Anatomical considerations related to photosynthesis in cotton (Gossypium hirsutum L.) leaves, bracts, and the capsule wall

Light and electron microscopy was used to relate histologicaland ultrastructural differences of cotton (Gossypium hirsutumL.) leaves, bracts, and capsule walls to their different photosyntheticactivities. Light microscopy revealed that the leaf thicknesswas approximately 152µm, had a well-defined internal organizationwith elongated palisade mesophyll cells and loosely packed spongymesophyll cells. In contrast, the bract was thinner (111 µm),lacked a defined palisade layer, and was largely composed ofinternal air spaces. The capsule wall was very thick (1013µm)and composed of numerous tightly packed, paren-chymatous corticalcells with little or no intercellular air space. Chloroplastswith well-defined granal stacks and extensive stroma lamellaewere observed in each of these three tissues, however, theirdensity was always greater in the palisade cells of the leafcompared to spongy mesophyll cells of the bract and the parenchymatouscells of the capsule wall. The low rates of photosynthesis inthe bracts and the capsule wall were associated with the internalorganization of these tissues. Key words: Cotton, photosynthesis, anatomy, cuticle, tissues     

Structural Characteristics and Fatty Acid Composition of Psophocarpus tetragonolobus Seeds

Winged bean (Psophocarpus tetragonolbtis) seed coat in the hilarregion consists of a double layer of sclereids, tracheid barand spongy parenchyma cells. This is contrasted to the seedcoat structure on either side of the hilar region, which hasa single layer of sclereids, columnar cells and crushed parenchymacells. Cotyledonary cells are large (50 to 100µm in diameter)and have cell walls 2·4 to 4·7 µm thickwith pit-pair structures. Protein bodies and lipid bodies arethe main structural components of the cytoplasm while only asmall number of starch granules are present in each cell. Themajor portion of the lipid can be removed by non-polar solventsand contains oleic and linoleic acids as the predominant unsaturatedfatty acids. High levels of behenic acid were present in both‘free’ and ‘bound’ lipids. Psophocarpus tetragonolobus (L.) DC., winged bean, seed structure, seed coat, protein bodies, lipid bodies, fatty acids, oleic acid, linoleic acid     

Ultrastructure of Protein Crystals in Potato and Tomato Trichomes

Large protein crystals were located in the leaf and stem trichomesof Solanum tuberosum L. and Lycopersicon esculentum Mill. Inpotato the crystals ranged from 1.05 to 4.5 µm (average2.3 µm) on a side and in tomato they ranged from 1.16to 3.5 µm (average 2.7 µm) on a side. The proteinnature of the crystals was determined by histochemical stainingwith Coumassie brilliant blue R250 and aniline blue black. Thecrystalline structure of the inclusions was observed in ultrathinsections using electron microscopy. In potato, in cleared areasof the cytoplasm, ribosomes were observed scattered among proteinfilaments. The filaments were approximately 7 nm in diameter.Morphologically similar crystals were observed in the tomatotrichomes but the protein filaments were smaller (approximately4 nm in diameter). Protein crystals were also observed in palisadeand spongy parenchyma and epidermal leaf cells in tomato. Protein crystals, trichomes, potato, Solanum tuberosum L., tomato, Lycopersicon esculentum Mill., ultrastructure     

Leaf anatomy of highbush blueberry grownin vitro and during acclimatization toex vitro conditions

Leaves of micropropagated highbush blueberry (Vaccinium corymbosum) cv. ‘Bluetta’ have been observed during the acclimatization phase. In vitro-developed leaf cells were circular and small, the spongy parenchyma was discontinuous and disorganized and formed by 1–2 layers of cells with large intercellular spaces and the palisade to spongy mesophyll thickness ratio was 1:1.5. After rooting ex vitro, the first leaves formed under natural conditions showed substantial changes in the anatomical characteristics. After 6 months, the plants produced leaves similar to those in field-grown plants. The palisade cells were rectangular, the spongy parenchyma was formed by 3–4 layers of cells and the intercellulars were around the stomata. Leaves from field-grown plants lost 24 % of water during 150 min after excision while leaves from in vitro shoots lost about 50 % of water in the same time. Leaves from in vitro shoots showed a higher number of smaller stomata (361 per mm²), with the guard cells forming a circular ring; the stomata frequency in field-grown leaves was 241 per mm² and the guard-cells were elliptical.     

Leaf anatomy during leaf development of photoautotrophically <Emphasis Type="Italic">in vitro</Emphasis>-grown tobacco plants as affected by growth irradiance

Tobacco (Nicotiana tabacum L.) plants were cultured in vitro photoautotrophically at three levels of irradiance (PAR 400–700 nm): low (LI, 60 μmol m⁻² s⁻¹), middle (MI, 180 μmol m⁻² s⁻¹) and high (HI, 270 μmol m⁻² s⁻¹). Anatomy of the fourth leaf from bottom was followed during leaf development. In HI and MI plants, leaf area expansion started earlier as compared to LI plants, and both HI and MI plants developed some adaptations of sun species: leaves were thicker with higher proportion of palisade parenchyma to spongy parenchyma tissue. Furthermore, in HI and MI plants palisade and spongy parenchyma cells were larger and relative abundance of chloroplasts in parenchyma cells measured as chloroplasts cross-sectional area in the cell was lower than in LI plants. During leaf growth, chloroplasts crosssectional area in both palisade and spongy parenchyma cells in all treatments considerably decreased and finally it occupied only about 5 to 8 % of the cell cross-sectional area. Thus, leaf anatomy of photoautotrophically in vitro cultured plants showed a similar response to growth irradiance as in vivo grown plants, however, the formation of chloroplasts and therefore of photosynthetic apparatus was strongly impaired.     

Leaf-like Structure in the Photosynthetic, Succulent Stems of Cacti

This research examined the hypothesis that as cacti evolve tothe leafless condition, the stem epidermis and cortex becomemore leaflike and more compatible with a photosynthetic role.All cacti in the relict genus Pereskia have non-succulent stemsand broad, thin leaves. All members of the derived subfamilyCactoideae are ‘leafless’, having an expanded cortexthat is the plant's only photosynthetic tissue. In Pereskia,leaves have a high stomatal density (mean: 50.7 stomata mm^–2in the lower epidermis, 38.1 mm^–2 in the upper epidermis),but stems have low stomatal densities (mean: 11.3 mm ₂, threeof the species have none). Stems of Cactoideae have a high stomataldensity (mean: 31.1 mm^–2, all species have stomata). Theouter cortex cells of stems of Cactoideae occur in columns,forming a palisade cortex similar to a leaf palisade parenchyma.In this palisade cortex, the fraction of tissue volume availablefor gas diffusion has a mean volume of 12.9%, which is identicalto that of Pereskia leaf palisade parenchyma. Pereskia stemcortex is much less aerenchymatous (mean: 5.3% of cortex volume).Cactoideae palisade cortex has a high internal surface density(0.0207 cm₂ cm^–2 which is higher than in Pereskia stemcortex (0.0150 cm₂ cm^–3) but not as high as Pereskia leafpalisade parenchyma (0.0396 cm₂ cm^–3). Pereskia stem cortexhas no cortical bundles, but Cactoideae cortexes have extensivenetworks of collateral vascular bundles that resemble leaf veins. Cactaceae, cactus, intercellular space, stomatal density, internal surface/volume, evolution     

The Effect of Salinity on Growth of Phaseolus vulgaris L.: I. Anatomical Changes in the First Trifoliate Leaf

When plants of Phaseolus vulgaris were grown in culture solutioncontaining 48 m mol l^–1 sodium chloride, the first trifoliateleaves were always smaller in area than those of control plants.The leaves of the salt-treated plants however could become thicker.This increase in thickness was brought about by the increasein the thickness of the spongy parenchyma layer. The palisadeparenchyma layer was always thinner than that in the controlleaves. While these latter leaves expanded predominantly bycell division, this only held for the early stages of expansionof the leaves of salt-treated plants. In this case cell divisionceased when the leaves were about half their maximal size andfurther increase in area was brought about by an increase involume of the spongy parenchyma cells.     

Stomata and Structure of Tetraploid Apple Leaves cultured in Vitro

Leaves of anther-derived tetraploid apple (Malus pumila Mill.)shoots were examined by low-temperature scanning electron microscopy(LT-SEM). Leaves were serrate and wide with an undulating adaxialsurface due to convex epidermal cells, apparently without crystallineepicuticular wax. Stomata were absent from the adaxial surface,except for the marginal teeth which exhibited 40-60 stomataper leaf; they probably originated from residual mitotic activity.One third of abaxial stomata was occluded by the residual cuticleof the mother guard cell across the stomatal pore which rupturedwhen the stomata became functional. The stomatal index was 7·2(± 1·6) with 60-75 stomata mm^-2, i.e. abaxialstomata of tetraploid leaves expanded in vitro were less frequentthan those in triploid leaves either cultured in vitro (475-575stomata mm^-2) or grown on the tree (320-390 stomata mm^-2) wherethe stomatal index was 21 (± 4). Freeze-fracture transsectionsshowed that the tetraploid in vitro leaves were composed ofa layer of adaxial epidermal cells, followed by a single layerof palisade cells and four to five layers of spongy mesophyllcells and the abaxial layer of epidermal cells, in contrastto juvenile seedling-grown apple leaves in which the two layersof palisade cells comprised the majority (52-60%) of the leafvolume. The same morphological features, such as wide and lesspointed leaves, reduced stomatal density and stomatal index,and increased stomatal size that were previously reported fortree-grown tetraploid leaves were also expressed in vitro. Thus,causes of the stomatal deformation in tissue-cultured Rosaceaeare interpreted to be in part genetic and not purely environmental.Copyright1994, 1999 Academic Press Malus pumila Mill., apple, biotechnology, breeding, cryo-preservation, CO₂, juvenile, low temperature-scanning electron microscopy (LT-SEM), micropropagation, ploidy, stomata, tissue-culture, transpiration     

Light Environment within a Leaf I. Optical Properties of Paradermal Sections of Camellia Leaves with Special Reference to Differences in the Optical Properties of Palisade and Spongy Tissues

The attenuance (apparent absorbance), angular distribution oftransmitted light (scattering) and reflectance of paradermalsections of Camellia leaves were measured spectrophotometricallyand the data for the palisade and spongy tissues were compared. Attenuance in tissues could be expressed by Beer's law onlyfor wavelengths of strong absorption. At 680 nm, the apparentextinction coefficient of chlorophyll (e) for the spongy tissuewas about 1.4 times that for the palisade tissue. The largere for the spongy tissue is attributable mostly to the more effectiveincrease in the pathlength of light due to scattering at theinterfaces between the air space and cells because the differencebetween e for the two tissues was minimized by infiltrationof the air space in the tissues with a medium whose refractiveindex was similar to the index of the leaf cells. Scatteringwas larger for wavelengths of weak absorption, and the relativeincrease in attenuance caused by elongating the optical pathlengthwas even more prominent. Based on these data, we report an ecophysiological discussionof the internal light environment of a leaf and the meaningof the differentiation of mesophyll into the palisade and spongytissues. (Received May 18, 1983; Accepted September 21, 1983)     

Structural Adaptation of the Leaf Mesophyll to Shading

Structural characteristics of the mesophyll were studied in five boreal grass species experiencing a wide range of light and water supply conditions. Quantitative indices of the palisade and spongy mesophyll tissues (cell and chloroplast sizes, the number of chloroplasts per cell, the total cell and chloroplast surface area per unit leaf surface area) were determined in leaves of each of the species. The cell surface area and the cell volume in spongy mesophyll were determined with a novel method based on stereological analysis of cell projections. An important role of spongy parenchyma in the photosynthetic apparatus was demonstrated. In leaves of the species studied, the spongy parenchyma constituted about 50% of the total volume and 40% of the total surface area of mesophyll cells. The proportion of the palisade to spongy mesophyll tissues varied with plant species and growth conditions. In a xerophyte Genista tinctoria, the total cell volume, cell abundance, and the total surface area of cells and chloroplasts were 30–40% larger in the palisade than in the spongy mesophyll. In contrast, in a shade-loving species Veronica chamaedris, the spongy mesophyll was 1.5–2 times more developed than the palisade mesophyll. In mesophyte species grown under high light conditions, the cell abundance and the total cell surface area were 10–20% greater in the palisade mesophyll than in the spongy parenchyma. In shaded habitats, these indices were similar in the palisade and spongy mesophyll or were 10–20% lower in the palisade mesophyll. In mesophytes, CO₂ conductance of the spongy mesophyll accounted for about 50% of the total mesophyll conductance, as calculated from the structural characteristics, with the mesophyll CO₂ conductance increasing with leaf shading.     

Ultrastructural Changes in Chloroplasts of Quercus rotundifolia Lam. in Response to Evernic Acid

The amount of total chlorophyll, chlorophylls a and b as wellas the ratio of a to b decreased in chloroplasts isolated fromQuercus rotundifolia leaves, kept for 17 d in a solution of35.5 µM evernic acid in 1 mM Na HCO₃, when compared withthe chloroplasts of control leaves (kept in NaHCO₃). The chloroplastsin the spongy parenchyma were smaller and the amount of starchand plastoglobuli lower. The number of grana per chloroplastsection, the number of thylakoids per grana and the height ofgrana stacks were also less in the chloroplasts of leaves treatedwith evernic acid. Quantitative ultrastructural differenceswere determined by means of electron microscopy and image analysistechniques. Quercus rotundifolia Lam., chloroplasts, ultrastructure, lichens, evernic acid     

Cortical Bundles in the Persistent, Photosynthetic Stems of Cacti

We examined 62 species in 45 genera of the cactus subfamilyCactoideae; all had collateral cortical bundles that permeatedthe broad, water-storing inner cortex and extended to the baseof the outer, photosynthetic palisade cortex. Mean distancebetween cortical bundles was 0.75 mm, similar to the mean spacing(0.74 mm) of veins in leaves of Pereskia, a genus of relictleaf-bearing cacti. In 16 species, both young and extremelyold stem cortex was available for study: in all of these, olderbundles had larger amounts of phloem than did younger bundles,indicating that phloem had been produced for many years. Inten species, older bundles also had more xylem than youngerbundles. In two genera (Rhipsalis and Selenicereus) there werecaps of primary phloem fibres, and in a single species (Pilosocereusmortensenii) cortical bundle xylem contained libriform fibres.All cortical bundle tracheary elements were narrow (radius range,0.91–8.2 µm; mode, 1.8–2.7 µm), similarto Pereskia leaf vein elements (radius range, 1.8–2.7µm); this was much narrower than stem wood vessels (radiusrange, 10–42 um; mode, 23–28 µm). Longitudinalconduction of water and nutrients probably occurs predominantlyin stem wood, with cortical bundles maintaining the broad, voluminouscortex, the outer part of which is the plant's photosynthetictissue and the inner part of which stores water and starch.The cortex of the Cactordeae contains numerous leaflike characters;homeotic genes may be involved in its morphogenesis. Cactaceae, cortical bundles, homeotic, xylem, phloem, evolution     

The Preservation of Plant Cells, particularly Sieve Tubes, by Vacuum Freeze-drying

A vacuum freeze-drying apparatus is described. Cell contentswere preserved in small, rapidly frozen pieces of plant tissuedried for four hours at – 30° C. After drying, specimenswere either directly embedded with the resin ‘Epikote’or fixed with 2 per cent osmium tetroxide in benzene and subsequentlyembedded in ester wax or Epikote resin. Mesophyll cells and border parenchyma cells were preserved inleaf pieces, and cell contents are comparable with the protoplastsof living cells. In soybean leaf, files of parenchyma cellsoccur between palisade and spongy mesophyll cells, linking fineveins. Hand sections of frozen-dried Epikote-embedded petiolephloem from Primula obconica revealed a mature sieve tube containingstrands. Preservation by freeze-drying is taken as conclusiveevidence for the existence of transcellular strands in livingsieve tubes.     

LEAF ANATOMY OF TISSUE-CULTURED LIQUIDAMBAR STYRACIFLUA (HAMAMELIDACEAE) DURING ACCLIMATIZATION

Structural changes accompanying the acclimation process were observed in leaves of sweetgum, Liquidambar styraciflua, using light and transmission electron microscopy (TEM). Comparisons were made of leaves obtained from tissue culture, plantlets acclimated after transfer from the in vitro environment to soil, and field grown trees. Leaves of cultured plantlets lacked a differentiated palisade parenchyma and had spongy parenchyma interspersed with large air spaces. Field grown leaves showed distinct palisade and spongy tissues and a high cell density. New leaves from acclimated plantlets showed an elongation of the upper mesophyll with fewer intercellular spaces than cultured plants. Cells from leaves from in vitro plantlets had large vacuoles, limited cytoplasmic content and flattened chloroplast with an irregularly arranged internal membrane system. Acclimated and field leaf cells had a greater cytoplasmic content than cultured leaves, with the former having more dominate vacuoles. Chloroplasts had evident grana. Acclimated and field leaves had a well developed cuticle unlike leaves from culture.     

Leaf micromorphology of Antarctic pearlwort Colobanthus quitensis (Kunth) Bartl.

The leaf micromorphology of Antarctic pearlwort, Colobanthus quitensis (Kunth) Bartl. was analyzed. Plants were collected at King George Island (62°5′S, 58°23′W). Leaves were analyzed by optical and scanning electron microscopy, and quantitative analyses performed on leaf tissues and their internal geometry. C. quitensis leaves are ca. 588 μm thick, and composed of palisade and spongy parenchyma, respectively ca. 171 and 312 μm thick. Cuticles are thin and cover short epidermal cells. The central vein is surrounded by two bundles of achlorophyllous cells. Sclerenchymatic tissues are poorly developed. SEM analysis reveals faint striations over leaf surfaces. Stomata are present on both surfaces, but restricted to the leaf margins on the abaxial side. The ratio of mesophyll cell surface area per unit leaf area (Ames/A) is 34.2. The number of cells per cross-sectional area occupied was 24% higher for the palisade than for the spongy tissue, which determines a higher cell surface area per cross-sectional area for the former tissue. The authors correlate these results to plant ecological distribution in Antarctica and to water and carbon economy. Accepted: 14 January 2000     

Differential Responses of Buckwheat Leaf Cells to Growth Substances Stimulating Cell Division

Isolated buckwheat cotyledons form calli, roots or buds whencultured in an appropriate medium. A medium containing high2,4-D (5 mg 1^–1) and low KN (01 mg I^–1), which inducescallus formation, was found to stimulate cell division in thelayer between palisade and spongy parenchyma tissue after 72h. Low 2,4-D and low KN (01 mg I^–1 each), which stimulatesroot formation in buckwheat cotyledons, induces divisions primarilyin spongy parenchyma cells. In a high benzylaminopurine (10^–5M) and a low IAA (10^–6 M) medium, which favours bud induction,cell divisions were localized to the palisade layer. The differentialresponsiveness of leaf cells to various hormone treatments isdiscussed.     

Identification of the Excitable Cells in the Petiole of Mimosa pudica by Intracellular Injection of Procion Yellow

Excitable cells in the petiole of Mimosa pudica were locatedby microelectrode technique and stained with Procion YellowMx4R which was previously filled in the electrode and injectediontophoretically into the cells. Microscopic observations ofsections of the stained petioles revealed that protoxylem parenchymacells and narrow phloem cells were excitable. The protoxylemlocalized just inside the metaxylem was composed almost entirelyof the parenchyma cells which were 106.3±5.2 µmlong (mean±EM, n=15) and 14.2±0.6 µm indiameter (n =33). The excitable phloem cells were 76.4±4.1µm long (n=7) and 7.0±0.3 pan in diameter (n=37)and were thought to be companion cells or narrow parenchymacells or both. Amplitudes of action potentials recorded fromthe petiolar surface had a linear relation to those from theexcitable cells in the same petiole. From this fact and thearrangement of excitable cells in the petiole, we conclude thatwhen the transmission of action potential takes place in thepetiole all excitable cells in it are activated. ¹ Present address: 1st Department of Physiology, Hamamatsu UniversitySchool of Medicine, Handa-cho 3600, Hamamatsu 431-31, Japan. (Received September 7, 1982; Accepted November 8, 1982)     

Effect of UV-B Radiation on Leaf Optical Properties Measured with Fibre Optics

Changes in the internal light microenvironment in leaves ofplants of Brassica campestris L. cv. Emma, B. carinata L., andMedicago saliva L. cv. Armour in response to exposure to UV-B(UV-B, 280–320 nm) radiation were measured using a fibreopticmicroprobe. Plants were exposed for 2 weeks either to high visiblelight or to supplemental ultraviolet-B radiation. The spectral regime (400–700 nm; PAR) was measured eithermidway through the leaf palisade or the spongy mesophyll. Afterexposure to UV-B radiation leaves of Brassica campesiris attenuatedtransmitted light more than the controls. At the same time bothforward and back scattered light increased in the palisade andspongy mesophylls. In contrast, UV-treatment of Medicago salivaleaves increased light transmission into the palisade, whilethe back scattered component showed little change. Leaves ofcariiwla showed little change in response to UV. Other responsesto UV-B radiation included increases in leaf thickness, decreasedtotal chlorophyll content, and changes in UV-B screening pigmentsand chlorophyll fluorescence induction kinetics. Brassica campestriswas most sensitive to exposure to enhanced levels of UV-B radiation,whereas leaves of B. carinata were the least sensitive. Ourdata indicate that exposure to UV-B radiation altered the lightmicroenvironment within leaves of the species different ways.These changes appeared to be caused by alterations in pigmentcontent and leaf anatomy. In turn, the altered distributionof PAR within the leaf could influence photosynthesis. Key words: Brassica campestris, Brassica carinata, fibre optics, light scattering, Medicago saliva, optical properties, ozone depletion, photosynthesis, ultraviolet radiation     

Changes in chloroplast morphology of different parenchyma cells in leaves of Haberlea rhodopensis Friv. during desiccation and following rehydration

The size, shape, and number of chloroplasts in the palisade and spongy parenchyma layers of Haberlea rhodopensis leaves changed significantly during desiccation and following rehydration. The chloroplasts became smaller and more rounded during desiccation, and aggregated in the middle of the cell. The size and number of chloroplasts in the palisade parenchyma cells were higher than in spongy parenchyma. The good correlation observed between the size or number of chloroplasts and the cross-sectional area of mesophyll cells, the cross-sectional width of the leaf and its water content suggested that the palisade cells were more responsive to water availability than the spongy cells. Changes in chloroplast number during desiccation and rehydration process are characteristic features for desiccation-tolerant plants (especially in homoiochlorophyllous strategy).     

Ageing-related Anatomical and Ultrastructural Changes in Leaves of Birch (Betula pendula Roth.) Clones as Affected by Low Ozone Exposure

Effects of ozone on the leaf anatomy and ultrastructure of fivebirch (Betula pendula Roth.) clones were studied during onegrowing season in open-field conditions. Cumulative ozone exposurewas 1·5 times higher than ambient. Ozone exposure decreasedtotal leaf thickness in one, ozone sensitive, clone. The effecton palisade spongy mesophyll thickness was clone-specific, whilethe amount of palisade intercellular space was reduced in allclones. A second effect was a change in the relative amountsof adaxial and abaxial epidermis. In palisade and spongy parenchymacells of all clones, ozone increased the number of irregularand spherical shaped chloroplasts, the electron density of chloroplaststroma, swelling and curling of thylakoids, translucency ofthe mitochondrial matrix and also the amount of cytoplasmiclipids. In the sensitive clone shorter chloroplasts and reducedamount of starch were observed in ozone-exposed plants, whilst,in the tolerant clone, the size of chloroplasts and the amountof starch were unaffected. Ozone effects on number, size andelectron density of plastoglobuli and vacuolar tannin were clone-dependent.At the ultrastructural level, the normal leaf ageing processprogressed at different rates in the birch clones. Ozone acceleratedsenescence-related structural changes, in accordance with earlierobservations of deciduous species.Copyright 1995, 1999 AcademicPress Betula pendula Roth., birch, clones, ageing, ozone, leaf anatomy, ultrastructure