The effect of nitrogen-deprivation on mating and reproduction of Chlamydomonas reinhardtii

Abstract

The importance of Chlamydomonas reinhardtii flagella in mating was studied in this experiment using wild-type, biflagellated populations of both mating types (Wt+ and Wt-) and mutant, nonflagellated populations (M-). All populations were grown without nitrogen for 48 hours in continuous light, to provide sufficient time and appropriate conditions for gametes to form. After 48 hours, four sample cultures were created. These included Wt+/Wt- and Wt+/M- combinations which would remain in a nitrogen-rich medium for the duration of the experiment, as well as Wt+/Wt- and Wt+/M- combinations which would remain in a nitrogen-free medium for an additional 120 hours before being re-suspended in regular medium. The cell abundance of each sample type was studied at 24 hour intervals for a total of 216 hours. It was hypothesized that the Wt+/Wt- cell abundance in the samples exposed to nitrogen deprivation would recover sooner than the cell abundance in the Wt+/M- samples which had also been exposed to nitrogen deprivation after returning to regular medium because functional flagella are required for successful protective zygote formation in nitrogen-deprived conditions. The cell abundance in the samples grown in regular medium during the entire experiment were used as a control, showing regular growth curves for each mating type population. It was observed that the Wt+/Wt- which had gone through nitrogen deprivation had significantly higher cell abundance at t=192 hours than the Wt+/M- mating pair in the same conditions (2.21 x 105 cells ± 1.34 x 104 cells/mL compared to 6.60 x 104 cells ± 1.63 x 104 cells/mL respectively). Based on these results, zygote formation was successful between Wt+/Wt- in the nitrogen-deprived conditions, due to functional flagella, and this aided in the continuation of reproduction upon return to a nitrogen rich environment.