PLANT PHYSIOLOGY , Vol 111, Issue 2 447-457, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Alterations in Structural Polysaccharides during Liquefaction of Tomato Locule Tissue
G. W. Cheng and D. J. Huber
Horticultural Sciences Department, P.O. Box 110690, University of Florida, Gainesville, Florida 32611
The locule tissue of tomato (Lycopersicon esculentum, Mill.) undergoes
extensive liquefaction during ripening. In this study, the solubility,
molecular mass, and glycosyl composition of locule pectic and
alkali-soluble polysaccharides were examined with the aim of identifying
features contributing to the unique properties of this tissue.
Ethanol-insoluble solids were prepared from de-seeded locule tissue from
tomato fruit at the immature green (IMG), mature green, and breaker stages
of development. Ethanol-insoluble pectins were extracted sequentially in
H2O, 50 mM trans-1,2-diaminocyclohexane-N,N,N[prime],N[prime]-tetraacetic
acid, 50 mM Na2CO3, and 4 M KOH. At the IMG stage, nearly 85% of the locule
pectins were solubilized by water,
trans-1,2-diaminocyclohexane-N,N,N[prime],N[prime]-tetraacetic acid, and
Na2CO3 solutions. Solubility increased only slightly with further locule
development. The noncovalently associated polymers were of high molecular
mass throughout liquefaction. Polymers extracted in mild alkali were of
considerably lower molecular mass. Locule pectins in IMG fruit were heavily
glycosylated with galactose, arabinose, and xylose. All pectin classes
exhibited similar deglycosylation trends during liquefaction. Locule
hemicelluloses were rich in glucose, xylose, and arabinose. These polymers
collectively showed molecular mass downshifts with minimal compositional
changes during liquefaction. The KOH-soluble material also included
xylose-rich acidic polymers not matching the neutral sugar profile of the
noncovalently associated pectic polymers.
