首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The behavior of visitors to the flowers of the orchidEpipactis thunbergii was studied, with special attention to the role of the epichile in the pollination process. Only four species of syrphid flies legitimately pollinated the flower, among whichSphaerophoria macrogaster was regarded as the most effective pollinator. The movable epichile, possessing a furrow at its base, played a critical role in the pollination process: it threw the syrphid fly onto the stigmatic surface when both sides of the basal slanting surface of the furrow were presumably pressed in the direction of the hypochile by the fore (and middle) legs of the retreating syrphid fly. At this moment, the fly received a set of pollinia on the thorax.  相似文献   

2.
Extrafloral nectaries situated on the adaxial side of the petiolebase are differentiated into a long head, comprising subepithelialground tissue surrounded by a layer of elongated palisade-likeepithelial cells and a short stalk from the nectary meristem.Many ultrastructural changes occur in epithelial and subepithelialcells of the nectary, from the young to secretory stages, suchas an increase in the amount of cytoplasm rich in mitochondriawith well developed cristae, rough endoplasmic reticulum (rER),smooth endoplasmic reticulum (sER) tubules and Golgi bodies.Plasmalemma invaginations with secretory vesicles occur longthe radial walls. Substantial amounts of secretory materialaccumulate in the gap between the radial walls and subcuticularspace, probably carried by the secretory vesicles from the cytoplasmat the secretory stage. Before cessation of secretion the cytoplasmbecomes vesiculated and the volume of the vacuome increases.At the post secretory stage, cytolytic processes and death ofcells occur. The subepithelial cells attain their maturity priorto epithelial cells. Histochemical localization reveals thepresence of lipids, proteins and insoluble polysaccharides withinthe epithelial cells and in the secretory material depositedin the subcuticular space as well as the gap between the radialwalls of the epithelial cells and outside the cuticle. Fine structure, nectary, Plumeria rubra, granulocrine secretion  相似文献   

3.
There are few anatomical studies of the reproductive organs of Swietenia macrophylla, despite its economic importance. This study aims to describe the structural and ultrastructural organization of the petaline nectaries in mahogany flowers. Flower buds and flowers at anthesis were collected, fixed, and processed for studies under light and electron microscopy. Nectaries occur in the median region of the petal, on the abaxial surface. Nectar is produced at all stages, from the very young buds until anthesis. The nectary presents a uniseriate epidermis, without stomata; intercellular spaces among the epidermal cells are frequent and contiguous to the subcuticular space. The secretory tissue consists of two to five layers of cells, which are rich in organelles. The nectaries lack vasculature, and the secretory tissue is isolated from the petaline mesophyll by an endodermoid layer. In the staminate flowers, the number of nectaries is less than that observed in pistillate ones.  相似文献   

4.
Changes in the obturator of the peach (Prunus persica) havebeen investigated and related to pollen tube growth in thisregion. At anthesis, the cells of the obturator are active andrich in starch reserves. Twelve days after anthesis these cellsproduce a secretion that stains for carbohydrates and for proteins.As the secretion is produced, starch vanishes from these cellsand they degenerate and collapse as callose is accumulated.Secretion is independent of pollination as it takes place ina similar fashion both in pollinated and in unpollinated flowers. Pollen tube growth along the obturator surface depends on thissecretion for, although pollen tubes reach the base of the styleseven days after pollination, they cannot grow on the obturatoruntil five days later, when the secretion is produced. Thisdiscontinuous secretion taking place at the obturator may providea mechanism that controls the entrance of pollen tubes intothe ovary in the peach. Prunus persica, peach, obturator, pollen tube  相似文献   

5.
Flowering and nectar secretion were studied in Platanthera chlorantha in two years. Nectar was secreted and accumulated in this orchid's spur, originating from part of the labellum. The nectary spur was, on average, 32 mm long. It produced 6.86 micro l nectar in 1999 and 7.84 micro l in 2000. The number of flowers per inflorescence and the volume of nectar secreted per flower were not correlated. Nectar secretion and flower longevity differed depending on pollination and flower position in the inflorescence. Among pairs of pollinated and unpollinated flowers there was no difference in the volume of nectar produced; however, the life span of pollinated flowers was shorter than that of unpollinated ones. Within an inflorescence, the lowest-positioned flowers had the largest nectar production and the longest life compared with flowers positioned higher up.  相似文献   

6.
M. Whitear    G. Zaccone  S. Fasulo    A. Licata 《Journal of Zoology》1991,224(4):669-676
The axillary glands of Ictalurus are lobulated invaginations of the epidermis, opening at a pore between the pectoral spine and the cleithrum. Holocrine cells lining a false lumen form a viscous secretion. The secretory cells originate in the tenuous basal layer of the gland wall. Secretion is initiated by the formation of compound vesicles in cells that become very large and have complex cytoplasm of a varied appearance. Golgi systems are well developed and the perinuclear cytoplasm may contain many mitochondria and sacs of ribosomal endoplasmic reticulum; some tracts of cytoplasm are vesicular and contain free ribosomes. Some cells contain numerous large lysosomes, and some have extensive contents of fibrillar masses imperfectly separated by membranes, that recall the appearance of the mucous secretion of goblet cells. The secretory cells break down, releasing the degenerating organelles, including the nuclei, into the false lumen. Some structures are still recognizable in the secretion even after it has been expelled, but the main part of the formed secretion consists of the mucus-like masses. Various leucocytes are found in the gland walls and embedded in the secretion. The fine structure differentiates the holocrine cells of the axillary gland from the club cells of the epidermis, and from the venom glands associated with the fin spines of catfishes. The function of the axillary gland secretion remains unknown.  相似文献   

7.
Nectar resorption and sugar translocation were studied in Cucurbita pepo (Cucurbitaceae) and Platanthera chlorantha (Orchidaceae) by micro-autoradiography. In both species, nectar was resorbed in pollinated and unpollinated flowers and ovules developing into seeds were found to be the main sugar sink. In C. pepo, the mobility of resorbed sugars in pollinated female flowers was higher than in unpollinated ones; male flowers showed lower mobility of resorbed sugar. In P. chlorantha, radioactivity was detected in pollinated flowers below and above labelled unpollinated ones: the nearer the flower, the stronger the accumulation of label in developing fruits.  相似文献   

8.
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.  相似文献   

9.
The structure of the essential oil secretory tissues of Prostanthera ovalifolia R.Br was investigated using bright- and dark-field optical microscopy, and scanning and transmission electron microscopy. The leaves of P. ovalifolia have glandular trichomes of the peltate type common to many Lamiaceae species. The trichomes consist of a basal cell embedded in the epidermis, a stalk cell with heavily cutinized walls and a 16-celled secretory head, but they differ from those of many previously reported Lamiaceae species in their morphological form defined by the elevated cuticle. The sub-cuticular space contains a mixture of lipid and aqueous phases. Secretory cells have dense cytoplasm with many leucoplasts present. Volatile terpenoids are eliminated from the cytoplasm into the sub-cuticular space, the site of essential oil accumulation, via granulocrine secretion.  相似文献   

10.
Embryo sac development has been investigated in unpollinated,cross pollinated and gibberellic acid (GA2) treated flowersof Pyrus communis L. While pollination and GA3 treatments donot alter embryo sac development, they prolong embryo sac viability.In untreated unpollinated flowers, ovules degenerate between12 and 21 d after anthesis, while in cross pollinated and GA3treated flowers this degeneration is postponed by about 10 d.Thus, in a cross pollinated flower this extends the period overwhich a successful fertilization can take place. This increasedperiod of viability is accompanied by an elongation of the embryosac itself. Elongation takes place two weeks prior to fertilizationin cross pollinated flowers. The extension of life span of embryo sacs following pollinationand treatment with gibberellic acid indicates that a stimulusinduced by ‘pollination’ could be mediated by GA3Whatever its mechanism of operation, the prolongation of embryosac viability by pollination represents a selective advantage,in that the period at which the ovules are receptive to fertilizationmust be significantly extended. Embryo sac, gibberellic acid, Pyrus communis, pear, pollination  相似文献   

11.
 In the flowers of Platanthera chlorantha nectar is secreted and accumulated in a spur. Previous studies of this species revealed that after the period of secretion and cessation, rapid nectar resorption occurs. The aim of this study was the observation of nectar resorption on the structural level using tritium labelled sucrose. For this purpose, during the peak of nectar secretion, 10 μl of nectar accumulated in the spur was replaced with the same volume of labelled sucrose (10 μCi). Small fragments of spurs were sampled between 12–36 h of incubation, at the resorption phase. Afterwards, they were fixed and embedded in epoxy resin. Material for the microautoradiographic study was prepared with the dipping technique. The cells of secretory epidermis and unicellular secretory papillae had dense, strong stained cytoplasm, a large nucleus and small vacuoles. A characteristic feature of these cells was the presence of numerous starchless plastids, mitochondria and ER profiles. Many vesicles occurred in the close vicinity of the cell wall. In the cuticle covering cell walls no pores or cracks were observed. Presence of [3H] sucrose was detected mainly in the walls of the nectary cells, which would indicate an apoplastic route of resorbed nectar. Received August 3, 2002; accepted November 10, 2002 Published online: June 2, 2003  相似文献   

12.

Background and Aims

The occurrence of nectaries in fruits is restricted to a minority of plant families and consistent reports of their occurrence are not found associated with Fabaceae, mainly showing cellular details. The present study aims to describe the anatomical organization and ultrastructure of the pericarpial nectaries (PNs) in Erythrina speciosa, a bird-pollinated species, discussing functional aspects of these unusual structures.

Methods

Samples of floral buds, ovaries of flowers at anthesis and fruits at several developmental stages were fixed and processed by the usual methods for studies using light, and scanning and transmission electron microscopy. Nectar samples collected by filter paper wicks were subjected to chemical analysis using thin-layer chromatography.

Key Results

The PNs are distributed in isolation on the exocarp. Each PN is represented by a single hyaline trichome that consists of a basal cell at epidermal level, stalk cell(s) and a small secretory multicellular head. The apical stalk cell shows inner periclinal and anticlinal walls impregnated by lipids and lignin and has dense cytoplasm with a prevalence of mitochondria and endoplasmic reticulum. The secretory cells show voluminous nuclei and dense cytoplasm, which predominantly has dictyosomes, rough endoplasmic reticulum, plastids, mitochondria and free ribosomes. At the secretory stage the periplasmic space is prominent and contains secretion residues. Tests for sugar indicate the presence of non-reducing sugars in the secretory cells. Nectar samples from PNs contained sucrose, glucose and fructose.

Conclusions

The secretory stage of these PNs extends until fruit maturation and evidence suggests that the energetic source of nectar production is based on pericarp photosynthesis. Patrolling ants were seen foraging on fruits during all stages of fruit development, which suggests that the PNs mediate a symbiotic relationship between ants and plant, similar to the common role of many extrafloral nectaries.  相似文献   

13.
Postbloom fruit drop (PFD) is an important disease caused by the fungus Colletotrichum acutatum. PFD is characterised by the formation of necrotic lesions on the petals and stigmas of flowers as well as premature abscission of the fruit in Citrus spp. We compare the ultrastructure of the epidermis of uninoculated Citrus sinensis petals with that of petals inoculated with the fungus to understand the changes that occur upon C. acutatum infection. Healthy petals have a cuticle with parallel striations covering the uniseriate epidermis. This pattern consists of vacuolated parietal cells whose cytoplasm contains mitochondria, plastids with an undeveloped endomembrane system and a slightly dense stroma, a poorly developed rough endoplasmic reticulum, polysomes, few lipid droplets, and a nucleus positioned near the inner periclinal wall. In damaged regions, the cytoplasm of some cells is densely packed with well-developed endoplasmic reticulum, a large number of hyperactive dictyosomes, numerous mitochondria, and many lipid droplets. The plastids have an electron-dense stroma, starch grains, and a large amount of electron-dense lipid droplets, which can be released into vacuoles or the endoplasmic reticulum. Multivesicular bodies and myelin bodies are frequently observed in the vacuole, cytoplasm, and periplasmic space. Vesicles migrate through the cell wall and are involved in the deposition of cuticular material. In the later stages of infection, there is deposition of new cuticle layers in plaques. The outer periclinal walls can be thick. These observations indicate that epidermal cells respond to the pathogen, resulting in cuticular and parietal changes, which may limit further infection.  相似文献   

14.
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.  相似文献   

15.
Potassium antimonate was used to localize Ca2+ in tobacco ovules from 0 to 7 d after anthesis in pollinated and emasculated flowers. Antimonate binds “loosely bound” Ca2+ into calcium antimonate; less-soluble forms are unavailable and free calcium usually escapes. Ovules are immature at anthesis. Abundant calcium precipitates in nucellar cells surrounding the micropylar canal. A difference between calcium in the two synergids emerges at 1 d, which is enhanced in pollinated flowers. The future receptive synergid accumulates more precipitates in the nucleus, cytoplasm and cell walls. After fertilization, micropyle precipitates diminish, and the ovule is unreceptive to further tube entry. In emasculated flowers 6 d after anthesis, ovular precipitates essentially disappear; however, flowers pollinated at 4–5 d and collected 2 d later largely restore their prior concentration of precipitates. Ovular precipitates occur initially in the nucellus, then the embryo sac, and finally the synergid and micropylar filiform apparatus. Possibility, calcium is released from the embryo sac, although no structural evidence of exudate formation was observed. Calcium precipitates in the ovule correlate with the ability of the ovule to be fertilized, suggesting that successful pollen tube entry and later development may require calcium of the class precipitated by antimonate. Received: 14 August 1996 / Accepted: 9 October 1996  相似文献   

16.
The stigmatic papillae of sweet cherry were examined to determine developmental characteristics of the wet-stigma surface. Early stages of secretion are detectable 1 wk prior to anthesis by using a 1% crystal violet solution. The number of stainable cells and the amount of interstitial staining subsequently increase, although secretions are not visible on unstained specimens until anthesis. Auto-fluorescence above 500 nm (excited by 335–480 nm) becomes microscopically detectable at floral maturity and grows more intense after anther dehiscence. Light microscopy of plastic sections shows that papillae degenerate in peripheral regions of unpollinated mature stigmas, and that this is even more pronounced in pollinated ones. The distal portions of the papillae are covered with a homogeneous cuticular cap, which when viewed with electron microscopy encloses a subcutaneous secretion prior to cuticle exfoliation. Other exudates observed with electron microscopy prior to anthesis are interstitial electron-translucent globules and surrounding matrix, and assorted vesicles, lipid globules, and starch grains which are present at floral maturity. Flowers observed under field conditions in the terminal secretion stage accumulate trichomatous structures. Our observations indicate that the stigma of Prunus avium L. is characterized by several phases of secretion which appear to be facilitated by mechanical abrasion. A model for the primary pollen-receptive area is proposed and suggestions are made concerning the origin of the secretions.  相似文献   

17.
The organic acid-secreting trichomes of chickpea (Cicer arietinum L.) were exposed to 2.5 mm lanthanum nitrate for 24 hr, and this concentration did not inhibit trichome secretion compared with that of controls. We subsequently used this nontoxic concentration of lanthanum to examine endocytosis. In the stalk cells of these secretory trichomes, exogenously applied lanthanum nitrate was present in cell walls and vacuoles, as well as within both invaginations in the plasma membrane and vesicles in the peripheral cytoplasm between the plasma membrane and the tonoplast. In the head cells, lanthanum nitrate was present in cell walls and in vesicles that form a layer in the cytoplasm around the edge of the head cells, but was not present in vacuoles. We propose that fluid phase endocytosis targeted to the vacuole takes place in the stalk cells and that endocytosis occurs in the head cells to remove excess plasma membrane after the fusion of secretory vesicles with the plasma membrane. This is the first demonstration of endocytosis in secretory trichomes.  相似文献   

18.
19.
Stigmatic hairs of the cotton flower were studied through their developmental stages up to anthesis. Stigmatic hairs invariably develop from a densely straining band of epidermal cells opposite the transmitting tissue cells. At anthesis, these are single cell structures measuring up to 300 μm long. At the 5-mm stage of stylar length (7–10 days before anthesis), some stigmatic hair cells begin to accumulate an osmiophilic substance between the plasmalemma and the cell wall, possibly synthesized in the endoplasmic reticulum. This material is apparently never secreted outside the cell wall. Immediately following this secretory phase in some stigmatic hair cells a second secretory phase starts. A dense osmiophilic substance, different in appearance from the previous phase, accumulates in the vacuoles of each hair cell. Concomitantly, dimorphism develops in the cytoplasmic densities of stigmatic hair. Some stigmatic hair cytoplasm appears very dense and shows signs of degeneration while other cytoplasm appears normal. A third secretory phase, which begins at anthesis, occurs in the normal hair cells. This phase is characterized by enhanced activity in the cytoplasm of the endoplasmic reticulum and Golgi apparatus. Large vesicles containing granular material are seen fusing with the plasmalemma. Coincident with this activity there is dissolution of the middle layers of the cell wall and the cuticle is ruptured at various points. The dense osmiophilic substance that had accumulated in the vacuole breaks down into fine granular material. Significance of these changes is discussed in relation to the pollen germination mechanism on the dry type stigma of cotton.  相似文献   

20.
The aim of the paper is to determine what happens with plasmodesmata when mucilage is secreted into the periplasmic space in plant cells. Ultrastructural analysis of the periendothelial zone mucilage cells was performed on examples of the ovule tissues of several sexual and apomictic Taraxacum species. The cytoplasm of the periendothelial zone cells was dense, filled by numerous organelles and profiles of rough endoplasmic reticulum and active Golgi dictyosomes with vesicles that contained fibrillar material. At the beginning of the differentiation process of the periendothelial zone, the cells were connected by primary plasmodesmata. However, during the differentiation and the thickening of the cell walls (mucilage deposition), the plasmodesmata become elongated and associated with cytoplasmic bridges. The cytoplasmic bridges may connect the protoplast to the plasmodesmata through the mucilage layers in order to maintain cell-to-cell communication during the differentiation of the periendothelial zone cells.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号