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Plant Physiol, January 2001, Vol. 125, pp. 464-475
Developmental Regulation of Indole-3-Acetic Acid Turnover in
Scots Pine Seedlings1
Karin
Ljung,2
Anders
Östin,23
Laetitia
Lioussanne, and
Göran
Sandberg*
Department of Forest Genetics and Plant Physiology, The Swedish
University of Agricultural Sciences, S-901 83 Umeå, Sweden
Indole-3-acetic acid (IAA) homeostasis was investigated during seed
germination and early seedling growth in Scots pine (Pinus sylvestris). IAA-ester conjugates were initially hydrolyzed in the seed to yield a peak of free IAA prior to initiation of root elongation. Developmental regulation of IAA synthesis was observed, with tryptophan-dependent synthesis being initiated around 4 d and
tryptophan-independent synthesis occurring around 7 d after imbibition. Induction of catabolism to yield 2-oxindole-3-acetic acid
and irreversible conjugation to
indole-3-acetyl-N-aspartic acid was noticed at the same
time as de novo synthesis was first detected. As a part of the
homeostatic regulation IAA was further metabolized to two new
conjugates:
glucopyranosyl-1-N-indole-3-acetyl-N-aspartic acid and glucopyranosyl-1-N-indole-3-acetic acid. The
initial supply of IAA thus originates from stored pools of IAA-ester
conjugates, mainly localized in the embryo itself rather than in the
general nutrient storage tissue, the megagametophyte. We have found
that de novo synthesis is first induced when the stored pool of
conjugated IAA is used up and additional hormone is needed for
elongation growth. It is interesting that when de novo synthesis is
induced, a distinct induction of catabolic events occurs, indicating
that the seedling needs mechanisms to balance synthesis rates for the homeostatic regulation of the IAA pool.
1
This work was supported by The Swedish Council
of Forestry and Agricultural Research and The Foundation for Strategic Research.
2
These authors contributed equally to the paper.
3
Present address: National Institute of Working
Life, S-907 13 Umeå, Sweden.
*
Corresponding author; e-mail goran.sandberg{at}genfys.slu.se; fax
46-90-7865901.
© 2001 American Society of Plant Physiologists
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