Corolla Growth Research Articles

Temporal Distinction between Male and Female Floral Organ Development in Nicotiana tabacum cv. Xanthi (Solanaceae).

Early floral developmental investigations provide crucial evidence for phylogenetic and molecular studies of plants. The developmental and evolutionary mechanisms underlying the variations in floral organs are critical for a thorough understanding of the diversification of flowers. Ontogenetic comparisons between anthers and pistil within single flowers were characterized over time in Nicotiana tabacum cv. Xanthi. The ages of 42 tobacco flower or flower primordia were estimated using corolla growth analysis. Results showed that the protodermal layer in carpel primordia contributes to carpel development by both anticlinal and periclinal divisions. Periclinal divisions in the hypodermal layer of the placenta were observed around 4.8 ± 1.3 days after the formation of early carpel primordia (ECP) and ovule initiation occurred 10.0 ± 0.5 days after ECP. Meiosis in anthers and ovules began about 8.9 ± 1.1 days and 14.4 ± 1.3 days after ECP, respectively. Results showed an evident temporal distinction between megasporogenesis and microsporogenesis. Flower ages spanned a 17-day interval, starting with flower primordia containing the ECP and anther primordia to the tetrad stage of meiosis in megasporocytes and the bicellular stage in pollen grains. These results establish a solid foundation for future studies in order to identify the developmental and molecular mechanisms responsible for the mating system in tobacco.

Corolla retention after pollination facilitates the development of fertilized ovules in Fritillaria delavayi (Liliaceae)

Corollas (or perianths), considered to contribute to pollinator attraction during anthesis, persist after anthesis in many plants. However, their post-floral function has been little investigated within a cost-benefit framework. We explored the adaptive significance of corolla retention after anthesis for reproduction in Fritillaria delavayi, a perennial herb endemic to the alpine areas of the Hengduan Mountains, southwestern China. We examined whether the persistent corollas enhance reproductive success during seed development. Persistent corollas increased fruit temperature on sunny days, and greatly decreased the intensity of ultraviolet-B/C (UV-B/C) radiation reaching fruits. When corollas were removed immediately after pollination, fecundity and progeny quality were adversely affected. Measurements of flower mass and size showed no further corolla growth during fruiting, and respiration and transpiration tests demonstrated that both respiration rate and transpiration rate of corollas were much lower during fruiting than during flowering, indicating a slight additional resource investment in corolla retention after anthesis. Thus, seed production by F. delavayi may be facilitated by corolla retention during seed development at only a small physiological cost. We conclude that corolla retention may be an adaptive strategy that enhances female reproductive success by having a protective role for ripening seeds in the harsh conditions at high elevation.

A phylogenetic analysis of trait convergence in the spring flora1This article is part of a Special Issue entitled “Pollination biology research in Canada: Perspectives on a mutualism at different scales”.

In temperate deciduous forests, spring flowering plants exhibit remarkable similarity in a number of characteristics, including reproductive, vegetative, and ecological traits. The apparent convergence of floral traits, especially corolla colour, among spring flowering species has been well documented, but remains poorly understood. Here we review adaptive hypotheses and predictions that have been proposed to explain the apparent correlation between spring flowering and a suite of traits. We investigated the correlation between flowering phenology (i.e., spring or nonspring) and several key traits using phylogenetic comparative methods. Through this analysis we were able to confirm the existence of a correlation for five of the six traits examined. Specifically, spring flowering is shown to have evolved in a correlated fashion with reproductive schedule (perennial vs. annual), light corolla colour, fruit type, growth form, and forest strata layer. In general, our survey determined that spring flowering species are perennial, have light coloured corollas, a herbaceous growth form, and tend to occupy the understory of the forest. These results are discussed in light of the reviewed adaptive hypotheses and the spring pollination environment.

Temporal, spatial and hormonal regulation of the S‐adenosylmethionine synthetase gene in petunia

Gibberellic acid (GA3) promotes corolla elongation and pigmentation in petunia flowers. We have previously shown that G.A3 induces pigmentation by activating specific genes of the anthocyanin biosynthetic pathway. The aim of the present work was to examine whether GA3 induces also the expression of genes from other metabolic pathways in petunia corollas that may be associated with growth. Recently we reported the cloning of the petunia sam gene coding for S‐adenosylmethionine synthetase (SAM‐S). In the present work we show that sam expression is induced by GA3 in both corollas and stems. The expression of the gene was correlated with corolla elongation. GA3 and the cylokinin, N‐6‐benzyladenine (BA) promoted corolla growth and sam expression, whereas abscisic acid (ABA) inhibited corolla elongation and repressed sam mRNA accumulation. An analysis of sam expression in stems indicated a high level in young, elongating internodes and a very low level in the mature, non‐elongating stem zone. The results of the present study show that the effect of GA3 on gene expression in the corolla of petunia, is not restricted to the anthocyanin biosynthetic pathway, they also suggest a possible role for sam in GA3‐induced corolla and stem elongation.

Rates of corolla growth in tobacco determined with the plastochron index

The growth of vegetative and reproductive shoots of Nicotiana tabacum L. cv. Xanthi is analyzed with the plastochron index to estimate the relationship between corolla growth and time. The plastochron of leaves 9 through 20 declines steadily at each successive node. The flower plastochron increases steadily during the growth of an individual cyme, with the most distal flower to open having the longest plastochron. Variation in the flower plastochron is the result of variation in the rate of flower initiation, not the growth rate of individual flowers. The corolla has an extended phase of approximately constant relative growth in length (between 0.2 · d(-1) and 0.3 · d(-1)) until a peak of growth (0.5 · d(-1)) 2-3 d before anthesis. Corollas also have periodic peaks and troughs of growth that are low in amplitude (0.1 · d(-1)), but persist throughout most of corolla development. The pattern of corolla expansion contrasts strongly with earlier reports of the pattern of tobacco leaf growth.

Effects of carbohydrate and water status on flower opening of cut Madelon roses

Abstract Flowering stems of ‘Madelon’ roses ( Rosa hybrida L.) severed from the intact plant at the commercially recommended cutting stage and placed in water showed little growth of the corolla and virtually no flower opening. Inclusion of sucrose and an antimicrobial compound in the solution resulted in growth and opening as in unsevered flowers. Flowers placed in water without antimicrobial compounds had a low water potential as a result of vascular blockage in the lowermost segment of the stem. The decrease in water potential was correlated with inhibition of corolla growth and flower opening. The negative effect of water potential on growth and opening was independent of the positive effect of sucrose. Flower opening of ‘Sonia’ roses, cut at the same stage as ‘Madelon’ roses, was as in unsevered flowers. The level of starch in the corolla of ‘Sonia’ roses was twice as high as in ‘Madelon’ roses. ‘Madelon’ roses cut at a later stage of development contained more corolla starch than those cut earlier and both growth and opening were no longer inhibited. The data suggest that the poor opening of cut ‘Madelon’ roses was initially due to relatively low levels of reserve carbohydrates in the corolla while later it was partially due to a low water potential.

Stamens and gibberellin in the regulation of corolla pigmentation and growth in Petunia hybrida

Removal of stamens, or even of only the anthers, at an early stage of corolla development, before the start of main anthocyanin production, inhibited both growth and pigmentation of attached corollas of Petunia. When only one or two stamens were removed from one side, the inhibition was restricted to the corolla side adjacent to the detached stamens. Application of gibberellic acid (GA3) substituted for the stamens in its effect on both growth and pigmentation. In detached corollas, isolated at the early-green stage and grown in vitro in sucrose medium, GA3 promoted growth and was essential for anthocyanin synthesis. A marked enhancement of anthocyanin production was observed 48 h before the increase in corolla growth rate. Corollas detached at later stages were able to continue their growth and pigmentation in sucrose without GA3. When Paclobutrazol (β-[(4-chlorophenyl)-ethyl]-α(1,1-dimethylethyl)-H-1,2,4-triazol-1-ethanol), an inhibitor of gibberellin biosynthesis, was added to the growth medium of in-vitro-grown corollas, pigmentation was inhibited but there was no effect on corolla growth. Low levels of GA3 counteracted the Paclobutrazol effect on pigmentation but did not affect growth. The above results indicate that the effect of GA3 (and probably that of the stamens) on corolla growth is independent of its effect on pigmentation. Gibberellic acid and paclobutrazol had no effect on [(14)C]sucrose uptake by in-vitro-grown corollas. The activity of phenylalanine ammonialyase was correlated with the effect of stamens and GA3 on pigmentation in corollas grown in vivo and in vitro.

Endogenous Levels and Transport of 1-Aminocyclopropane-1-Carboxylic Acid in Stamens of Ipomoea nil (Convolvulaceae)

Filament and corolla growth in flowers of Ipomoea nil are inhibited by ethylene production. Anthers inhibited filament growth in vitro during younger stages of development even in the presence of the growth promoter gibberellic acid (GA(3)). To test whether the anthers could be sources of 1-aminocyclopropane-1-carboxylic acid (ACC) endogenous levels of ACC and ethylene production were monitored using gas chromatography. To also test whether the filaments could be transport vectors for ACC the movement of [(14)C]ACC was assessed by scintillation counting from donor agarose blocks, through filament sections, and into receiver agarose blocks. While ACC levels fluctuated in anthers 87 to 21 h before anthesis, anthers contained increased levels of ACC from 15 to 6 hours before anthesis. Ethylene production also fluctuated but peak levels were shifted about 6 hours closer to anthesis than ACC levels within the anthers. Both ACC and ethylene levels in filaments showed fluctuations similar to those in the anthers. [(14)C]ACC movement became increasingly basipetal during development. Older stages showed greater polar [(14)C]ACC efflux rates, while all stages showed constant polar influx rates. Low levels of endogenous ACC were transported basipetally from the anther through the filament into agarose blocks at all stages of development. Corresponding levels of endogenous ethylene production remained constant between the various stages during ACC transport. We have evidence that stamens of I. nil have a role as source tissues and transport vectors for ACC, to stimulate corolla growth, such as corolla unfolding and senescence.

INTERACTING ROLES OF GIBBERELLIN AND ETHYLENE IN COROLLA EXPANSION OF IPOMOEA NIL (CONVOLVULACEAE)

The relatively rapid and extensive corolla expansion in Ipomoea nil (L.) Roth cv. ‘Scarlett O'Hara’ appears to be initiated by a shift in the balance between a growth promoter (gibberellin, GA) and a growth inhibitor (ethylene) two days before anthesis. The effects of applied growth regulators in vitro, were measured as a change in area of segments from whole young corollas 16–17 mm long. Applied gibberellic acid (GA3) strongly promoted growth, while a GA action inhibitor (ancymidol) reduced growth. Inhibitors of GA biosynthesis (AMO‐1618, paclobutrazol, tetcyclasis, and chlorocholine chloride) had little effect, implying that the GAs were not being synthesized within the corolla segments, at least at this stage of corolla growth. Both the level of endogenous GAs and response of the segments to sucrose increased as the corolla size also increased from 15 to 20 mm in length. Applied 1‐aminocyclopropane‐l‐carboxylic acid (ACC), an ethylene precursor, inhibited the response of corollas to applied GA3. Applications of ethylene biosynthesis inhibitors (AVG and cobalt ions) promoted growth of the corolla segments. Rapid ethylene production by corollas 15–17 mm long (48 hr before flower opening) appeared to inhibit the growth that may have been induced by low levels of endogenous GAs. Older corollas (longer than 18 mm) had very low levels of ethylene production and much higher levels of GA‐like substances; these changes apparently allow the corollas to begin to expand in vivo and to strongly respond to sucrose applications alone in vitro. Acid‐induced growth does not seem to be an important component of corolla expansion; applied fusicoccin (a proton efflux promoter) and sodium orthovanadate (a proton efflux inhibitor) had no significant effect on growth of the 16–17 mm long corollas. Buffers (Good's and phosphate) over a wide pH range had no effect on corolla expansion. Taken together, our results indicate that the regulation of corolla expansion depends (at least in part) on compensatory shifts in the levels of two plant growth regulators [PGRs], ethylene and GA.

Influence of Stamens, Gibberellic Acid and Sucrose on Corolla Growth in Gladiolus

Summary Studies were made using flower buds of gladiolus to examine the influence of stamens on corolla growth and to test whether or not the effect of stamens could be replaced by gibberellic acid (GA 3 ) and/or sucrose. It was observed that the growth of the corolla was promoted by stamens in the early stages but the stamen effect decreased and the corolla became independent as the growth of the flower bud advanced. In the early stages of corolla growth GA 3 was able to replace the promotory effect of stamens. Sucrose promoted the growth of younger buds only when used in concert with GA 3 . It is inferred that in an intact spike the gibberellins required for corolla growth are supplied by the stamens until the stage when separation of the outer bract occurs.

The Role of Ethylene in Corolla Unfolding in Ipomoea nil (Convolvulaceae)

The roles of ethylene in corolla growth and senescence have been extensively studied; light, temperature, and abscisic acid (ABA) have already been implicated in rapid corolla opening (unfolding) in morning glory. In the present study, a possible interaction between ABA and ethylene production was examined. While applied ABA promoted corolla unfolding, it also promoted ethylene production. Furthermore, the effect of ABA could be eliminated by the ethylene biosynthesis inhibitors, aminoethoxyvinyl glycine (AVG) and cobalt ions. Simultaneously applied aminocyclopropane carboxylic acid (ACC) augmented the ABA response, but ACC applied alone promoted corolla unfolding as effectively as ABA alone. Measurements of ethylene production during eight successive stages of flower opening showed that the ethylene burst widely reported to occur in opened flowers prior to corolla senescence actually begins before the corolla unfolds. Ethylene production seems to be a later part of the sequence of biochemical events that leads to both corolla unfolding and synchronized inrolling and senescence.

THE ROLE OF ETHYLENE IN COROLLA UNFOLDING IN IPOMOEA NIL (CONVOLVULACEAE).

The roles of ethylene in corolla growth and senescence have been extensively studied; light, temperature, and abscisic acid (ABA) have already been implicated in rapid corolla opening (unfolding) in morning glory. In the present study, a possible interaction between ABA and ethylene production was examined. While applied ABA promoted corolla unfolding, it also promoted ethylene production. Furthermore, the effect of ABA could be eliminated by the ethylene biosynthesis inhibitors, aminoethoxyvinyl glycine (AVG) and cobalt ions. Simultaneously applied aminocyclopropane carboxylic acid (ACC) augmented the ABA response, but ACC applied alone promoted corolla unfolding as effectively as ABA alone. Measurements of ethylene production during eight successive stages of flower opening showed that the ethylene burst widely reported to occur in opened flowers prior to corolla senescence actually begins before the corolla unfolds. Ethylene production seems to be a later part of the sequence of biochemical events that leads to both corolla unfolding and synchronized inrolling and senescence.

Physiology of flower bud growth and opening

Flower growth and opening are commonplace events, but physiologically intricate and inadequately explained. In this review, we have brought together and evaluated information on this subject to focus attention on the dynamic facets of flower development. In particular, the physiological basis of flower bud dormancy, nature of cleistogamy, mechanism of flower bud growth and turgor maintenance and role of stamens in corolla growth have been examined. The regulation of flower movements and opening by temperature and light, and circadian rhythms in flower opening have been discussed, along with a consideration of the role of the petal epidermis in light perception. It is emphasized that studies on flower physiology need to be intensified in view of the lacunae in our basic knowledge as well as to provide a sound basis for improving yields of both agricultural and horticultural crops.

The Roles of Plant Hormones in the Growth of the Corolla of Gaillardia grandiflora (Asteraceae) Ray Flowers

Corolla elongation and the roles of plant hormones in this process in Gaillardia grandiflora Van Houtte ray flowers were examined. The sterile ray flowers elongated during a 2-day period, and corolla growth was accompanied by fresh and dry weight increases and epidermal cell elongation (greatest near the base of the corolla) but not by cell division. Corollas excised from young ray flowers were measured during treatment in vitro with solutions of plant growth regulators. They elongated in response to gibberellins and fusicoccin but did not respond to auxins, cytokinins, abscisic acid, ethylene, or inhibitors of ethylene biosynthesis. Sequential and simultaneous hormone applications indicated no additive or synergistic effects between hormones, but auxin did reduce gibberellin-promoted growth. Analyses of endogenous auxins showed no significant variation, and ethylene production decreased prior to elongation, while a 20-fold increase in endogenous gibberellin activity was observed just prior to rapid corolla elongation. It appears that corolla growth in Gaillardia is accomplished by an increase in gibberellin activity alone, that multiple hormone interactions are not important in the control of corolla growth, and that part of the mode of action of gibberellin is acid-induced growth.

THE ROLES OF PLANT HORMONES IN THE GROWTH OF THE COROLLA OF GAILLARDIA GRANDIFLORA (ASTERACEAE) RAY FLOWERS

Corolla elongation and the roles of plant hormones in this process in Gaillardia grandiflora Van Houtte ray flowers were examined. The sterile ray flowers elongated during a 2‐day period, and corolla growth was accompanied by fresh and dry weight increases and epidermal cell elongation (greatest near the base of the corolla) but not by cell division. Corollas excised from young ray flowers were measured during treatment in vitro with solutions of plant growth regulators. They elongated in response to gibberellins and fusicoccin but did not respond to auxins, cytokinins, abscisic acid, ethylene, or inhibitors of ethylene biosynthesis. Sequential and simultaneous hormone applications indicated no additive or synergistic effects between hormones, but auxin did reduce gibberellin‐promoted growth. Analyses of endogenous auxins showed no significant variation, and ethylene production decreased prior to elongation, while a 20‐fold increase in endogenous gibberellin activity was observed just prior to rapid corolla elongation. It appears that corolla growth in Gaillardia is accomplished by an increase in gibberellin activity alone, that multiple hormone interactions are not important in the control of corolla growth, and that part of the mode of action of gibberellin is acid‐induced growth.

Morphogenic Potentialities of Flower Buds of Kalanchoe pinnata Pers. grown in vitro

Excised flower buds of Kalanchoe pinnata Pers. representing two early stages of development (designated sets I and II), were cultured on modified White's medium (WB). They failed to attain full development on WB or on WB containing any of the following supplements: indole-3yl-acetic acid (IAA), 2,4-dichlorophenoxyacetic acid (2,4-D), naphthaleneacetic acid (NAA), kinetin, or coconut milk (CM). A slight stimulation of the growth of corolla was caused by kinetin (10 ppm). IAA (I ppm) and NAA (I ppm) induced rooting from the cut end of the pedicel and from the proliferated torus tissue situated between the sepals and petals. 2,4-D (I ppm) either singly or in concert with CM (10 per cent) stimulated the formation of shoot buds and root growth. Addition of kinetin (I and 10 ppm) to WB favoured shoot formation, but suppressed rooting. Flower buds of set II developed shoot buds more readily than those of set I. Thus, the primordia floral organs present in the immature buds lose their ability for normal morphogenesis under culture conditions. Buds destined to form flowers can be made to revert to vegetative growth.

Effect of Gibberellic Acid on Corolla Size

IN a previous communication1 I reported that emasculation of Glechoma hederacea flower buds resulted in a reduction in corolla size similar to that found in naturally occurring female flowers, and I suggested that the anthers produced a hormone causing enlargement of the corolla. An attempt to replace this by the application of β-indolylacetic acid to emasculated buds was ineffective—low concentrations having no effect and high concentrations (500 and 1,000 p.p.m.) causing inhibition of corolla growth.