Bundle Sheath Extensions Research Articles

Morphological and physicochemical traits of leaves of different life-forms of various broadleaf woody plants in interior Alaska

The morphological and physicochemical traits of leaves are important in terms of plant adaptation to various growth environments, because such traits play central roles in various functions including photosynthesis. We measured the toughness, mass per unit area (LMA), nitrogen content, and δ15N levels of the leaves of different life-forms of 39 broadleaf woody plants in interior Alaska. The plants were divided into three life-forms based on the maximum height of adult plants: understory (<1 m), small (≥1 m to <5 m), and canopy (≥5 m). Evergreen species accounted for a large proportion of understory woody plants (44%), whereas most small (87%) and canopy (100%) trees were deciduous. Higher LMA, increased toughness, and higher C-to-N ratios prolonged leaf life-span in evergreen species. We also evaluated the presence or absence of bundle-sheath extensions (BSEs), which contribute to the mechanical support of leaves and enhance photosynthetic ability by improving hydraulic properties. In total, 11 species (28%) had homobaric leaves (BSEs were absent) and 28 species (72%) had heterobaric leaves; these proportions are similar to those of woody plants of other temperate deciduous forests. The δ15N values reflected the presence of root symbionts such as ericoid mycorrhiza or Frankia sp. Our results suggest that leaf traits may affect both the life-form of the host plants and leaf longevity in both evergreen and deciduous species.

Distribution of homobaric and heterobaric leafed species in the Brazilian Cerrado and seasonal semideciduous forests

Plant species can be classified into heterobaric and homobaric, depending on whether their leaves present bundle sheath extensions (BSEs) (heterobaric) or not (homobaric). Incidences of the two leaf types seem to be related to growth environment and the light stratification. The Brazilian Cerrado and seasonal semideciduous forests are contrasting environments mainly with regard to irradiance and air humidity. However, studies comparing the distributions of homobaric and heterobaric species in these vegetation types are lacking. We investigate the presence/absence of leaf BSEs across diverse habits (herbs, shrubs and trees) in a seasonal semideciduous forest, cerrado sensu stricto (open physiognomy) and cerradão (forest physiognomy) to evaluate the influence of plant habit and growth environment on the distribution of homobaric and heterobaric species. Leaves from 131 species in 54 angiosperm families were analysed using standard methods of light microscopy. The distribution of the different leaf types in each environment was analysed using the χ2 test and Fisher’s exact test (P<0.05). Homobaric and heterobaric leafed species occur in all environments and do not correlate with plant habit. Of the total number of species examined, 103 (78.6%) exhibited homobaric leaves and 28 (21.4%) presented heterobaric leaves. Of the total of heterobaric species, 8.8% occurred in the seasonal semideciduous forest, 50% in the cerradão and 41.2% in the cerrado sensu stricto. This model of distribution may be related to the higher irradiances in Cerrado. Homobaric leaves of shrubs and trees were thicker in all environments, while heterobaric leaves of herbs were thicker in the Cerrado. This study finds a tendency for the distribution pattern of homobaric or heterobaric leaves to reflect both the growth environment and the taxonomic grouping. Since leaf type is a constitutive characteristic, interspecific differences in leaf type may reflect particular physiological behaviours, linking them to success in colonising particular environments.

The influence of leaf anatomy on the internal light environment and photosynthetic electron transport rate: exploration with a new leaf ray tracing model.

Leaf photosynthesis is determined by biochemical properties and anatomical features. Here we developed a three-dimensional leaf model that can be used to evaluate the internal light environment of a leaf and its implications for whole-leaf electron transport rates (J). This model includes (i) the basic components of a leaf, such as the epidermis, palisade and spongy tissues, as well as the physical dimensions and arrangements of cell walls, vacuoles and chloroplasts; and (ii) an efficient forward ray-tracing algorithm, predicting the internal light environment for light of wavelengths between 400 and 2500nm. We studied the influence of leaf anatomy and ambient light on internal light conditions and J The results show that (i) different chloroplasts can experience drastically different light conditions, even when they are located at the same distance from the leaf surface; (ii) bundle sheath extensions, which are strips of parenchyma, collenchyma or sclerenchyma cells connecting the vascular bundles with the epidermis, can influence photosynthetic light-use efficiency of leaves; and (iii) chloroplast positioning can also influence the light-use efficiency of leaves. Mechanisms underlying leaf internal light heterogeneity and implications of the heterogeneity for photoprotection and for the convexity of the light response curves are discussed.

Altitudinal changes in leaf hydraulic conductance across fiveRhododendronspecies in eastern Nepal

This study investigated altitudinal changes in leaf-lamina hydraulic conductance (KL) and leaf morphological traits related to KL using five Rhododendron species growing at different altitudes (2500-4500 m above sea level) in Jaljale Himal region in eastern Nepal. Sun leaves were collected from the highest and the lowest altitude populations of each species, and KL was measured with a high pressure flow meter method. Leaf-lamina hydraulic conductance ranged from 7.7 to 19.3 mmol m-2 s-1 MPa-1 and was significantly positively correlated with altitude. The systematic increase with altitude was also found in KL, leaf nitrogen content and stomatal pore index. These relationships suggest that plants from higher-altitude habitats had a large CO2 supply to the intercellular space in a leaf and high CO2 assimilation capacity, which enables efficient photosynthesis at high altitude. The variation in KL was associated with the variation in several leaf morphological traits. High KL was found in leaves with small leaf area and round shape, both of which result in shorter major veins. These results suggest that the short major veins were important for efficient water transport in unlobed leaves of Rhododendron species. The extent of lignification in bundle sheaths and bundle sheath extension was associated with KL Lignified compound primary walls inhibit water conduction along apoplastic routes. All species analyzed had heterobaric leaves, in which bundle sheath extensions developed from minor veins, but strongly lignified compound primary walls were found in Rhododendron species with low KL It is still unclear why cell walls in bundle sheath at minor veins were markedly lignified in Rhododendron species growing at lower altitude. The lignified cell wall provides a high pathogenic resistance to infection and increases the mechanical strength of cell wall. The data imply that lignified bundle sheath may provide a trade-off between leaf hydraulic efficiency and leaf mechanical toughness or longevity.

Anatomical characterization of vegetative organs and scapes of Rondonanthus (Eriocaulaceae, Poales)

Eriocaulaceae is a pantropical family and comprises ten genera. Rondonanthus is endemic to the north region of South America and comprises six species. The anatomy of roots, stem, leaves, and scapes were studied in four species to characterize the genus and to identify characteristics with taxonomic value. The following characteristics are diagnostic of Rondonanthus: roots—heterogeneous cortex with an aerenchyma supported by arm cells and vascular cylinder with a central metaxylem vessel element; stems—idioblasts with druses in the cortex and in the pith; leaves—Malpighian hairs, hypodermis in the adaxial surface, chlorenchyma with arm cells, druse idioblasts in the mesophyll, and vascular bundle sheath extensions with rounded cells; scapes—Malpighian hairs and chlorenchyma with arm cells. Rondonanthus capillaceus differed from the remaining studied species by presenting roots with a homogeneous cortex with thin-walled cells; filiform leaves without stomata and trichomes but with a chlorophyllous epidermis and a parenchymatous mesophyll and only one central vascular bundle without sheath extension. Such differences may be related to the habitat, since this species grows on river margins and requires hydrodynamic organs. The number of vascular bundles in the leaves is a useful characteristic to differentiate among species.

Occurrence of homobaric and heterobaric leaves in two forest types of southern Brazil

In ombrophilous forests, light stratification provokes different adjustments by plants for better use of the environmental conditions of each stratum. Among the morphological traits that vary with strata, the presence of bundle sheath extensions (BSEs) is related to water transport, photosynthesis, and leaf mechanical support and classifies leaves as homobaric or heterobaric. This study analyzed the proportion of these types of leaves in a Lowland Ombrophilous Dense Forest (LLODF) and a Mixed Ombrophilous Forest (MOF), and among the strata of each forest type. The morphological leaf traits of 89 LLODF tree species and 57 MOF tree species were examined. The proportion of homobaric and heterobaric leaves did not differ between forests. However, in both forest types, the distribution of species with heterobaric or homobaric leaves depended on strata, with heterobaric species occurring mainly in higher strata, and homobaric species in lower strata. Thus, light stratification acts as an ecological filter on the composition of the vegetation of these forests, favoring heterobaric species in places with higher light intensity and temperature, such as the highest strata of canopy. On the other hand, homobaric species are more frequent in lower strata, where light is less available and humidity higher.

Stomatal conductance scales with petiole xylem traits in Populus genotypes.

Progress has been made in linking water transport in leaves with anatomical traits. However, most of our current knowledge about these links is based on studies that sampled phylogenetically distant species and covered a wide range of leaf size and morphology. Here we studied covariation of leaf anatomical traits and hydraulic capacity in five closely related hybrid poplar genotypes. Variation in stomatal conductance and leaf hydraulic conductance was not linked to vein density or other anatomical lamina properties. A strong correlation was found between stomatal conductance and the transport capacity of the petiole, estimated from the diameter and number of xylem vessels. An inverse relationship existed between leaf size and major vein density. The role of bundle sheath extensions is discussed. Our data suggests that petiole xylem is an important predictor of gas exchange capacity in poplar leaves.

Systematic Importance of Leaf Anatomical Characters in Some Species of &amp;lt;i&amp;gt;Microcos&amp;lt;/i&amp;gt; Linn. Section &amp;lt;i&amp;gt;Eumicrocos&amp;lt;/i&amp;gt; Burret. in Nigeria

The leaf anatomy of six Microcos L. species belonging to section Eumicrocos in Nigeria was investigated by transverse sectioning of the lamina and examined by light microscope to determine their taxonomic significance in species delimitation and classification. The common anatomical characteristics in all the species are as follows: the uniseriate epidermis; the hypostomatic and bifacial leaves; presence of 2 layers of palisade tissues; presence of bundle sheath extension to both epidermises; presence of glandular and non-glandular trichomes; presence of secretory ducts on abaxial surface; presence of druse crystal in the mesophyll and midrib and; sclerenchyma cells associated with the phloem. Anatomical characters which are significant for species delimitation include: the presence/absence of sclerenchyma cells associated with the xylem in the midrib; presence/absence of starch grains in the mesophyll and midrib; the presence/absence of secretory ducts on the adaxial surface of the midrib; the presence/absence of medullary plates in midrib; the number of secretory ducts in the midrib and the midrib adaxial outline. The section can be separated into two distinct groups based on the number of spongy tissue layers in the mesophyll, number of sclerenchyma cells associated with the phloem and presence/absence of sclerenchyma cells in xylem both groupings correlated with those obtained from foliar epidermal and pollen characters. The importance of these characters is discussed in relation to the taxonomy of the taxon.

Anatomia da lâmina foliar de onze espécies lenhosas dominantes nas savanas de Roraima

O conhecimento da anatomia da folha é crucial para o entendimento da adaptação das plantas ao ambiente. O objetivo deste estudo foi descrever a anatomia da lâmina foliar de 11 espécies lenhosas, frequentes nas savanas do extremo norte da Amazônia, com ênfase na identificação de atributos adaptativos a ecossistemas abertos, sujeitos a forte insolação e déficit hídrico sazonal. Amostras de folhas foram coletadas e processadas segundo técnicas usuais para estudos de anatomia e histoquímica. Bowdichia virgilioides, Byrsonima coccolobifolia, By. crassifolia, By. verbascifolia, Casearia sylvestris, Curatella americana, Erythroxylum suberosum, Himatanthus articulatus, Miconia albicans, Roupala montana e Xylopia aromatica apresentaram caracteres típicos de plantas heliófilas e xerófilas, como cutícula espessa e estômatos predominantes na face abaxial, além de forte investimento em tecido fotossintético. Em oito das onze espécies, o parênquima paliçádico (PP) ocupa 50% ou mais do espaço do mesofilo. Curatella americana, mesofilo isobilateral, e Bo. virgilioides, mesofilo homogêneo, foram as espécies com maior investimento em PP (~80% e 100%, respectivamente). Além disso, destaca-se a presença de hipoderme (Bo. virgilioides e X. aromatica) ou de epiderme estratificada, densos indumentos, idioblastos cristalíferos e extensões da bainha de feixes. Em síntese, este conjunto de atributos estruturais protege a lâmina foliar contra o excesso de luminosidade, aumenta a resistência mecânica, minimiza a transpiração e contribui para manutenção do balanço hídrico da planta, favorecendo, portanto, o estabelecimento destas espécies nas savanas sazonais do norte da Amazônia.

Anatomy, Histochemistry, and Antifungal Activity of Anacardium humile (Anacardiaceae) Leaf.

Leaves of Anacardium humile are used in Brazilian traditional medicine for the treatment of intestinal disturbances and skin lesions. This study aimed to define leaf diagnostic structural characters, to propose a new method of phytochemical analysis of secretions, prospect flavonoids and alkaloids, and to evaluate their inhibitory activity on Candida albicans. Common anatomical, phytochemical, and microbiological methods were used. Leaves of Anacardium occidentale were used as a reference for the structural analyses. The main structural characters were closed vascular system, absence of ducts at the medulla, bilateral mesophyll, absence of bundle sheath extension, and secretory idioblasts at the xylem. The ducts present schizogenous origin, and secreting activity is restricted to the initial phases of leaf blade expansion. The proposed new phytochemical method is practical and inexpensive and has potential for wide application. The abundance of tannins and flavonoids is related to medicinal use. A single peak in high-performance liquid chromatography indicated the presence of a pure substance not previously reported. The extract had a strong inhibitory effect on C. albicans. The obtained results confirm the potential of A. humile for the prospection of new bioactive compounds.

Stomatal patchiness of grapevine leaves. I. Estimation of non-uniform stomatal apertures by a new infiltration technique

Non-uniform stomatal behaviour of vine leaves is associated with a heterobaric leaf structure. A microscopical analysis of cross sections of glasshouse- and in vitro-grown Silvaner leaves indicates single airspaces which are pneumatically isolated by vessels, bundle sheath extensions and the abaxial and adaxial epidermes. A pressure-regulated infiltration technique is presented by which the infiltration process and the infiltration capacity (percentage of the surface area of infiltrated airspaces) can be estimated and photographed using a light microscope. The average surface area of airspaces ranged from 0.10 mm 2 (Regent) to 0.14 mm 2 (Silvaner), the number of stomata per airspace from 35 (Regent) to 42 (Silvaner). The infiltration capacity of turgid leaves is shown to be negatively correlated with the surface tension of the infiltrated liquid and positively with stomatal conductance and with infiltration pressure, except for very low stomatal conductances (e.g. 12 mmol H 2 O m -2 s -1 ). The latter relationship follows a saturation curve confirming heterogenous stomatal aperture over the leaf blade. The distribution of stomatal apertures does not appear to be bimodal but to follow a bell-shaped curve. There is some evidence for the stomata of an airspace to behave heterogenously as well.

Leaf anatomy is associated with the type of growth form in Neotropical savanna plants

Scleromorphic leaf structures are associated with plants growing under drought-prone conditions, high irradiances, and nutrient-poor soils. Sclerophylly can also be a valuable deterrent against herbivores. However, comprehensive studies of leaf anatomical traits encompassing different growth forms are lacking. The savannas of central Brazil (Cerrado) are characterized by high species diversity and a variety of growth forms. We performed a field study to characterize leaf anatomical traits and leaf mass per area (LMA) in 57 co-occurring Cerrado species of distinct plant families (located at different positions in the angiosperm phylogeny) and categorized according to the following growth forms: trees, palms, shrubs, subshrubs, vines, grasses and herbs. Plant growth form and leaf structure were interrelated. Four groups with distinct leaf anatomical syndromes were identified by NMDS analysis: grasses, palms, herbaceous (herbs, vines, and most subshrubs), and woody (trees and shrubs) plants. Trees and shrubs had scleromorphic dorsiventral leaves, with high tissue thickness and LMA. Herbaceous plants had thin, mesomorphic leaves. While most herbaceous plants had dorsiventral type of mesophyll, grasses and palms had homogenous mesophyll with sclerenchymatous bundle sheath extensions. Palms differed from grasses by having thicker leaves and sclerenchymatous hypodermis. In conclusion, Neotropical savannas cannot be exclusively described as scleromorphic vegetation.

Capsule structure in three species ofDyckia(Bromeliaceae): Ontogenetic and taxonomic issues1

Dyckia is characterized by conserved external floral and fruit morphology. Considering the conservative morphology of Dyckia fruits, anatomical features could be an important source of phylogenetically useful characters. The objectives of this study were to characterize fruit ontogeny and dehiscence in three species of Dyckia (Dyckia distachya, Dyckia reitzii, and Dyckia remotiflora), and in the process to identify characters that contribute to the systematics of the genus and family. Differences were found among species in the number of mesophyll/mesocarp layers, presence of pluristratified hypodermis, presence of mucilage secretory structures, and presence of perivascular bundle sheath extensions. In addition, a xerochastic mechanism of dehiscence in Dyckia denticidal capsules is described here for the first time. As a potential source of characters, fruit anatomical features can be useful at the generic and specific levels.

Occurrence of stomatal patchiness and its spatial scale in leaves from various sizes of trees distributed in a South-east Asian tropical rainforest in Peninsular Malaysia.

In this study, we demonstrated the occurrence of stomatal patchiness and its spatial scale in leaves from various sizes of trees grown in a lowland dipterocarp forest in Peninsular Malaysia. To evaluate the patterns of stomatal behavior, we used three techniques simultaneously to analyze heterobaric or homobaric leaves from five tree species ranging from 0.6 to 31 m in height: (i) diurnal changes in chlorophyll fluorescence imaging, (ii) observation and simulation of leaf gas-exchange rates and (iii) a pressure-infiltration method. Measurements were performed in situ with 1000 or 500 μmol m(-2) s(-1) photosynthetic photon flux density. Diurnal patterns in the spatial distribution of photosynthetic electron transport rate (J) mapped from chlorophyll fluorescence images, a comparison of observed and simulated leaf gas-exchange rates, and the spatial distribution of stomatal apertures obtained from the acid-fuchsin-infiltrated area showed that patchy stomatal closure coupled with severe midday depression of photosynthesis occurred in Neobalanocarpus heimii (King) Ashton, a higher canopy tree with heterobaric leaves due to the higher leaf temperature and vapor pressure deficit. However, subcanopy or understory trees showed uniform stomatal behavior throughout the day, although they also have heterobaric leaves. These results suggest that the occurrence of stomatal patchiness is determined by tree size and/or environmental conditions. The analysis of spatial scale by chlorophyll fluorescence imaging showed that several adjacent anatomical patches (lamina areas bounded by bundle-sheath extensions within the lamina) may co-operate for the distributed patterns of J and stomatal apertures.

COMPARATIVE LEAVES ANATOMY OF PANDANUS, FREYCINETIA AND SARARANGA (PANDANACEAE) AND THEIR DIAGNOSTIC VALUE

Study in leaves anatomy of twenty nine samples of the species classified under Pandanus, Freycinetia and Sararanga of Pandanaceae had been undertaken to unravel generic relationship among of these taxa with a view to provide a set of diagnostic characters for taxonomic identification. The fourth genus of Pandanaceae, Benstonea is not included in this analysis since there are no representative samples. Four anatomical diagnostic characters had been identified at the generic level such as present and absent of papillae, stomatal arrangement types, present and absent of bundle sheath extension and hypodermal thickness and its shape. Pandanus has papillae, amphistomatous stomata, bundle sheath extension present and hypodermis thin and rectangular; Freycinetia lacked of papillae, stomata hypostomatous or amphistomatous, bundle sheath extension absent and hypodermis thick and hexagonal or rounded; meanwhile Sararanga has no papillae, stomata amphistomatous, bundle sheath extension absent and hypodermis thin and flatten. An identification key to those genera based on anatomical diagnostic characters is provided.

A mutation that eliminates bundle sheath extensions reduces leaf hydraulic conductance, stomatal conductance and assimilation rates in tomato (Solanum lycopersicum).

Bundle sheath extensions (BSEs) are key features of leaf structure whose distribution differs among species and ecosystems. The genetic control of BSE development is unknown, so BSE physiological function has not yet been studied through mutant analysis. We screened a population of ethyl methanesulfonate (EMS)-induced mutants in the genetic background of the tomato (Solanum lycopersicum) model Micro-Tom and found a mutant lacking BSEs. The leaf phenotype of the mutant strongly resembled the tomato mutant obscuravenosa (obv). We confirmed that obv lacks BSEs and that it is not allelic to our induced mutant, which we named obv-2. Leaves lacking BSEs had lower leaf hydraulic conductance and operated with lower stomatal conductance and correspondingly lower assimilation rates than wild-type leaves. This lower level of function occurred despite similarities in vein density, midvein vessel diameter and number, stomatal density, and leaf area between wild-type and mutant leaves, the implication being that the lack of BSEs hindered water dispersal within mutant leaves. Our results comparing near-isogenic lines within a single species confirm the hypothesised role of BSEs in leaf hydraulic function. They further pave the way for a genetic model-based analysis of a common leaf structure with deep ecological consequences.

Anatomically Preserved Early Cretaceous Bennettitalean Leaves: Nilssoniopteris corrugata n. sp. from Vancouver Island, Canada

Early Cretaceous fossilized leaves assignable to the extinct seed plant order Bennettitales occur within an exceptionally diverse Early Cretaceous (Valanginian) flora of anatomically preserved plant fossils at Apple Bay on Vancouver Island, British Columbia, Canada. One of the bennettitalean leaf types has an entire margin, with laminae that are attached near the adaxial surface of the midvein. Leaves are 10–15 mm wide with an adaxial surface that shows distinct corrugations, and a midrib that is exposed adaxially. The vascular system of the midrib consists of a crescent-shaped ring of collateral bundles. Lateral veins diverge from midrib at ∼90°, are typically simple but occasionally branch at base of the lamina. Vein density is 12–15 per cm. Leaves are hypostomatic with syndetocheilic stomata that are randomly oriented between veins. Internal anatomy consists of an adaxial hypodermis of closely-spaced isodiametric cells, mesophyll that is differentiated into adaxial palisade and abaxial spongy zones, and collateral bundles that show a distinct bundle sheath with bundle sheath extensions. This novel combination of characters represents the diverse bennettitalean genus Nilssoniopteris. Nilssoniopteris corrugata new species is only the second species of the genus for which internal anatomy is preserved. This species increases the known variation of bennettitalean leaf anatomy, and reinforces our appreciation for the global distribution of bennettitalean seed plants during the Mesozoic.

Anatomically Preserved Early Cretaceous Bennettitalean Leaves: Nilssoniopteris corrugata n. sp. from Vancouver Island, Canada

Early Cretaceous fossilized leaves assignable to the extinct seed plant order Bennettitales occur within an exceptionally diverse Early Cretaceous (Valanginian) flora of anatomically preserved plant fossils at Apple Bay on Vancouver Island, British Columbia, Canada. One of the bennettitalean leaf types has an entire margin, with laminae that are attached near the adaxial surface of the midvein. Leaves are 10–15 mm wide with an adaxial surface that shows distinct corrugations, and a midrib that is exposed adaxially. The vascular system of the midrib consists of a crescent-shaped ring of collateral bundles. Lateral veins diverge from midrib at ∼90°, are typically simple but occasionally branch at base of the lamina. Vein density is 12–15 per cm. Leaves are hypostomatic with syndetocheilic stomata that are randomly oriented between veins. Internal anatomy consists of an adaxial hypodermis of closely-spaced isodiametric cells, mesophyll that is differentiated into adaxial palisade and abaxial spongy zones, and collateral bundles that show a distinct bundle sheath with bundle sheath extensions. This novel combination of characters represents the diverse bennettitalean genus Nilssoniopteris. Nilssoniopteris corrugata new species is only the second species of the genus for which internal anatomy is preserved. This species increases the known variation of bennettitalean leaf anatomy, and reinforces our appreciation for the global distribution of bennettitalean seed plants during the Mesozoic.

Anatomy and Histochemistry of Roots and Shoots in Wild Rice (Zizania latifolia Griseb.)

Wild rice (Zizania latifolia Griseb.) is a famous, perennial, emergent vegetable in China. The current work explores the anatomy and histochemistry of roots, stems, and leaves and the permeability of apoplastic barriers of wild rice. The adventitious roots in wild rice have suberized and lignified endodermis and adjacent, thick-walled cortical layers and suberized and lignified hypodermis, composed of a uniseriate sclerenchyma layer (SC) underlying uniseriate exodermis; they also have lysigenous aerenchyma. Stems have a thickened epidermal cuticle, a narrow peripheral mechanical ring (PMR), an outer ring of vascular bundles, and an inner ring of vascular bundles embedded in a multiseriate sclerenchyma ring (SCR). There is evidence of suberin in stem SCR and PMR sclerenchyma cells. Sheathing leaves are characterized by thick cuticles and fibrous bundle sheath extensions. Air spaces in stems and leaves consist of mostly lysigenous aerenchyma and pith cavities in stems. Apoplastic barriers are found in roots and stems.

Sites of action of elevated CO2 on leaf development in rice: discrimination between the effects of elevated CO2 and nitrogen deficiency.

Elevated CO2 concentrations (eCO2) trigger various plant responses. Despite intensive studies of these responses, the underlying mechanisms remain obscure. In this work, we investigated when and how leaf physiology and anatomy are affected by eCO2 in rice plants. We analyzed the most recently fully expanded leaves that developed successively after transfer of the plant to eCO2. To discriminate between the effects of eCO2 and those of nitrogen deficiency, we used three different levels of N application. We found that a decline in the leaf soluble protein content (on a leaf area basis) at eCO2 was only observed under N deficiency. The length and width of the leaf blade were reduced by both eCO2 and N deficiency, whereas the blade thickness was increased by eCO2 but was not affected by N deficiency. The change in length by eCO2 became detectable in the secondly fully expanded leaf, and those in width and thickness in the thirdly fully expanded leaf, which were at the leaf developmental stages P4 and P3, respectively, at the onset of the eCO2 treatment. The decreased blade length at eCO2 was associated with a decrease in the epidermal cell number on the adaxial side and a reduction in cell length on the abaxial side. The decreased width resulted from decreased numbers of small vascular bundles and epidermal cell files. The increased thickness was ascribed mainly to enhanced development of bundle sheath extensions at the ridges of vascular bundles. These observations enable us to identify the sites of action of eCO2 on rice leaf development.