Polyuronide Degradation and Hemicellulose Modifications in Ripening Tomato Fruit

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Abstract
Hemicelluloses and polyuronides from the cell wall of ripening tomato (Lycopersicon esculentum Mill. cv. Rutgers) fruit were examined using gel-filtration chromatography. Gel filtration of polyuronides revealed that these polymers were extensively degraded during ripening, as evidenced by the increase in the quantity of polymers that fractionated on the gel. Low molecular weight polyuronides were first evident in fruit harvested at the turning stage and they constituted the major portion of the polyuronides obtained from fruit at more advanced stages of ripening. The appearance of degraded polyuronides corresponded well with the activity of endo-D-galacturonanase, which appeared to be solely responsible for the degradation of these wall polymers. The cell wall hemicelluloses were also affected during ripening; gel-filtration analyses revealed marked changes in the molecular-weight distribution of these polymers. Hemicelluloses from immature green and mature green fruit were similar chromatographically, whereas those from fruit harvested during ripening showed progressively lower quantities of high molecular weight polymers and higher quantities of low molecular weight polymers (<40,000). These changes coincided with the degradation of the pectic polysaccharides; however, in vitro studies using isolated cell wall showed that pectin degradation occurred independently of the changes in hemicelluloses.

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