Molecular and cellular investigations of photosynthesis driven carbon fixation in the seagrass Zostera muelleri

University of Technology Sydney. Faculty of Science.Seagrasses are marine foundation species that have evolved to live in shallow coastal waters, an environment regularly subjected to changes through tidal patterns and anthropogenic activity. Global seagrass coverage is declining worldwide, mainly driven by decreasing water quality due to anthropogenic activity. Therefore, there is an urgent need to better understand seagrass biology, particularly the way their growth will be impacted by changing environments in order to assist their preservation. Through the use of emerging techniques such as gene expression analyses, the underlying mechanism driving photosynthesis can now be explored at the molecular level and is an emerging field in seagrass research. The overarching aim of my thesis was to identify the molecular mechanisms driving carbon metabolism in the seagrass . To accomplish this aim, a combination of physiological and molecular analytical tools were used to measure changes in photosynthesis in response to decreased O₂ concentrations in the water column, decreased irradiance and chemical inhibition of carbonic anhydrase (CA). The results presented in this thesis describe the ways in which genes associated with carbon metabolism were regulated in response to the different environmental factors as listed above. Specifically, we found that in low O₂ conditions, photosynthetic efficiency was enhanced while genes involved in the photorespiratory and recycling of TCA cycle intermediates were down-regulated. In addition, we found that under reduced irradiance conditions, ¹³C uptake was reduced and this correlated with a down-regulation of genes involved in photosynthetic, photorespiratory and recycling of TCA cycle intermediates pathways. Finally, when exposed to inhibition of CA, . plants displayed a decrease in photosynthetic rate concomitant with up-regulation of photosynthetic and photorespiratory genes, suggesting the presence of a compensatory mechanism in this seagrass specie in order to overcome CA inhibition. In view of these results, we provide further details to the carbon metabolism pathways in . and presents new techniques in molecular analysis that can be applied to different areas of seagrass research