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PubMed2006

Integration of flowering dates in phenology and pollen counts in aerobiology: analysis of their spatial and temporal coherence in Germany (1992-1999).

We studied the possibility of integrating flowering dates in phenology and pollen counts in aerobiology in Germany. Data were analyzed for three pollen types (Betula, Poaceae, Artemisia) at 51 stations with pollen traps, and corresponding phenological flowering dates for 400 adjacent stations (< 25 km) for the years 1992-1993 and 1997-1999. The spatial and temporal coherence of these data sets was investigated by comparing start and peak of the pollen season with local minima and means of plant flowering. Our study revealed that start of birch pollen season occurred on average 5.7 days earlier than local birch flowering. For mugwort and grass, the pollen season started on average after local flowering was observed; mugwort pollen was found 4.8 days later and grass pollen season started almost on the same day (0.6 days later) as local flowering. Whereas the peak of the birch pollen season coincided with the mean flowering dates (0.4 days later), the pollen peaks of the other two species took place much later. On average, the peak of mugwort pollen occurred 15.4 days later than mean local flowering, the peak of grass pollen catches followed 22.6 days after local flowering. The study revealed a great temporal divergence between pollen and flowering dates with an irregular spatial pattern across Germany. Not all pollen catches could be explained by local vegetation flowering. Possible reasons include long-distance transport, pollen contributions of other than phenologically observed species and methodological constraints. The results suggest that further research is needed before using flowering dates in phenology to extrapolate pollen counts.

Artemisia↗

PubMed2004

Chalcone synthase as a reporter in virus-induced gene silencing studies of flower senescence.

Agrobacterium-mediated infection of petunia (Petunia hybrida) plants with tobacco rattle virus (TRV) bearing fragments of Petunia genes resulted in systemic infection and virus-induced gene silencing (VIGS) of the homologous host genes. Infection with TRV containing a phytoene desaturase (PDS) fragment resulted in reduced abundance of PDS transcripts and typical photobleaching of photosynthetic tissues. Infection with TRV containing a chalcone synthase (CHS) fragment resulted in silencing of anthocyanin production in infected flowers. The silencing phenotype ranged from scattered white spots on the normal purple background to entirely white flowers. Symptoms in the V26 cultivar were a diffuse mosaic, but infection of some purple-flowered commercial cultivars resulted in large white sectors and even entirely white flowers. Abundance of CHS transcripts in the white flowers was less than 4% of that in purple flowers on the same plant. Infection with TRV containing a tandem construct of PDS and CHS resulted in leaf photobleaching and white patterns on the flowers. Transcripts of CHS and PDS were reduced both in leaves and in flowers confirming simultaneous silencing of both genes by the tandem construct. We tested the effects of infection with TRV containing CHS and a fragment of a petunia gene encoding for 1-aminocyclopropane-1-carboxylate oxidase (ACO4) Abundance of transcripts encoding ACO4 and ACO1 were reduced (by 5% and 20%, respectively) in infected flowers. Whether the flowers were treated with ACC or pollinated, the white (silenced) flowers or flower sectors produced less ethylene and senesced later than purple (non-silenced) tissues. These results indicate the value of VIGS with tandem constructs containing CHS as reporter and a target gene as a tool for examining the function of floral-associated genes.

Acyltransferases↗

PubMed2004

Up and down asymmetrical world for flower blooming.

Form of plant body shows vertical polarity. Photosynthetic organs deploy upwards to seek light. Root system extends downward for water. In addition to this major polarity, flowers has similar features, because they bloom in the world where up and down asymmetry dominates. Many flowering plants co-evolved with pollinator animals. Success of their reproduction is linked to the shape of flower organs in many ways. Orientation of inflorescence and each individual flowers, arrangement and shape of flower organs exhibit various up and down asymmetry. Some flowers mimic female of its pollinator animal. In such case, posture of the target animal is copied to the flower. Since animal posture and shape have vertical polarity, flower happens to equip same kind of polarity. Tropic response of pistils is another up and down feature that improves fitness of flowering plants. Certain lily flowers show phototropism to bend pistil upward. Azalea flower depends on gravity as the major environmental cue, and light as the secondary signal for up. Molecular machinery for those tropic responses seems to be shared with other tropism expressed in shoot and root. However, certain differences are found in distribution of sediment amyloplast, or spatial allocation of photo-sensing and bending site. Tropic responses result in adaptation of those flowers against behavior of pollinator animals and terrestrial environment, where gravity affects living organisms and interaction among them.

Biological Evolution↗

PubMed1995

QTL analysis of flowering time in Arabidopsis thaliana.

Quantitative trait loci (QTL) analyses based on restriction fragment length polymorphism maps have been used to resolve the genetic control of flowering time in a cross between two Arabidopsis thaliana ecotypes H51 and Landsberg erecta, differing widely in flowering time. Five quantitative trait loci affecting flowering time were identified in this cross (RLN1-5), four of which are located in regions containing mutations or loci previously identified as conferring a late-flowering phenotype. One of these loci is coincident with the FRI locus identified as the major determinant for late flowering and vernalization responsiveness in the Arabidopsis ecotype Stockholm. RLN5, which maps to the lower half of chromosome five (between markers mi69 and m233), only affected flowering time significantly under short day conditions following a vernalization period. The late-flowering phenotype of H51 compared to Landsberg erecta was due to alleles conferring late flowering at only two of the five loci. At the three other loci, H51 possessed alleles conferring early flowering in comparison to those of Landsberg erecta. Combinations of alleles conferring early and late flowering from both parents accounted for the transgressive segregation of flowering time observed within the F2 population. Three QTL, RLN1, RLN2 and RLN3 displayed significant genotype-by-environment interactions for flowering time. A significant interaction between alleles at RLN3 and RLN4 was detected.

Alleles↗

PubMed2002

Rapid determination of volatile constituents of Michelia alba flowers by gas chromatography-mass spectrometry with solid-phase microextraction.

The volatile constituents of Michelia alba flowers, including fresh flowers, frozen flowers and withered flowers, were investigated by GC-MS. The volatiles in a simulated natural environment were sampled by solid-phase microextraction (SPME), with a 100 microm polydimethylsiloxane fiber at 25+/-5 degrees C for 4 h. The fibers were desorbed in a GC injection liner at 250 degrees C for 3 min. With headspace SPME-GC-MS analysis, 61 peaks were separated. The main compounds in headspace of fresh Michelia alba flowers included alpha-myrcene, (S)-limonene, (R)-fenchone, linalool, camphor, caryophyllene, germacrene D, etc., a greater number of compounds than for frozen flowers and withered flowers. At the same time, the biomarkers of fresh flowers were compared with the frozen flowers and withered flowers. In this study, headspace SPME-GC-MS afforded a simple and more sensitive sampling method for fresh Michelia alba flowers and other fresh flowers.

Gas Chromatography-Mass Spectrometry↗

PubMed2000

The mating consequences of sexual segregation within inflorescences of flowering plants.

Many co-sexual plants segregate female and male function among flowers on an inflorescence through dichogamy or the production of unisexual flowers. Sexual segregation may reduce self-pollination among flowers within inflorescences (geitonogamy), thereby increasing the pollen available for export to other plants. To assess these complementary roles we manipulated the simultaneously hermaphroditic (adichogamous) flowers of Eichhornia paniculata to produce ten-flowered inflorescences with either female above male flowers (female/male inflorescences) or male/female inflorescences, which competed for mating opportunities with five-flowered adichogamous inflorescences. Because of the upward movement of bumble-bees, selfing increased upward in adichogamous inflorescences (overall female selfing rate s+/-s.e.=0.320+/-0.026). Female flowers of male/female inflorescences selfed less than flowers in corresponding positions in adichogamous inflorescences so s fell to 0.135+/-0.027. In contrast, all-female flowers of female/male inflorescences selfed similarly to upper flowers on adichogamous inflorescences, elevating s (0.437+/-0.043). During 1997, male/female inflorescences sired more outcrossed seeds than female/male or adichogamous inflorescences, whereas during 1994 flowers on male/female inflorescences received fewer visits than those of adichogamous inflorescences, reducing their outcross siring success. Hence, sexual segregation limits geitonogamy and enhances outcross siring success when it does not affect pollinator behaviour, illustrating the importance of both female and male function in inflorescence design.

Animals↗

PubMed1967

Flowering Responses of the Long-day Plant Lemna gibba G3.

Lemna gibba L., strain G3, exhibits a qualitative long-day flowering response with a critical daylength on a 24-hour cycle of about 10 hours. Evidence is presented that the onset of daughter frond formation in a given frond inhibits the activity of the flowering meristem. Consequently, flower induction can only occur in fronds smaller than about 0.05 to 0.07 mm long. Although a minimum of 1 long day seems to be sufficient to induce the formation of flower primordia, at least 6 long days are required to obtain mature flowers since long days are also required for the early stages of flower development. The critical night length on 24, 48 and 72-hour cycles is respectively 14, 16, and 18 to 22 hours. The close similarity between the critical night length for the different cycle lengths is explained in terms of an inhibitory effect of darkness both on flower initiation and flower development. A 10-hour dark period is more inhibitory to flowering on a 36-hour cycle than on 24, 48, 60 or 72-hour cycles. It is suggested that darkness inhibits flowering through the formation of a light-labile flower inhibitor which acts to inhibit the functioning of the flowering stimulus.

Journal Article↗

PubMed2000

Mutagenesis of plants overexpressing CONSTANS demonstrates novel interactions among Arabidopsis flowering-time genes.

CONSTANS (CO) promotes flowering of Arabidopsis in response to long photoperiods. Transgenic plants carrying CO fused with the cauliflower mosaic virus 35S promoter (35S::CO) flowered earlier than did the wild type and were almost completely insensitive to length of day. Genes required for CO to promote flowering were identified by screening for mutations that suppress the effect of 35S::CO. Four mutations were identified that partially suppressed the early-flowering phenotype caused by 35S::CO. One of these mutations, suppressor of overexpression of CO 1 (soc1), defines a new locus, demonstrating that the mutagenesis approach is effective in identifying novel flowering-time mutations. The other three suppressor mutations are allelic with previously described mutations that cause late flowering. Two of them are alleles of ft, indicating that FT is required for CO to promote early flowering and most likely acts after CO in the hierarchy of flowering-time genes. The fourth suppressor mutation is an allele of fwa, and fwa soc1 35S::CO plants flowered at approximately the same time as co mutants, suggesting that a combination of fwa and soc1 abolishes the promotion of flowering by CO. Besides delaying flowering, fwa acted synergistically with 35S::CO to repress floral development after bolting. The latter phenotype was not shown by any of the progenitors and was most probably caused by a reduction in the function of LEAFY. These genetic interactions suggest models for how CO, FWA, FT, and SOC1 interact during the transition to flowering.

Arabidopsis↗

PubMed2000

Evolution of reproductive strategies in the sexually deceptive orchid Ophrys sphegodes: how does flower-specific variation of odor signals influence reproductive success?

The orchid Ophrys sphegodes Miller is pollinated by sexually excited males of the solitary bee Andrena nigroaenea, which are lured to the flowers by visual cues and volatile semiochemicals. In O. sphegodes, visits by pollinators are rare. Because of this low frequency of pollination, one would expect the evolution of strategies that increase the chance that males will visit more than one flower on the same plant; this would increase the number of pollination events on a plant and therefore the number of seeds produced. Using gas chromatography-mass spectrometry (GC-MS) analyses, we identified more than 100 compounds in the odor bouquets of labellum extracts from O. sphegodes; 24 compounds were found to be biologically active in male olfactory receptors based on gas chromatography with electroantennographic detection (GC-EAD). Gas chromatography (GC) analyses of odors from individual flowers showed less intraspecific variation in the odor bouquets of the biologically active compounds as compared to nonactive compounds. This can be explained by a higher selective pressure on the pollinator-attracting communication signal. Furthermore, we found a characteristic variation in the GC-EAD active esters and aldehydes among flowers of different stem positions within an inflorescence and in the n-alkanes and n-alkenes among plants from different populations. In our behavioral field tests, we showed that male bees learn the odor bouquets of individual flowers during mating attempts and recognize them in later encounters. Bees thereby avoid trying to mate with flowers they have visited previously, but do not avoid other flowers either of a different or the same plant. By varying the relative proportions of saturated esters and aldehydes between flowers of different stem positions, we demonstrated that a plant may take advantage of the learning abilities of the pollinators and influence flower visitation behavior. Sixty-seven percent of the males that visited one flower in an inflorescence returned to visit a second flower of the same inflorescence. However, geitonogamy is prevented and the likelihood of cross-fertilization is enhanced by the time required for the pollinium deposited on the pollinator to complete its bending movement, which is necessary for pollination to occur. Cross-fertilization is furthermore enhanced by the high degree of odor variation between plants. This variation minimizes learned avoidance of the flowers and increases the likelihood that a given pollinator would visit several to many different plants within a population.

Animals↗

PubMed1999

Plant reproductive phenology over four years including an episode of general flowering in a lowland dipterocarp forest,Sarawak, Malaysia.

The first systematic observation of a general flowering, a phenomenon unique to lowland mixed-dipterocarp forests in Southeast Asia, is presented. During general flowering, which occurs at irregular intervals of 3-10 yr, nearly all dipterocarp species together with species of other families come heavily into flower. We monitored reproductive phenology of 576 individual plants representing 305 species in 56 families in Sarawak, Malaysia. Observations continued for 53 mo from August 1992 and covered one episode of a general flowering cycle. Among 527 effective reproductive events during 43 mo, 57% were concentrated in the general flowering period (GFP) of 10 mo in 1996. We classified 257 species into flowering types based on timing and frequency of flowering. The most abundant type was "general flowering" (35%), which flowered only during GFP. The others were "supra-annual" (19%), "annual" (13%), and "sub-annual" (5%) types. General flowering type and temporal aggregation in reproductive events were commonly found among species in various categories of taxonomic groups, life forms, pollination systems, and fruit types. Possible causes for general flowering, such as promotion of pollination brought about by interspecific synchronization and paucity of climatic cues suitable for flowering trigger, are proposed, in addition to the predator satiation hypothesis of Janzen (1974).

Journal Article↗

PubMed2006

Visual targeting of components of floral colour patterns in flower-naïve bumblebees (Bombus terrestris; Apidae).

Floral colour patterns are contrasting colour patches on flowers, a part of the signalling apparatus that was considered to display shape and colour signals used by flower-visitors to detect flowers and locate the site of floral reward. Here, we show that flower-naïve bumblebees (Bombus terrestris) spontaneously direct their approach towards the outside margin of artificial flowers, which provides contrast between these dummy flowers and the background. If no floral guides are present, the bumblebees continue to approach the margin and finally touch the marginal area of the dummy flower with the tips of their antennae. Whilst approaching dummy flowers that also have a central floral guide, the bumblebees change their direction of flight: Initially, they approach the margin, later they switch to approaching the colour guide, and finally they precisely touch the floral guide with their antennae. Variation of the shape of equally sized dummy flowers did not alter the bumblebees' preferential orientation towards the guide. Using reciprocal combinations of guide colour and surrounding colour, we showed that the approach from a distance towards the corolla and the antennal contact with the guide are elicited by the same colour parameter: spectral purity. As a consequence, the dummy flowers eliciting the greatest frequency of antennal reactions at the guide are those that combine a floral guide of high spectral purity with a corolla of less spectral purity. Our results support the hypothesis that floral guides direct bumblebees' approaches to the site of first contact with the flower, which is achieved by the tips of the antennae.

Animals↗

PubMed2002

Opposing effects of reduced DNA methylation on flowering time in Arabidopsis thaliana.

Demethylation of DNA promotes flowering in plants from the vernalization-responsive ecotype C24 of Arabidopsis thaliana (L.) Heynh., but delays flowering in the ecotype Landsberg erecta which is not responsive to vernalization. To investigate these contrasting effects of low methylation we have monitored flowering times and expression of two repressors of flowering, FLC and FWA, in low-methylation plants from three late-flowering mutants in the ecotype Landsberg erecta. Demethylation of DNA decreased FLC expression in the vernalization-responsive mutants, but was not associated with a promotion of flowering; rather, in some lines, demethylation delayed flowering. The opposing effects of demethylation could be explained by its differential effect on the expression of two repressors of flowering. FLC was down-regulated in plants with low methylation, promoting flowering, while FWA was activated in response to demethylation, which probably delays the transition to flowering. Expression of the FWA gene did not delay flowering in plants of ecotype C24; our data suggest that the FWA protein of C24 may be non-functional.

Arabidopsis↗

PubMed2004

Flowering of Arabidopsis cop1 mutants in darkness.

To elucidate the role of the COP1 gene in flowering, we analyzed flowering of cop1 mutant lines in darkness. When grown in the presence of 1% (w/v) sucrose, the cop1-6 mutant flowered in darkness, but cop1-1 and cop1-4 did not. However, cop1-1 and cop1-4 flowered in darkness when grown in the presence of 5% (w/v) sucrose. Therefore, the COP1 gene represses not only photomorphogenesis in seedlings but also flowering in darkness. Comparison of mRNAs levels of floral identity genes in cop1-6 and wild-type plants grown in darkness revealed increased mRNA levels of genes that act downstream of CO and reduced FLC mRNA level in cop1-6. Double mutants of cop1-6 and each of the late-flowering mutations cry2-1, gi-2, co-1, and ld-1 flowered in darkness. All of the double mutants except cry2-1 cop1-6 flowered later than cop1-6, demonstrating that cop1-6 is epistatic to cry2-1 for early flowering. The ld-1 cop1-6 double mutant flowered much earlier than the ld-1 mutant. The delay in flowering in the double mutants was not strongly influenced by the light conditions, whereas that of the gi-2 cop1-6 double mutant was reduced in darkness.

Arabidopsis↗

PubMed2005

Distinct roles of GIGANTEA in promoting flowering and regulating circadian rhythms in Arabidopsis.

The circadian clock acts as the timekeeping mechanism in photoperiodism. In Arabidopsis thaliana, a circadian clock-controlled flowering pathway comprising the genes GIGANTEA (GI), CONSTANS (CO), and FLOWERING LOCUS T (FT) promotes flowering specifically under long days. Within this pathway, GI regulates circadian rhythms and flowering and acts earlier in the hierarchy than CO and FT, suggesting that GI might regulate flowering indirectly by affecting the control of circadian rhythms. We studied the relationship between the roles of GI in flowering and the circadian clock using late elongated hypocotyl circadian clock associated1 double mutants, which are impaired in circadian clock function, plants overexpressing GI (35S:GI), and gi mutants. These experiments demonstrated that GI acts between the circadian oscillator and CO to promote flowering by increasing CO and FT mRNA abundance. In addition, circadian rhythms in expression of genes that do not control flowering are altered in 35S:GI and gi mutant plants under continuous light and continuous darkness, and the phase of expression of these genes is changed under diurnal cycles. Therefore, GI plays a general role in controlling circadian rhythms, and this is different from its effect on the amplitude of expression of CO and FT. Functional GI:green fluorescent protein is localized to the nucleus in transgenic Arabidopsis plants, supporting the idea that GI regulates flowering in the nucleus. We propose that the effect of GI on flowering is not an indirect effect of its role in circadian clock regulation, but rather that GI also acts in the nucleus to more directly promote the expression of flowering-time genes.

Arabidopsis↗

PubMed2006

Poplar FT2 shortens the juvenile phase and promotes seasonal flowering.

Many woody perennials, such as poplar (Populus deltoides), are not able to form flower buds during the first several years of their life cycle. They must undergo a transition from the juvenile phase to the reproductive phase to be competent to produce flower buds. After this transition, trees begin to form flower buds in the spring of each growing season. The genetic factors that control flower initiation, ending the juvenile phase, are unknown in poplar. The factors that regulate seasonal flower bud formation are also unknown. Here, we report that poplar FLOWERING LOCUS T2 (FT2), a relative of the Arabidopsis thaliana flowering-time gene FT, controls first-time and seasonal flowering in poplar. The FT2 transcript is rare during the juvenile phase of poplar. When juvenile poplar is transformed with FT2 and transcript levels are increased, flowering is induced within 1 year. During the transition between vegetative and reproductive growth in mature trees, FT2 transcripts are abundant during reproductive growth under long days. Subsequently, floral meristems emerge on flanks of the axillary inflorescence shoots. These findings suggest that FT2 is part of the flower initiation pathway in poplar and plays an additional role in regulating seasonal flower initiation that is integrated with the poplar perennial growth habit.

Arabidopsis↗

PubMed2004

A flower image retrieval method based on ROI feature.

Flower image retrieval is a very important step for computer-aided plant species recognition. In this paper, we propose an efficient segmentation method based on color clustering and domain knowledge to extract flower regions from flower images. For flower retrieval, we use the color histogram of a flower region to characterize the color features of flower and two shape-based features sets, Centroid-Contour Distance (CCD) and Angle Code Histogram (ACH), to characterize the shape features of a flower contour. Experimental results showed that our flower region extraction method based on color clustering and domain knowledge can produce accurate flower regions. Flower retrieval results on a database of 885 flower images collected from 14 plant species showed that our Region-of-Interest (ROI) based retrieval approach using both color and shape features can perform better than a method based on the global color histogram proposed by Swain and Ballard (1991) and a method based on domain knowledge-driven segmentation and color names proposed by Das et al.(1999).

Algorithms↗

PubMed2004

[Carpel development in male flowers of cucumber (Cucumis sativus. L)].

Carpel development in cucumber male flowers was studied by morphological, histochemical and isoenzyme electrophoretic analyses. The results showed that: (1) cell number of the carpel in male flowers increased continuously during the development of male flowers, and the carpel in male flowers was abundant in RNA content; (2) the carpel in male flowers at latter developmental stage was differentiated, and a placenta-like structure was formed in the carpel of male flowers during anthesis, while the ovule did not appear as that of mature female flowers; (3) The POD and esterase isoenzyme electrophoretic profiles of carpel varied from the development of male flowers, which further indicated that the carpel in mature male flowers was no longer at the stage of primordium. It could be deduced from the results that carpel of cucumber male flowers develops continuously in a distinct pattern with that of female flowers during sex expression process.

Cell Count↗

PubMed2006

[Inheritance of the white-flower and its influence to related characters in eggplant (Solanum melongem Linn)].

The inheritance of the white-flower and its influence to related characters in eggplant were studied with the white-flowered mutant of XIANLVQIE and its maternal bred. Result showed that the flower color was attributed to a couple of complete dominance genes. Purple color flower "Col" was dominant to the white "col". Compared with the purple-flowered strain, the white-flowered strain not only grew more blooming, but also had more stamens in one flower, less pollens in one anther and less seeds in one fruit. In the meanwhile, in white-flowered eggplants, microspore and fruit was bigger, and yield was higher than purple-flowered. The white-flowered strain could be used as a variety and the white-flowered character could be used as a marker to appraise purity of hybrid in eggplant.

Flowers↗