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Biophysical, physiological and biochemical processes regulating seed germination

Published online by Cambridge University Press:  19 September 2008

G. E. Welbaum ,
K. J. Bradford ,
Kyu-Ock Yim ,
D. T. Booth  and
M. O. Oluoch
G. E. Welbaum*
Affiliation:
Department of Horticulture, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0327, USA
K. J. Bradford
Affiliation:
Department of Vegetable Crops, University of California, Davis, CA 95616-8631, USA
Kyu-Ock Yim
Affiliation:
Department of Vegetable Crops, University of California, Davis, CA 95616-8631, USA
D. T. Booth
Affiliation:
USDA/ARS High Plains Grass Research Station, Cheyenne, WY 82009, USA
M. O. Oluoch
Affiliation:
Department of Horticulture, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0327, USA
*
*Correspondence Fax +1-540-231-3083 E-mail welbaum@vt.edu
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Abstract

In the physiological sense, germination begins with seed water uptake and ends with the initiation of elongation by the embryonic axis, usually the radicle. The driving forces and constraints on expansion by the embryo are examined, particularly for seeds in which the embryo is surrounded by endosperm and testa tissues that restrict growth. Models have been developed to predict germination based on thermal time, hydrotime and combined hydrothermal time. These population-based models indicate that the timing of germination is closely tied to physiologically determined temperature and water potential thresholds for radicle emergence which vary among individual seeds in a population. The restraint imposed by tissues surrounding the radicle is a major determinant of the threshold water potential. Enzymatic weakening of these tissues is a key event regulating the timing of radicle emergence. Considerable evidence suggests that endo-β-mannanase is involved in this process in a number of species, although it is doubtful that it is the sole determinant of when radicle emergence occurs. Molecular and biochemical studies are revealing the complexity of events occurring in endosperm and embryo cells associated with the completion of germination. Unique permeability properties and the presence of enzymes associated with pathogen resistance suggest additional functional roles for the tissues enclosing the embryo. The insights gained from physiology and modelling are being extended by the application of molecular techniques to identify and determine the function of genes expressed in association with germination. Single-seed assay methods, in vivo reporters, specific modification of gene expression and mutagenesis will be critical technologies for advancing our understanding of germination

Keywords

endo-β-mannanasegerminationhydrothermal timemodellingpuncture forcesemipermeabilitythermal time
Type
Research Papers
Information
Seed Science Research , Volume 8 , Issue 2 , June 1998 , pp. 161 - 172
Copyright
Copyright © Cambridge University Press 1998

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