Sucrose-phosphate synthase from etiolated rice seedlings

PAGNUSSAT GABRIELA; CURATTI LEONARDO; SALERNO GRACIELA

Vancouver, Canada

Congreso; Annual Meeting of the American Society of Plant Physiologysts; 1997

American Society of Plant Physiologysts

Sucrose-phosphate synthase (SPS) catalyzes the formation of sucrose-P from UDP-Glc and fructose-6P and plays a key role in sucrose synthesis. Its activity is allosterically modulated by Glc-6P (activator) and Pi (inhibitor), and covalent modification in response to light. The aim of this work was to study SPS regulation properties and expression patterns in etiolated rice seedlings and embryos to be compared to those found in leaves. SPS was assay by measuring either sucrose-P or UDP. SPS was partially purified by DEAE-Sephacell chromatography and gel filtration. Polyclonal antibodies were rose against SPS 116 kDa polypeptide. A homologous probe was synthesized from the published rice SPS sequence. Two SPS activities (SPS-1 and SPS-2) were separated inn DEAE-Sephacell chromatography from etiolated rice seedlings. SPS-1 eluted at the same salt concentration as the enzyme from green leaves. SPS-2 could not be detected in the elution profile of green leaves but was present in embryos. SPS-1 has similar response to effectors than SPS from green leaves harvested in the darkness. SPS-2 was poorly inhibited by Pi and highly activated by Glc-6P. These results suggest that SPS-1 could be related to the enzyme present in photosynthetic tissues while SPS-2 could be similar to the form expressed in embryos. Immuno- and mRNA “in situ” localization were performed in photosynthetic and non-photosynthetic tissues. Results show a differential location of SPS, suggesting distinct SPS functions: possibly sucrose resynthesis in etiolated and young tissues and sucrose synthesis from assimilated carbon in mature green leaves. These data support the existence of more than one enzyme form.