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PubMed2002

Comparison of peptides in the phloem sap of flowering and non-flowering Perilla and lupine plants using microbore HPLC followed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

Physiological evidence indicates that flower formation is hormonally controlled. The floral stimulus, or florigen, is formed in the leaves as a response to an inductive photoperiod and translocated through the phloem to the apical meristem. However, because of difficulties in obtaining and analyzing phloem sap and the lack of a bioassay, the chemical nature of this stimulus is one of the major unsolved problems in plant biology. A combination of microbore high-performance liquid chromatography (HPLC) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was used to compare the contents of the phloem sap from flowering and non-flowering plants. Instead of using one- or two-dimensional gel electrophoresis, microbore HPLC separations allowed us to detect proteins/peptides that were very small and present at very low levels. We detected more than 100 components in the phloem sap of Perilla ocymoides L. and Lupinus albusL. Sequences for 16 peptides in a mass range from 1 to 9 kDa were obtained. Two of these could be identified, 11 showed similarity to known or deduced protein sequences, and three showed no similarity to any known protein or translated gene sequence. Four of these peptides were specific to, modified, or increased in plants that were flowering, indicating their possible role in flower induction. The sequences of these peptides showed similarities to two purine permeases, a protein with similarity to protein kinases, and a protein with no similarities to any known protein.

Biological Transport↗

PubMed2003

Sexual allocation in single-flowered hermaphroditic individuals in relation to plant and flower size.

Gender expression in hermaphroditic plant species usually departs from strict equisexuality. Study of those departures can aid understanding of non hermaphroditic breeding systems and prevalence of hermaphroditism within angiosperms. Plant size is one of the most studied factors in relation to gender modification. We studied variation in gender expression in the hermaphroditic, mostly single-flowered Paeonia cambessedesii. We separately studied gender modification with increasing plant and flower size using a variety of currencies: number of ovules and stamens, dry mass, N and P. Flower size and number of floral structures (petals, stamens, carpels, and ovules) increased with plant size. Number of ovules increased more rapidly with increasing plant size than number of stamens, indicating a bias towards femaleness with increasing plant size. A similar pattern was found when regressing number of stamens and number of seeds against plant size. Number of floral structures increased with increasing flower mass, but no significant difference was found between stamens and ovules in their rate of increase. Thus, gender modification at plant level was not consistent with patterns at flower level. No differential allocation to stamens vs gynoecium, or sexual structures vs petals was found when using dry mass, N or P as currencies. However, a disproportionate increase in female allocation was found when number of structures was utilised as currency. Study of size-dependent gender expression will benefit from contrast of results obtained using several analysis levels and allocation currencies.

Animals↗

PubMed2006

Regulation of flowering in the long-day grass Lolium temulentum by gibberellins and the FLOWERING LOCUS T gene.

Seasonal control of flowering often involves leaf sensing of daylength coupled to time measurement and generation and transport of florigenic signals to the shoot apex. We show that transmitted signals in the grass Lolium temulentum may include gibberellins (GAs) and the FLOWERING LOCUS T (FT) gene. Within 2 h of starting a florally inductive long day (LD), expression of a 20-oxidase GA biosynthetic gene increases in the leaf; its product, GA(20), then increases 5.7-fold versus short day; its substrate, GA(19), decreases equivalently; and a bioactive product, GA(5), increases 4-fold. A link between flowering, LD, GAs, and GA biosynthesis is shown in three ways: (1) applied GA(19) became florigenic on exposure to LD; (2) expression of LtGA20ox1, an important GA biosynthetic gene, increased in a florally effective LD involving incandescent lamps, but not with noninductive fluorescent lamps; and (3) paclobutrazol, an inhibitor of an early step of GA biosynthesis, blocked flowering, but only if applied before the LD. Expression studies of a 2-oxidase catabolic gene showed no changes favoring a GA increase. Thus, the early LD increase in leaf GA(5) biosynthesis, coupled with subsequent doubling in GA(5) content at the shoot apex, provides a substantial trail of evidence for GA(5) as a LD florigen. LD signaling may also involve transport of FT mRNA or protein because expression of LtFT and LtCONSTANS increased rapidly, substantially (>80-fold for FT), and independently of GA. However, because a LD from fluorescent lamps induced LtFT expression but not flowering, the nature of the light response of FT requires clarification.

Base Sequence↗

PubMed2006

SUPPRESSOR OF FRIGIDA4, encoding a C2H2-Type zinc finger protein, represses flowering by transcriptional activation of Arabidopsis FLOWERING LOCUS C.

FLOWERING LOCUS C (FLC), a strong floral repressor, is one of the central regulators of flowering in Arabidopsis thaliana. The expression of FLC is increased by FRIGIDA (FRI) but decreased by vernalization, a long period of cold exposure that accelerates flowering. Although many aspects of FLC regulation have been reported, it is not known how FLC is transcriptionally activated by FRI at the molecular level. We isolated suppressor of FRIGIDA4 (suf4), a mutant that flowers early as a result of low FLC expression. SUF4 encodes a nuclear-localized protein with two C2H2-type zinc finger motifs and a Pro-rich domain. SUF4 protein interacts with FRI and FRIGIDA-LIKE1 (FRL1), two genes for which single mutations have the same phenotype as suf4. SUF4 also bound to the promoter of FLC in a chromatin immunoprecipitation assay, suggesting that SUF4 acts as a transcriptional activator of FLC after forming a complex with FRI and FRL1. In addition, suf4 suppresses luminidependens (ld), a late-flowering mutation that causes an increase of FLC, and SUF4 protein directly interacts with LD. Thus, we propose that LD binds to SUF4 to suppress its activity in the absence of FRI.

Arabidopsis↗

PubMed1995

Inhibition of flower formation by antisense repression of mitochondrial citrate synthase in transgenic potato plants leads to a specific disintegration of the ovary tissues of flowers.

The tricarboxylic acid (TCA) cycle constitutes a major component of the mitochondrial metabolism of eucaryotes, including higher plants. To analyze the importance of this pathway, we down-regulated mitochondrial citrate synthase (mCS; EC 4.1.3.7), the first enzyme of the TCA cycle, in transgenic potato plants using an antisense RNA approach. Several transformants were identified with reduced citrate synthase activity (down to approximately 6% of wild-type activity). These plants were indistinguishable from wild-type plants in the greenhouse during vegetative growth. A major change, however, was seen upon initiation of the generative phase (flower formation). In the case of transgenic plants with a strong reduction in citrate synthase activity (< 30% of wild-type levels), flower buds formed > 2 weeks later as compared with wild-type plants. Furthermore, flower buds from these plants did not develop into mature flowers but rather were aborted at an early stage of development. Microscopic analysis showed that in these cases ovaries disintegrated during flower development. We conclude that the TCA cycle is of major importance during the transition from the vegetative to the generative phase.

Citrate (si)-Synthase↗

PubMed1995

Regulation of flowering time: Arabidopsis as a model system to study genes that promote or delay flowering.

The time that plants flower is often tightly regulated and adapted to the locations in which they grow. The basis of this regulation has been analysed using genetic and physiological approaches since the early decades of this century. The study of flowering time in the model plant species Arabidopsis thaliana has allowed many genes involved in regulating flowering time to be identified as mutations, and for the genetic interactions between these mutations to have been studied. Furthermore, two genes required to promote flowering of Arabidopsis have recently been isolated, and their sequences have provided some insight into the identity of proteins involved in regulating flowering time.

Arabidopsis↗

PubMed1994

Carbohydrate Status of Tulip Bulbs during Cold-Induced Flower Stalk Elongation and Flowering.

The effect of a cold treatment on the carbohydrate status of the scales and flower stalk of Tulipa gesneriana L. cv Apeldoorn bulbs during growth after planting was studied and compared with bulbs not given cold treatment. Bulbs were stored dry for 12 weeks at 5[deg]C (precooled) or 17[deg]C (noncooled). Only the 5[deg]C treatment led to rapid flower stalk elongation and flowering following planting at higher temperatures. Precooling enhanced mobilization of starch, fructans, and sucrose in the scales. The cold-stimulated starch breakdown was initially accompanied by increased [alpha]-amylase activity per scale. In noncooled bulbs, [alpha]-amylase activity slightly decreased or remained more or less constant. Cold-induced flower stalk elongation was partially accompanied by a decrease in the sucrose content and an increase in the glucose content and invertase activity per g dry weight. The starch content in internodes initially decreased and subsequently increased; [alpha]-amylase activity per g dry weight of the lowermost internode showed a peak pattern during starch breakdown and increased thereafter. The internodes of noncooled bulbs, on the contrary, accumulated sucrose. Their glucose content and invertase activity per g dry weight remained low. Starch breakdown was not found and [alpha]-amylase activity per g dry weight of the lowermost internode remained at a low level. Precooling of tulip bulbs thus favors reserve mobilization in the scales and flower stalk and glucose accumulation in the elongating internodes.

Journal Article↗

PubMed1991

A flourishing time for flower development. Workshop on Flower Development, sponsored by Fundación Juan March, Madrid, Spain, March 11-13, 1991.

Molecular genetics has recently erupted in the field of flower development, an area of research traditionally cultivated by plant physiologists. The isolation and molecular characterization of seven homeotic genes (four in Antirrhinum majus and three in Arabidopsis thaliana) that control both floral organogenesis and the transition from inflorescences to floral meristems is leading to major breakthroughs in the understanding of the mechanisms governing flower development. This has already had a great impact among plant physiologists, who are incorporating mutant analysis into studies of floral induction and flower development. We are still missing data about the nature of the pollen product of the S-locus in self-incompatibility systems, although current experimental approaches might provide this information in the near future. Gene technology appears to have a high potential in hybrid seed production through the construction of male sterile plants as well as of plants able to restore fertility. The study of genes regulating pigment formation in flowers continues to provide interesting data on gene expression in plants, in which phenomena such as co-suppression and methylation seem to play an important role. Altogether, one can predict that very exciting times are coming in the field of flower development.

Gene Expression Regulation↗

PubMed2003

Terminal flower2, an Arabidopsis homolog of heterochromatin protein1, counteracts the activation of flowering locus T by constans in the vascular tissues of leaves to regulate flowering time.

The flowering time of plants is tightly regulated by both promotive and repressive factors. Molecular genetic studies using Arabidopsis have identified several epigenetic repressors that regulate flowering time. Terminal flower2, (TFL2), which encodes a homolog of heterochromatin protein1 represses flowering locus T (FT) expression, which is induced by the activator constans (CO) in response to the long-day signal. Here, we show that TFL2, CO, and FT are expressed together in leaf vascular tissues and that TFL2 represses FT expression continuously throughout development. Mutations in TFL2 derepress FT expression within the vascular tissues of leaves, resulting in daylength-independent early flowering. TFL2 can reduce FT expression even when CO is overexpressed. However, FT expression reaches a level sufficient for floral induction even in the presence of TFL2, suggesting that TFL2 does not maintain FT in a silent state or inhibit it completely; rather, it counteracts the effect of CO on FT activation.

Arabidopsis↗

PubMed2002

Changes in flower coloration and sepal anthocyanins of Cyanic delphinium cultivars during flowering.

The changes in flower color related to sepal pigmentation of cyanic Delphinium cultivars were investigated during anthesis. The sepal hues of the purple and blue flowered varieties observed on the initial day of unfurling had changed with a decrease in hue angle three days after anthesis. In both the purple and blue cultivars, violdelphin (3) was the major component on day one of anthesis, and the chromaticity improved with increasing sepal concentrations of violdelphin (3) and cyanodelphin (4) after three days of unfurling. The flower hue was dominated by the constitution of acylated anthocyanins, and the chromaticity was ordered by the sepal concentration. The biosynthesis of cyanodelphin (4) from violdelphin (3) was postulated since an increase in the sepal concentration of cyanodelphin (4) was accompanied by a decrease in violdelphin (3). Acylation of the anthocyanins was initiated by an increase in the respective possible precursors, tulipanin (2) and violdelphin (3), to subsequently synthesize violdelphin (3) and cyanodelphin (4) during flowering.

Anthocyanins↗

PubMed2003

The synergistic activation of FLOWERING LOCUS C by FRIGIDA and a new flowering gene AERIAL ROSETTE 1 underlies a novel morphology in Arabidopsis.

The genetic changes underlying the diversification of plant forms represent a key question in understanding plant macroevolution. To understand the mechanisms leading to novel plant morphologies we investigated the Sy-0 ecotype of Arabidopsis that forms an enlarged basal rosette of leaves, develops aerial rosettes in the axils of cauline leaves, and exhibits inflorescence and floral reversion. Here we show that this heterochronic shift in reproductive development of all shoot meristems requires interaction between dominant alleles at AERIAL ROSETTE 1 (ART1), FRIGIDA (FRI), and FLOWERING LOCUS C (FLC) loci. ART1 is a new flowering gene that maps 14 cM proximal to FLC on chromosome V. ART1 activates FLC expression through a novel flowering pathway that is independent of FRI and independent of the autonomous and vernalization pathways. Synergistic activation of the floral repressor FLC by ART1 and FRI is required for delayed onset of reproductive development of all shoot meristems, leading to the Sy-0 phenotype. These results demonstrate that modulation in flowering-time genes is one of the mechanisms leading to morphological novelties.

Arabidopsis↗

PubMed2001

Flowering in time: genes controlling photoperiodic flowering in Arabidopsis.

Successful sexual reproduction in plants relies upon the strict coordination of flowering time with favourable seasons of the year. One of the most important seasonal cues for the model plant Arabidopsis thaliana (Arabidopsis) is day length. Genes influencing flowering time in Arabidopsis have been isolated, some of which are involved in the perception and signalling of day length. This review discusses recent progress that has been made in understanding how Arabidopsis integrates environmental and internal signals to ensure a sharp transition to flowering and new insights on the role of the circadian clock in controlling the expression of genes that promote flowering in response to day length.

Arabidopsis↗

PubMed2004

Daffodil flowers delay senescence in cut Iris flowers.

Visible symptoms of tepal senescence in cut Iris x hollandica (cv. Blue Magic) flowers were delayed by placing one cut daffodil flower (Narcissus pseudonarcissus, cv. Carlton) in the same vase. Addition of mucilage, exuded by daffodil stems, to the vase water had the same effect as the flowering daffodil stem. The active compound in the mucilage was identified as narciclasine (using LC/MS, GC/MS, 1H and 13C-NMR, and comparison with an authentic sample of narciclasine). The delay of senescence, either by mucilage or purified narciclasine, was correlated with a delayed increase in protease activity, and with a considerable reduction of maximum protease activity. Narciclasine did not affect in vitro protease activity, but is known to inhibit protein synthesis at the ribosomal level. Its effects on senescence and protease activity were similar to those of cycloheximide (CHX), another inhibitor of protein synthesis, but the effective narciclasine concentration was about 100 times lower than that of CHX. It is concluded that the delay of Iris tepal senescence by daffodil stems is due to narciclasine in daffodil mucilage, which apparently inhibits the synthesis of proteins involved in senescence.

Adhesives↗

PubMed2007

Repression of flowering in Arabidopsis requires activation of FLOWERING LOCUS C expression by the histone variant H2A.Z.

The histone variant H2A.Z has been implicated in numerous chromatin-mediated processes, including transcriptional activation, euchromatin maintenance, and heterochromatin formation. In yeast and humans, H2A.Z is deposited into chromatin by a conserved protein complex known as SWR1 and SRCAP, respectively. Here, we show that mutations in the Arabidopsis thaliana homologs of two components of this complex, ACTIN-RELATED PROTEIN6 (ARP6) and PHOTOPERIOD-INDEPENDENT EARLY FLOWERING1 (PIE1), produce similar developmental phenotypes and result in the misregulation of a common set of genes. Using H2A.Z-specific antibodies, we demonstrate that ARP6 and PIE1 are required for the deposition of H2A.Z at multiple loci, including the FLOWERING LOCUS C (FLC) gene, a central repressor of the transition to flowering. Loss of H2A.Z from chromatin in arp6 and pie1 mutants results in reduced FLC expression and premature flowering, indicating that this histone variant is required for high-level expression of FLC. In addition to defining a novel mechanism for the regulation of FLC expression, these results support the existence of a SWR1-like complex in Arabidopsis and show that H2A.Z can potentiate transcriptional activation in plants. The finding that H2A.Z remains associated with chromatin throughout mitosis suggests that it may serve an epigenetic memory function by marking active genes and poising silenced genes for reactivation.

Arabidopsis↗

PubMed1992

Foraging ability of rufous hummingbirds on hummingbird flowers and hawkmoth flowers.

We examine the suitability of ornithophilous flowers and sphingophilous flowers in Ipompsis and Aquilegia for nectar foraging by the hummingbird Selasphorus rufus. In S. rufus, bill length averages 18.9 mm in females and 17.3 mm in males. Maximal tongue extension approximates bill length, suggesting that birds can feed from floral tubes up to 33.5 mm in length. However, their ability to do so is limited by two factors. First, the maximal depth at which S. rufus can extract nectar decreases with the width of the floral tube. Second, feeding time is shortest in short floral tubes and progressively increases as the tubes lengthen because of increased time required for tongue extension and retraction. Hence, nectar foraging occurs with optimal efficiency in moderately broad floral tubes with lengths that do not exceed or only slightly exceed the bill length plus </=5-mm tongue extension. In most ornithophilous taxa of Ipomopsis and Aquilegia, the floral tubes have lengths and widths in the optimal range for nectar foraging by S. rufus, whereas in the sphingophilous taxa, the basal nectar either may be reached but at much higher cost or, more frequently, is beyond reach of bills and tongues. The flower-visiting habits of S. rufus and other hummingbirds in nature are generally congruent with these conclusions and support the case for coadaptation between these plants and pollinators.

Journal Article↗

PubMed2001

In vitro control of floral transition in tomato (Lycopersicon esculentum Mill.), the model for autonomously flowering plants, using the late flowering uniflora mutant.

In vitro control of floral transition in tomato (Lycopersicon esculentum Mill.), the model plant for autonomously flowering species has been investigated using the late flowering mutant uniflora (uf). Apices collected from truly vegetative plants were cultivated on solid media supplemented with different combinations of growth regulators and chemicals. Several chemical factors implicated in the promotion of floral transition of the uf mutant have been identified: sucrose, cytokinins and nitrogenous nutrients have all to be supplied at optimal concentrations. In contrast, gibberellic acid was found to be inhibitory. These results are discussed in relation to knowledge accumulated on the nature of the flowering signals circulating, at floral transition, in other plants, especially in photoperiodic species. This study suggests that tomato could constitute an adequate model to investigate the genetic and physiological control of floral transition and contribute in unravelling pathways which are constitutively regulating this important step of plant life cycle.

Adenine↗

PubMed2001

Bollworm (Lepidoptera: Noctuidae) survival on 'Bollgard' and 'Bollgard II' cotton flower bud and flower components.

Genetically modified cotton, Gossypium hirsutum L., cultivars ('Bollgard') that produce crystalline proteins from Bacillus thuringiensis (Berliner) are valuable tools for managing lepidopteran insect pests in the United States. However, high numbers of bollworm, Helicoverpa zea (Boddie), larvae have been observed feeding in white flowers of these cultivars. Fresh tissue bioassays were conducted to investigate bollworm survival on Bollgard and 'Bollgard II' cottons. Bollworm survival was higher on square and flower anthers than on other floral structures on 'Deltapine 5415' (conventional cotton) and 'NuCOTN 33B' (Bollgard). Bollworm survival at 72 h was higher on all floral structures from Deltapine 5415 than on corresponding structures from NuCOTN 33B. ELISA tests indicated that CryIA(c) expression varied among plant parts; however, bollworm survival did not correlate with protein expression levels. Trends in bollworm survival on Bollgard II were similar to those on Bollgard and conventional cotton; however, survival was lower on all structures of Bollgard II than on corresponding structures of Bollgard and conventional cotton. These data support field observations of bollworm injury to white flowers and small bolls and provide a better understanding of larval behavior on Bollgard cotton.

Animals↗

PubMed2003

The flowers that bloom in the spring: RNA processing and seasonal flowering.

Seasonal flowering in plants responds to hormonal and environmental cues that lead to expression of genes for flowering and growth. A new paper in this issue of Cell describes how one regulatory gene controls its own expression at the level of mRNA polyadenylation, adding an exciting new model for both the RNA processing and plant gene expression fields.

Flowers↗