Preferential Accumulation by Mesophyll Cells at Low and by Veins at High Exogenous Amino Acid and Sugar Concentrations in Commelina benghalensis L. Leaves

The contribution to solute uptake by mesophyll cells and veinsin leaf discs, was assessed through a study of uptake in relationto concentration for ¹⁴C-labelled substrates (sucrose, glucose,arginine, proline, valine and -aminoisobutyric acid) using isolatedmesophyll cells and stripped leaf discs of Commelina benghalensisL. Uptake per unit fresh weight was higher in mesophyll cellsthan in discs at low substrate concentrations (lower than about0·5 mol m^–3). At higher concentrations, uptakeby discs exceeded that by mesophyll cells except for glucoseuptake which was higher in mesophyll cells over the whole concentrationrange. The profiles of uptake versus concentration displayedbiphasic kinetics in mesophyll cells and discs. Comparison ofthe uptake characteristics obtained by iterative fitting confirmedthat the high-affinity systems of uptake prevail in the mesophyllcells, whereas the low-affinity systems are dominant in theveins. The results provide good evidence that, supplementaryto direct vein loading, a pathway via the mesophyll contributesstrongly to the photosynthate loading by veins in stripped discs. Key words: Commelina benghalensis L., amino acid uptake, mesophyll, minor veins, phloem loading, sugar uptake     

Effect of Phosphorus Nutrition on the Cellular Distribution of Acid Phosphatase in the Leaves of Lycopersicon esculentum L.

A histochemical study using light microscopy has been made ofthe distribution of acid phosphatase (EC 3.1.3.2 [EC] ) activity intransverse sections of fully expanded leaves of Lycopersiconesculentum grown in phosphate-deficient or sufficient media.Leaf tissues were prepared by two methods and were embeddedin paraffin wax. The location of acid phosphatase activity inleaf sections was determined by trapping orthophosphate releasedfrom p-nitrophenyl phosphate with lead acetate and subsequentlyconverting the lead phosphate to optically dense lead sulphide.In leaf sections from control tissue lead sulphide depositswere larpely confined to the spongy mesophyll cells. Whereasthe staining of the palisade cells was limited and of a granularnature, the staining of the spongy mesophyll cells was heavierand coincident with the outline of the individual cells. Moreover,the minor veins were more heavily stained than the surroundingmesophyll cells. Sections of phosphorus-deficient tissues wereheavily stained in both the palisade and spongy mesophyll layersand heavy deposits of lead sulphide were present in the regionsof the minor veins. It is suggested that the enhanced acid phosphataseactivity of the mesophyll cells in fully expanded leaves couldbe involved in the remobilization of phosphate within phosphorus-deficientplants, or be part of a phosphate transporting system, concentratingthe intracellular phosphate from the limiting supply in thesolution bathing the mesophyll cells. Lycopersicon esculentum L., tomato, acid phosphatase, phosphorus nutrition     

Extracellular Components Implicated in the Stationary Organization of the Actin Cytoskeleton in Mesophyll Cells of Vallisneria

In mesophyll cells of Vallisneria gigantea Graebner, an aquaticangiosperm, the association of the plasma membrane with thecell wall at the end wall has been reported to be indispensablefor the mechanism that maintains the stationary organizationof the bundles of microfilaments (MFs) [Masuda et al. (1991)Protoplasma 162: 151]. To identify putative extracellular componentsthat might play a crucial role in this mechanism, we examinedthe effects of two exogenously applied synthetic hexapeptides,GRGDSP and ARYDEI, which include an RGD and an RYD motif, respectively.The RGD motif is known as a recognition site in molecules requiredfor adhesion to the substratum at sites of focal contacts. Within24 h, both peptides (at concentrations of 1–15 mM) inducedextremely abnormal patterns of cytoplasmic streaming, as wellas the striking disruption of the arrangement of bundles ofMFs. GRGESP and ARYEEI peptides, used as controls, had no detectableeffects. Immunofluorescence microscopy revealed that polyclonalantibodies against the ARYDEI peptide bound to the cell wallsof mesophyll cells while a preimmune serum did not. Westernblotting analysis demonstrated that the antibodies recognizedpolypeptides of 54 kDa and 27 kDa in an extract of total proteinsfrom the leaves of Vallisneria. The results suggest that someextracellular protein(s), with a conserved RGD or RYD motifin its amino acid sequence, might be involved in the maintenanceof the stationary organization of the bundles of MFs. (Received August 13, 1996; Accepted January 23, 1997)     

Cellular Levels of Ribulose 1,5 Bisphosphate Carboxylase and Chloroplast Compartment Size in Wheat Mesophyll Cells

Pyke, K. A. and Leech, R. M. 1987. Cellular levels of ribulose1,5 bisphosphate carboxylase and chloroplast compartment sizein wheat mesophyll cells.—J. exp. Bot. 38: 1949–1956. The amount of the photosynthetic enzyme ribulose 1,5 bisphosphatecarboxylase (RUBISCO),as determined in mesophyll cells in primarywheat leaves was related to the size of the chloroplast compartmentwithin the cell for wheat species of three ploidy levels. Asimilar comparison was made for several genotypes of the hexaploidbreadwheat Triticum aestivum. Estimation of total chloroplastvolume per mesophyll cell was made assuming chloroplasts tobe oblate spheroid in shape. A significant correlation was found between the amount of RUBISCOper cell and the total chloroplast volume per cell for diploid,tetraploid and hexaploid wheat species. A significant correlationbetween cellular RUBISCO level and total chloroplast volumeper cell was also observed for a range of genotypes of the hexaploidT. aestivum but these genotypes of T. aestivutn accumulate agreater amount of RUBISCO per unit chloroplast volume than doany other wheat species. For these genotypes of T. aestivumthe stromal concentration of RUBISCO was estimated at 0·5mol m^–3 with a ribulose Msphosphate binding site concentrationof 4·0 mol m^–3. These results are discussed with respect to a gene dosage hypothesisto explain the accumulation of RUBISCO in leaf mesophyll cells. Key words: Ribulose, bisphosphate carboxylase, wheat chloroplasts, mesophyll cells     

Rhizobium Attachment and Curling in Asparagus, Rice and Oat Plants

Observations by scanning electron microscopy revealed that rhizobiaattach to the surface of rice protoplasts with regenerated cellwalls, isolated mesophyll cells of asparagus, and root hairsof rice and oat seedlings. Those strains of rhizobia, namelyRhizobium leguminosarum biovar trifolii, Bradyrhizobium japonicumand Bradyrhizobium sp., attach to the cells of these monocotsin the same manner as they attach to the host dicots tested.Escherichia coli did not attach. These results suggest thatthe attachment of rhizobia is not a host-specific process. Whenoat seedlings were infected by R. l. trifolii, hair curlingwas observed. The interactions between monocot plants and rhizobiais discussed in this paper. (Received June 12, 1989; Accepted November 9, 1989)     

Differentiation of Photorespiratory Activity between Mesophyll and Bundle Sheath Cells of C4 Plants I. Glycine Oxidation by Mitochondria

Mitochondria were isolated from mesophyll protoplasts and bundlesheath protoplasts or strands which were obtained by enzymaticdigestion of six C₄ species: Zea mays, Sorghum bicolor, Panicummiliaceum, Panicum capillare, Panicum maximum and Chloris gayana,representative of three C₄ types. Photorespiratory glycine oxidationand related enzyme activities of mesophyll and bundle sheathmitochondria were compared. Mesophyll mitochondria showed good P/O ratios with malate andsuccinate as substrate but lacked the ability to oxidize glycine.On the other hand, mitochondria isolated from bundle sheathprotoplasts of P. miliaceum and bundle sheath strands of Z.mays possessed glycine oxidation activity similar to that ofmitochondria from C₃ plant leaves. The two enzymes involvedin glycine metabolism in mitochondria, serine hydroxymethyltransferaseand glycine decarboxylase, were also assayed in the mitochondriaof the two cell types. The activities of the two enzymes inbundle sheath mitochondria were in the range found in C₃ mitochondria.In contrast, the activities in mesophyll mitochondria were eithernot detectable or far lower than those in bundle sheath mitochondriaand ascribed to contaminating bundle sheath mitochondria. The present results indicate the deficiency of a complete glycineoxidation system in mesophyll mitochondria and also a differentiationbetween mesophyll and bundle sheath cells of C₄ plants withrespect to the photorespiratory activities of the mitochondria. (Received June 8, 1983; Accepted August 29, 1983)     

Lack of Influence of the Epidermis on Underlying Cell Development in Leaflets ofPisum sativumvar.argenteum(Fabaceae)

We explored whether epidermal pressure regulates cell and organgrowth in leaflets ofPisum sativumvar.argenteum,a mutant cultivarof the garden pea characterized by reduced adhesion betweenthe epidermis and subjacent mesophyll. Developing leaflets ofleaves arising at three positions on the seedling axis werepeeledin situand grown to maturity in humidity chambers. Themature anatomy and morphology could be accurately assessed becausewound responses normally associated with peeling were preventedby theArgmutation that permitted peeling without damage to themesophyll and by the humidity chambers that protected peeledareas from desiccation. The mesophyll cell size, state of differentiation,and layering pattern as well as the overall morphology of mature,peeled leaflets were indistinguishable from those of mature,intact leaflets grown under the same conditions. The epidermisexerted no detectable regulatory effect on the expansion ofthe leaflets as a whole or on the tissue layers and cells withinthe leaflets.Copyright 1999 Annals of Botany Company. Biomechanics, compression, epidermis, leaf development, mesophyll, pressure, wound response,Pisum sativumvar.argenteum.     

Differential Stimulation of PEP-carboxylation in Guard Cells and Mesophyll Cells by Ammonium or Fusicoccin

Dark CO₂-fixation in guard cells of Vicia faba was much moresensitive to ammonium than in mesophyll cells. Addition of ammonium(5.0 mol m^–3; pH₀ 7.6) caused up to a 7-fold increasein dark CO₂-fixation rates in guard cell protoplasts (GCP),whereas in leaf slices, mesophyll cells, and mesophyll protoplaststhe increase was only about 1.4-fold. In both cell or tissuetypes, total CO₂-fixation rates were higher in the light (2–12-foldhigher in GCP and 28-fold in mesophyll); these rates were onlyslightly changed by ammonium treatment. However, separationof ¹⁴C-labelled products after fixation of CO₂ in the lightby GCP revealed a large ammonium-induced shift in carbon flowfrom starch and sugars to typical products of C₄-metabolism(mainly malate and aspartate). In contrast, in mesophyll cellsamino acid and malate labelling was only moderately increasedby ammonium at the expense of sucrose. The data suggest thatin vivo ammonium might facilitate stomatal opening and/or delaystomatal closing through an increased production of organicacids. Key words: PEP-carboxylation, guard cell protoplasts, ammonium, fusicoccin     

Major Element Composition of Epidermal and Mesophyll Tissues2Commelina Communis L. and Vicia Faba L.: Some Further Considerations of the Role of Ions in Stomatal Functioning

Epidermal and mesophyll tissues of Commelina communis L. andVicia faba L. were analysed by atomic absorption spectrometryfor the major plant inorganic cations and anions (K, Na, Ca,Mg, P, NO₃-N, Cl) when stomata of the leaf were open and closed.Water-soluble and residual levels of the elements were estimatedand a charge balance of the soluble fraction made. The major portion of K, Na, Cl, and P was extracted in the water-solublefraction of the epidermal and mesophyll tissues of both species.In both species the bulk of Ca remained in the insoluble residueof the epidermis whereas in mesophyll tissue it was equallydistributed be-between the two fractions in C. communis butmainly in the insoluble residue in V. faba. Magnesium was predominantlyfound in the water-soluble fraction of V. faba mesophyll tissueand distributed approximately equally between the two fractionsin the epidermal tissue. In C. communis Mg was slightly moreabundant in the water-soluble fraction of both mesophyll andepidermis. In both species no statistically significant differences inthe levels of the elements could be detected between epidermaland mesophyll tissues from leaves with open stomata and thesame tissues from leaves with closed stomata, suggesting thatthere was no major flux of ions between mesophyll and epidermisduring stomatal movements. Regardless of whether the stomata were open or closed, therewere considerably more water-soluble inorganic cations thananions present in all tissues of both species with K being themajor cation and Cl being the major anion. In V.faba and C-communis epidermis there was 49–53 per cent and 56%68per cent excess cation respectively. In the mesophyll tissuethe excess cation was 63–75 per cent and 75%78 per centin V.faba and C. communis respectively. When the partitioning of the levels of the elements betweenepidermis and mesophyll of a leaf is considered, except forNO₃-N in both species and Na in V. faba, 20 per cent or lessof each element was present in the epidermis.     

Conditions for the Attachment of Calystegia Cells to Solid Substrates

Mechanically isolated mesophyll cells of Calystegia sepium L.incubated in thin layers of non-agitated liquid media readilyattach to their substrate (culture vessel). Conditions for thisattachment of living plant cells are: a medium consisting ofa low concentration of at least one macroelement and one sugar,a pH value between 5 and 7, and a substrate with a hydrophiliccharacter (e.g. glass, polystyrene). Calystegia sepium, mesophyll cells, cell attachment     

Differentiation of Photorespiratory Activity between Mesophyll and Bundle Sheath Cells of C4 Plants II. Peroxisomes of Panicum miliaceum L.

Peroxisomes were isolated by sucrose density gradient centrifugationfrom mesophyll and bundle sheath protoplasts of a C₄ plant,Panicum miliaceum L. The equilibrium density in the gradientwas 1.25 for bundle sheath peroxisomes and 1.23 for mesophyllperoxisomes, the former density being similar to that of peroxisomesof wheat mesophyll protoplasts. Photorespiratory and other microbody enzymes were assayed forthe peroxisomes of P. miliaceum to detect possible differentiationat an enzyme level. The specific activities of photorespiratoryenzymes, except for hydroxypyruvate reductase, in bundle sheathperoxisomes were 40–60% of those in wheat peroxisomes,when compared on a protein basis, and only 20–30% in mesophyllperoxisomes. However, peroxisomes from both cell types containedsignificant levels of all the enzymes involved in the photorespiratoryglycolate pathway, when compared with castor bean glyoxysomes.The activity of hydroxypyruvate reductase in the peroxisomesof P. miliaceum was comparable to or higher than that in wheatperoxisomes. Two ß-oxidation enzymes and urate oxidasewere detected in the peroxisomes in a similar level to thatin wheat peroxisomes. These results suggest that the peroxisomes of mesophyll andbundle sheath cells of P. miliaceum are essentially similarto those of C₃ plants, and that they cannot be differentiatedexcept for a difference in equilibrium density in a sucrosegradient. (Received December 24, 1984; Accepted April 9, 1985)     

Flag Leaf Anatomy of Triticum and Aegilops Species in Relation to Photosynthetic Rate

Quantitative anatomical and other measurements were made onfully expanded flag leaves of a series of diploid, tetraploidand hexaploid Triticum and Aegilops species, and photosyntheticrates per unit leaf area were measured at light saturation (P_max). Diploids had the highest P_max, hexaploids the lowest with tetraploidsbeing intermediate. The anatomical features of tetraploids andhexaploids were generally similar, but different from the diploids.The diploids had thinner leaves with less dry matter and chlorophyllper unit area. The surface area of the mesophyll cells per unitvolume of mesophyll tissue was similar for all ploidy levels,as was the ratio mesophyil cell surface area per unit leaf area.It is argued that while these anatomical features are unlikelyto account for the observed variation in Pmax, it is possiblethat other structural factors with which they are correlatedmay causally influence P_max. One such feature is the averagediffusion path length from the plasmalemma at the cell surfaceto the sites of carboxylation. Anatomy, photosynthesis, mesophyll, cell size, Triticum, Aegilops, polyploidy     

Pyruvate Uptake by Mesophyll and Bundle Sheath Chloroplasts of a C4 Plant, Panicum miliaceum L.

Intact chloroplasts were isolated from mesophyll and bundlesheath protoplasts of a C₄ plant, Panicum miliaceum L., to measurethe uptake of [1-¹⁴C]pyruvate into their sorbitol-impermeablespaces at 4?C by the silicone oil filtering centrifugation method.When incubated in the dark, both chloroplasts showed similarslow kinetics of pyruvate uptake, and the equilibrium internalconcentrations were almost equal to the external levels. Whenincubated in the light, only mesophyll chloroplasts showed remarkableenhancement of the uptake, the internal concentration reaching10–30 times of the external level after 5 min incubation.The initial uptake rate of the mesophyll chloroplasts was enhancedabout ten fold by light and was saturated with increasing pyruvateconcentration; K_m and V_max were 0.2–0.4 mM and 20–40µmol(mg Chl)^–1 h^–1, respectively. The lightenhancement was abolished by DCMU and uncoupling reagents suchas carbonylcyanide-m-chlorophenylhydrazone and nigericin. Theseresults indicate the existence of a light-dependent pyruvatetransport system in the envelope of mesophyll chloroplasts ofP. miliaceum. The uptake activity of mesophyll chloroplastsboth in the light and the dark was inhibited by sulfhydryl reagentssuch as mersalyl and p-chloromercuriphenylsulfonate, but thebundle sheath activity was insensitive to the reagents. Thesefindings are further evidence for the differentiation of mesophylland bundle sheath chloroplasts of a C₄ plant with respect tometabolite transport. (Received July 3, 1986; Accepted October 8, 1986)     

Effects of Light Quality on Photosynthetic Carbon Metabolism in C4 and C3 Plants: Rapid Movements of Photosynthetic Intermediates Between Mesophyll and Bundle Sheath Cells

The influence of varying light intensity and quality on thecarbon labelling patterns in Rumex vesicarius (a C₃ plant),Setaria italica (a malate-formingC₄ plant), and Amaranthus paniculatus(an aspartate-forming C₄ plant) was studied. In A. paniculatusand B. vesicarius blue light decreased the transfer of radioactivityto sugars and starch but in S. italica only slightly decreasedradioactivity in sugar phosphates, sucrose, and insolubles.Negligible transfer was observed from the C₄ acids to sugarphosphates, sucrose, and starch under dim blue-green and blue-yellowlights in S. italica and A. paniculatus. Blue light favouredthe formation of malate, aspartate, and alanine in all threeplants. The differential effect of blue and red light suggesteda variation in the mechanisms of C₄-photosynthesis in Setariaand Amaranthus. Leaves of S. italica and A. paniculatus were allowed to photosynthesizein ¹⁴CO₂ for 5 s and then the distribution of the labelled productsbetween the mesophyll and the bundle sheath cells was determinedduring subsequent photosynthesis in ¹²CO₂. Malate and aspartatewhich appeared initially in the mesophyll layer moved rapidlyinto the bundle sheath cells. Phosphoglyceric acid originatingin the bundle sheath moved swiftly to the mesophyll layer. Sugarphosphates were recovered from both the mesophyll and the bundlesheath cells. Most of the starch was found in the bundle sheathcells while sucrose and alanine were localized in the mesophyllcells.     

The Anisotropy of the Mesophyll and CO2 Capture Sites in Vicia faba L. Leaves at Low Light Intensities

Experiments are reported on the spatial distributions of isotopiccarbon within the mesophyll of detached leaves of the C₃ plantVicia faba L. fed ¹⁴CO₂ at different light intensities. Eachleaf was isolated in a cuvette and ten artificial stomata providedspatial continuity between the ambient atmosphere (0.03–0.05%v/v CO₂) and the mesophyll from the abaxial leaf side. Paradermalleaf layers exhibited spatial profiles of radioactivity whichvaried with the intensity of incident light in 2 min exposures.At low light, when biochemical kinetics should limit CO₂ uptake,sections through palisade cells contained most radioactivity.As the light intensity was increased to approximately 20% offull sunlight, peak radioactivity was observed in the spongycells near the geometric mid-plane of the mesophyll. The resultsindicate that diffusion of carbon dioxide within the mesophyllregulated the relative photosynthetic activity of the palisadeand spongy cells at incident photosynthetically active lightintensities as little as 110 µE m^–2 s^–1 whenCO₂ entered only through the lower leaf surface. Key words: CO₂ capture sites, Vicia faba L., Artificial stomata     

Intracellular Ca2+ Concentration and Cytoplasmic Streaming in Vallisneria Mesophyll Cells

Intracellular Ca²⁺ concentration regulating the cytoplasmicstreaming in Vallisneria mesophyll cells was estimated. Theleaf segment was cut open at the middle of the mesophyll celllayers and the exposed mesophyll cells were treated with testsolutions of various Ca²⁺ concentrations in the dark. This allowedA23187 [GenBank] , a calcium ionophore, to exert its full effect on thecell membrane. The streaming was induced or maintained in solutions which containedCa²⁺ at lower than 10^–6M. However, Ca²⁺ at concentrationshigher than 10^–5M had a definite, inhibitory effect. Theinduction and cessation of streaming could be repeated by alternatelychanging the solutions. (Received March 14, 1986; Accepted May 15, 1986)     

The Structure of the Mesophyll of Flag Leaves in Three Triticum Species

Flag leaves of Triticum urartu, T. monococcum and T. aestivumcv. Professeur Marchal were examined by light and electron microscopyand by separating cells to determine whether differences inleaf anatomy could be related to known differences in theirlight-saturated rates of photosynthesis. Mesophyll cells fromthe three species were lobed and orientated with their longaxis parallel to the veins. The longest, most-lobed cells flankedthe sclerenchyma associated with the veins. Mean cell dimensionswere greatest in Professeur Marchal, but there was no significantdifference in the ratio of the mesophyll cell surface area tocell volume amongst the three species. Flag leaves of T. urartushowed the highest rates of photosynthesis and were also thethickest, with closely-spaced veins from which many of the mesophyllcells radiated. These flag leaves also had significantly more(21.9 per cent) air-filled space, and the highest ratio (15.2)of mesophyll cell surface exposed to this air-filled space perunit leaf area. Ways in which these anatomical characteristicsmay contribute to the higher rate of photosynthesis are discussed. Triticum urartu, Triticum monococcum, Triticum aestivum, flag leaves, morphology, mesophyll     

Influence of Genome on Leaf Anatomy of Triticum and Aegilops

The leaf mesophyll of Triticum and Aegilops is constructed fromcells with one to ten arms. Volume of mesophyll cells per unitleaf area was larger in some monogenomic (A and B genome) plantsthan in polyploids, while leaf volume per unit leaf area wassmaller in the former than in the latter. Consequently, thecompactness of leaf blade is higher in these monogenomic plantsthan in the polyploids. D genome plants showed a much lowervolume of both mesophyll cells and leaf blade per unit leafarea, but the compactness of the leaf blade was generally higherthan in the polyploids. Mesophyll surface area per unit leaf area tended to be largerin the A and B genome than in the D genome and polyploid plants.Out of the polyploids, AB genome plants showed a larger mesophyllsurface area per unit leaf area as compared with AG and ABDgenome plants. Therefore, either the D or the G genome seemsto have the effect of decreasing the mesophyll surface areaper unit leaf area. A decrease of the compactness of leaf bladeand the mesophyll surface area per unit leaf area in the polyploidswas considered to be associated with the reduction of theirphysiological activities on the unit leaf area basis. Triticum, Aegilops, wheat, mesophyll surface area, leaf anatomy, genome, photosynthesis     

Digitoxin Biosynthesis in Isolated Mesophyll Cells and Cultured Cells of Digitalis

In the laminae of Digitalis, most of the digitoxin present isfound in the mesophyll. A new method for determining the amountof digitoxin biosynthesis using a digitoxin antibody was devisedto estimate this activity in isolated mesophyll cells and culturedcells. Isolated mesophyll cells showed significant activity,which suggests that the site of biosynthesis and the accumulationof cardenolides in a lamina of Digitalis is mainly in the mesophyllcells. Of five liquid cultures of D. purpurea; green shoot-formingcultures, white shoot-forming cultures, root-forming cultures,undifferentiated green cells and undifferentiated white cells,the green shoot-forming cultures had the highest activity. Thewhite shoot-forming cultures had about one-third the activityof the green shoot-forming cultures, and the other three cultureshad very low activity. No stimulatory effect of light was foundduring the 48-h incubation. (Received January 19, 1984; Accepted June 8, 1984)     

Effects of Copper Toxicity on Leaves of Oregano (Origanum vulgare subsp. hirtum)

The effects of increasing concentrations of soil copper on anumber of leaf structural parameters in oregano plants werestudied to determine the effect of copper toxicity. Copper-stressedleaves were small and chlorotic and underwent a thickening oftheir lamina, due principally to an increase in the number andvolume of mesophyll cells. The number of stomata and glandularand non-glandular hairs increased significantly. Chloroplastsof mesophyll cells declined dramatically in number and volume.Grana and stroma thylakoids of chloroplasts did not undergoany noticeable alterations, but starch grains disappeared, plastoglobulibecame larger and the double membrane limiting the chloroplastbecame dilated. Leaf chlorosis was determined by total chlorophyllanalysis and measurement of the leaf Cu, Fe and Mg content.The effects of copper toxicity on oregano leaves comprised significantstructural alterations which reflect reduced metabolic activity.Copyright 2001 Annals of Botany Company Origanum vulgare subsp, hirtum, oregano, copper toxicity, leaf, structure and ultrastructure, morphometry, inorganic elements, tissue relative volumes