Matrix glycan depolymerisation and xyloglucan endohydrolase activities in ethylene-treated watermelon (Citrullus lanatus) fruit
- Autores: Yasar Karakurt, Noboru Muramatsu, Jiwon Jeong, Brandon M. Hurr, D. J. Huber
- Localización: Journal of the science of food and agriculture, ISSN 0022-5142, Vol. 88, Nº 4, 2008, págs. 684-689
- Idioma: inglés
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Resumen
BACKGROUND: Ethylene-induced placental tissue water soaking in harvested watermelon fruit is accompanied by cell separation and collapse, depolymerisation of water- and chelator-soluble pectins, a reducton in total uronic acids and increased polygalacturonase activity. The aim of this study was to investigate whether ethylene-induced changes in placental tissue cell walls also affected matrix glycans (hemicelluloses). RESULTS: Polymers from 0 and 6 day air-treated fruits were similar in molecular mass distribution, with the majority of polymers eluting within the void volume of Sepharose 6B. Polymers from ethylene-treated fruit showed significant molecular mass downshifts involving xyloglucan. Xylose and glucose together comprised nearly 70% of 2 mol L−1 alkali-soluble neutral sugars. Treatment of watermelon fruit with ethylene was not accompanied by changes in matrix glycan composition, indicating that in situ depolymerisation did not result in altered solubility and/or loss of xyloglucan. Cell-free protein extracts from watermelon placental tissue from both air- and ethylene-treated fruits degraded tamarind seed xyloglucan, resulting in significant molecular mass downshifts without production of oligomers and monomers. The capacity of cell-free extracts to degrade tamarind xyloglucan and watermelon matrix glycans was similar for 6 day ethylene- and air-treated fruits. CONCLUSION: Collectively the data suggest that enhanced depolymerisation of xyloglucan in ethylene-treated watermelon fruit arises from factors other than altered enzyme levels. Accordingly, the depolymerisation of pectin and matrix glycans would not appear to be solely responsible for ethylene-induced water soaking in watermelon. Copyright © 2007 Society of Chemical Industry
