Flowering requirements of Polymnia canadensis (Asteraceae) and their influence on its life history variation

The purpose of this study is to determine the flowering requirements of Polymnia canadensis and how they correspond to the occurrence of winter annuals, biennials, and short-lived monocarpic perennials in this species. Polymnia canadensis has a vernalization requirement for flowering, and even very small plants (i.e., those with one pair of leaves) can be vernalized. Vernalized plants can flower under both long- and short days. However, to flower plants must attain a minimum postvernalization size. Plants of this primarily monocarpic species that do not die after they flower once require another period of vernalization to flower a second time (i.e., to be dicarpic). Vernalized plants exposed to high temperatures can be devernalized; these must be re-vernalized in order to flower.     

Changes in RNA levels in the shoot apex of Silene during the transition to flowering

Changes in RNA concentration in the shoot apical meristem during induction and the transition to flowering were measured histochemically in Silene coeli-rosa (L.) Godron, a long-day plant. In the apices of plants induced by 7 long days the RNA concentration increased to about 25 per cent higher than in non-induced plants. Three long days did not induce flowering but resulted in a transient rise in RNA concentration. When plants were given long days interrupted by varying numbers of short days successful induction was accompanied by a sustained increase in RNA concentration but those treatments which were not inductive gave only transient increases in RNA. Gibberellic acid had no effect on induction or apical growth rates but increased the RNA concentration by 50 per cent or more in both induced and non-induced plants. Plants induced to flower at 13° C had the same RNA concentration and growth rate at the apex as in non-induced plants at 20° C. Since changes in RNA concentration in the apex could occur without changes in growth rate and without flowering, and induction could occur without a change in RNA concentration or growth rate, it is suggested that the increase in RNA and growth rate which normally occur at the transition to flowering might not be essential for the formation of a flower but may be more closely related to the rapid growth associated with the formation of the inflorescence.Abbreviations LD long day - SD short-day     

Inhibition of growth and synchronised cell division in the shoot apex in relation to flowering in Silene

When plants of Silene coeli-rosa (L.) Godron were induced by seven long days, then exposed to darkness for 48 h before being returned to short days, they went on to initiate flowers with a delay of about 2 d. The synchronisation of cell division which normally occurs before flower initiation was suppressed, showing that it is not essential for flowering. Periods of darkness of up to 240 h inhibited apical growth and leaf initiation but did not prevent eventual flowering in short days. The commitment of the apex to flower was therefore maintained while apical growth was inhibited.Abbreviations SD short day(s) - LD long day(s)     

Differences in Heat Requirements of Flower and Leaf Buds Make Hysteranthous Trees Bloom before Leaf Unfolding

To clarify which agroclimatic requirements control the sequential occurrence of flowering and leaf unfolding in hysteranthous plants, Partial Least Squares (PLS) regression analysis was used to identify the chilling and forcing period of leaf and flower buds. The Dynamic Model and the Growing Degree Hour Model were applied to estimate the chilling and heat requirement for leaf unfolding and flowering, based on the phenological records of apricot and mountain peach and daily maximum and minimum temperature data in Beijing during 1963-1988. The results indicated that PLS regression analysis is a useful approach to calculate the chilling and heat requirements of plants when long term phenological observations are available. Leaf and flower buds were found to have similar chilling requirements but different heat requirements, which explained the earlier occurrence of flowering compared to leaf unfolding. The heat requirements of flower buds of apricot and mountain peach were 28297±8762 and 14572±5812 Growing Degree Hours, respectively, while heat requirements of vegetative buds were almost twice as high. In view of the importance and usefulness of phenological observations, species level ground observations in China should be continued and extended.     

叶芽花芽需热量差异导致植物先花后叶

为探究植物先花后叶的影响因素,本研究以1963—1988年间北京地区杏和山桃展叶和始花物候资料及相应的日最高、最低温度数据为基础,利用偏最小二乘回归法确定杏和山桃叶芽及花芽的需冷期和需热期,进而利用动态模型和生长度小时模型分别估算叶芽和花芽的需冷和需热量。结果表明,依据长期物候观测资料,利用偏最小二乘回归法进行植物需冷和需热量的估算非常有效。先花后叶植物叶芽和花芽需冷量几乎相同,需热量的差异是导致植物先花后叶的主要原因。杏和山桃花芽的需热量分别为2829．7±876．2和1457．2±581．2生长度小时,而相应叶芽需热量却是花芽的两倍之多。基于物候观测的重要性及实用性．中国物种水平上的地面观测应得到进一步深入发展。     

Effect of Photoperiod and Chlorogenic Acid on Morphogenesis in Leaf Discs of Streptocarpus Nobilis

Leaf discs from vegetative plants greatly increase their phenolic content when cultivated in vitro. Under long days the values remained constant, and were higher when compared with short days cultures. Under short days total phenolics decreased after 10 d, corresponding to the induction and expression of in vitro flowering. The effect of photoperiod and chlorogenic acid (0.01 mM) on leaf discs cultured from induced and non-induced plants, were analyzed regarding the neo-formation of roots, as well as vegetative and flower buds. Chlorogenic acid enhances the regeneration of roots in all treatments tested, with the highest stimulation on induced leaf discs cultivated in short days. The flowering was not affected by chlorogenic acid, but an inhibitory effect was observed on the neo-formation of vegetative buds in non-induced explants maintained in short days. Vegetative buds were reduced by 50% in flower-induced leaf discs cultivated under short days.     

The effect of LAB 173711 and ethephon on time of flowering and cold hardiness of peach flower buds

Peach flowers are often killed during bloom by spring frosts. LAB 173711, a compound with abscisic (ABA)-like activity, and ethephon delayed flowering in peach trees. In greenhouse experiments, LAB 173711, at concentrations of 10^?3–10^?2 M, was most effective in delaying bloom when applied after a 5°C cold storage period, rather than before the dormancy breaking treatment. In contrast, ethephon delayed bloom most effectively when applied before 5°C cold storage; ethephon caused flower bud abscission when treatments were made after the chilling requirement had been satisfied. In field experiments, ethephon delayed flowering by 6–7 days, which reduced bud injury after a spring frost during bloom. No flower bud injury was found on ethephon-treated trees after temperatures of ?4.3°C; whereas without ethephon 25% of the flower buds were frost damaged. LAB 173711 delayed the time to 50% bloom by 2–3 days. However, this was not long enough to avoid low-temperature injury to the flower buds.     

Short and long term effects of root and shoot chilling of ransom soybean

The immediate short term effects on some physiological processes and the long term effects on morphology and reproductive development of root- and shoot-chilled soybeans (Glycine max L. cv Ransom) were studied. Roots or shoots of 16- or 17-day-old plants were chilled at 10°C for one week, and then rewarmed to 25°C. Leaf elongation rate, net CO₂ uptake rate, and stomatal conductance decreased during root or shoot chilling. Root chilling had only temporary effects on water relations, while shoot chilling caused large changes in potentials during chilling. Most processes measured returned to control levels after two days of rewarming. Root-chilled plants harvested 90 days after emergence were similar in morphology and seed weight to controls. Shoot-chilled plants showed a large increase over controls in axillary branch growth, but an early abortion of flowers and a delayed resumption of flowering caused a 78% reduction in seed weight. Root chilling in this study was found to have little or no long term effect on the plants, while shoot chilling caused significant changes in vegetative morphology, and a delay in flowering and subsequent pod filling.     

Effect of growth substances on flowering and sex expression in isolated apical buds of Spinacia oleracea

Apical buds of Spinacia oleracea L. cv. Matador were isolated from 7-day-old vegetative seedlings and grown in sterile culture under inductive long, or non-inductive short photoperiods. Flowering of isolated apices was inducible in long days in approximately 75% of the plants, and in short days by gibberellin treatment (about 40%) or by raising the temperature to 30–32°C (13%). In long days the percentage of flowering was further increased by gibberellin treatment (up to 90%), while it was unaffected by abscisic acid and was strongly decreased by Amo 1618 (55%). In long days the ratio of male to female plants was near 1. The percentage of female plants in long days was increased by gibberellins, and the percentage of male ones decreased by kinetin; as a consequence, the ratio of male to female plants was lowered to about 0.50 in both cases. Abscisic acid and Amo 1618 had the opposite effect, probably because they decreased the flowering in female plants, so that the sex ratio was shifted to 2.6 and 6.8, respectively. Simultaneous treatment with GA₃ reversed the effect of abscisic acid on the sex ratio, but the reversal of the shift to maleness induced by Amo 1618 was only partial. In short days, gibberellins also stimulated the flowering in female plants more than in male. However, when the flowering was induced by higher temperature, most flowering plants were male and kinetin increased their percentage further. The above results have been discussed in terms of different requirements for flowering in male and female plants.     

CONSTANS delays flowering and affects tuber yield in potato

CONSTANS (CO) has a central role in the photoperiodic regulation of flowering in Arabidopsis thaliana. We show here that potato (Solanum tuberosum ssp. andigena) plants constitutively expressing Arabidopsis CO (pACo plants) flower late under all photoperiodic conditions tested. Exogenous application of gibberellic acid to pACo plants corrected their short stem phenotype but not their late flowering. To further understand the effect of CO in potato, we used three photoperiodic conditions: short days (SD), which strongly induce tuberisation of wild type plants, SD supplemented with a night break (SD+NB), which are moderately inductive, and tuberisation-inhibiting long days. Tuberisation of pACo plants was delayed under SD and very strongly delayed or completely inhibited under SD+NB, suggesting that CO affects an autonomous pathway controlling potato tuberisation. In addition, tuber yield, a trait of high agronomic relevance, was significantly increased in pACo plants expressing moderate CO levels. Our results indicate that CO affects flowering and stem elongation through distinct mechanisms and suggest that its effects on flowering and tuberisation in potato are photoperiod-independent.     

The transition to reproductive phase inchenopodium murale L. ecotype 197 - Early flowering long-day plant

Five days of suitable continuous light induced flowering in the majority ofChenopodium murale L. ecotype 197 plants as early as at the phase of the first pair of leaves. At the time of initiation of the 2nd to 4th pairs of leaves the capacity of plants to flower was reduced, the number of flowering plants being significantly lower under the same inductive light treatment. The capacity to flower increased again at the phase of the 5th and the 6th pairs of leaves. Inductive light treatment brought about a marked growth activation of organs present before induction, shoot apex elongation, precocious formation of new leaves and activation of axillary meristems. The course of these changes in plants of different age is demonstrated. The terminal flower developed during 5 short days following inductive light treatment. The paper shows similarities and differences between long-daymutale L. ecotype 197 and short-day C.rubrum L. ecotype 374 grown under practically uniform conditions.     

Effects of Different Photoperiods and Chilling Treatments on Growth and Reproduction of Cardamine flexuosa With. and Its Ecological Implications

Abstract Phenotypic variability of Cardamine flexuosa (Cruciferae) was examined in response to different lengths of exposure to low temperature (5°C) at the juvenile stage, and to two photoperiod regimes (8 and 16 hrs day-lengths) in the subsequent growth period. The results indicated that this species had a facultative chilling or long-day requirement for flowering. The long-day and chilling treatments both caused an earlier onset of stem internode elongation. Longer chilling treatments reduced the number of nodes and increased internode length under both long and short photoperiod regimes. Prolonged chilling treatments followed by long-day photoperiod remarkably induced more numerous basal branches and inflorescences, as a result producing more siliques. Remarkable rosette leaves Were formed at the base of the main stem when partial chilling and the short-day treatment suppressed stem internode elongation. The responses to chilling and long-day treatment closely resembled the synchronized flowering of this species in spring in the field. Delayed flowering under the short-day treatment resembled size- or age-dependent flowering in late summer to autumn in the field populations.     

SPATIAL AND TEMPORAL VARIATION IN CHASMOGAMY AND CLEISTOGAMY IN OXALIS MONTANA (OXALIDACEAE)

Chasmogamous (CH) and cleistogamous (CL) flower production was investigated in natural populations of the perennial herb Oxalis montana in southern Quebec, Canada. Every 10–12 days during two flowering seasons, we recorded the reproductive output of approximately 2,000 plants distributed among five forest sites. The percentage of plants flowering, proportion of flowering plants producing CH and CL flowers, CH and CL flower number per flowering plant, and the proportion of flowers that are CL differed significantly among sites and corresponded to site differences in forest type and habitat quality. Unlike patterns in most CL species, however, reproduction by cleistogamy increased in sites with habitat conditions favorable to plant growth and sexual reproduction, and decreased in less productive sites. Chasmogamous and CL flower production increased with increasing plant size but plant size explained a significantly greater proportion of the variation in CL flower numbers. The percentage of flowering plants producing CH flowers decreased between years while the proportion of CL flowers increased at all sites during the second flowering season. The somewhat unusual aspects of reproduction in Oxalis may stem from its perennial habit which allows use of stored resources in adjusting the balance of cleistogamy versus chasmogamy in different environmental regimes.     

Flower bud differentiation in Salix pentandra as affected by photoperiod, temperature and growth regulators

Flower bud initiation in seedlings and vegetatively propagated plants of Salix pentandra from different locations has been studied under controlled conditions. In mature plants flower bud formation was induced by 2-chloroethyltrimethylammoniumchloride (CCC) and by short day treatment. The effect of CCC was antagonized by GA₃. The critical photoperiod for flower bud formation was about 18 h for a southern clone (from 49°48'N), but cuttings of a northern ecotype (from 69°39'N) formed flower buds even at 24 h photoperiod. Generally, flower bud formation occurred simultaneously with apical growth cessation. However, apical growth cessation was not a prerequisite for floral initiation and flower buds were also found in elongating plants. Seedlings up to 60 days old did not form flower buds in growth chamber studies. The length of the juvenile phase has not been studied in detail, but cuttings taken from seedlings approximately 20 cm high and 60 days old were able to develop flower buds when treated with CCC. A gradual transition from the juvenile to the mature phase was obtained by repeated pruning of seedlings grown at 18°C and 24 h photoperiod.     

The effect of LAB 173711 and ethephon on time of flowering and cold hardiness of peach flower buds

Peach flowers are often killed during bloom by spring frosts. LAB 173711, a compound with abscisic (ABA)-like activity, and ethephon delayed flowering in peach trees. In greenhouse experiments, LAB 173711, at concentrations of 10^–3–10^–2 M, was most effective in delaying bloom when applied after a 5°C cold storage period, rather than before the dormancy breaking treatment. In contrast, ethephon delayed bloom most effectively when applied before 5°C cold storage; ethephon caused flower bud abscission when treatments were made after the chilling requirement had been satisfied. In field experiments, ethephon delayed flowering by 6–7 days, which reduced bud injury after a spring frost during bloom. No flower bud injury was found on ethephon-treated trees after temperatures of –4.3°C; whereas without ethephon 25% of the flower buds were frost damaged. LAB 173711 delayed the time to 50% bloom by 2–3 days. However, this was not long enough to avoid low-temperature injury to the flower buds.     

Effects of growth temperature and chilling duration on leaf phenology of <Emphasis Type="Italic">Fauria crista</Emphasis>-<Emphasis Type="Italic">galli</Emphasis> subsp. <Emphasis Type="Italic">japonica</Emphasis>, an alpine snowbed geophyte

I examined the effects of growth temperature and winter duration on the leaf phenology of Fauria crista-galli plants, which have an indeterminate growth habit. After a 220-day chilling treatment, the leaf expansion and green periods of plants maintained at 25/20°C were much longer than those of plants maintained at 15/10°C and of plants at the natural habitat obtained in a previous study. The results indicate that early growth cessation and early leaf senescence in the natural habitat are not only due to endogenous rhythm but determined to some extent by cool summer temperatures. When grown at 15/10°C, the green period of individual leaves and plants was much shorter after a long chilling treatment (220 days) than after a short chilling treatment (110 days). The plants sprouted during or immediately after the termination of chilling treatment, suggesting that the decrease in the green period results partly from an advance of endogenous developmental stages during the chilling treatment and that the timing of snowmelt potentially affects the time of leaf senescence in the natural habitat.     

EXPERIMENTAL CONTROL OF FLOWERING IN LEMNA. II. SOME EFFECTS OF MEDIUM COMPOSITION,CHELATING AGENTS AND HIGH TEMPERATURES ON FLOWERING IN L. PERPUSILLA 6746

Hillman , William S. (Yale U., New Haven, Conn.) Experimental control of flowering in Lemna. II. Some effects of medium composition, chelating agents and high temperatures on flowering in L. perpusilla 6746. Amer. Jour. Bot. 46(7): 489–495. Illus. 1959.—-L. perpusilla 6746 flowers as a short-day plant on Hutner's medium (containing ethylenediaminetetraacetic acid [EDTA]) at constant temperatures from 25 to 30°C., but eventually flowers also in old cultures under 16 or 24 hr. of light. This old-culture flowering is more pronounced in dilute medium. Flowering is rapid under both long and short days at constant temperatures from 25 to 28°C. in media not containing EDTA; the addition of 10^-5 M EDTA or of similar or higher concentrations of numerous other chelating agents suppresses flowering under long days but not under short (8 hr. light). This effect does not depend on promotion or inhibition of vegetative growth. At 29 to 30°C., a short-day requirement is manifested even in media permitting flowering under long days at the lower temperatures. Temperatures above 31°C. completely inhibit flowering under all conditions. Brief periods of high temperature given to plants under short-day conditions inhibit flowering when given during the dark period but not during the light period. The implications of these observations for the further study of flowering are discussed.     

Environmental control of flowering and sex expression in Carex flava

The environmental control of flowering and sex expression has been studied under controlled environment conditions in three populations of the sedge Carex flava L. A dual floral induction requirement was demonstrated in all populations. Low temperature (< 12°C) was obligatory for, and short photoperiods strongly enhanced, primary induction and inflorescence initiation. Stem elongation and inflorescence development were promoted by long photoperiods, although most plants developed stunted flower stems also under short day (SD) conditions. Growth vigour, abundance of flowering and primary induction requirements varied widely among the populations, with critical exposure times for full flowering varying from less than 9 to about 12 weeks in SD at 9°C, and from about 9 to more than 15 weeks in long days (LD). Sex expression in the normally male terminal spike was shifted towards femaleness by marginal or incomplete primary induction. Primary induction in LD resulted in a complete change to entirely female inflorescences, whereas marginal induction in SD resulted in a similar sex reversal in some plants. The results are discussed in relation to environmental and hormonal factors known to modify sex expression in flowering plants and the significance of the results to Carex systematics and classification.     

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.     

Climatic flowering requirements of bipolar sedges, Carex spp., and the feasibility of their trans-equatorial migration by mountain-hopping

A selection of northern and southern hemisphere populations of a range of bipolar Carex species was grown in controlled environments for comparison of their temperature and daylength requirements for flowering. All studied species have basically the same dual induction requirements for flowering but differ quantitatively in their respective critical temperatures and daylengths for primary and secondary floral induction. Usually, low temperature or short days (SD), over a wider range of temperatures, were required for initiation of inflorescence primordia, whereas long days (LD) advanced but were not obligatory for heading and flower development. It is concluded that no change or adaptation in the flowering requirements would have been necessary for these plants to migrate across the tropics and their penetration into the southern hemisphere by mountain-hopping. The flowering requirements of these and a range of other bipolar plant species are compatible with the hypothesis that absence of an obligatory long day floral induction requirement has facilitated or been a prerequisite for trans-equatorial migration of plants by mountain-hopping and the establishment of bipolar species distributions.