Leaf structure and anatomy as related to leaf mass per area variation in seedlings of a wide range of woody plant species and types

The structural causes of variation in leaf mass per area, and of variations in leaf structure accounted for by leaf habit and life form, were explored in a set of laboratory-grown seedlings of 52 European woody species. The leaf traits analysed included density, thickness, saturated mass/dry mass, and leaf nitrogen per mass and per area. Other traits described the anatomy of leaves, most of them relating to the lamina (proportions of palisade and spongy parenchymata, epidermis, air space and sclerified tissues, expressed as volume per leaf area, and per-cell transversal areas of epidermis and parenchymata), and another referring to the mid rib (transversal section of sclerified tissues). Across the whole set of species leaf mass per area was correlated with leaf density but not with thickness, and this was confirmed by taxonomic relatedness tests. Denser leaves corresponded with greater proportion of sclerified tissues in the lamina, smaller cells and lower water and N contents, but no relation was found with the proportion of air space in the lamina. Taxonomic relatedness analysis statistically supported the negative association of leaf density with saturated to dry leaf mass ratio. Thicker leaves also exhibited greater volume per leaf area and greater individual cell area in each of the tissues, particularly parenchyma. Mean leaf mass per area and leaf thickness were lower in deciduous than in evergreen species, but no significant differences in leaf density, proportion of sclerified tissues in the lamina or cell area were found between the two groups. Leaf mass per area was higher in trees and subshrubs than in shrubs and climbers-plus-scramblers, this rank being equal for leaf density and proportion of sclerified tissues in the lamina, and reversed for cell area. Given the standardised environment and ontogenetic phase of the seedlings, we conclude that variation in leaf structure and anatomy among species and species groups has a strong genetic basis, and is already expressed early in the development of woody plants. From an ecological viewpoint, we can interpret greater leaf mass per area across this species set as greater allocation to support and defence functions, as shown predominantly by species from resource-poor environments. Received: 16 August 1999 / Accepted: 29 March 2000     

COMPARISON OF TETRAPLOID AND SINGLE GENE-INDUCED GIGAS VARIANTS IN CHICKPEA (CICER ARIETINUM). II. MORPHOLOGICAL AND ANATOMICAL LEAF CHARACTERS

Two genomic variants of a chickpea (Cicer arietinum L.) parental line have been developed which exhibit gigas characters. The two genotypes were the result of a single-gene mutation (gigas) and induced tetraploidy of a single parental line. The two genotypes plus parental strain were investigated to determine the similarity-of-effect of polyploidy and this single-gene mutation on leaf anatomy and morphology. Leaves consisted of two rows of alternatively arranged leaflets. Both the tetraploid and parental lines had the same mean number of leaflets per leaf while the gigas plants had fewer, but mean total leaf surface area was greater in the gigas plants. Quantitative comparison of mesophyll and vascular tissue and air space volume density (V_v) showed that leaves of the tetraploid plants had the greatest mesophyll cell density (V_vm) and least air space density. Mesophyll cell density was equal in the parental and single-gene mutant while parental leaves had the greatest vascular tissue density. The greater mesophyll cell density values of the polyploid were due to larger mean mesophyll cell size, not to greater cell numbers per unit area. Leaf models based on tissue density and leaflet size showed tetraploid plants had the greatest productivity potential per unit of leaflet surface area. However, if models were based on a whole leaf, gigas plants had the greatest productivity potential since they had larger total leaf area. The effectiveness of using structural models to predict physiological potential in plant tissues will be tested in future studies.     

Genome-Dependent Factors in the Development of Leaf Phototrophic Tissues in Diploid and Alloploid Wheat Species

Growth and mesostructure of the photosynthetic apparatus were studied in leaves of ten Triticum L. species. Plants with the A^u genome were shown to develop larger leaf assimilation areas due to expanding areas of individual leaves and an increase in the absolute growth rate. Leaf and mesophyll thickness and mesophyll cell size decreased in the G-genome species. Leaf compactness, which depended on cell size and number per unit leaf area and leaf folding, determined the specific patterns of internal leaf organization in wheat species with diverse genotypes. These patterns did not affect cell plastid-to-cytoplasm ratio as shown by the stable indices of cell surface area/cell volume, cell surface area per chloroplast, and cell volume per chloroplast. The structural indices of leaf phototrophic tissues, mesophyll density, and mesophyll CO₂ conductance in alloploids, as compared to diploid species, depended on both ploidy and genome constitution.     

Structure of the Photosynthetic Apparatus in Leaves of Freshwater Hydrophytes: 1. General Characteristics of the Leaf Mesophyll and a Comparison with Terrestrial Plants

The structure of photosynthetic elements was investigated in leaves of 42 boreal plant species featuring different degrees of submergence (helophytes, neustophytes, and hydatophytes). The mesophyll structure types were identified for all these species. Chlorenchyma tissues and phototrophic cells were quantitatively described by such characteristics as the sizes of cells and chloroplasts in the mesophyll and epidermis, the abundance of cells and chloroplasts in these tissues, the total surface area of cells and chloroplasts per unit leaf area, the number of plastids per cell, etc. The hydrophytes typically had thick leaves (200–350 m) with a well-developed aerenchyma; their specific density per unit area (100–200 mg/dm²) was lower than in terrestrial plants. Mesophyll cells in aquatic plants occupied a larger volume (5–20 × 10³m³) than epidermal cells (1–15 × 10³m³). The number of mesophyll cells per unit leaf area was nearly 1.5 times higher than that of epidermal cells. Chloroplasts were present in the epidermis of almost all species, including emergent leaves, but the ratio of the chloroplast total number to the number of all plastids varied depending on the degree of leaf submergence. The total number of plastids per unit leaf area (2–6 × 10⁶/cm²) and the surface of chloroplasts per unit leaf area (2–6 cm²/cm²) were lower in hydrophytes than in terrestrial plants from climatically similar habitats. The functional relations between mesophyll parameters were similar for hydrophytes and terrestrial plants (a positive correlation between the leaf weight per unit area, leaf thickness, and the number of mesophyll cells per unit leaf area), although no correlation was found in hydrophytes between the volume of mesophyll cells and the leaf thickness. Phototrophic tissues in aquatic plants contributed a larger fraction to the leaf weight than in terrestrial plants, because the mechanical tissues were less developed in hydrophytes. The CO₂assimilation rates by leaves were lower in hydrophytes than in terrestrial plants, because the total surface area of chloroplasts per unit leaf area is comparatively small in hydrophytes, which reduces the conductivity for carbon dioxide diffusion towards the carboxylation sites.     

Effects of polyploidy on photosynthesis

In polyploid plants the photosynthetic rate per cell is correlated with the amount of DNA per cell. The photosynthetic rate per unit leaf area is the product of the rate per cell times the number of photosynthetic cells per unit area. Therefore, the photosynthetic rate per unit leaf area will increase if there is a less than proportional increase in cell volume at higher ploidal levels, or if cell packing is altered to allow more cells per unit leaf area. In autopolyploids (Medicago sativa, C₃ species, and Pennisetum americanum, C₄ species) there is a doubling of photosynthesis per cell and of cell volume in the tetraploid compared to the diploid. However, there is a proportional decrease in number of cells per unit leaf area with this increase in ploidy such that the rate of photosynthesis per leaf area does not change. There is more diversity in the relationship between ploidal level (gene dosage) and photosynthetic rates per unit leaf area in allopolyploids. This is likely to reflect the effects of natural selection on leaf anatomy, and novel genetic interactions from contributed genomes which can occur with allopolyploidy. In allopolyploid wheat (C₃ species) a higher cell volume per unit DNA at the higher ploidal level is negatively correlated with photosynthesis rate per unit leaf area. Although photosynthesis per cell increases with ploidy, photosynthesis per leaf area decreases, being lowest in the allohexaploid, cultivated bread wheat (Triticum aestivum). Alternatively, doubling of photosynthetic rate per cell with doubling of DNA, with apparent natural selection for decreased cell volume per unit DNA, results in higher rates of photosynthesis per leaf area in octaploid compared to tetraploid Panicum virgatum (C₄) which may be a case of allopolyploidy. Similar responses probably occur in Festuca arundinacea. Therefore, in some systems anatomical factors affecting photosynthesis are also affected by ploidal level. It is important to evaluate that component as well as determining the effect on biochemical processes. Current information on polyploidy and photosynthesis in several species is discussed with respect to anatomy, biochemistry and bases for expressing photosynthetic rates.Abbreviations Chl chlorophyll - RuBPC ribulose-1,5-bisphosphate carboxylase     

The anatomical and compositional basis of leaf mass per area

Leaf dry mass per unit leaf area (LMA) is a central trait in ecology, but its anatomical and compositional basis has been unclear. An explicit mathematical and physical framework for quantifying the cell and tissue determinants of LMA will enable tests of their influence on species, communities and ecosystems. We present an approach to explaining LMA from the numbers, dimensions and mass densities of leaf cells and tissues, which provided unprecedented explanatory power for 11 broadleaved woody angiosperm species diverse in LMA (33–262 g m^?2; R² = 0.94; P < 0.001). Across these diverse species, and in a larger comparison of evergreen vs. deciduous angiosperms, high LMA resulted principally from larger cell sizes, greater major vein allocation, greater numbers of mesophyll cell layers and higher cell mass densities. This explicit approach enables relating leaf anatomy and composition to a wide range of processes in physiological, evolutionary, community and macroecology.     

Relationships between photosynthesis, nitrogen and leaf structure in 14 grass species and their dependence on the basis of expression

The relationships between leaf structure, nitrogen concentration and CO₂ assimilation rate ( A ) were studied for 14 grass species grown in the laboratory under non-limiting nutrient conditions. Structural features included leaf thickness and density, and the proportion of leaf volume occupied by different types of tissue (mesophyll, epidermis, vessels and sclerenchyma). Relationships were assessed for data expressed per unit leaf area and fresh mass. The latter was found to be closely related to leaf volume, which allowed us to use A per unit leaf fresh mass ( A _fm) as a surrogate of A per unit leaf volume. Assimilation rate per unit leaf area ( A _a) was positively correlated with leaf thickness and with the amount of mesophyll per unit leaf area; the relationship with leaf nitrogen content per unit area was only marginally significant. A _fm was negatively correlated with leaf thickness and positively with fresh mass-based leaf organic nitrogen concentration. A multiple regression involving these two variables explained 81% of the variance in A _fm. The value of A _fm was also significantly related to the proportion of mesophyll in the leaf volume, but surprisingly the correlation was negative. This was because thin leaves with high A _fm and nitrogen concentration had proportionally more mechanically supportive tissues than thick ones; as a consequence, they also had a lower proportion of mesophyll. These data suggest that, in addition to leaf nitrogen, leaf thickness has a strong impact on CO₂ assimilation rate for the grass species studied.     

Leaf morphology and water status changes in Triticum durum under water stress

Water relations, leaf morphology and the chemical composition of cell walls in irrigated and unirrigated plants of three durum wheat eultivars were measured at two growth stages (booting and flowering). Plant response to water stress differed at the two stages: cell wall elasticity increased at booting and osmotic potential values decreased at flowering; this may be due to the changes in stress history, leaf development and plant growth stage between the two harvests. Leaf tissue characteristics were modified by water stress only at flowering: accumulation of fibrous constituents and hemicellulose in the cell walls, reduction of acid detergent fiber (ADF) per unit of leaf area, increase in specific leaf weight (SLW), decrease in turgid weight/dry weight ratio (TW/DW) and alteration in mesophyll cell morphology (cell area / ceil perimeter ratio) were observed.
Generally, cv. Valforte (the less drought-resistant cultivar) had the greatest mesophyll cell area and perimeter and it had greater values of neutral detergent fiber (NDF) at the booting stage than cv. Appulo. Reactivity to water stress differed in the eultivars: Valforte showed the greatest increase in hemicellulose content and decrease in cell dimensions under drought at flowering.
No significant relationships between osmotic potential and mesophyll cell characters were observed; there were no correlations among cell wall elasticity, cell morphology and the chemical components of leaf tissue. The total fiber content and the hemicellulose per unit of leaf area were correlated with the TW/DW ratio at flowering. This parameter decreased more in plants subjected to water stress owing to accumulation of hemicellulose. Correlations between leaf structural constituents and $$ suggest that the absorptive capacity of the cell wall may significally affect the osmotic volume of the cell.     

Basic Types of Structural Changes in the Leaf Mesophyll during Adaptation of Eastern Pamir Plants to Mountain Conditions

Quantitative characteristics of mesophyll structure were compared in leaves of eleven alpine plant species grown under natural conditions in the Eastern Pamirs at various altitudes, from 3800 to 4750 m. Basic types of changes in mesophyll structure, associated with plant adaptation to mountain conditions, were characterized. These changes manifested themselves in different numbers of cell layers and cell sizes in the palisade tissue and, as a consequence, in changed leaf thickness and cell number per unit of leaf area. Three plant groups were identified by the changes in the leaf structural characteristics depending on the type of mesophyll structure, ecological group of plant species, and altitude of plant habitat. The first group comprised alpine xerophytes with an isopalisade structure, in which the volume of palisade cells decreased and their number per unit of leaf area increased with the altitude of plant habitat. The number of mesophyll layers and leaf thickness decreased or did not change with altitude. The second group comprised subalpine plant species with a dorsoventral structure of mesophyll; these species occur below the line of continuous night frost. In these plant species, the number of mesophyll layers, leaf thickness, and cell number per unit of leaf area increased with altitude. The third group comprised mesophyte plants with a dorsoventral and homogenous mesophyll structure, which are encountered in a wide range of habitats, including the nival belt (from 4700 to 5000 m). In this group, cell volume increased and cell number per unit of leaf area decreased with altitude. We present a general scheme of leaf structural changes, which explains the changes in the quantitative characteristics of mesophyll as a function of altitude and highland environmental conditions.     

Glucose-6-phosphate-dehydrogenase activity in the shoot apical meristem,leaf primordia,and leaf tissues of Dianthus chinensis L.

The oxidation of carbohydrate by the pentose-phosphate pathway in the shoot apical meristem and developing leaf primordia of Dianthus chinensis was assessed by measuring the activity of glucose-6-phosphate dehydrogenase (EC 1.1.1.49). On a kg^-1 dry weight h^-1 basis, activity rose from 250 mmol in the apical meristem to 550 mmol in the first two leaf primordia and then declined to 350 mmol in the sixth pair of leaf primordia, and finally to 200 mmol in leaves just emerged from the shoot bud. Measurements of activity in the sixth leaf pair from the apex showed differential distribution in leaf tissues. Epidermal and mesophyll tissue had about the same activity as whole-leaf tissue, but vascular bundles had 70% greater activity. Within the vascular tissue, activity in the phloem was twice as high as in the xylem. When activity was expressed on a per-cell basis, there was a continuous increase from 20 fmol in the apex to 2 pmol in the sixth leaf pair. Activity on a per unit cell volume basis showed that cells of the apical meristem and the epidermis, mesophyll and xylem of the sixth leaf pair had similar values, about 30 amol; only the two youngest pairs of primordia and the phloem had values two or three times this amount.     

The relationship between anatomy and photosynthetic performance of heterobaric leaves

Heterobaric leaves show heterogeneous pigmentation due to the occurrence of a network of transparent areas that are created from the bundle sheaths extensions (BSEs). Image analysis showed that the percentage of photosynthetically active leaf area (Ap) of the heterobaric leaves of 31 plant species was species dependent, ranging from 91% in Malva sylvestris to only 48% in Gynerium sp. Although a significant portion of the leaf surface does not correspond to photosynthetic tissue, the photosynthetic capacity of these leaves, expressed per unit of projected area (Pmax), was not considerably affected by the size of their transparent leaf area (At). This means that the photosynthetic capacity expressed per Ap (P*max) should increase with At. Moreover, the expression of P*max could be allowing the interpretation of the photosynthetic performance in relation to some critical anatomical traits. The P*max, irrespective of plant species, correlated with the specific leaf transparent volume (lambda(t)), as well as with the transparent leaf area complexity factor ((CF)A(t)), parameters indicating the volume per unit leaf area and length/density of the transparent tissues, respectively. Moreover, both parameters increased exponentially with leaf thickness, suggesting an essential functional role of BSEs mainly in thick leaves. The results of the present study suggest that although the Ap of an heterobaric leaf is reduced, the photosynthetic performance of each areole is increased, possibly due to the light transferring capacity of BSEs. This mechanism may allow a significant increase in leaf thickness and a consequent increase of the photosynthetic capacity per unit (projected) area, offering adaptive advantages in xerothermic environments.     

Construction costs and mesostructure of leaves in hydrophytes

Construction costs (CC) and parameters of leaf structure (specific leaf weight, dry matter content, volume of photosynthesizing cells, and the number of cells per leaf area unit) were determined for 19 species of aquatic higher plants. The CC of 1 g dry matter varied from 0.98 g glucose in Lemna gibba L. to 1.48 g glucose in Nuphar pumila (Timm) DC. and Potamogeton natans L. The CC of leaf area unit varied to a greater extent than the CC of 1 g dry wt (from 10 to 97 g glucose/m²) and depended on the type of mesophyll structure. In leaves of hydrophytes with dorsoventral mesophyll structure, the CC of 1 m² leaf area was 3–9 times larger than in leaves with homogeneous structure. Variations in CC of 1 m² leaf area in hydrophytes were affected insignificantly (by 2% only) by variations of CC per 1 g dry wt and were mainly determined (by 82%) by changes in specific leaf weight. Two-factor analysis of variance has shown that the CC of 1 g dry wt in hydrophytes depended on the attachment of plants to the sediment: the CC was 1.2 times larger in rooted hydrophytes than in free floating plants. The second factor (the extent of submergence) potentiated the effect of rooting on CC. Reliable differences were found between the leaf CC for hydrophytes belonging to four groups distinguished by the extent of their contact with water and sediment. In a group series: rooted hydrophytes with floating leaves → submerged rooted hydrophytes → free floating submerged hydrophytes → free floating surface inhabiting hydrophytes, the CC of 1 g dry wt decreased by 1.3 times. Path analysis has shown that this trend was due to the increase in photosynthesizing cell volume and to reduction in number of cells per leaf area unit, which caused the decrease in dry matter content. The decrease in the content of leaf dry matter was accompanied by changes in its chemical composition: the content of carbon and nitrogen decreased. This led to a consistent decrease in leaf CC expressed per 1 g dry wt upon the increase in extent of plant hydrophilicity.     

Leaf anatomy and photosynthetic acclimation in <Emphasis Type="Italic">Valeriana jatamansi</Emphasis> L. grown under high and low irradiance

Relationship of leaf anatomy with photosynthetic acclimation of Valeriana jatamansi was studied under full irradiance [FI, 1 600 mol(PPFD) m^–2 s^–1] and net-shade [NS, 650 mol(PPFD) m^–2 s^–1]. FI plants had thicker leaves with higher respiration rate (R _D), nitrogen content per unit leaf area, chlorophyll a/b ratio, high leaf mass per leaf area unit (LMA), and surface area of mesophyll cell (S _mes) and chloroplasts (S _c) facing intercellular space than NS plants. The difference between leaf thickness of FI and NS leaves was about 28 % but difference in photon-saturated rate of photosynthesis per unit leaf area (P _Nmax) was 50 %. This indicates that P _Nmax can increase to a larger extent than the leaf thickness with increasing irradiance in V. jatamansi. Anatomical studies showed that the mesophyll cells of FI plants had no open spaces along the mesophyll cell walls (higher S _c), but in NS plants wide open spaces along the mesophyll cell wall (lower S _c) were found. Positive correlation between S _c and P _Nmax explained the higher P _Nmax in FI plants. Increase in mesophyll thickness increased the availability of space along the mesophyll cell wall for chloroplasts (increased S _c) and hence P _Nmax was higher in FI plants. Thus this Himalayan species can acclimate to full sunlight by altering leaf anatomy and therefore may be cultivated in open fields.     

Measurement of Cell Wall Volume using Confocal Microscopy and its Application to Studies of Forage Degradation

The distribution of cell wall material between different plantcell types may contribute significantly to the variation indegradability of plant material with a similar overall chemicalcomposition but different anatomy. Assessment of the degradabilityof cell walls in a section suitable for digestion is a three-dimensional(3-D) problem because of the thickness of section required (50–100µm). Optical sectioning of thick sections using confocallaser scanning microscopy (CLSM) provides a method of estimatingthe volume of cell wall material present in tissue sectionsbefore and after digestion, and of visualizing the plant tissueusing 3-D image reconstruction. The use of CLSM enables degradabilitymeasurements to be made on cellsin situand can provide moreimmediate and relevant information than can be obtained by mechanicalfractionation of the tissues. The CLSM method has been usedto visualize thick sections taken from maize and barley internodesbefore and after degradation with cell wall degrading enzymes.Quantitative measurements of cell wall volume and mean cellwall thickness were made on a series of optical sections, andthe potential of the method for quantitation of cell wall degradabilityis assessed. Image analysis; plant anatomy; confocal microscopy; degradation; maize     

Temporal and Spatial Development of the Cells of the Expanding First Leaf of Arabidopsis thaliana (L.) Heynh

The three-dimensional quantitative leaf anatomy in developingyoung (9–22 d) first leaves of wild type Arabidopsis thalianacv. Landsberg erecta from mitosis through cell and leaf expansionto the cessation of lamina growth has been studied. The domainsof cell division, the relative proportion of the cell typespresent during development and the production of intercellularspace in the developing leaf have been determined by image analysisof entire leaves sectioned in three planes. Mitotic activityoccurs throughout the youngest leaves prior to unfolding andcell expansion is initiated firstly at the leaf tip with a persistentzone of mitotic cells at the leaf base resulting in a gradientof development along the leaf axis, which persists in the olderleaves. Major anatomical changes which occur during the developmentare, a rapid increase in mesophyll volume, an increase in thevein network, and expansion of the intercellular spaces. Thepattern of cell expansion results in a 10-fold variation inmesophyll cell size in mature leaves. In the youngest leavesthe plan area of mesophyll cells varies between 100 µm²and 400 µm² whereas in mature leaves mesophyll cells rangein plan area from 800 µm² to 9500 µm². The volumesof mesophyll tissue and airspace under unit leaf area increase3-fold and 35-fold, respectively, during leaf expansion. Thevolume proportions of tissue types mesophyll:airspace:epiderrnal:vascularin the mature leaf are 61:26:12:1, respectively. This studyprovides comparative information for future identification andanalysis of leaf development mutants of Arabidopsis thaliana. Key words: Arabidopsis, quantitative leaf anatomy, leaf expansion, image analysis     

A COMPARATIVE ANALYSIS OF CELL MORPHOLOGY IN MATURING TISSUES OF ROOTS FROM SHOCKED AND UNSHOCKED BULBS OF ALLIUM CEPA L.

A shock pressure pulse of 60 pounds per square inch (psi; 4.22 kg/cm²) effectively inhibited root growth of onion bulbs. Morphological changes observed after shock included a reduction in cell number in transverse section, a decrease in cell length, a decrease in cell volume, and an increase in cell cross-sectional area. Mitotic activity was consistently increased one day after shock, and this may have accounted for the increased cell number per millimeter of root tip segment 8 days after shock. The development of the tissues appeared normal after shock exposure; however, the tissue response to pressures seems to depend on whether they are exposed to prolonged confining pressures or a brief pressure pulse. Responses which were unique to shock treatment include a decrease in cell number in transverse section, reduced cell volume, and increased radial enlargement of the cell. These responses have not been observed under prolonged pressure treatment.     

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     

Secondary cell wall deposition causes radial growth of fibre cells in the maturation zone of elongating tall fescue leaf blades

A gradient of development consisting of successive zones of cell division, cell elongation and cell maturation occurs along the longitudinal axis of elongating leaf blades of tall fescue (Festuca arundinacea Schreb.), a C3 grass. An increase in specific leaf weight (SLW; dry weight per unit leaf area) in the maturation region has been hypothesized to result from deposition of secondary cell walls in structural tissues. Our objective was to measure the transverse cell wall area (CWA) associated with the increase in SLW, which occurs following the cessation of leaf blade elongation at about 25 mm distal to the ligule. Digital image analysis of transverse sections at 5, 15, 45, 75 and 105 mm distal to the ligule was used to determine cell number, cell area and protoplast area of structural tissues, namely fibre bundles, mestome sheaths and xylem vessel elements, along the developmental gradient. Cell diameter, protoplast diameter and area, and cell wall thickness and area of fibre bundle cells were calculated from these data. CWA of structural tissues increased in sections up to 75 mm distal to the ligule, confirming the role of cell wall deposition in the increase in SLW (r2 = 0.924; P < or = 0.01). However, protoplast diameter of fibre cells did not decrease significantly as CWA increased, although mean thickness of fibre cell walls increased by 95 % between 15 and 105 mm distal to the ligule. Therefore, secondary cell wall deposition in fibre bundles of tall fescue leaf blades resulted in continued radial expansion of fibre cells rather than in a decrease in protoplast diameter.     

Leaf Structure of Tobacco In Vitro Grown Plantlets as Affected by Saccharose and Irradiance

Tobacco plantlets were cultured in vitro under high (200 µmol m^–2 s^–1) or low (60 µmol m^–2 s^–1) irradiance with or without saccharose in the medium. Light microscopy and image analysis were used to evaluate the effect of these culture conditions on leaf anatomy. Addition of saccharose resulted in thicker leaves (all leaf layers) and larger mesophyll cells under both growth irradiances. Various irradiance affected leaf anatomy differently when plantlets had been cultivated in presence or absence of saccharose in the medium. While under high irradiance in presence of saccharose leaf thickness and number of chloroplasts per cell section were increased, plantlets grown under high irradiance in absence of saccharose had thinner leaves and less chloroplasts per cell section. The changes were more pronounced in palisade parenchyma layer.     

Comparative analyses of leaf anatomy of dicotyledonous species in Tibetan and Inner Mongolian grasslands

Knowledge of the leaf anatomy of grassland plants is crucial for understanding how these plants adapt to the environment. Tibetan alpine grasslands and Inner Mongolian temperate grasslands are two major grassland types in northern China. Tibetan alpine grasslands occur in high-altitude regions where the low temperatures limit plant growth. Inner Mongolian temperate grasslands are found in arid regions where moisture is the limiting factor. Few comparative studies concerning the leaf anatomy of grassland plants of the Tibetan Plateau and Inner Mongolian Plateau have been conducted. We examined leaf characteristics at 71 sites and among 65 species, across the alpine grasslands of the Tibetan Plateau and the temperate grasslands of the Inner Mongolian Plateau. We compared the leaf structures of plants with different life forms and taxonomies, and their adaptation to arid or cold environments. We explored relationships among leaf features and the effects of climatic factors (i.e., growing season temperature and precipitation) on leaf characteristics. Our results showed that (i) there were significant differences in leaf anatomy between Tibetan alpine and Inner Mongolian temperate grasslands. Except for mesophyll cell density, the values obtained for thickness of leaf tissue, surface area and volume of mesophyll cells were larger on the Tibetan Plateau than on the Inner Mongolian Plateau. (ii) Within the same family or genus, leaf anatomy showed significant differences between two regions, and trends were consistent with those of whole species. (iii) Leaf anatomy of woody and herbaceous plants also showed significant differences between the regions. Except for mesophyll cell density, the values obtained for the thickness of leaf tissue, and the surface area and volume of mesophyll cells were larger in herbaceous than in woody plants. (iv) Leaf anatomical traits changed accordingly. Total leaf thickness, thicknesses of lower and upper epidermal cells, and surface area and volume of mesophyll cells were positively correlated, while mesophyll cell density was negatively associated with those traits. (v) Growing season temperature had stronger effects on leaf anatomy than growing season precipitation. Although the communities in Tibetan and Inner Mongolian grasslands were similar in appearance, leaf anatomy differed; this was probably due to the combined effects of evolutionary adaptation of plants to environment and environmental stress induced by climatic factors.