[Induction and reversibility of surface events by deprivation and refeeding with vitamin B12 in euglena gracilis]

Cortical structure and function in euglenoids with reference to trypanosomes, ciliates, and dinoflagellates

The membrane skeletal complex (cortex) of euglenoids generates and maintains cell form. In this review we summarize structural, biochemical, physiological, and molecular studies on the euglenoid membrane skeleton, focusing specifically on four principal components: the plasma membrane, a submembrane layer (epiplasm), cisternae of the endoplasmic reticulum, and microtubules. The data from euglenoids are compared with findings from representative organisms of three other protist groups: the trypanosomes, ciliates, and dinoflagellates. Although there are significant differences in cell form and phylogenetic affinities among these groups, there are also many similarities in the organization and possibly the function of their cortical components. For example, an epiplasmic (membrane skeletal) layer is widely used for adding strength and rigidity to the cell surface. The ER/alveolus/amphiesmal vesicle may function in calcium storage and regulation, and in mediating assembly of surface plates. GPI-linked variable surface antigens are characteristic of both ciliates and the unrelated trypanosomatids. Microtubules are ubiquitous, and cortices in trypanosomes may relay exclusively on microtubules and microtubule-associated proteins for maintaining cell form. Also, in agreement with previous suggestions, there is an apparent preservation of many cortical structures during cell duplication. In three of the four groups there is convincing evidence that part or all of the parental cortex persists during cytokinesis, thereby producing mosaics or chimeras consisting of both inherited and newly synthesized cortical components.

DNA flow cytometry of control Euglena and cell cycle blockade of vitamin B12-starved cells

Vitamin B12 starvation in Euglena induces a cell cycle arrest that leads to unbalanced growth. Microfluorometry and flow cytometry analyses of cellular DNA fluorescence after Hoechst 33258 staining were performed on control and vitamin B12-deficient cells. Convergent results are obtained with both methods. Histograms that represent arrested cells are unimodal, with a mode channel value nearly twice that of the G1 control cell peak. Dispersion of fluorescence values is great, and values from 2C and over 4C are observed and discussed. It appears that vitamin B12 starvation in Euglena leads to defective DNA synthesis. Blocked cells have different DNA content, corresponding to blockade of DNA replication during the S phase. A second block prevents the onset of mitosis even for 4C cells.

Synchronization of division in vitamin B12-starved Euglena gracilis

Vitamin B12 deficiency arrests cell division in Euglena gracilis. B12 starvation for short periods made it possible to induce synchronous growth by addition of the vitamin. Culture conditions were established to optimize replenishment synchrony. The DNA content of E. gracilis in steady state culture and vitamin B12 deficiency culture was measured by flow cytofluorometry and was consistent with colorimetric determinations. The cell volume and DNA distributions of E. gracilis in synchronous culture were analyzed and the sequential changes during the division cycle were computed. Synchronous culture permits more definitive studies of shifts in cell volume and DNA distributions, in which the biochemical events required for cell division are presumably synchronized.