Calcium changes in ovules and embryo sacs of Plumbago zeylanica L.

Calcium was localized in ovules of Plumbago zeylanica from 1 day before anthesis to 3 days after anthesis using potassium antimonate and transmission electron microscopy in pollinated and emasculated flowers. At 1 day before anthesis, embryo sacs (containing an egg cell, a central cell and zero to three accessory cells) appear mature and contain abundant calcium precipitates (ppts), in contrast to nucellar cells. At anthesis, the vacuoles of nucellar cells have enlarged, and micropylar cells, in particular, are heavily labeled with calcium ppts. As pollen tubes elongate through ovular tissues, ppts diminish in ovular cells and become concentrated in the pollen tube cell wall. After fertilization, the calcium ppts sharply diminish in fertilized ovules; in unfertilized ovules, calcium ppts remain abundant up to 3 days after anthesis (when unfertilized ovules are shed). The distribution of calcium in the ovule changes in apparent response to fertilization, suggesting that calcium content may be related to the attraction and receipt of the pollen tube. In contrast with conventionally-organized embryo sacs with synergids, Plumbago accumulates calcium in the egg cell. Received: 30 December 1999 / Revision accepted: 24 March 2000     

LABILE SEX EXPRESSION IN ANDROMONOECIOUS SOLANUM HIRTUM: FLORAL DEVELOPMENT AND SEX DETERMINATION

Sex expression (the proportions of hermaphrodite and staminate flowers produced) of the andromonoecious species Solatium hirtum is labile, and this lability of whole plant sex expression is due to labile sex expression of individual floral buds. In this paper I examine the developmental processes that underlie the differences in floral sex expression of hermaphrodite and staminate flowers of Solarium hirtum, focusing particularly on the processes responsible for the observed lability of floral sex expression. Differences in bud growth rate and relative growth of floral organs in these buds are evident at about the time of megasporocyte meiosis (11–12 days before anthesis). However, gynoecial sterility in staminate buds does not occur until just 6–7 days before anthesis. At this time, abnormalities in ovule development occur in staminate buds: the ovules begin to appear necrotic, the integumentary tapetum collapses, and the megagametophytes of many ovules cease normal development. These observations are consistent with the predictions of labile floral development.     

Size-dependent reproduction in Australian alpine Ranunculus

Abstract The effect of plant size on reproduction in four species of alpine Ranunculus (R. muelleri, R. dissectifolius, R. graniticola and R. niphophilus) was investigated in two sites over two seasons in the field on a total of 190 plants. The effects of plant size (number of leaves) and number of flowers on the number of anthers, ovules and seed per flower and per plant were determined. There was a positive relationship between several measures of reproduction and plant size in all four species, indicating that reproduction is size-dependent. All the results indicate that the main factor controlling the amount of seed produced by alpine Ranunculus is the size of the plant. Specifically, bigger plants produced more seed by producing more flowers, not by producing more ovules per flower, or higher seed set per flower. Correspondingly, bigger plants produced more anthers by producing more flowers, rather than by producing flowers with more anthers. The total number of seeds produced by a plant was directly proportional to plant size in the four species. Therefore, reproductive effort should not vary with plant size in the four species.     

Influence of intraovular reserves on ovule fate in apricot (Prunus armeniaca L.)

 In many plant species with multiovulate ovaries, a considerable reduction in the number of ovules takes place. However, the underlying physiological causes are not clear. In Prunus spp., although flowers present two ovules, usually only one seed is produced. We have followed the development and degeneration of the two ovules in apricot (Prunus armeniaca L.) and examined the extent to which carbohydrates within the ovule might be involved in determining the fate of the ovule. While the primary ovule grows in the days following anthesis, growth of the secondary ovule is arrested. Starch distribution along the different ovular tissues exhibits several changes that are different in the two ovules. Primary ovule growth is inversely related to starch content and this growth takes place independently of pollination since it occurs in the same way in pollinated and unpollinated flowers. In the secondary ovule, starch disappears simultaneously from all ovular structures and callose is layered at the chalazal end of the nucellus. The size of the secondary ovule does not change significantly from anthesis to degeneration, and callose starts to accumulate 5 days after anthesis. Likewise, this process occurs independently of pollination. These results are discussed in terms of the implications of the starch content of ovules in fertilization success and ovule fate. Received: 26 August 1997 / Revision accepted: 17 December 1997     

Homeotic, Meristic and Cytological Floral Mutants of Thryptomene calycina (family Myrtaceae)

Twenty plants with various phenotypic abnormalities to the flowerswere selected from very large populations of Thryptomene calycinain the Grampian and Black Ranges. Most of these had impairedreproductive function. Normal flowers were epigynous with fivesepals, five petals, five anthers, a single style and two anatropousovules. The mutants were two partially male sterile, tetraploidplants with large flowers, one of which occasionally producedadditional flowers from the leaf axils with peduncles as wellas pedicels; one plant which produced a proportion of hexapetaloidflowers with six stamens; three gross mutants with fleshy, bracteoidpointed petals and sepals, no stamens, vestigial styles andstigmas, exposed ovules and no inferior ovary; one plant withfleshly, bracteoid pointed sepals, vestigial style and stigmabut with exposed ovular structures replaced by four to fivesterile ovules generally inside an abnormal ovary; two plantswith reduced ovary diameter and sterile ovules, shortened style,five reduced sepals and petals and five to eight anthers; threeanthocyanin-free plants; three plants with pink sepals; twoplants with half-sized flowers which produced a proportion offasciated stems; one plant which occasionally produced flowerswithout pedicels which virtually resulted in organs which wereleaf-flower composites; two plants which produced sepals andpetals which contained chlorophyll and prematurely senesced,and had partial substitution of petals by anthers.Copyright1993, 1999 Academic Press Thryptomene calycina, Myrtaceae, Victorian lace flower, floral mutations, mutants, homeotic, meristic, tetraploid, fasciation, male sterility, cut flowers     

Arabidopsis ovule is the target for Agrobacterium in planta vacuum infiltration transformation

The visual marker GUS has been utilized in this study to understand the Arabidopsis thaliana vacuum infiltration transformation process by Agrobacterium tumefaciens. High transformation frequencies of up to 394 transgenic seeds per infiltrated plant were achieved. The results showed that the majority of the transgenic seeds from single infiltrated plants were from independent transformation events based on Southern analysis, progeny segregation, distribution of transgenic seeds throughout the infiltrated plants and the microscopic analysis of GUS expression in ovules of infiltrated plants. GUS expression in mature pollen and anthers was monitored daily from 0 to 12 days post-infiltration. In addition, all ovules from a single infiltrated plant were examined every other day. GUS expression frequencies of up to 1% of pollen were observed 3-5 days post-infiltration, whereas frequencies of up to 6% were detected with ovules of unopened flowers 5-11 days post-infiltration. Most importantly, transgenic seeds were obtained only from genetic crosses using infiltrated plants as the pollen recipient but not the pollen donor, demonstrating Agrobacterium transformation through the ovule pathway.     

Determining critical pre- and post-anthesis periods and physiological processes in Lycopersicon esculentum Mill. exposed to moderately elevated temperatures

To determine the thermosensitive periods and physiological processes in tomato flowers exposed to moderately elevated temperatures, tomato plants (Lycopersicon esculentum Mill., cv. NC 8288) were grown at 28/22 degrees C or 32/26 degrees C day/night temperature regimes and then transferred to the opposite regime for 0-15 d before or 0-24 h after anthesis. For plants initially grown at 28/22 degrees C, moderate temperature stress before anthesis decreased the percentage of fruit set per plant, but did not clarify the thermosensitive period. The same level of stress did not significantly reduce fruit set when applied immediately after anthesis. For plants initially grown at 32/26 degrees C, fruit set was completely prevented unless a relief period of more than 5 d was provided before anthesis. The same level of stress relief for 3-24 h after anthesis also increased fruit set. Plants were most sensitive to 32/26 degrees C temperatures 7-15 d before anthesis. Microscopic investigation of anthers in plants grown continuously at high temperature indicated disruption of development in the pollen, endothecium, epidermis, and stomium. This disruption was reduced, but still observable in plants relieved from high temperature for 10 d before anthesis.     

CYTOPLASMIC EFFECTS ON THE DIFFERENTIATION OF ANTHERS AND OVULES OF COTTON

Reciprocal crosses of Upland cotton with a hybrid derived from (Gossypium anomalum × G. thurberi) × G. hirsutum produced progenies differing significantly in anther development and in the production of supernumerary ovules outside the ovary. Plants with G. anomalum cytoplasm produced fewer anthers than the reciprocal hybrids with G. hirsutum cytoplasm, had a higher percentage of sterile anthers, and were far more likely to form external ovules on an abnormally thickened tip of the staminal tube. The number of locules and ovules within the ovary was not significantly affected by cytoplasm.     

REVERSIBLE ANTHER OPENING IN LILIUM PHILADELPHICUM (LILIACEAE): A POSSIBLE MEANS OF ENHANCING MALE FITNESS

Studies of Lilium philadelphicum on Isle Royale National Park, Lake Superior, show that thecae (pollen-containing sacs) of dehisced anthers close in the rain, thus protecting the pollen and prolonging the pollen donor phase of the flower. To our knowledge, this is the first report of anthers with longitudinal dehiscence reclosing after opening. Individual flowers of L. philadelphicum are long lived (8–11 d), do not shorten their flowering period in response to successful fertilization of the ovules, and are primarily pollinated by butterflies. Butterflies do not forage in the rain and may first visit a flower several days after anthesis. Under such circumstances, strong selection may exist to protect pollen during unfavorable weather conditions in order to prolong the pollen donor phase. Flowers with long pollen donor phases are likely to contribute more offspring to the next generation than flowers with short pollen donor phases.     

Heterodichogamy in Kingdonia (Circaeasteraceae, Ranunculales)

Background and Aims

Preliminary field observations in 2001 and 2002 suggested that Kingdonia uniflora (Circaeasteraceae, Ranunculales) exhibits heterodichogamy, an unusual kind of reproductive heteromorphy, hitherto unreported in Ranunculales and known from only one other genus in basal eudicots.

Methods

During several subsequent years flowers were observed in the field. Flowers were fixed in FAA and studied with microtome sections series and with the scanning electron microscope.

Key Results

The flowers proved to be heterodichogamous, with protandrous and protogynous morphs, which have a 1 : 1 ratio. Both morphs equally set fruit. Each year a single flower is formed at the tip of a rhizome or more rarely two flowers. The flowers are already open when they appear at the soil surface, before they are receptive and before pollen is dispersed. In both floral morphs the styles elongate early and the stigmas are positioned above the anthers before anthesis begins. In protogynous flowers the stigmas become receptive in this position; later the styles become reflexed and then the anthers dehisce. In contrast, in protandrous flowers the stamen filaments elongate during early anthesis such that the dehiscing anthers come to lie above the (still unreceptive) stigmas; after dehiscence of all anthers in a flower the styles begin to elongate and become receptive.

Conclusions

This is the first record of heterodichogamy in a representative of Ranunculales, in an herbaceous eudicot, and in a plant with uniflorous ramets. The occurrence of heterodichogamy in Kingdonia in which clonal reproduction appears to be dominant might be an adaptation to avoid mating between the ramets from a common mother individual (genet).Key words: Kingdonia, Circaeasteraceae, Ranunculales, heterodichogamy, reproductive heteromorphy     

"Real" and Feed Pollen of Lagerstroemia indica: Ecophysiological Differences

Abstract: Lagerstroemia indica is heterantheric, its flowers bearing two kinds of stamens: six peripheral stamens with long, curved filaments and large anthers producing blue-green pollen, capable of emitting pollen tubes and fertilizing ovules; or a central tuft of 35 - 40 smaller anthers producing yellow feed pollen that does not germinate and is collected by insects, mainly bees. The two types of pollen differ in volume, number of pores, pore intine protrusion, wall structure, pollenkitt quality, hydration state, viability at anthesis, longevity and mono- and disaccharide composition. Although total sugar concentrations (glucose, fructose and sucrose) are the same in both types, relative concentrations are different, "real" pollen being sucrose-rich (S / [G + F] = 1.2) and feed pollen glucose-fructose-rich (S / [G + F] = 0.3). A lower degree of dehydration, pore intine protrusion and higher monosaccharide content could make feed pollen more digestible for pollinators. On the other hand, the cytological features of "real" pollen (high dehydration, higher sucrose content) points to longer viability and reproductive function.     

Is pollen removal or seed set favoured by flower longevity in a hummingbird-pollinated Salvia species?

Background and Aims

The period between the beginning of anthesis and flower senescence modulates the transport of pollen by pollinators among conspecific flowers, and its length may therefore influence reproductive success. This study evaluated whether floral longevity favours pollen removal from the anthers over fecundity (seed set) in an ornithophilous species that does not undergo pollen limitation.

Methods

Field investigations were conducted on floral longevity, nectar production, pollinator behaviour, and variations in fruit set (FS), mean number of seeds per fruit (MSF) and pollen removal by hummingbirds (PR) during the anthesis of Salvia sellowiana in south-east Brazil.

Key Results

Anthesis of flowers exposed to pollinators lasted 4 d, as well as on flowers with pollen removed from the anthers or deposited on the stigma. The longevity of bagged flowers was significantly higher (approx. 9 d). FS and PR reached 87·2 and 90 %, respectively, in natural conditions. PR increased gradually over the period of anthesis; however, FS and MSF reached their maxima in the first hours of anthesis. Nectar production was continuous, but the secretion rate was reduced after pollination. The removal of nectar from non-pollinated flowers stimulated its production.

Conclusions

The longevity of anthesis in S. sellowiana seems to be related to the mechanism of gradual dispensing of pollen, resulting in greater male reproductive success. This is in agreement with the pollen-donation hypothesis. The small number of ovules (four) of S. sellowiana and the high frequency and the foraging mode of its pollinators may favour the selection for floral longevity driven by male fitness in this system.     

大叶相思花部形态与开花生物学研究

对大叶相思(Acacia auriculiformis)栽培植株进行观察,用光学显微镜和扫描电子显微镜(SEM)对其花部形态和开花生物学特征进行研究。结果表明,大叶相思开花期为8～12月,穗状花序由114.9±11.9朵花组成,每朵花含124.1±16.5枚雄蕊,每雄蕊含有8粒16合花粉,单花花粉量为15885粒;雌蕊1枚,具14.4±1.8个胚珠,柱头凹陷,属于湿柱头类型。P/O值为1103.1;大叶相思花在夜间开放,开花可分为5个阶段。开花期间观察到雌蕊先于雄蕊伸出花冠和雄蕊先于雌蕊伸出花冠并存的现象,推测雌雄基本同熟。SEM观察花药在开花的第2阶段形成开裂线,第4阶段完全开裂并开始散粉。雄蕊于开花第1天的9: 00～12: 00大量散粉;雌蕊柱头在开花第1天上午出现分泌物,随后逐渐减少。开花后3~4 d柱头开始凋零,柱头可授期约为3 d,以开花第1天10: 00之后的可授性最佳。     

倒地铃花的形态分化与花药结构研究

利用体视显微镜、半薄切片和超薄切片法对倒地铃(Cardiospermum halicacabum Linn.)雄花和假两性花开花过程及花药发育过程进行了观察和比较研究。结果显示:(1)花蕾发育早期,倒地铃雄花和假两性花的花蕾形态没有区别;花蕾发育后期,雄花雌蕊退化,假两性花雌蕊继续发育,花蕾外部形态出现差异;开花时雄花花药开裂,假两性花花药不开裂。(2)倒地铃雄花和假两性花均具四室花药,呈蝶形;花药壁细胞从外到内依次是表皮、药室内壁、中层(2层)和绒毡层;花药壁发育为基本型,绒毡层为单核分泌型,四分体为四面体型,花粉粒两核;开花时雄花和假两性花中层都有残留;小孢子液泡化时,绒毡层开始降解,两核花粉粒时,假两性花绒毡层降解较快。(3)雄花药室内壁次生加厚完全,裂口区发育,连接同侧花粉囊的连接组织降解,花药开裂;假两性花药室内壁次生加厚不完全,具唇形细胞,药隔细胞壁未降解,同侧花粉囊未连通,花药四室,不开裂;假两性花成熟花粉粒细胞质稀少,内壁不完整。本研究结果表明,倒地铃的雄花是由两性花在发育早期雌蕊停止发育形成的,假两性花则由两性花在发育晚期雄蕊功能退化造成的。     

Honeybee‐assisted wind pollination in bamboo Phyllostachys nidularia (Bambusoideae: Poaceae)?

Floral syndromes and pollination of three species of Phyllostachys bamboos were studied in Central China in 1999 and 2000. All were protogynous. Stigmas were receptive and had pollen deposited on them 2 days before anther dehiscence. The period of anthesis in the three bamboos was 3 days. Individual pollen grains of the three species were similar in size (30–40 μm in diameter) and had features typical of wind-pollinated plants. The ratios of pollen to ovules (p/o ratio) in P . nidularia , P . heteroclada and P . nuda were 6500, 12 700 and 33 000, respectively. Mean pollen loads on each flower (one ovule) of these three species were 7.3, 8.8 and 9.4 grains, respectively. Pollen transfer in P . heteroclada and P . nuda depended on wind, and no flower visitors were seen in the field. However, in P . nidularia , Apis cerana Fab. was a frequent pollen collector observed from 1200 to 1330 h. The visits undertaken by thousands of honeybees resulted in a large number of pollen grains being released from the anthers in a short time (10–15 min) in one day, which accelerated and synchronized the release of pollen from the anthers that seemed to enhance the chance of pollination. Given that honeybees played an indirect role in pollen transfer this could partly explain the low p/o ratio in P . nidularia . Reviewing the literature, we found insect visits to flowers of bamboos were not infrequent phenomena. We suggest pollination efficiency should be considered as one selective factor in attempts to understand mast flowering in bamboo. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 138 , 1–7.     

Chronology of the differentiation of cotton (Gossypium hirsutum L.) fiber cells

Cotton fibers are single elongated cells that develop from epidermal cells of the ovule. The chronology of fiber differentiation was investigated using cultured ovules. Epidermal cells differentiate into fiber cells approx. 3 d before anthesis. When ovules were cultured on a defined medium, fiber growth could be initiated on ovules any time between 2 d preanthesis and the time of anthesis by adding indole-3-acetic acid and gibberellic acid to the medium. In the absence of phytohormones, fibers did not grow, and when ovules between 2 d preanthesis and anthesis were cultured without hormones past the day of anthesis and hormones then added, most ovules failed to produce fibers. The results define the timing of fiber differentiation from epidermal cells, and also define a window of time when differentiated cells are capable of further development. During this window, fiber cells are latent awaiting appropriate stimulation which in the intact plant is apparently associated with anthesis.Abbreviations GA₃ gibberellic acid - IAA indole-3-acetic acid     

Origin of gynogenetic embryos of Beta vulgaris L.

Haploid plants of Beta vulgaris were obtained by gynogenesis from ovules isolated from male-fertile and annual and biennial male-sterile plants. We show that on a N6 basal medium, supplemented with 2.85 M IAA and 0.94 M Kinetin or 0.88 M BAP, haploids originate directly through embryogenesis. In order to determine the optimal developmental stage of the ovule of Beta vulgaris for gynogenesis, we carried out a histological study of whole ovules from open male-sterile flowers (collected 1 to 5 days after flowering) and unopened male-fertile flowers (collected 1 to 3 days before anthesis). In all cases, the gametophyte appeared completely differentiated. These results suggest that maturity of the gametophyte is reached a few days before anthesis and therefore ovules from unopened flowers are already suitable for plating. A developmental study of the haploid cells of the sugarbeet embryo sac during the first week of in vitro culture showed that the viable gynogenetic embryo originated only from the egg cell.     

Reproductive ecology of dioecious Siparuna (Monimiaceae) in Ecuador–a case of gall midge pollination

The reproductive ecology of the dioecious genus Siparuna , belonging to the primitive family Monimiaceae, was investigated in Ecuador. Thirteen species were studied, and species growing at high altitudes (above 500 m) were compared with species growing at lower altitudes. The genus has specialized flowers pollinated by Cecidomyiidae (Asynapta sp. and other genera) that lay eggs chiefly in male flowers since these are more easily accessible than female flowers due to their morphology. Several traits ensure that pollen transfer is accomplished: 1. long flowering of individuals and single flowers; 2. specific floral morphology (unisexuality, landing platform, restricted pore) allowing the flowers to be visited by Cecidomyiidae seeking egg-laying sites, and 3. a low number of ovules that have to be pollinated in each flower. The low number of ovules per flower results in a high pollen-ovule (P/O) ratio even though pollen production in male flowers is only moderate.
High altitude species had larger flowers, higher pollen-ovule ratios, fewer ovules per female flower, and longer periods of anthesis. Gender differences were seen in the longer functionality of female flowers; the larger numbers of male flowers produced; and the average diameter at breast height (DBH) biased for one of the two sexes depending on the species investigated, with no clear trend in the size distributions of individuals of both sexes. Sex ratios departed significantly from unity both to male and female bias but usually were in favour of males. There were no general differences in the ratio of functional male to female flowers at the time of observation nor in the sizes of male and female flowers. The evolution of unisexual flowers in Siparuna can be explained as a result of the differential predation by larvae: unimportant in male flowers, destructive if occurring in female flowers.     

BREEDING SYSTEM EVOLUTION IN LEAVENWORTHIA: BREEDING SYSTEM VARIATION AND REPRODUCTIVE SUCCESS IN NATURAL POPULATIONS OF LEAVENWORTHIA CRASSA (CRUCIFERAE)

Populations of Leavenworthia crassa (Cruciferae) studied for 3 years exhibited among- and within-population genetic variation for a suite of floral and reproductive traits (flower width, petal length, anther position, ability to set seeds in the absence of pollinators, time to first flowering) associated with breeding system. We used electrophoretic markers to show that a population with small, monomorphically colored flowers with introrse anthers had a significantly lower outcrossing rate (t = 0.03) than did a population with larger, polymorphically colored flowers with extrorse anthers (t = 0.33). In the more-outcrossing population the correlation between higher maternal plant outcrossing rate and the suite of six traits approached significance (P < 0.067), with greater petal size, greater flower width, and reduced ability to set seeds in the absence of pollinators contributing significantly. Plants in selfing populations had a generally higher reproductive success, with a higher number of flowers per plant, a smaller proportion of unfertilized ovules, a smaller proportion of fertilized ovules aborted, a higher rate of fruit set, and overall a larger number of seeds matured than did plants from the more outcrossing populations. Pollen limitation did not appear to account for lower reproductive success in outcrossing populations. Resource limitation did not differ substantially between populations. However, within-ovary patterns of fertilization, abortion, and seed weight were significantly less random in outcrossing populations than in selfing populations, suggesting that differential gamete and embryo success may be responsible for lower reproductive success in outcrossing populations.