Title: Are Freeze-induced Changes in the Phosphorylation State of Pheophorbide a Oxygenase Responsible for the Canola Green Seed Problem? Authors
|Hall, Pamela -|
|Grennan, Aleel -|
Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2010
Publication Date: June 1, 2010
Citation: Hall, P.K., Ort, D.R., Grennan, A.K. 2010. Are Freeze-induced Changes in the Phosphorylation State of Pheophorbide a Oxygenase Responsible for the Canola Green Seed Problem? American Society of Plant Biologists Annual Meeting. Available: http://abstracts.aspb.org/pb2010/public/P08/P08054.html. Technical Abstract: As canola (Brassica napus) seeds develop, the photosynthetic apparatus in the seed embryo is systematically degraded to produce mature seeds containing undetectable amounts of chlorophyll. This natural degradation process can be interrupted, however, by exposure of the plant to freezing temperatures early during development. Such an event results in higher chlorophyll content in the canola seeds at maturity, which largely devalues the oil as removal of photoactive chlorophyll is required. Freezing temperatures inhibit activation of pheophorbide a oxygenase (PaO), a major enzyme responsible for catabolizing chlorophyll into colorless compounds. Previous studies have shown that this enzyme's activity is likely inhibited at the post-translational level, as dephosphorylation of PaO appears to be correlated with an increase in activity. This study aims to explore the control mechanism of PaO activity, specifically by investigating the effects of protein phosphorylation of PaO. Using site-directed mutagenesis at putative reversible phosphorylation sites on the Arabidopsis thaliana PaO gene, we are imitating phosphorylation and dephosphorylation and measuring enzyme activity in these mutants. We hypothesize that activity will be hindered in those mimicking phosphorylation and induced in those mimicking dephosphorylation. These observations would support a role of phosphorylation in the suppression of PaO activity under freezing conditions.