生物多样性2007,15(6):652-657doi:10.1360/biodiv.070207Biodiversity Sciencehttp: //www.biodiversity-science.net兼论其与传粉者的关系芭蕉科花蜜腺形态比较：任宗昕,2王红!1（中国科学院昆明植物研究所生物多样性与生物地理学重点实验室，昆明650204)2（中国科学院研究生院，北京100049)摘要：对狭义芭蕉科3个属的代表性种芭蕉(Musabasjoo)、象腿蕉(Enseteglaucum)和地涌金莲(Musellalasiocarpa)的花蜜腺形态进行了比较研究。结果表明它们的蜜腺属于隔膜蜜腺。雌花的蜜腺着生于子房的上部，胚珠的上方；雄花蜜腺占据了整个败育子房的位置。蜜腺结构由许多腔道组成，这些腔道在横切面上呈现出复杂的发散式迷宫状结构。这3种植物花蜜腺的栅栏状表皮细胞、维管束和蜜腺开口方式相似，而从纵切面和横切面上观察其结构存在一些差异。PAS反应显示象腿蕉泌蜜组织中淀粉粒含量高于其他两个种：芭蕉和象腿蕉的蜜腺腔里有许多纤维状物质存在。3种植物的传粉综合征多样化，花序和花的特征（如花序下垂或直立、苞片的颜色、泌蜜量和泌蜜时间等)和传粉样式之间有密切关系。它们的蜜腺结构和传粉者行为之间没有明显的相关性，但是胶质或水质的花蜜对传粉者的取食方式有一定影响。关键词：隔膜蜜腺，形态比较，Musabasjoo,Enseteglaucum，Musellalasiocarpa，传粉者Morphological comparison of floral nectaries in Musaceae, with refer-encetoitspollinatorsZongxin Ren'2, Hong Wang"1KeyLaboratory of Biodiversity and Biogeography,KunmingInstituteof Botany,ChineseAcademy of Sciences,Kunming6502042GraduateUniversityoftheChineseAcademyofSciences,Beijing100049Abstract:The floral nectaries of three species of Musaceae s.s.representing the genera Musa,Ensete andMusella were comparatively investigated.Our observations revealed that nectaries of these three genera be-longed to the interlocular septal type.Infemaleflowers,nectaries were limited to the upper part of the ova-ries above the locules,while in male flowers (with aborted ovaries)nectaries entirely occupied the abortedovaries.AtransectionofnectaryductssuggestedacomplexandhighlyproliferatedlabyrinthinestructureThe three species shared a few common features in the palisade-like epithelial cells,vascular supplies,andnectary openings.However, they showed somedifferences in longitudinal section and transectinal outline.Thenectaries of Enseteglaucumhad thehighest starch content,and thoseof Musabasjoo and E.glaucumhadfibrillarmaterialpresented innectarducts.Pollinationsyndromes amongthethree species showed highdiversity,while inflorescenceand flower characters (such as pendant or erect inflorescences, bract color,nectar volume and production over time, etc.)and pollination patterns were highly correlated.There were nostrong correlations between nectary structures and pollinator behavior,although gelatinous or watery nectarwasassociatedwiththeforagingpreferenceofpollinatorsKey words: septal nectaries,morphological comparison, Musa basjoo, Enseteglaucum, Musella lasicarpa,pollinatorsrestricted to the Old World (Cronquist, 1981; Anders-Introductionson, 1998). Musa, the source of edible bananas andplantains, is primarily distributed in tropical AsiaThe family Musaceae sensu stricto is a conspicuous(withextensionsintothesubtropics)andlimitedareastropical and subtropical groupofplants encompassingof northeastern Australia. In addition to providingthegenera Musa,Enseteand Musella,all of which aremankind with the most-consumed fruit in the world,Received August 9, 2007; accepted October 10, 2007*Authorfor correspondence.E-mail:wanghong@mail.kib.ac.cn(C)1994-2019ChinaAcademicJournalElectronicPublishingHouse.All rightsreserved.http:/www.cnki.net
生物多样性 2007, 15 (6): 652–657 doi: 10.1360/biodiv.070207 Biodiversity Science http: //www.biodiversity-science.net —————————————————— Received August 9, 2007; accepted October 10, 2007 * Author for correspondence. E-mail: wanghong@mail.kib.ac.cn 芭蕉科花蜜腺形态比较: 兼论其与传粉者的关系 任宗昕1, 2 王 红1﹡ 1 (中国科学院昆明植物研究所生物多样性与生物地理学重点实验室, 昆明 650204) 2 (中国科学院研究生院, 北京 100049) 摘要: 对狭义芭蕉科3个属的代表性种芭蕉(Musa basjoo)、象腿蕉(Ensete glaucum)和地涌金莲(Musella lasiocarpa) 的花蜜腺形态进行了比较研究。结果表明它们的蜜腺属于隔膜蜜腺。雌花的蜜腺着生于子房的上部, 胚珠的上方; 雄花蜜腺占据了整个败育子房的位置。蜜腺结构由许多腔道组成, 这些腔道在横切面上呈现出复杂的发散式迷宫 状结构。这3种植物花蜜腺的栅栏状表皮细胞、维管束和蜜腺开口方式相似, 而从纵切面和横切面上观察其结构存 在一些差异。PAS反应显示象腿蕉泌蜜组织中淀粉粒含量高于其他两个种; 芭蕉和象腿蕉的蜜腺腔里有许多纤维 状物质存在。3种植物的传粉综合征多样化, 花序和花的特征(如花序下垂或直立、苞片的颜色、泌蜜量和泌蜜时 间等)和传粉样式之间有密切关系。它们的蜜腺结构和传粉者行为之间没有明显的相关性, 但是胶质或水质的花蜜 对传粉者的取食方式有一定影响。 关键词: 隔膜蜜腺, 形态比较, Musa basjoo, Ensete glaucum, Musella lasiocarpa, 传粉者 Morphological comparison of floral nectaries in Musaceae, with reference to its pollinators Zongxin Ren1, 2, Hong Wang1* 1 Key Laboratory of Biodiversity and Biogeography, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650204 2 Graduate University of the Chinese Academy of Sciences, Beijing 100049 Abstract: The floral nectaries of three species of Musaceae s. s. representing the genera Musa, Ensete and Musella were comparatively investigated. Our observations revealed that nectaries of these three genera belonged to the interlocular septal type. In female flowers, nectaries were limited to the upper part of the ovaries above the locules, while in male flowers (with aborted ovaries) nectaries entirely occupied the aborted ovaries. A transection of nectary ducts suggested a complex and highly proliferated labyrinthine structure. The three species shared a few common features in the palisade-like epithelial cells, vascular supplies, and nectary openings. However, they showed some differences in longitudinal section and transectinal outline. The nectaries of Ensete glaucum had the highest starch content, and those of Musa basjoo and E. glaucum had fibrillar material presented in nectar ducts. Pollination syndromes among the three species showed high diversity, while inflorescence and flower characters (such as pendant or erect inflorescences, bract color, nectar volume and production over time, etc.) and pollination patterns were highly correlated. There were no strong correlations between nectary structures and pollinator behavior, although gelatinous or watery nectar was associated with the foraging preference of pollinators. Key words: septal nectaries, morphological comparison, Musa basjoo, Ensete glaucum, Musella lasicarpa, pollinators Introduction The family Musaceae sensu stricto is a conspicuous tropical and subtropical group of plants encompassing the genera Musa, Ensete and Musella, all of which are restricted to the Old World (Cronquist, 1981; Andersson, 1998). Musa, the source of edible bananas and plantains, is primarily distributed in tropical Asia (with extensions into the subtropics) and limited areas of northeastern Australia. In addition to providing mankind with the most-consumed fruit in the world
第6期任宗昕和王红：芭蕉科花蜜腺形态比较：兼论其与传粉者的关系653the genus also includes fiber producing Musa textilisunderstanding of therelationshipbetween monocotsand their pollinators (Bernardello et al.,1991:Kuch-and numerous ornamental species.Ensete has a dis-continuous distributionfrom tropical Africa to tropicalmeister et al.,1997;Strange et al.,2004; StpiczynskaAsia, and Musella, a monotypic genus, is endemic toet al.,2005).Primarywork on nectary,floral mor-phologyand anatomy inMusahas been conducted bySoutheast Asiaincluding southwestern China.Thai-land,Vietnam, Laosand Myanmar.numerousresearchers,includingWhite(1928),FahnLarge inflorescence size,visual conspicuousness,(1949),Fahn et al. (1961), Fahn & Kotler (1972)floral odor and copiousnectar production in MusaceaeFahn & Benouaiche (1979), and Kirchoff (1992).Tilkhave been identified as classic examples of adapta-&Pai(1974)described thefloral anatomyofEnsetetions forsunbird and batpollination.Accordingtosuperbum.Recent anatomic studies in the familyprevious reports, pollination syndromes in this familyMusaceae have focused on ovule development andgrowth (Fortescue & Turner, 2005a, b).However, un-show high diversity (Faegri & van der Pijl, 1979, En-dress,1994).BothMusa and Ensetehave been identi-til now there has been no detailed comparative studyfiedasornithophilousand/orchiropterophilous.Musaof the nectaries in Musaceae.In this paper, our objec-species with erect inflorescences are considered tobetives are to further the study of nectaries in the threesunbird-pollinated, while other species with pendantgenera of Musaceae s.s.(including the first report oninflorescences arepollinatedbybats(Nur,1976;ItinoMusella lasiocarpa)andtounderstand the relationshipet al., 1991; Liu et al.,2002a).Ensete, with pendantbetweennectarystructureandpollinationsvndromesinflorescences,greenishbracts,and odiferousflowers.arepollinatedbybats(Nur,1976).In contrast,Materials and MethodsMusella, a striking member of this family with erectinflorescences, bright yellow bracts and odorlessMature flowers of three species representing all threeflowers, is pollinated by insects such as honey beesgenera (Musa, Ensete and Musella) were collectedand bumblebees (Liu et al., 2002b)from Xishuangbanna Tropical Botanical Garden inIngeneral,a commonfeature of nectariesis thatsouthern Yunnanand KunmingBotanicalGardeninthey provide an advantage for plants: either by at-central Yunnan, China (Table 1).Voucher specimenstractingforagers that offerdefensefrompredatorsinwere deposited at the herbarium of Kunming Institutethe case of extrafloral nectaries, or by attracting polli-ofBotany,ChineseAcademyofSciences(KUN)nators inthe case of floral nectaries.Thus thetermFresh flowers were fixed and stored in forma-nectaryhasecologicalsignificance.inthatnectarieslin-acetic acid-alcohol (FAA),with perianths and sta-are the sites where liquid substances involved inmensremoved.Ovariescontainingnectariferoustissueplant-animal interactions are produced and offeredwere dehydrated through alcohol/xylol series and em-(Pacini et al., 2003).Flowers of the family Musaceaebedded in paraffin (LEICA-EG1160).Serial transverseare usuallypollinated byanimals,withnectarand/orand longitudinal sections were cut usinga microtomepollen presented to pollinators as a reward. According(LEICA-RM2135)at8μmthickandmountedonto Schmid (1985),specialized adaptations to bird andslides by Haudt's adhesive. Hematoxylin and fastbat pollinationprobablynecessitatedvarious morpho-green wereused to stain the sections.Potassium pe-logical andanatomicalmodificationstoproducein-riodate and Schiff's reagent reaction (PAS)were concreased amounts of nectar required by these large pol-ductedtostainstarches.Sectionswereobservedandlinators. Considering the high diversity of pollinationmicrographed under an Olympus-VANOXmicro-syndromes in the family Musaceae, it appears to usscope.that a comparative anatomical study of nectary struc-ture could provide valuable information about the re-lationships between nectary characters and variousResultstypesand behaviorsofpollinators.In monocotyledons, nectary occurs in the septa ofThere were obvious differences between male andthe ovary, called septal nectary (SN)(Fahn, 1979)orfemaleflowers in Musaceae.Basal inflorescences andgynopleural nectary (Smets et al.,2000).According toflowers were specialized to function as females (withSchmid (1985),a septal nectary is defined as the fol-fully degenerated anthers producing no pollen),whilelowing:a nectariferous (sugar-or nectar-secreting)flowers in themiddle and apex functioned as malescavity resulting from the lack of intercarpellary post-(with nonfunctional stigmas and ovaries).Thereweregenital fusion and lying in a septal radius. The septalnectaries of monocotyledons show high diversitycorresponding anatomical differences between thenectaries offemale flowers and those in male and ster-(Daumann,1970,Fahn,1979),andcomparativestud-ile flowers.Somestudies(Tilk&Pai,1974;Fahn,ies of septal nectaries arethusvery importantforour(C)1994-2019 China Academic Journal Electronic Publishing House.All rights reserved.http://www.cnki.net
第 6 期 任宗昕和王红: 芭蕉科花蜜腺形态比较: 兼论其与传粉者的关系 653 the genus also includes fiber producing Musa textilis and numerous ornamental species. Ensete has a discontinuous distribution from tropical Africa to tropical Asia, and Musella, a monotypic genus, is endemic to Southeast Asia, including southwestern China, Thailand, Vietnam, Laos and Myanmar. Large inflorescence size, visual conspicuousness, floral odor and copious nectar production in Musaceae have been identified as classic examples of adaptations for sunbird and bat pollination. According to previous reports, pollination syndromes in this family show high diversity (Fægri & van der Pijl, 1979; Endress, 1994). Both Musa and Ensete have been identified as ornithophilous and/or chiropterophilous. Musa species with erect inflorescences are considered to be sunbird-pollinated, while other species with pendant inflorescences are pollinated by bats (Nur, 1976; Itino et al., 1991; Liu et al., 2002a). Ensete, with pendant inflorescences, greenish bracts, and odiferous flowers, are pollinated by bats (Nur, 1976). In contrast, Musella, a striking member of this family with erect inflorescences, bright yellow bracts and odorless flowers, is pollinated by insects such as honey bees and bumblebees (Liu et al., 2002b). In general, a common feature of nectaries is that they provide an advantage for plants: either by attracting foragers that offer defense from predators in the case of extrafloral nectaries, or by attracting pollinators in the case of floral nectaries. Thus the term nectary has ecological significance, in that nectaries are the sites where liquid substances involved in plant–animal interactions are produced and offered (Pacini et al., 2003). Flowers of the family Musaceae are usually pollinated by animals, with nectar and/or pollen presented to pollinators as a reward. According to Schmid (1985), specialized adaptations to bird and bat pollination probably necessitated various morphological and anatomical modifications to produce increased amounts of nectar required by these large pollinators. Considering the high diversity of pollination syndromes in the family Musaceae, it appears to us that a comparative anatomical study of nectary structure could provide valuable information about the relationships between nectary characters and various types and behaviors of pollinators. In monocotyledons, nectary occurs in the septa of the ovary, called septal nectary (SN) (Fahn, 1979) or gynopleural nectary (Smets et al., 2000). According to Schmid (1985), a septal nectary is defined as the following: a nectariferous (sugar- or nectar-secreting) cavity resulting from the lack of intercarpellary postgenital fusion and lying in a septal radius. The septal nectaries of monocotyledons show high diversity (Daumann, 1970; Fahn, 1979), and comparative studies of septal nectaries are thus very important for our understanding of the relationship between monocots and their pollinators (Bernardello et al., 1991; Küchmeister et al., 1997; Strange et al., 2004; Stpiczyńska et al., 2005). Primary work on nectary, floral morphology and anatomy in Musa has been conducted by numerous researchers, including White (1928), Fahn (1949), Fahn et al. (1961), Fahn & Kotler (1972), Fahn & Benouaiche (1979), and Kirchoff (1992). Tilk & Pai (1974) described the floral anatomy of Ensete superbum. Recent anatomic studies in the family Musaceae have focused on ovule development and growth (Fortescue & Turner, 2005a, b). However, until now there has been no detailed comparative study of the nectaries in Musaceae. In this paper, our objectives are to further the study of nectaries in the three genera of Musaceae s. s. (including the first report on Musella lasiocarpa) and to understand the relationship between nectary structure and pollination syndromes. Materials and Methods Mature flowers of three species representing all three genera (Musa, Ensete and Musella) were collected from Xishuangbanna Tropical Botanical Garden in southern Yunnan and Kunming Botanical Garden in central Yunnan, China (Table 1). Voucher specimens were deposited at the herbarium of Kunming Institute of Botany, Chinese Academy of Sciences (KUN). Fresh flowers were fixed and stored in formalin-acetic acid-alcohol (FAA), with perianths and stamens removed. Ovaries containing nectariferous tissue were dehydrated through alcohol/xylol series and embedded in paraffin (LEICA-EG1160). Serial transverse and longitudinal sections were cut using a microtome (LEICA-RM2135) at 8 µm thick and mounted on slides by Haudt’s adhesive. Hematoxylin and fast green were used to stain the sections. Potassium periodate and Schiff’s reagent reaction (PAS) were conducted to stain starches. Sections were observed and micrographed under an Olympus-VANOX microscope. Results There were obvious differences between male and female flowers in Musaceae. Basal inflorescences and flowers were specialized to function as females (with fully degenerated anthers producing no pollen), while flowers in the middle and apex functioned as males (with nonfunctional stigmas and ovaries). There were corresponding anatomical differences between the nectaries of female flowers and those in male and sterile flowers. Some studies (Tilk & Pai, 1974; Fahn
654生物多样性BiodiversityScience第15卷Table1Materials used in the current studyTaxaLocationHabitatAltitude (m)OriginXTBG*Wild550Musa basjooMenglun, Xishuangbanna, southern Yunnan550EnseteglaucumXTBG*CultivatedMenglun, Xishuangbanna, southern YunnanKBG**1,900Musella lasiocarpaCultivatedKunming, central Yunnan*XTBG, Xishuangbanna Tropical Botanical Garden; **KBG, Kunming Botanical Garden1979; Kirchoff, 1992) suggested these differencesnectary ducts in Musabasjoowas narrower thanthatwere due to the position of ovules and nectaries inof the other two taxa.The results of the PAS reaction showed that thefemaleflowers.In the femaleflowers of Musaceae,nectaries of Ensetehad higher starch content than thenectaries were limited totheupperpartof the ovaryabovethe locules.In male flowers with aborted ova-other taxa, and some fibrillar materials in the nectaryries, the nectaries entirely occupied the aborted ova-lumen were also stained red (Fig. lk, p).ries.Exceptpositional differencesbetweenfemale andmaleflowers,studies cited above and our own obser-Discussionvationsfound the same nectary morphology in boththe male and female flowers.Because of this, ourIn monocots, the septal nectaries may be either in-studyfocused primarily on male floral nectaries in thefralocular or interlocular (Schmid, 1988; Simpson,three genera.1998,Smets et al.,2000).Our observationsinDisregarding ovary position, nectaries of the stud-Musaceae indicated that nectaries were limited to theied taxa showed the following features in commonupper part of the ovaries above the locules in the fe-First, the positions of septal nectaries were at the un-male flowers.This suggested that the nectaries offused regions ofthecarpel margins.The nectary couldthese three genera belonged to the interlocular septalbe divided into basal (Fig. la, g, I), middle (Fig. 1b, h,nectary category. Based on his observations and a re-m),and upper regions (Fig.lc, d, i, n).A transectionviewof the literature,Fahn (1953)proposedageneralof nectaryducts revealed a complexand highly prolif-evolutionary trend of flower nectaries in shifting theirerated labyrinthine structure. In the middle region,position in an acrocentripetal direction.He also sugnectary ducts formed a three-to six-armed stargested that the nectaries of Musaceae were the mostpattern, becoming tri-radiate towards to upper regionspecialized in the monocots.Thisview was supported(Fig. lb, h, m) and ultimately form three lobes (Fig.bySchmid(1985),whocategorizedthenectariesoflc, i, n). The nectaries of these epigynous flowersMusaceaeaslabvrinthinecommonnectarialcavitiesopened at thetop oftheovary,betweenthefurrowsofwith convoluted proliferations of the carpellary walls,the styles and the stamens.One of the nectary open-and also pointed out that the "liliad" type of innerings usuallyappeared between a stylarfurrow and oneseptal nectary (non-labyrinthine distinct septal nectar-of the perianth lobes (Fig. le, j, o). One-layered pali-ies) could be regarded as an evolutionary startingsade-like epithelial cells were perpendicular to thepoint for nectary phyletic trends, with the nectaries ofnectary surface, which possessed a cuticle.The nec-Musaceae being the most advanced. Just as pollen hadtary parenchyma usually had two to six layers of iso-primary and secondary presentation, Pacini et aldiametric cells. These small cells had thin walls, rela-(2003)and Nepi etal.(2006)applied the terminologytively large nuclei,densegranular cytoplasm, and"secondarynectar presentation'to describethenectausmall vacuoles.With abundant vascular supplies,therepresentationwhenthesiteofnectarproductionandthewerenumerousvascularbundles near the nec-site of nectar emission were different, a viewpointtar-secreting tissue (Fig. 1f, k, p).with which we whollyagreed.The septal nectary,be-Our study also demonstrated differences in longitu-ing a cavity inside the ovary, is not directly exposed todinal sectionand transectinal outlineamongthethreenectar-feeding animals (Smets et al.,2000),so septaltaxa. As shown in Table 2,the ratio of nectary lengthnectaries have secondary nectar presentation. Thetoovary lengthin Musa basjoowas approximatelynectaries of thesethree epigynous flowers openatthe1:2, while in Musella and Ensete it was more than 2:3,topoftheovary.betweenthefurrowsofthestvlesandwithnectaries occupying most of thelengthof thethe stamens, and thus also belongto this categoryovaries.In Musa basjoo,the transectional outline onlyOur study confirms Fahn's suggestion that threehadathree-armedstarshapedphase.whiletheotherovary locules develop,with themajor portion of thetwo had five-or six-armed phases and formed a highlynectary limited to the upper part of the ovary aboveproliferated and labyrinthine structure.The width ofthe locules in female flowers of Musaceae, while(C)1994-2019 China Academic Journal Electronic Publishing House.All rights reserved.http://www.cnki.net
654 生 物 多 样 性 Biodiversity Science 第 15 卷 Table 1 Materials used in the current study Taxa Location Habitat Altitude (m) Origin Musa basjoo XTBG* Wild 550 Menglun, Xishuangbanna, southern Yunnan Ensete glaucum XTBG* Cultivated 550 Menglun, Xishuangbanna, southern Yunnan Musella lasiocarpa KBG** Cultivated 1,900 Kunming, central Yunnan *XTBG, Xishuangbanna Tropical Botanical Garden; **KBG, Kunming Botanical Garden 1979; Kirchoff, 1992) suggested these differences were due to the position of ovules and nectaries in female flowers. In the female flowers of Musaceae, nectaries were limited to the upper part of the ovary above the locules. In male flowers with aborted ovaries, the nectaries entirely occupied the aborted ovaries. Except positional differences between female and male flowers, studies cited above and our own observations found the same nectary morphology in both the male and female flowers. Because of this, our study focused primarily on male floral nectaries in the three genera. Disregarding ovary position, nectaries of the studied taxa showed the following features in common. First, the positions of septal nectaries were at the unfused regions of the carpel margins. The nectary could be divided into basal (Fig. 1a, g, l), middle (Fig. 1b, h, m), and upper regions (Fig. 1c, d, i, n). A transection of nectary ducts revealed a complex and highly proliferated labyrinthine structure. In the middle region, nectary ducts formed a three- to six-armed star pattern, becoming tri-radiate towards to upper region (Fig. 1b, h, m) and ultimately form three lobes (Fig. 1c, i, n). The nectaries of these epigynous flowers opened at the top of the ovary, between the furrows of the styles and the stamens. One of the nectary openings usually appeared between a stylar furrow and one of the perianth lobes (Fig. 1e, j, o). One-layered palisade-like epithelial cells were perpendicular to the nectary surface, which possessed a cuticle. The nectary parenchyma usually had two to six layers of isodiametric cells. These small cells had thin walls, relatively large nuclei, dense granular cytoplasm, and small vacuoles. With abundant vascular supplies, there were numerous vascular bundles near the nectar-secreting tissue (Fig. 1f, k, p). Our study also demonstrated differences in longitudinal section and transectinal outline among the three taxa. As shown in Table 2, the ratio of nectary length to ovary length in Musa basjoo was approximately 1:2, while in Musella and Ensete it was more than 2:3, with nectaries occupying most of the length of the ovaries. In Musa basjoo, the transectional outline only had a three-armed star shaped phase, while the other two had five- or six-armed phases and formed a highly proliferated and labyrinthine structure. The width of nectary ducts in Musa basjoo was narrower than that of the other two taxa. The results of the PAS reaction showed that the nectaries of Ensete had higher starch content than the other taxa, and some fibrillar materials in the nectary lumen were also stained red (Fig. 1k, p). Discussion In monocots, the septal nectaries may be either infralocular or interlocular (Schmid, 1988; Simpson, 1998; Smets et al., 2000). Our observations in Musaceae indicated that nectaries were limited to the upper part of the ovaries above the locules in the female flowers. This suggested that the nectaries of these three genera belonged to the interlocular septal nectary category. Based on his observations and a review of the literature, Fahn (1953) proposed a general evolutionary trend of flower nectaries in shifting their position in an acrocentripetal direction. He also suggested that the nectaries of Musaceae were the most specialized in the monocots. This view was supported by Schmid (1985), who categorized the nectaries of Musaceae as labyrinthine common nectarial cavities with convoluted proliferations of the carpellary walls, and also pointed out that the “liliad” type of inner septal nectary (non-labyrinthine distinct septal nectaries) could be regarded as an evolutionary starting point for nectary phyletic trends, with the nectaries of Musaceae being the most advanced. Just as pollen had primary and secondary presentation, Pacini et al. (2003) and Nepi et al. (2006) applied the terminology ‘secondary nectar presentation’ to describe the nectar presentation when the site of nectar production and the site of nectar emission were different, a viewpoint with which we wholly agreed. The septal nectary, being a cavity inside the ovary, is not directly exposed to nectar-feeding animals (Smets et al., 2000), so septal nectaries have secondary nectar presentation. The nectaries of these three epigynous flowers open at the top of the ovary, between the furrows of the styles and the stamens, and thus also belong to this category. Our study confirms Fahn’s suggestion that three ovary locules develop, with the major portion of the nectary limited to the upper part of the ovary above the locules in female flowers of Musaceae, while
第6期任宗昕和王红：芭蕉科花蜜腺形态比较：兼论其与传粉者的关系655Fig.1Sections ofmaleflowersatanthesisof Musella lasiocarpa,Musabasjooand Enseteglaucum (Bars:0.1mmforf,kandp;0.2 mm for others).E, epidermis; Nt, nectar-secreting tissue; Vb, vascular bundle; Nc, nectary canal, Sc, style canal. Musella lasio-carpa:(a)Baseofovary,showinglargecavity:(b)Middleof ovary,showingmoreorlesssix-armed starpatternofnectarcanals:(c)Tri-radiated shape at the upper part of ovary; (d) Three ducts (arrow); (e) Transactional sections of a flower, showing nectary opening(arrow), (f) Details showing one-layered palisade-like epithelial cells, nectar-secreting tissue and ramified vascular bundles. Musabasjoo: (g)Base of ovary,nectary canals showing labyrinthine pattern but no arm structures; (h)Three-armed structure at the middleof ovary:(i)Tri-radiate shapeattheupperpart of ovary,(i)Transactional sections ofaflower,showingthenectary opening,(k)Details showing one-layered palisade-like epithelial cells, nectar-secreting tissue and ramified vascular bundles. Ensete glaucum: (l)Base of ovary,showing six-armed star shape; (m)4-or 5-armed star structure at the middle of ovary;(n)Three ducts at the opening,(o)Transactional sections ofa flower,showingtheopening of thenectary canal;(p)Details showingone-layeredpalisade-likeepithelial cells, nectar-secretingtissueandramifiedvascularbundles,(C)1994-2019ChinaAcademicJournalElectronicPublishingHouse.All rightsreserved.http://www.cnki.net
第 6 期 任宗昕和王红: 芭蕉科花蜜腺形态比较: 兼论其与传粉者的关系 655 Fig. 1 Sections of male flowers at anthesis of Musella lasiocarpa, Musa basjoo and Ensete glaucum (Bars: 0.1 mm for f, k and p; 0.2 mm for others). E, epidermis; Nt, nectar-secreting tissue; Vb, vascular bundle; Nc, nectary canal; Sc, style canal. Musella lasiocarpa: (a) Base of ovary, showing large cavity; (b) Middle of ovary, showing more or less six-armed star pattern of nectar canals; (c) Tri-radiated shape at the upper part of ovary; (d) Three ducts (arrow); (e) Transactional sections of a flower, showing nectary opening (arrow); (f) Details showing one-layered palisade-like epithelial cells, nectar-secreting tissue and ramified vascular bundles. Musa basjoo: (g) Base of ovary, nectary canals showing labyrinthine pattern but no arm structures; (h) Three-armed structure at the middle of ovary; (i) Tri-radiate shape at the upper part of ovary; (j) Transactional sections of a flower, showing the nectary opening; (k) Details showing one-layered palisade-like epithelial cells, nectar-secreting tissue and ramified vascular bundles. Ensete glaucum: (l) Base of ovary, showing six-armed star shape; (m) 4- or 5-armed star structure at the middle of ovary; (n) Three ducts at the opening; (o) Transactional sections of a flower, showing the opening of the nectary canal; (p) Details showing one-layered palisade-like epithelial cells, nectar-secreting tissue and ramified vascular bundles
生物多样性656Biodiversity Science第15卷Table 2Comparison ofnectary anatomy inthe studiedtaxaCharacterMusella lasiocarpaMusa basjooEnsete glaucum12Longitudinal outline (length ratio ofMore than 2/3More than 2/3the nectary/ovary)Transectional outlineSix-armed star shape (Fig. la)Basal regionLabyrinthine structure (Fig, Ig)Large cavity (Fig, 11)Middle regionSix-armed star shape, becomingThree-armed star becomingFour or five-armed star shape be-tri-radiate (Fig. Ib)tri-radiate (Fig. lh)coming tri-radiate (Fig. Im)Upper regionThree separated ducts (Fig, 1d)Three separated ducts (Fig. li)Three separated ducts (Fig. In)Secretory cuticle arrangementRegularIrregularIrregularPAS reaction (relative starch con-Low (Fig, If)Low (Fig. 1k)High (Fig. Ip)tent)PresentFibrillar materialAbsentPresentfilling the entirety of aborted ovaries with a labyrinthThe exuberance in development of nectaries inmaleof nectaryductsin maleflowers.FollowingSchmidflowers due to the loss of ovulation also has a protec-(1985),we can summarizethe role of several nectarytive or supportivefunction,because it is importantforfeatures that increase nectar output in these three taxa:these flowers to support themselves during the activi-(1) higher longitudinal extent of septal nectaries, es-ties of the relatively larger pollinating bats and sun-pecially in male flowers where the nectaries entirelybirds.Based on ourobservations,bumblebees usuallyfill the aborted ovary (in Musella and Ensete,the lon-burrowed their entire body into the corolla tubes ofMusella when theyforaged fornectar presented on thegitudinalextentofSNsarelongerthanthatofMusa)(2)the lack of intercarpellary (postgenital)fusion insurface of the inferior ovary.Therefore, the develop-SNs, creating a common nectary cavity and increasingment of septal nectaries in Musella also has a potentialnectarial surface area,(3)undulation and convolutionprotective function.to form a labyrinthine shape, thereby increasing nec-According to previous reports, flower characterstarial surface area, (4)the epidermal nectar-secreting(such aspendant orerect inflorescences,bract color,cells form a palisade by increasing the tangential size;andnectarvolumeandproductionovertime,etc.)and(5)the number of layers of nectar-secreting cells ispollination syndromes of Musaceae are highly corre-abouttwotofive,moreorlessforminglated (Nur,1976; Itino et al.,1991; Liu et al.,2002b)asubepidermal secretory tissue, and (6)since there arebut our study indicated that there were no strong cor-numerousvascular bundles near theSNs,it seems thatrelations between nectary structures and pollinatorbehavior.We could see some differences amongthesethe inferior ovary in Musaceae flowers would haveallowed a great number of vascular bundles to servethree plant flowers,from the longitudinal extent andthe nectaries and thus to facilitate increased nectartransactional outline of floral nectary, to the PAS re-outpctording to Liu et al.(2002b),the mean volumeaction result (Table 2), but apparently these differ-ofnectaroffemaleflowers inMusellalasiocarpawasences had littlecorrelation withdifferent pollination600.25 ± 133.57μL, and in male flowers it wassyndromes. However, in Musa and Ensete, there werea lotof fibrillarmaterialsinnectarystructures,and335.14±72.23μL,andthesugarconcentrationofnectar was gelatinous, since if it was watery the nectarnectar was 14.99-15.33%.Another species Musa itin-would be lost due to the horizontal or inclined positionerans pollinated by sunbirds and bats had 206.06±of the flower.Moreover,the gelatinous nectar was29.6μL and 126.6±27.2μL nectar production inapparently easier for bats to lap up with their tongues.each female and male flower in the morning, with aThus,wateryorgelatinousnectarwasassociatedwithsugar concentration of 20.7-23.1% (Liu et al., 2002a).the foraging preferences of insect and bat pollinators,Musa acuminata subsp.halabanensis and M. salac-respectively.censis also showed high nectar production, and sugarconcentration of nectar was 21-25% and 18-21%,respectively (Itino et al., 1991).However, the resultsAcknowledgementsof thePASreactionshowedthatthenectaryofEnseteWe thankProf.Hanxin Liang for herkind assistancehad higher starch content than the other taxa. Addi-in the laboratory,and Jimmy Triplett of the Depart-tional investigations should be further carried out toment of Ecology, Evolution & Organismal Biology,understandnectarproductionpatternofMusa basjoolowa State Universityforrevisingan earlier version ofand Enseteglaucum.(C)1994-2019 China Academic Journal Electronic Publishing House.All rights reserved.http://www.cnki.net
656 生 物 多 样 性 Biodiversity Science 第 15 卷 Table 2 Comparison of nectary anatomy in the studied taxa Character Musella lasiocarpa Musa basjoo Ensete glaucum Longitudinal outline (length ratio of the nectary / ovary) More than 2/3 1/2 More than 2/3 Transectional outline Basal region Six-armed star shape (Fig. 1a) Labyrinthine structure (Fig. 1g) Large cavity (Fig. 1l) Middle region Six-armed star shape, becoming tri-radiate (Fig. 1b) Three-armed star becoming tri-radiate (Fig. 1h) Four or five-armed star shape becoming tri-radiate (Fig. 1m) Upper region Three separated ducts (Fig. 1d) Three separated ducts (Fig. 1i) Three separated ducts (Fig. 1n) Secretory cuticle arrangement Regular Irregular Irregular PAS reaction (relative starch content) Low (Fig. 1f) Low (Fig. 1k) High (Fig. 1p) Fibrillar material Absent Present Present filling the entirety of aborted ovaries with a labyrinth of nectary ducts in male flowers. Following Schmid (1985), we can summarize the role of several nectary features that increase nectar output in these three taxa: (1) higher longitudinal extent of septal nectaries, especially in male flowers where the nectaries entirely fill the aborted ovary (in Musella and Ensete, the longitudinal extent of SNs are longer than that of Musa); (2) the lack of intercarpellary (postgenital) fusion in SNs, creating a common nectary cavity and increasing nectarial surface area; (3) undulation and convolution to form a labyrinthine shape, thereby increasing nectarial surface area; (4) the epidermal nectar-secreting cells form a palisade by increasing the tangential size; (5) the number of layers of nectar-secreting cells is about two to five, more or less forming a subepidermal secretory tissue; and (6) since there are numerous vascular bundles near the SNs, it seems that the inferior ovary in Musaceae flowers would have allowed a great number of vascular bundles to serve the nectaries and thus to facilitate increased nectar output. According to Liu et al. (2002b), the mean volume of nectar of female flowers in Musella lasiocarpa was 600.25 ± 133.57 µL, and in male flowers it was 335.14 ± 72.23 µL, and the sugar concentration of nectar was 14.99–15.33%. Another species Musa itinerans pollinated by sunbirds and bats had 206.06 ± 29.6 µL and 126.6 ± 27.2 µL nectar production in each female and male flower in the morning, with a sugar concentration of 20.7–23.1% (Liu et al., 2002a). Musa acuminata subsp. halabanensis and M. salaccensis also showed high nectar production, and sugar concentration of nectar was 21–25% and 18–21%, respectively (Itino et al., 1991). However, the results of the PAS reaction showed that the nectary of Ensete had higher starch content than the other taxa. Additional investigations should be further carried out to understand nectar production pattern of Musa basjoo and Ensete glaucum. The exuberance in development of nectaries in male flowers due to the loss of ovulation also has a protective or supportive function, because it is important for these flowers to support themselves during the activities of the relatively larger pollinating bats and sunbirds. Based on our observations, bumblebees usually burrowed their entire body into the corolla tubes of Musella when they foraged for nectar presented on the surface of the inferior ovary. Therefore, the development of septal nectaries in Musella also has a potential protective function. According to previous reports, flower characters (such as pendant or erect inflorescences, bract color, and nectar volume and production over time, etc.) and pollination syndromes of Musaceae are highly correlated (Nur, 1976; Itino et al., 1991; Liu et al., 2002b), but our study indicated that there were no strong correlations between nectary structures and pollinator behavior. We could see some differences among these three plant flowers, from the longitudinal extent and transactional outline of floral nectary, to the PAS reaction result (Table 2), but apparently these differences had little correlation with different pollination syndromes. However, in Musa and Ensete, there were a lot of fibrillar materials in nectary structures, and nectar was gelatinous, since if it was watery the nectar would be lost due to the horizontal or inclined position of the flower. Moreover, the gelatinous nectar was apparently easier for bats to lap up with their tongues. Thus, watery or gelatinous nectar was associated with the foraging preferences of insect and bat pollinators, respectively. Acknowledgements We thank Prof. Hanxin Liang for her kind assistance in the laboratory, and Jimmy Triplett of the Department of Ecology, Evolution & Organismal Biology, Iowa State University for revising an earlier version of