title: Sugar/osmoticum levels modulate differential abscisic acid-independent expression of two stress-responsive sucrose synthase genes in Arabidopsis.
abstract: Sucrose synthase (Sus) is a key enzyme of sucrose metabolism. Two Sus-encoding genes (Sus1 and Sus2) from Arabidopsis thaliana were found to be profoundly and differentially regulated in leaves exposed to environmental stresses (cold stress, drought or O(2) deficiency). Transcript levels of Sus1 increased on exposure to cold and drought, whereas Sus2 mRNA was induced specifically by O(2) deficiency. Both cold and drought exposures induced the accumulation of soluble sugars and caused a decrease in leaf osmotic potential, whereas O(2) deficiency was characterized by a nearly complete depletion in sugars. Feeding abscisic acid (ABA) to detached leaves or subjecting Arabidopsis ABA-deficient mutants to cold stress conditions had no effect on the expression profiles of Sus1 or Sus2, whereas feeding metabolizable sugars (sucrose or glucose) or non-metabolizable osmotica [poly(ethylene glycol), sorbitol or mannitol] mimicked the effects of osmotic stress on Sus1 expression in detached leaves. By using various sucrose/mannitol solutions, we demonstrated that Sus1 was up-regulated by a decrease in leaf osmotic potential rather than an increase in sucrose concentration itself. We suggest that Sus1 expression is regulated via an ABA-independent signal transduction pathway that is related to the perception of a decrease in leaf osmotic potential during stresses. In contrast, the expression of Sus2 was independent of sugar/osmoticum effects, suggesting the involvement of a signal transduction mechanism distinct from that regulating Sus1 expression. The differential stress-responsive regulation of Sus genes in leaves might represent part of a general cellular response to the allocation of carbohydrates during acclimation processes.
authors.affiliation: Umeâ Plant Science Centre, Department of Plant Physiology, Umeâ University, 901 87 Umeâ, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Déjardin
authors.forename: L N
authors.initials: LN
authors.lastname: Sokolov
authors.forename: L A
authors.initials: LA
authors.lastname: Kleczkowski
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism; D000064:Acclimatization / Q000502:physiology*; D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000096:biosynthesis / Q000235:genetics*; D015687:Cell Hypoxia; D003080:Cold Temperature; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D051599:Glucose-1-Phosphate Adenylyltransferase; D005964:Glucosyltransferases / Q000096:biosynthesis / Q000235:genetics*; D009154:Mutation; D009713:Nucleotidyltransferases / Q000378:metabolism; D009997:Osmotic Pressure; D018515:Plant Leaves / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D018749:RNA, Plant / Q000032:analysis; D015398:Signal Transduction; D013395:Sucrose / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D012333:RNA, Messenger; D018749:RNA, Plant; D013395:Sucrose; D000040:Abscisic Acid; D005964:Glucosyltransferases; C022699:sucrose synthase; C578062:sucrose synthase-1, Arabidopsis; D009713:Nucleotidyltransferases; D051599:Glucose-1-Phosphate Adenylyltransferase