Ethylene and flower senescence

The end of the relatively short life of carnations held in air is associated with climacteric rises in ethylene production and respiration, and coordinate rises in activity of the enzymes of the ethylene biosynthetic pathway. Carnation sensescence is associated with derepression of specific genes, increased polyribosome activity, and major changes in patterns of protein synthesis. Isotopic competition assays indicate the presence in carnation petals of ethylene binding activity with the expected characteristics of the physiological ethylene receptor. Inhibition of ethylene production and/or ethylene binding (whether in selected varieties, or by treatment with chemicals) results in longer-lived carnations. Examination of other flowers shows that the carnation is not a universal paradigm for flower senescence. The response to ethylene varies widely, and in many species petal wilting occurs without any apparent involvement of ethylene.     

Somatic polyploidy and its consequences for flower coloration and flower morphology in azalea

Flower colour variegation is not only a phenomenon of importance to horticulture, the phenotype involved is also often used as a scientific model system for the study of complex gene regulation processes. In the course of such studies on azalea, we observed a correlation between flower colour patterns, flower morphology and somatic polyploidy. Using high-resolution flow cytometry of nuclear DNA, the ploidy level was determined in flowers of different azalea sport families. Sports exhibiting variegated flowers with broad (>7 mm), differently coloured, petal edges (picotee type) proved to be tetraploid in the petal edge but diploid in the rest of the flower tissue. Neither flower colour pattern nor ploidy differences are periclinal chimeric in origin, but seem to be correlated with the topographic location of the cells within the flower tissue, i.e. the margin of the petals. The possible role of gene dosage effects and cell size involved in the remarkable correlation between somatic polyploidy, (flavonoid) gene expression and flower morphology is discussed.     

Effects of nectar concentration and flower depth on flower handling efficiency of bumble bees

Summary Fluid viscosity only affected ingestion rates of bumble bees (Bombus) for solutions greater than 35–40% sucrose (mass of solute per mass of solution). This contrasts with previously published models based on fluid dynamics which predicted continuous depression of ingestion rates with increasing viscosity. Individual bees maintained constant lapping rates regardless of sucrose concentration (up to at least 70%). The decline in ingestion rates at higher concentrations apparently resulted from the tongue not contacting liquid long enough to become saturated due to reduced capillary flow. Increasing flower depth similarly decreased the volume of liquid ingested per lap, and did not affect lapping rate. Morphologically dissimilar bees drank at different rates because glossa length affects lapping rate and volume ingested per lap, and body mass affects lapping rate. An additional species-specific component to lapping rate also influenced ingestion rates. Deviations from a regression model derived to explain ingestion rates as a function of glossa length, body mass, flower depth and liquid viscosity suggest mechanistic and behavioralaspects to flower probing time. Because of the relation between ingestion rate and liquid viscosity, the sucrose concentration maximizing a bee's rate of net energy uptake should lie between 50–65%, depending primarily on specific conditions of nectar volume, inflorescence size and flight time between inflorescences.     

花色形成与花生长的调控

结合笔者的研究结果,对光、糖和GAs在花生长及花色形成中的作用和可能的调节机制进行了综述。光通过光受体介导的高辐照度反应(HIR)和光合作用调控花生长及花色素苷合成;糖作为碳源和渗透调节因子,影响花瓣细胞的生长及花色素苷积累,依赖己糖激酶的信号途径可能在糖的调控中起作用;GAs通过调节特异基因的转录间接地诱导花色素苷合成途径中结构基因的表达。     

Cytoplasmic accumulation of flavonoids in flower petals and its relevance to yellow flower colouration

It is widely accepted that the mix of flavonoids in the cell vacuole is the source of flavonoid based petal colour, and that analysis of the petal extract reveals the nature and relative levels of vacuolar flavonoid pigments. However, it has recently been established with lisianthus flowers that some petal flavonoids can be excluded from the vacuolar mix through deposition in the cell wall or through complexation with proteins inside the vacuole, and that these flavonoids are not readily extractable. The present work demonstrates that flavonoids can also be compartmented within the cell cytoplasm. Using adaxial epidermal peels from the petals of lisianthus (Eustoma grandiflorum), Lathyrus chrysanthus and Dianthus caryophyllus, light and laser scanning confocal microscopy studies revealed a significant concentration of petal flavonoids in the cell cytoplasm of some tissues. With lisianthus, flavonoid analyses of isolated protoplasts and vacuoles were used to establish that ca 14% of petal flavonoids are located in the cytoplasm (cf. 30% in the cell wall and 56% in the vacuole). The cytoplasmic flavonoids are predominantly acylated glycosides (cf. non-acylated in the cell wall). Flavonoid aggregation on a cytoplasmic protein substrate provides a rational mechanism to account for how colourless flavonoid glycosides can produce yellow colouration in petals, and perhaps also in other plant parts. High vacuolar concentrations of such flavonoids are shown to be insufficient.     

Ethylene and the annona flower

The annona (Annona hybrida) flower is protogynous, and reaches its male stage about 26 hours after the beginning of the female stage. A rise in ethylene production was found to precede the male stage. Much more ethylene was produced by the reproductive organs than by the petals, with the anthers producing most of the ethylene. Ethylene treatments advanced the male stage, but not the female stage. Exposing flowers to hypobaric pressure postponed the onset of their male stage. Application of various growth substances causing ethylene production by the flower advanced the male stage.     

Optimal flower lifetimes

Summary ESS floral lifetimes satisfy the product theorem from sex allocation theory. The dimensionless time investment per flower is a symmetric function of two dimensionless gain : cost ratios, one for each gender function.     

Analysis of flavonoids in flower petals of soybean near-isogenic lines for flower and pubescence color genes

W1, W3, W4, and Wm genes control flower color, whereas T and Td genes control pubescence color in soybean. W1, W3, Wm, and T are presumed to encode flavonoid 3'5'-hydroxylase (EC 1.14.13.88), dihydroflavonol 4-reductase (EC 1.1.1.219), flavonol synthase (EC 1.14.11.23), and flavonoid 3'-hydroxylase (EC 1.14.13.21), respectively. The objective of this study was to determine the structure of the primary anthocyanin, flavonol, and dihydroflavonol in flower petals. Primary component of anthocyanin in purple flower cultivars Clark (W1W1 w3w3 W4W4 WmWm TT TdTd) and Harosoy (W1W1 w3w3 W4W4 WmWm tt TdTd) was malvidin 3,5-di-O-glucoside with delphinidin 3,5-di-O-glucoside as a minor compound. Primary flavonol and dihydroflavonol were kaempferol 3-O-gentiobioside and aromadendrin 3-O-glucoside, respectively. Quantitative analysis of near-isogenic lines (NILs) for flower or pubescence color genes, Clark-w1 (white flower), Clark-w4 (near-white flower), Clark-W3w4 (dilute purple flower), Clark-t (gray pubescence), Clark-td (near-gray pubescence), Harosoy-wm (magenta flower), and Harosoy-T (tawny pubescence) was carried out. No anthocyanins were detected in Clark-w1 and Clark-w4, whereas a trace amount was detected in Clark-W3w4. Amount of flavonols and dihydroflavonol in NILs with w1 or w4 were largely similar to the NILs with purple flower suggesting that W1 and W4 affect only anthocyanin biosynthesis. Amount of flavonol glycosides was substantially reduced and dihydroflavonol was increased in Harosoy-wm suggesting that Wm is responsible for the production of flavonol from dihydroflavonol. The recessive wm allele reduces flavonol amount and inhibits co-pigmentation between anthocyanins and flavonols resulting in less bluer (magenta) flower color. Pubescence color genes, T or Td, had no apparent effect on flavonoid biosynthesis in flower petals.     

Pollination and flower diversity in scrophulariaceae

The Botanical Review - The flowers of the Scrophulariaceae show a great diversity in form, especially of the corolla. The most common pollinators are bees collecting nectar, pollen, or oil; other...     

Flowering and seasonal changes in flower sex ratio and frequency of flower visitors in a population of Saxifraga hirculus

The open, dish-shaped flowers of Saxifraga hirculus reflected ultraviolet and yellow light, contained very small amounts of nectar, and contained an average of about 75300 pollen grains per flower. Almost 11% of the pollen was inviable. Stigmatic pollen loads and seed set decreased during the course of the season. The plant appeared to be fully between-ramet compatible and partially within-ramet compatible. Seed set for the population was 30.3%. The protandrous flower opened during the day and had male and female phases of nine and three days, respectively. The protandrous system reduced the number of pollination days by a third.
At least 26 species of insects, 16 of which were syrphids, visited the flowers. Based on the number of flower visits, four species were the dominant visitors of S. hirculus: Eurimyia lineata and Neoascia tenur (Diptera: Syrphidae); Asindulum nigrum (Diptera: Mycetophilidae), and Zygaena trlfolii (Lepidoptera: Zygaenidae). Eurimyia lineata was the most frequent visitor (51% of all visits). As the season advanced, the visits by E. lineata decreased, whereas the visits by A. nigrum increased. Z. trifolli disappeared completely towards the end of the season. Only two thirds of the pollination days were "good" foraging days for these visitor species. The four major visitor species spent an average of 11.7, 27.4, 30.7 and 22.6 s per flower, respectively. Estimates suggest that about 6.5 visits (which is equal to 2.6 min of flower-visiting) and 2100 grains of pollen were required to produce one seed.     

Comparative evolution of flower and fruit morphology

Angiosperm diversification has resulted in a vast array of plant morphologies. Only recently has it been appreciated that diversification might have proceeded quite differently for the two key diagnostic structures of this clade, flowers and fruits. These structures are hypothesized to have experienced different selective pressures via their interactions with animals in dispersal mutualisms, resulting in a greater amount of morphological diversification in animal-pollinated flowers than in animal-dispersed fruits. I tested this idea using size and colour traits for the flowers and fruits of 472 species occurring in three floras (St John, Hawaii and the Great Plains). Phylogenetically controlled analyses of nearest-neighbour distances in multidimensional trait space matched the predicted pattern: in each of the three floras, flowers were more divergent from one another than were fruits. In addition, the spacing of species clusters differed for flowers versus fruits in the flora of St John, with clusters in flower space more divergent than those in fruit space. The results are consistent with the idea that a major driver of angiosperm diversification has been stronger selection for divergent floral morphology than for divergent fruit morphology, although genetic, physiological and ecological constraints may also play a role.     

Jasmonates in flower and seed development

Jasmonates are ubiquitously occurring lipid-derived signaling compounds active in plant development and plant responses to biotic and abiotic stresses. Upon environmental stimuli jasmonates are formed and accumulate transiently. During flower and seed development, jasmonic acid (JA) and a remarkable number of different metabolites accumulate organ- and tissue specifically. The accumulation is accompanied with expression of jasmonate-inducible genes. Among these genes there are defense genes and developmentally regulated genes. The profile of jasmonate compounds in flowers and seeds covers active signaling molecules such as JA, its precursor 12-oxophytodienoic acid (OPDA) and amino acid conjugates such as JA-Ile, but also inactive signaling molecules occur such as 12-hydroxy-JA and its sulfated derivative. These latter compounds can occur at several orders of magnitude higher level than JA. Metabolic conversion of JA and JA-Ile to hydroxylated compounds seems to inactivate JA signaling, but also specific functions of jasmonates in flower and seed development were detected. In tomato OPDA is involved in embryo development. Occurrence of jasmonates, expression of JA-inducible genes and JA-dependent processes in flower and seed development will be discussed.     

Style-controlled wilting of the flower

Differences in rate of wilting in cross-, self-and unpollinated flowers of self-incompatiblePetunia hybrida L. clone W166H appeared to be significant. Wilting rate was fastest following cross-pollination and slowest in unpollinated flowers. The difference between wilting behaviour of cross- and self-pollinated flowers was not caused by rate of pollen tube growth and not by the incompatibility (recognition or rejection) reaction either. It is assumed, that, following pollination, the wilting reaction is only retarded after penetration of pollen tubes of the same genetic composition as the style (complete self-pollination). The number of viable pollen grains necessary to initiate a maximal wilting-rate of flowers following cross- and self-pollination is about 800, which means that a fifth of the stigmatic surface must be covered with living pollen grains. It is suggested that pollen tube penetration and injury of the style have a similar influence on the initiation of wilting.Wilting-rate following pollination is faster in young plants as compared with wilting in old plants. The wilting process of unpollinated and self-pollinated flowers started in the early morning and lasted till afternoon. Cross-pollinated flowers wilted independently of the hour of the day. The role of flower-wilting as a means of communication to the environment with regard to pollination of the style is discussed.     

Molecular evolution of flower development

Flowers, as reproductive structures of the most successful group of land plants, have been a central focus of study for both evolutionists and ecologists. Recent advances in unravelling the genetics of flower development have provided insight into the evolution of floral structures among angiosperms. The study of the evolution of genes that control floral morphogenesis permits us to draw inferences on the diversification of developmental systems, the origin of floral organs and the selective forces that drive evolutionary change among these plant reproductive structures.     

Genetic control of flower development

Flowering plants are the most highly evolved and complex organisms within the plant kingdom. The flower consists of several distinct organ systems that are responsible for higher plant reproduction. Cells within specific floral organs differentiate into spores and gametes required by the plant to complete its life cycle. Flower development represents an excellent model for understanding the molecular and physiological processes that control organ differentiation in higher plants. Rapidly emerging gene tagging procedures are facilitating the isolation of genes that control flower morphogenesis.     

Origins of flower morphology

Flowers evolved in many steps, probably starting long before flowering plants (angiophytes) originated. Certain parts of flowers are conservative and have not changed much during evolution; others are evolutionarily highly plastic. Here conservative features are discussed and an attempt is made to trace them back through their evolutionary history. Microsporangia and ovules (which develop into seeds) are preangiophyte floral elements. Angiospermy, combined with postgenital fusion, was the most prominent key innovation in angiophytes. Angiospermy and thecal organization of stamens originated earlier than all clades of extant angiosperms (the crown group of angiophytes). Differentiation of a perianth into calyx and corolla and syncarpy appeared after the first branching of the basalmost clades of extant angiosperms. Sympetaly and floral tubes as well as tenuinucellar, unitegmic ovules originated as major innovations in the clade that led to asterids. An obvious trend in flower evolution is increased synorganisation of parts, which led to new structures. Fixation of floral organ number and position was a precondition for synorganization. Concomitantly, plasticity changed from number and position of organs to shape of the new structures. Character distribution mapped onto cladograms indicates that key innovations do not appear suddenly, but start with trials and only later become deeply rooted genetically in the organization. This is implied from the common occurrence of reversals in the early history of an innovation. J. Exp. Zool. (Mol. Dev. Evol.) 291:105-115, 2001.     

Size constraints and flower abundance determine the number of interactions in a plant–flower visitor web

The number of interactions with flower visitor species differs considerably among insect pollinated plants. Knowing the causes for this variation is central to the conservation of single species as well as whole plant–flower visitor communities. Species specific constraints on flower visitor numbers are seldom investigated at the community level. In this study we tested whether flower size parameters set constraints on the morphology of the potential nectar feeding visitors and thus determine the number of visitor species. We studied three possible constraints: the depth and width of tubular structures hiding the nectar (nectar holder depth and width) and the size of flower parts that visitors can land on (size of the alighting place). In addition we assess the role of flower abundance on this relationship. We hypothesized that the stronger size constraints and the smaller flower abundance, the smaller the number of visitor species will be. Our study of a Mediterranean plant–flower visitor community revealed that nectar holder depth, nectar holder width and number of flowers explained 71% of the variation in the number of visitor species. The size of the alighting place did not restrict the body length of the visitors and was not related to visitor species number. In a second step of the analyses we calculated for each plant species the potential number of visitors by determining for each insect species of the local visitor pool whether it passed the morphological limits set by the plant. These potential numbers were highly correlated with the observed numbers (r²=0.5, p<0.001). For each plant species we tested whether the observed visitors were a random selection out of these potential visitors by comparing the mean of the observed and expected proboscis length distributions. For most plant species the observed mean was not significantly different from the random means. Our findings shed light on the way plant–flower visitor networks are structured. Knowing the constraints on interaction patterns will be an important prerequisite to formulate realistic null models and understand patterns of resource partitioning as well as coevolutionary processes.     

Mechanisms and function of flower and inflorescence reversion

Flower and inflorescence reversion involve a switch from floral development back to vegetative development, thus rendering flowering a phase in an ongoing growth pattern rather than a terminal act of the meristem. Although it can be considered an unusual event, reversion raises questions about the nature and function of flowering. It is linked to environmental conditions and is most often a response to conditions opposite to those that induce flowering. Research on molecular genetic mechanisms underlying plant development over the last 15 years has pinpointed some of the key genes involved in the transition to flowering and flower development. Such investigations have also uncovered mutations which reduce floral maintenance or alter the balance between vegetative and floral features of the plant. How this information contributes to an understanding of floral reversion is assessed here. One issue that arises is whether floral commitment (defined as the ability to continue flowering when inductive conditions no longer exist) is a developmental switch affecting the whole plant or is a mechanism which assigns autonomy to individual meristems. A related question is whether floral or vegetative development is the underlying default pathway of the plant. This review begins by considering how studies of flowering in Arabidopsis thaliana have aided understanding of mechanisms of floral maintenance. Arabidopsis has not been found to revert to leaf production in any of the conditions or genetic backgrounds analysed to date. A clear-cut reversion to leaf production has, however, been described in Impatiens balsamina. It is proposed that a single gene controls whether Impatiens reverts or can maintain flowering when inductive conditions are removed, and it is inferred that this gene functions to control the synthesis or transport of a leaf-generated signal. But it is also argued that the susceptibility of Impatiens to reversion is a consequence of the meristem-based mechanisms controlling development of the flower in this species. Thus, in Impatiens, a leaf-derived signal is critical for completion of flowering and can be considered to be the basis of a plant-wide floral commitment that is achieved without accompanying meristem autonomy. The evidence, derived from in vitro and other studies, that similar mechanisms operate in other species is assessed. It is concluded that most species (including Arabidopsis) are less prone to reversion because signals from the leaf are less ephemeral, and the pathways driving flower development have a high level of redundancy that generates meristem autonomy even when leaf-derived signals are weak. This gives stability to the flowering process, even where its initiation is dependent on environmental cues. On this interpretation, Impatiens reversion appears as an anomaly resulting from an unusual combination of leaf signalling and meristem regulation. Nevertheless, it is shown that the ability to revert can serve a function in the life history strategy (perenniality) or reproductive habit (pseudovivipary) of many plants. In these instances reversion has been assimilated into regular plant development and plays a crucial role there.