Structures contributing to the completion of conifer seed germination |
| |
Authors: | E Tillman-Sutela A Kauppi |
| |
Institution: | (1) Finnish Forest Research Institute, P.O. Box 16 FIN-96301 Rovaniemi, Finland e-mail: eila.tillman@metla.fi Fax: +358-16-3364640, FI;(2) Department of Biology, University of Oulu, P.O. Box 3000 FIN-90401 Oulu, Finland, FI |
| |
Abstract: | The variety of interpretations of the origin and role of the tissues surrounding the emerging radicle of conifer seeds prompted
us to study changes during germination. The structures contributing to the opening of the seed coat and protrusion of the
radicle in pine and spruce seeds were examined using light microscopy and field emission scanning electron microscopy. The
opening of the seed coat was mainly mechanical and primarily affected by the enlargement of the imbibed endotesta cells lining
the micropylar canal. The hypertrophied nucellar apex, swelling remnants and mucous substances in the micropyle further enhanced
the testa splitting which was reinforced by the straightening of the folded nucellar cap. The expansion of the imbibed megagametophyte
and the embryo were conducive to the seed coat opening only at a later stage. This was followed almost immediately by the
appearance of the root cap showing an early geotropic response typical for taproots and assuring an immediate anchoring of
the emerged embryo to the ground. The translucent tissue composed of elongating cell rows preceded and surrounded the protruding
radicle and derived mainly from two origins: the micropylar end of the megagametophyte and the root cap. Observations about
the origin of the sheath clarify the reasons for previous interpretations about the putative role of the massive embryo root
cap in testa splitting and germination. The protective and adhesive function of the sheath is concluded to be essential to
the conifer embryos, which present the epigeal type of germination.
Received: 7 July 1999 / Accepted: 11 August 1999 |
| |
Keywords: | Pinaceae Micropyle Nucellar cap Megagametophyte Radicle |
本文献已被 SpringerLink 等数据库收录! |
|