Survival strategies of the mediophycean diatom ditylum brightwellii (T west) grunow

Abstract

This project is aimed at building on the less known life history strategies in Ditylum brightwellii, by focusing examination on the production and morphology of various cell types. Vegetative cell enlargement was induced by allowing cultures of cells to deplete their medium of nutrients and subsequently introducing nutrient replete medium. Enlargement was examined by light microscope, epifluorescence microscope with DAPI and PDMPO (2-(4-pyridyl)-5-((4-(2dimethylaminoethylaminocarbamoyl)methoxy)phenyl)oxalole) stain. Attempts at observation enlarged cells under the scanning electron microscope were unsuccessful due to fragility of enlarged valves. Vegetative cell enlargement was confirmed to occur as cells enlarged and their non-enlarged valves remained on the cell. D. brightwellii was observed to vegetatively enlarge their cells through two methods: one-step enlargement, and multi-step enlargement. During one-step enlargement, a single D. brightwellii cell will enlarge without producing supernumerary valves. Multi-step enlargement is the opposite, where D. brightwellii cells produce progressively larger supernumerary valves. Resting cells were observed to occur in all samples and were not induced through any experimental methods. Resting cells were observed to exit the valves (naked cells) and produce pseudopod-like structures. The pseudopod structures were observed to move freely on a microscope slide and could extent or retract. Resting spores were induced by inoculating D. brightwellii into a nitrogen depleted medium, also known as T medium. Resting spores were induced after 2 weeks of being inoculated in the nitrogen depleted medium. D. brightwellii cells plasmolysed in the T medium and remained plasmolysed until they became resting spores. The plasmolysed cells lost the colour within their chloroplasts and retracted to a portion of the cell.