title: Plastidial alpha-glucan phosphorylase is not required for starch degradation in Arabidopsis leaves but has a role in the tolerance of abiotic stress.
abstract: To study the role of the plastidial alpha-glucan phosphorylase in starch metabolism in the leaves of Arabidopsis, two independent mutant lines containing T-DNA insertions within the phosphorylase gene were identified. Both insertions eliminate the activity of the plastidial alpha-glucan phosphorylase. Measurement of other enzymes of starch metabolism reveals only minor changes compared with the wild type. The loss of plastidial alpha-glucan phosphorylase does not cause a significant change in the total accumulation of starch during the day or its remobilization at night. Starch structure and composition are unaltered. However, mutant plants display lesions on their leaves that are not seen on wild-type plants, and mesophyll cells bordering the lesions accumulate high levels of starch. Lesion formation is abolished by growing plants under 100% humidity in still air, but subsequent transfer to circulating air with lower humidity causes extensive wilting in the mutant leaves. Wilted sectors die, causing large lesions that are bordered by starch-accumulating cells. Similar lesions are caused by the application of acute salt stress to mature plants. We conclude that plastidial phosphorylase is not required for the degradation of starch, but that it plays a role in the capacity of the leaf lamina to endure a transient water deficit.
authors.affiliation: Institute of Plant Sciences, University of Bern, CH-3013 Bern, Switzerland. sam.zeeman@ips.unibe.ch
authors.forename: Samuel C
authors.initials: SC
authors.lastname: Zeeman
authors.forename: David
authors.initials: D
authors.lastname: Thorneycroft
authors.forename: Nicole
authors.initials: N
authors.lastname: Schupp
authors.forename: Andrew
authors.initials: A
authors.lastname: Chapple
authors.forename: Melanie
authors.initials: M
authors.lastname: Weck
authors.forename: Hannah
authors.initials: H
authors.lastname: Dunstan
authors.forename: Pierre
authors.initials: P
authors.lastname: Haldimann
authors.forename: Nicole
authors.initials: N
authors.lastname: Bechtold
authors.forename: Alison M
authors.initials: AM
authors.lastname: Smith
authors.forename: Steven M
authors.initials: SM
authors.lastname: Smith
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000502:physiology*; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D002736:Chloroplasts / Q000201:enzymology*; D009154:Mutation; D006005:Phosphorylases / Q000378:metabolism*; D018515:Plant Leaves / Q000187:drug effects / Q000201:enzymology*; D013213:Starch / Q000737:chemistry / Q000378:metabolism*; D024941:Starch Phosphorylase / Q000378:metabolism; D013314:Stress, Mechanical; D014867:Water / Q000494:pharmacology
chemical_list: D014867:Water; D013213:Starch; D006005:Phosphorylases; D024941:Starch Phosphorylase