Some Factors Governing Respiration,Glucose Metabolism and Iodoacetate Sensitivity in Tetrahymena pyriformis*

SYNOPSIS. The physiologic response of Tetrahymena pyriformis W to glucose, as measured by the respiratory rate in a buffered suspension, was found to be altered by exposure of the culture to this carbohydrate in the peptone-based growth medium. Glucose-grown cells had an elevated respiratory rate in the presence of glucose in the Tris-buffered suspension, while cells not grown with the glucose supplement required sodium and potassium for the response. Orthophosphate elevated the rate of oxygen consumption independently of the glucose effect. The endogenous respiratory of glucose and non-glucose cultured cells were significantly diffe The 2 types of cells responded differently to the cations, sod and potassium, and were not identical in sensitivity to iodoacet Iodoacetate poisoning was found to be due to inhibition of “uncompetitive” type, potentiated by glucose, orthophosphate, the absence of potassium.     

Shock Pulse Effects on Wheat Growth

Wheat seedlings (Triticum aestivum cv. Pacific Blue Stem) grown under continuous low-level illumination were used to study the effects of pressure variation and its duration. Growth was determined by dry weights, leaf length, and types of secondary roots produced. Two sublethal shock pulses (1.41 and 2.82 kg cm ^?2) and three pressure duration intervals (0.1, 1.0 and 10.0 seconds) were studied. The results indicated a general overall reduction in growth associated with the shock pulse and that the pressure duration interval influenced the shock- growth response. The long pressure duration interval was found to be the most influential on shock pulse response. Present knowledge indicates that a pulse rise-time of 1 ms and a pressure duration interval of at least 1.0 second affect plant growth at sublethal shock pulses, such that the growth response is linear or bi-directional, depending on the magnitude of the shock pulses, and either linear or complex with respect to pressure duration interval for any shock pulse level.     

The Invasive Nature of an Infectious Bacterial Symbiont

ABSTRACT. Xenosomes are infectious bacterial symbionts that exist exclusively in the cytoplasm of the small philasterine marine ciliate Parauronema acutum. We have used this host-symbiont system as a model to study infection. In the past we postulated that infection took place by a process in which the symbionts escaped digestion and entered into the host's cytoplasm through the food vacuole during phagocytosis. This is clearly not the case. We now present evidence based on electron microscopic observations that the symbionts infect in a manner involving direct penetration of the protozoan's cell membranes. We have obtained additional data that suggest that, following entrance of the symbionts into the cytoplasm, only a single xenosome is required to establish an infection.     

Kinetic studies of a (Na++ K++ Mg2+)ATPase in sugar beet roots. III. A proposed model for the (Na++ K+) activation and its significance for field properties

A microsomal (Na⁺+ K⁺+ Mg²⁺)ATPase preparation from sugar beet roots was used. The activation by simultaneous addition of Na⁺ and K⁺ at different levels was examined in terms of steady state kinetics. The observed data can be summarized in the following way: 1. The apparent affinity between the enzyme and the substrate MgATP depends on the ratio between Na⁺ and K⁺. At low Na⁺ concentration (below 5 mM), the apparent K_m decreases with increasing concentrations of K⁺ (1–20 mM). At 5 mM Na⁺, the K⁺ level does not change the apparent K_m, while at Na⁺ levels above 10 mM, the apparent K_m between enzyme and substrate increases with increasing concentration of K⁺. 2. When the MgATP concentration is kept constant, homotropic cooperativity (concerning one type of ligand) and heterotropic cooperativity (concerning different types of ligands) exist in the activation by Na⁺ and K⁺. The Na⁺ binding is cooperative with different K_m values and Hill coefficients (n) in the presence of low and high concentration of K⁺. At low Na⁺ level (< 5 mM). a negative cooperativity exists for Na⁺ (n_Na < 1) which is more pronounced in the presence of high [K⁺]. When the concentration of Na⁺ is raised the negative cooperativity disappears and turns into a positive one (n_Na > 1). Only K⁺ binding in the presence of low [Na⁺] shows cooperativity with a Hill coefficient that reflects changes from negative to positive homotropic cooperativity with increasing concentrations of K⁺ (n_K < 1 → n_K > 1). In the presence of [Na⁺] > 10 mM, the changes in n_k are insignificant. 3. A model is proposed in which one or two different K sites and one or two Na sites control the catalytic activity, with multiple interactions between Na⁺, K⁺ and MgATP. 4. In the presence of Na⁺ (< 10 mM), K⁺ is probably bound to two K sites, one of which translocates K⁺ through the membrane by an antiport Na⁺/K⁺ mechanism. This could be connected with an elevated K⁺ uptake in the presence of Na⁺ and could therefore explain some field properties of sugar beets.     

Messenger Discriminating Species of Initiation Factor F<Subscript>3</Subscript>

Species of the polypeptide chain initiation factor F₃ with high selectivity toward either MS2 or T4 phage messenger RNAs have been isolated from normal E. coli cells.     

The development of shoots in Phragmites communis Trin.

In aerial shoots of Phragmites communis Trin., final height,and often growth-rate, depend on the width of the emergent budwhich determines the basal diameter of the mature stem. In theearly stages there is internal competition for food reservesand smaller shoots may be harmed. Growth is faster during the early phase of growth, and it isincreased in wider buds, warmer weather, and more humid habitats.Any of these factors may be of over-riding importance, e.g.a summer-emerged shoot grows faster than a spring one of equalwidth. Minor fluctuations in environment have more effect earlythan later. New nodes develop more rapidly late in the yearthan early.