The Floral Nectary ofDigitalis purpureaL., Structure and Nectar Secretion

The floral nectary of the foxglove (Digitalis purpureaL.), locatedat the base of the ovary, was examined by: scanning electronmicroscopy; quantitative bright-field microscopy via computer-aided3-D reconstruction from serial sections; morphometric procedures;transmission electron microscopy and measurement of nectar effluxunder different experimental conditions. Time-lapse video recordingvia a microscope with incident light clearly showed that thenectar escaped from the apertures of modified stomata. The volumeflux via individual stomatal apertures was 0.31±0.1 nlmin^-1; therefore only a fraction of the total number of stomataper nectary (115±8) would be sufficient to dischargethe amount of nectar reported in previous publications. Thestomatal apertures are continuous with intercellular spacestraversing the small-celled nectariferous tissue. The latteris vascularized only by phloem, whose termini consists of rowsof slender cells. These sieve-like cells are surrounded by moreor less isodiametrical sheath cells with dimensions similarto the secretory cells. Details of nectary functioning are basedon enhanced structural information, complementary data on nectardischarge after experimental manipulations and the nature ofthe effluence.Copyright 1998 Annals of Botany Company Digitalis purpureaL.; foxglove; floral nectary; (ultra-)structure; 3-D reconstruction; morphometry; nectar flow; time-lapse video recording.     

Development of trichomes in the Abutilon nectary gland

Nectary trichomes of Abutilon striatum var. thompsonii arise by sequential periclinal divisions of outpushings from epidermal cells so producing trichomes that, when mature, are about 12 cells long. All epidermal cells within the nectary undergo this transformation. Later, anticlinal divisions lead to a multiseriate lower part of the trichome. The original epidermal cell becomes the basal cell which increases substantially in volume during development, thus leading to lateral separation of the trichomes. Above the basal cell is the stalk cell which develops an apoplastic barrier in its anticlinal (outer) wall. Secretion ultimately takes place from a capitate tip cell. An initially very thin cuticular layer, which overlies the whole trichome, eventually becomes as thick as the cell wall itself (approx. 0.4 μm). The pre-secretory hairs contain numerous small, condensed mitochondria; poorly differentiated plastids; dictyosomes with coated vesicles; small vacuoles; and a large amount of smooth endoplasmic reticulum ("secretory reticulum") which contrasts with the rough endoplasmic reticulum seen during earlier developmental stages. As secretion proceeds, vacuolation becomes more extensive. Plasmodesmata are present between all the cells of the trichome and diminish in frequency from about 12.0 μm^-2 in the stalk cell to about 4.0 μm^-2 in the apical cells. This variation in plasmodesmatal frequency along the trichome is seen at all stages of development. The ultrastructural evidence would be consistent with the hypothesis that the pre-nectar flows through the plasmodesmata from cell to cell, is loaded into a "secretory compartment", and is then unloaded into the apoplast from all cells of the trichome distal to the stalk cell.     

X-Ray Microanalysis and Ultrastructural Studies of Cell Compartments of Dunaliella parva

Hajibagheri, M. A., Gilmour, D. J., Collins, J. C. and Flowers,T. J. 1986. X-ray microanalysis and ultrastructural studiesof cell compartments of Dunaliella parva. -J. exp. Bot. 37:1725–1732. Ultrastructural studies of the unicellular green alga Dunaliellaparva showed the presence of cytoplasmic vacuoles. X-ray microanalysiswas performed on sections of cells which had been freeze substitutedin acetone. It was found that the concentrations of both Naand Cl were much higher in the vacuoles than in the cytoplasm.When cells were grown in 0·4 kmol m^–3 NaCl theNa and Cl concentrations in the vacuoles were 349 and 283 molm ^–3 respectively, whilst cytoplasmic Na and Cl concentrationswere 37 and 26 mol m^–3. Corresponding values for cellsgrown in 1·5 kmol m^–3 NaCl were 392 mol m^–3Na and 325 mol m^–3 Cl in the vacuoles and 36 mol m^–3Na and 30 mol m^–3 Cl in the cytoplasm. Immediately afterexposure to an increase in external salinity Na and Q concentrationsincreased in both vacuoles and cytoplasm. The results are discussedwith reference to compartmental models for the ionic relationsof Dunaiiella. Key words: X-ray microanalysis, ultrastructural studies, Dunaliella parva     

The estimated pore diameter for plasmodesmal channels in the Abutilon nectary trichome should be about 4 nm, rather than 3 nm

By injecting varous-size fluorescent probes into Abutilon striatum Dicks nectary trichomes, Terry and Robards (1987, Planta 171: 145–157) arrived at an estimate of 3 nm for the physical diameter of the channels involved in cell-to-cell movement. However, their calculations contain an arithmetic error in the volume assumed for the cell into which the probes diffused. (The actual volume is ten times larger.) The corrected calculations give a physical diameter of about 4 nm. Received: 5 January 1999 / Accepted: 29 January 1999     

玉吊钟多细胞根毛的发育及其超微结构研究

玉吊钟气生不定根根尖区域的部分表皮细胞经分裂可形成多细胞根毛。根毛长０．０３ｍｍ左右,具单列细胞、双列细胞和叉状分枝类型,由基细胞和毛体细胞二部分组成。电镜显示,基细胞内部结构与表皮细胞相似。组成毛体的细胞都有分泌功能。在分泌活动期,细胞内形成大量内质网,并膨大成囊泡状或溢出囊泡,分泌停止,内质网即消失;其细胞结构的变化及主要由内质网参与分泌活动与蜜腺细胞在分泌活动中的结构变化类似。故推测多细胞根     

Calcium Deposition in Idioblasts of Mulberry Leaves

Large, rounded idioblasts were observed in adaxial leaves ofmulberry plants; they were clearly distinguishable from epidermal,trichome and parenchyma cells. The size and density of idioblastsvaried according to leaf age. Cytological features of idioblastswere as follows: the outermost region (‘cap’) ofidioblasts was situated on the adaxial surface as a dome-likeprotrusion; a cylindrical protuberance extended from the capregion to the inner part of the idioblast; in idioblasts frommature leaves a crystal mass was suspended from the lower tipof the cylindrical protuberance. Elemental analysis of idioblastsdemonstrated that silicon (Si) was localized in both the capregion and the cylindrical protuberance but calcium (Ca) waspresent in the large crystal, indicating site-specific cellularlocalization of Ca and Si within an idioblast. Histochemicalassays showed that a distinct Ca crystal filled the vacuolesof idioblasts in mature leaves, while immature leaves had manyidioblasts without Ca deposition. The increase in the Ca contentof leaves was directly proportional to the increase in leafage and appeared to be closely related to the Ca sink capacityof the developing idioblast vacuoles. The maximum sink capacitywas quantified to be approximately 40 ng per idioblast whenmulberry plants were grown hydroponically with excess Ca.Copyright1999 Annals of Botany Company Morus alba, idioblast, Ca deposition, Ca sink capacity, silicon, X-ray microanalysis, histochemistry, scanning electron microscopy.     

Comparative account of nectary structure in Hexisea imbricata (Lindl.) Rchb.f. (Orchidaceae)

• Background and Aims Despite the number of orchid speciesthat are thought to be pollinated by hummingbirds, our knowledgeof the nectaries of these orchids is based solely on a singlespecies, Maxillaria coccinea (Jacq.) L.O. Williams ex Hodge.Nevertheless, it is predicted that such nectaries are likelyto be very diverse and the purpose of this paper is to comparethe nectary and the process of nectar secretion in Hexisea imbricata(Lindl.) Rchb.f. with that of Maxillaria coccinea so as to beginto characterize the nectaries of presumed ornithophilous Neotropicalorchids. • Methods Light microscopy, transmission electronmicroscopyand histochemistry were used to examine the histology and chemicalcomposition of nectary tissue and the process of nectar secretionin H. imbricata. • Key Results and Conclusions The nectary of H. imbricatahas a vascular supply, is bound by a single-layered epidermiswith few stomata and comprises two or three layers of subepidermalsecretory cells beneath which lie several layers of palisade-likeparenchymatous cells, some of which contain raphides or mucilage.The secretory cells are collenchymatous and their walls havenumerous pits with associated plasmodesmata. They contain thefull complement of organelles characteristic of secretory cellsas well as intravacuolar protein bodies but some of the secretoryepidermal cells, following secretion, collapse and their anticlinalwalls seem to fold. Nectar secretion is thought to be granulocrineand, following starch depletion, lipid droplets collect withinthe plastids. The nectar accumulates beneath the cuticle whichsubsequently forms swellings. Finally, nectar collects in thesaccate nectary spur formed by the fusion of the margins ofthe labellum and the base of the column-foot. Thus, althoughthe nectary of H. imbricata and M. coccinea have many featuresin common, they nevertheless display a number of important differences.     

Extrafloral Nectaries in Cipadessa (Meliaceae)

This is the first report of an extrafloral nectary (EFN) fromAsian Meliaceae and from subfamily Melioideae. The pinnatelycompound leaf of Cipadessa baccifera has 25–35 small,ellipsoidal EFNs abaxially on the rachis, with occasional EFNson leaflets. EFNs secrete nectar until leaf maturity, then graduallywither. Each convex, ellipsoidal EFN is parenchymatous, withouta palisade epidermis, a delimiting nectary sheath, or any vascularaffiliation. This EFN differs markedly from the typical ‘Flachnektarien’EFN described earlier from neotropical Swietenia species. Cipadessa baccifera (Roth.) Miq., extrafloral nectary, Meliaceae, nectary anatomy     

Avoidance of sodium accumulation by the stomatal guard cells of the halophyte Aster tripolium

X-ray microanalysis has revealed that the sodium content ofthe stomatal guard cells of Aster tripolium remains much lowerthan that of other leaf cells when the plants are grown at highsalinity. Large amounts of sodium did, in contrast, accumulatein epidermal and subsidiary cells, and particularly in the mesophylltissue, suggesting that a mechanism exists to limit the extentof its entry into guard cells. Even in plants grown at highsalinity, the content of potassium was much higher than thatof sodium in the guard cells, consistent with the view thatthis is a major ion involved in determining stomatal movementsin this halophyte. Determinations were also made for the nonhalophyte Commelinacommunis, and it was found that the guard cells accumulatedlarge amounts of sodium when it was presented to them as analternative to potassium. It is suggested that the acquisition by the guard cells of someability to restrict the intake of sodium ions may be an importantcomponent of sodium-driven regulation of transpiration, andhence of salinity tolerance, in A. tripolium. Key words: Salinity tolerance, sodium, potassium, stomata, Aster tripolium     

Characteristics of Action Potentials in Willow (Salix viminalis L.)

After application of electric stimuli (square DC pulses) extra-andintracellular potentials were recorded on willow shoots. Theall-or-nothing law, strength-duration relation, and generalcharacteristics of the action potential were investigated. Byusing inhibitors of ionic channels (tetraethylammonium, MnCl₂,LaCl₃), the excitability of willow could be completely blocked.Treatment with the phosphorylation uncoupler dinitrophenol induceda depolarization and disappearance of excitability, indicatingthe participation of a metabolic component of the membrane potential.By using energy-dispersive X-ray microanalysis, the distributionof chloride, potassium and calcium was measured in differenttissues of non-stimulated and stimulated willow shoots. It was shown that stimulation of the plant was followed by ionshifts which were most striking in the phloem cells. While theircontent of potassium and chloride was diminished after stimulation,the amount of cytoplasmic calcium increased slightly. Thesedisplacements lead to the conclusion that Ca²⁺ influx as wellas K⁺ and Cl^– efflux are involved in the propagation ofaction potentials. Key words: Action potential, electrical stimuli, energy-dispersive X-ray microanalysis, ion shifts, Salix viminalis     

Distribution of Silicified Cells in the Leaf Blades of Pleioblastus chino(Franchet et Savatier) Makino (Bambusoideae)

Distribution of silicified cells in the leaf blades of Pleioblastuschino was investigated using a light microscope and a scanningelectron microscope equipped with an energy dispersive X-raymicroanalyser. The most dense accumulation of silica was foundin epidermal tissues. Little silica was deposited in vascularbundles and chlorenchyma, while more was deposited in bundlesheath and fusoid cells. In the epidermis, silica density andfrequency of silicified cells differed depending on cell type,although silica deposition was observed in most cell types.Heavy deposition was found in silica cells, bulliform cells,micro hairs and prickle hairs. Silica cells were the cell typemost frequently silicified (96.9–99.7%) in the adaxialand abaxial epidermis. Silica may be deposited as leaf tissuesage.Copyright 2000 Annals of Botany Company Pleioblastus chino(Franchet et Savatier) Makino, bamboo, silicified cells, leaf blade, epidermis, chlorenchyma, silica, clearing method, freeze-fracturing, freeze-drying, light microscopy, scanning electron microscopy, X-ray microanalysis     

Etude infrastructurale de la stipule de Vicia faba L. au niveau du nectaire

Summary In the extrafloral nectary of the broad bean there is evidence of two fundamental types of cells: one with dense hyaloplasm, well developed ergastoplasm and golgi apparatus, all features of glandular cells, and another with opposite features. The cells of the head of the secretory hairs and those of the subjacent epidermis which are not prolonged with such a hair are of the first type. The epidermal cells prolonged with a hair and the pedicellar cell of this hair are of the second type. Moreover, the companion cells of the subjacent conducting bundle look like cells of the first type, especially those of the head of the secretory hairs owing to their numerous wall protuberances. Cells of the second type are presumably involved in transit processes between phloem and trichome, and cells of the first type in excretory processes.

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Ce travail fait partie d'une Thèse de Doctorat d'Etat sur la cyto-physiologie des nectaires. — (Travail effectué au Laboratoire de Bot. Appl. et Microbiologie et au Centre de Microscopie électronique de la Faculté des Sciences de Bordeaux (France).     

Ultrastructural Aspects of the Nectary Spur of Limodorum abortivum (L) Sw. (Orchidaceae)

The ultrastructure of the nectary spur of Limodorum abortivum(L) Sw. was examined before and after anthesis. In cross sectionthe nectary spur shows an internal epidermal layer of thin-walledcells bordering the secretory cavity and 10–12 layersof parenchyma cells. The ultrastructure of the secretory cellssuggests the involvement of ER, Golgi and plastids in nectarsecretion. The nectar accumulated in the sub-cuticular spaceis released into the nectariferous cavity by rupture of theouter layer of the cuticle. Limodorum abortivum (L) Sw., Orchidaceae, nectary spur, nectar secretion, ultrastructure, anthesis, endoplasmic reticulum, dictyosomes, plastids     

Ultrastructure, Development and Secretion in the Nectary of Banana Flowers

The nectaries of Musa paradisiaca L. var. sapientum Kuntze werefound to secrete in addition to the sugar solution, a polysaccharidemucilage and a very electron dense, homogenous material whichwas apparently protein. The polysaccharide had already startedto appear outside the epithelial cells of the nectary at veryearly stages of nectary development. At somewhat later developmentalstages the very dense homogenous material appeared in the formof droplets between the plasmalemma and cell wall in massesin the nectary lumen. Nectar secretion started in flowers whenthe bract in the axil of which they occurred had just recoiled.The ER elements were dilated and formed vesicles and the Golgibodies were very active, at the stage of the nectar secretionand at stages preceding it, except at the stage just beforesecretion. In all stages of nectary development the dilatedER elements and most large Golgi vesicles contained fibrillarmaterial. It is suggested that both ER and the Golgi apparatusare involved in the secretion of the sugar solution and of thepolysaccharides. There was not enough evidence as to where inthe cell the very dense homogenous material is synthesized. A few developmental stages of the nectaries of the male flowersof the Dwarf Cavendish banana, which do not secrete nectar,were also studied. It was seen that at early stages of development,the ultra-structure of the nectary of this banana variety wassimilar to that of M. paradisiaca var. sapientum. However, theepithelial nectary cells of the Dwarf Cavendish banana disintegratedbefore maturation of the nectary. Musa paradisiaca L, banana, floral nectaries, ultrastructure     

Cell surface elemental composition of Microcystis aeruginosa: high-Si and low-Si subpopulations within the water column of a eutrophic lake

Energy-dispersive X-ray microanalysis (10 kV microprobe) wascarried out to determine the surface elemental composition ofsingle cells of Microcystis aeruginosa within mixed phytoplanktonpreparations, sampled at different depths (0–8 m) withina stratified eutrophic lake. Mean elemental concentrations (mmolkg^–1 dry weight) throughout the sampled water column were:magnesium, 125; silicon (Si), 1864; phosphorus, 341; sulphur,122; chlorine, 88; potassium, 282; calcium, 63. Although somesignificant differences in elemental composition occurred withdepth, the underlying pattern was one of relative uniformitywithin the top 8 m of the water column. At each depth, the frequencydistribution of Si was bimodal, indicating two distinct subpopulationsof cells with cell surface Si concentrations ranging from 0to 1000 mmol kg^–1 (overall mean 112, low-Si cells) andfrom 1000 to 6800 mmol kg^–1 (overall mean 3649, high-Sicells). The two subpopulations occurred mixed together withinindividual colonies, and both included dividing and non-dividingcells. Both cell types had a wide range of sizes, but high-Sicells reached a higher maximum size in both dividing (diametergreater by 0.90 µm) and non-dividing (difference of 0.44µm) cells. This difference in size is consistent withSi being present as a surface layer (up to 0.2–0.4 µmin thickness) in high-Si cells. Support for the presence ofa surface layer of Si [with aluminium (Al)] is also providedby correlation analysis (Si and Al are significantly negativelycorrelated with other cell elements), principal component analysis(Si and Al occur as a distinct subgroup) and lower mean concentrationsof elements (other than Al) in high-Si cells (due to reducedX-ray contribution from the cell interior). The proportion ofhigh-Si cells in the water column was locally high in the 2m depth sample, and had an overall value of 40.5% for the wholedata set. The biological significance of high- and low-Si cellsis not known.     

Ion Compartmentation in the Marine Fungus Dendryphiella salina in Response to Salinity: X-ray Microanalysis

X-ray microanalysis was performed on hyphae of the filamentousmarine fungus Dendryphiella salina growing at different salinitiesto give sodium, potassium and chloride concentrations in thecytoplasm, vacuole and cell wall. Sodium and chloride concentrationsincreased with salinity in all compartments. Cytoplasmic andvacuolar sodium and chloride concentration were broadly similar,and vacuolar contents represented, at most, 19% of the totalprotoplasmic content of an individual ion species. Potassiumconcentrations decreased to some extent with salinity, althoughconcentrations were not severely affected by competition withsodium uptake. Results are discussed with regard to the roleof ions in the overall osmotic adjustment in this species. Key words: Dendryphiella salina, marine fungus, salt-tolerance, x-ray microanalysis     

Changes in the elemental composition of Asterionella formosa during the diatom spring bloom

Changes in the elemental composition of the diatom Asterionellaformosa within mixed phytoplankton samples were determined overthe spring bloom period using energy dispersive X-ray microanalysis.Using a 10 kV electron microprobe, X-ray information from thetop 1–2 µm of the cell revealed overall mean concentrationsof: Si (4636 mmol kg^–1 dry wt), P (82), S (54), Cl (71)K (94) and Ca (90). Concentrations of all elements showed widevariation within each date sample, with unimodal frequency distributionsapproximating to a Normal distribution. Correlation of the entiredata set demonstrated clear statistical associations betweenelements, including Si, P and K. Uptake of Si during the courseof the diatom bloom led to a major fall in lake water concentration(1.0 to 0.07 mg l^–1), which correlated with a decreasein the mean cell Si concentration (6735 to 3107 mmol kg^–1dry wt) during the final phase of the bloom. Mean cell concentrationsof P and K also showed marked decreases with time, in closeparallel with cell Si. These changes in P and K were attributedto the high level of internal correlation with Si and not toany significant decrease in P and K availability in the environment.     

Role of trichome ofPteris vittata L. in arsenic hyperaccumulation

Environmental scanning electron microscope (ESEM) fitted with an energy dispersive X-ray microanalyzer (EDX) was used to investigate the surface micromorphology and arsenic (As) micro-distribution in Chinese brake (Pteris vittata L.). It was found that amounts of trichome, which possessed multicellular structure with the average length of 160 μm and with an average diameter of 28 μm, existed in the frond ofP. vittata, and the density of trichome on the pinnate axial surface was higher than that on the petiole. Visible X-ray peak of As was recorded in the epidermal cell and trichome. The relative weight of As in the pinnate trichome, which contained the highest concentration of As among all tissues of the plant, was 2.4 and 3.9 times as much as that in the epidermal and mesophyllous cells, respectively. The As concentrations in the basal and stalk cells of the same trichome were higher than that in its cap cell. This is the first time to report that the trichome ofP. vittata plays an important role in arsenic hyperaccumulation. The finding from the present study implies that much attention should be paid to the role of the trichome in understanding the hyperaccumulation and detoxicity of As in the hyperaccumulator and improving the ability of As accumulation.     

Role of trichome ofPteris vittata L. in arsenic hyperaccumulation

Environmental scanning electron microscope (ESEM) fitted with an energy dispersive X-ray microanalyzer (EDX) was used to investigate the surface micromorphology and arsenic (As) micro-distribution in Chinese brake (Pteris vittata L.). It was found that amounts of trichome, which possessed multicellular structure with the average length of 160 μm and with an average diameter of 28 μm, existed in the frond ofP. vittata, and the density of trichome on the pinnate axial surface was higher than that on the petiole. Visible X-ray peak of As was recorded in the epidermal cell and trichome. The relative weight of As in the pinnate trichome, which contained the highest concentration of As among all tissues of the plant, was 2.4 and 3.9 times as much as that in the epidermal and mesophyllous cells, respectively. The As concentrations in the basal and stalk cells of the same trichome were higher than that in its cap cell. This is the first time to report that the trichome ofP. vittata plays an important role in arsenic hyperaccumulation. The finding from the present study implies that much attention should be paid to the role of the trichome in understanding the hyperaccumulation and detoxicity of As in the hyperaccumulator and improving the ability of As accumulation.