Spongy Mesophyll Research Articles

Influencing factors and structural characterization of hyperhydricity of in vitro regeneration in Brassica oleracea var. italica

Yu, U., Zhao, Y.-Q., Zhao, B., Ren, S. and Guo, Y.-D. 2011. Influencing factors and structural characterization of hyperhydricity of in vitro regeneration in Brassica oleracea var. italica. Can. J. Plant Sci. 91: 159-165. This study examines factors that affect the occurrence of hyperhydric tissue in in vitro cultures of Brassica oleracea variety italica. The anatomy of normal and hyperhydric leaves of plantlets regenerated from the hypocotyls was compared using scanning electron microscopy and transmission electron microscopy. In hyperhydric leaves palisade tissue was absent and the spongy mesophyll displayed large, unorganized intercellular spaces. Hyperhydric leaves had abnormal stomata with deformed guard cells. Significant ultrastructural differences were observed between chloroplasts in normal and hyperhydric leaves. The effects of zeatin, indoleacetic acid, silver nitrate and sucrose on the formation of hyperhydric shoots were studied. Zeatin was the most important factor, followed by sucrose concentration, AgNO3 and indoleacetic acid. The process of hyperhydricity was found to be reversed by increasing the agar concentration and eliminating NH4NO3 from the macro-elements in the MS medium. This is the first report of hyperhydricity in Brassica oleracea, and our study gives a better understanding of the factors that influence hyperhydricity during in vitro regeneration in Brassica crops.

The effectiveness of stilbenes in resistant Vitaceae: Ultrastructural and biochemical events during Plasmopara viticola infection process

Leaves of different Vitis vinifera L. cultivars, susceptible or resistant to downy mildew, Chasselas, Solaris, IRAC 2091 (cvs. Gamaret x Bronner) and Muscadinia rotundifolia were inoculated with Plasmopara viticola. Samples were then examined by scanning and transmission electron microscopy, by light microscopy and for their ability to synthesise stilbenes. These phytoalexins were strictly analysed at infection sites. In the susceptible Chasselas, P. viticola colonises, at 72h post-infection (hpi), all of the spongy mesophyll with functional haustoria and produces mainly the non toxic piceide. No necrotic zone was observed on Chasselas leaves. The ultrastructural response to downy mildew infection is different in each of the other three resistant grape cultivars. In Solaris, where leaf necrosis are rapidly induced, the infection is restricted to the upper part of the loose spongy mesophyll, and associated with a rapid cell wall disruption and the dispersion of cytoplasmic content along with the production of viniferins. In IRAC 2091, leaf necrosis are quite similar to those observed on Solaris but the infected plant cell, as well as the haustoria, show high electron dense cellular particles without any recognisable organelles, probably related to the effect of the toxic compound pterostilbene, which is synthesised in this grape cultivar. In M. rotundifolia leaf necrosis are much more scarce and smaller than in other cultivars, but pathogen and plant cells are both strongly affected, with concomitant expulsion of cytoplasmic materials through the stomata after P. viticola penetration. In this cultivar, the concentration of all identified stilbenes exceeds 1×10³ μmol mg(-1) FW. The critical role of stilbenes in the resistance of Vitis spp. is discussed.

Plasmodesmal receptor-like kinases identified through analysis of rice cell wall extracted proteins

In plants, plasmodesmata (PD) are intercellular channels that function in both metabolite exchange and the transport of proteins and RNAs. Currently, many of the PD structural and regulatory components remain to be elucidated. Receptor-like kinases (RLKs) belonging to a notably expanded protein family in plants compared to the animal kingdom have been shown to play important roles in plant growth, development, pathogen resistance, and cell death. In this study, cell biological approaches were used to identify potential PD-associated RLK proteins among proteins contained within cell walls isolated from rice callus cultured cells. A total of 15 rice RLKs were investigated to determine their subcellular localization, using an Agrobacterium-mediated transient expression system. Of these six PD-associated RLKs were identified based on their co-localization with a viral movement protein that served as a PD marker, plasmolysis experiments, and subcellular localization at points of wall contact between spongy mesophyll cells. These findings suggest potential PD functions in apoplasmic signaling in response to environmental stimuli and developmental inputs.Electronic supplementary materialThe online version of this article (doi:10.1007/s00709-010-0251-4) contains supplementary material, which is available to authorized users.

Micromorpho-Anatomical Examination of 2,4-D Phytotoxicity in Grapevine (Vitis vinifera L.) Leaves

The anatomical and micro-morphological alterations as induced by the auxinic herbicide, 2,4-D (2,4-dichlorophenoxy acetic acid) have not yet been elucidated for a commercially important fruit crop such as grapevine despite its super sensitivity to 2,4-D. Light and scanning electron microscopy techniques were employed to examine 2,4-D induced internal and external structural abnormalities in Merlot grapevines (Vitis vinifera L.). Healthy leaves were dorsiventrally flattened with well developed patterns of cellular structure and composition involving adaxial palisade parenchyma and abaxial spongy mesophyll. Dorsiventral variations in epidermal features involved large epidermal cells on the adaxial surface, and trichomes and stomata with turgid elliptical guard cells on the abaxial surface. The 2,4-D injured leaves were small and enated; the veins were fasciated with rugose bands of lamina existing between fasciated veins. The epidermal cells aggregated instead of being positioned coplanar to the epidermal plane. The adaxial elongated palisade parenchyma cells were transformed into an ovoid shape with intercellular spaces. An extensive development of replacement tissues took place on the abaxial surface wherein the stomata became roundish and were either raised or sunken with collapsed and cracked guard cells that developed abnormal outer stomatal ledges. These abnormalities are expected to severely perturb the vital functions of photosynthesis and transpiration ultimately leading to vine death attributable, at least in part, to the injured leaves.

The infection processes of Sclerotinia sclerotiorum in cotyledon tissue of a resistant and a susceptible genotype of Brassica napus

Sclerotinia sclerotiorum can attack >400 plant species worldwide. Very few studies have investigated host-pathogen interactions at the plant surface and cellular level in resistant genotypes of oilseed rape/canola (Brassica napus). Infection processes of S. sclerotiorum were examined on two B. napus genotypes, one resistant cultivar 'Charlton' and one susceptible 'RQ001-02M2' by light and scanning electron microscopy from 2 h to 8 d post-inoculation (dpi). The resistant 'Charlton' impeded fungal growth at 1, 2 and 3 dpi, suppressed formation of appresoria and infection cushions, caused extrusion of protoplast from hyphal cells and produced a hypersensitive reaction. At 8 dpi, whilst in 'Charlton' pathogen invasion was mainly confined to the upper epidermis, in the susceptible 'RQ001-02M2', colonization up to the spongy mesophyll cells was evident. Calcium oxalate crystals were found in the upper epidermis and in palisade cells in susceptible 'RQ001-02M2' at 6 dpi, and throughout leaf tissues at 8 dpi. In resistant 'Charlton', crystals were not observed at 6 dpi, whereas at 8 dpi they were mainly confined to the upper epidermis. Starch deposits were also more prevalent in 'RQ001-02M2'. This study demonstrates for the first time at the cellular level that resistance to S. sclerotiorum in B. napus is a result of retardation of pathogen development, both on the plant surface and within host tissues. The resistance mechanisms identified in this study will be useful for engineering disease-resistant genotypes and for developing markers for screening for resistance against this pathogen.

A Role for AUXIN RESISTANT3 in the Coordination of Leaf Growth

The characteristically flat structure of Arabidopsis thaliana vegetative leaves requires coordinating the growth of the epidermal, palisade mesophyll, spongy mesophyll and vascular tissues. Mutations disrupting such coordination or the specific growth properties of any of these tissues can cause hyponasty, epinasty, waviness or other deviations from flatness. Here, we show that the incurvata6 (icu6) semi-dominant allele of the AUXIN RESISTANT3 (AXR3) gene causes leaf hyponasty. Cotyledons and leaves of icu6/AXR3 plants exhibited reduced size of adaxial pavement cells, and abnormal expansion of palisade mesophyll cells. Enhanced auxin responses in the adaxial domain of icu6/AXR3 developing cotyledons and leaves correlated with increased cell divisions in the adaxial epidermis. Leaf incurvature in icu6/AXR3 leaves was alleviated by loss-of-function alleles of the ASYMMETRIC LEAVES1 (AS1) and AS2 genes, which restrict the expression of class I KNOX genes to the shoot apical meristem and regulate cell proliferation in leaf primordia. Taken together, our results suggest that an interaction between auxin responses and the AS1-AS2 pathway coordinates tissue growth during Arabidopsis thaliana leaf expansion.

Quantifying arsenic-induced morphological changes in spinach leaves: implications for remote sensing

Arsenic (As) is a common soil contaminant that can be accumulated into plant parts. The ability to detect As in contaminated plants is an important tool to minimize As-induced health risks in humans. Near-infrared (NIR) spectra are strongly affected by leaf structural characteristics. Therefore, quantitative analyses of structural changes in the arrangement of mesophyll cells caused by As will help to explain spectral responses to As. The objectives of this study were to use stereological methods to quantify internal structural changes in leaves with As treatment in spinach plants, and to relate these changes to leaf spectral properties in NIR spectra. Hydroponically grown spinach was treated with 0, 5, 10 and 20 μmol l−1 for four weeks in a growth chamber. Spectral properties of leaves were obtained for visible and infrared frequencies. Leaf structural properties, such as mesophyll thickness and mesophyll surface area, were measured using stereological methods. Quantitative analysis of leaf structure showed that total leaf thickness and intercellular spaces in spongy mesophyll cells decreased with increasing As treatment. Changes in leaf reflectance in NIR wavelengths were strongly correlated with leaf As concentration and leaf structural changes. Multiple linear regression of leaf reflectance values at the highest correlated wavelengths (1048, 1098 and 1080 nm) generated an R 2 value of 0.69. Results from this study support the hypothesis that relationships between leaf structure and reflectance may be useful in the interpretation of spectral data to detect plant leaf As concentration.

ANATOMICAL CHARACTERISTICS OF LEAF MESOPHYLL ON ROSA RUGOSA AND THEIR HYBRID PLANT

The variation in structure of the leaf mesophyll tissue on Rosa rugosa and their hybrid plants were anatomically compared. In R. rugosa, the epidermal cells composed large, thick cuticle with wax layers on the abaxial and adaxial side. The lower epidermal cells are significantly developed with enlarged, tightly packed. These cells can be brought about by various stresses, such as drought, waterlogging, salt damage, excess heat, damage to the leaf by pest and other agents. Especially they may also act as a water storage tissue in plants. The palisade cells found tightly packed, and connected to the bundle sheath cells at the level of the phloem. In contrast to the R. rugosa, the thin leaves have long palisade cells that occupy approximately one-third to one-half of the blade thickness in hybrid plants. In these leaves, palisade cells and spongy mesophyll are not clearly differentiated. These cells are loosely arranged and contained intercellular spaces. Epidermal cells on both side flattened and composed thin layers compared to the R. rugosa. In the leaves of R. rugosa, volatile organic compounds (VOCs) such as Rugosal A or pectic substances are observed throughout in the epidermal cells. They stained in red-purplish color with toluidine blue-O. We conclude that the wild rose plant, R. rugosa may be a useful germplasm source for the plant breeders.

Untangling metabolic and spatial interactions of stress tolerance in plants. 1. Patterns of carbon metabolism within leaves

The localization of the key photoreductive and oxidative processes and some stress-protective reactions within leaves of mesophytic C(3) plants were investigated. The role of light in determining the profile of Rubisco, glutamate oxaloacetate transaminase, catalase, fumarase, and cytochrome-c-oxidase across spinach leaves was examined by exposing leaves to illumination on either the adaxial or abaxial leaf surfaces. Oxygen evolution in fresh paradermal leaf sections and CO(2) gas exchange in whole leaves under adaxial or abaxial illumination was also examined. The results showed that the palisade mesophyll is responsible for the midday depression of photosynthesis in spinach leaves. The photosynthetic apparatus was more sensitive to the light environment than the respiratory apparatus. Additionally, examination of the paradermal leaf sections by optical microscopy allowed us to describe two new types of parenchyma in spinach-pirum mesophyll and pillow spongy mesophyll. A hypothesis that oxaloacetate may protect the upper leaf tissue from the destructive influence of active oxygen is presented. The application of mathematical modeling shows that the pattern of enzymatic distribution across leaves abides by the principle of maximal ecological utility. Light regulation of carbon metabolism across leaves is discussed.

Visualizing Localizations and Movement of Anthracene in Kandelia candel (L.) Druce Leaves by Fluorescence Microscopy

Here, for the first time, fluorescence microscopy (FM) was coupled with leaf autofluorescence to visualize and track trace levels of anthracene (An) in living Kandelia candel (L.) Druce leaves, without destructive chemical extraction techniques. The experimental results revealed that, after tracking over 96 hours, An adsorbed onto the leaf surface was moved through the upper cuticle and through the stomata of the lower side into the internal leaf tissues. An was identifiable in six separate locations within the K. candel leaves: the first hypodermis, the second hypodermis, and the upper palisade tissue moving from the upper cuticle; the lower hypodermis and the lower palisade tissue moving from the stomata of the lower side; and the spongy mesophyll moving from both sides. Under the same exposure conditions, the impact of An adsorbed at the center of the upper side of the leaf surface was much less than that at the edges of the leaf surface. However, after 96 hours of exposure to An, the amount of An transferred into the inner leaf tissues at the center of the leaf was higher than at the edges, which might provide important new information concerning how An enters, is moved, and is distributed within the K. candel leaves. Furthermore, this FM technique provided us with a noninvasive tool for visualizing and tracking the movement and storage locations of PAHs within K. candel leaves based only on the autofluorescence of leaf tissues as revealed by fluorescence microscopy.

Differences in morpho-anatomical structure of ozone-sensitive and ozone-resistant tobacco cultivars

Tropospheric ozone causes visible injuries in selected plants. Some plant species have been recognized as resistant and sensitive to ozone. Differences in the response to ozone of two kinds of plants are interesting because of practical implications. Resistant cultivars (without visible symptoms) will be more valuable for agriculture, forestry and horticulture. It is, however, necessary to find out the reason of the occurrence of the visible symptoms. The presented studies focused on selected morphological and anatomical differences between well-known ozone-sensitive (Bel W3) and -resistant (Bel B) cultivars of tobacco plants. Daily growth of the sensitive cultivar was higher than that of the resistant one. This tendency was also valid for the leaf growth which might have been the response of the sensitive cultivar to decreased photosynthetic leaf area (necrosis) caused by ozone. Morphological investigations revealed thinner upper epidermal cells in the sensitive cultivar. Moreover, a decrease of spongy mesophyll cell layers was observed. The obtained results suggest that it is the anatomical structure that may be partly responsible for ozone resistance - wider epidermal cells, more spongy mesophyll cell layers.

Leaf anatomical characteristics and physiological responses to short-term drought in Ziziphusmauritiana (Lamk.)

The aim of this work was to study the association between leaf anatomical characteristics and response to short-term drought stress in Ziziphus mauritiana Lamk. Six Z. mauritiana cultivars (Seb, Gola, Umran, Keitly, Q-29 and B-5/4) under field conditions in Israel's Negev desert were studied. Width of palisade mesophyll, spongy mesophyll and epidermis, xylem number and diameter in mid-vein were investigated with light microscopy. Short-term (3 weeks) drought stress tolerance was evaluated by monitoring plant response (leaf transpiration, diffusive resistance, chlorophyll fluorescence, leaf water potential and leaf relative water content). Greater epidermis and mesophyll widths and xylem diameters and densities were associated with increased tolerance to short-term water deficit expressed by preliminary wilting symptoms and proportional differences between initial and final physiological parameters. Significantly larger differences were found in Keitly, Umran and B-5/4 than in Seb, Gola and Q-29, indicating that the former cultivars are more sensitive to drought stress. Our results indicate that tolerance in descending order was Seb, Q-29, Gola, B-5/4, Keitly and finally Umran. The existence of an association between anatomical characteristics and short-term drought stress tolerance based on physiological responses is suggested.

Macro- and microscopic leaf characteristics of six grapevine genotypes ( Vitis spp.) with different susceptibilities to grapevine downy mildew

This work reports the leaf morphology of six grapevine genotypes, five belonging to Vitis vinifera and one to Vitis ripari a. Earlier studies on these genotypes showed different levels of susceptibility to grapevine downy mildew ( Plasmopara viticola ). The aim of this work was to detect differences between the leaf morphology of these cultivars at the macro- and microscopic levels, and to characterize morphological traits which could be associated with susceptibility and resistance to downy mildew. An ampelographic description of each genotype was used to develop a scheme illustrating the characteristic leaf morphology. The density and morphology of the trichomes and the stomatal index was assessed by means of microscopical techniques. Distinct macro and microscope differences among the genotypes were seen. No clear relation between ampelographic characteristics and susceptibility to downy mildew was observed. The two cultivars that in earlier studies were found to be the least susceptible to downy mildew were the most similar in terms of their spongy mesophyll. Both showed very little or no wax on the abaxial surface of their leaves.

Caractérisation histologique de la bractée inflorescentielle de Tilia cordata

Tilia's inflorescence includes a bract which is fused with the base of peduncle. Histology technic was used to investigate Tilia bract. Our studies allow us to see that the vascular system of bract is similar to the vascular system of stem, moreover the lamina part of the bract does not show a adaxial palisade mesophyll; only a spongy mesophyll is present. With a vascular system of stem and in the absence of palisade tissue, we suggest Tilia bract is a cladode structure.

Do changes in light direction affect absorption profiles in leaves?

Leaf anatomy plays a functional role in propagating light through the leaf; palisade mesophyll has been shown to facilitate the channelling of collimated light deeper into the spongy mesophyll. Direct measurements of the propagation of diffuse light into the leaf, however, are absent. Using chlorophyll fluorescence imaging of leaf cross-sections, we measured light absorption profiles in leaves under direct (collimated), diffuse and low-angle monochromatic light. Low-angle and diffuse light was absorbed closer to the irradiated surface than direct light perpendicular to the surface. The shapes of internal absorption profiles indicated that leaves were influenced by the directional quality of the incident light. In addition, absorption profiles revealed that leaves were not simple light absorbing objects and that cellular anatomy influences the direction of light travelling into the mesophyll. These findings also suggest a mechanism for previously measured differences in leaf level photosynthesis under opposing light regimes.

10.1007/s11183-008-1008-1

Hydroponic experiments were conducted to study the effect of Pb on growth, leaf antioxidant enzyme activities, and ultrastructure of the accumulating ecotype (AE) and non-accumulating ecotype (NAE) of Sedum alfredii Hance. AE was found to be more tolerant to excessive Pb levels in growth medium. Concentrations of Pb in the shoots of the AE were 1.98 times higher than those in the NAE when 0.2 mM Pb was supplied. Both chlorophyll a and b did not decrease significantly in AE plants after Pb treatment, while a significant decrease was noted in chlorophyll a and b of NAE plants treated with Pb concentrations greater than 0.05 mM. The results showed that activities of superoxide dismutase (SOD) and catalase (CAT) were elevated in the leaves of AE under Pb stress. However in NAE, Pb-caused enhancement was noticed only in the activity of SOD while activity of CAT was declined as compared to the control plants. With increased Pb level, malondialdehyde (MDA) content increased significantly in both ecotypes of S. alfredii, indicating that Pb toxicity led to lipid peroxidation and membrane damage, but MDA content in the leaves of NAE was always higher than in AE plants. The ultrastructural analysis of the spongy mesophyll cells revealed that excessive Pb concentrations obviously damaged the cell membrane, chloroplasts, and mitochondria of both the ecotypes but damage was more severe in NAE. Although growth, leaf physiology, and ultrastructure of both the ecotypes were affected by Pb treatment, deleterious effects were more pronounced in NAE.

Immunogold labelling to localize polyphenol oxidase (PPO) during wilting of red clover leaf tissue and the effect of removing cellular matrices on PPO protection of glycerol‐based lipid in the rumen

The enzyme polyphenol oxidase (PPO) reduces the extent of proteolysis and lipolysis within red clover fed to ruminants. PPO catalyses the conversion of phenols to quinones, which can react with nucleophilic cellular constituents (e.g. proteins) forming protein-phenol complexes that may reduce protein solubility, bioavailability to rumen microbes and deactivate plant enzymes. In this study, we localized PPO in red clover leaf tissue by immunogold labelling and investigated whether red clover lipid was protected in the absence of PPO-induced protein-phenol complexes and plant enzymes (lipases). PPO protein was detected to a greater extent (P < 0.001) within the chloroplasts of mesophyll cells in stressed (cut/crushed and wilted for 1 h) than freshly cut leaves for both palisade (61.6 and 25.6 Au label per chloroplast, respectively) and spongy mesophyll cells (94.5 and 40.6 Au label per chloroplast, respectively). Hydrolysis of lipid and C18 polyunsaturated fatty acid biohydrogenation during in vitro batch culture was lower (P < 0.05) for wild-type red clover than for red clover with PPO expression reduced to undetectable levels but only when cellular matrices containing protein-phenol complexes were present. Damaging of the leaves resulted in over a doubling of PPO detected within mesophyll cells, potentially as a consequence of conversion of the enzyme from latent to active form. PPO reduction of microbial lipolysis was apparent in macerated red clover tissue but not in the absence of the proteinaceous cellular matrix, suggesting that the PPO mechanism for reducing lipolysis may be primarily through the entrapment of lipid within protein-phenol complexes.

Morpho-anatomical and physiological responses of two Dendranthema species to waterlogging

The responses to waterlogging of the two Dendranthema species D. nankingense (Nakai) Tzvel. and D. zawadskii (Herb.) Tzvel. contrast considerably. Although the stress induced wilting and leaf chlorosis in both species, symptoms were more apparent and appeared earlier in the intolerant D. nankingense. In the more tolerant D. zawadskii, adventitious roots formed above the flooding level, and aerenchyma developed in the root, stem and leaf. The D. zawadskii palisade parenchyma was thicker, and larger intercellular spaces developed in the spongy mesophyll. The activities of alcohol dehydrogenase, pyruvate decarboxylase and lactate dehydrogenase were enhanced in roots of both species following the imposition of stress. In D. zawadskii the rise in ADH activity was more pronounced, while D. nankingense showed a significantly higher LDH activity. The activities of superoxide dismutase, ascorbate peroxidase and catalase were all higher in the leaves of D. zawadskii than in D. nankingense, and the leaves of D. nankingense showed a higher content of malondialdehyde throughout the period of waterlogging. Photosynthesis was decreased in both species, and there was a significant fall in the intercellular CO 2 concentration in D. zawadskii. These data suggested that the greater relative waterlogging tolerance of D. zawadskii appears to depend on a combination of metabolic and morpho-anatomical responses.

Localizing Starch Reserves in Mandevilla sanderi (Hemsl.) Woodson Using a Combined Histochemical and Biochemical Approach

Mandevilla sanderi is a plant of tropical origin of great horticultural interest because of its abundant flowering and its persistent foliage. Vegetative propagation requires the removal of leafy branches on the mother plant to produce cuttings. This loss of biomass must be compensated for by the growth of new branches thanks to the mobilization of reserves within the plant. Lack of knowledge about the physiology of this species therefore makes it necessary to characterize its different organs both at the level of their anatomic organization as well as at the level of their ability to store starch. After histological characterization of the different organs (leaves, stems, and roots), starch reserves were localized by histochemical analysis and quantified by biochemical analysis. Starch grains are mainly found in the parenchymatous cortex, the parenchymatous pith and xylem parenchyma cells, in tuberous roots and stems, and in the palisade and spongy mesophyll of leaves. In 22-week-old plants, the greatest quantity of starch is found in the leaves, whereas the tuberous roots have the highest concentration. The histological description of the different organs of Mandevilla sanderi and the localization of starch reserves allow us to assess the potential role of the different organs in plant growth and development. In the particular case of mother plant management, it is hoped that this knowledge will make it possible to optimize conditions for removing leafy branches.

Micromorphology, anatomy and volatile constituents of leaf in some Lamiaceae species

The objective of this study is to determine the range of variation in certain micromorphological, anatomical and biochemical characters of leaf within three spontaneous Lamiaceae species: Hyssopus officinalis L. (from Montenegro Republic), Thymus comosus Heuff. and Ocimum basilicum L. (both from Romania) The research material was collected in anthesis stage of plant development. Anatomical characters of leaf epidermis were examined by light microscopy. Scanning electron microscopy was used to examine leaf surface and trichomes. The qualitative analysis of the volatile oils has been carried out using GC-MS. All examined species had bifacial heterofacial and amphistomatous leaf. The stomata are diacytic. The glandular hairs consist of one epidermic basal cell, a uni- or multicellular stalk and a uni- or multicellular secretory head. The non-glandular trichomes are simple, short or long, multicellular uniseriate. The variable micromorphological and anatomical characters of leaf are rather quantitative than qualitative, as follows: 1. the mesophyll thickness; 2. the density of stomata and trichomes; 3. the number and size of intercellular air spaces of spongy mesophyll. The volatile oils produced by the investigated species differ in their composition. The aromatic value and therapeutical efficiency of these products strictly depend on the moment of plant development, metabolic transformations and climatic conditions. Among the analyzed species, the main constituents of volatile oils are: thymol, carvacrol, β-cariophylene, germacrene D, δ-cadinol, linalool and methylchavicol.