The use of microcomputers for the quantitation of light intensity patterns using digitized video signals

We have developed an inexpensive yet versatile microcomputer-basedsystem for quantitating light intensity levels in autoradiographs.This system employs a standard video camera interfaced to ananalog-to-digital convertor. A program has been written forthis system which can measure intensities within a defined regionof an autoradiograph, permitting an easy and accurate quantitationof spots or bands of irregular shape. Received on June 18, 1985; accepted on September 3, 1985     

Oral Ultrastructure and Oral Development of the Misaligned Undulating Membrane Mutant of Tetrahymena thermophila1

The misaligned undulating membrane (mum) mutant of Tetrahymena thermophila is a non-conditional, single gene recessive mutation. The major effect of the mum mutation is the production of multiple undulating membrane (UM) fragments in the oral apparatus (OA). The ultrastructure of the UM fragments of mum OAs is identical to that of the single UM of wild-type OAs. Analysis of OA development at midbody using a combination of light microscopy of protargol-stained cells and SEM of demembranated whole cells showed that the phenotypic effect of the mum mutation first becomes evident during mid to late stage 4 and is fully manifested in early stage 5. The effect of the mutation involves a proliferation of excess basal bodies in the UM field. Subsequent events in the development of the mum OA from mid to late stage 5 are identical to those in wild-type OAs. This study suggests that the mum mutation establishes conditions that allow the production of multiple UMs and thus reveals that the UM field is competent for the complete and coordinated development of several adjacent UMs. This level of regional control is not clearly evident when a single UM is present. The comparison of development of wild-type and mum OAs required an extensive reanalysis of stages 4 and 5 of normal oral development. On the basis of current and previous observations, we propose a new and more subdivided staging system for oral development in Tetrahymena.     

Activation of tyrosinase in mouse melanoma cell cultures

Summary Tyrosinase activity increased in Cloudman S-91 mouse melanoma cell homogenates incubated at 37°C for a minimum of 8 h. Enzyme activity continued to increase for 48h at which time the maximal level of activation was observed. Activation did not occur at 4°C and did not occur in the cytosol fraction of the cell, suggesting that the response was localized to melanosomes. The activated enzyme was resistant to solubilization with the nonionic detergent, Triton X-100, and preparation of homogenates in this detergent did not inhibit the temperature-dependent activation of the melanosomal fraction of the cell. The activation process increased the V _Max of tyrosinase 10-fold and lowered the K _M by a factor of 2 as determined by the tyrosine hydroxylase assay. The increase in tyrosinase activity was detectable by three assay methods: tyrosine hydroxylation, melanin synthesis, and by tyrosine decarboxylation. The formation of melanin, however, was found to be 1/20 that of either tyrosine hydroxylation or decarboxylation, a finding which suggests that the melanin pathway may be blocked at 5,6-dihydroxyindole. The “self-activation” response could not be mimicked by incubating cell homogenates with cyclic AMP-dependent protein kinase. Activated tyrosinase could be inhibited by the addition of fresh cell extracts, a finding which suggests that tyrosinase inhibitors may be present in these cells. This investigation was supported by Public Health Service grants CA41425 and CA30393 awarded by the National Cancer Institute, Bethesda, MD and by a research grant from the Proctor and Gamble Company.     

Ultrastructural evidence for the biflagellate origin of the uniflagellate fungal zoospore

Summary The morphological similarities between the kinetosome and the second centriole of the zoospores of Phlyctochytrium kniepii and P. punctatum (Chytridiomycetes) suggest that the second centriole in the chytrid zoospore is a vestigial flagellum base. It is suggested that the term vestigial kinetosome may also be used when referring to the structure which is presently termed the second centriole of the chytrid zoospore. Morphological similarities between the chytrid zoospores of P. kniepii and P. punctatum and the zoospores of Rhizidiomyces apophysatus (Hyphochytridiomycetes) are noted. The possible biflagellate origin of fungi with uniflagellate zoospores is discussed. The third fiber (C fiber) of the kinetosome triplet is shown to form as an outgrowth of the B fiber of the kinetosome doublet.     

Carbon metabolism in Bradyrhizobium japonicum bacteroids

Abstract Carbon metabolism in Bradyrhizobium japonicum bacteroids is reviewed. Additionally, the bacteroid tricarboxylic acid (TCA) cycle and its regulation under oxygen-limited conditions is considered, with emphasis on possible sites of TCA cycle rate-limiting reactions. Furthermore, we consider other adaptive pathways that may be employed by these organisms while in symbiosis. These pathways include: (1) a poly-β-hydroxy-butyrate shunt, (2) a malate-aspartate shuttle, (3) an α-ketoglutarate-glutamate shunt, (4) a modified dicarboxylic acid cycle, and (5) fermentation pathways leading to lactate, acetaldehyde and ethanol. The effects of oxygen limitation on host carbon metabolism are also considered briefly.     

Genetic and morphological divergence among sympatric canids

Numerous studies have suggested that the extent of character divergence observed between two sympatric species reflects the intensity of competition for resources or space. However, the influence of time on divergence is often overlooked. We examined the relationship between time and character divergence in two groups of congeneric, sympatric canids on two continents: South American foxes and African jackals. Character divergence was assessed from measurements of body mass and dental and cranial shape. Divergence time was estimated from data on mitochondrial DNA restriction site polymorphisms. Our findings indicate that African jackals are morphologically similar despite having diverged more than 2 million years ago. By contrast, South American foxes differ substantially in both size and morphology after only 250,000 years of evolution. Thus, the lack of character divergence among the African jackals cannot be explained as a result of very recent common ancestry.     

Pre-inoculation of Ri T-DNA-transformed pea roots with Pseudomonas fluorescens inhibits colonization by Pythium ultimum Trow: an ultrastructural and cytochemical study

The influence exerted by Pseudomonas fluorescens, strain 63-28R, in stimulating plant defense reactions was investigated using an in-vitro system in which Ri T-DNA-transformed pea (Pisum sativum L.) roots were subsequently infected with Pythium ultimum. Cytological investigations of samples from P. fluorescens-inoculated roots revealed that the bacteria multiplied abundantly at the root surface and colonized a small number of epidermal and cortical cells. Penetration of the epidermis occurred through the openings made by the disruption of the fibrillar network at the junction of adjacent epidermal cell walls. Direct cell wall penetration was never observed and bacterial ingress into the root tissues proceeded via an intercellular route. Striking differences in the extent of fungal colonization were observed between bacterized and non-bacterized pea roots following inoculation with P. ultimum. In non-bacterized roots, the pathogen multiplied abundantly through most of the tissues while in bacterized roots, pathogen growth was restricted to the epidermis and the outer cortex. At the root surface, the bacteria interacted with the pathogen, in a way similar to that observed in dual culture tests. Most Pythium cells were severely damaged but fungal penetration by the bacteria was never observed. Droplets of the amorphous material formed upon interaction between the bacteria and the host root were frequently found at the fungal cell surface. Incubation of sections with a -1,4-exoglucanase-gold complex revealed that the cell wall of markedly altered Pythium hyphae was structurally preserved. Successful penetration of the root epidermis was achieved by the few hyphae of P. ultimum that could escape the first defensive line in the rhizosphere. Most hyphae of the pathogen that penetrated the epidermis exhibited considerable changes. The unusual occurrence of polymorphic wall appositions along the host epidermal cells was an indication that the host plant was signalled to defend itself through the elaboration of physical barriers.Abbreviations AGL Aplysia gonad lectin - PGPR plant growth-promoting rhizobacteria The authors wish to thank Sylvain Noël for excellent technical assistance. This study was supported by grants from the Fonds Québécois pour la formation de chercheurs et l'Aide à la Recherche (FCAR), the Natural Sciences and Engineering Council of Canada (NSERC) and the Ministère de l'Industrie, du Commerce, de la Science et de la Technologie (SYNERGIE).