2007 Annual Report - Central Queensland University

2007 Centre for Plant & Water Science Annual Reportdays to observe possible diurnal trend in levels of stevioside and rebaudioside A. As acarbohydrate reserve, stevioside and rebaudioside A content was expected to decline at dawnand increase at dusk. Gathered data did not display this trend. Future experiments will includesucrose and starch analysis to verify carbohydrate level in the leaf during leaf sampling. Also,number of plants per treatment will be increased.Osmoregulator functionality of steviol glycosides was tested in two plants subjected to waterstressor regular irrigation. Treatments were maintained for 6 days and leaves were sampledfrom the middle section of the stem (n=5) for stevioside and rebaudioside A analysis. SG levelswere expected to increase with water stress to maintain osmotic balance within the plant.Increase in stevioside and rebaudioside A content of the leaves was not observed within theshort duration of the treatment. The abrupt water stress made it impossible to test healthy leavesbeyond the 6-day treatment. It is possible that change in SG levels will be more evident inmilder water stress conditions. Mild and high water stress conditions will be incorporated infuture experiments.Steviol glycoside level variability within a plant and between plantsSG levels in top young, middle mature, bottom mature and senescent leaves of a single S.rebaudiana plant was investigated. Top young leaves had the highest SG level (% leaf DW)followed by the middle mature and bottom mature leaves. Senescent leaves had the least SGand results were in accordance to the literature (Bondarev, Sukhanova et al. 2003). Results frominitial investigation will be verified with a larger plant survey.SG levels across a number of available S. rebaudiana plants were also determined. Plants withhigh stevioside (13% DW) and high rebaudioside (7% DW) content were identified and seedswill be collected for future germination experiments.PROJECT STAFF Principal Investigators:Co-supervisors:Ria Adelle Reyes/Kerry WalshDavid MidmoreFUNDINGCentral Queensland University(International Postgraduate Research Scholarship)46