title: The ram1 mutant of Arabidopsis exhibits severely decreased beta-amylase activity.
abstract: Despite extensive biochemical analyses, the biological function(s) of plant beta-amylases remains unclear. The fact that beta-amylases degrade starch in vitro suggests that they may play a role in starch metabolism in vivo. beta-Amylases have also been suggested to prevent the accumulation of highly polymerized polysaccharides that might otherwise impede flux through phloem sieve pores. The identification and characterization of a mutant of Arabidopsis var. Columbia with greatly reduced levels of beta-amylase activity is reported here. The reduced beta-amylase 1 (ram1) mutation lies in the gene encoding the major form of beta-amylase in Arabidopsis. Although the Arabidopsis genome contains nine known or putative beta-amylase genes, the fact that the ram1 mutation results in almost complete loss of beta-amylase activity in rosette leaves and inflorescences (stems) indicates that the gene affected by the ram1 mutation is responsible for most of the beta-amylase activity present in these tissues. The leaves of ram1 plants accumulate wild-type levels of starch, soluble sugars, anthocyanin, and chlorophyll. Plants carrying the ram1 mutation also exhibit wild-type rates of phloem exudation and of overall growth. These results suggest that little to no beta-amylase activity is required to maintain normal starch levels, rates of phloem exudation, and overall plant growth.
authors.affiliation: Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005-1892, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Laby
authors.forename: D
authors.initials: D
authors.lastname: Kim
authors.forename: S I
authors.initials: SI
authors.lastname: Gibson
mesh_terms: D000872:Anthocyanins / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D001692:Biological Transport; D050260:Carbohydrate Metabolism; D002734:Chlorophyll / Q000378:metabolism; D017343:Genes, Plant / Q000235:genetics; D009154:Mutation; D018547:Plant Stems / Q000235:genetics / Q000378:metabolism; D013213:Starch / Q000378:metabolism; D001614:beta-Amylase / Q000235:genetics* / Q000378:metabolism
chemical_list: D000872:Anthocyanins; D002734:Chlorophyll; D013213:Starch; D001614:beta-Amylase