Thesis

Examining morphological and physiological changes in Zygnema irregulare during a desiccation and recovery period

The Mediterranean climate in southern California results in the existence of temporary streams which present challenges to fresh-water algae since they must persist through long, dry summers to regrow once water returns. This study focused on a green-algal species, Zygnema irregulare, in an attempt to better understand the methods by which it tolerates desiccation and recovers once conditions are favorable. Z. irregulare was desiccated for two-months and then provided with full moisture for another month under laboratory conditions to observe any morphological and physiological changes. By the end of desiccation, there was a significant increase in the proportions of pre-akinete and akinete cells, 56% and 19% of the filaments respectively. Increases in the thickness of cell wall and pectin layers were also observed, with a 220% increase in the secondary cell wall and an increase of 470% for thae secondary pectin layer. The decreases in the proportions of pre-akinete and akinetes and the thickness of the cell wall and pectin layers after moisture was reintroduced suggests this change is triggered in part by desiccation. During desiccation, an increase of 34% in moisture content within Z. irregulare filaments was observed, supporting the theory that pectin layers trap in moisture to potentially slow desiccation in Zygnema species until mature akinetes are formed. Germination of akinetes and recovery of pre-akinetes was observed to occur within 7-14 days. Intracellular modification combined with structural changes which may delay the rate of moisture loss provides Z. irregulare with the ability to survive and reproduce after desiccation.

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