Initiation Of Flower Primordia Research Articles

CLAVATA Signaling Ensures Reproductive Development in Plants across Thermal Environments

The ability to thrive in diverse environments requires that species maintain development and reproduction despite dynamic conditions. Many developmental processes are stabilized through robust signaling pathways that cooperatively ensure proper development.1 During reproduction, plants like Arabidopsis thaliana continuously generate flowers on growing indeterminate inflorescences.2 Flower primordia initiation and outgrowth depends on the hormone auxin and is robust across diverse environments.3-6 Here, we show that reproductive development under different thermal conditions requires the integration of multiple pathways regulating auxin-dependent flower production. In colder/ambient temperatures, the receptor complex CLAVATA2/CORYNE (CLV2/CRN) is necessary for continuous flower outgrowth during inflorescence development. CLV2/CRN signaling is independent of CLAVATA1 (CLV1)-related receptor signaling but involves the CLAVATA3 INSENSITIVE RECEPTOR KINASE (CIK) family co-receptors, with higher order cik mutant combinations phenocopying clv2/crn flower outgrowth defects. Developing crn inflorescences display reduced auxin signaling, and restoration of auxin biosynthesis is sufficient to restore flower outgrowth in colder and ambient temperatures. In contrast, at higher temperatures, both clv2/crn signaling and heat-induced auxin biosynthesis via YUCCA family genes are synergistically required to maintain flower development. Our work reveals a novel mechanism integrating peptide hormone and auxin signaling in the regulation of flower development across diverse thermal environments.

Diverse Developmental Responses to Warming Temperatures Underlie Changes in Flowering Phenologies.

Climate change has resulted in increased temperature means across the globe. Many angiosperms flower earlier in response to rising temperature and the phenologies of these species are reasonably well predicted by models that account for spring (early growing season) and winter temperatures. Surprisingly, however, exceptions to the general pattern of precocious flowering are common. Many species either do not appear to respond or even delay flowering in, or following, warm growing seasons. Existing phenological models have not fully addressed such exceptions to the common association of advancing phenologies with warming temperatures. The phenological events that are typically recorded (e.g., onset of flowering) are but one phase in a complex developmental process that often begins one or more years previously, and flowering time may be strongly influenced by temperature over the entire multi-year course of flower development. We propose a series of models that explore effects of growing-season temperature increase on the multiple processes of flower development and how changes in development may impact the timing of anthesis. We focus on temperate forest trees, which are characterized by preformation, the initiation of flower primordia one or more years prior to anthesis. We then synthesize the literature on flower development to evaluate the models. Although fragmentary, the existing data suggest the potential for temperature to affect all aspects of flower development in woody perennials. But, even for relatively well studied taxa, the critical developmental responses that underlie phenological patterns are difficult to identify. Our proposed models explain the seemingly counter-intuitive observations that warmer growing-season temperatures delay flowering in many species. Future research might concentrate on taxa that do not appear to respond to temperature, or delay flowering in response to warm temperatures, to understand what processes contribute to this pattern.

Construction of an interspecific genetic map based on InDel and SSR for mapping the QTLs affecting the initiation of flower primordia in pepper (Capsicum spp.).

Re-sequencing permits the mining of genome-wide variations on a large scale and provides excellent resources for the research community. To accelerate the development and application of molecular markers and identify the QTLs affecting the flowering time-related trait in pepper, a total of 1,038 pairs of InDel and 674 SSR primers from different sources were used for genetic mapping using the F2 population (n = 154) derived from a cross between BA3 (C. annuum) and YNXML (C. frutescens). Of these, a total of 224 simple PCR-based markers, including 129 InDels and 95 SSRs, were validated and integrated into a map, which was designated as the BY map. The BY map consisted of 13 linkage groups (LGs) and spanned a total genetic distance of 1,249.77 cM with an average marker distance of 5.60 cM. Comparative analysis of the genetic and physical map based on the anchored markers showed that the BY map covered nearly the whole pepper genome. Based on the BY map, one major and five minor QTLs affecting the number of leaves on the primary axis (Nle) were detected on chromosomes P2, P7, P10 and P11 in 2012. The major QTL on P2 was confirmed based on another subset of the same F2 population (n = 147) in 2014 with selective genotyping of markers from the BY map. With the accomplishment of pepper whole genome sequencing and annotations (release 2.0), 153 candidate genes were predicted to embed in the Nle2.2 region, of which 12 important flowering related genes were obtained. The InDel/SSR-based interspecific genetic map, QTLs and candidate genes obtained by the present study will be useful for the downstream isolation of flowering time-related gene and other genetic applications for pepper.

Dynamics of endogenous auxins, cytokinins and abscisic acid-like inhibitor in embryonic shoots of young Scots pine (Pinus silvestris L.) at the time of flower primordia initiation

Auxins, cytokinins and ABA-like inhibitor were determined in the embryonic shoots of young pines. It was stated that the transition from vegetative to reproductive stage of pine development is connected with the decrease of the IAA level. In the group of vegetative plants an unknown auxin-like substance was detected. This substance appeared in the period of generative development initiation. It was also stated that differentiation of female inflorescences was connected with the increase of the level of ABA-like inhibitor. However the differentiation of male ones was connected with decrease of the amount of this inhibitor. No correlation between sex determination and the level of auxins and cytokinins was observed.

Auxins and gibberellins in embryonic shoots of Scots pine in relation to flower sex differentiation

Flower sex differentiation in Scots pine is correlated with endogenous balance of auxins to gibberellins. Male flower primordia initiation is connected with high amounts of gibberellins whereas the initiation of female ones is associated with a high level of auxins and a low content of gibberellins.

Endogenous growth regulators in embryonic shoots of Scots pine at the time of male and female flower primordia initiation

The initiation of Scots pine male flower primordia is connected with a high content of gibberellins and a low level of auxins, whereas the initiation of female flower primordia is correlated with a high content of auxins and a low level of gibberellins. There is lack of direct correlation between the content of cytokinins or abscisic acid and flower sex differentation.

A Molecular Framework for Auxin-Mediated Initiation of Flower Primordia

A classical role of the hormone auxin is in the formation of flowers at the periphery of the reproductive shoot apex. Mutants in regulators of polar auxin transport or in the auxin-responsive transcription factor MONOPTEROS (MP) form naked inflorescence "pins" lacking flowers. How auxin maxima and MP direct initiation of flower primordia is poorly understood. Here, we identify three genes whose expression is directly induced by auxin-activated MP thatfurthermore jointly regulate flower primordium initiation. These three genes encode known regulators offlower development: LEAFY (LFY), which specifiesfloral fate, and two AINTEGUMENTA-LIKE/PLETHORA transcription factors, key regulators of floral growth. Our study thus reveals a mechanistic link between flower primordium initiation and subsequent steps in flower morphogenesis. Finally, we uncover direct positive feedback from LFY to the auxin pathway. The auxin LFY module we describe may have been recruited during evolution to pattern other plant organ systems.

Use of male gametocide: An alternative to cumbersome emasculation in coriander (Coriandrum sativum L.)

New varieties of the coriander are traditionally bred using either mass selection or pure line selection or recurrent selection. Attempts to use hybridization to combine desirable traits were scarcely successful due to cumbersome emasculation. Hence, using male gametocides as an alternative to hand emasculation offers immense scope. The present study is taken up to assess five gametocides viz. Gibberellic acid, 2, 4-D, Maleic Hydrazide, Ethrel and Surf Excel at different concentrations which were sprayed at the time of flower primordia initiation. Pollen viability and pollen germination were assessed periodically. The results indicated that none of the gametocides evaluated resulted in pollen sterility and pollen germination was unaffected. However, spraying of Maleic Hydrazide at 125 ppm resulted in suppression of anther dehiscence due to severe agglutination of the pollen. Repeat spraying of Maleic Hydrazide at 100 ppm from 25 DAS on wards until the cessation of flowering caused suppression of anther dehiscence during entire flowering period. Successful crosses were obtained using Maleic Hydrazideas chemical emasculation agent. Key words: Coriander, coriandrum, emasculation, male gametocide, crossing, hybridization.

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.

Modelling the Masting Behaviour of Betula platyphylla var. japonica using the Resource Budget Model

A masting model of Betula platyphylla var. japonica, a major wind-pollinated tree in Hokkaido, northern Japan, was constructed from the perspective of the resource budget model. An 11-year data series of pollen dispersal by birch showed marked annual fluctuations in flowering. Although flowering fluctuated widely among years, a reciprocal relationship was observed between two consecutive years; very little flowering occurred after a mast year. This suggests that there is a negative relationship between current fruiting and flower bud induction. There was a significant positive relationship in flowering between regions, which suggests that weather conditions regulate flowering in birch. A model that included weather variables and resource allocation systems among years explained 94·5% of the observed annual fluctuations in flowering. In the model, warm spring conditions from bud burst to flower bud development and little flowering in the previous year (t−1) resulted in increased flowering in the current year (t), whereas abundant flowering in year t−2 resulted in a decrease in flowering in the current year (t). The latter indicates that flowering in year t−2 affects resource storage after overwintering; the balance is carried forward to year t−1 and affects the initiation of flower primordia before bud burst. In the model, fluctuating weather conditions in the previous spring strongly affected the masting behaviour of birch.

Growth changes in the shoot apex ofSinapis albaduring transition to flowering

The aim of the work was to report morphological changes which occur in the shoot apex during the morphogenetic switch to flowering in the model long day (LD) plant, Sinapis alba. During the floral transition induced by 1 LD the growth rate of all components of the shoot apex is modified profoundly. The earliest changes, detected at 24 h after start of LD, include a decrease in plastochron duration and an increase of growth of leaf primordia. One day later, the meristem dome starts to increase in volume, apical internodes have an increased height and there is a precocious outgrowth of axillary meristems. All these changes precede initiation of flower primordia, which starts at about 60 h after the start of LD. Later changes include meristem doming, a decrease in the plastochron ratio and a shift to a more complex phyllotaxis. All the changes, except the decreased plastochron ratio, are characteristics of an apex with an increased tempo of growth. The stimulation of longitudinal growth (height of apical intemodes) is more marked and occurs earlier than the reduction of radial growth (plastochron ratio).

Shoot development and flowering in potato (Solanum tuberosum L.)

The shoot system of potato is a configuration of stems with terminal inflorescences. In this review, shoot development is quantified in terms of stem production, while stem development is quantified in terms of leaf and flower primordia production per stem, which are functions of the rates and the durations of primordia initiation. The effect of the position of the stem in the shoot system on number of leaves and flowers per stem is also evaluated. Flowering of individual stems is described by the ‘time to flower primordia initiation’ (expressed in number of leaves produced) and ‘flower production’ (a function of the number and the development of flower primordia). At warmer temperatures and longer daylengths the number of leaves and flower primordia per stem, and the number of stems per shoot increase by prolonging stem production and primordia development. Temperature and photoperiod also affect flower primordia survival by altering assimilate production and partitioning. The photothermal response of the number of leaves per stem is small compared to the response of stem production; at higher temperatures, flower primordia survival becomes the principal factor determining flower production. The similarity of the signals leading to flower primordia initiation and tuberization, and the relation between shoot and tuber growth are discussed.

Einfluß eines Wachstumsregulators auf die ‘Sink’‐Kapazität von Raps (Brassica napus L.)

Abstract Influence of a Plant Growth Regulator on the ‘Sink’ Capacity of Oilseed Rape (Brassica napus L.)A pot experiment was carried out to examine the effect of the plant growth regulator Triapenthenol (RSW) on the apical dominance of oilseed rape and its corresponding effect on the plant's ‘sink’ capacity. RSW's influence on the number of flower primordia, flowers, pods, yield and yield structure of the whole plant and of different fractions of the plant (main shoot, lateral shoots 1–3, lateral shoots >3; 1st, 2nd and 3rd‐order lateral shoots) and its effect on gibberellin content and shoot height was measured.RSW diminished dominance of the main shoot and of 1st‐order lateral shoots: the initiation of flower primordia was increased to about 34% and 116%, respectively, in fraction lateral shoots higher than 3 and 3rd‐order lateral shoots. Buds developed in a more synchronized pattern leading to a significantly improved number of flowers and pods in fraction lateral shoots higher than 3. Despite an increased number of pods per plant, grain yield remained unchanged because of a decrease in the number of seeds per pod and an unaffected thousand‐kernel weight.A decreased content of gibberelhn A19 (GA19), GA20, GA1 and GA8 was evident after application of RSW, and a correlation between gibberellin‐content and shoot height was found.The results of this study suggest that high levels of such GAs, that primarily promote shoot elongation and strengthen the apical dominance within the plant, limit the plant's ‘sink’ capacity. These effects may be due to a gibberellin‐promoted auxin‐synthesis.

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.

Flowering requirements in Bromus inermis, a short‐long‐day plant

Smooth bromegrass plants (Bromus inermis Leyss.) have a dual photoperiodic requirement for flowering. At temperatures ranging from 6 to 24°C, short days (SD) are necessary for primary induction while a transition to long days (LD) is required for initiation of flower primordia, culm elongation and flower development (secondary induction). Critical photoperiods for primary induction (50% flowering) were 13.5 h (15°C) and 12 h (24°C) in the American cv. Manchar and 14.5 and 13 h, respectively, in the Norwegian cv. Löfar. For the secondary induction the respective critical photoperiods were 14 and 15 h in ‘Manchar’ and 16 and 17.5 h in ‘Löar’, which also appeared to be better adapted to low temperatures. Low temperature vernalization in LD for up to 16 weeks at 3°C was unable to cause primary induction and temperatures below 12°C also strongly reduced the SD effect. At optimum temperature (15‐2TC) 4 to 6 weeks of 8‐10 h SD treatments were needed for optimal primary induction effect. A minimum of 8 LD cycles of 24 h were required for complete secondary induction in ‘Manchar’, while more than 16 cycles were needed in ‘Löfar’. Seedlings grown in SD developed a rosette type of growth with shoots growing in a decumbent position, while those in LD grew upright and formed elongated vegetative culms. Rate of leaf initiation was enhanced by about 60% by LD while tillering was promoted by SD.

Amylase and Invertase Activities and Carbohydrate Contents in Relation to Physiological Sink in Carnation

AbstractIn carnation, Dianthus caryophyllus L. cv. Hanacy, initiation of flower primordia was followed by mobilization of polysaccharides from leaves to developing flower buds and mature flowers. This process functioned by integrative activities of amylase and invertase, ensuring abundant flow of the mobilized carbohydrates from the source to the sink. Successive stages of floral development exhibited different sink strengths as indicated by amylase and invertase activities and carbohydrate contents in stem apices, which increased with progression of floral development.

INITIATION AND DEVELOPMENT OF FLOWERS IN BEANS UNDER SUBOPTIMAL TEMPERATURE CONDITIONS

Four bean (Phaseolus vulgaris L.) cultivars of the north-temperate zone were examined for rate of initiation of flower primordia under day–night growth cabinet temperatures of 20/12 and 15/12 C. The cultivars Limelight and Probatine were fairly tolerant to the 15/12 C regime whereas Glamis and Tendercrop suffered tissue damage and delayed growth. When the four cultivars were exposed to 7/7 C for 10 days immediately after flower primordia had formed, flower development of Limelight and Probatine during the period was delayed, whereas the flower primordia of Glamis and Tendercrop were destroyed. Limelight and Probatine were sufficiently tolerant of low temperatures to be of value in a breeding program designed to produce cultivars suitable for growing at suboptimal temperatures.

Morphological Development of Buds of Olive as Related to Low-Temperature Requirement for Inflorescence Formation

1. In this investigation a comparison was made of the morphological development of buds on olive trees held under either greenhouse temperature conditions or natural winter temperature conditions at Davis, California. 2. The flowering ability of olive trees exposed only to a portion of the natural winter chilling period was compared with that of trees exposed to the entire natural chilling period. 3. Buds from chilled trees started increasing in fresh weight about the first of February, while buds from non-chilled trees showed no increase in weight. 4. A comparison of longisections of buds from chilled and non-chilled trees sampled February 19 shows that, by this date, there was an elongation of the axis and broadening of the apical meristem with incipient initiation of lateral organs in buds of only the chilled trees. There was no evidence of initiation of flower primordia in buds from chilled trees until March 18. 5. During the period November 6, 1961, to April 2, 1962, there was little or no evidence of morphological change in buds from non-chilled trees. 6. These morphological studies show that the initiation of flower primordia in the olive is completely inhibited by high-temperature treatment during the fall and winter months. 7. Trees exposed to 1240 hours of temperatures below 45⚬ F. formed very few inflorescences as compared to those exposed to the entire natural chilling period (1852 hours below 45⚬ F.). 8. It appears that the striking increase in ability of buds to form inflorescences after an increase in low-temperature exposure from 1240 to 1850 hours below 45⚬ F. was associated with the initial morphological changes in the buds in response to low-temperature treatment.

Photoperiodic Behavior of Sunflower

1. The sunflower, Helianthus annuus L., var. Mammoth Russian, has been shown to be a short-day type plant. It will, however, flower under a wide range of photoperiodic conditions, including excessively long days (as long as 20 hours) and a regime in which the daily dark periods are interrupted by 1-hour light periods if it be permitted to grow for a sufficiently long period. 2. Short photoperiods promote flowering both by hastening the initiation of flower primordia and by hastening the development of primordia into macroscropic floral structures. 3. Interruption of the dark periods by light is effective in inhibiting both the initiation of flower primordia as well as the development of primordia into macroscopic floral structures. 4. Sunflower thus exhibits a wide range of photoperiodic conditions under which flowering may take place plus an unusual variability in the time of flowering among individual plants in a given population. This may be related to the phenomenon pointed out by Habermann and Wallac...

Studies on the Flowering and Fruiting of Summer vs. Autumn Soybean Types : (5) Effects of the day length after flower primordia initiation upon the flowering process with reference to the adaptation to planting time in autumn soybean type

[in Japanese]