EFFECTS OF ARSENATE ON GROWTH OF NITROGEN-AND PHOSPHORUS-LIMITED CHLORELLA VULGARIS (CHLOROPHYCEAE) ISOLATES1

The effects of arsenate on the growth characteristics of five isolates of the freshwater alga, Chlorella vulgaris Beij., were examined. Two field isolates originated from arsenic-contaminated sites in Yukon, Canada and Kyushi, Japan; two reference isolates were obtained from the University of Texas Culture Collection. One isolate was selected for arsenic-tolerance in the laboratory. All five strains survived in culture solutions containing high arsenate concentrations. Arsenate (1–25 mM As) reduced photosynthesis and cell growth, as reflected by induced lag periods, slower growth rates, and lower stationary cell yields. Field isolates had shorter lag periods, higher growth rates, and enhanced cell yields compared to lab isolates when exposed to the same arsenic concentrations. Growth of the phosphorus-limited field strains was stimulated by the addition of arsenic. The cell yield of phosphorus-limited C. vulgaris Yukon, when treated with arsenic, was two times that of the phosphorus-limited control. This pattern was not evident when photosynthesis was used as a measure of cell response.     

Effect of Temperature on the Formation of Microsclerotia of Verticillium dahliae

Microsclerotium formation by six isolates of Verticillium dahliae was studied at different temperatures both in vitro and in Arabidopsis thaliana . In vitro mycelial growth was optimal at 25°C, but microsclerotium formation was greatest at 20°C (two isolates) or 15–20°C (one isolate). Seedlings of A. thaliana were root-dipped in a conidial suspension, planted, and either placed at 5, 10, 15, or 25°C, or left at 20°C until the onset of senescence, after which some of the plants were placed at 5, 10, 15, or 25°C. The amount of microsclerotia per unit of shoot weight was assessed in relation to isolate and temperature. The optimal temperature for production of microsclerotia was 15–25°C. Two isolates each produced about 10 times more microsclerotia than each of the other four isolates. For these isolates, high R ²_adj.-values of 0.77 and 0.66 were obtained, with temperature and its square as highly significant (P   < 0.001) independent variables. R ²_adj.-values for the other isolates varied between 0.28 and 0.39. Moving plants to different temperatures at the onset of senescence led to microsclerotial densities that were intermediate between densities on plants that had grown at constantly 20°C and plants grown at other temperatures. This suggests that vascular colonization rate and rate of microsclerotium formation are similarly affected by temperature. The senescence rate of plants appeared unimportant except for plants grown at 25°C, which showed the highest amounts of microsclerotia per unit of plant weight in the most rapidly senescing plants.     

Effect of Repeated Convulsive Seizures on Brain γ-Aminobutyric Acid Metabolism in Three Sublines of Mice Differing by Their Response to Acoustic Stimulations

The turnover rates and steady-state levels of gamma-aminobutyric acid (GABA) have been determined in 15 brain areas of three sublines of inbred mice differing in their susceptibility to audiogenic seizures: Rb3, which is seizure resistant; Rb2, which develops clonic seizures; and Rb1, which develops tonic-clonic seizures. In the Rb1 subline, GABA steady-state levels are lower than in the Rb3 subline in three of the 15 areas examined (cerebellum, anterior colliculus, and amygdala), whereas in the Rb2 subline, steady-state levels are either higher (posterior colliculus and hippocampus) or lower (amygdala) than in the Rb3 subline. GABA turnover rates differ in three brain areas in Rb1 (amygdala, raphe, and hypothalamus) and in a single area (amygdala) in Rb2 when compared with Rb3. Only one area has similar variations of GABA turnover rate and steady-state levels in the two susceptible sublines: the amygdala. After 2 weeks of repeated auditory stimulations (two times a day, 8,000 Hz, 100 dB), additional alterations in GABA metabolism are observed: mainly large increases in GABA turnover rates (from 40% to three- to fourfold). The Rb2 subline displays a greater number of alterations (increases of turnover rates in pons, cerebellum, anterior and posterior colliculus, amygdala, olfactory bulbs and tubercles, striatum, and frontal cortex) than the Rb1 subline (increases of turnover rates in cerebellum, posterior colliculus, olfactory tubercles, raphe, and frontal cortex and a decrease in hypothalamus). In the Rb3 subline, increases of the turnover rate in amygdala and olfactory tubercles and decreases in olfactory bulbs and hippocampus are observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Frost resistance of winter rape leaves as related to the changes in water potential and growth capability

Differential thermal analysis indicated that the frost resistance of winter rape leaves ( Brassica napus L. var. oleifera L. cv. Gòrczanski), collected from plants grown in the cold (5/2°C), relies mainly on their ability to supercool to −9 to −11°C, i.e. consists in freezing avoidance. Initiation of ice formation in the cold-acclimated leaves resulted in the death of more than 50% of the cells as determined with a conductivity method. The development of freezing tolerance appeared to be an attribute of the second stage of plant hardening and was induced by the exposure of plants to a slightly subzero temperature (−5°C) for 18 h. Such a treatment brought about a sudden and persistent water potential decrease in the leaves, despite the fact that they had reabsorbed water from the medium prior to water potential measurements. Water potential changes were associated with a higher growth capability of the leaves as checked by determinations of disk area increments. It is suggested that the increased frost tolerance of the cold-grown winter rape leaves, subjected to subfreezing temperature, is related to the decreased water potential of the tissue caused by changes in turgor and/or in osmotic pressures of the cells.     

Molecular cloning of the plant plasma membrane H+-ATPase

Summary Mineral transport across the plasma membrane of plant cells is controlled by an electrochemical gradient of protons. This gradient is generated by an ATP-consuming enzyme in the membrane known as a proton pump, or H⁺-ATPase. The protein has a catalytic subunit of Mr=100,000 and is a prominent band when plasma membrane proteins are analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. We generated specific rabbit polyclonal antibody against the Mr=100,000 H⁺-ATPase and used the antibody to screen λgtll expression vector libraries of plant DNA. Several phage clones producing immunoreactive protein, and presumably containing DNA sequences for the ATPase structural gene, were isolated and purified from a carrot cDNA library and a Arabidopsis genomic DNA library. These studies represent our first efforts at cloning the structural gene for a plant plasma membrane transport protein. Applicability of the technique to other transport protein genes and the potential for use of recombinant DNA technology in plant mineral transport research are discussed.     

Velocity distribution of the anterograde and retrograde transport of extracellular particles byAmoeba proteus

Summary The transverse velocity profiles of the anterograde flow of particles on the cell surface and around it are approximately parabolic. The peak velocity is recorded close to the membrane and the descendent arm of the profile is viscosity-dependent. It indicates that the extracellular forward flow is probably generated by a forward movement of the fluid fraction of the membrane itself. The retrograde component of extracellular movements is manifested by particles kept on the cell surface by adhesion, which behave exactly as the ectoplasmic layer on the opposite side of the membrane,i.e., they probably reflect the movement of that fraction of the surface material which is attached to the cortical microfilaments. In the longitudinal profile, the velocity of anterograde flow rises from the tail to the front of amoeba, but is generally related to the effective cell locomotion rate and not to the movements of any intracellular layer. Around the cells deprived of any attachment to the substratum, which cannot locomote but manifest vigorous intracellular movements, the anterograde flow ceases at least along 2/3 of their lenght. It persists, however, around the frontal fountain zone, where other particles still move backwards together with the retracted ectoplasmic layer. This indicates that the role of the forward flow of and on the cell surface is to compensate for: (1) the increase of the surface area in the frontal regions due to locomotion, (2) the withdrawal of a part of material which is hauled back by the retracting cortical layer. A comprehensive scheme of the velocity distribution within the different layers of a moving amoeba and around it has been constructed on the basis of present and earlier data.Study supported by the Research Project CPBP 04.01 of the Polish Academy of Science.I dedicate this paper to Professor K. E. Wohlfarth-Bottermann with the best wishes for his 65th birthday.     

Scavenging of superoxide radical by ascorbic acid

Using acetaldehyde and xanthine oxidase as the source of suPeroxide radical, the second order rate constant for the reaction between ascorbic acid and superoxide radical was estimated to be 8.2 X 10⁷ M^-1 s^-1. In rats, the average tissue concentration of ascorbic acid was of the order of 10^-3 M and that of superoxide dismutase was of the order of 10^-6 M. So, taking together both the rate constants and the tissue concentrations, the efficacy of ascorbic acid for scavenging superoxide radical in animal tissues appears to be better than that of suPeroxide dismutase. The significance of ascorbic acid as a scavenger of superoxide radical has been discussed from the point of view of the evolution of ascorbic acid synthesizing capacity of terrestrial vertebrates.     

The influence of diet on the growth of Stenonema vicarium (Walker) (Ephemeroptera: Heptageniidae)

Laboratory studies compared the growth rate of Stenonema vicarium (Walker) nymphs on diets of detritus and natural stream periphyton. In three consecutive runs of the experiment, growth rates were consistently higher on periphyton (mean growth rate = 2.1% wet wt. d⁻¹) than detritus (mean = 1.8% wet wt. d⁻¹). The starting date of each run also significantly influenced growth rates. In each treatment growth rates generally decreased over the course of the 3 runs, and ca. one-half of the nymphs in the last run did not molt or grow. It appeared that growth of S. vicarium may be partially controlled by seasonal factors.