Date of Award

1-1-2004

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Natural Sciences

Faculty

Faculty of Computing, Health and Science

First Advisor

Dr Ian Bennett

Second Advisor

Professor Paul Lavery

Abstract

The development of a successful protocol for micropropagating seagrass provides a valuable tool for seagrass-restoration programs and a facility to study their biology (especially their physiology). This work reports on some of the culture requirements of some seagrasses that are commonly found in Western Australia: Posidonia coriacea, P. sinuosa, P. australis and Halophila ovalis. The protocol developed for H. ovalis allows very rapid multiplication and sustainable growth of cultures while the protocol developed for Posidonia requires further development. The culture of Posidonia cariacea proved to be problematic however experimental media that provided insights into its culture conditions. The carbohydrate source was the most important medium component as it affected the development of roots and leaves. The presence of sucrose in the culture media enhanced leaf growth (especially glucose) but decreased the proportion of white roots. More fresh weight, roots, leaves and the proportion of white roots were observed in Posidonia when they were grown in glucose-based media than in mannitol-based media. When mannitol was present in the media, the proportion of white roots was high, which could be attributed to its osmotic effects. Similar responses to sucrose, glucose and mannitol were also observed for P. australis and P. sinuosa. Halophila ovalis was able to grow rapidly on most experimental media. Growth was enhanced by the presence of sucrose in the media and was essential for rapid and sustained growth. Other media components altered the growth of this species, in particular levels of nitrogen (most importantly NH4) influenced root growth and morphology. When H. ovalis is grown in media in moderate or high levels of NH4, root length was significantly reduced and root hair was limited. When NH4 was omitted from the medium, roots were significantly longer and root hairs were prolific. Posidonia coriacea and Halophila ovalis have different growth strategies under natural conditions. H. ovalis is an early succession species that grows rapidly and responds to increased nutrients. P. coriacea is slower growing, colonises later and is Jess responsive to environmental changes than H. ovalis. While the growth responses observed for P. coriacea were significant (in some cases), the differences between means were considerably smaller when compared with H. ovalis. This may be due to the different growth strategies of these species or a lack of fundamental requirement in the conditions under which P. coriacea was grown. Much of what is reported in this thesis for Posidonia will need repeating if the reasons for these differences are identified in the future. In summary, in this thesis I have demonstrated that in vitro propagation of these seagrass species is possible, It is necessary for species-specific protocols to be developed which take into consideration the growth strategies employed by each species. This is particularly significant as many researchers attempt to draw comparisons between species and protocols. The protocols developed in this research increase the knowledge of the biology of these seagrasses and can be incorporated into transplantation protocols in the future.

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