Shock effects on some cryptogamic plants

Résumé La turgescence de la cellule et la plasticité de sa paroi subissent des changements après le choc; la condition de latence et la sporogénèse sont accélérées. Les organisms blessés régénèrent. Il se peut que la forme de la cellule détermine la sensibilité à la pression du choc.     

Shock effects on plants: Tannic acid and chlorogenic acid in yam roots

Résumé Les tanins de l'acide chlorogénique s'accumulent immédiatement après que les racines d'ignames ont été soumises à des chocs de 10 à 44 (0.6–2.66 kg/cm²), consistant en une pulsation de la pression comparable à une rafale d'air dans un tube. L'accumulation des tanins est inversement proportionelle à la pression. Mais, l'acide chlorogénique s'accumule progressivement avec élèvation du niveau du choc.     

Oxygen consumption and the evolution of order: negentropy criteria applied to the evolution of ants

Optimization of energy use by evolving organisms, predicted by theoretical extensions of the neo-Darwinian theory, i. contrasted with that of irreversible thermodynamics, which predicts an increase in orderliness and thus an increase in energy consumption per unit of biomass. We compared this index with estimates of social complexity among ant genera and species. Our results show that simple optimization models cannot explain experimental data, and that social complexity correlates differently with negentropy at different levels of analysis. Comparing the genera among Formicidae, workers (not colonies) from genera with highly social species are less negentropic than those of socially primitive ones. At the sub-generic level, social complexity correlated positively with negentropy among species, for major workers inAcromyrmex and for minor workers inAtta. The results illustrate the complexity of thermodynamic criteria in the study of evolution but also hint at their usefulness. In this case, they show that two different evolutionary routes to the complex Attini ant societies may exist.     

Shock effects onEuglena gracilis: The effect of the pressure duration

Résumé Les cultures d'Euglena gracilis ont été soumises à des chocs de 20 et 40 (1.21 et 2.41 kg/cm²). La pression engendrée par une pulsation durait de 25µsec, 4 et 10 sec. La durée de la pression servit de critère pour évaluer les effets des niveaux élevés du choc atmosphérique sur le photo-thermotropisme d'Euglena gracilis.

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This work was supported in part by funds from Advanced Research Projects Agency, Department of Defense, through the U.S. Geological Survey, under A.R.P.A. Order No, 938. Special thanks are expressed to Dr. C. L.Newcombe of San Francisco State College, and Dr. T.Sh. Hansford of the Geological Survey for making this study possible.     

Shock effects on the growth of radish seedlings: the effect of the pressure duration

Résumé Des semis de radis furent soumis à la pression produite par un choc atmosphérique. La pression engendrée par une pulsation augmentant rapidement durait de 0, 1 à 14 sec. La durée de la pression servit de critère pour évaluer les effets des niveaux élevés du choc atmosphérique.     

Oxygen consumption ofParagnetina media (Walker): Light-dark effect on respiratory rates

Résumé Le taux de consommation d'oxygène d'oxygène des Plécoptères (stonefly) fut étudié à différentes heures de la journée. On a déterminé en outre l'effet de la lumière et de l'obscurité sur la respiration de ces insects. La consommation d'oxygène fut significativement plus élevée dans l'obscurité.     

Comparative effect of silver ion and gibberellic acid on the induction of male flowers on femaleCannabis plants

Summary Silver ion applied as AgNO₃ to the shoot tip of female plants ofCannabis induces male flowers. It is more effective than gibberellic acid (GA₃) in maintaining the induced state.Acknowledgment. G.S. thanks the Council of Scientific and Industrial Research, New Delhi, India, for the award of a Junior Research Fellowship.     

Cytological effect of some medicinal plants used in the control of fertility

Summary The effects induced upon the cell cycle of Allium cepa meristems by 2 medicinal plants used in the control of fertility were studied. Infusions of Aristolochia triangularis induces typical c-mitotic figures. On the other hand, Stevia rebaudiana have no specific toxicological effects upon the cell cycle.This work was supported by a research grant from the Instituto para el Estudio de la Reproducción Humana, Asunción (Paraguay).     

Reticulate evolution and cladism: Tests for the direction of evolution

Summary Reticulate evolution between ancestral-descendant lineages can be critically tested for by investigating the relationship between out-group and mid-point roots on numerically derived cladograms. The western grass-snake provides a worked example for the theoretical test.     

The effect of weak electrical potential gradients on the transport of water in broad bean plants under stress

Summary Adequate moisture was transported by an electrical potential gradient of 1 V/cm of the correct polarity to maintain the turgid state of broad-bean plants subjected to severe stress conditions.Acknowledgments. A.P. is grateful to the University of stellenbosch for the financial aid and the privilege of conducting research on their premises.     

Action of isothiocyanates on germinating plants

Zusammenfassung Es wurde ein inhibitorischer Effekt des Allylisothiocyanates auf die Keimung von Erbsen, Weizen und Raps beobachtet, und dabei die Veränderungen des Stickstoff- und Zuckermetabolismus verfolgt: Isothiocyanate setzen die Atmung und anaerobe Glykolyse um etwa 30% herab und legen die Proteosynthese vollständig still.     

Signal transduction mechanisms in plants: an overview

This article provides an overview on recent advances in some of the basic signalling mechanisms that participate in a wide variety of stimulus-response pathways. The mechanisms include calcium-based signalling, G-protein-mediated-signalling and signalling involving inositol phospholipids, with discussion on the role of protein kinases and phosphatases interspersed. As a further defining feature, the article highlights recent exciting findings on three extracellular components that have not been given coverage in previous reviews of signal transduction in plants, extracellular calmodulin, extracellular ATP, and integrin-like receptors, all of which affect plant growth and development.     

Transformation: a tool for studying fungal pathogens of plants

Plant diseases caused by plant pathogenic fungi continuously threaten the sustainability of global crop production. An effective way to study the disease-causing mechanisms of these organisms is to disrupt their genes, in both a targeted and random manner, so as to isolate mutants exhibiting altered virulence. Although a number of techniques have been employed for such an analysis, those based on transformation are by far the most commonly used. In filamentous fungi, the introduction of DNA by transformation typically results in either the heterologous (illegitimate) integration or the homologous integration of the transforming DNA into the target genome. Homologous integration permits a targeted gene disruption by replacing the wild-type allele on the genome with a mutant allele on transforming DNA. This process has been widely used to determine the role of newly isolated fungal genes in pathogenicity. The heterologous integration of transforming DNA causes a random process of gene disruption (insertional mutagenesis) and has led to the isolation of many fungal mutants defective in pathogenicity. A big advantage of insertional mutagenesis over the more traditional chemical or radiation mutagenesis procedures is that the mutated gene is tagged by transforming DNA and can subsequently be cloned using the transforming DNA. The application of various transformation-based techniques for fungal gene manipulation and how they have increased our understanding and appreciation of some of the most serious plant pathogenic fungi are discussed. Received 9 May 2001; received after revision 2 July 2001; accepted 3 July 2001