REGULATION OF GROWTH PROCESSES DURING THE CELL CYCLE OF THE CHLOROCOCCAL ALGA SCENEDESMUS QUADRICAUDA UNDER A DNA REPLICATION BLOCK

Abstract

The kinetics of two growth parameters (total RNA and total protein accumulation) was followed in synchronized cultures of the chlorococcal alga Scenedesmus quadricauda (Turp.) Bréb. under conditions of inhibited DNA replication in the presence of 5‐fluorodeoxyuridine (25 mg.L‐1). In the control culture, growth processes occurred in several steps with a decreasing rate of accumulation of RNA and protein amount approximately at each doubled value of the preceding step. Oscillations in the rate of growth processes in the control culture were temporally related to the initiation of individual reproductive steps. At each doubling, the cell became committed to triggering a sequence of reproductive processes, starting with DNA replication and ending with protoplast fission. Three commitment points were attained in the control culture and, consequently, three replication rounds of DNA followed by three nuclear divisions and three protoplast fissions occurred during one cell cycle. If 5‐fluorodeoxyuridine (FdUrd) was added at the beginning of the cell cycle, no reproductive processes occurred, and the cells remained uninuclear with one genome and did not divide. RNA accumulation did not seem to be affected by the presence of FdUrd for at least one cell cycle, and three or four doublings in the amount of RNA occurred during this period. Protein accumulation was even more independent of reproductive processes in the cell and continued for a period of about two or three cell cycles, attaining six doublings at the end of this period. Therefore, oscillations in the rate of protein or RNA accumulation remained even if reproductive processes were inhibited.

Response of the Green Alga Chlamydomonas reinhardtii to the DNA Damaging Agent Zeocin

“…Total nucleic acids were extracted according to Wanka [33], as modified by Decallonne and Weyns [34]. The DNA assay was carried out as described by Decallonne and Weyns [35], with the modifications of Zachleder [36] (see also [37]).…”

Accumulation of energy reserves in algae: From cell cycles to biotechnological applications

“…Specific inhibition of nuclear DNA synthesis by fluorodeoxyuridine (FdUrd) was used to study the regulation of cell cycle events and starch reserve synthesis in the chlorococcal alga Scenedesmus quadricauda (Zachleder, 1994;Zachleder, 1995). FdUrd inhibits the enzyme thymidylate synthase, which catalyzes the reductive methylation of 2′-deoxyuridylate to form deoxythymidylate (Bachmann et al, 1983;Cisneros et al, 1993;Follmann, 1983).…”

DNA Damage during G2 Phase Does Not Affect Cell Cycle Progression of the Green Alga Scenedesmus quadricauda

“…Total nucleic acids were extracted according to Wanka [79] , as modified by Decallonne and Weyns [80] . The DNA assay was carried out as described by Decallonne and Weyns [81] , with the modifications of Zachleder [82] (see also [83] ). Statistical comparison of the data was done by the unpaired Student's t-test between untreated and analyzed samples.…”