SUMMARY. A preliminary survey of the influence of a number of antihistamines on growth of several protozoa indicated that not only growth but also pigment formation in green forms was inhibited. Subsequently, it was demonstrated that molar concentrations of the drugs of less than 1 times 10−3 caused chlorosis of cultures of Euglena gracilis var. bacillaris, Chlamydomonas pseudococcum, and Chlorella vulgaris.With the aid of one of the antihistamines, Pyribenzamine (CIBA), a permanently colorless culture of Euglena was obtained. This culture has been maintained in the chlorotic state in antihistamine‐free medium through eighteen serial transfers in constant light. Comparative spectro‐photometric studies were made of the pigments extracted from this new euglenid strain with those from normal green, dark‐grown and streptomycin‐bleached euglenas. Although the dark‐etiolated forms retained small amounts of chlorophylls, neither of the drug‐bleached cultures showed evidence of these pigments. Quantitatively, the carotenoid picture in dark‐bleached and streptomycin‐grown organisms was similar, but these pigments were greatly reduced in the Pyribenzamine‐treated strain. Further studies on the identity of the carotenoids in the new euglenid are in progress.
Mass cultures of Chlamydomonas moewusii have been synchronized by means of light-dark shifts. Division of at least 91 percent of the population was made to occur in 1/24 of the life cycle of the cells. The advantages of working with synchronized cultures of obligate autotrophs are discussed.
SYNOPSIS. Cultures of Chlamydomonas moewusii begun with log‐phase cells of any age had the same lag phases and showed slight but demonstrable synchronous division. Those begun with stationary‐phase cells had longer lag phases and showed pronounced synchronously reproductive tendencies. Cultures grown under favorable or unfavorable conditions, and their log‐phase cells compared, behaved like log‐ and stationary‐phase cells respectively. Both stationary phase and unfavorably grown cultures shared some of the characteristics of cultures synchronized by light‐dark cycling. A light‐dark cycled population divides synchronously in direct response to the cycle, and not as a result of being transferred from one medium to another. Synchronous division will occur as 8‐fold increases with initial cell densities as low as 10 cells/ml and as high as 100,000 cells/ml. Initial concentrations above 100,000/ml will result in synchronous bursts of less than 8 times the cell number. Cycled cells will continue to divide synchronously when exposed to continuous illumination for an additional 24 hr (i.e., 1 entire “cycle” period). After 12 more hr, they divide exponentially. Continuously illuminated young log cells when subjected to a light‐dark regimen begin growing and dividing synchronously by the end of the 1st 12‐hr dark period (i.e., during the 2nd 24‐hr cycle). The synchronized cell cycle is described cytologkally and quantitatively, and the degree of synchrony for each of the phases of the cell cycle analyzed. After comparing the data from the synchronously and randomly growing cultures, an hypothesis is suggested to explain exponential and synchronous growth and division.
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