title: Callose synthase GSL7 is necessary for normal phloem transport and inflorescence growth in Arabidopsis.
abstract: One isoform of callose synthase, Glucan Synthase-Like7 (GSL7), is tightly coexpressed with two isoforms of sucrose synthase (SUS5 and SUS6) known to be confined to phloem sieve elements in Arabidopsis (Arabidopsis thaliana). Investigation of the phenotype of gsl7 mutants of Arabidopsis revealed that the sieve plate pores of stems and roots lack the callose lining seen in wild-type plants. Callose synthesis in other tissues of the plant appears to be unaffected. Although gsl7 plants show only minor phenotypic alterations during vegetative growth, flowering stems are reduced in height and all floral parts are smaller than those of wild-type plants. Several lines of evidence suggest that the reduced growth of the inflorescence is a result of carbohydrate starvation. Levels of sucrose, hexoses, and starch are lower in the terminal bud clusters of gsl7 than in those of wild-type plants. Transcript levels of "starvation" genes expressed in response to low sugars are elevated in the terminal bud clusters of gsl7 plants, at the end of the night, and during an extended night. Pulse-chase experiments with (14)CO(2) show that transport of assimilate in the flowering stem is much slower in gsl7 mutants than in wild-type plants. We suggest that the callose lining of sieve plate pores is essential for normal phloem transport because it confers favorable flow characteristics on the pores.
authors.affiliation: John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, United Kingdom. alison.smith@bbsrc.ac.uk
authors.forename: D H Paul
authors.initials: DH
authors.lastname: Barratt
authors.forename: Katharina
authors.initials: K
authors.lastname: Kölling
authors.forename: Alexander
authors.initials: A
authors.lastname: Graf
authors.forename: Marilyn
authors.initials: M
authors.lastname: Pike
authors.forename: Grant
authors.initials: G
authors.lastname: Calder
authors.forename: Kim
authors.initials: K
authors.lastname: Findlay
authors.forename: Samuel C
authors.initials: SC
authors.lastname: Zeeman
authors.forename: Alison M
authors.initials: AM
authors.lastname: Smith
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D050260:Carbohydrate Metabolism / Q000187:drug effects; D002247:Carbon Isotopes; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics; D005936:Glucans / Q000378:metabolism; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism*; D056626:Inflorescence / Q000033:anatomy & histology / Q000235:genetics / Q000254:growth & development* / Q000648:ultrastructure; D009154:Mutation / Q000235:genetics; D052585:Phloem / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D018547:Plant Stems / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D013395:Sucrose / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D029681:Arabidopsis Proteins; D002247:Carbon Isotopes; D005936:Glucans; D013395:Sucrose; C048306:callose; D005964:Glucosyltransferases; C478648:cellulose synthase; C020570:1,3-beta-glucan synthase