The Effects of Light Intensity on the Growth Rates of Green Algae

FREAR AND BURRELL-ASSIMILATION OF HYPONITRITE-NITROGEN tion of pyridine nucleotides by spinach grana and coupled carbon dioxide fixation. Nature 167: 768769. 1951. 29. VISHNIAC, W. and OCHOA, S. Fixation of carbon dioxide coupled to the photochemical reduction of pyridine nucleotides bv chloroplast preparations. Jour. Biol. Chem. 195: 75-93. 1952. 30. ZBINOVSKY. V. and BURRIS. R. H. Metabolism of

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infiltrated organic acids by tobacco leaves. Plant Physiol. 27: 240-249. 1952. 31. ZUCKER, M. and NASON, A. A pyridine nucleotidehydroxylamine reductase from Neurospora. Jour. Biol. Chem. 213: 463-478. 1955. 32. ZUCKER, M. and NASON, A. Enzymatic reduction of hydroxylamine to ammonia by reduced pyridine nucleotides. Federation Proc. 13: 328. 1954.

THE EFFECTS OF LIGHT INTENSITY ON THE GROWTH RATES OF GREEN ALGAE 12,'3
CONSTANTINE SOROKIN 4 AND ROBERT W. KRAUSS DEPARTMENT OF BOTANY-. UNIVERSITY OF MARYLAND, COLLEGE PARK, MARYLA,-ND

Aimong the environmental factors affectingf the growth rates of unicellular algae, light is frequently at an improper level. In many laboratory cultures used for physiological research the light intensity is too low to permit logarithmic growth. In nature the intensity is well above saturation and may be high enough to inhibit growth during much of the day. The intensities for saturation and inhibition depend on the suitability of other factors of the environment, e.g., temperature, CO2 level, and nutrient supply. In attempting to predict the performance of an alga under a given set of conditions it is necessary to know its potential under optimum conditions. Such information is basic to the evaluation of physiological studies and to the design and operation of culture apparatus. This paper describes the growth responses of five green algae to different light intensities under comp,arable environmental conditions. 1'IATERIAL AND METHODS The algae for these studies included: Chlorella pyrenoidosa from the collection of Dr. Van

Cited: 1. BRISTOL ROACH, B. M. On the influence of light and of glucose on the growth of a soil alga. Ann. Bot. 42: 317-345. 1928. 2. KOK, B. A critical consideration of the quantum yield of Chlorella-photosynthesis. Enzymologia 13: 1-56. 1948. 3. KOK, B. On the interrelation of respiration and photosynthesis in green plants. Biochim. Biophys. Acta 3: 625-631. 1949. 4. KOK, B. Photo-induced interactions in metabolism of green plant cells. Symposia Soc. Exp. Biol. 5: 211-221. 1951. 5. MYERS, J. Culture conditions and the development of the photosvnthetic mechanism. IV. Influence 7. 8. 9. 10. of light intensity on photosynthetic characteristics of Chlorella. Jour. Gen. Physiol. 29: 429-440. 1946. MYERS, J. Growth characteristics of algae in relation to the problems of mass culture. In: Algal Culture. From Laboratory to Pilot Plant. J. S. Burlew, ed. Pp. 37-54 Carnegie Instituition of Washington, Washington, D. C. 1953. MYERS, J. and CLARK, L. B. Cuilture conditions and the development of the photosynthetic mechanism. II. An apparatus for the continuous culture of Chlorella. Jour. Gen. Physiol. 28: 103-112. 1944. PHILLIPS, J. N., JR. The growth rate of Chlor ella pyrenoidosa as a function of intensity and intermittency of illumination. Ph.D. thesis. Univ. of Texas, Austin 1953. PHILLIPS, J. N., JR. and MYERs, J. Growth rate of Chlorella in flashing light. Plant Physiol. 29: 152-161. 1954. SOROKIN, C. and MYERS, J. A high-temperature strain of Chlorella. Science. 117: 330-331. 1953. THE OXYGEN AFFINITY OF A FLAVIN OXIDASE INVOLVED IN THE RESPIRATION OF STREPTOCOCCUS FAECALIS 1 2 DONALD J. NIEDERPRUEM AND DAVID P. HACKETT DEPARTMENT OF BioLOGy, THE UNIVERSITY OF BUFFALO, BUFFALO 14, NEW YORK The characterization of the oxidases involved in cell respiration has been based largely on experiments with enzyme inhibitors. In addition, it is possible to characterize an oxidase by its affinity for oxygen, which may be determined by measuring the oxygen consumption as a function of oxygen concentration. This information is especially valuable in those cases where the tissue respiration is insensitive to such classical inhibitors as cyanide and carbon monoxide (see 1, 4, 6). Although it has often been assumed that this " insensitive " respiration is mediated by oxidases which are flavoproteins, recent studies (15, 17) have shown that these same tissues may exhibit a high oxygen affinity, much greater than that exhibited by most isolated flavin oxidases (12). This poses the following question: are there some other flavin oxidases with a relatively high oxygen affinity which could account for this type of respiration? To answer this, a study was made with Streptococcus faecalis (B33A) whose respiration is known to be mediated by a flavoprotein oxidase (2, 3). The great advantage of this particular organism is that it does not contain any cytochromes (13), wlhich might complicate the interpretation of the restults. The culture methods employed were those described previously by Seeley and Vandemark (11). The cells were harvested in a centrifuge, resuspended in distilled water, and their respiratory rates deter1 Received October 7, 1957. 2This work was stupported in part by a grant from the National Science Foundation. mined, in the presence of glucose, by standard manometric techniques at 37.5° C (16). To test the effect of cyanide on respiration Robbie 's Ca(CN)2Ca(OH) 2 mixtures were added to the center well (10). Cell-free extracts were obtained by grinding freshly harvested cells with alumina (A-301, Alcoa) in phosphate buffer (0.05 M, pH 7). The slurry was centrifuged at 2,000 x G for 30 minutes in the cold and the supernatant fraction, referred to as the enzyme solution, was used in the spectrophotometric assays. The oxidation of reduced diphosphopyridine nucleotide (DPNH) was followed at 340 mu in a Beckmann DU spectrophotometer at room temperature, using cuvettes with a 1 cm light path. The effects of oxygen concentration were determined in vaccine-stoppered cuvettes which had been flushed 10 minutes with the appropriate gas mixtures. To obtain complete anaerobiosis, the special cell of Lazarow and Cooperstein was employed (8). Optical density units were converted to DPNH concentration by assuming a molecular extinction coefficient of 6.22 x 106 sq cm/mole (5). Protein was determined by the method of Stadtman et al (14). In preliminary experiments, the well known fact that the respiration of S. faecalis is not inhibitedl by cyanide (9, 11) was confirmed using 0.001NM HCN. Following this, the effect of oxygen concentration on the oxygen consumption of whole cells was determined manometrically. The respiratory rates in vessels gassed with 5, 20 and 100 % O2 showed only slight differences, whether the vessels were gassed initially or after a period in air. The rate in 5 % O, was not