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Articles

Gametogenesis in Chlamydomonas eugametos

I. Light Requirements ^1,2

^a Department of Botany, University of Maryland, College Park, Maryland 20742

Male and female mating types of Chlamydomonas eugametos Moewus show an absolute light requirement for gametogenesis. Increasing light intensity from 0.3 to 1.2 mw cm^–2 during nitrogen starvation (a precondition for gametogenesis) caused an increase in gametogenesis throughout a 28-hour period. Gametogenesis was measured by determining the percentage of paired cells after a 1-hour mixing period. Light requirements for the male and female differed. There was a 9-hour lag period in gametogenesis in the male, but no lag in the female. Gametogenesis was reduced 50% in the female and 90% in the male when 6.0 µM 3-(3,4-dichlorophenyl)-1, 1-dimethyl-urea was in the N-starvation medium. Sodium acetate, 1.8 mM, in the N-starvation medium increased gametogenesis in both mating types and eliminated the 9-hour lag in the male for cells irradiated for 3, 6, 9, 12, 15, 18, or 23 hours during the last part of a 23-hour N-starvation period. Sodium acetate concentrations higher than 1.8 mM inhibited the mating process. 3-(3,4-Dichlorophenyl)-1, 1-dimethylurea inhibition of gametogenesis was decreased in the male but increased in the female, when sodium acetate was added to the N-starvation medium. These results indicate a nonphotosynthetic as well as a photosynthetic role for light in the gametogenesis of both mating types. Also, the male will not undergo gametogenesis unless a required amount of energy is provided either in the medium or through photosynthesis.

⁴ This article is dedicated to the memory of my father, Jack Lorch.

¹ This investigation was supported in part by the Maryland Agriculture Experiment Station Project K-11.

² Scientific Article No. A-1785, Contribution No. 4576.