Plant Physiology 109: 751-759 (1995)
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Class I ß-1,3-glucanases in the endosperm of tobacco during
germination
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Gerhard Leubner-Metzger, Corinne Fründt, Regina Vögeli-Lange
(1), Frederick Meins, Jr.
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Friedrich Miescher Institute, Box 2543, CH-4002 Basel, Switzerland
(1) Present address: Botanical Institute, University of Basel, Hebelstrasse
1, CH-4056 Basel, Switzerland
Received: 9 June 1995 / Accepted: 14 July 1995
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Abstract. Rupture of the seed coat and rupture of the endosperm
are separate events in the germination of Nicotiana tabacum L. cv.
"Havana 425" seeds. Treatment with 10-5 M abscisic acid (ABA) did not appreciably
affect seed-coat rupture but greatly delayed subsequent endosperm rupture
by more than 100 h and resulted in the formation of a novel structure consisting
of the enlarging radicle with a sheath of greatly elongated endosperm tissue.
Therefore, ABA appears to act primarily by delaying endosperm rupture and
radicle emergence. Measurements of ß-1,3-glucanase activity, antigen
content, and mRNA accumulation together with reporter gene experiments showed
that induction of class I ß-1,3-glucanase genes begins just prior
to the onset of endosperm rupture but after the completion of seed-coat
rupture. This induction was localized exclusively in the micropylar region
of the endosperm where the radicle will penetrate. ABA treatment markedly
inhibited the rate of ß-1,3-glucanase accumulation but did not delay
the onset of induction. Independent of the ABA concentration used, onset
of endosperm rupture was correlated with the same ß-1,3-glucanase
content/seed. These results suggest that ABA-sensitive class I ß-1,3-glucanases
promote radicle penetration of the endosperm, which is a key limiting step
in tobacco seed germination.
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