Spongy Mesophyll Layers Research Articles

Links between leaf anatomy and leaf mass per area of herbaceous species across slope aspects in an eastern Tibetan subalpine meadow.

Leaf anatomy varies with abiotic factors and is an important trait for understanding plant adaptive responses to environmental conditions. Leaf mass per area (LMA) is a key morphological trait and is related to leaf performance, such as light‐saturated photosynthetic rate per leaf mass, leaf mechanical strength, and leaf lifespan. LMA is the multiplicative product of leaf thickness (LT) and leaf density (LD), both of which vary with leaf anatomy. Nevertheless, how LMA, LT, and LD covary with leaf anatomy is largely unexplored along natural environmental gradients. Slope aspect is a topographic factor that underlies variations in solar irradiation, air temperature, humidity, and soil fertility. In the present study, we examined (1) how leaf anatomy varies with different slope aspects and (2) how leaf anatomy is related to LMA, LD, and LT. Leaf anatomy was measured for 30 herbaceous species across three slope aspects (south‐, west‐, and north‐facing slopes; hereafter, SFS, WFS, and NFS, respectively) in an eastern Tibetan subalpine meadow. For 18 of the 30 species, LMA data were available from previous studies. LD was calculated as LMA divided by LT. Among the slope aspects, the dominant species on the SFS exhibited the highest LTs with the thickest spongy mesophyll layers. The thicker spongy mesophyll layer was related to a lower LD via larger intercellular airspaces. In contrast, LD was the highest on NFS among the slope aspects. LMA was not significantly different among the slope aspects because higher LTs on SFS were effectively offset by lower LDs. These results suggest that the relationships between leaf anatomy and LMA were different among the slope aspects. Mechanisms underlying the variations in leaf anatomy may include different solar radiation, air temperatures, soil water, and nutrient availabilities among the slope aspects.

The implication of leaf anatomical structure for the selective breeding of lilacs.

The cultivars of the common lilac (Syringa vulgaris) grown in the south of the Russian Far East are not always winter-hardy and are often damaged by fungal diseases due to a very humid climate. A promising trend in the selective breeding of lilacs in Russia is the creation of new breeding material based on the gene pool of the broadleaf lilac (S. oblata) and its hybrids in order to introduce valuable adaptive traits into cultivars. The present work aimed to identify the traits of leaf anatomy in species and cultivars of Syringa resistant and susceptible to Pseudocercospora lilacis, the causative agent of brown leaf spot disease. The study was carried out on the living collection of the Botanical Garden-Institute, Far Eastern Branch, Russian Academy of Sciences (Vladivostok). The leaf anatomical structure of two Syringa species showing different degrees of resistance to P. lilacis in the monsoon climate of the Far East (resistant S. oblata and weakly resistant S. vulgaris, and also their hybrid cultivars) has been analyzed. The differences between species, subspecies, and cultivars are quantitative: they differ in the number of spongy mesophyll layers, the cell height in the f irst layer of palisade mesophyll, the cell height in the upper and lower epidermises, and the thickness of both mesophylls. The interspecif ic hybrids resistant or weakly resistant to P. lilacis (brown leaf spot disease) mainly retain the leaf anatomy structure of the maternal plant. One of the traits determining the resistance of hybrid lilac cultivars is an increased number of spongy mesophyll layers in the leaf blade. The study of leaf anatomy has shown that the four-layered spongy mesophyll leaf parenchyma correlates with the resistance of lilacs from the subsection Euvulgaris to P. lilacis. In S. oblata, this trait is inherited down the maternal line. To establish lilac cultivars resistant to fungal diseases, it is advisable to cross the two species (S. oblata and S. vulgaris) or their cultivars using one of S. oblata subspecies as a maternal plant.

Maximum CO2 diffusion inside leaves is limited by the scaling of cell size and genome size.

Maintaining high rates of photosynthesis in leaves requires efficient movement of CO2 from the atmosphere to the mesophyll cells inside the leaf where CO2 is converted into sugar. CO2 diffusion inside the leaf depends directly on the structure of the mesophyll cells and their surrounding airspace, which have been difficult to characterize because of their inherently three-dimensional organization. Yet faster CO2 diffusion inside the leaf was probably critical in elevating rates of photosynthesis that occurred among angiosperm lineages. Here we characterize the three-dimensional surface area of the leaf mesophyll across vascular plants. We show that genome size determines the sizes and packing densities of cells in all leaf tissues and that smaller cells enable more mesophyll surface area to be packed into the leaf volume, facilitating higher CO2 diffusion. Measurements and modelling revealed that the spongy mesophyll layer better facilitates gaseous phase diffusion while the palisade mesophyll layer better facilitates liquid-phase diffusion. Our results demonstrate that genome downsizing among the angiosperms was critical to restructuring the entire pathway of CO2 diffusion into and through the leaf, maintaining high rates of CO2 supply to the leaf mesophyll despite declining atmospheric CO2 levels during the Cretaceous.

Can hydraulic design explain patterns of leaf water isotopic enrichment in C3 plants?

H2 18 O enrichment develops when leaves transpire, but an accurate generalized mechanistic model has proven elusive. We hypothesized that leaf hydraulic architecture may affect the degree to which gradients in H2 18 O develop within leaves, influencing bulk leaf stable oxygen isotope enrichment (ΔL ) and the degree to which the Péclet effect is relevant in leaves. Leaf hydraulic design predicted the relevance of a Péclet effect to ΔL in 19 of the 21 species tested. Leaves with well-developed hydraulic connections between the vascular tissue and the epidermal cells through bundle sheath extensions and clear distinctions between palisade and spongy mesophyll layers (while the mesophyll is hydraulically disconnected) may have velocities of the transpiration stream such that gradients in H2 18 O develop and are expressed in the mesophyll. In contrast, in leaves where the vascular tissue is hydraulically disconnected from the epidermal layers, or where all mesophyll cells are well connected to the transpiration stream, velocities within the liquid transport pathways may be low enough that gradients in H2 18 O are very small. Prior knowledge of leaf hydraulic design allows informed selection of the appropriate ΔL modelling framework.

Autofluorescence study and selected cyanidin quantification in the Jewel orchids Anoectochilus sp. and Ludisia discolor.

Anoectochilus sp. and Ludisia discolor are known as Jewel orchids. Both species are terrestrial wild orchids that grow in shaded areas of forests. The Jewel orchids are renowned for the beauty of their leaves, which are dark-green laced with silvery or golden veins. The orchids are used as a cure in various parts of Asia. Overharvesting and anthropogenic disturbances threaten the existence of the Jewel orchids in the wild, necessitating human intervention in their survival. An understanding of the structure and adaptations of a plant may assist in its survival when propagated outside of its habitat. In this study, ex vitro leaves of Anoectochilus sp. and L. discolor were subjected to freehand sectioning, and then inspected through brightfield and fluorescence microscopy. The study indicated that all parts of both plants presented typical monocotyledonous characteristics except the leaves. The leaves displayed dorsiventrality with distinct palisade and spongy mesophyll layers. The spongy mesophyll layer contained cells which fluoresced a bright red when exposed to ultraviolet, blue, and green light wavelengths, hinting at the presence of anthocyanins for photoprotection. Cyanidin was detected in the leaves of L. discolor, as enumerated through high performance liquid chromatography (HPLC). The observations indicated that Anoectochilus sp. and L. discolor are well-adapted to live under shaded conditions with minimal exposure to light.

Shading and natural rooting biostimulator enhance potential for vegetative propagation of dogwood plants (Cornus alba L.) via stem cuttings

Auxins have been widely used to stimulate rhizogenesis in stem woody cuttings. Recently, more environmentally friendly biostimulators are reported to enhance rhizogenesis. Also, stock plants shading appears to be an easy and effective method to increase rooting of cuttings. The aim of the study was to examine the effect of shading and exogenous application of auxin or biostimulator AlgaminoPlant on rooting potential of two cultivars of dogwood (Cornus alba L.) and to detect anatomical modifications induced by shading that may be related to rooting ability. Stock plants were shaded with a nursery net reducing 50% of light for 6weeks prior to cuttings' harvest while the control stock plants were grown under ambient light. Cuttings from shaded and non-shaded plants were treated with a commercial rooting powder (1% IBA), sprayed with water solution of IBA (200mg·l−1) or with biostimulator AlgaminoPlant (0.2% v/v), whereas the control cuttings were sprayed with water. The effects of treatments were evaluated after 8weeks of rooting in a plastic tunnel. The two cultivars tested differed in natural as well as induced rooting potential, both in cuttings harvested from shaded stock plants and those grown under ambient light. Shading of stock plants significantly improved rooting abilities in comparison to control cuttings from plants grown under ambient light. Shading reduced diameters of stem and pith, with thinner layers of cortex, epidermis and collenchyma; vascular bundles and diameters of xylem vessels were also smaller. The thickness of leaf blades collected from shaded stock plants was lower due to thinner epidermal as well as spongy and palisade mesophyll layers. The best effects in rooting were obtained when shading was followed by the application of rooting inducers. The effects of synthetic auxin IBA and biostimulator AlgaminoPlant were similar; therefore, the latter is a viable option to reduce widespread use of rooting inducing chemicals based on synthetic auxins.

Virtual microstructural leaf tissue generation based on cell growth modeling

A cell growth algorithm for virtual leaf tissue generation is presented based on the biomechanics of plant cells in tissues. The algorithm can account for typical differences in epidermal layers, palisade mesophyll layer and spongy mesophyll layer which have characteristic differences in the shape of cells, arrangement of cells and void fractions present in each layer. The cell is considered as a closed thin walled structure, maintained in tension by turgor pressure. The cell walls are modelled as linear elastic elements which obey Hooke's law. A Voronoi tessellation was used to generate the initial topology of the cells in the spongy mesophyll layer. Then two layers of brick structured cells are added to the top of it to represent the palisade mesophyll and upper epidermis and a single layer is added at bottom of the Voronoi tessellation to represent the lower epidermal layer. Intercellular air spaces are generated by separating the Voronoi cells along the edges starting from where three Voronoi cells are in contact (schizogenous origin) and/or by deleting some of the Voronoi cells (lysigenous origin). Cell expansion then results from turgor pressure acting on the yielding cell wall material. To find the sequence of positions of each vertex and thus the shape of the tissue with time, a system of differential equations for the positions and velocities of each vertex is established and solved using the ordinary differential equation solver in MatLab. Statistical comparison of the cellular characteristics with 2D cross-sectional slices of real leaf tissue of tomato is excellent. The virtual tissues can be used to systematically study effects of leaf structure on water and gas exchange.

LEAF ADAPTABILITY OF lWO NON·TIMBER FOREST SPECIES Caryota urens L. AND Elettaria carrlamomum VAR. MAJOR PLANTED IN THE Pinus caribaea ENRICHMENT BUFFER ZONE IN SINHARAJA MAB RESERVE, SRI LANKA

Caryota urens L. and Elettaria cardamomum var. major are indigenous non-timberspecies which are used as market or sustainable goods and services for human orindustrial consumption. Both species thrive well in disturbed forest areas in the southwesternpart of Sri Lanka. Being understorey species, the growth of these species areaffected by sun light which is highly variable and often limiting resource in the forest.In a Pinus enrichment study established in 1991, leaf anatomical adaptability of these twospecies after 12 years of initial establishment under the Pinus buffer zone of the SinharajaMAB .reserve was investigated. Different light levels in the study area were created bythinning Pinus trees at different densities.Lower epidermis of C. urens showed highest (7.75 %) and lowest (6.35 %) stomatalindices in 2 pine rows removed treatment (2R) and 5 pine rows removed treatment (5R)respectively. Corresponding values for E. cardamomum were 6.00 % (highest) in theclosed canopy control (CU) and 5.22 % (lowest) in 1 pine row removed treatment (lR).The highest thickness of C. urens leaf cuticle (0.2611 ±0.02), leaf blade (22.2711 ±2.l4),upper epidermis (1.7511 ±0.10), lower epidermis (1.8311 ±0.06), palisade layer (6.2511±0.87) and spongy mesophylliayer (11.7411 ±1.30) were observed in 5R treatment thatreceived relatively high light levels than other treatments.E. cardamomum leaves showed highest thickness of leaf blade (22.4311 ±O.88), lowerepidermal layer (2.1211 ±O.ll), spongy mesophyll layer (10.3211 ±O.57) in 3 pine rowsremoved treatment (3R). The highest cuticle thickness (0.2311 ±O.OI) was recordered in 3pine rows under planting treatment (3U) while lR treatment showed highest upperepidermal layer thickness of 2.2111 ±0.15. Palisade layer was highest (4.74J! ±0.55) inCU.Results revealed that C. urens shows leaf adaptability to grow under relatively high sunlight levels (5R treatment) while E. cardamomum shows most of the leaf adaptabilitycharacters to grow under moderate light levels (3R treatment).The knowledge gained by this study is useful to recommend the optimum lightrequirements in terms of leaf anatomical traits of the study species.

EFFECT OF LIGHT AND SOIL MOISTURE ON SEEDLING LEAF ANATOMY OF FOUR CANOPY TREE SPECIES IN A LOWLAND RAIN FOREST, SRI LANKA

This study examined the variation in leaf structure among seedlings of four canopy tree species that have been characterized as late-successional and relatively shade-tolerant. Seedlings of Dipterocarpus zeylanicus Thw., D. hispidus Thw., Mesua ferrea L., and M. nagassarium (Burm.f) Kosterm., were grown for two years within replicated environmental shelters that had various light and soil moisture treatments. These treatments reflected the range of microenvironments that have been observed within the mixed-dipterocarp forest of southwestern Sri Lanka. Three light treatments exposed seedlings to uniform diffuse light conditions simulating radiation at the forest understorey and forest edge (PPFD, 50, 350, and 800 mmol m-2 s-1). Two treatments also exposed seedlings to direct radiation comparable to the centers of 200m2 and 400m2 canopy openings. A control treatment exposed seedlings to full sun (1600 mmol m-2 s-1). For each light treatment seedlings were grown in either soil watered to field capacity or soil that was consistently <30% of field capacity. After two years, leaf samples were taken for each species and light-soil moisture combination. Measures were made of leaf blade thickness, stomatal frequency, and thicknesses of upper epidermal, palisade mesophyll, and lower epidermal cell layers. Significant differences in measures of leaf structure were shown among species and among the various treatments. In general all species showed leaf dimensions and cell layers that increased with increase in amount of light and decrease in availability of soil moisture. Largest dimensions were therefore recorded from leaves exposed to full sun but grown in relatively dry soil. Mesua ferrea exhibited the thickest leaf blades followed by M. nagassarium, D. zeylanicus and lastly D. hispidus. Dipterocarpus zeylanicus had greater thicknesses of epidermal and palisade mesophyll layers than M. ferrea. This suggested that M. ferrea has a much thicker spongy mesophyll layer than the other species. Unlike Mesua, both Dipterocarpus species exhibited double rows of cells within the palisade mesophyll and lower epidermal layers in certain treatments. This phenomenon increased in frequency with amount of light. Greatest densities of stomata were measured for D. hispidus followed in declining order by M. ferrea, M. nagassarium and D. zeylanicus. Difference in shade anddroughttolerance among species in relation to site specialization is discussed.

Anatomical responses of leaves of Black Locust (Robinia pseudoacacia L.) to urban pollutant gases and climatic factors

This study investigates responses in the leaf anatomy of Black Locust (Robinia pseudoacacia L.) to the atmospheric pollutants, SO2, NO2 and O3 and climate in Tehran. The anatomical variables studied include thickness of the leaf lamina and of its main constituent tissues and the length and density of stomata. We present evidence that, in response to urban air pollution, the spongy mesophyll layer is thinner, the upper cuticle of the leaf thicker and stomatal density and the ratio of palisade parenchyma to spongy parenchyma are increased. Similar responses were also detected in relation to a climatic gradient. Stomatal density and thickness of the leaf lamina and of its mesophyll layer were all higher under warmer drier conditions. This overlap in anatomical response to two very different suites of environmental variables may reflect a functional overlap between mechanisms designed to restrict water loss in dry climates and those that minimize the uptake of toxic gases in polluted habitats.

Seasonal variation in photosynthesis and diel carbon balance under natural conditions in two Peperomia species that differ with respect to leaf anatomy1

Abstract The occurrence of crassulacean acid metabolism (CAM) and C3 photosynthetic activities in Peperomia species has been linked to the differential distribution of C3 and C4 photosynthetic enzymes within the distinct leaf tissue layers. Our objectives were to test if relative thickness of the spongy mesophyll layer is an indication of CAM and if the distribution of water in the leaf tissue changes in response to drought. Under field conditions we studied photosynthesis and water relations of Peperomia obtusifolia and P. macrostachya, species that differ in leaf anatomy. Gas exchange and titratable acidity were measured over a complete 24 hour photoperiod. Plant water status was determined at dawn while chlorophyll a fluorescence data were collected during the day (12 noon). Thickness of the distinct leaf layers was determined with the aid of a calibrated light microscope. Gas exchange and titratable acidity showed that when well-hydrated, P. obtusifolia has typical C3 activity and P. macrostachya has ...

Intraspecific variation in leaf morphology and photosynthetic traits in Boninia grisea Planchon (Rutaceae) endemic to the Bonin Islands, Japan

Abstract Boninia grisea is a woody species comprising two varieties that have adapted to habitats with different wind conditions. Boninia grisea var. grisea is a tree occurring in forests on mountain slopes, whereas B. grisea var. crassifolia is a shrub occurring at sites exposed to strong wind at forest edges and on mountain plateaus. The former has somewhat larger and thinner leaves than the latter. Despite the differences in habitat wind conditions and leaf morphology, plants of both taxa are found in a wide range of light environments from sunny to shady. We measured leaf morphological and photosynthetic traits for B. grisea plants of both taxa growing in the field and attempted to clarify the differences between them in terms of leaf morphological and photosynthetic acclimation to sun and shade. Boninia grisea var. crassifolia had a thicker leaf upper epidermis and a thicker spongy mesophyll layer with thicker cell walls than B. grisea var. grisea, suggesting that the former had mechanically tough leaves. Under sunny conditions, the stomatal conductance and area‐based photosynthetic capacities of the two B. grisea taxa were comparable. Under shady conditions, B. grisea var. crassifolia had thicker leaves with a higher photosynthetic light saturation, area‐based nitrogen content and stomatal conductance than B. grisea var. grisea, suggesting that the former was less acclimated to deep shade than the latter.

Investigating Cytoskeletal Function in Chloroplast Protrusion Formation in the Arctic‐Alpine Plant Oxyria digyna

Arctic and alpine plants like Oxyria digyna have to face enhanced environmental stress. This study compared leaves from Oxyria digyna collected in the Arctic at Svalbard (78 degrees N) and in the Austrian Alps (47 degrees N) at cellular, subcellular, and ultrastructural levels. Oxyria digyna plants collected in Svalbard had significantly thicker leaves than the samples collected in the Austrian Alps. This difference was generated by increased thickness of the palisade and spongy mesophyll layers in the arctic plants, while epidermal cells had no significant size differences between the two habitats. A characteristic feature of arctic, alpine, and cultivated samples was the occurrence of broad stroma-filled chloroplast protrusions, 2 - 5 microm broad and up to 5 microm long. Chloroplast protrusions were in close spatial contact with other organelles including mitochondria and microbodies. Mitochondria were also present in invaginations of the chloroplasts. A dense network of cortical microtubules found in the mesophyll cells suggested a potential role for microtubules in the formation and function of chloroplast protrusions. No direct interactions between microtubules and chloroplasts, however, were observed and disruption of the microtubule arrays with the anti-microtubule agent oryzalin at 5 - 10 microM did not alter the appearance or dynamics of chloroplast protrusions. These observations suggest that, in contrast to studies on stromule formation in Nicotiana, microtubules are not involved in the formation and morphology of chloroplast protrusions in Oxyria digyna. The actin microfilament-disrupting drug latrunculin B (5 - 10 microM for 2 h) arrested cytoplasmic streaming and altered the cytoplasmic integrity of mesophyll cells. However, at the ultrastructural level, stroma-containing, thylakoid-free areas were still visible, mostly at the concave sides of the chloroplasts. As chloroplast protrusions were frequently found to be mitochondria-associated in Oxyria digyna, a role in metabolite exchange is possible, which may contribute to an adaptation to alpine and arctic conditions.

A mutational analysis of the ABA1 gene of Arabidopsis thaliana highlights the involvement of ABA in vegetative development

Much of the literature on the phytohormone abscisic acid (ABA) describes it as a mediator in triggering plant responses to environmental stimuli, as well as a growth inhibitor. ABA-deficient mutants, however, display a stunted phenotype even under well-watered conditions and high relative humidity, which suggests that growth promotion may also be one of the roles of endogenous ABA. Zeaxanthin epoxidase, the product of the ABA1 gene of Arabidopsis thaliana, catalyses the epoxidation of zeaxanthin to antheraxanthin and violaxanthin, generating the epoxycarotenoid precursor of the ABA biosynthetic pathway. This paper gives a description of the molecular and phenotypic characterization of a large series of mutant alleles of the ABA1 gene, which cause different degrees of ABA deficiency, four of them previously isolated (aba1-1, aba1-3, aba1-4, and aba1-6) and the remaining five novel (sañ1-1, sañ1-2, sañ1-3, sañ1-4, and sre3). Molecular analysis of these alleles provides insights into the domains in which they compromise zeaxanthin epoxidase function. The size of the leaves, inflorescences, and flowers of these mutants is reduced, and their rosettes have lower fresh and dry weights than their wild types, as a result of a diminished cell size. Low concentrations of exogenous ABA increase the fresh weight of mutant and wild-type plants, as well as the dry weight of the mutants. The leaves of aba1 mutants are abnormally shaped and fail to develop clearly distinct spongy and palisade mesophyll layers. Taken together, these phenotypic traits indicate, as suggested by previous authors, that ABA acts as a growth promoter during vegetative development. The abnormal shape and internal structure of the leaves of aba1 mutants suggests, in addition, a role for ABA in organogenesis.

Altered cell cycle distribution, hyperplasia, and inhibited differentiation in Arabidopsis caused by the D-type cyclin CYCD3.

CYCD3;1 expression in Arabidopsis is associated with proliferating tissues such as meristems and developing leaves but not with differentiated tissues. Constitutive overexpression of CYCD3;1 increases CYCD3;1-associated kinase activity and reduces the proportion of cells in the G1-phase of the cell cycle. Moreover, CYCD3;1 overexpression leads to striking alterations in development. Leaf architecture in overexpressing plants is altered radically, with a failure to develop distinct spongy and palisade mesophyll layers. Associated with this, we observe hyperproliferation of leaf cells; in particular, the epidermis consists of large numbers of small, incompletely differentiated polygonal cells. Endoreduplication, a marker for differentiated cells that have exited from the mitotic cell cycle, is inhibited strongly in CYCD3;1-overexpressing plants. Transcript analysis reveals an activation of putative compensatory mechanisms upon CYCD3;1 overexpression or subsequent cell cycle activation. These results demonstrate that cell cycle exit in the G1-phase is required for normal cellular differentiation processes during plant development and suggest a critical role for CYCD3 in the switch from cell proliferation to the final stages of differentiation.

Physiology of Eucalyptus plantlets grown photoautotrophically in a scaled-up vessel

Nodal cuttings of Eucalyptus camaldulensis L. plantlets were cultured photoautotrophically (sugar-free nutrient medium and with enriched CO2 and high photosynthetic photon flux) in a scaled-up vessel (volume 4.0 liters) under forced ventilation (SV-treatment). After 28 d of culture, physiological aspects of the plantlets were compared with plantlets grown photomixotrophically (20 g l−1 sucrose in the medium) in a Magenta vessel (volume 0.4 liters) under natural ventilation (control). In the SV-treatment net photosynthetic rates were enhanced, normal stomatal closing and opening were observed, and the epicuticular leaf-wax content was significantly higher than the control. The anatomical study showed well-organized palisade and spongy mesophyll layers of SV leaves. The SV-treatment also allowed in vitro acclimatization, and after transplanting ex vitro, the transpiration rate and the percent water loss was lower than those of the control and thus the SV plantlets acclimatized easily ex vitro.

Impacts of elevated CO 2 and/or O 3 on leaf ultrastructure of aspen ( Populus tremuloides) and birch ( Betula papyrifera) in the Aspen FACE experiment

Impacts of elevated atmospheric O 3 and/or CO 2 on three clones of aspen ( Populus tremuloides Michx.) and birch ( Betula papyrifera Marsh.) were studied to determine, whether or not elevated CO 2 ameliorates O 3-induced damage to leaf cells. The plants were exposed for 3 years at the Aspen FACE exposure site in Wisconsin (USA) prior to sampling for ultrastructural investigations on 19 June 1999. In the aspen clones, elevated CO 2 increased chloroplast cover index, leaf and spongy mesophyll layer thickness, intercellular air space volume in mesophyll, amount of starch in chloroplasts and cytoplasmic lipids but decreased the number of plastoglobuli in chloroplasts. In contrast, elevated O 3 decreased chloroplast cover index, starch content, and the proportion of cytoplasm and intercellular space in mesophyll, and increased the proportion of vacuoles, the amount of condensed vacuolar tannins and the number of plastoglobuli. Ozone also caused structural thylakoid injuries (dilation, distortion) and stromal condensation in chloroplasts, which was ameliorated by elevated CO 2 by 5–66% in aspen clones and by 2–10% in birch. Birch ultrastructure was less affected by elevated CO 2 or O 3 stress compared to aspen. In the most O 3-sensitive aspen clone, thinner leaves and cell walls, lower proportion of cell wall volume, and higher volume for vacuoles was found compared to more-tolerant clones.

Leaf morphology and ozone sensitivity of two open pollinated genotypes of black cherry ( Prunus serotina) seedlings

Two black cherry families differing in sensitivity to ozone (O 3) were used to test the hypothesis that leaf morphology is related to foliar sensitivity to O 3. Two uninjured sections of leaf tissue were sampled from a single leaf collected from each of 12 open-grown O 3-tolerant and 12 O 3-sensitive seedlings. Standard histological techniques and light microscopy were used to examine 11 morphological characteristics. The O 3-sensitive genotype had significantly greater stomatal density, thinner palisade mesophyll layer and thicker spongy mesophyll layer, lower ratio of palisade to spongy mesophyll, greater leaf weight and leaf area. In addition, total leaf thickness, guard cell length, and specific leaf mass were also slightly greater for the O 3-sensitive genotype.

Leaf Heteroblasty in Pseudopanax crassifolius: Functional Significance of Leaf Morphology and Anatomy

Pseudopanax crassifolius (A. Cunn.) C. Koch. is a strongly heteroblastic tree indigenous to New Zealand. Changes in the morphology and anatomy of leaves are described for seedling, juvenile, transitional and adult phases of development. Seedlings produce five leaf types; all are relatively small, thin, anthocyanic, have a low specific weight, and are anatomically comparable to the leaves of many shade plants. Juvenile leaves are long, linear, deflexed, coriaceous and sharply-toothed. They have a high specific weight, a thick, ornamented cuticle, a multiseriate hypodermis composed of collenchyma, well developed palisade and many spongy mesophyll layers. Juvenile leaves are strong relative to adult leaves and to the leaves of other species. Leaf strength is provided by fibres associated with the midrib. Adult leaves are shorter, broader and less massive than juvenile leaves, and are oriented horizontally. Transitional leaves are morphologically intermediate between juvenile and adult leaves. The anatomy of juvenile, transitional and adult leaves is similar. The heteroblastic series may be associated with changes in leaf construction costs, light interception and heat dissipation.

Relationships between leaf anatomy and ozone sensitivity of Fraxinus pennsylvanica marsh. and Prunus serotina Ehrh.

It is well known that there are genetic differences in sensitivity of broad-leaved tree species to ozone (O 3). It would be helpful to know if individual trees in the field could be classified as sensitive or tolerant based on properties of sensitivity other than the presence/absence of foliar injury symptoms. We hypothesized that leaf anatomical characteristics allowing greater amounts of O 3 inside the leaf would be found in the leaves of sensitive individuals compared to the leaves of tolerant individuals. Light microscopy was used to examine 11 anatomical characters of leaves of field-grown Fraxinus pennsylvanica Marsh. and Prunus serotina Ehrh. trees that differed in O 3 sensitivity, as determined by injury symptoms. The characters were measured on uninjured areas of leaves collected in the field from trees classified as tolerant or sensitive. There were significant differences between sensitive and tolerant individuals of both species for several characters, including stomatal density, palisade mesophyll thickness and total mesophyll thickness, and the percentage of spongy mesophyll layer relative to total leaf mesophyll. Differences in stomatal density were inconsistent for the two species considered. The palisade mesophyll was significantly thinner by 27 and 17% in sensitive green ash and black cherry leaves compared to tolerant leaves, causing the percentage of spongy mesophyll layer relative to total leaf thickness to be 20-12% higher for sensitive compared to tolerant individuals. Consequently, the total leaf thickness was less for sensitive trees for both species. This aspect of leaf anatomy was consistent with shade leaf anatomy and may be associated with O 3 sensitivity for these two broad-leaved species.