Phosphoenolpyruvate carboxylase (PEPC) was examined during cold acclimation of seedlings of the freezing-tolerant cultivar (Medicago sativa ssp falcata cv Anik) and the relatively freezing-sensitive cultivar (Medicago sativa cv Trek) of alfalfa. With four days of cold acclimation, PEPC activity increased to 3.5-fold and 2-fold the control levels in Anik and Trek, respectively. This was associated with an increase in the level of a 110 kD PEPC protein and a decrease in the amount of a 120 kD PEPC polypeptide in both cultivars. The role of reversible phosphorylation in regulating PEPC activity was demonstrated by in vitro phosphorylation and dephosphorylation, which caused partial activation and deactivation of PEPC, respectively. In vivo phosphorylation experiments revealed that the 110 kD PEPC subunit is phosphorylated on serine residue(s) during cold acclimation in Anik but not in Trek. Increased PEPC activity could account for the 70% increase in the non-autotrophic or dark fixation of carbon observed in cold acclimated Anik seedlings. A possible role for dark carbon fixation in the cold-induced development of freezing tolerance is through the production of NADPH. Such a source of reducing power may be required for the repair of cold-induced damage and restoration of normal cellular functions.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.27318 |
| Date | January 1996 |
| Creators | Frank, Scott, 1971- |
| Contributors | Dhindsa, Rajinder (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Biology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001572078, proquestno: MQ29693, Theses scanned by UMI/ProQuest. |
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