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Methanol, pectin and pectinesterase changes during soybean seed maturation

Published online by Cambridge University Press:  22 February 2007

James L. Koch
Affiliation:
Seed Biology, 617 Bradfield Hall, Department of Crop and Soil Sciences, Cornell University Agricultural Experiment Station, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14853–1901, USA
Marcin Horbowicz
Affiliation:
Seed Biology, 617 Bradfield Hall, Department of Crop and Soil Sciences, Cornell University Agricultural Experiment Station, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14853–1901, USAResearch Institute of Vegetable Crops, 96–100 Skierniewice, Poland
Ralph L. Obendorf*
Affiliation:
Seed Biology, 617 Bradfield Hall, Department of Crop and Soil Sciences, Cornell University Agricultural Experiment Station, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14853–1901, USA
*
*Correspondence Tel: +1 607 255 1709 Fax: +1 607 255 2644 Email: rlo1@cornell.edu
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Abstract

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Methanol accumulates in maturing seeds, correlating with preharvest deterioration. Since the source of methanol may be from pectin de-methylation, methanol, cell wall uronic acid, pectin methyl esterification, pectinesterase (PE; EC 3.1.1.11) activity, and neutral sugar composition and partitioning of cell wall polysaccharides were determined during soybean (Glycine max [L.] Merrill) seed development, maturation, and desiccation in planta. Axis cell wall polysaccharides were more easily solubilized, richer in uronic acid, rhamnose, and xylose, and less rich in galactose than cotyledon cell wall polysaccharides. Methanol accumulated to 9.7 μg per two cotyledons and 0.5 μg per axis; total methanol decreased to 3 μg per two cotyledons during loss of green color. Total uronic acid increased from 0.12 to 0.27 mg per axis and 0.9 to 4 mg per cotyledon between 24 and 50 days after flowering (DAF). After loss of green color, pectin methyl esterification in axes increased from 7 to 24 mole% between 50 and 60 DAF but decreased to 14 mole%by 62 DAF in latter stages of seed desiccation. In cotyledons, methyl esterification ranged from 25 to 40 mole% and was 31 mole% after desiccation. PE activity increased 100 fold in axes, including a 30-fold increase in activity after loss of green color at 46 DAF. Cotyledon PE activity was 40-fold higher than in axes at 24 DAF, declined 75% by 56 DAF, and then increased 5 fold during desiccation. Pectin methyl de-esterification by PE is sufficient to be the sole source for methanol accumulation in seed tissues during development and maturation.

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Type
Research Article
Copyright
Copyright © Cambridge University Press 1999