Ultrastructure Of Interaction Research Articles

Cytology and ultrastructure of interactions between Ustilago esculenta and Zizania latifolia

Ustilago esculenta is a biotrophic smut fungus that parasitizes Zizania latifolia, an edible aquatic vegetable of the southern China region. Infection results in swelling of the upper parts of the Z. latifolia culm which are called jiaobai and have a unique flavor and delicacy and are popular among Chinese. The infection process of Z. latifolia by U. esculenta was investigated with light and electron microscopy. Distribution of hyphae was uneven in plants; hyphae were mainly present in the swollen upper parts (jiaobai), the nodal regions of mature culms and old rhizomes and buds or shoots. Hyphae were rare in the internodes of mature culms and were fewer in the internodes of old rhizomes. All new buds produced on the nodes of culms and rhizomes were infected by hyphae in November before and in March after overwintering. The hyphae grew into the buds from the parent nodes via intervascular tissues only or via parenchyma tissues and vascular bundles. Hyphae extended within and between the host cells and frequently formed hyphal aggregations or clusters, not only in the mature tissues but also in developing tissues. The typical interface between the fungal hyphal wall and invaginated host plasma membrane comprised a sheath. The sheath surrounding a hyphae comprised an outer electron-opaque matrix and an inner electron-dense layer. The electron-opaque matrix layers were thicker in jiaobai tissues, ranging from 0.28 to 0.85 μm. The electron-dense hyphal coatings were more conspicuous in the young buds or shoots and mature culms than in the jiaobai. The intercellular hyphae caused large cavity formation between the cells or rupture of host cell walls, for gaining entry into host cells. The broken host cell wall fused with the electron-opaque matrix of the hyphal sheath as an interactive interface. The teliospore wall and wall ornamentation development was the same in postmature jiaobai tissues with sporadic sori and in the huijiao (jiaobai tissues containing the massive sori), but a sheath enveloping the teliospore was more transparent in the process of teliospore development in the jiaobai than in the huijiao.

Ultrastructure of interaction in alginate beads between the microalgaChlorella vulgariswith its natural associative bacteriumPhyllobacterium myrsinacearumand with the plant growth-promoting bacteriumAzospirillum brasilense

Chlorella vulgaris, a microalga often used in wastewater treatment, was coimmobilized and coincubated either with the plant growth-promoting bacterium Azospirillum brasilense, or with its natural associative bacterium Phyllobacterium myrsinacearum, in alginate beads designed for advanced wastewater treatment. Interactions between the microalga and each of the bacterial species were followed using transmission electron microscopy for 10 days. Initially, most of the small cavities within the beads were colonized by microcolonies of only one microorganism, regardless of the bacterial species cocultured with the microalga. Subsequently, the bacterial and microalgal microcolonies merged to form large, mixed colonies within the cavities. At this stage, the effect of bacterial association with the microalga differed depending on the bacterium present. Though the microalga entered a senescence phase in the presence of P. myrsinacearum, it remained in a growth phase in the presence of A. brasilense. This study suggests that there are commensal interactions between the microalga and the two plant associative bacteria, and that with time the bacterial species determined whether the outcome for the microalga is senescence or continuous multiplication.

Ultrastructure of interaction in alginate beads between the microalga <i>Chlorella vulgaris</i> with its natural associative bacterium <i>Phyllobacterium myrsinacearum</i> and with the plant growth-promoting bacterium <i>Azospirillum brasilense</i>

Chlorella vulgaris, a microalga often used in wastewater treatment, was coimmobilized and coincubated either with the plant growth-promoting bacterium Azospirillum brasilense, or with its natural associative bacterium Phyllobacterium myrsinacearum, in alginate beads designed for advanced wastewater treatment. Interactions between the microalga and each of the bacterial species were followed using transmission electron microscopy for 10 days. Initially, most of the small cavities within the beads were colonized by microcolonies of only one microorganism, regardless of the bacterial species cocultured with the microalga. Subsequently, the bacterial and microalgal microcolonies merged to form large, mixed colonies within the cavities. At this stage, the effect of bacterial association with the microalga differed depending on the bacterium present. Though the microalga entered a senescence phase in the presence of P. myrsinacearum, it remained in a growth phase in the presence of A. brasilense. This study suggests that there are commensal interactions between the microalga and the two plant associative bacteria, and that with time the bacterial species determined whether the outcome for the microalga is senescence or continuous multiplication.

Ultrastructure of Interactions Between Cassava andXanthomonas campestrispv.manihotis: Cytochemistry of Cellulose and Pectin Degradation in a Susceptible Cultivar

Boher, B., Kpemoua, K., Nicole, M., Luisetti, J., and Geiger, J. P. 1995. Ultrastructure of interactions between cassava and Xunthomonas campestris pv. munihotis: Cytochemistry of cellulose and pectin degradation in a susceptible cultivar. Phytopathology 85777-788. A cytochemical investigation was carried out on the development of an aggressive strain of Xanthomonas campestris pv. manihotis, responsible for the cassava bacterial blight, to gain better insights into molecular and cellular mechanisms involved in leaf cell wall degradation by this pathogen. The use of anti-pectin monoclonal antibodies revealed that the plant middle lamellae were damaged during the infection process, from the epiphytic stage on the leaf surface to invasion of vascular bundles. In parallel, application of a ~-1,4-exoglucanase-gold probe to healthy and infected tissues indicated that primary and secondary cell walls were also altered. Quantitation of gold labeling confirmed that pectin was more severely degraded than cellulose. Accumulation of pectinlike compounds was also detected in occluded infected vessels. Bacterial-surrounding sheaths, which were routinely seen during pathogenesis early after leaf inoculation, had a dense or loosened fibrillar appearance and were differentiated from the pathogen cell wall. Close association occurred between extracellular fibrils and leaf cell walls, both at early and advanced stages of wall degradation. Bacterial extracellular sheaths were often seen deep in host cell walls, sometimes enclosing residual plant cell wall fragments. Our cytochemical data demonstrated that cell wall degradation of cassava by Xunthomonas campestris pv. manihotis plays an important role in host tissue colonization. It is also suggested that bacterial extracellular sheaths are involved in plant cell surface degradation.

Host-pathogen interaction between spring wheat and Septoria nodorum with reference to resistance breeding

Host-pathogen interaction between spring wheat and Septoria nodorum Berk. with applications for wheat breeding were studied. Ultrastructure of interactions was studied using electron microscopic techniques. Following inoculation, conidia of S. nodorum germinate, form appressoria anda penetration peg which directly penetrates through the cell walls. It is suggested that most penetration attempts fail because of cellular defence reactions, formation of papillae and cell wall alterations. Inoculation with low spore concentration reduced grain yield of Hankkija’s Taava cultivar by 10 % and 1000-grain weight by 14 %. Inoculation with high spore concentration on large plots of Tähti cultivar reduced grain yield by 32 % and 1000-grain weight by 18 %. Inoculation with high spore concentration on normal breeding plots of Tähti cultivar reduced grain yield by 35 % and 1000-grain weight by 21 % and the grain yield of Kadett cultivar by 27 % and 1000-grain weight by 20 %. Inheritance studies on F2 progenies of spring wheat crosses involving susceptible and moderately or highly resistant parents suggest that heredity component of symptom expression is moderate level and breeding success depends mainly on efficient screening techniques. Resistance was associated with tallness in crosses, and cultivar trials suggest that resistance is positively associated with late maturation time. Field screening techniques based on small plots and artificial inoculation showed that the most resistant entries were wild Triticum species and late and tall cultivars. Seedling plant tests based on attached seedling leaves and detached leaves revealed easily the most resistant and most susceptible cultivars. The overall correlation between seedling tests and field tests was quite high. The results are discussed in relation to wheat breeding strategies for resistance to S. nodorum.

Ultrastructure of interactions between pseudomonads and oat leaves

Ultrastructural studies were made on interactions between oat leaves and the compatible pathogen Pseudomonas coronafaciens and the incompatible bacteria P. coronafaciens var. atropurpurea, P. fluorescens and P. tabaci. Ruthenium red, a cytochemical stain for acidic polysaccharides, was used to enhance resolution of bacterial extracellular polysaccharide (EPS) in vivo. EPS accumulation and the attachment of bacteria to oat cell walls were assessed quantitatively. Two types of association between bacteria and cell walls were distinguished, (1) the encapsulation of bacteria by fibrillar materials on to smooth areas of plant wall (physical entrapment) and (2) attachment involving localized but pronounced modification (often degradation) of the underlying wall. Quantitative analyses showed that EPS accumulated rapidly around P. coronafaciens but not incompatible bacteria. Production of EPS by the pathogen appeared to prevent attachment to oat cell walls. The proportion of incompatible bacteria attached to plant cell walls increased between 2·5 and 12 h after inoculation, but only with P. fluorescens were more than 35% of attached bacteria associated with pronounced plant cell wall modifications. Our results suggest that attachment per se is unlikely to restrict bacterial multiplication in oats but may allow the transfer of factors causing the production of antibacterial compounds by challenged cells. Examination of EPS accumulation in tobacco gave results closely comparable to those recorded in oats. The compatible bacterium, in this case, P. tabaci, was surrounded by EPS whereas the incompatible P. coronafaciens was not, but was often attached to cell walls.

The ultrastructure of interactions between Botrytis species and broad bean leaves

Light and electron microscope studies were made on broad bean leaves undergoing resistant and susceptible reactions to infection with Botrytis spp. Following penetration of the abaxial cuticle, hyphae of each species expanded within swollen epidermal cell walls. Hyphae produced by the non-pathogens B. cinerea, B. elliptica and B. tulipae, and also the pathogen B. fabae when inoculum droplets contained