Scanning Electron Microscopy of Silica Deposits in the Culms, Floral Bracts and Awns of Barley (Hordeum sativum Jess.)

Deposits of silica in the culm internodes, floral bracts andawns of Hordeum sativum Jess (cv Deba Abed) have been investigatedusing the scanning electron microscope The deposits were isolatedfrom all organic matter by digestion with nitric and perchloricacids Two basic types of deposits were recognized, lumen andwall silicification, the latter with or without lumen infillings In the culm internodes, lumen deposits are derived from idioblasts(‘hats’), sclerenchyma and xylem vessels In thefloral bracts they are derived from idioblasts (‘hats’and astenform opals), epidermal long cells (dendriform opals),sclerenchyma and xylem vessels The shape of these deposits doesnot generally resemble the outline of the cell itself, but depositsderived from cell walls do closely resemble the infact cell.In the culm, the walls of stomatal cells, trichomes and, largelythe outer tangential walls of mature long epidermal cells, becomesilicified, together with some cork cells In the floral bracts,silica is found in most epidermal cell walls but is confinedto the trichomes, scutiform cells and costal epidermal cellsearly in their development At maturity concentrations of silicaare much higher in the floral bracts and awns than in the culmsand leaves The results are discussed in relation to the pattern of depositionand its possible functions. Hordeum sativum Jess, barley, silica deposits, opals, scanning electron microscopy     

Histopathology of Susceptible and Resistant Capsicum annuum Cultivars Infected with Ralstonia solanacearum

The vascular colonisation of resistant and susceptible hot chilli (Capsicum annuum) cultivars by Ralstonia solanacearum was examined using transmission electron microscopy. Tap roots of artificially-inoculated plants, grown in sterilised soil were investigated to observe the morphological barriers involved in the restriction of bacterial spread. In the resistant cultivar, several responses induced in response to bacterial infection, were observed. First, a cell wall coating material developed together with swelling of the primary wall of the xylem vessels, limiting the bacterial spread. Second, formation of various types of vesicles in the vascular parenchyma cells, which enveloped the bacterial mass and also partly restricted the pathogen spread. Third, induction of hypersensitive reaction in the xylem vessels resulted in the distortion and lysis of the bacteria. In the susceptible cultivar, vascular coating, production of vesicle and induction of hypersensitive reaction were not observed and bacterial spread was not limited. Rapid vascular colonisation of the susceptible cultivar seemed to be generalised which resulted in the rapid wilting of affected plants. Other reactions involved in both resistant and susceptible cultivars include disorganisation of cytoplasm of parenchyma cells, disintegration of nuclei, and rupturing of xylem vessel walls. The restriction of pathogen spread associated with the resistance in C. annuum to bacterial wilt was mainly attributed to some induced, morphological and physical barriers.     

STUDIES OF NECROTIC LESIONS IN CORN STALKS

Littlefield , Larry J., and Roy D. Wilcoxson . (U. Minnesota, St. Paul.) Studies of necrotic lesions in corn stalks . Amer. Jour. Bot. 49(10): 1072–1078. Illus. 1962.—In 3-day-old necrotic lesions in corn stalks caused by Fusarium graminearum, ground parenchyma cells were discolored and small amounts of a dark substance were present in the cells. The walls of phloem cells were also slightly discolored and a small amount of dark substance was present in the xylem cells. In older lesions the discoloration of parenchyma and phloem cells was more intense; many of the cells contained occluding substances; many phloem protoplasts collapsed, and xylem cells were partially to completely occluded. The occluding substance filling the cells appeared to be translocated from the lesion into the vessel elements extending beyond the lesion so that the bundles appeared as long, dark streaks in the stalk. The occluding substance in xylem, but not in phloem or parenchyma, stained with ruthenium red, a result indicating presence of pectin. Pectinase, however, did not remove the occluding substance. The pectinase dissolved the parenchyma cells in healthy tissues but not in the necrotic lesions. Necrosis in naturally infected plants began as small lesions, but the parenchyma cells quickly dissolved leaving the vascular bundles free of ground parenchyma. No occlusions were found in the central vascular system; a few xylem cells in the peripheral vascular system were occluded with the same substance observed in artificially inoculated plants. Phloem was entirely destroyed by the pathogen. The necrosis prevented upward movement of dye solution in the stalk, but did not measurably affect transpiration, probably because the lesions were not large. Yield was reduced in plants when lesions involved more than 50% of the tissue in inoculated internodes. Smaller lesions had no effect on yield.     

Defense response of resistant host Impatiens balsamina to the parasitic angiosperm Cuscuta japonica

The response of the stem of a resistant host (Impatiens baslamina) to infection by the parasitic flowering plant Cuscuta japonica was studied with light and electron microscopy. The intra- and interfascicular cambial cells in the host stem first reacted to the penetrating upper haustorium by dividing, and the differentiation of the host xylem (vascular) tissues proceeded toward interfascicular areas from vascular bundles. When the host vascular tissue was invaded by the endophyte (haustorial portion in the host stem), the host xylem was displaced, and host vessels became occluded with parenchyma cells, resulting in tyloses. As the parasitism progressed, areas of the host stem penetrated by the endophyte became swollen via secondary growth and cell division in the parenchymatous cortex, pith, and interfascicular areas. During this intrusion by the endophyte, darkly stained necrotic reactions were detected at the interface between the host tissue and the invading endophyte. The results suggested that in the host tissues penetrated by the parasite, the formation of secondary tissue and swellings caused by active cell division of ground tissue and host vessel occlusion by tyloses constitute the host structural defense against the parasite.     

Mucilage production during the incompatible interaction between Orobanche crenata and Vicia sativa

Orobanche spp. (broomrapes) are holoparasites lacking in chlorophyll and totally dependent on their host for their supply of nutrients. O. crenata is a severe constraint to legumes cultivation and breeding for resistance remains as one of the best available methods of control. However, little is known about the basis of host resistance to broomrapes. It is a multicomponent event, and resistance based on hampering development and necrosis of broomrape tubercles has been reported. In the present work, the formation of mucilage and occlusion of host xylem vessels associated with the death of O. crenata tubercles were studied histologically. Samples of necrotic O. crenata tubercles established on resistant and susceptible vetch genotypes were collected. The samples were fixed, sectioned and stained using different procedures. The sections were observed at the light microscopy level, either under bright field, epi-fluorescence or confocal laser scanning microscopy. A higher proportion of necrotic tubercles was found on the resistant genotype and this was associated with a higher percentage of occluded vessels. Mucilage is composed mainly by carbohydrates (non-esterified pectins) and the presence of polyphenols was also detected. The mucilage and other substances composed by parasite secretions and host-degraded products was found to block host vessels and obstruct the parasite supply channel, being a quantitative defensive response against O. crenata in vetch, and probably also in other legumes and plants. The presence of foreign substances (i.e. parasite secretions) and host-degraded products (i.e. carbohydrates from cell walls) inside host vessels seems to activate this response and leads to xylem occlusion and further death of established Orobanche tubercles.     

The root-tuber anatomy of Asphodelus aestivus

The root tubers of Asphodelus aestivus consist mostly of enlarged fleshy storage tissue. They are bounded by a multiple-layered velamen, responsible for rapid water uptake, water loss reduction, osmotic and mechanical protection. In the cortex area, thin-walled idioblasts contain numerous raphides of calcium oxalate in their large vacuole with a distinctive tonoplast. Wide morphological variations are observed among the raphide cross sections. Electron-dense compounds penetrate the raphide surface and raphide groove. Raphides seem to be vital for the protection of the root tuber parenchyma from herbivores. The cells of uniseriate endodermis are heavily thickened possessing a few plasmodesmata. The vascular cylinder is 20–28-arch and the root xylem consists of vessels in short radial rows, alternating with clusters of phloem cells. The presence of cells, which contain soluble polysaccharides in their large vacuole, is conspicuous after employing the Schiff's reagent. Exodermis cells and all cell walls, especially the thick ones of the endodermis, are also stained. Numerous parenchyma cells, especially those around vascular bundles are stained intensely, when exposed to Sudan Black B. These cells occurring as solitary idioblasts abundantly accumulate oil. Electron-dense remnants are evident within the vacuoles of the storage cells especially near the vascular tissue. The morphological features of A. aestivus root tubers and the major part of the total plant biomass are responsible for the species’ occurrence and frequent dominance in a wide array of arid environments. A. aestivus possessing root tubers is proved to be very efficient in storing water during the long summer drought, less susceptible to climatic stress and well synchronized with the climatic fluctuations of the Mediterranean environment.     

Vascular defense responses in rice: peroxidase accumulation in xylem parenchyma cells and xylem wall thickening.

The rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae is a vascular pathogen that elicits a defensive response through interaction with metabolically active rice cells. In leaves of 12-day-old rice seedlings, the exposed pit membrane separating the xylem lumen from the associated parenchyma cells allows contact with bacterial cells. During resistant responses, the xylem secondary walls thicken within 48 h and the pit diameter decreases, effectively reducing the area of pit membrane exposed for access by bacteria. In susceptible interactions and mock-inoculated controls, the xylem walls do not thicken within 48 h. Xylem secondary wall thickening is developmental and, in untreated 65-day-old rice plants, the size of the pit also is reduced. Activity and accumulation of a secreted cationic peroxidase, PO-C1, were previously shown to increase in xylem vessel walls and lumen. Peptide-specific antibodies and immunogold-labeling were used to demonstrate that PO-C1 is produced in the xylem parenchyma and secreted to the xylem lumen and walls. The timing of the accumulation is consistent with vessel secondary wall thickening. The PO-C1 gene is distinct but shares a high level of similarity with previously cloned pathogen-induced peroxidases in rice. PO-C1 gene expression was induced as early as 12 h during resistant interactions and peaked between 18 and 24 h after inoculation. Expression during susceptible interactions was lower than that observed in resistant interactions and was undetectable after infiltration with water, after mechanical wounding, or in mature leaves. These data are consistent with a role for vessel secondary wall thickening and peroxidase PO-C1 accumulation in the defense response in rice to X. oryzae pv. oryzae.     

Changes in Anatomical Features and Protein Pattern of Sunflower Partially Resistant and Susceptible Lines During Infection By Virulence Factors of Sclerotinia Sclerotiorum

Helianthus annuus L. as an oil seed crop is widely grown throughout the world. One of the most destructive diseases of sunflower is stem rot caused by Sclerotinia sclerotiorum. Oxalic acid is the major virulence factor of this necrotrophic pathogen. It is important to further investigate plant responses to this non-specific toxin. Therefore, in the present study, we compared the patterns of total soluble proteins and xylem morphology of partially resistant and susceptible sunflower lines after treatment with Sclerotinia culture filtrate. The basal stems of both lines were treated with 40 mM oxalic acid (pH 3.7) of fungus culture filtrate and samples were collected at 24, 48 and 72 hours post treatment. In SDS-PAGE protein pattern new protein bands appeared in both lines after treatment. These observations suggest induction of stress-related proteins upon culture filtrate treatment. The identities of these new proteins need to be more clarify in future investigations. The changes in xylem morphology and degree of lignification of both lines was studied by light microscopy and microtome sectioning techniques after treatment with S. sclerotiorum culture filtrate. Anatomical investigations revealed changes in xylem diameter and xylem lignification of treated lines at various time points. More lignin deposition in xylem vessels of partially resistant line has been observed after treatment. In addition, the size of xylem vessels in partially resistant line has been sharply decreased upon pathogen filtrate treatment. The results of this study will help us gain a more complete understanding of resistance mechanisms to this cosmopolitan and devastating pathogen.     

THE EFFECTS OF AUXINS AND KINETIN ON XYLEM DIFFERENTIATION IN THE PEA EPICOTYL

Sorokin , Helen P., S. N. Mathur , and Kenneth V. Thimann . (Harvard U., Cambridge, Mass.) The effects of auxins and kinetin on xylem differentiation in the pea epicotyl. Amer. Jour. Bot. 49(5): 444–454. Illus. 1962.—Treatment of isolated segments from the second internode of etiolated ‘Alaska’ pea epicotyls with indoleacetic acid or 2,4-D results in: (1) activation of fascicular cambium, and initiation of some interfascicular cambium, resulting in abundant production of secondary xylem, and in formation of hyperplastic tissue; (2) partial or even total occlusion of proto- and metaxylem. The secondary xylem formed consists of short vessel members with scalariformly reticulate or pitted walls, which often lack vertical connection with each other, being interrupted by unlignified cells. When IAA is used, the hyperplastic growth mainly takes the form of root primordia, whereas 2,4-D initiates the formation of callus, but not of root primordia. The growth of this callus causes a characteristic split at the base of the internode. Treatment with kinetin, alone or in combination with the auxin, changes the above structure markedly. It leads to the initiation, over the entire circumference of the core of the internode, of a still more active cambium, which forms several layers of secondary xylem; this consists mainly of long vessel members with pitted walls. Hyperplastic growth is completely absent, and the xylem does not become occluded. Thus the effect of kinetin is to make the xylem more normal and to alter the epicotyl structure from herbaceous to more-or-less woody.     

Micro-organisms at the cut surface and in xylem vessels of rose stems

Stems of cut rose flowers ( Rosa hybrida L. cv. 'Sonia') were placed in water to study the development of a population of micro-organisms at the cut surface and in the xylem vessels. The cut surface became covered with bacteria within 2 d of vase life. The bacteria were accompanied by an amorphous substance which was apparently bacterial slime. After 7 d of vase life many fungal hyphae were also found at the cut surface. Inside the xylem vessels the bacteria were often clustered at the inter-vessel pits. After 4 d of vase life most of the vessels that had been opened by cutting contained bacteria. Only a few xylem elements, located several centimeters from the cut surface, contained an amorphous substance. A few fungal hyphae were observed inside the xylem vessels. No yeasts were found, either at the cut surface or inside the xylem. Pseudomonas species accounted for more than 70% of the total bacterial population of the cut surface and the xylem vessels, and Enterobacter species (mainly Ent. agglomerans ) for less than 10%. Acinetobacter, Aeromonas, Alcaligenes, Bacillus, Citrobacter and Flavobacterium were occasionally observed.     

Secretion of vascular coating components by xylem parenchyma cells of tomatoes infected withVerticillium albo-atrum

Summary Massive infusion of conidia ofVerticillium albo-atrum into the xylem of tomato induces a cell wall coating response in resistant and susceptible near-isolines. In the early stages two types of coating material develop in the xylem vessels. The first, designated type A, is formed in association with xylem parenchyma cells that lack secondary walls; the localized accumulation of type A coating in the in the adjacent intercellular spaces, primary walls (i.e., pit membranes) and vessels occurs in conjunction with localized development of apposition wall layers within the parenchyma cells. Type B coating is initially formed in association with xylem parenchyma cells with secondary walls; the localized accumulation of typeB coating in the adjacent intercellular spaces, primary walls (i.e., pit membranes) and vessels occurs in conjunction with development of protective layers within the parenchyma cells. Most vessels are surrounded by a number of parenchyma cells including both cell types; therefore, in most vessels the coatings are mixed in later stages of development (i.e.,> 48 hours). The formation of both types of coating is stopped by the application of L--aminooxy--phenylpropionate, a specific inhibitor of phenylpropanoid synthesis. Histochemically, type A coating resembles lignin and type B, suberin. The data suggest that the coating response is due, wholly or in part to hypersecretion and/or chemical modification of normal cell wall components, induced by the pathogen.     

Resistance of Pepper Lines to the Movement of Cucumber Mosaic Virus

The multiplication and the migration of cucumber mosaic virus (CMV) were studied in greenhouse conditions in one susceptible ‘Yolo wonder’ and two resistant ‘Milord’ and ‘Vania’ pepper varieties. DAS-ELISA tests have revealed that the virus is replicated in inoculated leaves of the resistant varieties as high as in the susceptible variety. In the susceptible variety ‘Yolo wonder’, CMV migrated from the leaf lamina to the petiole two days after inoculation and it became systemic three days later regardless the season. In ‘Milord’ the virus migrated from the leaf lamina to the petiole five days after inoculation and it became systemic during the winter 16 days after inoculation. Whereas plants of the same genotype were not infected systemically during the summer. In ‘Vania’, during the two seasons, CMV spread from the blade to the petiole five days after inoculation, but the virus was not detected beyond the inoculated leaf. These results show that ‘Milord’ and ‘Vania’ are resistant to CMV migration. Therefore, the resistance to CMV migration is affected by plant genotype and temperature. The study of effect of pepper plant phenology on infection has revealed that resistance to CMV migration is also affected by the development stage of the plants.     

Human-Mouse Hybrid Cell Lines and Susceptibility to Poliovirus : I. Conversion from Polio Sensitivity to Polio Resistance Accompanying Loss of Human Gene-Dependent Polio Receptors

A number of human-mouse somatic hybrid cell lines have been prepared, containing from 3 to 12 human biarmed chromosomes. These lines were susceptible to poliovirus type 1, producing viral yields comparable to those of the human parental cells. A small proportion of the cells of these lines survived the polio infection, and their progeny were solidly resistant to reinfection with the virus. Both sensitive and resistant hybrids produced virus following infection with viral ribonucleic acid, indicating that the cytoplasm of the resistant hybrids was able to support viral multiplication. Viral adsorption studies carried out at 4 C showed that the resistant sublines had negligible ability to adsorb the virus. It was concluded that the hybrid cells became resistant to polio through loss of the human chromosome bearing the gene for the receptor substance.     

STEM ANATOMY AND ASPECTS OF DEVELOPMENT IN TOMATO

Aspects of anatomical development were correlated with internodal growth in tomato plants, variety ‘Yellow Plum,’ grown for more than 3 months. Internodal length was measured weekly in control plants and those harvested for anatomical study. Gross structure indicated progressive development with increasing age. Primary xylem and phloem first mature in distinct strands and the strands are joined laterally by procambium to form a continuous vascular cylinder. Primary phloem occurs on the outer periphery of the procambium between the early-formed vascular strands. Successive periclinal divisions in the procambium during internode elongation give rise to pronounced radial seriations of the cells. Procambial derivatives are included in the cylinder of thick-walled, lignified vascular cells that become prominent after elongation ceases. Secondary xylem is of greater radial width in the stem sectors which include protoxylem. During early secondary growth, vessels develop in the secondary xylem only in these sectors. Nucleate fibers and rays constitute the remainder of the secondary xylem. The rays exhibit an organization noted in other plants of reduced growth habit. Some of these interpretations do not agree with those described for tomato in earlier studies, and they are discussed in relation to pertinent aspects of development.     

Multiplication of Pseudomonas syringae pv. phaseolicola"in planta"

In the compatible combination of the halo blight disease of bean Pseudomonas phaseolicola was able to colonize large areas of the intercellular space of leaves, such that these confluent water congested areas became visible as water-soaked spots. Most of the plant cell walls in the infected region maintained their normal shape, even when the cytoplasm had collapsed. Some inward bending of plant cell walls preceded their rather slow degradation and final replacement by bacterial masses. Neighbouring plant cells appeared to be metabolically active. In resistant leaves no indications of active bacterial attachment or encapsulation could be observed. However, bacteria appeared to be more densely packed in resistant leaves, and relatively more plant cells completely collapsed as compared with susceptible leaves. From 8—14 days after inoculation, the bacterial concentration did not change much in susceptible or resistant leaves, indicating the absence of bactericidal components. Even Pseudomonas pisi snowed some multiplication in bean leaves (immune reaction), but its growth stopped earlier than that of P. phaseolicola. in the resistant cultivars, probably due to a different mechanism of resistance. Although less bacteria were determined in the intercellular washing fluid (IF) compared with leaf homogenates, the high bacterial concentrations in the IF supported our observation that an effective encapsulation of bacteria in resistant leaves did not occur.     

Certain aspects of resistance of plum trees to bacterial canker: Part II. On the nature of the bacterial invasion of Prunus sp. by Pseudomonas mors-prunorutn Wormald

A detailed histological study was made of the necrotic areas induced in the stem of a resistant and a susceptible variety of plum as the result of artificial inoculations of Ps. mors-prunorum Wormald. The pathogen was found to penetrate the tissues intercellularly, causing plasmolysis of cell contents, followed by disintegration of cell walls, and gradual invasion of the bacteria. The seasonal progress of infection was followed, the maximum cankers caused by winter inoculations in the susceptible host appearing in spring. Limitation of necrosis occurs in summer, generally accompanied by the production of new tissue composed of xylem elements. Viable bacteria were isolated in autumn from those cankers in which the area of necrosis had extended into the wood cylinder beyond the limiting periderm. The difference in the nature of the injury to the tissues of the resistant trees is quantitative rather than qualitative. The significance of the apparently more efficient host mechanism of periderm production in this variety is considered. Lesions similar in histological aspect were obtained as the result of the injection of cell-free filtrates of cultures of the causal organism.     

Possible Mechanisms Limiting Movement of Ralstonia solanacearum in Resistant Tomato Tissues

The distribution and appearance of Ralstonia solanacearum in the upper hypocotyl tissues of root‐inoculated tomato seedlings of resistant rootstock cultivar LS‐89 (a selection from Hawaii 7998) and susceptible cultivar Ponderosa were compared to clarify the mechanism that limits the movement of the bacterial pathogen in resistant tomato tissues. In stems of wilted Ponderosa plants, bacteria colonized both the primary and the secondary xylem tissues. Bacteria were abundant in vessels, of which the pit membranes were often degenerated. All parenchyma cells adjacent to vessels with bacteria were necrotic and some of them were colonized with bacteria. In stems of LS‐89 plants showing no discernible wilting symptoms, bacteria were observed in the primary xylem tissues but not in the secondary xylem tissues. Necrosis of parenchyma cells adjacent to vessels with bacteria was observed occasionally. The pit membranes were often thicker with high electron density. The inner electron‐dense layer of cell wall of parenchyma cells and vessels was thicker and more conspicuous in xylem tissues of infected LS‐89 than in xylem of infected Ponderosa or mock‐inoculated plants. Electron‐dense materials accumulated in or around pit cavities in parenchyma cells next to vessels with bacteria, and in vessels with bacteria. Many bacterial cells appeared normal in vessels, except for those in contact with the pit membranes. These results indicate that R. solanacearum moves from vessel to vessel in infected tissues through degenerated pit membranes and that restricted movement in xylem tissues was the characteristic feature in LS‐89. The limitation in bacterial movement may be related to the thickening of the pit membranes and/or the accumulations of electron‐dense materials in vessels and parenchyma cells.     

Elemental Sulfur and Thiol Accumulation in Tomato and Defense against a Fungal Vascular Pathogen

The occurrence of fungicidal, elemental S is well documented in certain specialized prokaryotes, but has rarely been detected in eukaryotes. Elemental S was first identified in this laboratory as a novel phytoalexin in the xylem of resistant genotypes of Theobroma cacao, after infection by the vascular, fungal pathogen Verticillium dahliae. In the current work, this phenomenon is demonstrated in a resistant line of tomato, Lycopersicon esculentum, in response to V. dahliae. A novel gas chromatography-mass spectroscopy method using isotope dilution analysis with 34S internal standard was developed to identify unambiguously and quantify 32S in samples of excised xylem. Accumulation of S in vascular tissue was more rapid and much greater in the disease-resistant than in the disease-susceptible line. Levels of S detected in the resistant variety (approximately 10 microg g-1 fresh weight excised xylem) were fungitoxic to V. dahliae (spore germination was inhibited >90% at approximately 3 microg mL-1). Scanning electron microscopy-energy dispersive x-ray microanalysis confirmed accumulation of S in vascular but not in pith cells and in greater amounts and frequency in the Verticillium spp.-resistant genotype. More intensive localizations of S were occasionally detected in xylem parenchyma cells, vessel walls, vascular gels, and tyloses, structures in potential contact with and linked with defense to V. dahliae. Transient increases in concentrations of sulfate, glutathione, and Cys of vascular tissues from resistant but not susceptible lines after infection may indicate a perturbation of S metabolism induced by elemental S formation; this is discussed in terms of possible S biogenesis.     

Analysis of the distribution of copper amine oxidase in cell walls of legume seedlings

Copper-containing amine oxidase (CuAO) has been proposed to play a role in H2O2 production in plant cell walls during cell development and in response to pathogen attack. We have compared the localisation of CuAO in pea (Pisum sativum L.), lentil (Lens culinaris M.) and chick pea (Cicer arietinum L.) grown under different light conditions, using both immuno- and histochemical techniques. The enzyme was detected by indirect immunofluorescence in the cell walls of parenchyma tissues of etiolated pea and lentil plants and was particularly abundant at intercellular spaces. Upon de-etiolation, CuAO largely disappeared from cortical cell walls except in the region of intercellular spaces. In the apical internode of light-grown seedlings, CuAO occurred mainly in cortical cell walls and, to some extent, in cell walls of xylem vessels. In both the elongation zone and mature regions of roots, CuAO was restricted to cortical cell walls and some cell junctions close to the meristem. Extensin epitopes co-localised to intercellular spaces of the cortex in de-etiolated pea, indicating that CuAO may have a role in cell wall strengthening at intercellular spaces. In chick pea, the localisation of the enzyme varied between different cultivars that have differing susceptibility to the fungus Ascochyta rabiei. In a susceptible cultivar Calia, immunogold labelling localised CuAO to cell walls of the cortex, as in lentil and pea, while in a resistant cultivar Sultano, it was most abundant in xylem vessels and, in light-grown plants, in the epidermis. These expression patterns are discussed with regard to the possible functions of amine oxidase in cell growth, cell differentiation and pathogen resistance.