Journal of Experimental Botany, Vol. 54, No. 383, pp. 715-725,
February 1, 2003
© 2003 Oxford University Press
Subcellular localization of ADPglucose pyrophosphorylase in developing wheat endosperm and analysis of the properties of a plastidial isoform
Received 1 May 2002; Accepted 17 October 2002
1 Department of Botany, College of Biological Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada
2 School of Biological Sciences, University of Manchester, 3.614 Stopford Building, Oxford Road, Manchester M13 9PT, UK
3 Advanced Technologies (Cambridge) Ltd., 210, Cambridge Science Park, Cambridge CB4 4WA, UK
4 To whom correspondence should be addressed. Fax: +1 519 767 1991. E-mail: itetlow{at}uoguelph.ca
5 Present address: Ciphergen Biosystems Ltd., Prior Road, Camberley, Surrey, GU15 1DA, UK.
Abbreviations: AGPase, adenosine 5' diphosphate glucose pyrophosphorylase; AGP-L, large subunit AGPase; AGP-S, small subunit AGPase; APPase, alkaline inorganic pyrophosphatase; DAP, days after pollination; DTT, dithiothreitol; 3-PGA, 3-phosphoglyceric acid; Pi, inorganic orthophosphate; PPi, inorganic pyrophosphate; UGPase, uridine 5' diphosphate glucose pyrophosphorylase.
The intracellular location of ADPglucose pyrophosphorylase (AGPase) in wheat during endosperm development was investigated by analysis of the recovery of marker enzymes from amyloplast preparations. Amyloplast preparations contained 20–28% of the total endosperm activity of two plastidial marker enzymes and less than 0.8% of the total endosperm activity of two cytosolic marker enzymes. Amylo plasts prepared at various stages of development, from 8–30 d post anthesis, contained between 2% and 10% of the total AGPase activity; this implies that between 7% and 40% of the AGPase in wheat endosperm is plastidial during this period of development. Two proteins were recognized by antibodies to both the large and small subunits of wheat AGPase. The larger of the two AGPases was the major form of the enzyme in whole cell extracts, and the smaller, less abundant, form of AGPase was enriched in plastid preparations. The results are consistent with data from other graminaceous endosperms, suggesting that there are distinct plastidial and cytosolic isoforms of AGPase composed of different subunits. The plastidial isoform of AGPase from wheat endosperm is relatively insensitive to the allosteric regulators 3-phosphoglycerate and inorganic orthophos phate compared with plastidial AGPase from other species. Amyloplast AGPase showed no sensitivity to physiological concentrations of inorganic orthophosphate. 15 mM 3-phosphoglycerate caused no stimulation of the pyrophosphorolytic reaction, and only 2-fold stimulation of the ADPglucose synthesizing reaction.
Key words: ADPglucose pyrophosphorylase, endosperm, localization, regulation, wheat.
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