Regulation of Sucrose Synthase Expression in Chenopodium rubrum: Characterization of Sugar Induced Expression in Photoautotrophic Suspension Cultures and Sink Tissue Specific Expression in Plants

Abstract

Summary The effect of source/sink modifications on the enzyme activity and on the steady state level of mRNA of sucrose synthase has been analyzed in Chenopodium rubrum . A sucrose synthase cDNA with high homology to sucrose synthases from both monocotyledonous and dicotyledonous plants has been cloned and used as a homologous probe for Northern blot analyses. Photoautotrophic suspension culture cells, which may be shifted to mixotrophic growth by adding sugars, have been used as a model system to investigate the transition between autotrophic and heterotrophic growth. The higher activity of sucrose synthase after preincubation in the presence of D-glucose, D-fructose or sucrose correlates with an elevated level of mRNA. The sucrose synthase gene was fully induced above a concentration of 20 mM glucose and the steady state level of mRNA was already elevated 1 h after the addition of glucose. Induction of sucrose synthase by 6-desoxyglucose suggests that the non-phosphorylated glucose is the signal for the sugar induced gene expression. Both the enzyme activity and the mRNA level showed a sink tissue specific distribution in plants. The data suggest that sucrose synthase is important both for sink metabolism and the source sink transition.