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PLANT PHYSIOLOGY , Vol 113, Issue 1 13-20, Copyright © 1997 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
A Single-Seed Assay for Endo-[beta]-Mannanase Activity from Tomato Endosperm and Radicle Tissues
D. W. Still, P. Dahal and K. J. Bradford
Department of Vegetable Crops, University of California, Davis, California 95616-8631
Completion of germination (radicle emergence) is an all-or-none
developmental event for an individual seed. Variation in germination timing
among seeds in a population therefore reflects variation among seeds in the
rates or extents of physiological or biochemical processes prior to radicle
emergence. For tomato (Lycopersicon esculentum Mill.) seeds, correlative
evidence suggests that endo-[beta]-mannanase activity weakens the endosperm
cap tissue opposite the radicle tip to permit radicle emergence. To test
whether endo-[beta]-mannanase activity is causally related to germination
rates, we have developed a sensitive assay suitable for use with individual
radicle tips or endosperm caps. We show that endo-[beta]-mannanase activity
varies at least 100-fold and often more than 1000-fold among individual
inbred tomato seeds prior to radicle emergence. Other sources of variation
(tissue size and experimental error) were evaluated and cannot account for
this range of activity. Endo-[beta]-mannanase activity was generally
10-fold greater in leachates from endosperm caps than from radicle tips.
Release of reducing sugars from individual endosperm caps also varied over
a considerable (9-fold) range. These extreme biochemical differences among
individual tomato seeds prior to radicle emergence indicate that results
obtained from bulk samples could be misleading if it is assumed that all
seeds exhibit the "average" behavior.
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