number of leaves. Widthand height of the capitulum receptacle increased daily witha growth rate depending on the starting size. Differences inmeristem size were detected already in vegetative plants ofdifferent sizes. In contrast, there was no influence of plantsize on floret primordium size. We combined the multiple regressionmodels in one simple model for prediction of floret numbersfrom numbers of leaves per plant at onset of flowering. Predictionsof this model agree with observed relationships in both inbredlines.Copyright 1994, 1999 Academic Press Asteraceae, capitulum, inflorescence, meristem, meristic character, Microseris pygmaea, morphogenesis, phenotypic plasticity     

Kinetics of the Daily Rate of Photosynthesis at Low Temperatures for two Conifers

The daily course of photosynthesis at low temperatures in 2 coniferous species, Pinus ponderosa Laws., and Pseudotsuga menziesii (Mirb.) Franco, were studied using controlled environment facilities. After having been grown at a 23° day, and 19° night for a year, seedlings were acclimatized for 4 months to either a 3°, 7° or 11° day all under 1200 ft-c of light and followed by a 16-hour night at 3°. Measurement of photosynthesis at 1200 ft-c revealed 3 separate responses. First, the rapidity at which the plants attained their maximum photosynthesis when the lights were turned on depended upon the species, the current temperature, and the previous temperature condition to which the plants had become acclimatized. The warmer the day temperature the sooner the daily maximum was reached. Second, fluctuations in the rate of photosynthesis during the day varied with the species and the day temperature. Photosynthesis in both fir and pine kept at an 11° day and pines kept at a 7° day attained a daily peak rate followed by a decline. This decline occurred even though temperature and light were kept constant, the CO₂ level was returned to 320 ppm from 290 ppm, and the plants were kept well watered. At a 3° day neither species showed this decline. Third, a plant transferred to another temperature acquired a new stable daily photosynthetic pattern. The number of days required for stabilization depended upon the previous temperature history of the plant. The adjustment rate was faster when the temperature was raised than when it was lowered.