Pollination Ecophysiology of Mercurialis annua L. (Euphorbiaceae), an Anemophilous Species Flowering all Year Round

Mercurialis annua L. is a dioecious anemophilous species thatflowers all year round in central and southern Italy. The flowersof both sexes are dimorphic: the female flower has a vestigialcalyx; the male flower consists only of a calyx that opens atanthesis. The anthers always dehisce after anthesis. The anthesisof male flowers seems to be temperature dependent, whereas antherdehiscence is related to relative humidity. The pollen grainsvary in volume according to the season: they are smaller whenrelative humidity is low and vice versa. They always decreasein volume after anther dehiscence and have the capacity to varyin volume and reach equilibrium with a changing environment.Viability is high, but may drop suddenly during heavy rain orhail that damage the exposed male flowers. The number of pollengrains per stigma varies from 0 to 300. The data is discussedin relation to the type of pollination and environmental characteristics.Copyright1994, 1999 Academic Press Mercurialis annua, dioecism, anthesis, anther dehiscence, pollen volume, pollen viability, anemophilous pollination, pollination ecology     

Mechanism of Anther Dehiscence in Rice (Oryza sativa L.)

This paper presents a new explanation of the mechanism of antherdehiscence in rice during the period from floret opening topollen dispersal. The theca dehisced on the stomium in the apicalpart and the anther wall in the basal part of the large locule.Comparison of the anther dehiscence process under various airhumidity conditions showed that the process, until the splittingat the apical and basal parts, was a moisture-requiring processwhereas the widening of the splits in both parts was a desiccatoryprocess. Observation of the anther transverse section, revealedthe marked development of the U-shaped thick cell wall in theendothecium adjacent to these two splits. From these observations,the anther dehiscence mechanism may be explained as follows.At the time of anthesis, pollen grains swell rapidly in responseto the floret opening and cause the theca to bulge, rupturingthe septum. The pollen pressure combined with the inward bendingof the locule walls adjacent to the stomium causes splittingof the stomium in the apical part of the theca. At the sametime, the septum rupture extends to the bottom of the largelocule supported by the pollen pressure. After these processes,the locule walls adjacent to both splits straighten probablydue to their water loss. This straightening widens the splitsand the swollen pollen grains overflow from the widened splits.Copyright1999 Annals of Botany Company Anther dehiscence, Oryza sativa L., pollen grain swelling, rice, septum, stomium, theca.     

Pollination, Pollen Viability and Pistil Receptivity in Cucurbita pepo

Cucurbita pepo carries male and female flowers on the same plant,and is pollinated by nectar-collecting bees. The nectaries aredimorphic in the two sexes and pollen is loaded and unloadedas the bees gain access to the nectar. Both types of flowerare open for only 6 h (from 0600 h to 1200 h); male flowersopen and close half an hour earlier than female flowers. Thelatter produce more nectar and are visited more often by thebees than the male flowers. Pollen viability determined by fluoresceindiacetate (fluorochromatic reaction) decreases by 20% duringanthesis and more rapidly after the flower closes. This decreaseis due to dehydration of the grain, especially around the porewhere the intine is exposed. An unusual feature of this speciesis that the grains do not dehydrate before anther dehiscence.Female receptivity has two aspects, that of the stigma lasting4 d, and that of the ovules lasting 2 d. The receptivity ofthe two sexes and the short period of anthesis are discussedin the light of the reproductive ecology of the species.Copyright1993, 1999 Academic Press Entomophilous pollination, anthesis, nectars, pollen viability, female receptivity, bees, pollinator efficiency, courgette Cucurbita pepo, Cucurbitaceae     

The effect of heat stress on tomato pollen characteristics is associated with changes in carbohydrate concentration in the developing anthers

Continuous exposure of tomato 'Trust' to high temperatures (day/night temperatures of 32/26 degrees C) markedly reduced the number of pollen grains per flower and decreased viability. The effect of heat stress on pollen viability was associated with alterations in carbohydrate metabolism in various parts of the anther during its development. Under control, favourable temperature conditions (28/22 degrees C), starch accumulated in the pollen grains, where it reached a maximum value 3 d before anthesis; it then diminished towards anthesis. During anther development, the concentration of total soluble sugars gradually increased in the anther walls and in the pollen grains (but not in the locular fluid), reaching a maximum at anthesis. Continuous exposure of the plants to high temperatures (32/26 degrees C) prevented the transient increase in starch concentration and led to decreases in the concentrations of soluble sugars in the anther walls and the pollen grains. In the locular fluid, however, a higher soluble sugar concentration was detected under the high-temperature regime throughout anther development. These results suggest that a major effect of heat stress on pollen development is a decrease in starch concentration 3 d before anthesis, which results in a decreased sugar concentration in the mature pollen grains. These events possibly contribute to the decreased pollen viability in tomato.     

LEVER ACTION ANTHERS AND THE FORCIBLE SHEDDING OF POLLEN IN TORENIA (SCROPHULARIACEAE)

The anthers of Torenia fournieri were found to shed pollen forcibly by lever action. Anther structure was modified for this function by a flangelike outgrowth of the lateral pollen sac wall forming a lever. When pressed, this lever causes an infolding of the thinner, subadjacent, pollen sac wall forcing pollen from the stomium. A force of 1–1.5 g pressing against the four levers of an anther pair resulted in the forcible shedding of 2,000–3,000 pollen grains in two parallel rows. During the 2-day anthesis the flowers shift from functioning as males to hermaphroditic outcrossers, and yet only have a pollen:ovule ratio of 98.6, a ratio more indicative of facultative autogamy. The outermost pair of anthers functions on the first day of anthesis, while the second, inner pair functions on both days. In each flower, the 2-day anther pair produces approximately twice as many pollen grains as the 1 -day anther pair, a pollen production highly correlated with the length of their functional lives. This difference in pollen production is apparent in the larger size of the 2-day anthers, a size difference that first appears with the initiation of the anther primordia.     

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。     

Floral organ growth and carbohydrate content during pollen development in Lilium

In order to understand floral sugar physiology, we correlated the growth of the organs with carbohydrate content in the flower of Lilium cv. “enchantment” during pollen development. In a previous work, we distinguished two phases in pollen ontogenesis: the anther growth phase, from the microspore mother cell until the vacuolated microspore, and the anther maturation phase, from the vacuolated microspore until anthesis. In the present work, we showed that during the growth phase, the anther underwent most of its size and dry weight growth, whereas the growth rate of nonanther organs was reduced. Anther and filament possessed the highest amounts of carbohydrates, which decreased progressively until the vacuolated microspore stage. During the maturation phase, sucrose and starch increased in all floral organs. Anther growth was completed at the Mi stage, whereas the nonanther organs began exponential growth. From these observations, we concluded that hierarchic nutritional correlations exist between the flower organs, in which the anther is the main actor: during the anther growth phase, the anther represents the highest sink strength floral organ, and mainly attracts assimilates through the filament. During the anther maturation phase, anther growth is achieved, its needs decrease, and assimilates are thus available for neighboring organs, which undergo intense growth until anthesis.     

CLEISTOGAMY IN SALPIGLOSSIS SINUATA

Cleistogamy in Salpiglossis sinuata L. (Solanaceae) involves a series of developmental events that includes germination of pollen tetrads en masse inside the anther, penetration of pollen tubes through the anther wall toward the stigma which is in contact with the anther, growth of pollen tubes down the style, and, finally, fertilization. This occurs within 6 days from the first appearance of the flower as compared to 10–12 days for normal anthesis of chasmogamous flowers. Coincident with these events in cleistogamous flowers are lack of corolla development and reduced size of androecium and gynoecium.     

The role of gibberellins in the growth of floral organs of Mirabilis jalapa

Evidence that the anther is a source of GAs which may be a mainfactor limiting the growth of floral organs of Mirabilis jalapais presented. GAs in floral tubes at different developmentalstages were surveyed using TLC followed by bioassay with ‘Tan-ginbozu’dwarf rice seedlings. The amount of GA_s in the floral tube increasedrapidly after the calyx became visible above the bract 8 daysbefore anthesis, reached a maximum 5 days before anthesis, thendeclined markedly thereafter. The stamen had relatively largeamounts of GAs and mainly accounted for the change of GA_s duringthe flower development. The GA content in the anther was 3 timesas much as that in the filament. Exogenously supplied GA3 promotedelongation of sections in excised flower organs. Extracts ofanthers also showed definite growth promotion of style sections.Removal of the anthers greatly reduced the final length of thefloral tube. (Received December 7, 1974; )     

Expression of a Gene for a Protein Similar to HIV-1 Tat Binding Protein 1 (TBP1) in Floral Organs of Brassica rapa

A cDNA for a protein similar to human immunodeficiency virusTat binding protein was isolated from an anther cDNA libraryof Brassica rapa. RNA in situ analysis in flower buds showedthat the gene for this cDNA was specifically expressed in thetapetum and middle layer of anthers and pollen. (Received February 15, 1997; Accepted May 28, 1997)     

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。     

Vibratory Collection of Actinidia deliciosa (Kiwifruit) Pollen

Dry, powdery pollen grains were expected from 'buzz pollinated'flower species. However, vibration of Actinidia deliciosa (kiwifruit)anthers (a buzz pollinated species) by a mechanical shaker,at similar vibrations to Bombus terrestris caused clumps ofpollen joined by small droplets of tapetal fluid to be ejected.Pollen that was largely covered with tapetal fluid could notbe removed by vibration, whereas dehydrated pollen was easilyremoved, even without vibration. The late desiccation of A.deliciosa anthers after anthesis meant that pollen removed byvibration depended on the anther maturity. The presence of thedroplets gives insects which vibrate while foraging advantagesover insects which do not. A vibration attachment on a commercialpollen harvester increased the weight of pollen collected by57% over the whole day; 91% in the afternoon.Copyright 1994,1999 Academic Press Actinidia deliciosa, Bombus spp., bumblebees, buzz pollinate, kiwifruit, pollen collection, tapetal fluid, vibration     

Flower Colour Changes in Lantana camara

Lantana camara flowers undergo colour change subsequent to anthesis.In the colour variant selected for the present study, pink buds,yellow newly-opened flowers and ageing orange, scarlet and magentaflowers are found in the same inflorescence. The flower pigmentswere chemically analysed and identified as delphinidin monoglucosideand ß-carotene. Thrips are regular pollinators of Lantana under Delhi conditions.Pollination was identified as the trigger for rapid anthocyaninsynthesis. Even the presence of one pollen grain on the stigmaof a yellow flower was sufficient to cause colour change. Injectionof a suspension of pollen into flowers opened in vitro causedpigment changes. An extract of Lantana pollen was also ableto simulate the effect of pollination, suggesting the involvementof a pollen factor. The post-pollination shift in petal colourationis caused by the masking of carotenoids by differential amountsof anthocyanin. As thrips are attracted to only yellow flowers,chromatic changes play a role in conserving pollinator energy. Key words: Anthecology, Floral pigments, Lantana camara, Pollination     

Aquaporins of the PIP2 class are required for efficient anther dehiscence in tobacco

Several processes during sexual reproduction in higher plants involve the movement of water between cells or tissues. Before flower anthesis, anther and pollen dehydration takes place before the release of mature pollen at dehiscence. Aquaporins represent a class of proteins that mediates the movement of water over cellular membranes. Aquaporins of the plasmamembrane PIP2 family are expressed in tobacco (Nicotiana tabacum) anthers and may therefore be involved in the movement of water in this organ. To gain more insight into the role these proteins may play in this process, we have analyzed their localization using immunolocalizations and generated plants displaying RNA interference of PIP2 aquaporins. Our results indicate that PIP2 protein expression is modulated during anther development. Furthermore, in tobacco PIP2 RNA interference plants, anther dehydration was slower, and dehiscence occurred later when compared with control plants. Together, our results suggest that aquaporins of the PIP2 class are required for efficient anther dehydration prior to dehiscence.     

Flower morphology,nectar traits and pollinators of Cerinthe major (Boraginaceae-Lithospermeae)

In April and May 2010, a natural population of Cerinthe major (Boraginaceae-Lithospermeae) was investigated with regard to: floral morphology, phenology, sexual receptivity during anthesis, the production of nectar and its sugar and amino acid content. The pollinator array of this species was also investigated. Cerinthe major has showy, pentamerous, hermaphroditic flowers with a deep yellow corolla tube arranged on numerous scorpioid inflorescences. Nectar and pollen are the main floral rewards for pollinators. The arrangement of stamens limits access to nectar and promotes pollen loading onto pollinator bodies as they force their way towards the source of nectar. By limiting the direct exposure of nectar to the environment, the corolla tube and the arrangement of anther filaments seemingly protect nectar from evaporation resulting from high temperatures and low relative humidity during flower anthesis. The green, annular nectary located at the base of the ovary lobes is composed of a very thin epidermis enclosing a dense mass of parenchyma. The epidermis lacks stomata, and the thin cuticle has an irregular surface. The parenchyma cells do not store starch during the pre-secretory stage, suggesting that immediate photosynthesis is the most likely source of nectar carbohydrates. Generally, anthesis lasts 4–5 days; the gynoecium becomes fully receptive on the second day and this is synchronous with anther dehiscence. Since nectar production begins during the bud stage, a substantial volume is available for flower visitors at anthesis. Nectar production decreases drastically in senescent flowers and, if not consumed, the nectar can be re-absorbed. Analysis of sugars revealed a sucrose-dominant nectar (sucrose = 93.18 ± 1.35%). Proline, GABA, taurine, leucine, citrulline and alanine were the main amino acids present and are probably implicated in pollinator flight performance.     

Cold-pretreatment of Excised Flower Buds in Float Culture of Tobacco Anthers

Pretreatment of excised flower buds at 7–9 °C is shownto be more effective in float culture of Nicotiana tabacum anthersthan pretreatment at 5 °C. The small temperature differenceresults in greatly enhanced embryo yields when the treatmentis given just before (stage 3), during (4) or just after (5)the first pollen division. Anther productivity (total embryoyield per anther) increases with the time of pretreatment toa peak beyond which further pretreatment is deleterious. Thepeak is attained sooner at 9 than at 7 °C and sooner inanthers pretreated at stage 5 than at stage 3. Peak productivityappears always to be the same. Owing to batch variations, accuratepretreatment-times cannot be specified. Suggested mean timesfor buds of mixed stage are about 12–14 days at 7 °Cand about 7–9 days at 9 °C. Anthers dehisce in culture, the time to dehiscence decreasingwith increasing anther stage. Mid-stage-5 anthers open withinthe first few days, sooner with pretreatment at 9 than at 7°C, and high-yielding free pollen cultures can be obtainedwithout mechanical disruption of the anthers. Buds survive longest when harvested at the beginning of theearly flowering period and kept at 7 °C. It is proposedthat the pretreatment exerts its effect not by altering thecourse of the first pollen division, as suggested by others,but by delaying anther deterioration and thus assuring survivalof a greater proportion of the pollen grains switched into embryogenesis. Nicotiana tabacum L., tobacco, anther culture, embryogenesis     

Periodicity of Pollen Development and Quantitative Cytochemistry of Exine and Intine Enzymes in the Grasses Lolium perenne L. and Phalaris tuberosa L.

Daily analysis of anther samples during flower development hasenabled an estimation of the duration of defined developmentalperiods in pollen of the grass Phalaris tuberosa. A similarsequence of pollen development has been established for ryegrass,Lolium perenne, where changes in activity of wall enzymes havebeen followed using quantitative cytochemical methods. Acidphosphatase, an intine enzyme, showed two periods of activity:during the vacuolate period corresponding to deposition of theintine polysaccharides; and in the maturation period correspondingto cytoplasmic activity. Non-specific esterase showed greatestactivity in the parietal tapetal cells until their dissolutionearly in the vacuolate period when an increase in pollen-associatedactivity occurred. These changes provide additional evidencefor the transfer of tapetal proteins to exine sites. Lolium perenne L., Phalaris tuberosa L., ryegrass, canary grass, pollen development, quantitative cytochemistry, enzyme activities, acid phosphatase, esterase     

Papillar integrity as an indicator of stigmatic receptivity in kiwifruit (Actinidia deliciosa)

Stigmatic receptivity is a major factor limiting fruit set inkiwifruit (Actinidia deliciosa). The aim of this work was toknow what determines the cessation of stigmatic receptivityin this species. Stigmatic receptivity has been analysed inkiwifruit through the capacity of the stigma to sustain pollengermination and has been related to stigmatic development anddegeneration.The stigma of kiwifruit flowers has a papillatesurface which from anthesis is covered with an abundant exudate.Papillae are unicellular and contain a number of phenolic deposits.During the lifetime of the flower these papillae gradually loseturgidity, while stigmatic secretion increases until 5 d afteranthesis when papillae start rupturing and the papillar contentis liberated into the germination medium. Stigmatic receptivityis high at anthesis and lasts for the next 4 d. However, itdrastically decreases 5 d after anthesis and it is nil 2 d later.The pattern of stigmatic receptivity closely fits that of papillarintegrity, indicating that stigmatic receptivity relies on thisintegrity. Since papillar integrity can easily be evaluatedin stigmatic arms, this criterion can be used as a quick methodto estimate stigmatic receptivity. Key words: Actinidia deliciosa, kiwifruit, stigma, receptivity, pollen     

Floral reward presentation favored the expression of male function in the pollen‐only flower Melastoma malabathricum

Abstract Animal‐pollinated plant species modulate the presentation of pollinator rewards to maximize reproductive success. In plants providing pollen as the only reward for pollinators, it is usually difficult to unravel the dual roles of reward presentation and the realization of male and female functions (pollen removal and deposition). Exploiting the two types of anther in the androecia of Melastoma malabathricum L., we examined whether the removal of pollen for reward is regulated primarily to favor male function or female function. Pollen removal by carpenter bees from the feeding and pollination anthers, as well as pollen deposition on the stigmas, were quantified during anthesis of M. malabathricum. There was no significant difference in pollen removal rates from the feeding and pollination anthers of M. malabathricum between the onset of anthesis and flower wilting. The stigmatic pollen loads exceeded the ovule number after three sonication bouts, and female function was satisfied earlier than male function. The results support the hypothesis that the presentation of pollination reward in this species is regulated primarily to favor the expression of male function, rather than female function, in agreement with the pollen‐donation hypothesis. A cooperative relationship between the feeding and pollination anthers was demonstrated in heterantherous flowers, which optimizes the balance in investments between pollinator rewards and “functional pollen” for gene transfer.