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PLANT PHYSIOLOGY , Vol 113, Issue 4 1125-1135, Copyright © 1997 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Amino Acid Utilization in Seeds of Loblolly Pine during Germination and Early Seedling Growth (I. Arginine and Arginase Activity)
J. E. King and D. J. Gifford
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 1S5
The mobilization and utilization of the major storage proteins in loblolly
pine (Pinus taeda L.) seeds following imbibition were investigated. Most of
the seed protein reserves were contained within the megagametophyte.
Breakdown of these proteins occurred primarily following radicle emergence
and correlated with a substantial increase in the free amino acid pool in
the seedling; the majority of this increase appeared to be the result of
export from the megagametophyte. The megagametophyte was able to break down
storage proteins and export free amino acids in the absence of the
seedling. Arginine (Arg) was the most abundant amino acid among the
principal storage proteins of the megagametophyte and was a major component
of the free amino acid pools in both the seedling and the megagametophyte.
The increase in free Arg coincided with a marked increase in arginase
activity, mainly localized within the cotyledons and epicotyl of the
seedling. Arginase activity was negligible in isolated seedlings.
Experiments with phenylphosphorodiamidate, a urease inhibitor, supported
the hypothesis that arginase participates in Arg metabolism in the
seedling. The results of this study indicate that Arg could play an
important role in the nutrition of loblolly pine during early seedling
growth.
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