Centre for Plant & Water Science - Central Queensland University

Centre for Plant & Water Science 2008 Annual Report
AUTOECOLOGICAL ROLE OF STEVIOL GLYCOSIDES IN Stevia
rebaudiana
SUMMARY
The physiological role of steviol glycosides (SG) in S. rebaudiana was explored by
monitoring change in SG content in response to environmental conditions. Roles explored
are carbohydrate reserve and osmoregulator. SG leaf content was determined through
HPLC analysis of leaf extracts. Future investigation will test SG as an insect-deterrent
compound. Near Infrared (NIR) spectroscopy will also be explored for non-invasive analysis
of SG in stevia leaves.
SG as an energy reserve
Changes in SG leaf in response to relative to light and CO 2 were monitored to test the
hypothesis that SGs function as an energy store in S. rebaudiana. Thirty plants were evenly
distributed to different photosynthetic conditions (control 14 h light/10 h dark cycle,
constant light, or constant dark). Two sets of five plants were maintained at either 500 or
1400 ppm CO 2 under a 14 h light/10 h dark cycle. Plants in both experiments were initially
acclimatized in a single growth cabinet at 25 o C and 65% relative humidity for one week
prior to treatment. Starch leaf content was observed to increase with increasing light
exposure whereas SG leaf content remained constant. The same behaviour was observed in
the CO 2 experiment wherein plants at 1400 ppm CO 2 had an overall (5%) increase in starch
leaf content over 4 days while SG content remained constant. Results from both experiments
indicate that SG is not used as an energy store.
Control
Light
Dark
[Left Figure.] Starch leaf content of control, constant light and constant dark group in the light experiment
[Right Figure.] % leaf DW of stevioside and rebaudioside A of control, constant light and constant dark group in the
light experiment
SG as an osmoregulator
Changes in SG leaf content were monitored under water stress conditions to test the
hypothesis that SGs can function as osmoregulatory compounds. Fifteen plants were evenly
distributed into three groups with the control group receiving 500 mL of water daily, the
mild water stress group receiving 150 mL of water daily and the severe water stress group
remaining unwatered until the end of the treatment period. Leaf osmotic potential was found
to increase with increasing water stress whereas SG leaf content remained constant
indicating that SG is not used as a leaf osmoregulator in S. rebaudiana.
PROJECT STAFF Principal Investigator:
Co-Principal Investigator:
Ria Reyes / Kerry Walsh
David Midmore
FUNDING International Postgraduate Research Scholarship (IPRS)
INCOME $2,000
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