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Free Content Synthesis, processing and export of cytoplasmic endo-β-1,4-xylanase from barley aleurone during germination

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Summary

We have identified the major endo-β-1,4-xylanase (XYN-1) in the aleurone of germinating barley grain, and show that it is expressed as a precursor of Mr 61 500 with both N- and C-terminal propeptides. XYN-1 is synthesized as an inactive enzyme in the cytoplasm, and only becomes active at a late stage of germination when the aleurone ceases to secrete hydrolases. A series of processing steps, mediated in part by aleurone cysteine endoproteases, yields a mature active enzyme of Mr 34 000. Processing and extracellular release of the mature enzyme coincide with the programmed cell death (PCD)-regulated disintegration of aleurone cells. We discuss the significance of delayed aleurone cell-wall degradation by endoxylanases in relation to the secretory capacity of the aleurone, and propose a novel role for aleurone PCD in facilitating the export of hydrolases.
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Keywords: aleurone; barley; germination; programmed cell death; secretion; xylanase

Document Type: Research Article

Affiliations: 1: Department of Applied Plant Sciences, TNO Nutrition and Food Research Institute, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands, and 2: Carlsberg Research Laboratory, Gamle Carlsberg Vej 10, DK-2500 Copenhagen, Denmark

Publication date: April 1, 2001

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