Stomata Cells Research Articles

Thiamine induced resistance to Plasmopara viticola in grapevine and elicited host–defense responses, including HR like-cell death

Recently, thiamine (VitaminB1) has been shown to induce resistance against Pseudomonas syringae in Arabidopsis plants through priming of defense responses. In this paper, we have demonstrated the efficiency of thiamine to induce resistance against downy mildew caused by the oomycete Plasmopara viticola in a susceptible Vitis vinifera cultivar "Chardonnay" under glasshouse controlled conditions by providing a dual mode of action involving direct antifungal activity and elicitation of host-defense responses. Thiamine-induced defense responses included the generation of hydrogen peroxide (H(2)O(2)) in both grapevine suspension cultured cells (SCC) and plant leaves, upregulation of an array of defense-related genes and the induction of other defense responses at subcellular level such as callose deposition in stomata cells, phenolic compounds accumulation and hypersensitive response (HR) like-cell death. Epifluorescence microscopy studies revealed dramatic changes in P. viticola individual developmental stages during its colonization of the intercellular space of the leaf mesophyll in thiamine-treated plants. Collectively, our report evidenced the efficiency of thiamine in the control of downy mildew in grapevine by direct and indirect effects, suggesting that thiamine could be an attractive alternative to chemical fungicides in disease management in vineyards.

EFFECTS OF SILICON ON YIELD CONTRIBUTING PARAMETERS AND ITS ACCUMULATION IN ABAXIAL EPIDERMIS OF SUGARCANE LEAF BLADES USING ENERGY DISPERSIVE X-RAY ANALYSIS

Effects of silicon (Si), supplied as calcium silicate (Ca-silicate) fertilizer on yield contributing parameters in sugarcane like chlorophyll content, gas exchange characteristics, leaf nutrient concentrations and its effects on soil fertility were evaluated. Seven rates of Ca-silicate (0, 20, 40, 60, 80, 120 and 150 g pot−1) were applied with traditional fertilizers and plants were grown in a greenhouse. The added Ca-silicate increased photosynthesis, transpiration and stomatal conductance significantly over the non-amended treatment. Leaf tissue contents of phosphorus (P), sulfur (S), calcium (Ca), magnesium (Mg) and sodium (Na) did not differ remarkably. With increasing silicate application, iron (Fe), copper (Cu), zinc (Zn) and manganese (Mn) contents significantly decreased in both leaf tissue and soil contents. Si amended treatments significantly increased yield in dry matter (26 to 70%) and in cane yield (30 to 66%) per pot over non-amended. The Si content up to 2.64% per dry mass was found in top visible dewlap (TVD) leaf tissues when amended with Ca-silicate fertilizer in our 12 months study. Soil pH, soil Si, and leaf tissues silicon content progressively increased with increasing rate of Ca-silicate. The available S, exchangeable potassium (K), Na, Ca and Mg increased more or less progressively as rate of Si application increased over non-amended. Nevertheless, the scanning electron microscopy (SEM) with energy dispersive x-ray analysis (EDAX) revealed that different rates of Ca-silicate responded differently in accumulation of Si and other elements in epidermal cells, silica cells and stomata cells.

Morphology, anatomy and ultrastructure of yarrow (Achillea millefolium L.) floral nectaries

The studies focused on the morphological and anatomical features as well as those related to the ultrastructure of nectary cells <i>Achillea millefolium</i> Asteraceae family. The nectary presence was confirmed only in the disk flowers at the pistil style base. The micromorphology of nectaries was investigated in SEM, and structure was observed in a light and transmission electron microscopes. A number of layers composing a gland, the size and shape of epidermal and glandular cells were determined. The secretory cell ultrastructure was analyzed. The discoidal nectary gland observed from above had a pentagonal shape, 181.5 µm height and 299.4 µm diameter. It was built of the monolayer epidermis and 6 layers of the secretory cells on average. The glandular cells appeared to be bigger (27 µm) than the epidermal cells (22 µm), a cell shape in both tissues differed as well. The nectar secretion occured through the modified stomata. The stomata cells were at distinguishable greater size and raised above the surface of epidermis. The nectaries were supplied by the vascular bundles running from the pistil style up to the nectary base, not getting into the gland. In the cells of the nectary epidermis observed in TEM the big cell nuclei, numerous plastids, mitochondria and vacuoles with fibrous secretion deposits and vesicular structures were found. In the cells of the nectary secretory tissue there were dense cytoplasm, many plastids, mitochondria, Golgi bodies and the extensive network of the endoplasmic reticulum.

Responce of leaves of three plant species to aluminium stress

Water culture experiments were undertaken for 14 days to examine the effect of increasing aluminum level (0, 10, 20 40 mg·dm<sup>-3</sup> AlCl<sub>3</sub>·6 H<sub>2</sub>O) on growth of sunflower, red pepper and radish leaves. The early stage of Al toxicity was characterized by curling or rolling of young leaves, marginal and veinal chlorosis, dark green leaves as soon as purpling of margins and veins of leaves. Reduction of leaf size and increased stomata density were observed with increasing Al concentration. Additionally, length of stomata cells decreased after Al-treatment.

Induction of somatic embryogenesis from different explants of shoot cultures derived from young Quercus alba trees

The induction of somatic embryogenesis from shoot apices and leaf explants of shoot cultures derived from 6- to 7-year-old white oak (Quercus alba L.) trees is reported in this study. Embryogenic response was obtained in two out of the three genotypes evaluated with embryo induction frequencies up to 50.7% for WOQ-1 and 3.4% for WOQ-5 genotypes. The embryogenic explants formed translucent nodular structures and cotyledonary-stage somatic embryos, which developed from callus tissue, indicating an indirect embryogenesis process. An efficient procedure was developed for WOQ-1 material on the basis of the most appropriate leaf developmental stage. Growing leaves excised from two nodes below the shoot apex showed the highest embryogenic induction index. These leaves contain cells in an undifferentiated state, as shown by the presence of precursor cells of stomata, absence of intercellular spaces and low starch content in the mesophyll cells. Nodular structures and/or somatic embryos began to arise 7–8 weeks after culture initiation, although most emerged after 9–12 weeks in culture. The sequence of application of media for somatic embryo induction was optimized with a two-step procedure consisting of culturing the explants in medium supplemented with 21.48 μM NAA and 2.22 μM BA for 8 weeks and transfer of explants into plant growth regulator-free medium for another 12 weeks. Clonal embryogenic lines were established and maintained by secondary embryogenesis. Embryo germination (30%) and plantlet conversion (16.6%) were achieved after cold storage for 2 months.

The specificity of cytokinin signalling in Arabidopsis thaliana is mediated by differing ligand affinities and expression profiles of the receptors

Arabidopsis thaliana has three membrane-located cytokinin receptors (AHK2, AHK3 and CRE1/AHK4), which are sensor histidine kinases containing a ligand-binding CHASE domain. Despite their structural similarity the role of these receptors differs in planta. Here we have explored which parameters contribute to signal specification. In a bacterial assay, the CHASE domain of AHK2 has a similar ligand binding spectrum as CRE1/AHK4. It shows the highest affinity for isopentenyladenine (iP) and trans-zeatin (tZ) with an apparent K(D) of 1.4 and 4.0 nm, respectively. Real-time PCR analysis of cytokinin primary response genes in double mutants retaining only single receptors revealed that all receptors are activated in planta by cytokinin concentrations in the low nanomolar range. However, there are differences in sensitivity towards the principal cytokinins iP and tZ. The activation of the cytokinin-sensitive P(ARR5) :GUS reporter gene in three different double mutants shows specific, but also overlapping, spatial domains of activity, which were for all receptors predominantly in the shoot apical meristems and root cap columella. AHK2 and AHK3 signal specifically in leaf parenchyma cells, AHK3 in stomata cells, and CRE1/AHK4 in the root vasculature. Promoter-swap experiments demonstrate that CRE1/AHK4 can functionally replace AHK2 but not AHK3. However, the cytoplasmic AHK3 histidine kinase (Hk) domain can be replaced by the CRE1/AHK4 Hk domain, which suggests that functionality is mediated in this case by the extracytosolic domain. Together, the data show that both differential gene expression and ligand preference contribute to specify the receptor activity.

Leaf morphophysiology of coffee plants under different levels of light restriction

The aim of this study was to evaluate the morphophysiological behavior of coffee leaves ( Coffea arabica L.) maintained under different levels of artificial shading in initial vegetative phase. The experiment was carried out from January to June/2007, in agricultural field of Universidade Estadual do Sudoeste da Bahia – UESB, Vitoria da Conquista, Bahia, Brazil. Four trials were carried out maintaining shading conditions (30, 50 and 70% of sun light radiance) and at a full sunlight, during 90 days after plantlet emergence. For each assay, Catuai (IAC144), Catucai 2SL and Acaua varieties were evaluated, following a randomized block design, considering number of leaves, leaf area, leaf relative water content, leaf water potential, number of ordinary epidermis and stomata cell and stomata index. Shading levels affect the water status of coffee plants, resulting in alterations of morphophysiology of leaves. Increase of leaf water content occurs simultaneously with decrease of modulus of water potential and proline content, denoting an interaction between shading and water content to coffee plants. Higher proline content was verified in Catuai leaves in comparison to Catucai variety. With light restriction there was a reduction of ordinary epidermis cell and stomata density. Upward of leaf area and leaf number was observed when the light restriction was similar or lower to 42,86 and 25,0 %, respectively.

Characterisation of HvALMT1 function in transgenic barley plants.

HvALMT1 from barley (Hordeum vulgare L.) encodes a protein capable of facilitating the transport of malate and other organic anions when expressed in Xenopus oocytes. The HvALMT1 gene is primarily expressed in guard cells of stomata, in regions behind the root apex and at lateral root junctions. We investigated the function of HvALMT1 in planta by overexpressing it in barley under the control of a constitutive promoter. Transgenic plants expressing HvALMT1 at levels four to 9-fold greater than controls showed reduced growth and plants showing the highest expression failed to set seed. Although measurements of conductance indicated that stomatal function was not totally impaired in the transgenic plants the time taken for the stomata to close in response to low light was significantly longer compared with controls. Elemental and metabolomic analyses of the transgenic barley shoots revealed that the concentration of calcium and levels of ascorbate, serine, threonine and pentanoate were consistently greater (2- to 14-fold) in plants that overexpressed HvALMT1, whereas whole-shoot tissue levels of fumarate were significantly lower (60-85% reduction). Transgenic plants also showed significantly greater efflux of malate and succinate from their roots than control plants. Efflux of these organic anions occurred independently of Al3+ and conferred greater Al3+ resistance in solution culture and in acidic soil. These results are consistent with HvALMT1 contributing to anion homeostasis in the cytosol and osmotic adjustment by transporting organic anions out of the cell or by sequestering them into cytosolic vesicles.

Equisetum species show uniform epicuticular wax structures but diverse composition patterns

Only few data on the epicuticular waxes (EWs) of horsetails are available. This contribution therefore focuses on the wax micromorphology and chemical composition of Equisetum species of the subgenera Equisetum and Hippochaete. Distribution patterns and structural details of EW on the shoots were studied by scanning electron microscopy. After extraction with chloroform, the chemical composition of wax isolates was analysed by gas chromatography. Epicuticular wax crystals were non-oriented platelets or membraneous platelets. They were usually located on subsidiary cells of stomata and adjacent cells. Other parts of the shoots were covered mainly with a smooth wax film or small granules only. The chemical constituents found were alkanes, esters, aldehydes, primary alcohols and free fatty acids in a range of C(20)-C(36) (in esters C(36)-C(56)). All species of the subgenus Hippochaete showed a similar pattern of fractions with high percentages of alkanes and aldehydes, whereas the subgenus Equisetum species had distinctly different wax compositions. Extracts from the internodes-surfaces without well-developed EW crystals and only few stomata-showed the lowest contents of aldehydes. The covering with EW crystals will provide unhindered gas exchange and, combined with intracuticular wax, may prevent excess water loss during winter in the evergreen shoots of the subgenus Hippochaete. The results indicate that the Equisetum wax micromorphology and biosynthesis are comparable to EW of other pteridophyte classes and mosses.

Homologue structure of the SLAC1 anion channel for closing stomata in leaves

SummaryThe plant SLAC1 anion channel controls turgor pressure in the aperture-defining guard cells of plant stomata, thereby regulating exchange of water vapor and photosynthetic gases in response to environmental signals such as drought or high levels of carbon dioxide. We determined the crystal structure of a bacterial homolog of SLAC1 at 1.20Å resolution, and we have used structure-inspired mutagenesis to analyze the conductance properties of SLAC1 channels. SLAC1 is a symmetric trimer composed from quasi-symmetric subunits, each having ten transmembrane helices arranged from helical hairpin pairs to form a central five-helix transmembrane pore that is gated by an extremely conserved phenylalanine residue. Conformational features suggest a mechanism for control of gating by kinase activation, and electrostatic features of the pore coupled with electrophysiological characteristics suggest that selectivity among different anions is largely a function of the energetic cost of ion dehydration.

Variability in epidermal characters of Ginkgo tzagajanica Samylina (Ginkgoales) from the Paleocene of the Tsagayan formation (Amur Region) and the taxonomy of tertiary species of Ginkgo

The study of new material on Ginkgo tzagajanica Samylina and earlier published data has shown that the epidermal morphology of the species in highly variable; several new characters were found. Occurrence of different states of characters was analyzed, their frequency distribution was revealed, and typical and rare states of characters within variation rows were determined. The specific diagnosis of G. tzagajanica was emended. The most variable characters are degree of undulation of the anticlinal walls of cells of abaxial and adaxial epidermises (the latter is more variable) and degree of development and number of papillae on ordinary epidermal cells. Less variable characters are degree of development of papillae on subsidiary cells of stomata and how the papillae cover the stomatal apertures. These are characters that bear maximal diagnostic significance for Cenozoic Ginkgo.

Excretion and folding of plasmalemma function to accommodate alterations in guard cell volume during stomatal closure in Vicia faba L.

Stomatal movement results in large and repetitive changes in cell volume and consequently surface area. While endocytosis has been extensively studied and is thought to be a major mechanism for accommodating the volume changes as evidenced mainly by fluorescent labelling and confocal imaging, studies at the ultrastructural level in intact guard cells of stomata regulated by natural factors have never been reported. Here, it is reported that excretion and folding of the plasmalemma are critical for accommodating the volume alterations in intact guard cells in Vicia faba L. Using transmission electron microscopy in combination with laser confocal microscopy, it was observed that in fully opened stomata the plasmalemma was smooth and tightly adhered to the cell walls while a whole large vacuole appeared in the cell. In the closed stomata, besides vacuole fragmentation, endocytosis of the tonoplast rather than the plasmalemma commonly occurred. Importantly, in stomata where pore closure was induced by circadian rhythm or CO2, numerous tiny vesicles were found outside the plasmalemma and, moreover, extensive folding of the plasmalemma could also be found in some regions of the cells. Additionally, an unknown structure was found at the interface between the plasmalemma and cell walls, especially in those areas of the cell where extensive folding occurred, suggesting that plasmalemma turnover is possibly associated with an interaction between the plasmalemma and cell walls. Collectively, the results strongly indicate that excretion and folding of the plasmalemma are critical for the accommodation of the cell volume alterations during stomatal movement.

Germination, penetration and sporulation of Alternaria ricini (Yoshii) Hansf. on castor leaf

The infection process of the leaf blight fungus Alternaria ricini was studied on castor leaves using scanning electron microscopy. Conidia germinated 9 h post-inoculation producing one to many germ tubes. The germ tubes were of various lengths, branched or unbranched, and terminated in bulbous appressoria on leaf cuticle, or penetrated the leaf through stomata. Appressoria were not formed where the germ tubes penetrated stomata. As the disease symptom appeared as small spots on leaves 11 days post inoculation, abundant conidia emerged from both surfaces of the leaf through epidermis and through stomatal openings, formed in chains on unbranched conidiophores. Conidiophores were solitary or in small clusters of 2 – 4. The emergence of conidiophores through stomata appeared to be random, as conidiophores pierced guard cells of stomata, where there was no emergence through those stomatal openings. The conidia were cylindrical while young and became bottle-shaped with terminal beaks when matured. Each conidium was born singly on a short unbranched conidiophore, and each conidiophore developed from a cushion-shaped base on the leaf surface.

Microtubule involvement in the deposition of radial fibrillar callose arrays in stomata of the fern Asplenium nidus L.

Aniline blue staining and callose immunolabeling revealed the deposition of significant callose quantities, in the form of fibrils, in the periclinal walls of guard cells (GCs) of stomata of the fern Asplenium nidus. The stomata that were at an early stage of differentiation displayed short callose fibrils at the junctions of the periclinal walls with the dorsal ones, which converged on the site of the future stomatal pore. In stomata being at an advanced stage of differentiation, callose fibrils were radially arranged around the stomatal pore, while in mature closed ones they were focused on the margins of the wall thickenings lining the stomatal pore. The pattern of the callose fibril organization resembled that of cellulose microfibrils in the same walls. Like the cellulose microfibrils, callose fibrils appeared coaligned with the underlying radial arrays of cortical microtubules (MTs). Moreover, the stomata treated with cellulose synthesis inhibitors (coumarin or dichlobenil) and those recovering from treatments with callose synthesis inhibitors (2-deoxy-D-glucose or tunicamycin) exhibited distinct radial callose fibril arrays. Cytochalasin B did not affect the organization of the radial callose fibril arrays. In contrast, oryzalin completely disturbed the pattern of callose deposition in the affected GCs. Therefore, the fibrillar callose orientation in the periclinal GC walls is probably controlled by MTs but not by actin filaments. The MTs seem to orient callose synthases in the plasmalemma, thus determining the fibrillar nature of callose deposits and their radial mode of arrangement. The cellulose microfibrils are not involved in the callose fibril alignment.

Effects of elevated atmospheric CO2 on spore capsules of the moss Leptobryum pyriforme

Growing Leptobryum pyriforme (Hedw.) Wilson under ten times ambient atmospheric CO2 concentrations showed that, while stomatal density and index decreased under elevated atmospheric CO2, the overall number of stomata per spore capsule remained unaltered. Capsule length increased, while the size of stomata and epidermal cells decreased. This study suggests that stomatal frequency measures used to investigate the influence of varying levels of atmospheric CO2 on angiosperms and gymnosperms may result in misleading conclusions when applied to bryophytes if considered in isolation from growth responses.

포도나무 갈색무늬병균(Pseudocercospora vitis (Lếv.) Speg.)의 병원성과 침입기작

포도 갈색무늬병균의 침입부위를 알고자 잎의 앞면과 뒷면에 병원균을 접종한 결과 포도 잎의 앞면에 병원균을 접종한 처리구는 전혀 침입이 없었으며, 같은 잎의 뒷면에 병원균을 접종한 모든 처리구에서는 접종 15일 후에, 접종 지점 수와 동일한 수의 병반이 형성되었다. 병원균 접종 후에 발병에 소요되는 기간을 조사한 결과, 포도 잎의 뒷면에 접종한 경우, 접종 8일 후부터 병반이 나타나기 시작하여, 접종 10일 후에는 거의 모든 접종 지점에 병반이 나타났다. 갈색무늬병에 감수성인 캠벨얼리 품종에서는 잎 뒷면에 부착한 분생포자가 발아하여, 기공을 통하여 직접 식물체 조직 속으로 쉽게 침입하는 것을 관찰할 수 있었다. 반면에 저항성인 거봉 품종에서는 분생포자가 기공 근처에서 발아하였어도 기공을 쉽게 인식하여 찾아가지 못하거나, 기공을 찾아도 침입을 하지 못하고 기공을 넘어서 계속 발아하기도 하였다. 또한 발아관이 기공에 도달하는 도중에 기공 주변을 감싸기도 하고 공변세포에 이르러서도 쉽게 기공을 통해 조직 속으로 침입하지 못하였다. 심지어 어렵게 기공을 인식하여 침입을 했어도 계속 발아하면서 감수성 품종과 달리 조직 속으로 침입하지 않고 다시 기공 밖으로 나오는 모습이 관찰되기도 하였다. 갈색무늬병에 감수성 품종과 저항성 품종에서의 단위면적당 기공 수를 조사한 결과, 감수성 품종인 캠벨얼리 품종이 저항성 품종인 거봉의 기공 수보다 많았고, 그 크기는 거봉 품종이 컸다. 따라서 갈색무늬병균은 단위면적당 기공 수의 다소가 침입을 좌우하고, 그 크기에 의해 좌우되지는 않는 것으로 추정된다. 저항성인 거봉 품종의 기공은 전체적으로 식물체의 표면과 기공을 구성하는 공변세포와의 높이 차이가 거의 없었던 것이 형태적으로 명확하게 관찰되는 반면, 감수성인 캠벨얼리 품종의 기공은 전체적으로 식물체의 표면과 기공을 구성하는 공변세포와의 높이 차이가 현저한 것을 주사전자현미경과 광학현미경을 이용하여 명확하게 관찰하였다. This study was carried out to know pathogenicity of the pathogen isolated in several location of Korea and penetration mechanism of the Pseudocercospora vitis (<TEX>$(L\acute{e}v)$</TEX>.) Speg. Inoculation tests at room temperature were performed on both sides of leaves with different isolates of the fungus. The typical symptoms appeared on the abaxial leaf surface, but no symptom was observed on the adaxial leaf surface with all isolates. The average incubation period was nine days, since all symptoms appeared from 8 to 10 days after inoculation. In order to know the mechanism of invasion of P. vitis to grapevine, the behavior of penetration hyphae through stomata were compared in two cultivars having different level of resistance. In order to know the mechanism of resistance of grape vine to P.vitis, two cultivars having different level of resistance were compared by counting the numbers and measuring size of the stomata per leaf. In a susceptible cultivar Campbell Early, the number of stomata was more than that of a resistance cultivar 'Kyoho'. In a susceptible cultivar 'Campbell Early', the fungus entered readily into stomata after inoculation. However, in a resistant cultivar 'Kyoho', the fungus seemed to pass over or surrounded only the guard cells. In comparison of height of guard cells of stomata between the two cultivars, significant differences were observed by scanning electron microscopy and light microscopy. The height of guard cells of 'Campbell Early' showed a little higher than those of 'Kyoho' known to be resistant to the fungus.

Caracterização morfoanatômica de plântulas de &lt;em&gt;Gomphrena elegans&lt;/em&gt; Mart. (Amaranthaceae)

Aiming to describe seedlings’ morphology and cotyledons and eophylls anatomy of Gomphrena elegans Mart., 100 seeds were put into plastic bags, with sand and fertilized soil (1:3), kept in the greenhouse under room conditions, with 50% shady and watered daily. Cotyledonous petiole and limb and seedlings eophylls were sectioned in median and border. They were then analyzed in transversal and paradermic sections. Seedlings initial morphology is epigeal-foliar, the root is axial, and hypocotyls and epicotyl are reddish. Venation is of pinnate type, camptodrome and brochidrodome in cotyledons and eophylls. Petiole and leaf show uniseriated epidermis with cells of varied sizes and anomocytic stomata. Druses of calcium oxalate occurred in leaves and petiole. Dorsiventral mesophyll shows one palisade parenchyma layer and several lacunary ones.

Equisetum Crude Drugs: Epidermal Characters for Identification

Epidermal characters of nine of the Central European Equisetum species were documented using both scanning electron and light microscopy. The arrangement of silica pilulae on the subsidiary cells of stomata as well as the type and the arrangement of papillae on the ridges of main stems and branches allow an unambiguous identification of the species even in the powdered state. A key for the identification is presented, and recommendations for an improved text for the monograph in the European Pharmacopeia are given.

Stomatal index response of Quercus robur and Quercus petraea to the anthropogenic atmospheric CO2 increase

The inverse relationship between numbers of stomata (stomatal frequency) on tree leaves and ambient CO2 concentration is increasingly applied for reconstructing past atmospheric CO2 levels. The abundance of leaf remains of Quercus robur in Holocene peat and lake deposits in Europe makes this species potentially suitable for high-resolution stomatal frequency analysis. In order to quantify the CO2 responsiveness of the species, the behavior of the stomatal index for Q. robur during the current anthropogenic CO2 increase is determined on the basis of buried, herbarium and modern leaf material from the Netherlands. The stomatal index (SI), expressing the ratio of the number of stomata in a given area divided by the total number of stomata and other epidermal cells in that same area, is used in order to minimize influences on stomatal frequency of environmental conditions other than CO2. The sigmoid SI response pattern recorded for Q. robur resembles that of the closely related species Q. petraea, although there is a difference in the timing of the response limitation of the two species to increasing atmospheric CO2. For calibration purposes only the linear phase of the sigmoidal response curve is taken into consideration in the presented CO2 response model, which allows confident combination of Q. robur and Q. petraea over the interval from 290 to 325 ppmv CO2. The model is conservative in reconstructing past CO2 mixing ratios outside the range of monitored response. As a result of the observed SI response limit, the model predicts CO2 levels below 325 ppmv with a mean error of 10.2 ppmv, whereas higher CO2 levels are underestimated.

A putative magnesium transporter AtMRS2-11 is localized to the plant chloroplast envelope membrane system

The AtMRS2 family of 10 Arabidopsis genes (and one pseudo-gene) belongs to a eukaryote subset of the CorA super-family of magnesium transporters. Of nine members of the Arabidopsis family expressed in yeast, three conferred the capability for magnesium uptake, with AtMRS2-11 the most effective. GFP fusions indicated that several members of the family were localized in yeast cells to regions other than the plasma membrane. Expression of the AtMRS2-11 gene was examined in plants. The protein is predicted to have a chloroplast leader peptide, and Western analysis showed it to be enriched in isolated chloroplasts. An AtMRS2-11:eGFP fusion protein expressed in transgenic plants was localized to the envelope membrane system of chloroplasts. The promoter of AtMRS2-11 is predicted to contain binding sites for transcription factors that are involved in light regulation. RT-PCR demonstrated that the RNA transcript levels of this gene show diurnal cycling, with a two-fold higher steady-state expression in the light. No change in steady-state expression was observed in etiolated seedlings during the first 2 h of light exposure. Expression of a GUS gene driven by a 2-kb AtMRS2-11 promoter fragment showed expression only in the tops of the plants, with highest staining in young leaves. In sections of leaf tissue, expression was evident in the spongy mesophyll and stomata cells. Overexpression of the AtMRS2-11 gene led to increased accumulation of protein but the plants showed no detectable phenotype. The results are consistent with the AtMRS2-11 gene playing a role in magnesium transport into chloroplasts/plastids.