Accumulation Of Hydroxyproline-rich Glycoproteins Research Articles

Immunolocalization and Changes of Hydroxyproline-Rich Glycoproteins During Symbiotic Germination of Dendrobium officinale.

Hydroxyproline-rich glycoproteins (HRGPs) are abundant cell wall components involved in mycorrhizal symbiosis, but little is known about their function in orchid mycorrhizal association. To gain further insight into the role of HRGPs in orchid symbiosis, the location and function of HRGPs were investigated during symbiotic germination of Dendrobium officinale. The presence of JIM11 epitope in developing protocorms was determined using immunodot blots and immunohistochemical staining procedures. Real-time PCR was also employed to verify the expression patterns of genes coding for extensin-like genes selected from the transcriptomic database. The importance of HRGPs in symbiotic germination was further investigated using 3,4-dehydro-L-proline (3,4-DHP), an inhibitor of HRGP biosynthesis. In symbiotic cultures, immunodot blots of JIM11 signals were moderate in mature seeds, and the signals became stronger in swollen embryos. After germination, signal intensities decreased in developing protocorms. In contrast, in asymbiotic cultures, JIM11 signals were much lower as compared with those stages in symbiotic cultures. Immunofluorescence staining enabled the visualization of JIM11 epitope in mature embryo and protocorm cells. Positive signals were initially localized in the larger cells near the basal (suspensor) end of uninfected embryos, marking the future colonization site of fungal hyphae. After 1 week of inoculation, the basal end of embryos had been colonized, and a strong signal was detected mostly at the mid- and basal regions of the enlarging protocorm. As protocorm development progressed, the signal was concentrated in the colonized cells at the basal end. In colonized cells, signals were present in the walls and intracellularly associated with hyphae and the pelotons. The precise localization of JIM11 epitope is further examined by immunogold labeling. In the colonized cells, gold particles were found mainly in the cell wall and the interfacial matrix near the fungal cell wall. Four extensin-like genes were verified to be highly up-regulated in symbiotically germinated protocorms as compared to asymbiotically germinated ones. The 3,4-DHP treatment inhibited the accumulation of HRGPs and symbiotic seed germination. In these protocorms, fungal hyphae could be found throughout the protocorms. Our results indicate that HRGPs play an important role in symbiotic germination. They can serve as markers for fungal colonization, establishing a symbiotic compartment and constraining fungal colonization inside the basal cells of protocorms.

Al-induced cell wall hydroxyproline-rich glycoprotein accumulation is involved in alleviating Al toxicity in rice

Cell wall components such as pectin and hemicelluloses have been proposed to be involved in aluminum resistance mechanisms in plants. However, whether hydroxyproline-rich glycoproteins (HRGPs), one of the most abundant proteins of the cell walls, are involved in Al resistance mechanisms remains elusive. In this study, two rice cultivars Xiushui 03 (Al resistant) and Xiushui 128 (Al sensitive) significantly differing in Al resistance were identified. In the absence of Al, no significant difference was observed in contents of glycoproteins and hydroxyproline in cell wall fractions of these two cultivars. At the early stage of Al toxicity, glycoproteins and hydroxyproline were significantly induced in these two cultivars, but levels of their accumulation in cell walls were much higher in cv. Xiushui 03 than in cv. Xiushui 128. At the late stage of Al toxicity, their accumulation in cell walls dramatically decreased in cv. Xiushui 128 and, however, still kept a high level in cv. Xiushui 03. The finding that Al-induced changes of glycoproteins and hydroxyproline were completely consistent indicates that Al-induced glycoproteins are HRGPs. Further observation utilizing transmission electron microscope showed that HRGPs were greatly accumulated in cell walls leading to thickening of cell walls in cv. Xiushui 03, however, HRGPs and cell walls greatly decreased in cv. Xiushui 128. These data suggest that Al-induced HRGP accumulation in cell walls is involved in alleviating Al toxicity in rice.

Hydroxyproline-rich glycoproteins accumulate in pearl millet after seed treatment with elicitors of defense responses against Sclerospora graminicola

The accumulation of hydroxyproline-rich glycoproteins (HRGPs) was investigated after induction of resistance in pearl millet against downy mildew caused by Sclerospora graminicola. Treatment of susceptible pearl millet seeds with various biotic and abiotic elicitors resulted in increased HRGP content in the cell walls of coleoptiles at 9 h after inoculation. Similar results with increased accumulation at 4–6 h after inoculation were obtained in suspension cells of pearl millet. Maximum HRGP accumulation was observed in seedlings raised from susceptible seeds treated with chitosan and Pseudomonas fluorescens. Western blot analysis with MAC 265 (a rat monoclonal antibody raised against pea HRGP) identified three proteins of 27, 17 and 14 kDa in resistant cultivars. The absence of the 14 kDa HRGP was observed in susceptible cultivars as reported earlier. The induced accumulation of the 14 kDa HRGP upon elicitor treatments was observed in the present study. Peroxidase and hydrogen peroxide, essential components for HRGP cross-linking, were also increased in samples treated with these elicitors. A tissue specific increase in HRGP at the regions around vascular bundles was observed upon chitosan treatment. The results presented will have a presumed importance in identifying the susceptible pearl millet varieties and improving those using elicitors of defense for field applications.

Infection induced oxidative cross-linking of hydroxyproline-rich glycoproteins (HRGPs) is associated with restriction of Colletotrichum sublineolum in sorghum

Hydroxyproline-rich glycoproteins (HRGPs) accumulation and oxidative cross-linking is one of the earliest defense responses in plants against pathogen infection. In the present study HRGP accumulation in three sorghum genotypes i.e. SC146 (resistant), cv. SC326 (intermediately resistant) and BTx623 (susceptible) as a response to Colletotrichum sublineolum isolate CP2126 infection is elucidated. HRGPs were monitored by hydroxyproline (Hyp) estimation. In genotypes SC146 and genotypes SC326 there was a significantly higher amounts of Hyp at 2 days after inoculation (dai) compared to genotype BTx623, indicating an infection induced accumulation of HRGPs. Western blot analysis of acid-ethanol extracted proteins with polyclonal antibody raised against pearl millet purified HRGPs identified four bands with molecular masses of ~65, 45, 17 and 14 kDa as HRGPs. Insolubilization of the 45 kDa protein in genotypes SC146 and SC326 upon infection with C. sublineolum indicates a role of this protein in cell wall cross-linking, coinciding with heavier accumulation of hydrogen peroxide. In addition, tissue print analysis using polyclonal antibody of pearl millet HRGPs recognized these cross-linked proteins to be HRGPs. These findings indicated that HRGPs in sorghum is a component of defense reaction against C. sublineolum infection.

Role of hydroxyproline-rich glycoproteins in resistance of pearl millet against downy mildew pathogen Sclerospora graminicola

Hydroxyproline-rich glycoproteins (HRGPs) are important plant cell wall components involved in plant defense response to pathogen attack. In the present study, a resistant pearl millet (Pennisetum glaucum) cultivar, IP18292, was compared with a susceptible cultivar, 7042S, to investigate the contribution of HRGPs in the successful defense against the phytopathogenic oomycete S. graminicola. Northern hybridization using MeHRGP cDNA, a heterologous probe from cassava, indicated steady accumulation of HRGP transcripts, from 2 h.p.i. onwards with a maximum at 6 h.p.i., in the resistant cultivar. This is followed by HRGPs accumulation at about 8 h.p.i. as revealed by Western-blot analysis. Immunocytochemical localization by tissue printing and confocal immunofluorescence microscopy indicated cell walls of parenchymatic cells and the vascular tissue of coleoptile as sites of HRGP deposition. In vitro studies in the presence of horseradish peroxidase and H2O2 showed cross-linking of pearl millet HRGPs, which occurred parallel to isodityrosine accumulation. Inducible high isodityrosine content was also observed in vivo in the resistant cultivar. Here, H2O2 was found to accumulate as twin burst at 1 and 6 h.p.i., whereas in the susceptible cultivar only an early single peak was detectable. Moreover, the amount of hydroxyproline in HRGPs was about twice as high in the resistant as in the susceptible cultivar. These results suggest that cell wall strengthening in S. graminicola-infected resistant pearl millet is brought about by a combination of polypeptide cross-linking of isodityrosine as well as by the high content of hydroxyproline in HRGPs, and H2O2, in contrast to the susceptible plant.

β-Amino butyric acid-induced resistance in pearl millet to downy mildew is associated with accumulation of defence-related proteins

Earlier studies had indicated that β-amino butyric acid (BABA) treatment of pearl millet seeds influenced seedling vigor and protected seedlings from downy mildew disease caused by the oomycetous biotrophic fungus Sclerospora graminicola. Application of 50mMBABAreduced disease severity and offered protection against S. graminicola of ∼74%. The protection induced was durable and operative during the vegetative and reproductive growth periods of the crop. In the present study an attempt was made to understand the biochemical basis for this protection. A close association was found between BABA-induced protection and increased accumulation of defence-related proteins like phenylalanine ammonia lyase, peroxidase, β-1,3-glucanase and cell wall hydroxyproline-rich glycoproteins (HRGP). Isoelectric focusing of β-1,3-glucanases indicated the presence of several isoforms, of which isoforms of pI 9.6 and 8.8 were markedly increased in BABA-treated seedlings upon S. graminicola infection. Increased accumulation of hydroxyproline-rich glycoproteins was also observed at 9 h after inoculation in these samples. Western blots with MAC 265, a monoclonal antibody against pea HRGP identified a 17-kDa HRGP molecule that significantly increased in concentration in BABA-treated pearl millet seedlings as a response to S. graminicola infection. The postinfectional protection offered by BABA involved induction of defence responses which were comparable to the highly resistant cultivar.

Accumulation of hydroxyproline-rich glycoproteins in pearl millet seedlings in response to Sclerospora graminicola infection

Hydroxyproline-rich glycoproteins (HRGPs) are important plant cell wall structural components that are known to be induced in response to pathogen attack. In the present study, accumulation of HRGPs in pearl millet seedlings in response to Sclerospora graminicola, the incitant of downy mildew disease was monitored by estimation of hydroxyproline (Hyp) in the hydrolyzed cell wall samples. In 2-day-old seedlings of a highly resistant cultivar of pearl millet inoculated with S. graminicola, a marked increase in Hyp content was observed in the coleoptiles as early as 2 h compared to that in a highly susceptible cultivar. A correlation was observed between the amount of Hyp induced in coleoptiles of different cultivars of pearl millet to S. graminicola infection and the host resistance. Electrophoretic separation of the acid–ethanol extracted proteins from these coleoptiles followed by periodic acid Schiff staining revealed three glycoproteins of molecular masses 27, 17 and 14 kDa. These three glycoproteins also reacted positively on western blots with MAC 265, a monoclonal antibody against pea HRGP, indicating that they are HRGPs. The 17 kDa HRGP was markedly increased in highly resistant cultivar to S. graminicola infection compared to highly susceptible cultivar. The 14 kDa HRGP was exclusively present in the highly resistant cultivar and not in highly susceptible cultivar. Histological studies showed cross-linking of proteins in the cell walls of only highly resistant cultivar against S. graminicola infection. In addition, immunocytochemical studies using MAC 265 antibodies recognized these cross-linked proteins to be HRGPs. These findings indicated that accumulation of HRGPs in cell walls of highly resistant pearl millet seedlings is a component of defense reaction against downy mildew pathogen S. graminicola.

Hydroxyproline‐rich glycoprotein accumulation in tobacco leaves protected against Erysiphe cichoracearum by potato virus Y infection

Tobacco cv. Havana 425 acquired resistance to a compatible isolate of Erysiphe cichoracearum after infection by a strain of potato virus Y (PVYN) that causes veinal necrosis; another common strain (PVYO) that does not cause necrosis gave less protection. Hydroxyproline‐rich glycoproteins (HRGPs), believed to be involved in resistance, were determined by analysing hydroxyproline (Hyp) in purified cell walls. Hyp content increased significantly in PVYN‐protected leaves, compared with untreated controls, 2–4 days after necrotic lesion symptoms developed. No further increase in Hyp was noted in PVYN‐protected leaves after E. cichoracearum challenge. Hyp increases were significantly higher in protected leaves of plants showing symptoms on day 7 than on day 10. Infection with the PVYO strain caused significant decrease in Hyp content, compared with uninoculated controls. Inoculation of virus‐free plants with E. cichoracearum induced moderate and transitory Hyp increases on day 2 or 3, followed by a quick decrease associated with a weak response by the compatible host. It is suggested that HRGP accumulation induced by PVYN (but not by PVYO) causes changes in the host cell wall that result in resistance to E. cichoracearum.

HydroxyproUne‐rich Glycoprotein Accumulation in TMV‐infected Tobacco Showing Systemic Acquired Resistance to Powdery Mildew

AbstractTobacco cv. Havana 425, with systemic‐acquired resistance (SAR) to an otherwise compatible Erysiphe cicho‐racearum DC. race after TMV infection, was infected with TMV basaily (4th and 5th leaves) and the hydroxyproline‐rich glycoproteins (HRGPs) were determined in two experiments (experiment 1 and experiment 2) by analysing cell wall hydroxyproline (Hyp) in the 6th leaf. In basal TMV infected plants Hyp content (μmol‐1 FW) was greater than in controls in both experiments: the increase was significant at all times except 16 days after TMV inoculation in experiment 1; the pool of data of experiment 2 was also significantly increased. In TMV protected +E. cichoracearum challenged leaves compared to untreated controls significant increases in Hyp were also noted between the pools of data in both experiments. No differences were found between Hyp content in protected compared to protected + challenged leaves in both experiments. These results show accumulation of HRGPs in Havana tobacco associated with TMV infection and SAR activation against E, cichoracearum. The accumulation appears to be due to the inducer, since no further increase was detected in protected leaves after challenging.

Purification, Elicitor Activity, and Cell Wall Localization of a Glycoprotein from Phytophthora parasitica var. nicotianae, a Fungal Pathogen of Tobacco

ABSTRACT A glycoprotein of 34 kDa (GP 34) was solubilized at acidic pH from the mycelium of Phytophthora parasitica var. nicotianae and was purified by ion exchange and gel permeation chromatography. Whole tobacco plants treated with GP 34 through their roots showed an enhanced lipoxygenase activity as well as hydroxyproline-rich glycoprotein accumulation, indicating that this molecule had elicitor properties. An antiserum raised against the pure glycoprotein allowed localization of GP 34 by immunogold-labeling on the cell surface of the mycelium when the fungus was grown in vitro. In the wall-less zoospores, GP 34 was limited to the flagellum surface. It was then abundantly synthesized at the onset of encystment. During infection of tobacco plants, labeling was very faint at early stages of colonization, particularly in the susceptible host cultivar. It appeared earlier in the resistant host cultivar and was restricted to the living fungus, declining with mycelium cell death.

Chemical Interactions with Bioherbicides to Improve Efficacy

Bioherbicides can be defined as plant pathogens, phytotoxins derived from pathogens or other microorganisms, augmentatively applied to control weeds. Although many pathogens with bioherbicidal potential have been discovered, most lack sufficient aggressiveness to overcome weed defenses to achieve adequate control. Plants use various physical and biochemical mechanisms to defend against pathogen infectivity, including callose deposition, hydroxyproline-rich glycoprotein accumulation, pathogenesis-related proteins (PR-proteins), phytoalexin production, lignin and phenolic formation, and free radical generation. Some herbicides, plant growth regulators, specific enzyme inhibitors, and other chemicals can alter these defenses. Various pathogens also produce chemical suppressors of plant defenses. Secondary plant metabolism is a major biochemical pathway related to several defense processes. Increased activity of a key enzyme of this pathway, phenylalanine ammonia-lyase (PAL), is often a response to pathogen attack, as demonstrated in two weeds and their associated bioherbicidal pathogens:Alternaria cassiaeon sicklepod andA. crassaon jimsonweed. Weakening of physical and biochemical defenses, and lowering of resistance to pathogen attack, may result from reduced production of phenolics, lignin, and phytoalexins caused by herbicides and other chemicals that affect cuticular component biosynthesis and/or key aspects of secondary plant metabolism. Potent PAL inhibitors [aminooxyacetic acid, α-aminooxy-β-phenylpropionic acid, and (l-amino-2-phenylethyl)phosphonic acid] have some regulatory action on secondary plant metabolism and pathogenicity. Various herbicides and other chemicals dramatically affect extractable PAL activity levels and/or substantially alter PAL product production. Some non-pathogenic organisms can alter herbicide efficacy, and some herbicides influence disease development in plants. Research has shown some synergistic interactions of microbes and chemicals with relevance to weed control. Further research on pathogen interactions with agrochemicals (or other chemicals/regulators) could result in increased efficacy of pathogen-herbicide combinations, reduction of herbicide and pathogen levels required for weed control, and expanded pathogen host range.

Elicitors and Suppressors of Hydroxyproline-Rich Glycoprotein Accumulation are Solubilized from Plant Cell Walls by Endopolygalacturonase

Treatment of bean cell walls with a pure endopolygalacturonase of the bean pathogen Colletotrichum lindemuthianum race beta released oligogalacturonides and pectic fragments which were separated according to their charge and size. Among galacturonic-acid-containing components, elicitors and suppressors of the plant cell wall hydroxyproline-rich glycoprotein (HRGP) were recovered. Two active small oligogalacturonides with degrees of polymerization of 2 and 3 were characterized by high-performance anion-exchange-chromatography pulsed amperometric detection and fast-atom-bombardment mass spectrometry; they elicited 40-70% hydroxyproline increase within 48 hours at 450 nmol/bean cutting. In contrast, pectic fragments of higher molecular mass, predominantly composed of galacturonic acid and containing sugars typical of the rhamnogalacturonan II domain of pectic polysaccharides, had the ability to substantially suppress hydroxyproline deposition. Maximum suppressor activity, 30-40% below the activity of the control, occurred in 48 hours. In view of the low one-cycle turnover of these proteins in the cell wall and of their structural role, these changes might significantly affect cell wall properties. Elicitation and/or suppression of hydroxyproline were correlated to modifications of HRGP-extensin gene expression. Northern-blot analysis of RNA showed that changes in the transcript intensity became clearly visible within the first 12 hours after the start of either treatment. The results show that pectic components of the plant extracellular matrix have the potential to regulate wall matrix biogenesis. Implications of this finding in plant defense and development are discussed.

Elicitors and Suppressors of Hydroxyproline-Rich Glycoprotein Accumulation are Solubilized from Plant Cell Walls by Endopolygalacturonase

Treatment of bean cell walls with a pure endopolygalacturonase of the bean pathogen Colletotrichum lindemuthianum race beta released oligogalacturonides and pectic fragments which were separated according to their charge and size. Among galacturonic-acid-containing components, elicitors and suppressors of the plant cell wall hydroxyproline-rich glycoprotein (HRGP) were recovered. Two active small oligogalacturonides with degrees of polymerization of 2 and 3 were characterized by high-performance anion-exchange-chromatography pulsed amperometric detection and fast-atom-bombardment mass spectrometry; they elicited 40-70% hydroxyproline increase within 48 hours at 450 nmol/bean cutting. In contrast, pectic fragments of higher molecular mass, predominantly composed of galacturonic acid and containing sugars typical of the rhamnogalacturonan II domain of pectic polysaccharides, had the ability to substantially suppress hydroxyproline deposition. Maximum suppressor activity, 30-40% below the activity of the control, occurred in 48 hours. In view of the low one-cycle turnover of these proteins in the cell wall and of their structural role, these changes might significantly affect cell wall properties. Elicitation and/or suppression of hydroxyproline were correlated to modifications of HRGP-extensin gene expression. Northern-blot analysis of RNA showed that changes in the transcript intensity became clearly visible within the first 12 hours after the start of either treatment. The results show that pectic components of the plant extracellular matrix have the potential to regulate wall matrix biogenesis. Implications of this finding in plant defense and development are discussed.

Ultrastructural and cytochemical aspects of the response of eggplant parenchyma cells in direct contact with Verticillium-infected xylem vessels

Changes that occurred in paratracheal parenchyma cells immediately adjacent to infected xylem vessels in eggplant stem tissues inoculated with Verticillium albo-atrum were investigated ultrastructurally and cytochemically. The response of these cells to vessel colonization was characterized by a rapid sealing-off of attempted sites of fungal penetration and a marked cytoplasmic reorganization. Accumulation of electron-opaque, globular structures in paramural spaces and formation of intracytoplasmic vesicles filled with osmiophilic deposits were among the most typical features of reaction. Large amounts of callose (β-1-3-glucan) were detected in the electron-opaque globules by means of gold labelling with a purified β-1,3-glucanase from tobacco. These callose-rich structures were found to be deposited over an amorphous matrix which was almost free of cellulose and pectin, but contained substantial amounts of glucosides and galactose residues. The occurrence of galactose in the matrix is discussed in relation to the possible accumulation of hydroxyproline-rich glycoproteins. Lipids and phospholipids were detected in the intracytoplasmic vesicles. Considering the known lipophilic nature of phytoalexins, the positive reaction observed upon treatment with the gold-complexed lipase suggested the presence of newly-synthesized secondary products. Support for this speculation came from the labelling pattern obtained with a laccase-gold complex specific for phenolic compounds. Finally, chitinase and β-1-3-glucanase were localized in vacuoles where they probably accumulated as a non-specific response to infection. Our results bring additional evidence that paratracheal parenchyma cells in direct contact with invaded vessels are signalled to mobilize a number of defence strategies among which formation of physical barriers at specific sites is one of the earliest and key events involved in protection against invasion of the xylem parenchyma cells.

Differential accumulation of hydroxyproline-rich glycoproteins in bean root nodule cells infected with a wild-type strain or a C4-dicarboxylic acid mutant of Rhizobium leguminosarum bv. phaseoli

An antiserum raised against deglycosylated hydroxyproline-rich glycoproteins (HPGPs) from melon (Cucumis melo L.) was used to study the relationship between Rhizobium infection and induction of HRGPs in bean (Phaseolus vulgaris L.) root nodule cells infected with either the wild-type or a C4-dicarboxylic acid mutant strain of Rhizobium leguminosarum bv. phaseoli. In effective nodules, where fixation of atmospheric dinitrogen is taking place, HRGPs were found to accumulate mainly in the walls of infected cells and in peribacteroid membranes surrounding groups of bacteroids. Internal ramifications of the peribacteroid membrane were also enriched in HRGPs whereas the peribacteroid space as well as the bacteroids themselves were free of these glycoproteins. In mutant-induced root nodules, HRGPs were specifically associated with the electron-dense, laminated structures formed in plastids as a reaction to infection by this mutant. The presence of HRGPs was also detected in the host cytoplasm. The aberrant distribution of HRGPs in infected cells of mutant-induced nodules likely reflects one aspect of the altered host metabolism in relation to peribacteroid-membrane breakdown. The possibility that the antiserum used for HRGP localization may have cross-reacted with ENOD 2 gene products is discussed in relation to amino-acid sequences and sites of accumulation.

Time-course study of the accumulation of hydroxyproline-rich glycoproteins in root cells of susceptible and resistant tomato plants infected by Fusarium oxysporum f. sp. radicis-lycopersici

The accumulation of hydroxyproline-rich glycoproteins (HRGPs) in cell walls of dicotyledonous plants is thought to be involved in the defense response to pathogens. An antiserum raised against deglycosylated HRGPs from melon was used for studying the subcellular localization of these glycoproteins in susceptible and resistant tomato (Lycopersicon esculentum Mill.) root tissues infected by Fusarium oxysporum f.sp. radicis-lycopersici. A time-course of HRGP accumulation revealed that these glycoproteins increased earlier and to a higher extent in resistant than in susceptible cultivars. In the compatible interaction, increase in HRGPs was largely correlated with pathogen invasion and appeared to occur as a result of wall damage. In the incompatible interaction, HRGPs accumulated in the walls of uninvaded cells, thus indicating a possible role in the protection against fungal penetration. The occurrence of substantial amounts of HRGPs in papillae, known to be physical barriers formed in response to infection, and in intercellular spaces provides additional support to the concept that such glycoproteins play an important role in disease resistance.

Hydroxyproline-rich glycoproteins in cell walls of pericarp from maize

Hydroxyproline-rich glycoprotein accumulation in maize ( Zea mays L.) pericarp cell walls was assayed by determining total hydroxyproline and by assessing protein extracts on western blots. Whole kernel dry weight and pericarp cell wall dry weight increased throughout kernel development of the three varieties studied, Golden × Bantam (GXB), Japanese Hulless (JHL) and South American Yellow (SAY). Total hydroxyproliner per mg dry weight and per pericarp increased throughout kernel development; a major increase occurred between 10 and 20 days after pollination. Soluble proteins from all three varieties were assayed on western blots reacted with a monoclonal antibody raised against PC-1, the major maize hydroxyproline-rich glycoprotein purified from GXB pericarp. Each of the maize varieties contained one major band that cross reacted with anti-PC-1 antibodies. This protein was a major part of the salt soluble proteins of the pericarp walls from all developmental times studied. PC-1 differed in electrophoretic mobility on native gels among the three varieties, and the popcorn proteins showed heterogeneity at different times after pollination as well. These maize wall proteins are strongly correlated with development and maturation of kernel pericarp, indicating a functional role for them in mechanical support and protection of the embryo and endosperm.

Time-course study of the accumulation of hydroxyproline-rich glycoproteins in root cells of susceptible and resistant tomato plants infected byFusarium oxysporum f. sp.radicis-lycopersici

Time-course study of the accumulation of hydroxyproline-rich glycoproteins in root cells of susceptible and resistant tomato plants infected byFusarium oxysporum f. sp.radicis-lycopersici

Immunogold localization of hydroxyproline-rich glycoproteins in necrotic tissue of Nicotiana tabacum L. cv. Xanthi-nc infected by tobacco mosaic virus

An antiserum raised against melon hydroxyproline-rich glycoprotein 2b was found to cross react specifically with deglycosylated hydroxyproline-rich glycoproteins from tobacco. This antiserum was used to study the subcellular localization of hydroxyproline-rich glycoproteins in Nicotiana tabacum cv. Xanthi-nc reacting hypersensitively to tobacco mosaic virus infection. The hypersensitive reaction was characterized by the formation of necrotic lesions around the point of virus entry. Leaf samples were collected 7 days after inoculation when lesions reached an average diameter of 3 mm. In the core of necrotic lesions, hydroxyproline-rich glycoproteins were localized in hemispherical excrescences formed along cell walls and in intercellular spaces filled with an electron-opaque material. However, they were not detected in host cell walls. In the halo surrounding the necrotic core, hydroxyproline-rich glycoproteins were found to be associated with an amorphous material frequently deposited in vascular parenchyma cells and with aggregated fibrils filling xylem vessels. In the green tissue bordering necrotic lesions, hydroxyproline-rich glycoproteins were nearly absent except in vessels which contained a fine network of intertwined fibrils. Farther away in the green tissue area, very low amounts of hydroxyproline-rich glycoproteins were detected. The accumulation of hydroxyproline-rich glycoproteins at strategic sites such as the intercellular spaces in the necrotic area is discussed in relation to plant stress and resistance.

Accumulation of hydroxyproline-rich glycoprotein mRNAs in infected or ethylene treated melon plants

Infection of melon plants by Colletotrichum lagenarium induces the production of five mRNA species (1·4, 1·65, 2·15, 3·2 and 4·5 kB) which hybridize to a genomic clone of hydroxyproline rich glycoproteins (HRGP) from carrot. Induction takes place 3 to 4 days after inoculation, which is consistent with the time course of accumulation of HRGP in the cell wall upon infection. mRNAs are expressed in leaves, stems, and roots. All transcripts, except the 4·5 kb species, are present among the cytosine-rich RNA isolated by affinity chromatography on an oligo(dG) cellulose column. Treatment of melon plants with ethylene leads to early induction of the 1·4 and 1·65 species and, to a lesser extent, the other three transcripts.