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PLANT PHYSIOLOGY , Vol 104, Issue 2 623-628, Copyright © 1994 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Cell-Wall Autohydrolysis in Isolated Endosperms of Lettuce (Lactuca sativa L.)
S. Dutta, K. J. Bradford and D. J. Nevins
Department of Vegetable Crops, University of California, Davis, California 95616-8741
Cell walls prepared from the endosperm tissue of hydrated lettuce (Lactuca
sativa L.) seeds undergo autohydrolysis. Release of carbohydrates is most
rapid (0.4-0.6 [mu]g per endosperm) within the 1st h of incubation in
buffer, but substantial autolysis is sustained for at least 10 h. Autolysis
is temperature sensitive, and the optimum rate occurs at pH 5. The rate of
autolysis increases markedly in the period just prior to radicle emergence.
The cell-wall polysaccharide composition in micropylar and lateral
endosperm regions differs significantly; the micropylar walls are rich in
arabinose and glucose with substantially lower amounts of mannose. Although
walls prepared from both micropylar and lateral regions undergo autolysis,
micropylar walls release carbohydrates at a higher rate than lateral walls.
Autolysis products elute as large polymers when subjected to size-exclusion
chromatography, suggesting that endo-enzyme activity is responsible for
release of fragments containing arabinose, galactose, mannose, and uronic
acids. Arabinose, galactose, mannose, and glucose are also released as
monomers. As a function of time, the ratio of polymers to monomers
decreases, indicating that exo-enzyme activity is also present.
Thermoinhibition or treatment with abscisic acid suppresses germination and
reduces the rates of autolysis of walls isolated from the endosperm by
about 25%. Treatments that alleviate thermoinhibition (kinetin and
gibberellic acid) increase the rates of autolysis by 20 to 30% when
compared to thermoinhibited controls.
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