Vascular Parenchyma Research Articles

Comparative cytopathology of Crinivirus infections in different plant hosts

SummaryWe used transmission electron microscopy to compare the cytopathology induced in plants by five criniviruses (genus Crinivirus; Lettuce infectious yellows virus (LIYV), Cucurbit yellow stunting disorder virus (CYSDV), Tomato infectious chlorosis virus (TICV), Tomato chlorosis virus (ToCV) and Beet pseudo‐yellows virus (BPYV) (Hartono et al., 2003)). We also compared the patterns of infection for plants and mesophyll protoplasts infected by LIYV and Beet yellows virus (BYV), type members of genera Crinivirus and Closterovirus, respectively. The main cytopathological effects induced in plants by criniviruses were common in young leaves and included alterations of the chloroplasts and the presence of BYV‐type inclusion bodies in companion cells. Virus‐like particles were present in sieve tubes and vascular parenchyma cells as scattered particles, or in companion cells as large masses forming cross‐banded inclusions. Depending on the virus and the plant, it was possible to find virions or virus‐like particles out of the phloem cells, but only in cells of the bundle sheath. Virion‐like particles were never found outside of the vascular tissue. Accumulation of electron‐dense material at the plasmalemma was common for criniviruses, but only LIYV infections produced characteristic conical electron‐dense plasmalemma deposits (PDs). The LIYV‐induced PDs have a crystalline‐like structure and were found at the internal side of plasmalemma.

Differential Regulation of nramp and irt Metal Transporter Genes in Wild Type and Iron Uptake Mutants of Tomato

Metal transporters regulated by iron can transport a variety of divalent metals, suggesting that iron regulation is important for specificity of iron transport. In plants, the iron-regulated broad-range metal transporter IRT1 is required for uptake of iron into the root epidermis. Functions of other iron-regulated plant metal transporters are not yet established. To deduce novel plant iron transport functions we studied the regulation of four tomato metal transporter genes belonging to the nramp and irt families with respect to environmental and genetic factors influencing iron uptake. We isolated Lenramp1 and Lenramp3 from tomato and demonstrate that these genes encode functional NRAMP metal transporters in yeast, where they were iron-regulated and localized mainly to intracellular vesicles. Lenramp1 and Leirt1 revealed both root-specific expression and up-regulation by iron deficiency, respectively, in contrast to Leirt2 and Lenramp3. Lenramp1 and Leirt1, but not Lenramp3 and Leirt2, were down-regulated in the roots of fer mutant plants deficient in a bHLH gene regulating iron uptake. In chloronerva mutant plants lacking the functional enzyme for synthesis of the plant-specific metal chelator nicotianamine Leirt1 and Lenramp1 were up-regulated despite sufficient iron supply independent of a functional fer gene. Lenramp1 was expressed in the vascular root parenchyma in a similar cellular pattern as the fer gene. However, the fer gene was not sufficient for inducing Lenramp1 and Leirt1 when ectopically expressed. Based on our results, we suggest a novel function for NRAMP1 in mobilizing iron in the vascular parenchyma upon iron deficiency in plants. We discuss fer/nicotianamine synthase-dependent and -independent regulatory pathways for metal transporter gene regulation.

LFA-1 is required for retention of effector CD8 T cells in mouse lungs

AbstractThe adhesion molecules involved in the migration and retention of activated effector CD8 T cells in the lung microcirculation and their recruitment into lung tissue are largely unknown. Here, we have analyzed the role of lymphocyte function–associated antigen-1 (LFA-1) and very late antigen-4 (VLA-4) on adhesion of influenza hemagglutinin (HA)–specific CD8 T-cell clone D4 under shear conditions in an in vitro binding assay and in an in vivo homing assay to the lungs of naive or transgenic Balb/c mice expressing HA (HA-Tg) by a lung-specific promoter. Blocking LFA-1 or intercellular adhesion molecule 1 (ICAM-1) significantly inhibited adhesion of D4 cells to lung vascular endothelium and parenchyma of lung sections. However, blocking VLA-4 or vascular cell adhesion molecule 1 (VCAM-1) had no effect on cell adhesion. Blocking LFA-1 in vivo significantly delayed lethal injury following adoptive transfer of D4 cells into HA-Tg mice as assessed by weight loss and histology. Residence time of adoptively transferred Indium 111 (111In)–labeled D4 cells in lungs of normal and HA-Tg mice as analyzed by dual modality imaging revealed a significantly shorter transit time of 4 hours for the D4 cells upon in vivo blockade of LFA-1. These results demonstrate a crucial role for LFA-1 in retention of activated CD8 T cells in normal mouse lungs and in the progression of lethal injury in HA-Tg mice.

Changes in plasmodesmata frequency in vascular bundles of maize seedling leaf induced by growth at sub-optimal temperatures in relation to photosynthesis and assimilate export

The frequency of plasmodesmata at the cell interfaces important for C4 photosynthesis was studied in two inbred lines of maize, KW 1074 (flint, chilling-tolerant) and CM 109 (dent, chilling-sensitive), grown until the third leaf stage at sub-optimal temperature (14/12 °C) in relation to the photosynthesis and assimilate export. The number of plasmodesmata linking mesophyll and bundle sheath as well as bundle sheath and parenchyma cells in the third leaf increased in both lines compared to control leaves at the same physiological stage grown at the optimal temperature (24/22 °C). The number of plasmodesmata on the mesophyll–bundle sheath interface increased relatively more in the KW 1074 line than in CM 109. At the sub-optimal temperature, there was also an increase in the plasmodesmata frequency between vascular parenchyma cells, but only in KW 1074 the differences were statistically significant. Plants of both lines grown at low temperature exhibited a decrease of Φ PSII. However, the light response curve of Φ PSII as well as the gas exchange rate in leaves of plants grown at sub-optimal temperature showed values higher in the KW 1074 than in the CM 109 line. KW 1074 seedlings also showed shorter the time interval between 14C incorporation into a leaf and 14C-assimilate appearance in the transport path. The genotypic difference in the photosynthetic competence of plants grown at sub-optimal temperatures might thus be related to the ability to increase the number of plasmodesmata at the interfaces between mesophyll, bundle sheath, and parenchyma cells. Such an increase in plasmodesmata density enable more efficient exchange of photosynthetic metabolites as well as export of sucrose at the temperatures which slow down the diffusion from cell to cell.

Identification, host range and infection process of Meloidogyne marylandi from turf grass in Israel

AbstractA population of a root-knot nematode species was isolated from Zoysia japonica in a turf nursery in Israel. Measurements and morphology of the second-stage juveniles and adult females, including perineal pattern, indicated this nematode to be Meloidogyne marylandi. In addition, esterase (Est) and malate dehydrogenase (Mdh) isozymes were studied for the first time for this species which is shown to be characterised by VS1 Est band and a N1c Mdh pattern. Host range tests showed that the turf grasses Stenotaphrum secundatum, Dactyloctenium australe and Paspalum vaginatum, corn (Zea mays) and oat (Avena sativa) were non-hosts or resistant. Kikuyu grass (Pennisetum clandestinum), wheat (Triticum aestivum), barley (Hordeum vulgare), bristle oat (Avena strigosa), Siberian millet (Echinochloa frumentaceae) and pearl millet (Pennisetum glaucum) were susceptible to the nematode. The second-stage juveniles of M. marylandi penetrated the elongation zone of wheat roots but did not reach the meristematic zone and settled with their anterior end toward the root tip. This contrasted with M. javanica or M. incognita which migrated to the meristematic zone, and turned around with their anterior toward the root base. Meloidogyne marylandi juveniles induced giant cells from vascular parenchyma cells and caused no or only small galls on the roots.

Plasmodesmata and the control of symplastic transport

In 1879 Eduard Tangle discovered cytoplasmic connections between cells in the cotyledons of Strychnos nuxvomica , which he interpreted to be protoplasmic contacts. This led him to hypothesize that ‘the protoplasmic bodies . . . are united by thin strands passing through connecting ducts in the walls, which put the cells into connection with each other and so unite them to an entity of higher order’ (Carr 1976). This challenged the then current view that cells functioned as autonomous units. It was after much research in many other species and cell types that Strasburger, in 1901, named these structures plasmodesmata (Carr 1976). During the division and differentiation of meristematic cells, plasmodesmata are formed across each developing cell plate, allowing cytoplasmic and endomembrane continuity to occur between all daughter cells, and ultimately, between all cells in a developing tissue (Mezitt & Lucas 1996). Those plasmodesmata that form during cell division are termed primary plasmodesmata (Jones 1976). Those that form de novo across existing cell walls are called secondary plasmodesmata (Ehlers & Kollmann 2001). The formation of secondary plasmodesmata allows cells to increase their potential for molecular trafficking and allows connections to be created between cells that are not related cytokinetically. As cells expand and differentiate, their fate determines the extent to which their cytoplasmic connectivity to other cells is maintained (Mezitt & Lucas 1996). Some cell types, such as those of the leaf mesophyll, remain closely connected to their neighbours, and may even lay down additional plasmodesmata to increase the continuity (Ding et al . 1992a). In other areas of the plant, for instance in vascular tissue, certain cells greatly reduce the number of plasmodesmata in their adjoining walls (Gamalei 1989). In this way, the cytoplasmic continuity can be altered depending on the tissue type (Botha & Evert 1988; Brown et al . 1995). However, although reductions in the number of plasmodesmata are common, only guard cells surrounding stomata (Erwee, Goodwin & van Bel 1985; Palevitz & Hepler 1985) and differentiating xylem elements (Lachaud & Maurousset 1996) lose all symplastic connections at maturity. In all other cells, some degree of intercellular connection is maintained. This plasmodesmal continuum that potentially exists throughout the whole plant is termed the symplast (Munch 1930). However, the symplast is not the open continuum that Munch originally hypothesized, but is divided into functional domains, each tightly regulated by different forms of plasmodesmata (Erwee & Goodwin 1985; Ehlers & Kollmann 2001). Plasmodesmata are now thought of as fluid, dynamic structures that can be modified both structurally and functionally to cope with the requirements of specific cells and tissues.

Anatomy and ontogenesis of hymenopteran leaf galls of Struthanthus vulgaris Mart. (Loranthaceae)

Leaves of Struthanthus vulgaris Mart. (Loranthaceae) exhibit galls induced by a Hymenoptera. These galls pass through five developmental stages. In the first stage, a small brown swelling is observed on the surface of the leaf. Internally, the chlorenchyma cells around the eggs of the gall-makers are divided. In the second stage, the gall enlarges and its surface assumes a wavy appearance with a depressed region in its center. Within this depression, an incompletely divided gall chamber with embryos is observed. Neoformed parenchyma is present around the chamber and the secondary walls of fibers and sclereids are no longer observed. The vascular parenchyma shows hyperplasia. In the third stage, the gall grows larger and adopts an ellipsoidal shape. Fissures appear on the gall epidermis and the neoformed parenchyma is conspicuous, with a cortical and a medullar region. In the medullar region, each gall chamber, with one inducer in larval phase, is lined with 1-2 layers of nutritive tissue. The gall is larger still at the fourth stage of development and a periderm coats most of the gall. New vascular bundles, sclereids, and fibers are formed. The gall-makers are in advanced larval phase and no nutritive tissue cells are observed. In the fifth stage, the gall reaches its definitive size and the inducers are in the pupa phase. At this stage, the cortical region undergoes slight hypertrophy. The senescent gall shows the orifices of the exit channel made by the adult gallmakers. The anatomical studies of the hymenopteran gall enabled to compare this gall with a dipteran one, previously discribed in the same plant host. It is suggested that during the maturation of the gall, specific key processes are triggered, which bring about a specific cecidogenesis.

PARASITIC NEMATODES ASSOCIATED WITH OLIVE IN COUNTRIES BORDERING THE MEDITERRANEAN SEA

PARASITIC NEMATODES ASSOCIATED WITH OLIVE IN COUNTRIES BORDERING THE MEDITERRANEAN SEA

Cellular and Subcellular Localization of Phototropin 1

Phototropin 1 (phot1) is a Ser/Thr photoreceptor kinase that binds two molecules of flavin mononucleotide as its chromophores and undergoes autophosphorylation in response to blue light. Phot1 is plasma membrane associated and, as with phot2, has been shown to function as a photoreceptor for phototropism, blue light-induced chloroplast movement, and blue light-induced stomatal opening. Phot1 likely also plays a redundant role with phot2 in regulating the rate of leaf expansion. Understanding the mechanism(s) by which phot1 initiates these four different responses requires, at minimum, knowledge of where the photoreceptor is located. Therefore, we transformed a phot1 null mutant of Arabidopsis with a construct encoding translationally fused phot1-green fluorescent protein (GFP) under the control of the endogenous PHOT1 promoter and investigated its cellular and subcellular distribution. This PHOT1-GFP construct complements the mutant phenotype, restoring second positive curvature. Phot1 is expressed strongly in dividing and elongating cortical cells in the apical hook and in the root elongation zone in etiolated seedlings. It is localized evenly to the plasma membrane region in epidermal cells but is confined largely to the plasma membrane region of the transverse cell walls in the cortical cells of both root and hypocotyl. It is found at both apical and basal ends of these cortical cells. In light-grown plants, phot1-GFP is localized largely in the plasma membrane regions adjacent to apical and basal cell end walls in the elongating inflorescence stem, where the photoreceptor is expressed strongly in the vascular parenchyma and leaf vein parenchyma. Phot1 also is localized to the plasma membrane region of leaf epidermal cells, mesophyll cells, and guard cells, where its distribution is uniform. Although phot1 is localized consistently to the plasma membrane region in etiolated seedlings, a fraction becomes released to the cytoplasm in response to blue light. Possible relationships between observed phot1 distribution and the various physiological responses activated by blue light are discussed.

Apical organization and maturation of the cortex and vascular cylinder inArabidopsis thaliana (Brassicaceae) roots

Developmental and physiological studies of roots are frequently limited to a post-germination stage. In Arabidopsis, a developmental change in the root meristem architecture during plant ontogenesis has not previously been studied and is addressed presently. Arabidopsis thaliana have closed root apical organization, in which all cell file lineages connect directly to one of three distinct initial tiers. The root meristem organization is dynamic and changes as the root ages from 1 to 4 wk post-germination. During the ontogeny of the root, the number of cells within the root apical meristem (RAM) increases and then decreases due to changes in the number of cortical layers and number of cell files within a central cylinder. The architecture of the initial tiers also changes as the root meristem ages. Included in the RAM's ontogeny is a pattern associated with the periclinal divisions that give rise to the middle cortex and endodermis; the three-dimensional arrangement of periclinally dividing derivative cells resembles one gyre of a helix. Four- or 5-wk-old roots exhibit a disorganized array of vacuolated initial cells that are a manifestation of the determinate nature of the meristem. Vascular cambium is formed via coordinated divisions of vascular parenchyma and pericycle cells. The phellogen is the last meristem to complete its development, and it is derived from pericycle cells that delineate the outer boundary of the root.

Use of multidetector row CT with volume renderings in right lobe living liver transplantation.

Multidetector row CT is a feasible diagnostic tool in pre- and postoperative liver partial transplantation. We can assess vascular anatomy and liver parenchyma as well as volumetry, which provide useful information for both donor selection and surgical planning. Disorders of the vascular and biliary systems are carefully observed in recipients. In addition, we evaluate liver regeneration of both the donor and the recipient by serial volumetry. We present how multidetector row CT with state-of-the-art three-dimensional volume renderings may be used in right lobe liver transplantation.

Genes encoding chitinase-antifreeze proteins are regulated by cold and expressed by all cell types in winter rye shoots.

One group of antifreeze proteins (AFPs) is composed of two chitinases that accumulate in the apoplast of winter rye leaves during cold acclimation. In this study, the 28- and 35-kDa chitinase-AFPs were localized in nonacclimated and cold-acclimated rye leaves by immunoelectron microscopy with an antiserum produced against the purified winter rye 35-kDa chitinase-AFP. In cold-acclimated winter rye leaves, labelled chitinase-AFPs were abundant in the walls of epidermal, parenchymal sheath and mesophyll cells and xylem vessels, while less label was present in walls of vascular parenchyma cells. In contrast, chitinase labelling was essentially absent in the nonacclimated cells except in xylem vessels. As shown by RNA blotting, the transcripts of chitinase-AFPs accumulated to a high level in rye leaves during cold acclimation, to a lesser extent in crowns and were not detectable in roots. mRNA transcripts of the 28-kDa chitinase-AFP were localized in rye leaves by in situ hybridization. The chitinase-AFP transcripts were found in the same cell types as the protein itself. We conclude that all metabolically active cell types in cold-acclimated winter rye leaves and crowns are able to synthesize chitinase-AFPs and secrete them into adjacent cell walls, where they may interact with ice to delay its propagation through the plant and modify its growth.

Ultrastructural localization of photosynthetic and photorespiratory enzymes in epidermal, mesophyll, bundle sheath, and vascular bundle cells of the C4 dicot Amaranthus viridis.

In the leaves of the NAD-malic enzyme (NAD-ME)-type C4 dicot Amaranthus viridis L., there are chloroplasts in the vascular parenchyma cells (VPC), companion cells (CC), ordinary epidermal cells (EC), and guard cells (GC), as well as in the mesophyll cells (MC) and the bundle sheath cells (BSC). However, the chloroplasts of the VPC, CC, EC, and GC are smaller than those of the MC and BSC. In this study, the accumulation of photosynthetic and photorespiratory enzymes in these leaf cell types was investigated by immunogold labelling and electron microscopy. Strong labelling for phosphoenolpyruvate carboxylase was found in the MC cytosol. Weak labelling was observed in the CC and GC cytosol. Labelling for pyruvate, Pi dikinase occurred to varying degrees in the chloroplasts of all cell types except CC. Labelling for the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase was detected in the chloroplasts of all cell types except MC. For both NAD-ME and the P-protein of glycine decarboxylase, intense labelling was found in the BSC mitochondria; weaker labelling was recognized in the VPC mitochondria. These data indicate that when not only the MC and BSC but also the other leaf cell types are included, the cell-specific expression of the enzymes in C4 leaves becomes more complex than has been known previously. These findings are discussed in relation to the metabolic function of epidermal and vascular bundle cells.

Cellular compartmentation of ammonium assimilation in rice and barley

This review describes immunolocalization studies of the tissue and cellular location of glutamine synthetase (GS; EC 6.3.1.2) and glutamate synthase (Fd GOGAT; EC 1.4.7.1 and NADH-GOGAT; EC 1.4.1.14) proteins in roots and leaves of rice (Oryza sativa L.) and barley (Hordeum vulgare L.). In rice, cytosolic GS (GS1) protein was distributed homogeneously through all cells of the root. NADH GOGAT protein was strongly induced and its cellular location altered by ammonium treatment, becoming concentrated within the epidermal and exodermal cells. Fd GOGAT protein location changed with root development, from a widespread distribution in young cells to becoming concentrated within the central cylinder as cells matured. Plastid GS protein was barely detectable in rice roots, but was the major isoform in leaves, being present in the mesophyll and parenchyma sheath cells. GS1 was specific to the vascular bundle, as was NADH GOGAT, whereas Fd GOGAT was primarily found in mesophyll cells. In barley roots, GS1 protein was found in the cortical and vascular parenchyma and its concentration was highest in N-deficient seedlings. Plastid GS protein was detected in both cortical and vascular cells, where different plastid forms, containing different concentrations of GS protein, were identified. In barley leaves, GS2 protein was detected in the mesophyll chloroplasts and GS1 was found in the mesophyll and vascular cells. N nutrition strongly influenced this distribution, with a marked increase in GS1 concentration in the vascular cells in response to nitrate and ammonium, and an increase in mesophyll GS2 concentration in nitrate-grown seedlings. Fd GOGAT protein was found in both the mesophyll and vascular plastids. These localization studies show that the GS/GOGAT cycle is highly compartmentalized at both the subcellular and cellular levels. Reasons for this compartmentation, and the roles of each isoform, are discussed.

Cellular compartmentation of ammonium assimilation in rice and barley

This review describes immunolocalization studies of the tissue and cellular location of glutamine synthetase (GS; EC 6.3.1.2) and glutamate synthase (Fd GOGAT; EC 1.4.7.1 and NADH-GOGAT; EC 1.4.1.14) proteins in roots and leaves of rice (Oryza sativa L.) and barley (Hordeum vulgare L.). In rice, cytosolic GS (GS1) protein was distributed homogeneously through all cells of the root. NADH GOGAT protein was strongly induced and its cellular location altered by ammonium treatment, becoming concentrated within the epidermal and exodermal cells. Fd GOGAT protein location changed with root development, from a widespread distribution in young cells to becoming concentrated within the central cylinder as cells matured. Plastid GS protein was barely detectable in rice roots, but was the major isoform in leaves, being present in the mesophyll and parenchyma sheath cells. GS1 was specific to the vascular bundle, as was NADH GOGAT, whereas Fd GOGAT was primarily found in mesophyll cells. In barley roots, GS1 protein was found in the cortical and vascular parenchyma and its concentration was highest in N-deficient seedlings. Plastid GS protein was detected in both cortical and vascular cells, where different plastid forms, containing different concentrations of GS protein, were identified. In barley leaves, GS2 protein was detected in the mesophyll chloroplasts and GS1 was found in the mesophyll and vascular cells. N nutrition strongly influenced this distribution, with a marked increase in GS1 concentration in the vascular cells in response to nitrate and ammonium, and an increase in mesophyll GS2 concentration in nitrate-grown seedlings. Fd GOGAT protein was found in both the mesophyll and vascular plastids. These localization studies show that the GS/GOGAT cycle is highly compartmentalized at both the subcellular and cellular levels. Reasons for this compartmentation, and the roles of each isoform, are discussed.

Citrus leprosis virus: properties, diagnosis, agro‐ecology and phytosanitary importance

Citrus leprosis disease, caused by citrus leprosis virus (CiLV), had severe effects on sweet oranges in Florida (US) until the 1920s, after which it became rare. In South America, it appeared in the 1930s, first in Argentina and then in Brazil, where it is now widespread and very dangerous. It has also been reported in Paraguay, Peru, Uruguay and Venezuela. CiLV is transmitted by three species of Brevipalpus, mainly Brevipalpus phoenicis. The virus mainly attacks sweet orange, but also citrange, citron, Cleopatra mandarin, grapefruit, lemon, mandarin, sour orange and tangor. CiLV is a non‐enveloped rhabdovirus characterized by bacilliform particles measuring 120–130 × 50–55 nm, present in mesophyll and vascular parenchyma within cisternae of the endoplasm reticulum. Viroplasm structures are present in the infected cells. CiLV has been partially purified and its dsRNA as been investigated. It is mechanical transmissible to 13 test plant species belonging to the genera Atriplex, Beta and Chenopodium (Chenopodiaceae), Gomphrena (Amaranthaceae), and Tetragonia (Tetragoniaceae). Using some of these herbaceous test plants, grown at a suitable temperature, it is possible to diagnose CiLV in 3–4 days. CiLV is covered by lists and requirements in phytosanitary regulations, but the information given is often misleading. For phytosanitary purposes, it is important to consider the following main points: (a) both CiLV and its vectors need to be considered; (b) sweet orange fruits can be infected even more than propagation material; and (c) CiLV does not infect susceptible citrus systemically, or any of its known hosts.

Characterization and localization of a wound-inducible type I serine-carboxypeptidase from leaves of tomato plants (Lycopersicon esculentum Mill.).

During the course of characterization of the wound-response related proteins from tomato (Lycopersicon esculentum Mill.) leaves, a serine carboxypeptidase (EC 3.4.16.1) was identified. An increase in peptidase activity in response to wounding, and the isolation of a protein with carboxypeptidase (CP) activity from tomato leaves had been reported previously, but the mRNA coding for the enzyme was not identified. We now report the isolation of a tomato leaf type I serine-CP cDNA whose corresponding mRNA is induced by wounding, systemin and methyl jasmonate. The protein sequence deduced from the cDNA exhibits homology to tomato CP, and barley and rice type I CPs. Southern blot results indicated that the CP gene is probably a member of a small gene family. Tomato CP mRNA was detected within 3 h after wounding, or treatment with systemin or methyl jasmonate. Employing Western blot analysis, CP protein was shown to increase 12 h after the treatments. Using the tomato def1 mutant, we have demonstrated that a functional octadecanoid pathway is necessary for CP transcription in response to wounding. Carboxypeptidase protein was immunolocalized as protein aggregates within the central vacuoles of palisade mesophyll cells as well as in vascular parenchyma where it had previously been found. Double labeling using antibodies specific for CP and inhibitor II indicated that the two proteins are colocalized in the vacuolar aggregates. Tomato CP is a member of the "late wound-inducible genes" whose mRNAs increase 4-12 h following wounding, in contrast to several "early wound-inducible genes", whose mRNAs appear within 30 min. The data support a role for the enzyme in protein turnover that occurs systemically in leaf cells in response to wounding.

Hydrogen Peroxide Acts as a Second Messenger for the Induction of Defense Genes in Tomato Plants in Response to Wounding, Systemin, and Methyl Jasmonate

The systemic accumulation of both hydrogen peroxide (H(2)O(2)) and proteinase inhibitor proteins in tomato leaves in response to wounding was inhibited by the NADPH oxidase inhibitors diphenylene iodonium (DPI), imidazole, and pyridine. The expression of several defense genes in response to wounding, systemin, oligosaccharides, and methyl jasmonate also was inhibited by DPI. These genes, including those of four proteinase inhibitors and polyphenol oxidase, are expressed within 4 to 12 hr after wounding. However, DPI did not inhibit the wound-inducible expression of genes encoding prosystemin, lipoxygenase, and allene oxide synthase, which are associated with the octadecanoid signaling pathway and are expressed 0.5 to 2 hr after wounding. Accordingly, treatment of plants with the H(2)O(2)-generating enzyme glucose oxidase plus glucose resulted in the induction of only the later-expressed defensive genes and not the early-expressed signaling-related genes. H(2)O(2) was cytochemically detected in the cell walls of vascular parenchyma cells and spongy mesophyll cells within 4 hr after wounding of wild-type tomato leaves, but not earlier. The cumulative results suggest that active oxygen species are generated near cell walls of vascular bundle cells by oligogalacturonide fragments produced by wound-inducible polygalacturonase and that the resulting H(2)O(2) acts as a second messenger for the activation of defense genes in mesophyll cells. These data provide a rationale for the sequential, coordinated, and functional roles of systemin, jasmonic acid, oligogalacturonides, and H(2)O(2) signals for systemic signaling in tomato plants in response to wounding.

Cellular localisation and function of a sucrose transporter OsSUT1 in developing rice grains

We previously reported the cloning and tissue-specific expression of a gene encoding a sucrose/proton symporter in rice (Oryza sativa L.), OsSUT1 (Hirose et al. 1997, Plant Cell Physiology38, 1389–1396). This gene is expressed at high levels in the filling grain, leaf sheath and stem. Expression in these tissues occurred only after heading i.e. during the development of the reproductive structure as a major sink. In this paper, we report localisation of the transcript and protein to specific cells in the filling rice grain by in situ hybridisation with a probe from theOsSUT1 cDNA, and immunolocalisation of OsSUT1 and proton-pumping ATPase (H+-ATPase). An OsSUT1 cDNA probe recognises a transcript of approximately 2.4 kb, and the SUT1 antibody recognises a protein of approximately 55 kDa in total membrane protein extracts from the filling grain, leaf sheath and stem. In the developing grain, OsSUT1 is expressed at low levels before heading, with expression reaching a peak approximately ten days after emergence of the panicle from the sheath. Transcript is then present throughout seed development, with expression falling substantially after about 25 days post-heading. Both transcript and protein are localised to the aleurone cells of the developing grain, and are also detected in the maternal tissue, particularly the nucellus, vascular parenchyma tissue and the nucellar projection. Tissue slices from filling rice grain showed high rates of sucrose uptake that were inhibited by pCMBS. The role of OsSUT1 in sucrose transport to the filling grain endosperm is discussed.

Pathogenesis of the human opportunistic pathogen Pseudomonas aeruginosa PA14 in Arabidopsis.

The human opportunistic pathogen Pseudomonas aeruginosa strain PA14 is a multihost pathogen that can infect Arabidopsis. We found that PA14 pathogenesis in Arabidopsis involves the following steps: attachment to the leaf surface, congregation of bacteria at and invasion through stomata or wounds, colonization of intercellular spaces, and concomitant disruption of plant cell wall and membrane structures, basipetal movement along the vascular parenchyma, and maceration and rotting of the petiole and central bud. Distinctive features of P. aeruginosa pathogenesis are that the surface of mesophyll cell walls adopt an unusual convoluted or undulated appearance, that PA14 cells orient themselves perpendicularly to the outer surface of mesophyll cell walls, and that PA14 cells make circular perforations, approximately equal to the diameter of P. aeruginosa, in mesophyll cell walls. Taken together, our data show that P. aeruginosa strain PA14 is a facultative pathogen of Arabidopsis that is capable of causing local and systemic infection, which can result in the death of the infected plant.