‘Lymphocyte-like’cells in ascidians: Precursors for vertebrate lymphocytes?

There has been much speculation that the evolutionary precursors of vertebrate lymphocytes may exist in the ascidians (proto chordates), but conclusive evidence has remained elusive especially as membrane bound immunoglobulin has not been detected in any invertebrate. This paper reviews new evidence which indicates that the ‘lymphocyte-like’ cells in ascidians have functional, as well as morphological, similarities with vertebrate lymphocytes. Firstly, these cells have been linked with in vivo non-self recognition events such as allograft rejection in solitary ascidians and non-fusion reactions between colonial ascidians. Secondly, they have been shown to be cytotoxic towards xenogenic targets in vitro and to use cytolytic mechanisms similar to those of cytotoxic T-cells. Thirdly, they are able to proliferate in vitro in response to mitogens or allogeneic cells. It is therefore suggested that, apart from immunoglobulin production and clonal selection, there is persuasive evidence that the ‘lymphocyte-like’ cells of ascidians constitute a primordial form of vertebrate lymphocyte.     

Integration of CAPS markers into the RFLP map generated using recombinant inbred lines of Arabidopsis thaliana

Konieczny and Ausubel have described a technique whereby Arabidopsis thaliana loci can be rapidly mapped to one of the ten chromosome arms using a small number of F2 progeny from crosses between the ecotypes Landsberg erecta and Columbia. The technique involves the use of 18 co-dominant, cleaved amplified polymorphic sequence (CAPS) markers which are evenly distributed throughout the Arabidopsis genome. We have mapped these 18 markers using recombinant inbred (RI) lines generated in our laboratory. These data enable a better integration of loci mapped relative to the CAPS markers into the restriction fragment length polymorphism (RFLP) map generated using Arabidopsis RI lines.     

Phytochrome B and at Least One Other Phytochrome Mediate the Accelerated Flowering Response of Arabidopsis thaliana L. to Low Red/Far-Red Ratio

We have investigated the involvement of phytochrome B in the early-flowering response of Arabidopsis thaliana L. seedlings to low red:far-red (R/FR) ratio light conditions. The phytochrome B-deficient hy3 (phyB) mutant is early flowering, and in this regard it resembles the shade-avoidance phenotype of its isogenic wild type. Seedlings carrying the hy2 mutation, resulting in a deficiency of phytochrome chromophore and hence of active phytochromes, also flower earlier than wild-type plants. Whereas hy3 or hy2 seedlings show only a slight acceleration of flowering in response to low R/FR ratio, seedlings that are doubly homozygous for both mutations flower earlier than seedlings carrying either phytochrome-related mutation alone. This additive effect clearly indicates the involvement of one or more phytochrome species in addition to phytochrome B in the flowering response as well as indicating the presence of some functional phytochrome B in hy2 seedlings. Seedlings that are homozygous for the hy3 mutation and one of the fca, fwa, or co late-flowering mutations display a pronounced early-flowering response to low R/FR ratio. A similar response to low R/FR ratio is displayed by seedlings doubly homozygous for the hy2 mutation and any one of the late-flowering mutations. Thus, placing the hy3 or hy2 mutations into a late-flowering background has the effect of uncovering a flowering response to low R/FR ratio. Seedlings that are triply homozygous for the hy3, hy2 mutations and a late-flowering mutation flower earlier than the double mutants and do not respond to low R/FR ratio. Thus, the observed flowering responses to low R/FR ratio in phytochrome B-deficient mutants can be attributed to the action of at least one other phytochrome species.     

Gas-chromatographic analysis of poly(3-hydroxyalkanoates) in bacteria

Summary The accuracy and reproducibility of the gas-chromatographic method for the analysis of PHB and PHA in whole cells of Alcaligenes eutrophus H16 and Pseudomonas putida KT2442 were determined. It was found that for analysis of PHA the methanolysis time in the assay had to be increased to 4 h. Accuracy of the PHB and PHA assay were 0.018 mg and 0.304 mg respectively, based on estimation of the measurement error.     

Analysis of aspartic acid and asparagine metabolism in Xenopus laevis oocytes using a simple and sensitive HPLC method

The amino acids in methanol-soluble extracts of Xenopus oocytes were measured using a method involving precolumn derivatization with phenylisothiocyanate and reverse phase HPLC of the derivatized amino acids. This technique allows the estimation of asparagine and glutamine pools in oocytes, estimated as 70 and 283 pmoles per oocyte, respectively. The pool sizes of the other amino acids were similar to previously reported results obtained using conventional ion exchange chromatography and postcolumn derivatization with ninhydrin. The advantages of the method developed here include picomolar sensitivity and the enhanced resolution of asparagine and glutamine from other amino acids. The kinetics of aspartic acid and asparagine utilization were monitored following microinjection of oocytes with [³H]aspartic acid and [¹⁴C]asparagine. The aspartic acid pool turned over rapidly with a half-time of <30 min. The asparagine pool was metabolized much more slowly and appeared to be utilized almost completely for protein synthesis. The absolute rate of protein synthesis in oocytes was calculated from the incorporation data and chemical pool measurements as ～25 ng/hr-oocyte. The methodology developed here may be useful in experimental situations involving limited amounts of biological material. © 1994 Wiley-Liss, Inc.     

A Fine Structural Analysis of Auxin-induced Elongation of Cucumber Hypocotyls, and the Effects of Calcium Antagonists and Ionophores

The fine structure of epidermal cells, particularly in relationto dictyosomes, has been examined in different regions of dark-growncucumber hypocotyls and in response to auxin treatment, usingboth dot overlay and image analysis techniques. The most noticeablechange in cell structure along the hypocotyls is the increasein vacuolar volume. The volume fraction occupied by dictyosomesand secretory vesicles also increased, whereas that for mitochondriaremained relatively constant. During auxin treatment, the volumefraction for dictyosomes showed an increase after 30 min followedby a fall, whereas that occupied by secretory vesicles fellsteadily over 90 min. The number of cisternae per dictyosomeshowed some increase after 2 h of auxin treatment, althoughthe increase in dictyosomal material with cell expansion waslargely accounted for by an increase in the number of dictyosomes. Auxin-stimulated elongation growth of the hypocotyls was inhibitedby a range of calcium antagonists, chelators and ionophores.The most marked inhibitions were observed with calcium chloride,the chelator chlortetracycline and the ionophores verapamil,nigericin and monensin. Linear transducer experiments showedthat these compounds generally caused an immediate reductionin the rate of growth. Fine structural observations carriedout on epidermal cells showed the most obvious effects withmonensin and nigericin which caused dictyosomes and secretoryvesicles to swell. EGTA and LaCl₃ caused secretory vesiclesto accumulate around dictyosomes, while the ionophore A23187had little effect. The results suggest that the concentration of Ca²⁺ in the cytoplasmmay be critical for cell elongation. Compounds which chelateCa²⁺ appear to be more effective inhibitors of growth in theinitial acid-induced phase, whereas those which affect ionicgradients are more disruptive in the second phase.Copyright1993, 1999 Academic Press Calcium, Cucumis sativus hypocotyle, dictyosomes, elongation growth, indoleacetic acid, stereology