A mutant of Arabidopsis thaliana lacking the ability to transport glucose across the chloroplast envelope.
At the end of a 12-h day leaves of the mutant of Arabidopsis thaliana L., TC265, contained 4-5 times more starch than those of the wild type. During a subsequent 12-h night the decline in the starch content of the leaves of the mutant was at least 50% of that of the wild-type leaves. Starch labelled in the light in a 30-min pulse in 14CO2 was rapidly broken down in a subsequent 12-h chase in the dark in air in the leaves of both mutant and wild type. Chloroplasts from leaves of the wild type took up [32P]Pi and [U-14C]glucose at 12 and 1.6 mumol/h per mg of chlorophyll respectively; chloroplasts from the mutant showed a similar rate for [32P]Pi but no uptake of [U-14C]glucose. The glucose content of freshly isolated chloroplasts from the mutant was twice that of chloroplasts from the wild type; this difference was accentuated when the isolated chloroplasts were incubated in the dark. SDS/PAGE of preparations of chloroplast envelopes showed that those from the mutant were deficient in a protein band of approximate molecular mass 40 kDa. It is suggested that in mutant TC265 the primary lesion is in a hexose transporter in the chloroplast envelope, and that this transporter moves the products of starch breakdown that are destined for sucrose synthesis from the chloroplast to the cytosol.
Trethewey
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RN
Department of Plant Sciences, University of Cambridge, U.K.
ap Rees
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D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism*; D001692:Biological Transport; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005947:Glucose / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D010710:Phosphates / Q000378:metabolism; D017440:Photoperiod; D013213:Starch / Q000378:metabolism
D009004:Monosaccharide Transport Proteins; D010710:Phosphates; D002734:Chlorophyll; D013213:Starch; D005947:Glucose