PhD defense Niels Christian Holm Sanden
You are all invited for the PhD defense of Niels Christian Holm Sanden.
The title of his PhD thesis is: Systemic infrastructure in plants From sieve elements to seed filling
Summary:
We encounter plants every day and almost any small piece of land on the globe will have its own distinct flora. Flowering plants conquered terrestrial ecological niches with tremendous success and today account for the vast majority of plant biomass and species richness. Several evolutionary inventions make flowering plants special - in my thesis, I investigated topics related to two important features: The vascular tissue and the seed.
The vasculature allow plants to transport water and solutes between organs. Dead cell remains in the xylem bring water from the roots to the leaves, whereas a living tissue, the phloem, translocates sugars from sources leaves to sink tissues such as roots and fruits. In the phloem, a special cell type - the sieve element - loses most of its cellular contents upon maturation and becomes a "hollow" tube that facilitates sap flow. Mature sieve elements lack the means to make their own proteins, which makes the protein machinery inside them an interesting population.
In my thesis, I reviewed the literature of known sieve element proteins and generated a list of new putative sieve element genes. I selected seven of these genes and showed that indeed, their protein products localize in mature sieve elements.
Although sugars are the main transported solutes in the phloem, several other classes of molecules enter the translocation stream to move from source leaves to sink tissues. I investigated a special case of this: The transport of glucosinolates in Arabidopsis from source tissues to the seed. Glucosinolates are specialized metabolites found in the Brassicales order, which act as defense compounds. Seeds are full of glucosinolates (responsible for e.g. the sharp taste of mustard seeds) but cannot synthesize them on their own and instead depend on maternal supply, which requires transporter proteins.
I contributed to the characterization of a newly discovered glucosinolate exporter and investigated at the cell-type level, where this exporter and well-characterized importers must be present to achieve seed loading of glucosinolates.
Principal supervisors:
Professor Alexander Schulz, Section for Transport Biology
Professor Barbara Ann Halkier Section for Molecular Plant Biology,
Assessment committee:
Chairperson: Professor Anja Thoe Fuglsang, Section for Transport Biology
Professor Yrjö Helariutta Viikki Plant Science Centre, University of Helsinki, Finland
Professor Mark Belmonte Dept. of Biological Sciences, University of Manitoba, Canada