THE PHOTOINDUCTIVE CONTROL OF SEED WEIGHT IN CHENOPODIUM RUBRUM L.

The determination of mean seed weight in Chenopodium rubrum L., a short-day, weedy annual, has been examined through the manipulation of photoperiod during the course of reproductive development. Individuals that develop seeds in relatively long photoperiods (15 L: 9 D) form many more seeds of smaller weight than individuals that develop seeds in relatively shorter photoperiods (12 L: 12 D). By altering the inductive photoperiod at different times during the course of reproductive development, it is shown that the effect of photoperiod is most strongly exerted between six and twelve days after the start of floral induction and is coincident with the determination of primordia as floral structures. The ecological significance of this early developmental determination is discussed.     

Photoperiod and Temperature Regulation of Floral Initiation and Anthesis in Soya Bean

Floral development includes initiation of floral primordia andsubsequent anthesis as discrete events, even though in manyinvestigations only anthesis is considered. For ‘Ransom’soya bean [Glycine max (L.) Merrill] grown at day/night temperaturesof 18/14, 22/18, 26/22, 30/26, and 34/30 °C and exposedto photoperiods of 10, 12, 14, 15, and 16 h, time of anthesisranged from less than 21 days after exposure at the shorterphotoperiods and warmer temperatures to more than 60 days atlonger photoperiods and cooler temperatures. For all temperatureregimes, however, floral primordia were initiated under shorterphotopenods within 3 to 5 days after exposure and after notmore than 7 to 10 days exposure to longer photoperiods. Onceinitiation had begun, time required for differentiation of individualfloral primordia and the duration of leaf initiation at shootapices increased with increasing length of photoperiod. Whileproduction of nodes ceased abruptly under photoperiods of 10and 12 h, new nodes continued to be formed concurrently withinitiation of axillary floral primordia under photoperiods of14, 15 and 16 h. The vegetative condition at the main stem shootapex was prolonged under the three longer photoperiods and issuggestive of the existence of an intermediate apex under theseconditions. The results indicate that initiation and anthesisare controlled independently rather than collectively by photoperiod,and that floral initiation consists of two independent steps—onefor the first-initiated flower in an axil of a main stem leafand a second for transformation of the terminal shoot apex fromthe vegetative to reproductive condition. Apical meristem, intermediate apex, floral initiation, anthesis, photoinduction, Glycine max(L.) Merrill, soya bean, photoperiod, temperature     

Timing of reproductive and vegetative development in Saxifraga oppositifolia in an alpine and a subnival climate

Morphogenesis of floral structures, dynamics of reproductive development from floral initiation until fruit maturation, and leaf turnover in vegetative short-stem shoots of Saxifraga oppositifolia were studied in three consecutive years at an alpine site (2300 m) and at an early- and late-thawing subnival site (2650 m) in the Austrian Alps. Marked differences in the timing and progression of reproductive and vegetative development occurred: individuals of the alpine population required a four-month growing season to complete reproductive development and initiate new flower buds, whereas later thawing individuals from the subnival sites attained the same structural and functional state within only two and a half months. Reproductive and vegetative development were not strictly correlated because timing of flowering, seed development, and shoot growth depended mainly on the date of snowmelt, whereas the initiation of flower primordia was evidently controlled by photoperiod. Floral induction occurred during June and July, from which a critical day length for primary floral induction of about 15 h could be inferred. Preformed flower buds overwinter in a pre-meiotic state and meiosis starts immediately after snowmelt in spring. Vegetative short-stem shoots performed a full leaf turnover within a growing season: 16 (+/-0.8 SE) new leaves per shoot developed in alpine and early-thawing subnival individuals and 12 (+/-1.2 SE) leaves in late-thawing subnival individuals. New leaf primordia emerged continuously from snowmelt until late autumn, even when plants were temporarily covered with snow. Differences in the developmental dynamics between the alpine and subnival population were independent of site temperatures, and are probably the result of ecotypic adaptation to differences in growing season length.     

Enzyme activity and electrophoretic pattern of isoenzymes of peroxidase,esterase and alkaline and acid phosphatase in relation to flowering inAmaranthus viridis L. - a quantitative SD plant

Amaranthus viridis is a quantitative SD plant in which inflorescence primordia are initiated under both 24- and 8-h photoperiods after 12 and 10 days, when 8 and 7 leaves are differentiated, respectively. Photoperiod plays a non-determinate role, whereas the maturity of plants linked with the attainment of minimum leaf number is significant and of primary importance in floral induction. This is further confirmed by the more or less identical nature of changes in the total enzyme activity and isoenzyme patterns of peroxidase, esterase and alkaline and acid phosphatase under the two photoperiods. These changes occur once the minimum vegetative growth has been achieved prior to the reproductive transformation, irrespective of the photoperiod, pointing to the activation of a general common pathway of events leading to floral induction.     

Bi-directional inflorescence development inArabidopsis thaliana: Acropetal initiation of flowers and basipetal initiation of paraclades

In this study we investigated Arabidopsis thaliana (L.) Heynh. inflorescence development by characterizing morphological changes at the shoot apex during the transition to flowering. Sixteen-hour photoperiods were used to synchronously induce flowering in vegetative plants grown for 30 d in non-inductive 8-h photoperiods. During the first inductive cycle, the shoot apical meristem ceased producing leaf primordia and began to produce flower primordia. The differentiation of paraclades (axillary flowering shoots), however, did not occur until after the initiation of multiple flower primordia from the shoot apical meristem. Paraclades were produced by the basipetal activation of buds from the axils of leaf primordia which had been initiated prior to photoperiodic induction. Concurrent with the activation of paraclades was the partial suppression of paraclade-associated leaf primordia, which became bract leaves. The suppression of bract-leaf primordia and the abrupt initiation of flower primordia during the first inductive photoperiod is indicative of a single phase change during the transition to flowering in photoperiodically induced Arabidopsis. Morphogenetic changes characteristic of the transition to flowering in plants grown continuously in 16-h photoperiods were qualitatively equivalent to the changes observed in plants which were photoperiodically induced after 30 d. These results suggest that Arabidopsis has only two phases of development, a vegetative phase and a reproductive phase; and that the production of flower primordia, the differentiation of paraclades from the axils of pre-existing leaf primordia and the elongation of internodes all occur during the reproductive phase.     

Genetic Regulation of Development in Sorghum bicolor: IV. GA(3) Hastens Floral Differentiation but Not Floral Development under Nonfavorable Photoperiods

Sorghum bicolor (L.) Moench lines with genetic differences in photoperiod requirement were planted in the field near Plainview, Texas (about 34° northern latitude) around June 1 and treated with gibberellic acid (GA₃) solutions applied in the apical leaf whorl. GA₃ hastened the date of floral differentiation (initiation). The greatest responses to GA₃ were by 90M and 100M, the latest of the genotypes, for which floral initiation dates were hastened an average of 19.5 and 21.7 days, respectively, for the 4 years beginning in 1980. There were very small differences in dates of anthesis between control and GA₃-treated plants. Microscopic examination of apical meristems collected between the date of floral initiation of GA₃-treated plants and the later date of initiation of control plants revealed: (a) several morphological characteristics of floral differentiation in the apical meristem of treated plants, (b) consistent occurrence of vegetative morphology in control plants, (c) a few meristems from GA₃-treated plants that appeared to be regressing in floral development and thus possibly exhibiting dedifferentiation. Dedifferentiation of prepanicle primordia into leaves would explain the observed equal or greater number of leaves in GA₃-treated plants rather than the expected smaller number. It is apparent that the presence of a morphological differentiated floral meristem in sorghum does not drive subsequent floral development in the absence of inductive photoperiods. This further suggests that initial floral differentiation and subsequent floral development may be controlled separately in sorghum.     

Pollination biology and the impact of floral display, pollen donors, and distyly on seed production in Arcytophyllum lavarum (Rubiaceae)

In animal-pollinated plants, two factors affecting pollen flow and seed production are changes in floral display and the availability of compatible mates. Changes in floral display may affect the number of pollinator visits and the availability of compatible mates will affect the probability of legitimate pollination and seed production. Distyly is a floral polymorphism where long-styled (pin) and short-styled (thrum) floral morphs occur among different individuals. Distylous plants frequently exhibit self and intra-morph incompatibility. Therefore changes in morph abundance directly affect the arrival of compatible pollen to the stigmas. Floral morph by itself may also affect female reproductive success because floral morphs may display differences in seed production. We explored the effects of floral display, availability of neighboring compatible mates, and floral morph on seed production in the distylous herb ARCYTOPHYLLUM LAVARUM. We found that floral display does not affect the mean number of seeds produced per flower. There is also no effect of the proportion of neighboring legitimate pollen donors on seed production in pin or thrum flowers. However, floral morphs differed in their female reproductive success and the thrum morph produced more seeds. Hand pollination experiments suggest that differences in seed production between morphs are the result of pollen limitation. Future research will elucidate if the higher seed production in thrum flowers is a consequence of higher availability of pollen donors in the population, or higher efficiency of the pin morph as pollen donor.     

Development and seed number in indeterminate soybean as affected by timing and duration of exposure to long photoperiods after flowering

BACKGROUND AND AIMS: Long photoperiods from flowering to maturity have been found to delay reproductive development in soybean (Glycine max) and to increase the number of seeds per unit land area. This study was aimed to evaluate whether sensitivity to photoperiod after flowering (a) is quantitatively related to the length of exposure to long days and (b) persists throughout the whole pod-setting period. It was also evaluated whether seed number was related to changes in the duration of post-flowering phenophases. METHODS: Two field experiments were conducted with an indeterminate cultivar of soybean of maturity group V. In expt 1, photoperiods 2 h longer than natural daylength were applied during different numbers of days from the beginning pod stage (R3) onwards, while in expt 2 these photoperiod extensions were imposed during 9 consecutive days starting at different times between R3 and R6 (full seed) stages. KEY RESULTS: There was a quantitative response of development to the number of cycles with a long photoperiod. The exposure to long photoperiods from R3 to R5 (beginning of seed growth) increased the duration of R3-R6 regardless of the timing of exposure. The stages of development comprised in the R3-R6 phase were delayed by current as well as by previous exposure to long days. A positive relationship was found between seed number and the duration of R3-R6, irrespective of the timing and length of exposure to the long photoperiod. CONCLUSIONS: Sensitivity to photoperiod remained high during the reproductive period and was highly and positively coupled with the processes of generation of yield.     

The Pattern of Reproductive Development in Chenopodium rubrum L.

Individual plants of Chenopodium rubrum were given differentnumbers of inductive cycles in a 12 h photoperiod and the patternof reproductive development was analysed after 40 d of growth.At least 2 inductive cycles are required to form any determinatereproductive organs and at least 12 cycles are required fornormal reproductive development. Individuals given a singleinductive cycle display a loss of apical dominance at thosenodes formed immediately after the treatment without the subsequentformation of any floral structures. Plants given between 2 and12 mductive cycles display both determinate reproductive organsand indeter minate vegetative shoots. The pattern of reproductivedevelopment on such plants depends upon the number of cyclesrelative to the developmental age of newly initiated primordia.It is suggested that the early events of floral induction mayinvolve a radical decrease in the ratio of auxin to cytokinin.     

Evolution of self-fertilization at geographical range margins? A comparison of demographic, floral, and mating system variables in central vs. peripheral populations of Aquilegia canadensis (Ranunculaceae)

Biogeographic models predict that geographically peripheral populations should be smaller, more sparsely distributed, and have a lower per-capita reproductive rate than populations near the center of a species' range. Plants in peripheral populations may, therefore, receive less pollinator visitation and outcross pollination, which may select for self-fertilization to provide reproductive assurance. We tested these predictions by comparing population size, plant density, seed production, floral traits, and mating system parameters between 10 populations of Aquilegia canadensis near the northern margin of the range with 10 near the range center. Contrary to predictions, peripheral populations were not smaller, less dense, nor less productive than central populations. Nevertheless, we detected substantial regional differences in key floral traits. Plants in central populations produced larger flowers with 68% greater herkogamy and had 30% more flowers open simultaneously than plants in northern populations. However, there was no regional difference in the mating system. In northern populations, 73% (range = 60-88%) of seeds were self-fertilized compared to 76% (51-100%) in central populations. In both regions, adult inbreeding coefficients were near zero, indicating very strong inbreeding depression despite high selfing. Marked geographic variation in key floral traits does not reflect evolutionary differentiation in the mating system.     

Effect of varying lengths of inductive and supplementary non-inductive photoperiods on vegetative growth and flowering of Impatiens balsamina

The photoperiodic requirement for flowering in Impatiens balsaminachanges with the length of the photoperiod. Floral buds wereinitiated with two 8 hr but with four 15 hr photoperiods andflowers opened with four 8 hr but twenty-eight 15 hr photoperiods.A part of the photoperiodic requirement for floral inductionin this plant can be substituted by LDs containing 4 or morehours of darkness (10). It indicates the identical nature ofthe floral stimulus produced during the dark period, whetherit forms a part of the inductive or non-inductive cycles. Theeffect of these supplementary non-inductive photoperiodic cyclesin causing floral bud initiation also depends on the lengthof the first inductive obligatory cycle. More floral buds andflowers were produced on plants exposed to 15 hr than 8 hr photoperiods,probably due to the higher number of leaves that were producedunder the former condition of weaker induction. The shorterthe dark period in the photoperiodic cycle, the weaker the induction,the slower the rate of extension growth but the more differentiationof leaves. ¹ Present address: Department of Biology, Guru Nanak Dev University,Amritsar-143005, India. (Received November 9, 1977; )     

Recovery process of genetic diversity through seed and pollen immigration at the northernmost leading-edge population of Fagus crenata

The range expansion of a plant species begins with colonization of ecological empty patches from posterior source populations. This process involves stochastic loss of genetic diversity. However, the founder population could restore genetic diversity by gene flow from posterior populations via seeds and pollen and its recovery affects evolutionary potential for species expansion. To clarify the recovery process of genetic diversity during species range expansion, gene flow via seeds and pollen was investigated at the expansion front of Fagus crenata. Based on eight nuclear microsatellite genotypes of a total of 150 individuals and 225 seeds at the northernmost leading-edge population, genetic diversity, fine-scale spatial genetic structure (FSGS), and genetic differentiation from other five northern populations were investigated. Moreover, both seed and pollen immigration and their effects on genetic diversity at different successional stages were analyzed. The leading-edge population showed lower genetic diversity and substantial genetic differentiation, reflecting its strong genetic drift. Non-significant FSGS and a negative inbreeding coefficient for mature trees may indicate that the earliest generation consisted of founders from foreign seed sources. The significant proportion of seed and pollen immigration increased the number of different alleles for later successional stages. The effective number of pollen parents from foreign sources (20.8) was markedly higher than that from the local source (2.1). These results indicated that pollen immigration incorporated new and rare alleles and increased the genetic diversity of the population. However, the proportion of foreign gene flow decreased during succession, probably due to the increased reproductive success of local individuals as they reached maturity and grew in size.     

Interactions of temperature and photoperiod in the control of flowering of latitudinal and altitudinal populations of wild strawberry (Fragaria vesca)

Floral induction and development requirements of a range of latitudinal and altitudinal Norwegian populations of the wild strawberry Fragaria vesca L. have been studied in controlled environments. Rooted runner plants were exposed to a range of photoperiods and temperatures for 5 weeks for floral induction and then transferred to long day (LD) at 20°C for flower development. A pronounced interaction of temperature and photoperiod was shown in the control of flowering. At 9°C, flowers were initiated in both short day (SD) and LD conditions, at 15 and 18°C in SD only, whereas no initiation took place at 21°C regardless of daylength conditions. The critical photoperiod for SD floral induction was about 16 h and 14 h at 15 and 18°C, respectively, the induction being incomplete at 18°C. The optimal condition for floral induction was SD at 15°C. A minimum of 4 weeks of exposure to such optimal conditions was required. Although the populations varied significantly in their flowering performance, no clinal relationship was present between latitude of origin and critical photoperiod. Flower development of SD-induced plants was only marginally advanced by LD conditions, while inflorescence elongation and runnering were strongly enhanced by LD at this stage. The main shift in these responses took place at photoperiods between 16 and 17 h. Unlike all other populations studied, a high-latitude population from 70°N ('Alta') had an obligatory vernalization requirement. Although flowering and fruiting in its native Subarctic environment and after overwintering in the field in south Norway, this population did not flower in the laboratory in the absence of vernalization, even with 10 or 15 weeks of exposure to SD at 9°C. Flowering performance in the field likewise indicated a vernalization requirement of this high-latitude population.     

Induction of flowering ofImpatiens balsamina treated with gibberellic acid and resorcinol

Under strictly non-inductive photoperiods (24-h photoperiods) floral buds were initiated on plants receiving 25 treatments with Reso (resorcinol) or 8 treatments with GA₃ (gibberellic acid) or GA₃ + Reso, while water treated control plants did not flower at all. Although a single treatment of plants with GA₃ or GA₃ + Reso is not adequate to cause induction under LD conditions, its effect is added to the sub-threshold induction caused by one SD (short day: 8-h photoperiod) cycle. The initiation of floral buds was hastened with an increasing number of SD cycles accompanying respective number of treatments, the effect of GA₃ alone or together with Reso being more pronounced than that of Reso alone. GA₃ increased the number of floral buds more than Reso, the number being the highest in plants receiving the respective number of treatments with the combination GA₃ + Reso under both inductive as well as non-inductive photoperiods. Deceased.     

Response to selection for photoperiod responsiveness on the density and location of mature GnRH-releasing neurons

Natural variation in neuroendocrine traits is poorly understood, despite the importance of variation in brain function and evolution. Most rodents in the temperate zones inhibit reproduction and other nonessential functions in short winter photoperiods, but some have little or no reproductive response. We tested whether genetic variability in reproductive seasonality is related to individual differences in the neuronal function of the gonadotropin-releasing hormone network, as assessed by the number and location of mature gonadotropin-releasing hormone-secreting neurons under inhibitory and excitatory photoperiods. The experiments used lines of Peromyscus leucopus previously developed by selection from a wild population. One line contained individuals reproductively inhibited by short photoperiod, and the other line contained individuals nonresponsive to short photoperiod. Expression of mature gonadotropin-releasing hormone (GnRH) immunoreactivity in the brain was detected using SMI-41 antibody in the single-labeled avidin-biotin-peroxidase-complex method. Nonresponsive mice had 50% more immunoreactive GnRH neurons than reproductively inhibited mice in both short- and long-day photoperiods. The greatest differences were in the anterior hypothalamus and preoptic areas. In contrast, we detected no significant within-lines differences in the number or location of immunoreactive GnRH neurons between photoperiod treatments. Our data indicate that high levels of genetic variation in a single wild population for a specific neuronal trait are related to phenotypic variation in a life history trait, i.e., winter reproduction. Variation in GnRH neuronal activity may underlie some of the natural reproductive and life history variation observed in wild populations of P. leucopus. Similar genetic variation in neuronal traits may be present in humans and other species.     

Effect of Gibberellic Acid and Phosfon on the Critical Dark Period Reqnirement for Flowering of Impatiens balsamina cv. Rose

The critical dark period requirement for flowering of Impatiens balsamina L. cv. Rose, an obligate short day plant, is about 8.5 hours. While GA₃ completely substituted for the dark period requirement, Phosfon prolonged it to 9.5 hours. GA₃ hastened and Phosfon delayed the initiation of floral buds under all photoperiods. Floral buds opened into flowers only during 8 and 14 hour photoperiods in control and Phosfon-treated plants but during all photoperiods in GA₃-treated ones. The delay in floral bud initiation and flowering was correlated with shifting up of the node bearing the first floral bud and flower respectively. While GA₃ increased the numher of floral buds and flowers in all photoperiods except 8-hour, Phosfon increased their number in the 14-hour photoperiod only. The number of flowering plants decreased with increasing photoperiod regardless of GA₃ and Phosfon application. The effect of Phosfon was completely or partially overcome, depending upon the photoperiod, by simultaneous application of GA₃.     

Inhibition of reproductive maturation and somatic growth of Fischer 344 rats by photoperiods shorter than L14:D10 and by gradually decreasing photoperiod

Photoperiod is the major regulator of reproduction in temperate-zone mammals. Laboratory rats are generally considered to be nonphotoresponsive, but young male Fischer 344 (F344) rats have a uniquely robust response to short photoperiods of 8 h of light. Rats transferred at weaning from a photoperiod of 16 h to photoperiods of < 14 h of light slowed in both reproductive development and somatic growth rate. Those in photoperiods < 13 h of light underwent the strongest responses. The critical photoperiod of F344 rats can be defined as 13.5 h of light, but photoperiods of 相似文献   

Effect of Gibberellic Acid, 2,3,5-Triiodobenzoic Acid and Indole Acetic Acid on Growth and Development of Impatiens balsamina during Different Photoperiods

This paper deals with the effect of 100 mg/1 each of GA₃ TIBA and IAA singly and in combination with each other on stem elongation, development of lateral branches and floral bud initiation in Impatiens balsamina plants exposed to 8-, 16- and 24-h photoperiods. GA₃ enhances stem elongation, the enhancing effect decreasing with IAA as well as with TIBA during 8-h but increasing during 16- and 24-h photoperiods. It decreases the number of lateral branches, the decrease being greatest during 16-, less during 8- and the least during 24-h photoperiods. The time taken for floral buds to initiate with and length of branches during 16-h photoperiods. During 8-h photoperiods, IAA delays the initiation of floral buds, while GA₃ hastens it when used together with TIBA or IAA or both. GA₃ increases the number of floral buds on the main axis but decreases it on lateral branches, while TIBA decreases the number on the main axis but increases it on lateral branches. IAA reduces the number of floral buds on the main axis only when used alone, but on both the main axis as well as on lateral branches when used together with GA₃ and TIBA. Floral buds were not produced on lateral branches when plants were treated with GA₃, TIBA and IAA all together. GA₃ and TIBA induced floral buds even under non-inductive photoperiods, the number of buds and reproductive nodes being less in TIBA- than in GA₃-treated plants during 24-h photoperiods. The time taken for floral buds to initiate with GA₃ and TIBA during noninductive photoperiods is much longer than that during 8-h inductive photoperiods with or without GA₃ or TIBA application. IAA completely inhibits the GA₃- and TIBA-caused induction during 24-h, but only delays it and reduces the number of reproductive nodes and floral buds during 16-h photoperiods.