PARENT SESSION
Posters P6C Photosynthesis, respiration and alternative electron sinks. Abstracts (660-680)

Characterization and expression of potato triosephosphate isomerase isoforms. Sonia Dorion¹, Parveen¹, Julie Jeukens¹, Jean Rivoal^*,1, ¹ IRBV, Montréal, QC, Canada

ABSTRACT- Triose phosphate isomerase (TPI) catalyzes the interconversion of dihydroxyacetone phosphate and glyceraldehyde 3 phosphate. Cytosolic and plastidic isoforms (respectively cTPI and pTPI) exist in plants. These two isoforms were separated and partially purified from potato leaves using a combination of chromatographic steps. Substrate saturation kinetics and regulatory properties were determined for both isoforms. A polyclonal immuneserum was raised against potato cTPI. This serum recognizes a single 27 kDa polypeptide in crude potato extracts and does not recognize TPI activity present in Percoll-purified potato chloroplasts, indicating that it is highly specific for cTPI. We surveyed the distribution of cTPI and pTPI in potato plants using a combination of analytical chromatography on DEAE fractogel and western blot analysis. We found that (i) the amount of extractable TPI activity is developmentally regulated in potato leaves, with high levels of activity associated with periods of growth; (ii) photosynthetic and non-photosynthetic tissues express both isoforms; (iii) cTPI always represents the bulk of extractable TPI activity and (iv) in leaf tissues highest levels of cTPI are present in expanding leaves whereas the highest pTPI levels are found in mature leaves. The results are consistent with the hypothesis that TPI isoform expression is developmentally regulated. pTPI is more prominent in mature leaves where it is involved in the Calvin cycle. cTPI is more abundant in growing tissues, where glycolysis and respiration fulfill a key function in production of energy and C skeletons for biosynthetic purposes.

KEY WORDS: glycolysis, Triose phosphate isomerase, enzyme expression, potato