Cooperative Enterprise and Organization Theory

Agribusiness,

Metabolism of stilbene phytoalexins in grapevines: Oxidation of resveratrol in single-cell cultures

Single-cell cultures of the fungus resistant grapevine varieties Pollux and Sirius and the susceptible ones Riesling and Optima have been established to study the metabolism of the stilbene phytoalexins resveratrol and viniferin. Cells of different varieties showed morphological differences (form and mechanical resistance) and their susceptibility to treatment with debris of killed mycelium of Bot1ytis cinerea reflected the varietal resistance under natural conditions. Most cells of Riesling and Optima were killed by toxic components of the mycelium within 60 h, whereas cultures of Pollux and Sirius showed only slight damage. Two types of peroxidases have been characterized which can take resveratrol as a substrate converting it to a brown pigment. Viniferin was observed as an intermediate product. Peroxidase activity in suscpetible varieties was reduced as compared to the resistant ones. The oxidation products of resveratrol inhibited the activity of peroxidase. The function of stilbene phytoalexins as precursors of lignin-like substances is discussed

Induktions- und Nachweismethoden für Stilbene bei Vitaceen

Die von Blättern verschiedener Rebarten und -sorten als Reaktion auf bestimmte Reize (Botiytis-Infektionen, UV-Licht, Zuckerlösungen, Galaktarsäure) gebildeten Stilbene Resveratrol und ε-Viniferin konnten dünnschichtchromatographisch identifiziert und quantifiziert werden.In einigen Varianten ließen sich auch ohne vorherige gezielte Induktion Resveratrol und/oder ε-Viniferin in geringen Konzentrationen nachweisen.Von den durchgeführten Versuchen stellt die Bestimmung der von Rebblättern nach Induktion mit Galaktarsäure in eine entsprechende Unterlage (Testkarton) abgegebene Stilbenmenge mittels visueller Bonitur unter langwelligem UV-Licht eine einfache und gut reproduzierbare Screening-Methode dar. Die erhaltenen Werte zeigten mit den dünnschichtchromatographisch ermittelten eine hoch signifikante Übereinstimmung und erlaubten eine hinreichend genaue und schnell durchzuführende Gruppierung der einzelnen Genotypen in solche mit keinem oder sehr geringem, geringem, mittlerem und hohem Stilbenproduktionsvermögen.Die Fähigkeit von Rebblättern, als ,,Antwort" auf einen definierten Reiz mit einer möglichst schnellen und hohen Stilbenproduktion zu reagieren, ist mit ihrer Botrytis-Anfälligkeit negativ korreliert. Die daraufhin untersuchten Reben ließen sich, mit Ausnahme einiger Varianten mit sowohl schwacher Stilbenbildung wie niedrigem Befall, in gering, mittel und hoch anfällige Arten und Sorten klassifizieren. Bei 6 daraufhin untersuchten Genotypen ergab sich zwischen dem Stilbenproduktionsvermögen der Rebblätter (induziert durch Galaktarsäure in Testkarton) und dem der Beeren (induziert in Saccharosemedium) eine positive, zwischen Stilbenbildung und Botrytis-Anfälligkeit dagegen eine negative Korrelation.Methods for induction and determination of stilbenes in VitaceaeThe stilbenes resveratrol and ε-viniferin produced by leaves of different grapevine species and varieties in response to certain stimulants (Botrytis infection, UV radiation, sugar solutions, mucic acid) have been identified by use of quantitative thin-layer chromatography. Without artificial induction, only small concentrations of resveratrol and/or ε-viniferin could be measured in the leaves of some grapevines.Leaf pieces were placed on filter cardboard soaked with an aqueous solution of mucic acid. The edges of the pieces excreted stilbenes into the cardboard, the concentrations of which were estimated under long wavelength (366 nm) UV radiation. A significant correlation was shown between the data obtained by visual appraisal and the results from thin-layer chromatography.Hence, this visual method allows quick and sufficiently reliable classification of grapevines according to their stilbene production.The susceptibility to B. cinerea was negatively correlated with the ability of grape leaves to produce stilbenes after defined stimulation. The grapevines investigated could be classified as low, middle or highly resistant. A few exceptions showed low stilbene production together with low susceptibility to B. cinerea.The stilbene production of leaves (induced by mucic acid) and that of berries (induced by saccharose solution) of 6 different grapevines were positively correlated. A negative correlation was found between stilbene production and susceptibility to B. cinerea.

Hysteretic Optimization For Spin Glasses

The recently proposed Hysteretic Optimization (HO) procedure is applied to the 1D Ising spin chain with long range interactions. To study its effectiveness, the quality of ground state energies found as a function of the distance dependence exponent, $\sigma$, is assessed. It is found that the transition from an infinite-range to a long-range interaction at $\sigma=0.5$ is accompanied by a sharp decrease in the performance . The transition is signaled by a change in the scaling behavior of the average avalanche size observed during the hysteresis process. This indicates that HO requires the system to be infinite-range, with a high degree of interconnectivity between variables leading to large avalanches, in order to function properly. An analysis of the way auto-correlations evolve during the optimization procedure confirm that the search of phase space is less efficient, with the system becoming effectively stuck in suboptimal configurations much earlier. These observations explain the poor performance that HO obtained for the Edwards-Anderson spin glass on finite-dimensional lattices, and suggest that its usefulness might be limited in many combinatorial optimization problems.Comment: 6 pages, 9 figures. To appear in JSTAT. Author website: http://www.bgoncalves.co

Focused Local Search for Random 3-Satisfiability

A local search algorithm solving an NP-complete optimisation problem can be viewed as a stochastic process moving in an 'energy landscape' towards eventually finding an optimal solution. For the random 3-satisfiability problem, the heuristic of focusing the local moves on the presently unsatisfiedclauses is known to be very effective: the time to solution has been observed to grow only linearly in the number of variables, for a given clauses-to-variables ratio $\alpha$ sufficiently far below the critical satisfiability threshold $\alpha_c \approx 4.27$. We present numerical results on the behaviour of three focused local search algorithms for this problem, considering in particular the characteristics of a focused variant of the simple Metropolis dynamics. We estimate the optimal value for the ``temperature'' parameter $\eta$ for this algorithm, such that its linear-time regime extends as close to $\alpha_c$ as possible. Similar parameter optimisation is performed also for the well-known WalkSAT algorithm and for the less studied, but very well performing Focused Record-to-Record Travel method. We observe that with an appropriate choice of parameters, the linear time regime for each of these algorithms seems to extend well into ratios $\alpha > 4.2$ -- much further than has so far been generally assumed. We discuss the statistics of solution times for the algorithms, relate their performance to the process of ``whitening'', and present some conjectures on the shape of their computational phase diagrams.Comment: 20 pages, lots of figure

Екатеринбургская неделя. 1883. № 50

This is the author’s accepted manuscript. The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-642-24364-6_12.acmid: 2050798 location: Saarbrücken, Germany numpages: 16acmid: 2050798 location: Saarbrücken, Germany numpages: 1

Diversified Late Acceptance Search

The well-known Late Acceptance Hill Climbing (LAHC) search aims to overcome the main downside of traditional Hill Climbing (HC) search, which is often quickly trapped in a local optimum due to strictly accepting only non-worsening moves within each iteration. In contrast, LAHC also accepts worsening moves, by keeping a circular array of fitness values of previously visited solutions and comparing the fitness values of candidate solutions against the least recent element in the array. While this straightforward strategy has proven effective, there are nevertheless situations where LAHC can unfortunately behave in a similar manner to HC. For example, when a new local optimum is found, often the same fitness value is stored many times in the array. To address this shortcoming, we propose new acceptance and replacement strategies to take into account worsening, improving, and sideways movement scenarios with the aim to improve the diversity of values in the array. Compared to LAHC, the proposed Diversified Late Acceptance Search approach is shown to lead to better quality solutions that are obtained with a lower number of iterations on benchmark Travelling Salesman Problems and Quadratic Assignment Problems

Solving satisfiability problems by fluctuations: The dynamics of stochastic local search algorithms

Stochastic local search algorithms are frequently used to numerically solve hard combinatorial optimization or decision problems. We give numerical and approximate analytical descriptions of the dynamics of such algorithms applied to random satisfiability problems. We find two different dynamical regimes, depending on the number of constraints per variable: For low constraintness, the problems are solved efficiently, i.e. in linear time. For higher constraintness, the solution times become exponential. We observe that the dynamical behavior is characterized by a fast equilibration and fluctuations around this equilibrium. If the algorithm runs long enough, an exponentially rare fluctuation towards a solution appears.Comment: 21 pages, 18 figures, revised version, to app. in PRE (2003

Hiding solutions in random satisfiability problems: A statistical mechanics approach

A major problem in evaluating stochastic local search algorithms for NP-complete problems is the need for a systematic generation of hard test instances having previously known properties of the optimal solutions. On the basis of statistical mechanics results, we propose random generators of hard and satisfiable instances for the 3-satisfiability problem (3SAT). The design of the hardest problem instances is based on the existence of a first order ferromagnetic phase transition and the glassy nature of excited states. The analytical predictions are corroborated by numerical results obtained from complete as well as stochastic local algorithms.Comment: 5 pages, 4 figures, revised version to app. in PR