Regulation of seed number and female incitation of mate competition by a pH-dependent proteinaceous inhibitor of pollen grain germination in Leucaena leucocephala

Summary Leucaena leucocephala generally produces pods with more than 7–9 seeds. This is regulated by the stigmatic inhibition of pollen grain germination when the pollen grains are less than a critical number in the stigma. This number-dependent inhibition of pollen grain germination is effected by a pH-dependent proteinaceous inhibitor active at the stigmatic pH. Only when the pollen grains in the stigma exceed the critical number, they inactivate the inhibitor by collectively raising the stigmatic pH and thus overcoming the inhibition. The adaptive significance of such pre-fertilization mechanism for the female in inciting mate competition among the pollen grains is discussed. The evolution of en masse pollen grain dispersal units is explained as a sexual selection strategy by males in response to such stigmatic inhibition by females.     

The effect of temperature on stigmatic receptivity in sweet cherry (Prunus avium L.)

Plant reproduction is highly vulnerable to environmental conditions such as temperature and, consequently, planet warming may have significant consequences on the reproductive phase with serious implication in agricultural crops. Although pollen tube growth is clearly affected by temperature, little information is available on its effect on the female side and on flower receptivity. In this work, the effect of temperature has been evaluated on stigmatic receptivity of sweet cherry in vivo, in the laboratory, and in planta, in the field. Results herein show that temperature has a clear effect on the duration of stigmatic receptivity. Thus, whereas high temperature reduced stigmatic receptivity, low temperature enlarged it. The stigma lost the capacity to offer support first for pollen penetration, second for pollen germination and, finally, for pollen adhesion. The effect of temperature was more pronounced on pollen germination and penetration than on pollen adhesion. High temperature reduced the germination capacity of the pollen as early as the first day after anthesis, a time when no apparent signs of stigma degeneration are apparent. This clear effect of temperature on stigmatic receptivity and pollen performance may have clear implication in crop performance and in establishing screening criteria of best‐adapted genotypes.     

部分中国传统月季花粉形态研究

利用扫描电镜观察了15个中国传统月季品种的花粉形态。结果表明:传统月季花粉为单粒花粉,呈长球形或超长球形（P/E为1.92～2.25）,大小为37.59～51.95 μm×17.02～25.33 μm。赤道面观椭圆形或长矩形,极面观三裂圆形,具三孔沟,沿极轴方向等间距环状分布。外壁纹饰条纹型,覆盖层具穿孔,在品种间具有相似性,但变异丰富,划分为4种类型。聚类分析结果表明,花粉大小和外壁纹饰特征在反映传统月季品种的类别上与形态分类基本一致。根据花粉形态演变规律可推断,样品中‘四面镜’可能为最原始的品种类型,‘月月粉’、‘月月红’及‘匍匐红’等品种较为进化。     

Sugars in Natural and Artificial Pollen Germination Substrates

The stigmatic exudates and pollen grains of five unrelated specieswere tested for sugars. Glucose, fructose, and sucrose werefound in the stigmatic fluid of Yucca aloifolia L. and glucoseand fructose in that of Oenothera adrummondii Hook. In in vitroexperiments with Y. aloifolia pollen, high germination percentageswere obtained in artificial media containing glucose or sucrose.Fructose, which is present in the stigmatic fluid of the Yuccasp. resulted in high in vitro pollen germination only when borateand calcium were added to the medium. Presence of bound sugarsis indicated in the stigmatic secretion of Citrus aurantiumL. and pollen of the single plant tested germinated at a lowpercentage in artificial sugar media. No sugars were detectedin the stigmatic fluids of Hemerocallis fulva L. and Zea maysL. and in these two species in vitro pollen germination in sugarymedia was negligible or absent. The pollen grains of all five species contain sucrose and thoseof Oenothera and Citrus also reducing sugars.     

Appearance and interaction of pollen and pistil pathway proteins in Gasteria verrucosa (Mill.) H. Duval

Patterns of proteins excreted during pollen germination, of germinating pollen and of the stylar and placental fluids excreted by cells along the pistil pathway of Gasteria verrucosa were analyzed by electrophoresis. The medium from germinating pollen contains several pollen exudate proteins as well as glycoproteins from the sticky pollen wall coating. No protein could be detected in the stigmatic exudate. The stylar fluid shows a protein pattern different from that of the placental fluid. The placental fluid contains some glycoproteins. After pollination, three pollen proteins begin to appear in the stylar fluid. Two of these pollen proteins remain present in the placental fluid. Some placental fluid proteins and glycoproteins are modified after pollination. The difference in protein patterns demonstrates the heterogeneity of proteins in the pollen tube pathway and suggests that proteins excreted by the pollen tube interact with other proteins in the pistil pathway, especially those in the placental fluid.     

Influence of the pH of the stigmatic exudate on male-female interaction in Rosa hybrida L

Summary The in vitro germination of rose pollen is influenced by the pH of the medium. Both germination percentage and length of emitted pollen tubes were maximal for in vitro germination and tube elongation at pH 5 and minimal at pH 3 and 9 (Rosa hybrida L. var P 30 pollen). Three varieties characterized by having a stigmatic exudate of pH = 5 and another three varieties having one of pH = 9 were pollinated with the same pollen. Pollination effectiveness, as indicated by hip set (number of hips/pollmated flowers × 100) and mean number of achenes per hip, were significantly different: it was much higher for the varieties with the stigmatic exudate of pH = 5. pH control on pollination efficiency and subsequent fecundation success is proposed and discussed.     

Stigmatic inhibition of pollen grain germination-its implication for frequency distribution of seed number in pods of Leucaena leucocephala (Lam) de Wit

Summary Seed number per pod is negatively skewed in Leucaena leucocephala. Post-fertilisation abortion of pods does not completely explain the skewed distribution. It is shown that a pre-fertilisation regulation effectively restricts the formation of pods with less than a certain number of seeds. The regulation is rendered through the inhibition of pollen grain germination by the stigmatic fluid when the pollen grain is less than a certain critical load in the stigma. Such a control is shown to have implications in the evolution of pollen package units, generation of male gametophytic competition and the economy of packing seeds in pods.     

Irregular Pollen Grains in Some Hypericum Species

In some 40 out of 238 Hypericum species examined, more than 10% of the pollen produced was irregular in aperture number and configuration. Production of such grains was often associated with pollen infertility, and seemed to be the result of faulty meiotic divisions. The morphology of the irregular grains closely follows Van Campo's `successiform' series and demonstrates that the phylogenetic advancement represented by this series consists not in the production of the more complex pollen types but in their selection as standard rather than as abnormal types.     

ROLE OF CALCIUM IN THE CALLOSE RESPONSE OF SELF-POLLINATED BRASSICA STIGMAS

In Brassica oleracea, sporophytic self-incompatibility prevents germination of self pollen, or normal growth of self pollen tubes. After self-pollination, the papillae of stigmas synthesize callose. The role of Ca⁺⁺ in the formation of stigmatic callose was tested by adding compounds that interact with Ca⁺⁺ to suspensions of pollen that were known to induce callose formation in self stigmas. The calcium channel antagonist, lanthanum, and the calcium chelating agent, EGTA, reduced or abolished the callose response to self-pollen suspensions. In the presence of Ca⁺⁺, the calcium ionophore, A23187, induced callose in stigmatic papillae when added to pollen suspensions, or alone. Therefore, callose deposition in response to incompatible pollinations appears to be a calcium-dependent process. Pretreatment of pistils with 100 μm 2-deoxy-D-glucose abolished the callose response to self-pollination, while self pollen remained inhibited and cross pollen grew normally in treated pistils. Thus, callose formation in the stigma is not an essential part of the self-incompatibility mechanism preventing the growth of self pollen in Brassica.     

Pollen morphology and germination inNarcissus

Pollen grains of several species and varieties ofNarcissus were examined with a light microscope and a scanning electron microscope. Normal pollen grains were kidney- or spindle-shaped with a germination furrow and a reticulate structure similar to that of the pollen grains ofAmaryllis. Pollen grains germinated within 2 to 3 hr. Percentage of germination was dependent upon temperature and treatment. Pollen tubes grew in length up to 1,000 μm and branched occasionally or behaved in strange fashion. Fresh pollen grains germinated more in distilled water at lower temperature than in sucrose-aqueous medium. Both in the presence and in the absence of stigmatic exudate calcium increased the percentage of germination. Gibberellic acid, abscisic acid and coumarin inhibited the pollen germination. Plasmoptysis occurred in all species and in all media tested except in a medium containing coumarin without stigmatic exudates. Plasmoptysis did not seem to be induced by hypotonic medium alone. Pollen of high germination capacity showed a high percentage of plasmoptysis. Based on the results obtained, evolution and sterility of theNarcissus plant was discussed.     

Arabinogalactan-protein secretion is associated with the acquisition of stigmatic receptivity in the apple flower

Background and Aims

Stigmatic receptivity plays a clear role in pollination dynamics; however, little is known about the factors that confer to a stigma the competence to be receptive for the germination of pollen grains. In this work, a developmental approach is used to evaluate the acquisition of stigmatic receptivity and its relationship with a possible change in arabinogalactan-proteins (AGPs).

Methods

Flowers of the domestic apple, Malus × domestica, were assessed for their capacity to support pollen germination at different developmental stages. Stigmas from these same stages were characterized morphologically and different AGP epitopes detected by immunocytochemistry.

Key Results

Acquisition of stigmatic receptivity and the secretion of classical AGPs from stigmatic cells occurred concurrently and following the same spatial distribution. While in unpollinated stigmas AGPs appeared unaltered, in cross-pollinated stigmas AGPs epitopes vanished as pollen tubes passed by.

Conclusions

The concurrent secretion of AGPs with the acquisition of stigmatic receptivity, together with the differential response in unpollinated and cross-pollinated pistils point out a role of AGPs in supporting pollen tube germination and strongly suggest that secretion of AGPs is associated with the acquisition of stigma receptivity.Key words: AGPs, arabinogalactan proteins, apple, Malus × domestica, pollen, pollen tube, stigma, stigmatic receptivity, flower receptivity     

Asynchronous development of stigmatic receptivity in the pear (Pyrus communis; Rosaceae) flower

While stigma anatomy is well documented for a good number of species, little information is available on the acquisition and cessation of stigmatic receptivity. The aim of this work is to characterize the development of stigma receptivity, from anthesis to stigma degeneration, in the pentacarpellar pear (Pyrus communis) flower. Stigma development and stigmatic receptivity were monitored over two consecutive years, as the capacity of the stigmas to offer support for pollen germination and pollen tube growth. In an experiment where hand pollinations were delayed for specified times after anthesis, three different stigmatic developmental stages could be observed: (1) immature stigmas, which allow pollen adhesion but not hydration; (2) receptive stigmas, which allow proper pollen hydration and germination; and (3) degenerated stigmas, in which pollen hydrates and germinates properly, but pollen tube growth is impaired soon after germination. This developmental characterization showed that stigmas in different developmental stages coexist within a flower and that the acquisition and cessation of stigmatic receptivity by each carpel occur in a sequential manner. In this way, while the duration of stigmatic receptivity for each carpel is rather short, the flower has an expanded receptive period. This asynchronous period of receptivity for the different stigmas of a single flower is discussed as a strategy that could serve to maximize pollination resources under unreliable pollination conditions.     

On factors influencing fruit-set and sterility in arecanut (Areca Catechu Linn.)

Summary (1) Histological studies on the stigmas of female flowers of areca indicate the possibility of the stigmatic surfaces being impacted upon by air spora. The presence of spores or hyphae together with pollen grains has been shown in stigmatic surface.(2) Air spora of arecanut plantation chiefly consist ofAspergillus, Penicillium, Actinomycetes, Mucor, Alternaria, Cladosporium andBacteria.(3) The types of fungi, bacteria and actinomycetes adhering to the stigma are isolated.(4) The metabolites of the fungi, bacteria and actinomycetes isolated from the stigmas of arecanut flowers inhibit,in vitro, considerably the germination of pollen grains and rate of growth of pollen tubes. In certain instances there is no germination of the pollen grains in the metabolites of fungi, bacteria and actinomycetes. In view of the results the significance of the air spora in affecting the normal course of pollination and fertilization is discussed.     

Self-incompatibility inCrocus vernus subsp.vernus (Iridaceae)

Outcross, self- and mixed pollinations were performed inCrocus vernus subsp.vernus, a species with bicellular pollen, dry stigmas and hollow style. No differences were noted among the above pollinations concerning the germination of pollen and the growth of pollen tubes until the top of ovary. Within 45 min after pollinations 62% of pollen grains germinated. Pollen tubes penetrated the papilla cuticle extending along the papilla wall; on entry into stigmatic lobes they continued growth in the stylar secretion to ovarian locules. Here, however, self-pollen tubes failed to reach or to enter the ovule micropyle; while pollen tubes from either outcross- or mixed pollinations grew until fertilizing ovules. These observations gave evidence of a self-incompatibility system inCrocus, which appeared to be neutralized by mentor effect. The ovary as site of incompatibility response is discussed.     

Isoenzyme Polymorphism in Flowering Plants I. Diffusion of Enzymes Out of Intact Pollen Grains

Esterases, leucine aminopeptidases, catalases, amylases and acid phosphatases diffuse out of intact and ungerminated pollen grains of Oenothera organensis, whether suspended in 1 % sodium chloride or in pollen medium. A total of 15 esterase isozymes are recorded; 5 of them appear within 5 minutes, 8 within 30 minutes, 9 within 2 hours, and 13 within 19 hours. Pollen grains suspended for 19 hours gave much stronger isozyme bands than macerated pollen grains. However, one esterase hand was consistently missing from the 19 hour suspensions, although present in all others. It is suggested as a working hypothesis that the early growth of pollen tubes and possibly even germination of pollen grains may be influenced by the metabolic products of pistillate tissues caused by the diffused pollen enzymes, and that inactivation of these enzymes by stigmatic or stylar components could lead to incompatibility reactions.     

3种生殖方式蒲公英花粉活力和柱头形态及可授性对比

利用离体萌发法、电镜扫描和联苯胺-过氧化氢法对有性生殖的东北蒲公英、专性无融合生殖的丹东蒲公英和兼性无融合生殖的蒙古蒲公英花粉活力、柱头表面形态及可授性进行观察和测定。结果显示:(1)3种蒲公英柱头均为干柱头,单细胞乳突,属于原始进化类型,都存在雌雄异熟和雌雄异位花部特征;东北蒲公英乳突饱满、紧密,蒙古蒲公英次之,丹东蒲公英干瘪、稀少。(2)东北蒲公英和丹东蒲公英柱头呈Y状时期花粉萌发率最高,分别为67.3%和19.8%,蒙古蒲公英柱头呈棒状时期萌发率最高,为23.3%。(3)3种蒲公英随着开花进行,柱头可授性增加,并且柱头在大Y状时期3种蒲公英为最佳授粉期,可授性柱头占样本柱头的比率分别是98.7%(东北蒲公英)、84.0%(蒙古蒲公英)、21.3%(丹东蒲公英)。研究表明,有性生殖蒲公英与无融合生殖蒲公英在花粉萌发力、柱头可授性和乳突上产生明显差别,为蒲公英在长期进化中性器官能量再分配提供证据。     

Impairment in reproductive development is a major factor limiting yield of black gram under zinc deficiency

Black gram [Vigna mungo (L.) Hepper] cv. IPU 94 plants grown in sand culture with deficient zinc (0.1 μM Zn) nutrition and those deprived of normal (1 μM) Zn supply at the initiation of flowering, showed decrease in dry matter production and especially seed yield. These plants showed a decrease in the size of anthers and stigmatic heads, pollen producing capacity of the anthers and stigmatic exudations. Zn deficiency caused structural alterations in exine and retarded germination of pollen grains and tube growth. The pollen extracts and stigmatic exudates of the Zn-deficient plants showed increase in activity of acid phosphatase isoforms and inhibition of esterase isoforms. Zn deficiency led to decrease in number of pods, seeds per pod and seed mass, altered seed coat topography and reduced seeds germinability. Low seed yield under Zn deficiency is attributed to a role of Zn in pollen function, as also in pollen-pistil interaction conducive to fertilization and development of seeds.     

STIGMA OF SOLANUM TUBEROSUM CV SHEPODY: MORPHOLOGY,ULTRASTRUCTURE,AND SECRETION

The stigma of Solarium tuberosum L. cv Shepody has a bilobed papillate surface covered with a viscous secretion at anthesis. The secretion originates as osmiophilic droplets in the cytoplasm, accumulates in the intercellular space, and fills the base of the papillae, after lifting and rupturing the cuticular layer covering the stigma surface. Cytochemical evidence shows that the stigmatic secretion is lipidic in nature; it did not stain with the periodic acid-Schiffs reaction for carbohydrate or Coomassie Brilliant Blue R-250 for proteins, but did stain with Sudan black or Nile red, a fluorescence probe for lipids. Sodium dodecylsulfate-polyacrylamide gel electrophoresis has revealed that the secretion contained three polypeptides that appeared to be 'indigenous' to the stigmatic secretion, and not contaminants. Comparative analyses of this and other proteins found in stigma secretions may provide clues to their possible roles in pollen grain adhesion and germination.     

POLLINATION IN LUPINUS NANUS SUBSP. LATIFOLIUS (LEGUMINOSAE)

Floral morphology and phenology and the timing of stigmatic receptivity and pollen viability were studied to elucidate the mechanisms by which self-pollination in Lupinus nanus subsp. latifolius is minimized under natural conditions. Pollen germination and pollen tube growth suggest that a physiological self-incompatibility system does not exist. Instead, self-pollination is minimized by protandry and by a collar of peristigmatic hairs, which initially inhibit access of autologous pollen to the stigma. These hairs subsequently wilt, permitting self-pollination of unvisited flowers. Pollen germinates in vivo one day before substantial metabolic enzyme activity can be detected. Citric acid cycle enzymes are not detectable in pollen, but those of anaerobic metabolism are. Beginning on the second day postanthesis, stigmatic secretions exude from weak areas on lateral walls of the elongate epidermal papillae, welling up in the interstices between these cells. This contrasts with the stigmas of other papilionoid legumes, in which secretions accumulate beneath the cuticle covering the stigmatic cells, and the often-thin cuticle must be ruptured before pollen and exudate can come into contact.     

Stigmatic RNase in calamondin (Citrus reticulata var. austera x Fortunella sp.)

In calamondin. which is self-compatible, ribonuclease (RNase) activity was found in the stigmatic diffusate. Tissue print experiments using calamondin styles demonstrated that most of the RNase is localized in the stigma. Stigmatic RNase activity was monitored at different developmental stages of the flower and was found to peak at anthesis. An SDS-PAGE-zymogram indicated the molecular mass of this RNase to be 24 kDa. In vitro germination of calamondin pollen showed a higher percentage of germination in the presence of diffusate from one stigma than in the control. However, diffusates from 3.5 and 7 stigmata per 100 μl aliquots of growth medium, exhibiting 15. 25 and 35 units ml⁻¹ RNase activity, respectively, had successively stronger inhibition effects on the percentage of germination. Diffusate from 7 stigmata inhibited pollen tube elongation, as well as pollen germination. Both the 24-kDa Stigmatic RNase and RNase TI significantly inhibited pollen germination and pollen tube elongation. In pollen tubes treated with either the 24-kDa stigmatic RNase or RNase TI, considerable deposition of callose was observed, as compared to the control which had only a thin callosic cell wall.