荇菜成熟花蜜腺的形态及其泌蜜过程的超微结构研究

荇菜花蜜腺共五枚,黄色,肾形,着生子房基部。它们由分泌表皮和泌蜜组织组成,属结构蜜腺。成熟蜜腺的分泌表皮具明显的角质层和气孔,还具少量短期生活的分泌毛,分泌毛不具明显的角质层。泌蜜组织具较小的胞间隙,胞间连丝发达。成熟蜜腺细胞中不人有丰富的线粒体,内质网,还有大量的质体。     

Nectar secretion inAbutilon: a new model

Summary Nectary trichomes ofAbutilon striatum secrete copious amounts of sucrose, fructose and glucose. The nectar emerges from transient pores in the cuticle overlying the trichome tip cells. Calculations of the required transmembrane fluxes, either across the tip cell plasmalemma or across the cell membrane of the whole trichome, give very high rates compared with those obtained from other situations in plants and, therefore, cast doubt on the possibility that nectar secretion inAbutilon is an eccrine process. Quantitative evaluation of the possibility of granulocrine secretion, by successive fusion of vesicles with the cell membrane, suggests that this is an even less probable mechanism of secretion. Rapid freezing followed by freeze-substitution or freeze-fracture replication reveals that an extensive secretory reticulum (SR) is present within the hair cells. As similar micrographs are obtained from conventional, chemical fixation it is argued that the secretory reticulum is a relatively stable endomembrane system. Freeze-fracture and freeze-substitution micrographs show that this internal membrane system is closely associated with the plasmalemma. Taken together with other structural information, as well as physiological data, it is concluded that prenectar is actively loaded into the secretory reticulum of all trichome cells. Increase in hydrostatic pressure within this compartment leads to the opening of sphincters which connect the cisternal space of the SR to the outside of the plasmalemma. Thus a pulse of nectar is forcibly expelled into an apoplastic compartment sealed to the outside by the impermeable cuticle and on the inside by the plasmalemma. As this apoplastic compartment is also sealed at the stalk cell, the only route for pressure release is via the transient pores which overlay the tip cell. Distension renders these patent so that, again, pulsed secretion is observed. This hypothesis overcomes the necessity for envisaging excessively high transmembrane fluxes or rates of vesicle fusion. It would imply the need for a continuing supply of prenectar to the hair cells accompanied by active loading into the SR. This loading process may well be supported by the hydrolysis of sucrose to glucose and fructose and is probably the site where ions and other low molecular weight solutes are filtered from the nectar.     

荇菜花蜜腺的发育研究

荇菜花蜜腺的发育过程可分为：起源期、生长期、分泌期以及泌蜜停止期等４个时期。荇菜的５枚花蜜腺均起源于子房基部的表皮及表皮内的２－４层细胞。这些细胞经反分化后分别成为蜜腺的原分泌表皮及原泌蜜组织,两部分细胞径不断地分裂分化,最冬成为成熟蜜腺。在蜜腺发育过程中,蜜腺的分泌表皮及蜜腺组织内的内质网、质体、线粒体、液泡等细胞器结构均发生了有规律的变化,内质网在蜜腺分泌期最为发达,且产生大量的分泌小泡。质体     

Developmental and comparative ultrastructure of glandular hairs in the two Urticaceae. I. Urtica dioica

Secretion produced by glandular hairs is deposited mainly in the periplasmic space of the head cells. It stains intensely for both proteins and polysaccharides. The ultrastructure of meristematic, differentiating, mature and senescent head cells as well as the stalk and basal cells has been described in comparison to that in other cell types of the leaf. The specific features of the head cells are the proliferation of the granular endoplasmic reticulum as well as the multiplication of the dictyosomes and mitochondria during transition to the secretion stage. However, the frequency of dictyosomes varies among secreting hairs. The ER produces neither secretory nor transition vesicles and does not anastomose with the plasmalemma. In the absence of transition vesicles, the transport of secretory proteins and enzymes of polysaccharide synthesis from the ER to dictyosomes apparently includes the cytosolic step. Dictyosomes, though not appearing hypersecretory, produce two types of smooth secretory vesicles generated by the trans Golgi reticulum. The vectorial transfer of prosecretion and membranes across the dictyosome stack proceeds via the transport (shuttle) vesicles. It is, therefore, concluded that exocytosis of smooth secretory Golgi vesicles is the sole mechanism of release of both proteins and polysaccharides. Coated vesicles occasionally seen near the plasmalemma are likely to be involved in the endocytotic membrane retrieval. The secretion product disappears during senescence of the hairs and the secretory cells undergo vacuolation by means of local autophagy.     

ULTRASTRUCTURE OF NECTARIES IN RELATION TO NECTAR SECRETION

In the last 15–20 years, ultrastructural studies have added new important cytological information to the relatively rich literature on the morphology and light microscopy of nectaries. On the basis of these studies, the following main conclusions can be drawn regarding the relation between the ultrastructure of nectaries and the process of nectar secretion: (1) the transport of the pre-nectar in the nectariferous tissue is mainly via the symplast; (2) the ER alone or the ER and the Golgi apparatus are involved in the process of secretion; (3) the elimination of nectar from the protoplast of the secretory cells is by reverse pinocytosis; (4) the outer walls of the secretory cells of nectaries in many plants possess wall ingrowths.     

On the mechanisms of nectar secretion: revisited

Background and Scope

Models of nectar formation and exudation in multilayered nectaries with modified stomata or permeable cuticle are evaluated. In the current symplasmic model the pre-nectar moves from terminal phloem through the symplasm into the apoplasm (cell walls and intercellular spaces) with nectar formation by either granulocrine or eccrine secretion and its diffusion outwards. It is concluded, however, that no secretory granules are actually produced by the endoplasmic reticulum, and that secretory Golgi vesicles are not involved in the transport of nectar sugar. Therefore, the concept of granulocrine secretion of nectar should be discarded. The specific function of the endomembrane system in nectary cells remains unknown. According to the apoplasmic model, the pre-nectar moves from the terminal phloem in the apoplasm and, on the way, is transformed from phloem sap into nectar. However, viewed ultrastructurally, the unloading (terminal) phloem of nectaries appears to be less active than that of the leaf minor veins, and is therefore not actively involved in the secretion of pre-nectar components into the apoplasm. This invalidates the apoplasmic model. Neither model provides an explanation for the origin of the driving force for nectar discharge.

Proposal

A new model is proposed in which nectar moves by a pressure-driven mass flow in the nectary apoplasm while pre-nectar sugars diffuse from the sieve tubes through the symplasm to the secretory cells, where nectar is formed and sugars cross the plasma membrane by active transport (‘eccrine secretion’). The pressure originates as the result of water influx in the apoplasm from the symplasm along the sugar concentration gradient. It follows from this model that there can be no combinations of apoplasmic and symplasmic pre-nectar movements. The mass-flow mechanism of nectar exudation appears to be universal and applicable to all nectaries irrespective of their type, morphology and anatomy, presence or absence of modified stomata, and their own vascular system.     

A Histochemical Study of Nectaries of Hibiscus rosa-sinensis

Different histochemical and cytochemical methods were employedon nectaries of Hibiscus rosa-sinensis. Light microscopy revealedthe presence of oil and mucilage cells in the subglandular tissue.Electron microscopy showed intense activity of ATPase in thephloem subtending the nectary. When CaCl₂ or tannic acid areadded to the fixative, electron-dense globular deposits areencountered in close contact with the plasmalemma of the secretorycells. In this case the endoplasmic reticulum appears in alternatingelectron-dense areas. In young nectaries the application oftannic acid results in electron-opaque deposits at the cellplate of dividing cells. The prolonged incubation of nectariesin OsO₄ results in an obvious difference in staining betweennectary hairs and subglandular cells. Structures stained selectivelywith OsO₄ are the endoplasmic reticulum, nuclear envelope, plastids,and mitochondria. The cytochemical experiments support the viewthat in nectaries of Hibiscus rosa-sinensis, the pre-nectaroriginates from the phloem and it is symplastically carriedvia the plasmodesmata to the secretory cells of the hair fromwhere it is secreted. The principal element which is involvedboth in the pre-nectar transport and nectar secretion is theendoplasmic reticulum. Key words: Lipid staining, polysaccharides, tannic acid, calcium binding sites, ATPase activity, osmium impregnation     

葡萄两性花花蜜腺的发育解剖学研究

葡萄两性花的花蜜腺位于子房基部的花盘上,共5枚,呈椭圆形,与雄蕊相间排列,属于花盘蜜腺,蜜腺由表皮和泌蜜组织组成,缺乏维管束,表皮具薄的角质层,无气孔器,蜜腺原基由子房基部表层细胞恢复分裂能力形成,在蜜腺发育过程中,泌蜜组织的液泡规律 性变化和多糖动态变化均不明显,原蜜汁由子房维管束的韧皮部提供,蜜汁通过表皮细胞排出。     

Floral nectar production and carbohydrate composition and the structure of receptacular nectaries in the invasive plant <Emphasis Type="Italic">Bunias orientalis</Emphasis> L. (Brassicaceae)

The data relating to the nectaries and nectar secretion in invasive Brassicacean taxa are scarce. In the present paper, the nectar production and nectar carbohydrate composition as well as the morphology, anatomy and ultrastructure of the floral nectaries in Bunias orientalis were investigated. Nectary glands were examined using light, fluorescence, scanning electron and transmission electron microscopy. The quantities of nectar produced by flowers and total sugar mass in nectar were relatively low. Total nectar carbohydrate production per 10 flowers averaged 0.3 mg. Nectar contained exclusively glucose (G) and fructose (F) with overall G/F ratio greater than 1. The flowers of B. orientalis have four nectaries placed at the base of the ovary. The nectarium is intermediate between two nectary types: the lateral and median nectary type (lateral and median glands stay separated) and the annular nectary type (both nectaries are united into one). Both pairs of glands represent photosynthetic type and consist of epidermis and glandular tissue. However, they differ in their shape, size, secretory activity, dimensions of epidermal and parenchyma cells, thickness of secretory parenchyma, phloem supply, presence of modified stomata and cuticle ornamentation. The cells of nectaries contain dense cytoplasm, plastids with starch grains and numerous mitochondria. Companion cells of phloem lack cell wall ingrowths. The ultrastructure of secretory cells indicates an eccrine mechanism of secretion. Nectar is exuded throughout modified stomata.     

Is nectar reabsorption restricted by the stalk cells of floral and extrafloral nectary trichomes?

Reabsorption is a phase of nectar dynamics that occurs concurrently with secretion; it has been described in floral nectaries that exude nectar through stomata or unicellular trichomes, but has not yet been recorded in extrafloral glands. Apparently, nectar reabsorption does not occur in multicellular secretory trichomes (MST) due to the presence of lipophilic impregnations – which resemble Casparian strips – in the anticlinal walls of the stalk cells. It has been assumed that these impregnations restrict solute movement within MST to occur unidirectionally and exclusively by the symplast, thereby preventing nectar reflux toward the underlying nectary tissues. We hypothesised that reabsorption is absent in nectaries possessing MST. The fluorochrome lucifer yellow (LYCH) was applied to standing nectar of two floral and extrafloral glands of distantly related species, and then emission spectra from nectary sections were systematically analysed using confocal microscopy. Passive uptake of LYCH via the stalk cells to the nectary tissues occurred in all MST examined. Moreover, we present evidence of nectar reabsorption in extrafloral nectaries, demonstrating that LYCH passed the stalk cells of MST, although it did not reach the deepest nectary tissues. Identical (control) experiments performed with neutral red (NR) demonstrated no uptake of this stain by actively secreting MST, whereas diffusion of NR did occur in plasmolysed MST of floral nectaries at the post‐secretory phase, indicating that nectar reabsorption by MST is governed by stalk cell physiology. Interestingly, non‐secretory trichomes failed to reabsorb nectar. The role of various nectary components is discussed in relation to the control of nectar reabsorption by secretory trichomes.     

Anatomical and ultrastructural changes of the floral nectary ofPisum sativum L. during flower development

Summary The floral nectary ofPisum sativum L. is situated on the receptacle at the base of the gynoecium. The gland receives phloem alone which departed the vascular bundles supplying the staminal column. Throughout the nectary, only the companion cells of the phloem exhibited wall ingrowths typical of transfer cells. Modified stomata on the nectary surface served as exits for nectar, but stomatal pores developed well before the commencement of secretion. Furthermore, stomatal pores on the nectary usually closed by occlusion, not by guard-cell movements. Pore occlusion was detected most frequently in post-secretory and secretory glands, and less commonly in pre-secretory nectaries. A quantitative stereological study revealed few changes in nectary fine structure between buds, flowers secreting nectar, and post-secretory flowers. Dissolution of abundant starch grains in plastids of subepidermal secretory cells when secretion commenced suggests that starch is a precursor of nectar carbohydrate production. Throughout nectary development, mitochondria were consistently the most plentiful organelle in both epidermal and subepidermal cells, and in addition to the relative paucity of dictyosomes, endoplasmic reticulum, and their associated vesicles, the evidence suggests that floral nectar secretion inP. sativum is an energy-requiring (eccrine) process, rather that granulocrine.Abbreviations ER endoplasmic reticulum - GA glutaraldehyde - SEM scanning electron microscopy     

油菜花蜜腺发育过程的超微结构变化与泌蜜机理的研究

油菜花蜜腺由２枚侧蜜腺和２枝中蜜腺组成,其基本结构类似。在蜜腺发育过程中,产蜜组织细胞内的内质网、高尔基体、质体和线粒体以及液泡都发生有规律变化。泌蜜前,细胞器的数量增加。其中,质体内积累淀粉,此过程与蜜腺内初皮部的分化并和线粒体的增加相关。泌蜜时,内质网数量增多,并产生小泡．小泡向质膜移动。泌蜜后,细胞液泡化,细胞器数量减少,细胞萎缩。根据观察结果分析,其原蜜汁来源于韧皮部,转运至产蜜组织细胞的质体、内质网和高尔基体内加工成蜜汁,最后通过胞吐和渗透相结合的方式泌出。     

Nectaries and male-biased nectar production in protandrous flowers of a perennial umbellifer <Emphasis Type="Italic">Angelica sylvestris</Emphasis> L. (Apiaceae)

Nectar is the most common floral pollinator reward. In dichogamous species, floral nectar production rates can differ between sexual phases. We studied the structure of nectaries located on the stylopodium and nectar production in protandrous umbellifer Angelica sylvestris. Our study species produced nectar in both floral sexual phases. Nectar sugar concentration was low (on average 22 ± 11 %, mean ± SD) and the nectar hexose rich and composed of sucrose, glucose, fructose and a small amount of amino acids, including β-alanine, a non-protein amino acid. Although nectar composition and sugar concentration varied little between floral sexual phases, nectar production showed a threefold reduction during the stigma receptive period. This is in contrast to other studies of Apiaceae that have reported female-biased nectar production, but in the direction predicted by plant sexual selection theory, suggesting that in pollen-unlimited species, floral rewards mainly enhance male reproductive success. The structure of the nectary was similar at the two sexual stages investigated, and composed of a secretory epidermis and several layers of nectariferous and subsecretory parenchyma. The nectary cells were small, had large nuclei, numerous small vacuoles and dense, intensely staining cytoplasm with abundant endoplasmic reticulum, mitochondria and secretory vesicles. They contained abundant resin-like material that may potentially act as defence against microbes. Starch was rarely observed in the nectary cells, occurring predominantly at the female stage and mainly in guard and parenchyma cells in close proximity to stomata, and in subsecretory parenchyma. The main route of nectar release in A. sylvestris seems to be via modified stomata.     

The Floral Nectaries of Hibiscus rosa-sinensis: 1. Development of the Secretory Hairs

Floral nectaries of Hibiscus rosa-sinensis occur on the lowerinner side of the fused sepals and each one consists of numerous(50000–55000) secretory hairs, occupying a cylinder-likezone completely lining the inner side of the sepals. Each hairoriginates from a single protodermal mother cell and, at maturity,it is built up of a basal cell, a stalk, 35–40 intermediatecells and a tip secretory cell. Development of protodermal cellsinto secretory hairs is asynchronous, the first cells to initiatedevelopment being those situated in the lowermost part of thecylindrical zone, and development progressing upwards. Volume increase of protodermal mother cells initiating developmentis accompanied by cell polarization manifested by organelledisplacement towards the apical region. Secretory hairs areformed through a sequence of transverse and, later on, anticlinaldivisions. Divisions of apical cells are preceded by well definedpre-prophase microtubule bands, which foreshadow the plane ofthe forthcoming division and predict with accuracy the sitesof parental walls where the new cell plate fuses at cytokinesis. Stalks consist of either one or two cells. Two-celled stalksoccur in 40 per cent of secretory hairs and derive from a transversedivision of one stalk cell; the wall formed is always depositedparallel to the proximal and distal walls, but never to thelateral ones. The significance of this mode of division is discussedin relation to the fact that lateral walls are entirely impregnatedwith a cutin-like material that blocks apoplastic movement ofsolutes. Hibiscus rosa-sinensis, nectaries, development, preprophase microtuble bands, stalk cells     

密花香薷花蜜腺的解剖学研究

密花香薷花密腺分布于子房基部和子房表面,属于一朵花中具二种花蜜腺类型,子房基部的盘状蜜腺由分泌表皮、产蜜组织及维管束三部分组成,分泌表皮上角质层局部有小孔。子房蜜腺由分泌表皮和产蜜组织组成。     

垂柳花蜜腺的发育解剖学研究

垂柳雌花蜜腺一枚,位于于房与花序轴之间,多呈扁平广卵形,由分泌表皮、泌蜜组织和维管束组成。雄花蜜腺呈基部相连的两枚突起,一枚位于花丝与花序轴之间,基部宽扁,上部棒状;另一枚位于花丝与苞片之间,棒状,仅由分泌表皮和泌蜜组织组成。雌、雄花蜜腺均起源于花托表面2—3层细胞。在蜜腺发育过程中,雌、雄花蜜腺泌蜜组织细胞的液泡发生规律性变化．雌花蜜腺为淀粉型蜜腺,而雄花蜜腺为非淀粉型蜜腺。雌、雄花蜜腺的原宜汁分别由蜜腺维管束韧应部或花丝维管束韧皮部提供,其蜜计最后均由分泌表皮细胞和变态气孔排出。     

高压冷冻及低温替代技术制备的拟南芥花蜜腺超微结构的研究

采用高压冷冻和低温替代技术对不同时期泌蜜前、泌蜜早期和泌蜜晚期的拟南齐(Arabidopsisthaliana L.)成熟花蜜腺的超微结构进行了研究。着重对小泡运输过程中是否与细胞质膜发生融合以及蜜腺组织中深色细胞与伴胞的区别等问题进行了讨论。拟南芥花中有一对较大的侧蜜腺以及2～4枚中蜜腺。中蜜腺位于2枚长雄蕊基部或它们之间,而侧蜜腺则位于两花瓣之间的短雄蕊附近。泌蜜前和泌蜜期,液泡的大小、高尔基体及内质网的数量、线粒体的分布以及质体内淀粉粒的大小都会发生一定的变化。当高尔基小泡从细胞内运输至细胞外时,并没有发生与细胞质膜融合的过程,与经典的“胞吐”假说不同。深色细胞在泌蜜期大量出现与筛分子旁的伴胞明显不同,前者与蜜腺顶端的气孔器相连,形成“通道”从而使蜜汁从蜜腺排出。     

THE FLORAL AND EXTRA-FLORAL NECTARIES OF PASSIFLORA. I. THE FLORAL NECTARY

Floral nectary development and nectar secretion in three species of Passiflora were investigated with light and electron microscopy. The nectary ring results from the activity of an intercalary meristem. Increased starch deposition in the amyloplasts of the secretory cells parallels maturation of the nectary phloem. Large membrane-bound protein bodies are observed consistently in phloem parenchyma cells, but their function is presently unknown. The stored starch serves as the main source of nectar sugars at anthesis. Plastid envelope integrity is maintained during starch degradation, and there is no evidence of participation of endoplasmic reticulum or Golgi in the secretion of pre-nectar. It is concluded that in these starchy nectaries granulocrine secretion, commonly reported for floral nectaries, does not occur.     

A macro- and micromorphological survey of floral and extrafloral nectaries in the epiphytic cactus Rhipsalis teres (Cactoideae: Rhipsalideae)

Floral and extrafloral nectaries in plants favor pollination and defense against herbivory. Despite their wide distribution in plants and differences in position, structure, and topography, their biological and systematic significance has been underutilized. This study investigated the macro- and micromorphology of floral and extrafloral nectaries in the epiphytic cactus Rhipsalis teres and reports unusual bristle-like structures (bracteoles) functioning as extrafloral nectaries in the cactus family. The floral nectary is disc-shaped embedded in the hypanthial floral cup with anomocytic stomata as secreting structures present on the epidermal nectarial tissue. Small multicellular bristle-like extrafloral nectar-secreting structures, homologues to bracts, were observed on the plants’ stems and function as bracteolar nectaries having a relatively long and continuous secretory activity throughout several stages of the reproductive structures. Both the floral and bracteolar nectaries are functional. It is possible that in the latter nectar discharge occurs though epidermal cells, which build up pressure inside as nectar accumulates, thereby ending with rupture of the cuticle to release the liquid. The nectar in both secreting structures is scentless and colorless, and the concentration from floral nectaries is slightly lower than that of the bracteolar nectaries, 70.6% and 76.4%, respectively. The relatively higher concentration in the latter might be correlated with exposure, relative humidity and water evaporation, leading to crystallization of sugars on the stem surface in a short period of time.