Characterization of the cell cycle in synchronous cultures of Chlamydomonas eugametos in relation to gametogenesis

Abstract

The cell cycle of Chlamydomonas eugmetos was synchronized at low cell densities by growing cells under conditions of alternating light and dark periods. Synchronization of the cell cycle was demonstrated by determining cell size, cytokinesis, and release of daughter cells. The microscopic data were in agreement with the accumulation patterns of mRNAs for ribulose bisphosphate carboxylase/oxygenase small subunit, histone H4 and P-tubulin. Cells of C. eugametos secrete a sticky material which enables cells to adhere to a solid substrate during cell division. The secretion of this material was also cell-cycle-regulated and preceded cytokinesis. Recently, it was reported that in synchronous exponential-phase cultures of high cell densities, young daughter cells temporarily behave like gametes during the cell cycle. However, under our growth conditions this was not observed. First, daughter cells did not agglutinate with normal gametes of the opposite mating type. Second, extraction of growing cells did not release any agglutinin activity as measured both by an in uitro agglutination assay and by an agglutinin-specific monoclonal antibody. We conclude therefore that gametogenesis in C. eugametos is not necessarily a normal phase of the cell cycle.

The importance of light and photoperiod in sexual reproduction and geographical distribution in the green snow alga,Chloromonas sp.-D (Chlorophyceae, Volvocales)

“…In Chlamydomonas and Chloromonas, pre-gamete immaturity is associated with the dark and gamete maturity is accomplished during the light (Hoham, 1975;Von Gromoff and Beck, 1993;Hoham et al, 1998). In the cell division cycle of Chlamydomonas, cells divide only during the dark period and daughter cells are released from the cell packs at the end of the dark period (Molendijk et al, 1992). Chloromonas sp.-D does not appear to have a similar dependence on a dark cycle, and so it could reproduce optimally at sites with a 24 : 0 photoperiod such as in Svalbard.…”

Domain conservation in several volvocalean cell wall proteins

“…eugametos cells were routinely grown on agar plates containing M 1 medium [ 31 ] at 20 ° C in a 12 h light/12 h dark regime; synchronous cultures were obtained by growing cells in liquid M 1 medium as described [30]. Gametes were obtained by flooding 2-to 4-week-old agar-plate cultures with sterile deionized water, and zygotes were produced by mixing gametes of UTEX 9 and UTEX 10 in glass Petri plates at the start of a light period; the plates were kept in continuous light for 24 h and then put in the dark.…”

“…Total RNA from different stages of the C. eugametos life cycle was isolated as described in Molendijk et al [30], and poly(A) + RNA was isolated by two passes over an oligo-dT cellulose column (Pharmacia) as detailed in Jacobsen [22]. Poly(A) + RNA (1.5/~g) or total RNA (10 #g) was translated in vitro in 50 #I reactions of a rabbit reticulocyte lysate system (Promega) with 35 Smethionine (Amersham).…”

“…These stages were: (a) young vegetative cells, harvested at the end of the dark period, when they were escaping from the mother cell wall and producing their own walls [ 30]; (b) young gametes of both mating types that were agglutinating in the presence of 5 mM cysteine (which prevents fusion and zygote formation [41]); and (c) 22-h-old zygotes, in which the gametic wall had been completely replaced by a zygotic wall [32,49]. In Fig.…”