Pollen-stigma adhesion in Brassica spp involves SLG and SLR1 glycoproteins.

The adhesion of pollen grains to the stigma is the first step of pollination in flowering plants. During this step, stigmas discriminate between pollen grains that can and cannot be permitted to effect fertilization. This selection is operated by various constituents of the cell walls of both partners. Several genes structurally related to the self-incompatibility system that prevents self-pollination in Brassica spp are known to target their products into the stigma cell wall. We proposed previously that one of these genes, the one encoding the S locus glycoprotein (SLG)-like receptor 1 (SLR1), which is coexpressed with that encoding SLG, may participate in pollen-stigma adhesion. Here, we exploit a biomechanical assay to measure the pollen adhesion force and show that it is reduced both by transgenic suppression of SLR1 expression and by pretreatment of wild-type stigmas with anti-SLR1 antibodies, anti-SLG antibodies, or pollen coat-protein extracts. Our results indicate a common adhesive function for the SLR1 and SLG proteins in the pollination process.     

Oleosin-like proteins are not present on the surface of tobacco pollen

Pollen-stigma interactions on wet- and dry-type stigmas involve similar processes: the hydration of the pollen, followed by pollen tube growth and penetration of the stigma. Furthermore, in some species, identical molecules, namely lipids, are used to achieve this. In addition to lipids, oleosin-like proteins of the pollen coat of dry-type stigma plants have been shown to be involved in pollen-stigma interactions. However, little information is present about the proteins on the surface of pollen of wet-type stigma plants, in particular that of the Solanaceae. To analyze proteins from the surface of pollen of Nicotiana tabacum (tobacco), a solanaceous plant, we used an antiserum raised against Brassica pollen coat, a dry-type stigma plant of the Brassicaceae. In addition we used a molecular approach to identify tobacco homologues of oleosin-like genes. Our results show that no proteins similar to Brassica oleracea pollen coat proteins are present on the surface of tobacco pollen, and that oleosin-like genes are not expressed in tobacco anthers or stigmas.     

Pollen-stigma adhesion in Arabidopsis: a species-specific interaction mediated by lipophilic molecules in the pollen exine.

To investigate the nature and role of cell adhesion in plants, we analyzed the initial step of pollination in Arabidopsis: the binding of pollen grains to female stigma cells. Here we show this interaction occurs within seconds of pollination. Because it takes place prior to pollen hydration, it also requires adhesion molecules that can act in a virtually dry environment. We developed assays that monitored adhesion of populations of pollen grains and individual cells. Adhesion between pollen and stigma cells is highly selective - Arabidopsis pollen binds with high affinity to Arabidopsis stigmas, while pollen from other species fails to adhere. Initial binding is independent of the extracellular pollen coat (tryphine), indicating that adhesion molecules reside elsewhere on the pollen surface, most likely within the exine walls. Immediately after pollination, the stigma surface becomes altered at the interface, acquiring a pattern that interlocks with the exine; this pattern is evident only with pollen from Arabidopsis and its close relatives. Purified exine fragments bind to stigma cells, and biochemical analyses indicate that this specific, rapid and anhydrous adhesion event is mediated by lipophilic interactions.     

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.     

Stigma factors regulating self-compatible pollination

Pollination is one of the most important steps during fertilization and sexual reproduction in plants, and numerous cell-cell interaction events occur between the pistil and the pollen grain/tube during this process. The pollen-stigma interaction is a highly selective process which leads to compatible or incompatible pollination. Previous studies in Solanaceae, Papaveraceae, and Brassicaceae provided some important insights into pollen-stigma recognition in self-incompatible systems. In recent years, considerable data have been available regarding pollen-stigma interaction during self-compatible pollination. In this review, we focus on discussing current knowledge on stigma factors that regulate pollen-stigma interaction in self-compatible systems in comparison with self-incompatible systems.     

TWO-DIMENSIONAL POLLINATION IN HYDROPHILOUS PLANTS: CONVERGENT EVOLUTION IN THE GENERA HALODULE (CYMODOCEACEAE), HALOPHILA (HYDROCHARITACEAE), RUPPIA (RUPPIACEAE), AND LEPILAENA (ZANNICHELLIACEAE)

In most plant species with abiotic pollination systems, pollen is dispersed in three dimensions. Theoretical considerations suggest, however, that there are significant advantages for two-dimensional pollination systems over three-dimensional systems, especially if pollen is dispersed in conveyances or aggregations of large diameter. We report that two-dimensional pollination systems occur in the genera Halodule, Halophila, Lepilaena, and Ruppia, where pollen grains are not transported through the water singly, but in rafts or search vehicles. These genera possess unusual pollen morphologies which facilitate assemblage of pollen grains into search vehicles. These floating search vehicles have large diameters, thus greatly increasing probability of encountering a stigma. The grains have a hydrophobic surface that appears to mediate adhesion by an external coating of proteins and carbohydrates. Similar adaptations to two-dimensional pollination are found in the target organs, the stigmas. The long filamentous stigmas of the marine genera float, as do the indusiate stigmas of the freshwater genera, creating small depressions in the water surface. Pollination occurs through the collision of a moving search vehicle with a floating stigma. The existence of similar pollen search vehicles, stigma morphologies, and flowering phenologies in these unrelated hydrophilous genera evidences convergent evolution towards efficient search strategies in surface-pollinated aquatic plants.     

Stigma development and receptivity of two Kalanchoë blossfeldiana cultivars

Several members of the Kalanchoë genus are popular as ornamental plants. Cross-breeding and wide hybridisation are essential to continuously introduce novel traits into cultivated plant material. This study aimed to identify the major factors related to the stigma affecting cross-pollination in the Kalanchoë blossfeldiana. Pollen tube growth after pollination of K. blossfeldiana ‘Jackie’ and ‘Reese’ was examined at different stigma developmental stages. Five distinct developmental stages were identified based on changes in morphology and activity of stigmatic peroxidase. After reciprocal pollination at the five stigma developmental stages, fluorescence microscopy was used to estimate the number of pollen tubes in situ. Both cultivars had receptive stigmas from stage I to IV, which concurred with the continuous expansion of the stigma covered with exudates. No pollen tube growth was observed at stage V for both cultivars. The number of pollen tubes was significantly higher in carpels pollinated at stage III, characterized by loose arrangement of the papillae and maximal amount of exudates, compared to all other developmental stages. Stigmas showing drying exudates and absence of peroxidase exhibited a relatively decreased number of pollen tubes in situ. No pollen tubes germinated on wilting stigmas. The arrangement of the papillae, the presence of exudates and peroxidase activity affected the number of pollen tubes in cross-pollination of K. blossfeldiana cultivars ‘Jackie’ and ‘Reese’. These results will help breeders to better select the optimal time for effective pollination. The findings may be applicable for other cultivars of K. blossfeldiana and relevant for different species of Kalanchoë.     

Involvement of SLR1 genes in pollen adhesion to the stigmatic surface in Brassicaceae

 The S-locus-related gene SLR1 is highly conserved and highly expressed in several species of the Brassicaceae family. Its function has not been determined, although several features would suggest a fundamental role in pollination. A second related gene (SLR2) is conserved and expressed in a subset of Brassica genotypes. We analysed the stigmatic expression of SLR1 and SLR2 genes among 11 different plants from various species or genera of the Brassicaceae and examined the extent of the pollen-stigma interaction during intraspecific, interspecific and intergeneric pollinations between them. Appropriate statistical tests on these variables (pollen adhesion, germination, penetration into the stigma, style and ovary, and SLR gene expression) showed that expression of SLR1 (but not SLR2) may be a factor in pollen-stigma adhesion. This hypothesis was supported by the observation of reduced pollen-stigma adhesion in transgenic B. napus plants modified for SLR1 expression. Received: 25 February 1997/Revision accepted: 24 June 1997     

The Impact of the Invasive Alien Plant,Impatiens glandulifera,on Pollen Transfer Networks

Biological invasions are a threat to the maintenance of ecological processes, including pollination. Plant-flower visitor networks are traditionally used as a surrogated for pollination at the community level, despite they do not represent the pollination process, which takes place at the stigma of plants where pollen grains are deposited. Here we investigated whether the invasion of the alien plant Impatiens glandulifera (Balsaminaceae) affects pollen transfer at the community level. We asked whether more alien pollen is deposited on the stigmas of plants on invaded sites, whether deposition is affected by stigma type (dry, semidry and wet) and whether the invasion of I. glandulifera changes the structure of the resulting pollen transfer networks. We sampled stigmas of plants on 10 sites invaded by I. glandulifera (hereafter, balsam) and 10 non-invaded control sites. All 20 networks had interactions with balsam pollen, although significantly more balsam pollen was found on plants with dry stigmas in invaded areas. Balsam pollen deposition was restricted to a small subset of plant species, which is surprising because pollinators are known to carry high loads of balsam pollen. Balsam invasion did not affect the loading of native pollen, nor did it affect pollen transfer network properties; networks were modular and poorly nested, both of which are likely to be related to the specificity of pollen transfer interactions. Our results indicate that pollination networks become more specialized when moving from the flower visitation to the level of pollen transfer networks. Therefore, caution is needed when inferring pollination from patterns of insect visitation or insect pollen loads as the relationship between these and pollen deposition is not straightforward.     

有花植物触敏柱头的闭合行为及其适应意义

有花植物触敏柱头的闭合行为一直是传粉生态学和进化生物学研究的热点问题之一。植物花的多裂片柱头在传粉者接触后迅速闭合的现象主要存在于玄参目的一些类群中。早在上个世纪初,植物学家就对花的柱头闭合现象进行过初步的研究,认为柱头闭合主要是由于花粉在柱头上萌发时吸收水分导致柱头细胞膨压降低而引起的;并对柱头闭合的适应性提出了一些假说。近年来,许多学者研究证实柱头闭合能促进花粉萌发及花粉管伸长,或减少花粉散出与柱头接受花粉间的相互干扰,提高传粉者访问过程中花粉的散播量,并且柱头的状态会直接影响传粉者的取食行为。到目前为止,对柱头闭合的机制及其避免自交的假说还存在许多争议。关于触敏柱头的闭合行为,尤其是其适应机制及其生态学意义还有待更加系统和深入的研究。本文概述了触敏柱头的研究进展,并对研究中尚存在的一些问题进行了讨论。     

桦木科植物花柱适应风媒传粉的特征

植物体为适应自己的传粉系统, 表现出高度的适应特征。风媒花植物为适应风传播花粉, 要形成特殊的结构, 以扩大接受花粉粒的面积。利用扫描电镜观察了桦木科(Betulaceae)6属18种植物花柱的形态及花粉粒在花柱上的萌发过程, 探讨了桦木科植物花柱适应风媒传粉的特征。结果表明, 桦木科植物的二心皮(铁木、云南鹅耳枥稀为三心皮)雌蕊具柱状花柱, 柱头不发达, 花柱表皮细胞长条状, 纵向排列紧密。传粉时, 花柱表皮细胞能执行柱头的功能, 接受花粉粒, 为花粉粒萌发提供场所和萌发条件。桦木科植物花柱有2种类型: 一种是花柱表皮细胞能形成乳突, 花粉管经乳突细胞进入花柱; 另一种是花柱表皮细胞不形成乳突, 花粉管经过花柱表皮细胞或胞间隙进入花柱。无论花柱表皮细胞是否形成乳突, 乳突的形态、大小以及花粉管和乳突的结合方式等在族间、属间、属内种间存在差异。与基部被子植物相比, 桦木科植物的花柱呈现适应风媒传粉的进化特征。桦木科植物花柱表皮细胞形成的乳突与基部被子植物柱头乳突功能相同, 是桦木科植物风媒传粉的适应策略。     

Relationship of stigma behaviors and breeding system in three Mazus (Phrymaceae) species with bilobed stigma

Sensitive stigma has been recognized to facilitate outcrossing. We hypothesized that species with different levels of sensitivity might have corresponding differences in components of their breeding system. In this study, three Mazus species with bilobed stigmas were used to test the hypothesis. We explored stigma behaviors of the species in reaction time, recovery time, permanent closing time, and the minimum pollen load causing permanent closure. We investigated floral traits, pollinator type and behavior, pollination intensity, and natural schedule of pollen deposition on stigma. Moreover, we evaluated the mating system of the species by checking seed set after controlled pollination treatments, namely, natural flowers with open pollination, enclosed flowers without pollination, and enclosed flowers with self and outcross hand pollination. Results indicated that stigma of M. pumilus (N. L. Burman) Steenis was not sensitive, whereas stigmas of M. miquelii Makino and M. stachydifolius (Turcz.) Maxim. closed and reopened quickly in response to pollination. Accordingly, hand pollination treatments revealed that seed set of self-spontaneous pollination in M. pumilus was similar to the other treatments. For M. miquelii, outcross pollen resulted in significantly higher seed set than self-pollen.Mazus stachydifolius was self-incompatible. Additionally, the corresponding characteristics in other components of the breeding system for each species were found. Our study indicated that the sensitivity of bilobed stigma might be linked with floral traits and the mating system in a given species. Sensitive stigma should be regarded as an evolutionary mechanism for enhancement of outcrossing.     

荞麦亲和与不亲和授粉后柱头和花粉管中ATP酶的超微细胞化学定位

利用磷酸铅淀淀技术对荞麦（Fagopyrum esculentum Monch.)pin型植株分别进行亲和授粉和不亲和授粉后的柱头、花粉粒、花粉管进行了ATPase的超微细胞化学定位。结果表明（1）亲和授粉和不亲和授粉后0.5h,柱头细胞的ATPase活性反应水平较低或基于无酶活性;柱头表面、柱头上附着的花粉粒内ATPase活性在不亲和授粉时较低,亲和授粉时较高,花粉粒内ATPase主要定位于线粒体和精子细胞;（2）授粉后1.5h,不亲和授粉的柱头细胞及花粉管的ATPase活性均较低,花粉管停止生长,细胞质开始解体;而亲和授粉的柱头细胞及花粉管的ATPase活性均较高,ATPase主要定位于柱头细胞的质膜、胞基质以及花粉管的壁、质体的膜、高尔基体、线粒体上。根据不同时期不同部位ATPase活性的差异,我们认为荞麦发生自交不亲和时,花粉管在花柱中停止生长不仅是因此花粉管得不到花柱中的营养物质而引起的,可能也与花粉管自身物质代谢发生障碍有关。     

FLORAL BIOLOGY OF MAGNOLIA

The floral biology of eight species of Magnolia native to the United States is described. The flowers are protogynous. They are pollinated by several species of beetles that enter buds as well as closed and open flowers to feed on nectar, stigmas, pollen, and secretions of the petals. Individual flowers persist from two to four days and undergo a series of petal, stigma, and stamen movements that assure pollination by beetles. It is suggested that the flowers of Magnolia are highly specialized for exclusive pollination by beetles. These specialization mechanisms produce large quantities of food for the beetles and deny other types of insects (bees, moths, etc.) access to the flowers at critical stages in the pollination process, i.e., when stigmas are mature and pollen is shed.     

荞麦亲和与不亲和授粉后柱头和花粉管中ATP酶的超微细胞化学定位

利用磷酸铅沉淀技术对荞麦(Fagopyrum esculentum Month.)pin型植株分别进行亲和授粉和不亲和授粉后的柱头、花粉粒、花粉管进行了ATPase的超微细胞化学定位。结果表明(1)亲和授粉和不亲和授粉后0.5h,柱头细胞的ATPase活性反应水平较低或基本无酶活性;柱头表面、柱头上附着的花粉粒内ATPase活性在不亲和授粉时较低,亲和授粉时较高,花粉粒内ATPase主要定位于线粒体和精子细胞;(2)授粉后1.5h,不亲和授粉的柱头细胞及花粉管的ATPase活性均较低,花粉管停止生长,细胞质开始解体;而亲和授粉的柱头细胞及花粉管的ATPase活性均较高,ATPase主要定位于柱头细胞的质膜、胞基质以及花粉管的壁、质体的膜、高尔基体、线粒体上。根据不同时期不同部位ATPase活性的差异,我们认为荞麦发生自交不亲和时,花粉管在花柱中停止生长不仅是因为花粉管得不到花柱中的营养物质而引起的,可能也与花粉管自身物质代谢发生障碍有关。     

Pollination in Nicotiana alata stimulates synthesis and transfer to the stigmatic surface of NaStEP, a vacuolar Kunitz proteinase inhibitor homologue

After landing on a wet stigma, pollen grains hydrate and germination generally occurs. However, there is no certainty of the pollen tube growth through the style to reach the ovary. The pistil is a gatekeeper that evolved in many species to recognize and reject the self-pollen, avoiding endogamy and encouraging cross-pollination. However, recognition is a complex process, and specific factors are needed. Here the isolation and characterization of a stigma-specific protein from N. alata, NaStEP (N. alata Stigma Expressed Protein), that is homologous to Kunitz-type proteinase inhibitors, are reported. Activity gel assays showed that NaStEP is not a functional serine proteinase inhibitor. Immunohistochemical and protein blot analyses revealed that NaStEP is detectable in stigmas of self-incompatible (SI) species N. alata, N. forgetiana, and N. bonariensis, but not in self-compatible (SC) species N. tabacum, N. plumbaginifolia, N. benthamiana, N. longiflora, and N. glauca. NaStEP contains the vacuolar targeting sequence NPIVL, and immunocytochemistry experiments showed vacuolar localization in unpollinated stigmas. After self-pollination or pollination with pollen from the SC species N. tabacum or N. plumbaginifolia, NaStEP was also found in the stigmatic exudate. The synthesis and presence in the stigmatic exudate of this protein was strongly induced in N. alata following incompatible pollination with N. tabacum pollen. The transfer of NaStEP to the stigmatic exudate was accompanied by perforation of the stigmatic cell wall, which appeared to release the vacuolar contents to the apoplastic space. The increase in NaStEP synthesis after pollination and its presence in the stigmatic exudates suggest that this protein may play a role in the early pollen-stigma interactions that regulate pollen tube growth in Nicotiana.     

Reproductive ecology of distylous Palicourea Padifolia (Rubiaceae) in a tropical montane cloud forest. I. Hummingbirds' effectiveness as pollen vectors

The adaptiveness of distyly has been typically investigated in terms of its female function, specifically pollen receipt. However, pollen loads on stigmas can only provide moderate support for Darwin's hypothesis of the promotion of legitimate crosses. To determine the effectiveness of hummingbirds as pollen vectors between floral morphs and the consequences in terms of male (pollen transfer) and female function (pollen receipt) in Palicourea padifolia (Rubiaceae), floral visitors, their foraging modes, and temporal patterns of floral visitation were observed and documented. Differences in pollen and stigma morphology, pollen flow, rates of pollen deposition, and/or stigmatic pollen loads were then evaluated for their contribution toward differences in reproductive output between floral morphs. A pollination experiment with stuffed hummingbirds that varied in bill size was done to evaluate the contribution of bill variation toward differences between floral morphs in pollen receipt and pollen transfer and female reproductive output. Anthers of long-styled flowers contained significantly more and smaller pollen grains than those of short-styled flowers, independently of corolla and anther lengths. The shape and orientation of the stigma lobes differed between morphs and were significantly longer among short-styled flowers. Hummingbird visitation rates did not differ significantly between floral morphs, and foraging movements from focal plants towards neighboring plants were independent of floral morph. Stigmatic pollen loads under field conditions and those after controlled hummingbird visitation, along with rates of pollen accumulation through the day indicated that stigmas of short-styled flowers receive proportionately more legitimate (intermorph) pollen grains than did those of long-styled flowers. However, the species of hummingbird was marginally significant in explaining variation in pollen deposition on stigmas. Lastly, intermorph pollinations of P. padifolia resulted in significant differences in fruit production between floral morphs, independent of pollination treatment and pollinator species; short-styled flowers proportionately developed almost twice the number of fruits developed by long-styled flowers.     

Localization of pectins and Ca2+ ions in unpollinated and pollinated wet (Petunia hybrida Hort.) and dry (Haemanthus albiflos L.) stigma

The subcellular localization of Ca2+ ions as well as esterified and deesterified pectins in unpollinated and pollinated wet (Petunia hybrida) and dry (Haemanthus albiflos) stigma was analyzed. Stigmas with different surfaces were found to differ in Ca2+ and pectin localization. In a wet Petunia hybrida stigma, Ca2+ ions were present in the exudate occurring in the intercellular spaces of secretory tissue before pollination. The exudate of an unpollinated stigma was the site of the localization of large amounts of deesterified pectins. Stigma penetration by pollen tubes induced the lysis of this category of pectins. The epidermal cells walls of the dry Haemanthus albiflos stigma before pollination lacked free and loosely bound Ca2+ ions. Pollination induced an accumulation of these ions in the apoplast of the stigma epidermal cells. In cells walls of an unpollinated stigma, mainly esterified pectins were present. Their deesterification took place after pollination at the site of pollen grain adhesion and then at the site of pollen tube growth. These results have shown that wet and dry stigmas differ in pectin metabolism and in the mechanism of forming a calcium environment at the site of pollen grain germination.     

Localization of adenylate cyclase activity in Populus: its relation to pollen-pistil recognition and incompatibility

Summary Adenylate cyclase has been localized cytochemically in female and male parents as well as during the pollen-stigma interaction with an original technique employing strontium as the capture ion and adenyl imidodiphosphate as the specific substrate. The specificity of the reaction was checked by using several controls. No final specific reaction product was detected in unpollinated P. deltoides stigmas or in the P. deltoides or P. alba pollen grains used for compatible and incompatible pollinations. In the compatible cross between P. deltoides × P. deltoides, fine dense precipitates were observed in the dictyosomes and the plasma membrane and exterior to the exine of hydrated pollen grains adhering to the stigma surface. Labeling of the stigmatic pellicle was also observed after pollen adhesion and hydration. This was accompanied by a strong reactivity of the cell wall and plasmalemma of the stigma papillae at the sites of pollen tube germination on the stigma surface and at the sites of penetration of pollen tubes between adjacent papillae. In the incompatible cross between P. deltoides x P. alba, adenylate cyclase activity was still present but reduced at the stigma surface following adhesion, hydration, and germination of P. alba pollen. This activity was completely abolished after the penetration of pollen tubes between stigma papillae. These findings suggest that in Populus, adenylate cyclase activity is correlated to pollen adhesion, hydration, and germination at the stigma surface, and that the abolition of this enzyme activity could be one of the cellular events governing the gametophytic phenotype of incompatibility in the cross between P. deltoides and P. alba.     

簇枝补血草花的二态性及繁育系统研究

白花丹科被列为异型花柱较多的科,该文以补血草属簇枝补血草为材料,通过对野外居群的花部特征、花期物候和繁育系统等研究,探讨花部形态多态性及其对生殖的影响。簇枝补血草具有两种类型植株,具玉米状柱头和A型花粉的植株称为C型植株;具乳头状柱头和B型花粉的植株称为P型植株,且A/B型花粉的大小、外壁纹饰不同。单花发育过程中两型植株的花萼、雌蕊大小差异明显,随着花的成熟差异逐渐消失。两型植株都为雌蕊高于雄蕊,柱头探出式雌雄异位;C型植株的花期较P型植株长约2 d。一天当中,A型花粉活力高峰期为13:00,B型花粉在11:00和15:00都表现为高峰期;玉米状柱头可授性最强时期在13:00～15:00,乳头状柱头则在15:00。两型花粉可育性在盛花期最高,终花期时B型花粉可育性明显高于A型。荧光染色观察发现花粉萌发和花粉管的生长速度都为:异型授粉＞同型授粉,B型花粉在乳头状柱头上不能完成受精。此外,人工授粉实验也表明异型授粉结实率显著高于同型,P型植株经同型授粉结实现象并不明显,存在少量无融合生殖。研究表明簇枝补血草花部具二态性,繁育系统为兼性异交,其中乳头状柱头对A型花粉亲和,对B型花粉不亲和,但玉米状柱头却对A/B型花粉都亲和,这打破了该科的异型自交不亲和的例证。