MAX1and MAX2 control shoot lateral branching in Arabidopsis

Plant shoots elaborate their adult form by selective control over the growth of both their primary shoot apical meristem and their axillary shoot meristems. We describe recessive mutations at two loci in Arabidopsis, MAX1 and MAX2, that affect the selective repression of axillary shoots. All the first order (but not higher order) axillary shoots initiated by mutant plants remain active, resulting in bushier shoots than those of wild type. In vegetative plants where axillary shoots develop in a basal to apical sequence, the mutations do not clearly alter node distance, from the shoot apex, at which axillary shoot meristems initiate but shorten the distance at which the first axillary leaf primordium is produced by the axillary shoot meristem. A small number of mutant axillary shoot meristems is enlarged and, later in development, a low proportion of mutant lateral shoots is fasciated. Together, this suggests that MAX1 and MAX2 do not control the timing of axillary meristem initiation but repress primordia formation by the axillary meristem. In addition to shoot branching, mutations at both loci affect leaf shape. The mutations at MAX2 cause increased hypocotyl and petiole elongation in light-grown seedlings. Positional cloning identifies MAX2 as a member of the F-box leucine-rich repeat family of proteins. MAX2 is identical to ORE9, a proposed regulator of leaf senescence (Woo, H. R., Chung, K. M., Park, J.-H., Oh, S. A., Ahn, T., Hong, S. H., Jang, S. K. and Nam, H. G. (2001) Plant Cell 13, 1779-1790). Our results suggest that selective repression of axillary shoots involves ubiquitinmediated degradation of as yet unidentified proteins that activate axillary growth

Convergence of Discretized Light Cone Quantization in the small mass limit

I discuss the slow convergence of Discretized Light Cone Quantization (DLCQ) in the small mass limit and suggest a solution.Comment: 8 pages, 5 Postscript figures, uses boxedeps.te

Integrated photonic delay-lasers for reservoir computing

Currently, multiple photonic reservoir computing systems show great promise for providing a practical yet powerful hardware substrate for neuromorphic computing. Among those, delay-based systems offer a simple technological route to implement photonic neuromorphic computation. Its operation boils down to a time-multiplexing with the delay length limiting the processing speed. As most optical setups end up to be bulky employing long fiber loops or free-space optics, the processing speeds are ranging from kSa/s to tens of MSa/s. Therefore, we focus on external cavities which are far shorter than what has been realized before in such experiments. We present experimental results of reservoir computing based on a semiconductor laser, operating in a single mode regime around 1550nm, with a 10.8cm delay line. Both are integrated on an active/passive InP photonic chip built on the Jeppix platform. Using 23 virtual nodes spaced 50 ps apart in the integrated delay section, we increase the processing speed to 0.87GSa/s. The computational performance is benchmarked on a forecasting task applied to chaotic time samples. Competitive performance is observed for injection currents above threshold, with higher pumps having lower prediction errors. The feedback strength can be controlled by electrically pumping integrated amplifiers within the delay section. Nevertheless, we find good performance even when these amplifiers are unpumped. To proof the relevance and necessity of the external cavity on the computational capacity, we have analysed linear and nonlinear memory tasks. We also propose several post-processing methods, which increase the performance without a penalty to speed

Renormalization of Tamm-Dancoff Integral Equations

During the last few years, interest has arisen in using light-front Tamm-Dancoff field theory to describe relativistic bound states for theories such as QCD. Unfortunately, difficult renormalization problems stand in the way. We introduce a general, non-perturbative approach to renormalization that is well suited for the ultraviolet and, presumably, the infrared divergences found in these systems. We reexpress the renormalization problem in terms of a set of coupled inhomogeneous integral equations, the ``counterterm equation.'' The solution of this equation provides a kernel for the Tamm-Dancoff integral equations which generates states that are independent of any cutoffs. We also introduce a Rayleigh-Ritz approach to numerical solution of the counterterm equation. Using our approach to renormalization, we examine several ultraviolet divergent models. Finally, we use the Rayleigh-Ritz approach to find the counterterms in terms of allowed operators of a theory.Comment: 19 pages, OHSTPY-HEP-T-92-01

ENOD40 encodes a peptide growth factor

Rhizobium bacteria induce the formation of nodules on the roots of leguminous plants. The nodules create the right biological niche for the rhizobia to carry out biological nitrogen fixation by which atmospheric nitrogen is reduced to ammonia. The nodule is a new organ that provides the plant with a nitrogen source for its growth and development. The formation of a nitrogen fixing root nodule is the final result of an extensive collaboration between the plant and the bacterium, which starts with the exchange of signals. The plant roots secrete flavonoids, which attract rhizobia and induce the expression of nodulation (nod) genes in the rhizobia. Due to the nod gene expression, specific lipochitooligosaccharide signals are produced, the so-called Nod factors, that induce several responses in the roots as a result of which nodule formation can start. The first plant responses are root hair deformation, expression of several plant genes and the mitotic reactivation of root cortical cells which leads to the formation of a nodule primordium. In chapter I a general overview is given of the signal exchange leading to the formation of a functional root nodule.The aim of the research, described in this thesis, was to analyse the role of the early nodulin gene ENOD40 in nodule development. To adress this issue, ENOD40 expression was determined in nodules and its actvity was studied in an in vitro model system. First an ENOD40 clone was isolated from pea using the available soybean ENOD40 cDNA as a probe. This made it possible to compare the expression pattern of ENOD40 in a determinate (soybean) and indeterminate (pea) nodule by in situ hybridisation. using the soybean and pea ENOD40 clones, respectively, as probes (chapter 2). Chapter 3 describes the isolation and characterisation of the soybean ENOD40-2 gene. A transcriptional fusion between the ENOD40-2 promoter and the β-glucuronidase reporter gene was used in Agrobacterium rhizogenes mediated transformation of Vicia hirsuta. Root nodules were induced on the transgenic hairy roots by infection with Rhizobium leguminosarum bv. viciae and activity of the ENOD40 promoter was analysed using GUS assay.Expression of the ENOD40 gene is detectable early after infection in the pericycle of the root, before cortical cell divisions take place. It was assumed that ENOD40 expression might be required for the induction of cortical cell division, and might function by influencing auxin and/or cytokinin levels which play a role in the induction of cell division. This hypothesis was tested in a model system, the tobacco protoplast cell division assay. With this assay, the interaction of ENOD40 with auxin and cytokinin was studied, and ENOD40 was shown to induce tolerance of high auxin and cytokinin concentrations in tobacco protoplasts (chapter 4, 6). Using the tobacco protoplast cell division assay it was demonstrated that an oligopeptide of 10 to 13 amino acids encoded by ENOD40 is the compound responsible for this effect. In addition, a conserved region in the 3' UTR of ENOD40 also has an effect (chapter 4).Tobacco cells are able to respond to a soybean ENOD40 cDNA clone and to the soybean ENOD40 peptide. This indicates in tobacco homologous genes might be present. The cloning of these genes by PCR based methods is described in chapter 4 and 5. The presence and activity of ENOD40 in legumes and a non legume indicates ENOD40 might play a general role in plant development. Therefore, in the concluding remarks (chapter 7) it is discussed whether peptides can play a more common role in plant development and whether and how the 3' UTR of ENOD40 mRNA might function