Page 240 - PC2019 Program & Proceedings

PLANT CANADA 2019

P53. Investigating high acetate as a regulator of senescence in Chlamydomonas reinhardtii
*1
Lee, C. ; D. Durnford 2
1 University of New Brunswick
2 UNB

While microalgae are typically immortal, cells approaching stationary phase when grown in batch culture
initiate senescence that can lead to cell death. How microalgae proceed through senescence and their
longevity in stationary phase depends on a number of factors. We tested the contribution of heterotrophic
nutrition and light levels on longevity in stationary phase cultures of Chlamydomonas reinhardtii. We
determined that cellular senescence is accelerated under high-acetate (30mM) compared to low-acetate
(10mM) conditions. Interestingly, this high-acetate acceleration of senescence can be rescued by reducing
light intensity, but so did increasing light intensity to moderate levels. Longevity of cells under different
light intensities and acetate conditions was inversely related to starch accumulation. To explore this
relationship, we examined stationary phase longevity in Chlamydomonas mutants with different
capacities for starch accumulation. We found that decreased starch biosynthesis is correlated with a
greater longevity of cultures in stationary phase. From these results, there is an unanticipated relationship
between longevity and the use of starch reserves. Furthermore, the protective effects of low and high light
illustrate the complexity of carbon metabolism in mixotrophic organisms. Our findings contribute to the
understanding of how microalgal carbon reserves affect survival under growth-limiting conditions in
response to carbon and light availability.

Christopher Lee (Clee5@unb.ca)

P54. Establishing a link between flavonol catabolism and auxin-mediated stem growth
Roepke, J.; G. Bozzo
University of Guelph

Flavonols occur as glycosides in plants. In Arabidopsis, flavonol bisglycosides accumulate in response to
high light intensity, nitrogen deficiency and low temperature. Moreover, the flavonol bisglycoside
kaempferol 3-O-α-rhamnoside-7-O-α-rhamnoside restricts stem elongation by inhibiting the basipetal
movement of endogenous auxin (i.e., indole-3-acetic acid). Our lab has demonstrated that the catabolism
of flavonol 3-O-β-glucoside-7-O-α-rhamnosides in Arabidopsis shoots requires hydrolysis by the β-
glucosidase BGLU15; all other flavonol bisglycosides (e.g., kaempferol 3-O-α-rhamnoside-7-O-α-
rhamnoside) are not degraded in BGLU15 knockout mutants (bglu15). Here, we investigated whether
indole-3-acetic acid levels and stem growth are altered in bglu15 plants. Initiation of the primary
inflorescence stem was delayed, stem length was decreased, and flavonol 3-O-β-glucoside-7-O-α-
rhamnoside levels were up to 10% greater in the apical region of bglu15 stems, compared to wild-type
plants, but not in the middle and basal longitudinal regions of the stem. The levels of other flavonol
bisglycosides were not altered by the bglu15 mutation, regardless of the longitudinal stem region. Also,
the levels of indole-3-acetic acid were as much as 28% greater in the apical region of bglu15 stems
relative to those of wild-type plants. These results suggest that flavonol 3-O-β-glucoside-7-O-α-
rhamnoside accumulation in the stem apex modulates auxin distribution in the primary inflorescence
stem. Future research will investigate whether polar auxin transport is reduced and whole plant
morphology is altered in bglu15 mutants.

Gale G. Bozzo (gbozzo@uoguelph.ca)

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