The Ultrastructure of the Digestive Glands in Pinguicula vulgaris L. (Lentibulariaceae) Relative to their Function. I. The Changes During Maturation

The digestive glands of Pinguicula vulgaris become fully maturewhilst still enclosed in the bud. All the gland cells remainintact on the fully expanded unstimulated leaves. As the secretoryhead cells mature, a special layer forms between the plasmalemmaand the cell wall. This layer is shown to be different fromthe typical labyrinthine wall of transfer cells and serves forthe storage of digestive enzymes. Ultrastructural analysis,including morphometry, indicates that the digestive enzymesare synthesized on the RER of the head cells and transferredinto the cell wall, particularly into the slime layer, and vacuoles.This transfer is achieved firstly through continuity of theendoplasmic reticulum with vacuoles (static) and the periplasmicspace (dynamic) and, secondly, into the latter through exocytosisof coated Golgi vesicles and of some vacuoles filled with enzymes. Pinguicula vulgaris L., carnivorous plant, digestive glands, ultrastructure, protein synthesis secretion     

Aluminate-Induced Changes in Morphology and Ultrastructure of Thinopyrum Roots

The effects of aluminate [Al(OH)_4$$$] on the morphology andultrastructure of root cells were studied in the salt-tolerantgrasses Thinopyrum bessarabicum (Savul. and Rayss) A. Lve (2) and Thinopyrum junceum (L.) A. Lve (6) by light and transmissionelectron microscopy. Seedlings were grown in nutrient solutioncontaining 1 mol m^–3 [Al] and 5 mol m^–3 Na₂CO₃ atpH 100. Light microscopy revealed that root tips of [Al]-treated plantsdisplayed bending. Many cells of the cortex in the elongatingregion contained a fibrillar/granular material which renderedthem densely staining. Radial (anticlinal) walls of the epidermalcells were either cleft apart of unusually thickened. Amyloplastsof the central root cap cells contained fewer starch grains,while their distribution was disturbed. Electron microscopy showed that the most serious effects of[Al] toxicity occurred at the cell walls of the epidermal androot cap cells, as they lost their fibrillar fine structureand contained an amorphous electron-dense material distributedall over the wall section. Electron-opaque droplets were encounteredat the plasma membrane region of epidermal cells, while theelectron-dense material observed in the vacuoles of cortex cellscould be aluminate which had accumulated there. Thus, despitethe presence of a barrier to aluminate uptake, some [Al] doesenter the symplast. However, the cytoplasm of many epidermalcells displayed a normal fine structure and contained the usualsubcellular components. Dictyosomes, in particular, were abundantand surrounded by many vesicles denoting an active state. Theseobservations stress the role of cell walls as the major [Al]pool and of the plasma membrane as the ultimate barrier thatprotects the cytoplasm. Results are further discussed in relation to the findings inother plant species and it is concluded that, although aluminateis less toxic than Al³⁺, it causes morphological, structuraland, presumably, functional damage-to the roots of the speciesinvestigated. Key words: Thinopyrum, aluminate toxicity, cell walls, root bending     

The Ultrastructure of the Digestive Glands in Pinguicula vulgaris L. (Lentibulariaceae) Relative to their Function. II. The Changes on Stimulation

The secretory cells of the digestive glands remain highly activeduring the entire period of prey digestion and absorption ofnutrients. They appear to play a major role in gland activity.A model of the digestive gland's activity on stimulation isproposed. It is very similar to that suggested earlier for Dionaeamuscipula. After the digestion and absorption cycle, destructiveprocesses are initiated in the glands. These appear similarto those observed in the glands of the ageing, unstimulatedleaf and are not associated with feeding. Pinguicula vulgaris L. carnivorous plant, digestive glands, ultrastructure, protein secretion absorption, senescence     

Effect of Abscisic Acid on Cell-Wall Metabolism in Guard Cells of Vicia faba L.

Cell-wall synthesis in guard cells of Vicia faba L. was examinedusing sonicated epidermal strips incubated with [¹⁴C]glucose.The cell walls of the guard cells incorporated [¹⁴C]glucoseat a lower level in the dark than in the light. Stomatal aperturein the epidermal strips was reduced by application of 1 µmabscisic acid (ABA) in the light but not in the dark. The ABAtreatment reduced the incorporation of [¹⁴C]glucose into thecell walls especially in the light. Fractionation of the labeledcell-wall components revealed that ABA inhibited the synthesisof pectic substances and cellulose, but did not affect hemicellulosesynthesis. Microautoradiographs of the cell-wall fraction ofthe epidermal strips showed that a large amount of radioactivitywas distributed at both ends of the guard cells in the absenceof ABA and that removal of pectic substances from the cell-wallfraction resulted in uniform distribution of the radioactivityin the cell walls of the guard cells. These results indicatedthat the synthesis of pectic substances was active at both endsof the guard cells and was inhibited by ABA. Measurement ofspecific activities of neutral sugars in the guard-cell wallsshowed that polymers composed of galactose underwent activeturnover and that synthesis of glucans was inhibited by ABA.These results revealed a strong correlation between the stomatalmovement and the synthesis of pectic substances and cellulosein the guard cells, suggesting that the cell-wall metabolismin the guard cells may play a role in the regulation of stomatalmovement. (Received October 9, 1987; Accepted March 9, 1988)     

Pathways for Nutrient Transport in the Pitchers of the Carnivorous Plant Nepenthes alata

Glands of the carnivorous pitcher plant Nepenthesalata are activein transport of materials into and out of the pitcher lumen,indicating dual functions in both secretion and absorption.This study examined the potential for open transport throughthese glands using the ultrastructural tracer lanthanum, whichis restricted to the apoplast, and the fluorescent symplastictracer, 6(5)carboxyfluorescein. Glandular uptake of lanthanumfrom the pitcher fluid occurred through the outer cell wallbetween irregularly spaced cutinized deposits, but was blockedfrom entering the underlying mesophyll cell walls by thick endodermal-likeregions. Similarly, lanthanum localization showed an open apoplasticpathway from the petiole to the endodermal regions in the glandbase. Thus, transport of materials into or out of the glandmust occur through the symplast. 6(5)Carboxyfluorescein showedthat these glands transport fluids directly from the pitcherfluid into vascular endings immediately beneath them via a symplasticroute. When applied to the petiolar vascular system, the fluorescenttracer freely entered immature pitchers, but was blocked fromentering the lumen of the mature pitcher by an endodermal zone.An ultrastructural survey showed infrequent pits with plasmodesmatalconnections to adjoining subepidermal cells. These results indicatethat the function of the gland is developmentally regulated.Prior to maturity, the primary function of the gland appearsto be secretion. However, at maturity, secretion is blockedby an endodermal layer, which limits the function of the glandto absorption. These studies support the theory that the glandsof Nepenthesalata are specialized for the bi-directional transportof materials.Copyright 1999 Annals of Botany Company Apoplastic transport, 6(5)carboxyfluorescein, carnivorous plants, digestive glands, endodermal layer,Nepenthesalata Blanco, lanthanum, pitcher plants.     

Regulation of Free Calcium Concentration in the Pitchers of the Carnivorous Plant Sarracenia purpurea: A Model for Calcium in the Higher Plant Apoplast?

The pitcher of the carnivorous plant Sarracenia purpurea L.contains an entrapped body of liquid within which its prey isdigested. Free calcium in the pitcher is derived from eitherthe pitcher walls or from prey falling into the pitcher; inthe absence of exogenous (prey-derived) calcium it will dependon the active and passive calcium regulatory properties of thepitcher walls and may to some extent therefore mimic calciumin the apoplast of plant cells. Using a calcium-specific electrode,the free calcium concentration of the pitchers of Sarraceniaplants was investigated and the effect of adding a variety ofconcentrations of calcium in water determined. The mean pitcherfree calcium concentration in vivo was 2.3 x 10^–5 M±2.5x 10^–5 M; when pitchers were washed and filled with watercontaining lower calcium concentrations, the concentration inthe pitcher water rose to 1–5 x 10^–5 M. When highercalcium concentrations (up to 1 x 10^–4 M) were added,the pitcher calcium concentration declined to 1–7 x 10^–5M. Concentrations of calcium above 1 x 10^–4 M were alsoreduced, but to a lesser extent. Metabolic inhibition of activeion transport, while inhibiting pitcher acidification, did notinhibit regulation of pitcher free calcium, suggested that itoccurs as a result of calcium exchange sites in the pitcherwalls. The data are discussed in relation to the physiologyof Sarracenia pitchers and to the usefulness of the pitcheras a model for free calcium in the higher plant apoplast. Sarracenia purpurea L., carnivorous plant, pitcher, free calcium, plant apoplast     

Osmocytosis and Vacuolar Fragmentation in Guard Cell Protoplasts: Their Relevance to Osmotically-lnduced Volume Changes in Guard Cells

Guard cell protoplasts were prepared from young leaves of peaplants. Under hypertonic conditions they shrink and large numbersof endocytotic (‘osmocytotic’) vacuoles are formedby invagination of the plasma membrane. In thin section theseare indistinguishable from other small vacuoles (‘mini-vacuoles’)which are formed by fragmentation of the large central vacuole.However, the two types of vacuole can be individually recognizedby labelling the central vacuole with neutral red and by performingthe osmotic shrinkage with fluorochromes such as Lucifer Yellow-CHor Cascade Blue present in the extracellular medium. Osmocytoticvacuoles do not fuse with the plasma membrane nor with the mini-vacuolesduring a subsequent swelling phase. After several hours, osmocytosedLucifer Yellow gradually leaks out of the endocytotic vacuoleswhen protoplasts are returned to hypotonic conditions. Thisleakage is not prevented by probenecid at concentrations (20–50mmol m^–3) which do not give rise to pathological changesin protoplast ultrastructure. In order to determine the relevanceof these observations to the situation in planta, intact guardcells in epidermal strips were first allowed to accumulate neutralred in their vacuoles and then subjected to osmotic shrinkagein the presence of external Lucifer Yellow. Osmocytotic vacuoleswere not formed, although the production of mini-vacuoles wasfrequently observed. Key words: Guard cell protoplasts, fluid phase markers, Pisum sativum, probenecid, osmocytosis, shrinkage-swelling cycles     

Alterations in ultrastructure and subcellular localization of Ca2+ in poplar apical bud cells during the induction of dormancy

In poplar (Populus deltoides Bartr. ex Marsh), bud dormancyand freezing tolerance were concomitantly induced by short-day(SD) photoperiods. Ultrastructural changes and the alterationin subcellular localization of calcium in apical bud cells associatedwith dormancy development were investigated. During the developmentof dormancy, the thickness of cell walls increased significantly,the number of starch granules increased, and there was a significantaccumulation of storage proteins in the vacuoles of the apicalbud cells. The most striking change was the constriction andblockage of the plasmodesmata. It was demonstrated that antimonate precipitation is a reliabletechnique for studying subcellular localization of calcium inpoplar apical bud cells. Under the long day (LD) photoperiod,electron-dense calcium antimonate precipitates were mainly localizedin vacuoles, intercellular spaces and plastids. Some antimonateprecipitates were also found in the cell walls and at the entranceof the plasmodesmata. However, there were few Ca²⁺ depositsfound in the cytosol and nucleus. After 20 d of SD exposure,when development of bud dormancy was initiated, calcium depositsin intercellular spaces were decreased, whereas some depositswere found in the cytosol and nuclei. From 28–49 d ofSD exposure, while dormancy was developing, a large number ofCa²⁺ precipitates were found in the cytosol and nuclei. Whendeep dormancy was reached after 77 d of SD exposure, Ca²⁺ depositsbecame fewer in both cytosol and nuclei, whereas numerous depositswere again observed in the cell walls and in the intercellularspaces. These results suggest that under the influence of SDphotoperiods, there are alterations in subcellular Ca²⁺ localization,and changes in ultrastructure of apical bud cells during thedevelopment of dormancy. The constriction and blockage of plasmodesmatamay cause the cessation of symplastic transport, limit cellularcommunication and signal transduction between adjacent cells,which in turn may lead to events associated with growth cessationand dormancy development in buds. Key words: Poplar, apical bud cells, Ca²⁺ subcellular localization, dormancy     

The Ultrastructural Basis of Chloride Tolerance in the Leaf of Frankenia

The ultrastructural distribution of chloride in the leaf ofthe halophyte, Frankenia, was investigated by the silver precipitationtechnique. A comparison was made between leaves of low saltstatus samples and those of high salt status samples. The mainfindings were: (1) The leaf apoplast becomes chloride-ladenunder saline conditions; (2) the presence of ‘specialized’vacuoles in mesophyll cells results in a lower chloroplast chloridecontent compared to cells lacking such vacuoles; (3) the primarysites of chloride in the salt gland are the electron dense microvacuoles,the cell walls, and the interfacial apparatus. These resultsare applied to a comprehensive hypothesis of chloride tolerancein the leaf of Frankenia.     

Uptake of Neutral Red by the Vacuoles of a Green Alga, Micrasterias pinnatifida

Neutral red (NR) in the culture medium entered the vacuolesof a green alga, Micrasterias pinnatifida, at a higher rateat pH 8 than at pH 5. NR remained soluble in vacuoles of cellscultured at pH 5, while it precipitated and formed granulesin cells cultured at pH 8. The vacuoles of cells cultured atpH 8 contained fibrils, but those of cells cultured at pH 5did not. The amount of NR that entered the cells was markedlyreduced by the addition to the medium of nigericin at 10^-5M,monensin at 10^-5M, bafilo-mycin A₁ at 10^-5M, or ammonium chlorideat 50 mM. The formation of NR granules in vacuoles were stronglyinhibited and the disorganization of NR granules were acceleratedby the addition of nigericin at 10^-5M, or bafilomycin A₁ at10^-5M to the culture medium. The possibility is discussed thatNR which enters vacuoles might become positively charged (NRH⁺)by protons brought into vacuoles by proton pumps and that NRH⁺might combine with some negatively charged macromolecules toform aggregates or granules. (Received April 18, 1996; Accepted May 27, 1996)     

Chromium VI Induced Structural and Ultrastructural Changes in Bush Bean Plants (Phaseolus vulgaris L.)

The effect of a growth reducing chromium VI concentration (9.6x 10^–5M Cr as Na₂CrO₄) on the structure and ultrastructureof different organs of bush bean plants (Phaseolus vulgarisL.) grown on perlite was studied using light, transmission electronand scanning electron microscopy. The structural and ultrastructuralalterations observed were quite different in the various organsanalysed and did not always stay in direct relation to the averageCr content of the whole organ. The primary toxicity effect seemedto be membrane damage, due to the high oxidation power of CrVI. It is suggested that chromium is retained in vacuoles andcell walls of roots, and that the chromium reaching the leavesmay be principally Cr III and present in cell walls. The alterationsobserved in the upper plant parts seemed principally due toindirect Cr effects on the content of essential mineral nutrients. Phaseolus vulgaris L., bush bean, chromium VI toxicity, structure, ultranstructure, light microscopy, transmission electron microscopy, scanning electron microscopy     

Intracellular Localization of 3H-IAA in the Apical Bud of Lycopersicon esculentum

Driss-Ecole, D. and Perbal, G. 1987. Intracellular localizationof ³H-IAA in the apical bud of Lycopersicon esculentum.—J.exp. Bot. 38: 1362–1372. High resolution autoradiography of ³H-IAA was performed on ultra-thinsections of the apical bud of Lycopersicon esculentum treatedby DCC or glutaraldehyde. A quantitative study of the localizationof the labelling in the compartments (cell wall, cytoplasm,vacuoles and nucleus) of four types of cells (cells of the lateralzone of the apex, cells of the pith meristem, proximal and distalcells of the upper part of the pith) was made. The statisticalanalysis of the results has proved that the variability of thelabelling of the cell compartments in the four cell types wassimilar after treatment by DCC or glutaraldehyde. The densityof labelling is higher in each compartment of the meristematiccells compared with those of the differentiating cells. Thecells of the pith meristem can be distinguished from the meristematiccells of the lateral zone of the apex by a greater density oflabelling in the cytoplasm and the nucleus. These two cellulartypes contain a high density of radioactivity in vacuoles. Byconsidering the percentage of labelling of each compartmentrelative to the total labelling in the cell, it can be shownthat the meristematic cells are characterized by a high percentagein the nucleus whereas the vacuoles of the differentiating cellscontain the highest percentage of radioactivity. Key words: ³H-IAA, tomato shoot     

Intracellular localization of capsaicin and its analogues, capsaicinoid, in Capsicum fruit 1. Microscopic investigation of the structure of the placenta of Capsicum annuum var. annuum cv. Karayatsubusa

Transverse sections of the placenta of hot pepper, Capsicumannuum var. annuum cv. Karayatsubusa, at different stages afterflowering were examined microscopically. Examination of thecellular structure of the placenta using a light microscoperevealed that some morphological changes took place mainly inthe epidermal tissue of the placenta during maturation. Elongationof the epidermal cells and many osmiophilic granules were recognizedin the epidermal cells of the placenta in which capsaicinoidwas being formed and actively accumulated. Moreover, a granule-likestructure having an absorption at 280 nm was also recognizedby ultraviolet microscopy around the same region where the osmiophilicgranules were observed. By electron microscopy, many electron-densegranules stained with glutaraldehyde and osmium tetroxide wereobserved both in the small vesicles and vacuoles of epidermalcells of the placenta. The electron-dense granules varied insize from smaller than 1 µm to larger than 2 µmin diameter. They were thought to be capsaicinoid and were observedonly in the epidermal cells. Therefore, the epidermal tissueappeared to be the site of capsaicinoid accumulation. ¹Formation and metabolism of pungent principle of Capsicum fruits.Part V. (Received December 27, 1979; )     

The digestive systems of carnivorous plants

To survive in the nutrient-poor habitats, carnivorous plants capture small organisms comprising complex substances not suitable for immediate reuse. The traps of carnivorous plants, which are analogous to the digestive systems of animals, are equipped with mechanisms for the breakdown and absorption of nutrients. Such capabilities have been acquired convergently over the past tens of millions of years in multiple angiosperm lineages by modifying plant-specific organs including leaves. The epidermis of carnivorous trap leaves bears groups of specialized cells called glands, which acquire substances from their prey via digestion and absorption. The digestive glands of carnivorous plants secrete mucilage, pitcher fluids, acids, and proteins, including digestive enzymes. The same (or morphologically distinct) glands then absorb the released compounds via various membrane transport proteins or endocytosis. Thus, these glands function in a manner similar to animal cells that are physiologically important in the digestive system, such as the parietal cells of the stomach and intestinal epithelial cells. Yet, carnivorous plants are equipped with strategies that deal with or incorporate plant-specific features, such as cell walls, epidermal cuticles, and phytohormones. In this review, we provide a systematic perspective on the digestive and absorptive capacity of convergently evolved carnivorous plants, with an emphasis on the forms and functions of glands.

A comparison of the forms and functions of digestive and absorptive glands in carnivorous plants sheds light on their convergent evolution.     

Cell-based imaging of sodium iodide symporter activity with the yellow fluorescent protein variant YFP-H148Q/I152L

The sodium iodide symporter (NIS) mediates iodide (I^–) transport in the thyroid gland and other tissues and is of increasing importance as a therapeutic target and nuclear imaging reporter. NIS activity in vitro is currently measured with radiotracers and electrophysiological techniques. We report on the development of a novel live cell imaging assay of NIS activity using the I^–-sensitive and genetically encodable yellow fluorescent protein (YFP) variant YFP-H148Q/I152L. In FRTL-5 thyrocytes stably expressing YFP-H148Q/I152L, I^– induced a rapid and reversible decrease in cellular fluorescence characterized by 1) high affinity for extracellular I^– (35 µM), 2) inhibition by the NIS inhibitor perchlorate, 3) extracellular Na⁺ dependence, and 4) TSH dependence, suggesting that fluorescence changes are due to I^– influx via NIS. Individual cells within a population of FRTL-5 cells exhibited a 3.5-fold variation in the rate of NIS-mediated I^– influx, illustrating the utility of YFP-H148Q/I152L to detect cell-to-cell difference in NIS activity. I^– also caused a perchlorate-sensitive decrease in YFP-H148Q/I152L fluorescence in COS-7 cells expressing NIS but not in cells lacking NIS. These results demonstrate that YFP-H148Q/I152L is a sensitive biosensor of NIS-mediated I^– uptake in thyroid cells and in nonthyroidal cells following gene transfer and suggest that fluorescence detection of cellular I^– may be a useful tool by which to study the pathophysiology and pharmacology of NIS. thyroid; fluorescence microscopy; FRTL-5 cells     

Inhibition of Sugar and Salt Elimination by Glands with the Amino Acid Analog p-Fluorophenylalanine

The amino acid analog p-fluorophenylalanine (FPA) inhibitedsugar and K⁺ secretion by nectary glands. FPA specifically reducedthe net excretion of Na⁺ and Cl^– by the salt glands ofthe halophyte Limonium vulgare and ³⁶Cl^–excretion by theglands of the pitcher walls of the carnivorous plant Nepenthes.Net uptake and net accumulation of Na⁺ and Cl^– by Limoniumleaf tissue and ³⁶Cl^– accumulation in Nepenthes pitchertissue were much less inhibited than excretion. The resultsare discussed in relation to literature reporting similar specificeffects of FPA on transport of ions from the symplast of barleyroots into the dead xylem elements. Limonium vulgare, Nepenthes hookeriana, salt-glands, excretion, p-fluorophenylalanine     

Difference in light-induced increase in ploidy level and cell size between adaxial and abaxial epidermal pavement cells of Phaseolus vulgaris primary leaves

Changes in nuclear DNA content and cell size of adaxial andabaxial epidermal pavement cells were investigated using brightlight-induced leaf expansion of Phaseolus vulgaris plants. Inprimary leaves of bean plants grown under high (sunlight) ormoderate (ML; photon flux density, 163 µmol m^–2s^–1) light, most adaxial epidermal pavement cells hada nucleus with the 4C amount of DNA, whereas most abaxial pavementcells had a 2C nucleus. In contrast, plants grown under lowintensity white light (LL; 15 µmol m^–2 s^–1)for 13 d, when cell proliferation of epidermal pavement cellshad already finished, had a 2C nuclear DNA content in most adaxialpavement cells. When these LL-grown plants were transferredto ML, the increase in irradiance raised the frequency of 4Cnuclei in adaxial but not in abaxial pavement cells within 4d. On the other hand, the size of abaxial pavement cells increasedby 53% within 4 d of transfer to ML and remained unchanged thereafter,whereas adaxial pavement cells continuously enlarged for 12d. This suggests that the increase in adaxial cell size after4 d is supported by the nuclear DNA doubling. The differentresponses between adaxial and abaxial epidermal cells were notinduced by the different light intensity at both surfaces. Itwas shown that adaxial epidermal cells have a different propertythan abaxial ones. Key words: Cell enlargement, endopolyploidization, epidermal pavement cells, incident light intensity, leaf expansion, nuclear DNA content, Phaseolus vulgaris     

Effects of Fusicoccin and Abscisic Acid on Sugar and lon Transport from Plant Glands

Fusicoccin (FC) inhibited net excretion of Cl^– by theglands of the pitchers of the carnivorous plant Nepenthes hookeriana;of Na⁺ and Cl^– by the salt glands of the halophytes Limoniumvulgare and L. pectinatum and of K⁺ in the nectar of Acer platanoidesflowers. It had no effect on K⁺ elimination with nectar of Impatienswalleriana (extrafloral nectaries) and Abutilon striatum. Abscisicacid (ABA) stimulated net excretion of K⁺ and Cl^– in Nepenthesand of Na⁺ and Cl^– in Limonium but had no effects on K⁺in nectar. Thus, FC and ABA had opposing effects on ion excretionby the salt eliminating glands of Limonium and Nepenthes. Bothcompounds, however, had similar effects on sugar secretion ofnectary glands which was either inhibited or unaffected by FCand ABA. It is suggested that the effects of FC and ABA on ion excretionby gland cells could be reconciled with literature showing FC-stimulationand possible ABA-inhibition of proton pumps at the plasmalemmaof plant cells. Nepenthes hookeriana, Limonium vulgare, Limonium pectinatum, Acer platanoides, salt-glands, nectaries, excretion, fusicoccin, abscisic acid, proton pump     

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     

Cellular Structure and Light Absorbtion in Leaves of Frithia pulchra (Mesembryanthemaceae)

In order to quantify the structural differences between celltypes of leaves from a ‘ window’ plant, an ultrastructuralmorphometric analysis was made of the epidermal, window andchlorenchyma tissues of Frithia pulchra. Epidermal cells arethe largest cells found in Frithia leaves and are characterizedby the presence of a thick outer tangential cell wall and numerousvacuolar inclusions. Epidermal tissue has an optical densityof 0.30. The transparent window tissue (i.e. optical density= 0.08) has a uniform ultrastructure throughout the length ofthe leaf. The vacuome comprises aproximately 97 per cent ofthe protoplasmic volume of window cells. Chlorenchyma cellspossess thin cell walls and are surrounded by numerous intercellularspaces. Cells of the apical chlorenchyma tissue possess approximately30 plastids per cell. These chloroplasts have an average individualvolume of 220 µm². Cells of the basal chlorenchyma tissuecontain chloroplasts that are five to six times smaller andmore numerous than those in cells of the apical chlorenchyma.The increased volume of chloroplasts in the apical comparedwith basal chlorenchyma cells (i.e. 31.4 and 20.2 per cent ofthe protoplasm, respectively) is positively correlated withtheir optical densities of 1.46 and 0.97, respectively. Frithia pulchra, stereology, leaf, light absorption, window plant