The Differential Susceptibility of Vetch (Vicia spp.) to Orobanche aegyptiaca: Anatomical Studies

Vetches (Vicia spp .) are important forage legumes in the MiddleEast and Mediterranean regions. Most vetches are highly susceptibleto the root holoparasites Orobanche aegyptiaca and O. crenata,suffering severe quality and yield losses. However, purple vetch(V. atropurpurea) has shown good resistance to Orobanche. Microscopicstudies were performed to reveal anatomical differences of host-parasiteinteractions between susceptible and resistant vetch. SusceptibleV. sativa‘Yovel’ and resistant V. atropupurea‘Popany’were grown in association with O. aegyptiaca seeds, on glassmicrofibre sheets in a polyethylene-bag system. Whole root observationsusing stereoscopic microscopy detected necrotic lesions surroundingthe attachments of Orobanche radicles on resistant vetch roots.Hand-cut sections examined under the light microscope revealedthat in both susceptible and resistant vetch genotypes the Orobancheseeds germinated, attached and penetrated the host root epidermisand cortex. A reddish-brown secretion was observed in the apoplastat the interface between the parasite haustorium and the hosttissues, including the cell walls of the resistant vetch xylemvessels. Fixed and embedded sections observed under the lightmicroscope showed that in the susceptible genotype the parasitehaustorium penetrated through the endodermis into the host vascularcylinder, successfully forming a continuum with host vascularvessels. However, in the resistant genotype, the parasite haustoriumwas blocked at the root endodermis layer. The blockage was coupledwith secretion of unidentified material, thus preventing theparasite from establishing. These findings indicate that mechanicaland possibly chemical barriers are responsible for the hostdefence mechanism(s) conferring resistance of V. atropurpureato O. aegyptiaca. Copyright 2000 Annals of Botany Company Broomrape, Vicia atropurpurea, Vicia sativa, parasitic plants, plant resistance, tissue sections.     

Gene expression changes associated with cytotoxicity identified using cDNA arrays

In order to investigate gene expression changes associated with cytotoxicity, we used cDNA arrays to monitor the expression of over 5,000 genes in response to toxic stress in the HepG2 liver cell line. Cells were treated with cytotoxic doses of acetaminophen, caffeine or thioacetamide for nine time points ranging from 1 to 24 h. Samples of mRNA from each time point were used to prepare radiolabeled cDNA, which was hybridized to nylon-membrane-based cDNA arrays. High-stringency washes were applied to reduce cross-hybridization. Analysis of spot intensities revealed that each compound led to approximately 150-250 gene expression changes that were sustained over at least three adjacent time points. The affected genes could be classified into clusters based on their temporal patterns of differential expression. A common set of 44 genes showed similar expression changes in response to all three compounds. Of these changes, 90% could be confirmed by quantitative RT-PCR analysis. The results indicate that detailed array-based time-course studies, coupled with a sensitive and highly specific confirmation assay, provide a powerful means of identifying cytotoxicity-associated gene expression changes. Electronic Publication     

Why did heterospory evolve?

The primitive land plant life cycle featured the production of spores of unimodal size, a condition called homospory. The evolution of bimodal size distributions with small male spores and large female spores, known as heterospory, was an innovation that occurred repeatedly in the history of land plants. The importance of desiccation‐resistant spores for colonization of the land is well known, but the adaptive value of heterospory has never been well established. It was an addition to a sexual life cycle that already involved male and female gametes. Its role as a precursor to the evolution of seeds has received much attention, but this is an evolutionary consequence of heterospory that cannot explain the transition from homospory to heterospory (and the lack of evolutionary reversal from heterospory to homospory). Enforced outcrossing of gametophytes has often been mentioned in connection to heterospory, but we review the shortcomings of this argument as an explanation of the selective advantage of heterospory. Few alternative arguments concerning the selective forces favouring heterospory have been proposed, a paucity of attention that is surprising given the importance of this innovation in land plant evolution. In this review we highlight two ideas that may lead us to a better understanding of why heterospory evolved. First, models of optimal resource allocation – an approach that has been used for decades in evolutionary ecology to help understand parental investment and other life‐history patterns – suggest that an evolutionary increase in spore size could reach a threshold at which small spores yielding small, sperm‐producing gametophytes would return greater fitness per unit of resource investment than would large spores and bisexual gametophytes. With the advent of such microspores, megaspores would evolve under frequency‐dependent selection. This argument can account for the appearance of heterospory in the Devonian, when increasingly tall and complex vegetative communities presented competitive conditions that made large spore size advantageous. Second, heterospory is analogous in many ways to anisogamy. Indeed, heterospory is a kind of re‐invention of anisogamy within the context of a sporophyte‐dominant land plant life cycle. The evolution of anisogamy has been the subject of important theoretical and empirical investigation. Recent work in this area suggests that mate‐encounter dynamics set up selective forces that can drive the evolution of anisogamy. We suggest that similar dispersal and mating dynamics could have underlain spore size differentiation. The two approaches offer predictions that are consistent with currently available data but could be tested far more thoroughly. We hope to re‐establish attention on this neglected aspect of plant evolutionary biology and suggest some paths for empirical investigation.     

Surgical treatment of nasal obstruction secondary to craniofacial fibrous dysplasia

Craniofacial fibrous dysplasia, a skeletal disorder most often affecting the mandible or maxilla, can cause a variety of complications. Nasal obstruction secondary to this unusual disorder presents a diagnostic and therapeutic challenge. The nasal obstruction in this case is due to expansion of fibrous lesions in adjacent bones as well as direct involvement of the turbinates with fibrous dysplasia. We describe the surgical correction of nasal obstruction in this unique setting and present a brief update of this intriguing disorder.     

PARATI – a dynamic model for radiological assessments in urban areas

The structure and mathematical model of PARATI, a detailed computer programme developed for the assessment of the radiological consequences of an accidental contamination of urban areas, is described with respect to the scenarios used for the estimation of exposure fields in a village or town, the models for the initial and secondary contamination with the radionuclide ¹³⁷Cs, the concepts for calculating the resulting radiation exposures and the changes with time of the contamination and radiation fields. Kerma rates at various locations in tropical urban areas are given, and the contribution of different contaminated surfaces to these rates after dry or wet deposition are discussed. Received: 12 April 1996 / Accepted in revised form: 30 August 1996     

High levels of expression of full length human pro-alpha 2(V) collagen cDNA in pro-alpha 2(V)-deficient hamster cells

A full length cDNA encoding human pro-alpha 2(V) collagen was constructed. Partial sequencing of the cDNA and primer extension analysis of mRNA from fibroblasts found that pro-alpha 2(V) mRNA differs from the mRNAs of other fibrillar collagens in the increased length of its 5'-untranslated region. The pro-alpha 2(V) cDNA was placed downstream of the human cytomegalovirus immediate early promoter/regulatory sequences for expression studies in cultured Chinese hamster lung cells. These cells have been shown previously to synthesize large quantities of pro-alpha 1(V) homotrimers as their only collagenous product. Transfection resulted in a number of clonal cell lines that express human alpha 2(V) RNA at levels comparable to, and in some cases greater than, levels found in normal human skin fibroblasts. Pro-alpha 2(V) chains produced in the majority of clonal lines were of sufficient quantity to complex all available endogenous pro-alpha 1(V) chains. Chimeric heterotrimers, composed of hamster alpha 1(V) and human alpha 2(V) chains in a 2:1 ratio, were stable to pepsin digestion and were found predominantly associated with the cell layer. Surprisingly, pro-alpha 2(V) chains, in excess to pro-alpha 1(V) chains, were found in the extracellular matrix and, in much greater abundance, in media. These chains were pepsin sensitive, indicating that pro-alpha 2(V) chains can be secreted as nonstable homotrimers or as free chains.