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Mesophyll conductance (gm) is a crucial leaf trait contributing to the photosynthetic rate (AN). Plant domestication typically leads to an enhancement of AN that is often associated with profound anatomical modifications, but it is unclear which of these structural alterations influence gm. We analyzed the implication of domestication on leaf anatomy and its effect on gm in 26 wild and 31 domesticated cotton genotypes (Gossypium sp.) grown under field conditions. We found that domesticated genotypes had higher AN but similar gm to wild genotypes. Consistent with this, domestication did not translate into significant differences in the fraction of mesophyll occupied by intercellular air spaces (fias) or mesophyll and chloroplast surface area exposed to intercellular air space (Sm/S and Sc/S, respectively). However, leaves of domesticated genotypes were significantly thicker, with larger but fewer mesophyll cells with thinner cell walls. Moreover, domesticated genotypes had higher cell wall conductance (gcw) but smaller cytoplasmic conductance (gcyt) than wild genotypes. It appears that domestication in cotton has not generally led to significant improvement in gm, in part because their thinner mesophyll cell walls (increasing gcw) compensate for their lower gcyt, itself due to larger distance between plasmalemma and chloroplast envelopes.

Mesophyll (M) chloroplasts in finger millet are known to aggregate to the bundle sheath side when leaves are constantly irradiated with extremely high-intensity light. This aggregative movement of M chloroplasts is also observed in natural environment, but whether a natural light regime is effective in inducing the response remains unclear. Abscisic acid is reported to trigger not only the aggregative movement but also stomatal closure, but photosynthetic responses accompanying the aggregative movement also remain unknown.We investigated changes in chloroplast positioning and photosynthetic traits under diurnal patterns of light, mimicking the natural light environment. M chloroplasts showed the aggregative movement with increasing light intensity whether it frequently fluctuated or not, and kept their aggregative positions in the midday. With decreasing light intensity, M chloroplasts returned to the random position in the evening. These results suggest that M chloroplasts often rearrange their intracellular positions during the daytime and that the chloroplast aggregative movement can be induced by a natural regime of light. The chloroplast aggregative movement was observed with increasing stomatal conductance, suggesting that stomatal closure is not crucial to trigger the chloroplast response.

Mesophyll conductance (gm ) is the diffusion of CO2 from intercellular air spaces (IAS) to the first site of carboxylation in the mesophyll cells. In C3 species, gm is influenced by diverse leaf structural and anatomical traits; however, little is known about traits affecting gm in C4 species. To address this knowledge gap, we used online oxygen isotope discrimination measurements to estimate gm and microscopy techniques to measure leaf structural and anatomical traits potentially related to gm in 18 C4 grasses. In this study, gm scaled positively with photosynthesis and intrinsic water-use efficiency (TEi ), but not with stomatal conductance. Also, gm was not determined by a single trait but was positively correlated with adaxial stomatal densities (SDada ), stomatal ratio (SR), mesophyll surface area exposed to IAS (Smes ) and leaf thickness. However, gm was not related to abaxial stomatal densities (SDaba ) and mesophyll cell wall thickness (TCW ). Our study suggests that greater SDada and SR increased gm by increasing Smes and creating additional parallel pathways for CO2 diffusion inside mesophyll cells. Thus, SDada , SR and Smes are important determinants of C4 -gm and could be the target traits selected or modified for achieving greater gm and TEi in C4 species.

Depending on the diversities of the plant species, the mechanisms of the stomatal opening are thought to be different. First, Paphiopedilum insigna var. sanderae do not have chloroplasts in the guard cells. However, the stomata of this plant function as normal. Plants lacking the chloroplasts in the guard cell imply that the chloroplasts in guard cells are not related to stomatal opening. The guard cells without chloroplasts cannot be the source cells of the photosynthetic products, and the guard cells must be act as the sink cells. Second, the distinctive features of guard cells are specialized cell walls, which are considerably thickened to 5 µm. In contrast, the thickness of mesophyll cell walls is less than 100 nm. In the guard cells, most of the photosynthetic products may be used for the production of cell walls. The low photosynthetic activities of chloroplasts in the guard cell cannot be sufficient to maintain the structures and functions of the guard cell walls. Third, 40~60 chloroplasts in the guard cell of Lilium longiflorum which is belong to angiosperm were found in the first time. Lilium longiflorum of the relationship with mesophyll cells cannot be completely excluded, but it is assumed that guard cell chloroplasts in Lilium longiflorum may play an important role for the stomatal opening.

Leaf function is influenced by leaf structure, which is itself related not only to the spatial arrangement of constituent mesophyll cells, but also their size and shape. In this study, we used confocal microscopy to image leaves of Triticum genotypes varying in ploidy level to extract 3D information on individual mesophyll cell size and geometry. Combined with X‐ray Computed Tomography and gas exchange analysis, the effect of changes in wheat mesophyll cell geometry upon leaf structure and function were investigated. Mesophyll cell size and shape were found to have changed during the course of wheat evolution. An unexpected linear relationship between mesophyll cell surface area and volume was discovered, suggesting anisotropic scaling of mesophyll cell geometry with increasing ploidy. Altered mesophyll cell size and shape were demonstrated to be associated with changes in mesophyll tissue architecture. Under experimental growth conditions, CO2 assimilation did not vary with ploidy, but stomatal conductance was lower in hexaploid plants, conferring a greater instantaneous water‐use efficiency. We propose that as wheat mesophyll cells have become larger with increased ploidy, this has been accompanied by changes in cell geometry and packing which limit water loss while maintaining carbon assimilation.

Genome-scale models capture the remarkable specialization of epithelial cells for oleoresin biosynthesis in needles of loblolly pine (Pinus taeda L.)., The shoot system of pines contains abundant resin ducts, which harbor oleoresins that play important roles in constitutive and inducible defenses. In a pilot study, we assessed the chemical diversity of oleoresins obtained from mature tissues of loblolly pine trees (Pinus taeda L.). Building on these data sets, we designed experiments to assess oleoresin biosynthesis in needles of 2-year-old saplings. Comparative transcriptome analyses of single cell types indicated that genes involved in the biosynthesis of oleoresins are significantly enriched in isolated epithelial cells of resin ducts, compared with those expressed in mesophyll cells. Simulations using newly developed genome-scale models of epithelial and mesophyll cells, which incorporate our data on oleoresin yield and composition as well as gene expression patterns, predicted that heterotrophic metabolism in epithelial cells involves enhanced levels of oxidative phosphorylation and fermentation (providing redox and energy equivalents). Furthermore, flux was predicted to be more evenly distributed across the metabolic network of mesophyll cells, which, in contrast to epithelial cells, do not synthesize high levels of specialized metabolites. Our findings provide novel insights into the remarkable specialization of metabolism in epithelial cells.

The leaf economics spectrum (LES) represents a suite of intercorrelated leaf traits concerning construction costs per unit leaf area, nutrient concentrations, and rates of carbon fixation and tissue turnover. Although broad trade-offs among leaf structural and physiological traits have been demonstrated, we still do not have a comprehensive view of the fundamental constraints underlying the LES trade-offs. Here, we investigated physiological and structural mechanisms underpinning the LES by analysing a novel data compilation incorporating rarely considered traits such as the dry mass fraction in cell walls, nitrogen allocation, mesophyll CO2 diffusion and associated anatomical traits for hundreds of species covering major growth forms. The analysis demonstrates that cell wall constituents are major components of leaf dry mass (18-70%), especially in leaves with high leaf mass per unit area (LMA) and long lifespan. A greater fraction of leaf mass in cell walls is typically associated with a lower fraction of leaf nitrogen (N) invested in photosynthetic proteins; and lower within-leaf CO2 diffusion rates, as a result of thicker mesophyll cell walls. The costs associated with greater investments in cell walls underpin the LES: long leaf lifespans are achieved via higher LMA and in turn by higher cell wall mass fraction, but this inevitably reduces the efficiency of photosynthesis.

The aim of this study was to evaluate the growth of rape ( Brassica napus L.) seedlings under different light intensities to select appropriate conditions for cultivation in an indoor system. Seedlings were grown under different light intensities of red and blue light provided by light-emitting diodes (LEDs) and their self-adjustment ability and changes in leaf microstructure were evaluated. Light was supplied by red LEDs with peak wavelengths of 630 (R 1 ) and 660 nm (R 2 ) and by blue LEDs (B) with a peak wavelength of 445 nm (the light intensity ratio of R 1 :R 2 :B was 3:3:2), at intensities of 400 (R 1 R 2 B400), 300 (R 1 R 2 B300), and 200 μmol m −2 s −1 (R 1 R 2 B200). Natural solar light served as the control (C). Plant height, stem diameter, root length, leaf area, and dry weight of rape seedlings gradually increased with increasing light intensity. The seedlings in the R 1 R 2 B400 treatment grew more vigorously, while those in the R 1 R 2 B200 treatment were weaker. The photosynthetic pigment contents did not differ significantly between the R 1 R 2 B400 treatment and C, but were significantly lower in the R 1 R 2 B300 and R 1 R 2 B200 treatments. The highest intercellular CO 2 concentration, stomatal conductance, and transpiration rate were in the R 1 R 2 B300 treatment. The highest photosynthetic rate was in the R 1 R 2 B400 treatment, and was related to more compact leaves, thicker and tidier palisade and spongy tissues, and well-developed chloroplasts. In contrast, the seedlings in the R 1 R 2 B200 treatment had disordered mesophyll cells, round chloroplasts, and fractured and fuzzy grana lamellae, all of which inhibited plant growth. In conclusion, the seedlings in the R 1 R 2 B400 treatment had well-developed leaves, which favored photosynthesis. Compared with the light intensities below 300 μmol m −2 s −1 , the light intensity of 400 μmol m −2 s −1 provided by a combination of red and blue LEDs was beneficial for cultivating strong and healthy rape seedlings in an artificial system.

The structure and functional organization of the photosynthetic apparatus of Siberian larch growing on the western slope of Northern and Sub-Arctic Urals were studied. The needle morphostructure, the mesophyll cell ultrastructure, and the pigment complex of chloroplasts were quantitatively characterized. Active photosynthesis of larch was observed during warm days with a low deficit of humidity. Photoassimilation depression under hot and dry weather was followed by a decrease in the stomatal conductance of needles. Under extreme conditions of mountains, Siberian larch has low photosynthesis. It decreased gradually from Nothern to Sub-Arctic Urals.

Leaves are beautifully specialized organs designed to maximize the use of light and CO2 for photosynthesis. Engineering leaf anatomy therefore brings great potential to enhance photosynthetic capacity. Here we review the effect of the dominant leaf anatomical traits on leaf photosynthesis and confirm that a high chloroplast surface area exposed to intercellular airspace per unit leaf area (Sc) is critical for efficient photosynthesis. The possibility of improving Sc through appropriately increasing mesophyll cell density is further analyzed. The potential influences of modifying mesophyll cell morphology on CO2 diffusion, light distribution within the leaf, and other physiological processes are also discussed. Some potential target genes regulating leaf mesophyll cell proliferation and expansion are explored. Indeed, more comprehensive research is needed to understand how manipulating mesophyll cell morphology through editing the potential target genes impact leaf photosynthetic capacity and related physiological processes. This will pinpoint the targets for engineering leaf anatomy to maximize photosynthetic capacity.HighlightCell morphology in leaves affects photosynthesis by controlling CO2 diffusion and light distribution. Recent work has uncovered genes that control cell size, shape, and number paving the way improved photosynthesis.

Chloroplasts regulate their growth to optimize photosynthesis. Quantitative data shows that the ratio of total chloroplast area to mesophyll cell area is constant across different cells within a single species, and also across species. Wild-type chloroplasts exhibit little scatter around this trend; highly irregularly-shaped mutant chloroplasts exhibit more scatter. Here we propose a model motivated by a bacterial quorum-sensing model consisting of a switch-like signalling network that turns off chloroplast growth. We calculated the dependence of the location of the relevant saddle-node bifurcation on the geometry of the chloroplasts. Our model exhibits a linear trend, with linearly growing scatter dependent on chloroplast shape, consistent with the data. When modelled chloroplasts are of a shape that grows with a constant area to volume ratio (disks, cylinders) we find a linear trend with minimal scatter. Chloroplasts with area and volume that do not grow proportionally (spheres) exhibit a linear trend with additional scatter.

Plants experience a number of limiting factors, as drought and heat, which are often coinciding stress factors in natural environment. This study evaluated the changes in mesophyll cell ultrastructure in the leaves of two varieties of winter wheat (Triticum aestivum L.), differing in their drought tolerance, under individual or combined drought and heat treatment. Although the individual stress factors affected leaf ultrastructure, the damaging effect of the combined drought and heat was more pronounced and manifested certain differences between genotypes. Chloroplasts and mitochondria were affected in a variety-specific manner under all adverse treatments. The organelles of the drought-tolerant Katya were better preserved than those in the sensitive variety Sadovo. Leaf ultrastructure can be considered as one of the important characteristics in the evaluation of the drought susceptibility of different wheat varieties.

There is a need to develop rice plants with improved photosynthetic capacity and efficiency in order to enhance potential grain yield. Alterations in internal leaf morphology may be needed to underpin some of these improvements. One target is the production of a ‘Kranz-like’ anatomy, commonly considered to be required to achieve the desired levels of photosynthesis seen in C4 crops. Kranz anatomy typically has two or three mesophyll cells interspersing adjacent veins. As a first step to determining the potential for such anatomical modifications in rice leaves, a population of rice deletion mutants was analysed for alterations in vein patterning and mesophyll cells in the interveinal regions. Significant variation is demonstrated in vein arrangement and the sequential distribution of major and minor veins across the leaf width, although there is a significant correlation between the total number of veins present and the width of the leaf. Thus the potential is demonstrated for modifying rice leaf structure. Six distinct rice mutant lines, termed altered leaf morphology (alm) mutants, were analysed for the architecture of their interveinal mesophyll cell arrangement. It is shown that in these mutant lines, the distance between adjacent minor veins and adjacent minor and major veins is essentially determined by the size of the interveinal mesophyll cells rather than changes in mesophyll cell number across this region, and hence interveinal distance changes as a result of cell expansion rather than cell division. This observation will be important when developing screens for traits relevant for the introduction of Kranz anatomy into rice. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

Exposure to an elevated CO2 concentration ([CO2]) generally decreases leaf N content per unit area (Narea) and stomatal density, and increases leaf thickness. Mature leaves can ‘sense’ elevated [CO2] and this regulates stomatal development of expanding leaves (systemic regulation). It is unclear if systemic regulation is involved in determination of leaf thickness and Narea—traits that are significantly correlated with photosynthetic capacity. A cuvette system was used whereby [CO2] around mature leaves was controlled separately from that around expanding leaves. Expanding leaves of poplar (Populus trichocarpa3P. deltoides) seedlings were exposed to elevated [CO2] (720 mmol mol 21 ) while the remaining mature leaves inside the cuvette were under ambient [CO2 ]o f 360 mmol mol 21 . Reverse treatments were performed. Exposure of newly developing leaves to elevated [CO2] increased their thickness, but when mature leaves were exposed to elevated [CO2] the increase in thickness of new leaves was less pronounced. The largest response to [CO2] was reflected in the palisade tissue thickness (as opposed to the spongy tissue) of new leaves. The Narea of new leaves was unaffected by the local [CO2] where the new leaves developed, but decreased following the exposure of mature leaves to elevated [CO2]. The volume fraction of mesophyll cells compared with total leaf and the mesophyll cell density changed in a manner similar to the response of Narea. These results suggest that Narea is controlled independently of the leaf thickness, and suggest that Narea is under systemic regulation by [CO2] signals from mature leaves that control mesophyll cell division.

The microscopic and ultrastructural characteristics of mesophyll cells in flag leaves of two rice lines (a thermosensitive line 4628 and a thermo-resistant line 996) under high temperature stress (37°C during 8:00–17:00 and 30°C during 17:00–8:00) were investigated using an optical and a transmission electron microscopy. The membrane permeability and malondialdehyde content increased under the high temperature stress, and the increase of both variables was greater in the line 4628 than in the line 996. Under the high temperature stress, the line 996 showed tightly arranged mesophyll cells in flag leaves, fully developed vascular bundles and some closed stomata, whereas the line 4628 suffered from injury because of undeveloped vascular bundles, loosely arranged mesophyll cells and opened stomata. The mesophyll cells in flag leaves of the line 4628 were severely damaged under the high temperature stress, i.e. the chloroplast envelope became blurred, the grana thylakoid layer was arranged loosely and irregularly, the stroma layer disappeared, many osmiophilic granules appeared within the chloroplast, the outer membrane of mitochondria and the nucleus disintegrated and became blurred, the nucleolus disappeared, and much fibrillar-granular materials appeared within the nucleus. In contrast, the mesophyll cells in flag leaves of the line 996 maintained an intact ultrastructure under the high temperature stress. From these results, it is suggested that the ultrastructural modification of the cell membrane system is the primary plant response to high temperature stress and can be used as an index to evaluate the crop heat tolerance.

Recent design-based stereological methods that can be applied to thick sections cut in an arbitrary direction are presented and their implementation for measuring mesophyll anatomical characteristics is introduced. These methods use software-randomized virtual 3D probes, such as disector and fakir test probes, in stacks of optical sections acquired using confocal microscopy. They enable unbiased estimations of the mean mesophyll cell volume, mesophyll cell number in a needle, and for the first time an internal surface area of needles or other narrow leaves directly from the fresh tissue cross-sections cut using a hand microtome. Therefore, reliable results can be obtained much faster than when using a standard microtechnical preparation. The proposed methods were tested on Norway spruce needles affected for 1 year by acid rain treatment. The effect of acid rain resulted in changes of mesophyll parameters: the ratio of intercellular spaces per mesophyll cell volume increased, while needle internal surface area, total number of mesophyll cells, and number of mesophyll cells per unit volume of a needle decreased in the treated needles.

Ozone induces characteristic symptoms in the chloroplasts of the needles of several coniferous species. Chloroplasts are (1) reduced in size and (2) the stroma is electron dense. Moreover, (3) these chloroplast alterations are more pronounced in the outer mesophyll cell layers and in the upper side of the needle compared to the inner layers and lower side. The syndrome, including the three symptoms (1)-(3), is found in the green needles of Scots pine and Norway spruce not only in the experimental fumigations, but also in mature trees in the field, and has potential for diagnosis of ozone stress. For sound ozone diagnostics all three symptoms must be present in the samples studied. The symptoms in relation to needle anatomy and physiology is discussed, and recommendations for sampling and analysis are given.

This study characterises some aspects of foliar anatomy of cork oak micropropagated plantlets, and rates of water loss by different types of leaves during the acclimatization period. Water loss from leaves of in vitro cultured plantlets was much higher than that of acclimatized plants or seedlings. Leaves from in vitro plantlets lost 53% of their water within the first 30 min under water stress conditions, while leaves from acclimatized plants lost 14%. Leaves of in vitro grown plants presented open stomata and collapsed guard cells, while acclimatized leaves presented closed stomata. Shade-leaf structure was observed in transverse sections of in vitro leaves, with large intercellular air spaces and a low mesophyll cell density, but with a differentiated palisade cell layer. Leaves from acclimatized plants showed a sun-leaf structure with small intercellular air spaces, high cell density and two or three palisade cell layers. During acclimatization leaf thickness increased, as well as cell compactness and differentiation. Stomatal density, stomatal aperture and guard cell protuberance decreased during the acclimatization period, while trichome density increased.

Internal leaf anatomy of 56 species in 21 families from alpine, forest, and desert habitats was examined for relationships between anatomical characteristics that might be linked functionally to photosynthesis. Leaf mesophyll architecture, particularly the amount of cell surface area exposed to intercellular spaces (Ames), expressed per unit leaf area (A), or Ames/A, has previously been associated with increased photosynthesis per unit leaf area. The numerical value of Ames/A is influenced by leaf anatomical characteristics that include leaf thickness; the amount of intercellular air space; and mesophyll cell size, shape, and density. The Ames/A values measured using digital image analysis of oblique and transverse sections of leaves ranged from 2 to 34. The most important single variable predicting Ames/A was not leaf thickness or cell dimensions but the percent of mesophyll volume occupied by intercellular air space, %IAS. In addition, the extent of contact between individual mesophyll cells appeared to...

Chloroplast number per cell is a frequently examined quantitative anatomical parameter, often estimated by counting chloroplast profiles in two-dimensional (2D) sections of mesophyll cells. However, a mesophyll cell is a three-dimensional (3D) structure and this has to be taken into account when quantifying its internal structure. We compared 2D and 3D approaches to chloroplast counting from different points of view: (i) in practical measurements of mesophyll cells of Norway spruce needles, (ii) in a 3D model of a mesophyll cell with chloroplasts, and (iii) using a theoretical analysis. We applied, for the first time, the stereological method of an optical disector based on counting chloroplasts in stacks of spruce needle optical cross-sections acquired by confocal laser-scanning microscopy. This estimate was compared with counting chloroplast profiles in 2D sections from the same stacks of sections. Comparing practical measurements of mesophyll cells, calculations performed in a 3D model of a cell with chloroplasts as well as a theoretical analysis showed that the 2D approach yielded biased results, while the underestimation could be up to 10-fold. We proved that the frequently used method for counting chloroplasts in a mesophyll cell by counting their profiles in 2D sections did not give correct results. We concluded that the present disector method can be efficiently used for unbiased estimation of chloroplast number per mesophyll cell. This should be the method of choice, especially in coniferous needles and leaves with mesophyll cells with lignified cell walls where maceration methods are difficult or impossible to use.

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.

The effects of foliar application of marine algae extract (RIC-1) on the growth and development of roots and shoots in satsuma mandarin were studied under plastic house conditions. The 500 times diluted sprays of this extract enhanced the formation of fibrous roots and at higher concentration (300 times diluted), root rotting occurred. While at lower concentration (1000 times diluted), the roots became comparatively thicker. The formation of new branches and their lengths were higher in all treated trees with maximum value at 500 times diluted spray compared to those of control. The number of leaves and their size in terms of length and width were significantly,higher in the treated trees having the maximum output under 500 times diluted treatment. Light microscopic observation revealed the accumulation of numerous starch grains in the mesophyll cells of leaves in the treated trees. The starch grain number/cell increased along the increased concentration of RIC-1 sprays from 1000 times diluted to 300 times diluted. The width of mesophyll cell layer also similarly increased in RIC-1 treated leaves, This study suggested 500 times diluted RIC-1 spray as optimum for the growth and development of roots, branches and leaves of satsuma mandarin trees under plastic house conditions.

We explored whether epidermal pressure regulates cell and organ growth in leaflets ofPisum sativumvar.argenteum,a mutant cultivar of the garden pea characterized by reduced adhesion between the epidermis and subjacent mesophyll. Developing leaflets of leaves arising at three positions on the seedling axis were peeledin situand grown to maturity in humidity chambers. The mature anatomy and morphology could be accurately assessed because wound responses normally associated with peeling were prevented by theArgmutation that permitted peeling without damage to the mesophyll and by the humidity chambers that protected peeled areas from desiccation. The mesophyll cell size, state of differentiation, and layering pattern as well as the overall morphology of mature, peeled leaflets were indistinguishable from those of mature, intact leaflets grown under the same conditions. The epidermis exerted no detectable regulatory effect on the expansion of the leaflets as a whole or on the tissue layers and cells within the leaflets.

Two wheat genotypes, viz. Uniculm 'Gigas' (V1) and Kalyansona (V2) were raised to maturity under two levels of nitrogen supply @ 30 (N1) and 120 (N2) kg ha -1 , under pot culture conditions. Laminae numbering 1 to 8 on the shoot were examined for area, net photosynthetic rate (P n ) and mesophyll cell characteristics, at full expansion. N resulted in greater reduction in the area of upper laminae in V1 than in V2. The flag and penultimate laminae maintained similar P n rates at both N levels in V1 despite a large reduction in area at N1. However, V2 exhibited about 25 % reduction in P n rates of the flag laminae at N1 as compared with N2. Mesophyll cell number per unit area gradually increased with laminae order in the genotypes. The greater number of mesophyll cells in the upper laminae was essentially due to a reduction in cell size and surface area as a result of low N availability. The large differences in laminae size due to N treatments, particularly in V1, are attributed to mesophyll cell numbers. However, the maintenance of P n rates in V1, even at low N supply, is a possible outcome of higher activity of the mesophyll cell constituents in this genotype.

Freshly isolated mesophyll and suspensions-cell protoplasts of S. tuberosum cvs. Desiree and Maris Piper were cultured in different media i.e. modified MS, V-KM and MS-KM. Protoplast plating efficiencies were higher in MS-KM medium. Resulting protoplast-derived calluses were transferred either onto the medium of Bokelmann and Roest (1983) or that of Lam (1977) for shoot regeneration. Calluses derived from mesophyll cell protoplasts differentiated about 2 weeks earlier than calluses derived from suspension-cell protoplasts. Shoot initiation was also about 2 weeks earlier from calluses subcultured onto the former medium as compared to the latter.

Advances achieved during last fifteen years in the understanding the development of chloroplast ultrastructure during natural leaf ontogeny are summarized. Life span of a typical C3 mesophyll cell chloroplast is outlined and placed into the scheme of cyclic plastid interrelationships. Possible modifications of this development by stresses, environmental factors or experimental treatments are also shown.

The influence of potassium (K) deficiency on leaf water and osmotic potentials, and concentrations of major solutes was determined to assess their contributions to the leaf growth of soybean plants grown in solution cultures containing 5.0 and 0.2 mM KCl. A deficient supply of K restricted leaf growth due to decreased mesophyll cell numbers and cell enlargement, though water content, water and osmotic potentials of the expanding leaves were not affected by the treatment. The osmolarity of the expanding leaves showed very similar values in both treatments, though the K+ concentration in the K-deficient plants was remarkably lower than that of the control. In response to the K-deficiency, some cations, anions, sugars and amino acids accumulated in the expanding leaf, compensating the decrease in K concentration approximately 92%. These findings suggest that the leaf growth depression observed in the K-deficient plant occurred when the water relations of the K-deficient leaves are maintained close to that of the control.

Potamogeton crispus L. grows as a winter producing annual in the shallow lakes of the Pongolo Floodplain, South Africa. Colonization of leaves by algal and bacterial epiphytes, as seen by scanning electron microscopy, followed the established pattern of increasing diversity and density with leaf age. It was apparent from the micrographs that the primary and subsequent colonizers were present even after death of the host leaf. Cross sections of leaves, viewed by transmission electron microscopy, illustrated that bacterial attachment did not damage the surface of young leaves. There was, however, extensive inward swelling and disorganization of the epidermal walls, characteristic of a reaction to invasion by pathogens. In older leaves the swelling was also present in mesophyll cells, while bacteria had invaded and degraded the epidermal cell wall. The bacterial invasion was concomitant with signs of senescence, and in dead leaves the organisms had penetrated and degraded the epidermis and mesophyll cell walls. The epiphyton/ host relationship may therefore be considered necrotrophic with important consequences for the transfer of energy from producers to consumers during decomposition.

summary Needle mesophyll cell ultrastructure of 1st to 9th yr needles from Norway spruce (Picea abies (L.) Karst.) trees of different ages was studied at three different sites to determine the normal features of needle ageing, and the impact of air pollution on the needle ageing process. The sites included one rural area and two industrial environments, of which one contained SO2 emissions and the other SO2 and F emissions. The ultrastuctural features of needle mesophyll cells of different ages were found to be remarkably similar when young (20-yr-old) and mature (> 50-yr-old) trees were compared. Senescence-related ultrastructural symptoms such as increase in the number and size of plastoglobuli and an increase in the large lipid accumulations were observed with increasing needle age. In addition, the occurrence of lipid bodies in the central vacuole and an increased number of dark grains in the cell wall were detected in ageing needles. No changes in chloroplast length were observed during the ageing of needles, although the width of the chloroplasts showed a tendency to increase. A poor differentiation of granal membranes and an increase in small cytoplasmic lipid bodies and irregularly-shaped lipid material were symptoms typical of needles in the industrial areas. The ageing symptoms appeared in younger needles and were more evident in industrial areas than at the control site, suggesting an accelerated ageing process in the industrial areas.

Light microscopy and transmission electron microscopy revealed the location of previously identified large protein body globoids within the cotyledons of Cucurbita maxima seedlings. Large globoids formed in the three cell layers of the spongy mesophyll above the lower epidermis. The large globoids share morphological similarities to typical globoids by being spherical and naturally electron dense, but they were approximately four times the size of regular globoids, ranging from 4 to 8 μm in diameter. The formation of the large globoid particles occurred around 3 days of seedling growth and likely resulted from fusion of a number of typically sized globoids. This method of formation was supported by the appearance of clusters of regular globoids prior to the formation of the unusually large globoids. The volume of a large globoid was less than the combined volume of all the typical-sized globoids found within a mesophyll cell earlier in seedling growth. Keywords: large globoids, cotyledon, Cucurbita maxima, mesophyll, seedling, protein bodies.

Effects of water stress on gas exchange characteristics were investigated in a crassulacean acid metabolism plant, Dendrobium Ekapol cv. Panda when water was withheld from pot. The diurnal CO2 exchange rate, phosphoenolpyruvate carboxylase activity, malate content, leaf water potential and relative water content were measured at O, 3, 7, 14, 21 days from the beginning of treatment. The data showed that the diurnal CO2 exchange of D. Ekapol was rapidly changed after starting of treatment, that is, CO2 uptake of phase 4 disappeared and those of phases 1 and 2 decreased by half. In addition even though plants were exposed to such a long series of water stress, the CO2 exchange rate maintained a positive value. It was indicated that D. Ekapol had strong tolerance to drought as a crassulacean acid metabolism plant. The CO2 balances of each phase were decreased quickly when leaf water potential was decreased frim -0.38 to - 0.4MPa, it was recognized that the response of CO2 exchange was sensitive to a slight change of leaf water potential. Non-stomatal factors in CO2 fixation were not damaged by water stress due to phosphoenolpyruvate carboxylase activity was increased. The close correlation was observed between leaf conductance and CO2 exchange rate in each phase, therefore, it was suggested that CO2 exchange under water stress was controlled more by stomata than biochemistry in mesophyll cell.

Ozone is present in much of the United States and has been shown to reduce growth and development of some coniferous tree species. Slash pine ( Pinus elliotti ) is a unique species which occurs naturally only in southern Florida and several of the Lower Keys. The purpose of this research was to determine if mesophyll cells of slash pine needles respond to ozone in a manner similar to that of other conifers, to determine exposure—response relationships of mesophyll cell injury and ozone exposure level, and if needles of native trees that exhibit chlorotic mottle have more mesophyll cell death than asymptomatic needles. Fumigations were performed at four ozone levels with 7-hr mean values of 0, 55, 67, and 71 ppb for 84 days. Results show that ozone injury symptoms occur to mesophyll cells of needles before visible needle injury (chlorotic mottle). The predominant injury to needles was cell necrosis. Ozone exposure—response relationships of exposure (ppm-hr) percentage of dead cells showed a highly statistically significant ( P ) linear relationship of y = 3.56+0.58 ( x ) with a correlation coefficient of 0.86. These results support the conclusion that mesophyll cells of needles of slash pine are very sensitive to ozone. Results presented also indicate that needles from native slash pine trees at Everglades National Park show chlorotic mottle, similar to that exhibited by many conifers, and that such visible injury was generally related to a higher percentage of cell necrosis compared with needles without symptoms.

summary The death of many mature red spruce (Picea rubens Sarg.) trees in the northeastern United States has sparked controversy over the roles natural factors and air pollutants play. The goal of this work was to investigate the effects of long-term ozone exposures on development of injury and, in particular, the expression of winter injury in red spruce. Red spruce seedlings were exposed to elevated levels of ozone during two growing seasons, starting just after budbreak, and continuing into the period of early frosts. Trees spent both winter periods under ambient conditions of light and temperature. No visible lesions on foliage that could be attributed to ozone developed during the growing seasons. Yellow and brown needles appeared each winter, with much more injury in the second year. However, in the spring after two seasons of ozone exposure, there was no significant effect of ozone on the overall appearance of the entire population of seedlings. Samples were taken for histology and ultrastructure approximately monthly. Ozone treatments increased mesophyll cell disruption after frosts in early winter in the first year, but not in the second. There was no correlation between histological injury in the autumn and visible symptoms in the spring, indicating that there may be different aspects of the winter injury syndrome. In the second summer from 20 to 40%, of all mesophyll cells were damaged. This damage was not related to ozone treatment, and probably resulted from high summer temperatures.

The anatomical structure of the second leaf blade of barley (Hordeum vulgare L. cv. Koral) was studied in plants exposed to a photosynthetic photon flux density (PPFD) of 200 /*mol m ~2 s~1 compared with those grown under 25 /?mol m-2 s~'. Design based stereological methods were used for the estimation of various leaf anatomical characteristics such as mesophyll volume, proportion of intercellular spaces, number of mesophyll cells, mean mesophyll cell volume, and internal leaf surface area. The structure of the mesophyll was more affected by different levels of PPFD than were the stomatal characteristics. Increased PPFD produced thicker leaves with a larger mesophyll volume having a higher number of less elongated mesophyll cells and a larger internal leaf surface area.

The structural changes in leaves of grapevine plants (Vitis vinifera L.) exposed to different ozone concentrations was investigated. Ozone fumigations were performed in open-top chambers at four different ozone levels (charcoal-filtered air (F), ambient air (N), ambient air + 25 mm3m-3 ozone (O-25) and ambient air + 50 mm3m-3 ozone (O-50)). The leaves of plants from chambers with increased ozone concentrations (O-25 and O-50) were significantly thicker than the controls (F), owing to increased thickness of the mesophyll layer. Observing O-50 leaves, it was found that the mesophyll cell wall displayed structural changes. In some places cell wall thickness increased up to 1 &micro ; ; m. We found callose deposits on the inner side of the cell walls of mesophyll cells. These data are in accord with the concept that the mesophyll cell wall acts as a barrier against the penetration of tropospheric ozone into the cells.

The internal conductance for CO(2) diffusion (g(i)) and CO(2) assimilation rate were measured and the related anatomical characteristics were investigated in transgenic rice leaves that overexpressed barley aquaporin HvPIP2;1. This study was performed to test the hypothesis that aquaporin facilitates CO(2) diffusion within leaves. The g(i) value was estimated for intact leaves by concurrent measurements of gas exchange and carbon isotope ratio. The leaves of the transgenic rice plants that expressed the highest levels of Aq-anti-HvPIP2;1 showed a 40% increase in g(i) as compared to g(i) in the leaves of wild-type rice plants. The increase in g(i) was accompanied by a 14% increase in CO(2) assimilation rate and a 27% increase in stomatal conductance (g(s)). The transgenic plants that had low levels of Aq-anti-HvPIP2;1 showed decreases in g(i) and CO(2) assimilation rate. In the plants with high levels of Aq-anti-HvPIP2;1, mesophyll cell size decreased and the cell walls of the epidermis and mesophyll cells thickened, indicating that the leaves had become xeromorphic. Although such anatomical changes could partially offset the increase in g(i) by the aquaporin, the increase in aquaporin content overcame such adverse effects.

Microtubule-like structures were observed in mesophyll cell chloroplasts during the ontogeny of the second leaf of wheat cultured in full nutrient solution as well as under nitrogen deficiency.

Leaves are among the most specialized of all plant organs, devoting most of their activity to the production of ribulose-l,5-bisphosphate carboxylase-oxygenase (RuBISCO). This key protein is mentioned here to introduce the chapter on leaves not only because of its importance as a primary enzyme for carbon fixation in the initial reaction of photosynthesis, but also to emphasize that all of the, structural and developmental adaptations of leaves are geared to maximize the production of RuBISCO.

According to a recent proposal (Oparka and Van Bel 1992), phloem loading is the transfer of photosynthates from the site of production via the mesophyll symplast to the sieve tubes. The definition implies that phloem loading comprises a range of sequential processes of which carbohydrate metabolism in the mesophyll and sieve element loading have received ample attention.

Xylem cells are formed from the procambium of the root and shoot in the primary xylem and from the vascular cambium in the secondary xylem. The main components of xylem cells are tracheary elements, which are characterized by the formation of secondary cell walls that thicken with annular, spiral, reticulate or pitted patterns. At maturity, differentiating tracheary elements lose their nuclei and cell contents, leaving behind hollow tubes that form vessels and trac-heids. In vitro, tracheary elements can be induced from the parenchymatous cells of various plant species by wounding and/or the application of phytohormones [1].

Gentiana, a member of the Gentianaceae family, is composed of 400 species widely distributed all over the world except for the African continent. Most of them are perennial herbs and are grown in the cool mountainous regions. Several species of Gentiana are used as economically important flowers and ornamental plants. G. scabra and G. triflora, which are distributed in the Far East, have especially been cultivated commercially in Japan for more than 40 years. Since the cultivar Iwate, which is an F1 hybrid between G. triflora and G. scabra, was bred in 1977, 33 cut flower and 16 pot flower cultivars have been registered until 1992 in Japan (Yoshiike 1992). Other species such as G. acaulis, G. sino-ornata, and G. verna are also used as plants for rock gardens in Europe.

In one- and two-year-old green needles ofPinus pinaster growing downwind from a coal-fired power station (main airborne pollutant SO2), mesophyll chloroplast alterations consisted in swelling of the lamellae (ranging in intensity from slight to pronounced), reduction of grana number, and granulation of the stroma. The most severely affected chloroplasts were almost spherical, with highly dilated and corrugated lamellae and lacunae in the stroma. There was a large increase in the amount of lipid-like material present as droplets in cytoplasm, vacuole and stroma chloroplasts; these droplets appeared to be expulsed from the chloroplasts to the cytoplasm and vacuole. The trees with the most severely affected chloroplasts stood southwest of the power station,i.e. downwind with respect to the winds prevailing most of the year. Chloroplasts from two-year-old needles were more affected than those from one-year-old needles.

Moricandia arvensis is of interest as it is a dicotyledonous species which has C3 - C4 intermediate photosynthesis, a mechanism which results in enhanced recapture of photorespired CO2. Leaves from cultured shoot tips were used as a source for mesophyll cell protoplasts. Approximately 1% of the protoplasts which survived the first few days of culture produced calli. On a suitable regeneration medium, 30-60% of the calli regenerated one or more shoots. From among the regenerating shoots eight were selected, transferred to soil and grown to flowering in the glasshouse; all were fertile. The development of a protoplast regeneration system provides the opportunity to use transformation and somaclonal variation as tools in the genetic analysis of the C3-C4 character in this species.

FIG. 2 – A. Electron micrographs of flexuous filamentous particles, about 720 nm long, strongly decorated with specific antiserum against Turnip mosaic virus (TuMV), note a dense halo surrounding particles; B. Dense laminar aggregates, scrolls and pin-wheel are observed in ultra-thin section of an infected horseradish mesophyll cell. Bars = 200 nm A B RESUMO Primeiro relato do Turnip mosaic virus em raiz-forte no Brasil Este trabalho relata a primeira ocorrencia do Turnip mosaic virus (TuMV) em plantas de raiz-forte (Armoracia rusticana G. Gaertn., B. Mey. & Scherb.) provenientes de cultivos comerciais no Estado de Sao Paulo. Ate entao, este virus somente havia sido descrito em especies do genero Brassica no Brasil.

The present revision of Christensenia is the first for this genus. Observations of exter­ nal and interna!foliar morphology, with particular emphasis on valid taxonomic charac­ ters of pinna indument and epidermis and soral paraphyses have shown that the taxa of the genus are C. aesculifolia Blume subsp. aesculifolia and subsp. korthalsii (de Vriese) Rolleri and C. lobbiana (de Vriese) Rolleri. Synangium outline, number of sporangia per synangium, and spore morphology are not systematically important. The morphology and physiology of adult porocyclocytic stomates and the presence, chemical composition, and density of microprojections of the mesophyll cell walls are adaptive and vary according to ambient humidity. The generic name Christensenia was proposed by Maxon (1905) to replace the later homonym Kaulfussia Blume. De Vriese and Harting (1853) recognized four species of Kaulfussia, K. aesculifolia Blume (Java and the Philippines), K. assamica Griff. (Assam), K. korthalsii de Vriese (Sumatra and the Philippines), and K. lobbiana de Vriese (Java). Baker (1874, p. 444) synonymized the three later species in K. aesculifolia, and most later scholars agreed, including Maxon (1905), although he did acknowledge variation within the inclusive species C. aesculifolia (Blume) Maxon. Christ (1907) described C. cumingiana from the Philippines. Christensen (1938, p. 528) mentioned "2 Malayan

French bean cultivars respond to cowpea rust infection by the production of naturally electron-opaque deposits on the surrounding mesophyll cell walls. Deposition of this material was inhibited by prior treatment of the leaves with actinomycin D, cycloheximide and blasticidin S, and was elicited by washings from fungal infection structures, or less reliably, by injection of water. Energy dispersive X-ray (EDX) analysis of rust-induced deposits revealed silicon as the only element (with an atomic number of 11 or higher) present in significant amounts. Concentrations were roughly proportional to the amount of electronopaque material present and no silicon was detected in walls lacking such deposits. Cytochemical tests at the light microscope level suggested that deposits only rarely contained high levels of phenolic compounds. Similarly, EDX analysis of FeCl3-treated tissue revealed only low levels of bound iron (possibly indicative of phenolic compounds) in the deposits while higher levels were found in deposit-lacking walls of cells in the immediate vicinity of the fungus. These results suggest that silicon, rather than phenolic compounds, is the primary electron-opaque component of the wall deposits formed in this non-host interaction and that, contrary to suggestions for silicon deposition in some other situations, formation of these deposits is controlled by metabolic activity of the protoplast.

Structural features related to the pathway of water movement in the leaf of hemlock, Tsuga canadensis (L.) Carr., have been examined in conjunction with investigations of plant water relations. Cell surface areas and volumes were determined by projecting 2-μm serial sections, measuring them with a map tracer, and multiplying cell perimeters by section thickness; or by the trace–cut–weigh method. Scanning electron microscope observations showed that the stomata are occluded with a continuous layer of rod-like wax particles. The average maximum distance over which water must move from the xylem of the single median bundle to the mesophyll is 770 μm, and each 40 μm of length of vein (the diameter of a mesophyll cell) supplies 196 cells. The palisade mesophyll consists of two layers, while the spongy mesophyll is arranged in sheets which radiate from the vascular bundle to the margin and alternate with large intercellular spaces. The mesophyll cell walls may provide the pathway through which the bulk of the water moves; the volume occupied by the mesophyll cell walls is 1.27 × 10−4 cm3 or 2.5% of total leaf volume. The total evaporative surface area of the mesophyll is 1.61 cm2 per leaf.

Leaves of twelve C3 species and six C4 species were examined to understand better the relationship between mesophyll cell properties and the generally high photosynthetic rates of these plants. The CO2 diffusion conductance expressed per unit mesophyll cell surface area (gCO2cell) cell was determined using measurements of the net rate of CO2 uptake, water vapor conductance, and the ratio of mesophyll cell surface area to leaf surface area (Ames/A). Ames/A averaged 31 for the C3 species and 16 for the C4 species. For the C3 species gCO2cell ranged from 0.12 to 0.32 mm s-1, and for the C4 species it ranged from 0.55 to 1.5 mm s-1, exceeding a previously predicted maximum of 0.5 mm s-1. Although the C3 species Cammissonia claviformis did not have the highest gCO2cell, the combination of the highest Ames and highest stomatal conductance resulted in this species having the greatest maximum rate of CO2 uptake in low oxygen, 93 μmol m-2 s-1 (147 mg dm-2 h-1). The high gCO2cell of the C4 species Amaranthus retroflexus (1.5 mm s-1) was in part attributable to its thin cell wall (72 nm thick).

Observations have been made on the anatomy of beech, Fagus grandifolia Ehrh., with an emphasis on quantitative features. All surface areas and volumes were determined by projecting 2-μm serial sections, measuring them with a map tracer, and multiplying cell perimeters by section thickness or by the trace–cut–weight method. The organization of tissues, including a complex reticulate venation, is typical of many dicotyledons. Of the minor veins, only the quinternaries and veinlets lack bundle sheath extensions and have wholly parenchymatous bundle sheaths, the cells of which are often oriented at right angles to the vein. There are 12.1 mm of vein per square millimetre of leaf surface area, and 10 μm of vein (the diameter of a mesophyll cell) serves about 21.5 mesophyll cells. The mean maximum distance over which water and solutes must move between vascular tissue and mesophyll is 55 μm. The mesophyll cell walls may provide the pathway through which the bulk of the water moves; the volume occupied by the mesophyll cell walls is 55.7 mm3 or 11% of total leaf volume. The evaporative surface of the mesophyll is 13.36 mm2/mm2 leaf surface area.