METHYLAMINE UPTAKE IN THE GREEN ALGA CHLORELLA PYRENOIDOSA1

Methylamine uptake in nitrogen-starved Chlorella pyrenoidosa Beij. follows Michaelis-Menten kinetics: maximum uptake is about 1.6 nmol μl^?1· cells · min^?1, half-saturation occurs at 4 μM methylamine, and the slope in the range where uptake is proportional to concentration is 0.4 nmol μl^?1· min^?1·μM^?1. In cells grown in the presence of a non-limiting nitrogen concentration, methylamine uptake is directly proportional to concentration up to at least 0.5 mM, and the slope is 1/500 that for starved cells. Similar uptake kinetics have been reported for Penicillium chrysogenum and attributed to an inducible “ammonium permease.” Apparently, a similar permease occurs in algae.     

ACCUMULATION AND REDUCTION OF ARSENATE BY THE FRESHWATER GREEN ALGA CHLORELLA SP. (CHLOROPHYTA)

Arsenate accumulation and reduction kinetics at both high and low phosphate concentrations were investigated in the green alga Chlorella sp, isolated from the arsenic-contaminated Upper Mystic Lake near Boston, MA. Growth rate, accumulated cellular arsenic, and release of As(III) were determined over a range of arsenate concentrations. Arsenate inhibited growth and reduced final cell yield at high phosphate concentration. However, growth rate, final cell yield, and cellular arsenic content were all enhanced by higher arsenate concentrations in cultures grown at a low concentration of phosphate. The traditional view that phosphate-limited cells are necessarily more sensitive to As(V) toxicity may not be correct. The reduction rates of As(V) by Chlorella sp. obtained in our laboratory were similar to net reduction rates measured in epilimnetic water from the Upper Mystic Lake, demonstrating the importance of phytoplankton in arsenic reduction in freshwater.     

INHIBITION OF PHOTOSYNTHESIS IN CHLORELLA PYRENOIDOSA BY THE IODO-ACETYL RADICAL

Photosynthesis in Chlorella pyrenoidosa is inhibited by iodo-acetic acid and iodo-acetamide, both of which attack the Blackman reaction. Since acetamide is without effect, the iodo-acetyl radical must be responsible. The study of the action of the acid is complicated by the fact that its ions penetrate slowly, if at all, so that negative results with this agent are without significance unless penetration can be established. The absorption spectrum of the cells is not affected by concentrations of iodo-acetamide which completely inhibit photosynthesis. This establishes that the chromophore groups of chlorophyll are not involved, and renders it unlikely that any other part of the molecule is. Inasmuch as cyanide likewise inhibits by way of the Blackman reaction, it would seem necessary to postulate that this complex can be attacked at two different loci, which may or may not be on the same molecule. The presence of the iodo-acetyl radical also gives rise to three other effects. (1) Concentrations (10^–5 M or less) too small to inhibit photosynthesis may increase the rate by interacting with the photochemical complex. (2) Concentrations (ca. 10^–4 M) which inhibit photosynthesis increase the rate of respiration. (3) Concentrations (10^–3 M or more) higher than those required to inhibit photosynthesis inhibit respiration.     

TEMPERATURE CHARACTERISTICS FOR THE METABOLISM OF CHLORELLA : III. THE CATALYTIC DECOMPOSITION OF HYDROGEN PEROXIDE BY CHLORELLA PYRENOIDOSA

The decomposition of hydrogen peroxide by intact Chlorella cells follows a first order course at very low temperatures, but at higher temperatures gives falling first order constants. Between 0.6° and 20°C. the value of µ is 10,500 calories.     

ULTRASTRUCTURE OF CHLORELLA PYRENOIDOSA AS AFFECTED BY ENVIRONMENTAL CHANGES

Chlorella pyrenoidosa (van Niel's strain) was cultured in four environmental conditions: light-glucose, light-galactose, dark-glucose, and dark-galactose. The gradual change in structure was observed when the cultures were transferred from light to darkness (dark adaptation). Cells grown in light contained well-developed chloroplasts and the normal cytoplasmic sub-units. During the transition to the complete heterotrophic mode of nutrition, the chloroplast regressed to the proplastid stage with a gradual reduction in thylakoid number. A prolamellar body was noted in the most regressed proplastid condition and plastid storage material was observed in all stages. The cell wall thickened during the transition. Cells adapted to darkness on galactose exhibited abundant cytoplasmic storage material with osmiophilic properties.     

蛋白核小球藻凝集素的分离纯化及部分性质研究

蛋白核小球藻藻粉的PBS抽提液经硫酸铵二步分级沉淀 ,再经DEAE Sepharose和SephadexG 10 0层析 ,从中分离纯化得到蛋白核小球藻凝集素 (CPL)。经测定 ,该凝集素为单个亚基的蛋白质 ,相对亚基分子量为 1 4× 10 4 — 1 5× 10 4 ,分子中不含糖。在氨基酸组成中 ,苯丙氨酸 (Phe)的含量最高 ,其次是天冬氨酸 (Asp)和谷氨酸 (Glu) ,不含组氨酸 (His)。CPL能够凝集兔、绵羊及鸽子红细胞 ,其中对兔红细胞的凝集活性最大 ,最低浓度为 6 88μg/mL ,对鸡、鸭及人红细胞 (A型、O型及B型 )无凝集活性。卵黏蛋白和 7种单糖对CPL的凝血活性具有抑制作用。CPL具有很好的热稳定性 ,在 90℃处理 10min不失活。     

ANALYSIS OF STARCH CONTENT IN CHLORELLA PYRENOIDOSA (CHLOROPHYTA) BY MORPHOLOGICAL AND QUANTITATIVE TECHNIQUES

Chlorella pyrenoidosa (Chick) was grown heterotrophically in batch culture on defined medium with glucose. Morphometric analysis of cells in the exponential growth phase showed that starch accounted for 57% of the volume of the chloroplast and 36% of the total cell volume. During the stationary growth phase, the amount of starch accounted for only 36% of the chloroplast volume and 13% of the total cell volume. This represented a 36% decrease in the amount of starch/cell between the exponential and stationary phase. Determination of starch as grams/cell using quantitative techniques on cell extracts showed a comparable decrease in the amount of starch during this same transition. Based on these results, morphometric techniques provided an accurate assay of starch and have the added advantage of visualization of cellular structures not available when quantitative techniques are used.     

RESPONSE OF CHLORELLA PYRENOIDOSA TO ALUMINUM AND LOW pH12

Chlorella pyrenoidosa, a green alga which has no measurable Ca requirement, tolerated much higher Al concentrations in solution than higher plants which require considerable Ca. This alga also gave significant positive yield responses to Al concentrations between 1.5 and 12 ppm (added at pH 4.6). The positive Al response was not attributable to V, Cr, Ni, Co, W, or Ti contaminants in the Al salt. A strain of C. pyrenoidosa having even greater Al tolerance was isolated, by subjecting the original Strain I (Fitzgerald) culture to increasing Al stress. This strain, I-Al, grew in stagnant cultures containing 48 ppm Al at an initial pH of 4.2. Its yield also was not significantly decreased by 48 ppm Al in aerated cultures when both inoculum and solution pH were 4.6. Under the same conditions the original Strain I organism was injured by 3 and 6 ppm Al and was killed by 12 ppm. Algal strains which differ in Al tolerance may be useful in (1) studies on the mechanism of Al toxicity and mineral nutrition in general; and (2) in raising the pH, precipitating Al, and thereby detoxifying Al-containing acid mine drainage water and commercial wastes.     

TEMPERATURE CHARACTERISTICS FOR THE METABOLISM OF CHLORELLA : II. THE RATE OF RESPIRATION OF CULTURES OF CHLORELLA PYRENOIDOSA AS A FUNCTION OF TIME AND OF TEMPERATURE

The respiration of the green alga Chlorella pyrenoidosa, suspended in Knop''s solution, has been studied in the dark as a function of time and of temperature. The rates of oxygen consumption and of carbon dioxide production (at constant temperature) decline for about 25 hours to a low, constant level. From an analysis of the curves it is suggested that two substances, A and B, are utilized, whose respiratory quotients are 1 and 0.65 respectively. The values of the temperature characteristics were found to be: for oxidation of A, 19,500 (0.6 to 11.5°C.) and 3,500 (11.5 to 28°C.); for oxidation of B, 5,600 (23.4 to 0.6°C.).     

THE FINE STRUCTURE OF SPOROGENESIS IN THE XANTHOPHYCEAN ALGA PSEUDOBUMILLERIOPSIS PYRENOIDOSA1,2

The fine structure of vegetative cells, sporogenesis, and zoospores of the xanthophycean alga Pseudo-bumilleriopsis pyrenoidosa is described. Cleavage in sporogenesis closely resembles that of certain aquatic fungi.     

TEMPERATURE CHARACTERISTICS FOR METABOLISM OF CHLORELLA : I. THE RATE OF O2 UTILIZATION OF CHLORELLA PYRENOIDOSA WITH ADDED DEXTROSE

The temperature characteristic for the rate of O₂ consumption by Chlorella pyrenoidosa suspended in Knop solution containing 1 per cent glucose was studied between 1° and 27°C. with the Warburg technic. The value of µ was found to be about 19,000 ±1,000 cal. There is some indication of a critical temperature at 20°C., with shift to a lower µ above this temperature. The effect of sudden changes in temperature on the rate of respiration and the variation of the latter with time at constant temperatures are discussed. It is concluded that the "normal" respiration (in absence of external glucose) does not appear in the determination of this temperature characteristic.     

FATTY ACID AND LIPID COMPOSITION OF THE ACIDOPHILIC GREEN ALGA CHLAMYDOMONAS SP.1

The lipid and fatty acid compositions of Chlamydomonas sp. isolated from a volcanic acidic lake and C. reinhardtii were compared, and the effects of pH of the medium on lipid and fatty acid components of Chlamydomonas sp. were studied. The fatty acids in polar lipids from Chlamydomonas sp. were more saturated than those of C. reinhardtii. The relative percentage of triacylglycerol to the total lipid content in Chlamydomonas sp. grown in medium at pH 1 was higher than that in other cells grown at higher pH. A probable explanation might be that Chlamydomonas sp. has two low pH adaptation mechanisms. One mechanism is the saturation of fatty acids in membrane lipids to decrease membrane lipid fluidity, and the other is the accumulation of triacylglycerol, as a storage lipid, to prevent the osmotic imbalance caused by high concentrations of H₂SO₄.     

AN EXPERIMENTAL SEPARATION OF OXYGEN LIBERATION FROM CARBON DIOXIDE FIXATION IN PHOTOSYNTHESIS BY CHLORELLA

Using intact cells of Chlorella pyrenoidosa it is possible to obtain oxygen by the reduction of certain reducible materials other than carbon dioxide. Of these, benzaldehyde was studied in some detail. This reduction does not involve the production of carbon dioxide from the benzaldehyde. Stoichiometrical relationships as expressed by the following equation: 2C₆H₅CHO + 2H₂O → 2C₆H₅CH₂OH + O₂ are somewhat difficult to obtain because the benzaldehyde can disappear from the reaction mixtures by dark reactions. The technique is now available which permits detailed studies of the oxygen-liberating mechanisms in photosynthesis.     

POTASSIUM IN POLYPHOSPHATE BODIES OF CHLORELLA PYRENOIDOSA (CHLOROPHYCEAE) AS DETERMINED BY X-RAY MICROANALYSIS1

Potassium is an important component information of polyphosphate bodies (PB) by Chlorella pyrenoidosa Chick. However, it was not detected in PB by X-ray energy dispersive microanalyses when the specimens were subjected to a standard preparation procedure for transmission electron microscopy. Intact cells were incinerated at 350 C on stainless steel grids coated with silicon monoxide. X-ray spectra from PB showed conspicuous peaks of energy counts in the Kα lines for phosphorus and potassium. It is proposed that potassium is a major cationic component of PB in C. pyrenoidosa grown in potassium sufficient medium.