ARS | Publication request: METABOLITE ANALYSES OF A DOUBLE MUTANT OF SUCROSE SYNTHASE (SUSY) GENES IN A DEVELOPING ENDOSPERM

Submitted to: Maize Genetics Conference Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: March 11, 1999
Publication Date: N/A

Technical Abstract: The enzyme SuSy plays a major role in energy metabolism by catalyzing the reversible conversion of sucrose and UDP to UDP-Glc and fructose. Both biochemical and genetic data suggest that in vivo role of the SuSy reaction is the production of UDP-Glc, a precursor and a substrate for starch and cellulose biosynthesis, respectively. In maize, Sh1 and Sus1, loci encode two isozymes of this enzyme. Developing endosperm, 21 DAP, of the double mutant, sh1sus1-1, exhibits ~ 0.5% of the total activity as compared to the Sh1Sus1 genotype (Chourey et al., 1998, MGG 25988-96). This mutant provides a unique opportunity to study carbon assimilation in developing maize endosperms. To do this, we quantified the levels of several key metabolites in the sh1sus1-1 endosperm, at various developmental stages, relative to Sh1Sus1, Sh1sus1-1, and sh1Sus1 genotypes. The double mutant was found to have reduced levels of UDP-Glc at all developmental stages, but the reduction was not proportional to the reduction in sucrose synthas activity. Interestingly, we observed that the level of ATP in the double mutant showed a greater reduction than the level of UDP-Glc when comparing the double mutant to other genotypes. These results suggest that in the absence of sucrose synthase activity, an alternative pathway can be used to produce UDP-Glc, but this alternative pathway requires more energy that the standard sucrose synthase pathway.