Tricarboxylic Acid Cycle Enzymes in Tetrahymena pyriformis after Infection of the Cockroach Periplaneta americana1

SYNOPSIS. Activities of enzymes of the tricarboxylic acid cycle in extracts of Tetrahymena pyriformis S, axenically recovered after living in the hemocoel of female cockroaches Periplaneta americana for 48 hr, were compared with activities in ciliates not exposed to the cockroach. Malic dehydrogenase activity was depressed after recovery from the cockroach; isocitric and succinic dehydrogenases and α-ketoglutaric oxidase activities were unchanged. Citrate synthetase activity was increased, and pyruvi oxidase activity decreased, after ciliates had been in the cockroach. These alterations persisted for several hundred generations after recovery from the insect.     

A System for Measuring the Uptake of Ions by Plants from Flowing Solutions of Controlled Composition

A system is described for growing plants in flowing solutionin which the concentration (activity) of some nutrient ionsis continuously monitored and held almost constant by meansof ion-selective electrodes which control the operation of nutrientpumps. By recording the concentration of a given ion in theflowing nutrient solution and the amount of that ion which isdelivered by the nutrient pumps, it is possible to follow nutrientuptake over long and short periods. A brief account is givenof the operation of the system using a nitrate ion-selectiveelectrode to examine aspects of uptake by perennial ryegrass (Lolium perenne L.).     

Bacterial rhamnolipids are novel MAMPs conferring resistance to Botrytis cinerea in grapevine

Rhamnolipids produced by the bacteria Pseudomonas aeruginosa are known as very efficient biosurfactant molecules. They are used for a wide range of industrial applications, especially in food, cosmetics and pharmaceutical formulations as well as in bioremediation of pollutants. In this paper, the role of rhamnolipids as novel molecules triggering defence responses and protection against the fungus Botrytis cinerea in grapevine is presented. The effect of rhamnolipids was assessed in grapevine using cell suspension cultures and vitro-plantlets. Ca²⁺ influx, mitogen-activated protein kinase activation and reactive oxygen species production form part of early signalling events leading from perception of rhamnolipids to the induction of plant defences that include expression of a wide range of defence genes and a hypersensitive response (HR)-like response. In addition, rhamnolipids potentiated defence responses induced by the chitosan elicitor and by the culture filtrate of B. cinerea . We also demonstrated that rhamnolipids have direct antifungal properties by inhibiting spore germination and mycelium growth of B. cinerea . Ultimately, rhamnolipids efficiently protected grapevine against the fungus. We propose that rhamnolipids are acting as microbe-associated molecular patterns (MAMPs) in grapevine and that the combination of rhamnolipid effects could participate in grapevine protection against grey mould disease.     

The Uptake of Nitrate by Lolium perenne from Flowing Nutrient Solution: II. EFFECT OF LIGHT, DEFOLIATION, AND RELATIONSHIP TO CO2 FLUX

Experiments with simulated swards of perennial ryegrass (Loliumperenne L.) grown in flowing nutrient solution with NO₃- heldat 0.1 mg N I^–1 show that the rate of NO₃- uptake wasrelated to diurnal, day-to-day, and seasonal changes in radiation.In summer the diurnal variation in NO₃-uptake ranged from 25to 50 mg N m^–2 h^–1 and the day-to-day variationranged from 500 to 1500 mg N m^–2 d^–1. Mean dailyrates of uptake over 12 d periods in summer and in winter averaged908 and 44 mg N m^–2, respectively. The pattern of NO₃-uptake followed that of CO₂ flux with the maximum rate of theformer occurring 5 or 6 h after the maximum CO₂ influx. Afterdefoliation, NO₃- uptake was severely curtailed for 2 d concomitantwith a very small influx of CO₂. Analysis of the changes thatoccurred in the rate of NO₃- uptake immediately after the switchingon or off of artificial light suggests that two reversible processesmay be involved in the relation between NO₃-uptake and radiation,one with a longer and the other with a shorter time constant.     

Edwin Grant Conklin

Son of a country physician, Edwin Grant Conklin grew up in centralOhio and was educated along traditional lines. A decision toenter biology as a profession came only after three years ofteaching a variety of subjects in a private school. Graduatestudy at Johns Hopkins and summer research opportunities atWoods Hole were the doors to a richly productive career as scholar,author and administrator. His research works in embryology andcytology gained him great eminence. An important theme in muchof his work was the role of the cytoplasm in development. Hewrote extensively on evolution and other subjects of generalinterest, among them science and religion, and the nature ofman.