Cutillas-Iturralde, A., Zarra, I. and Lorences, E. P 1993. Metabolism of cell wall polysaccharides from persimmon fruit. Pectin solubilization during fruit ripening occurs in apparent absence of polygalacturonase activity. -Physiol. Plant. 89: 369-375.. . .. .,^,, .,.,Pectins from persimmon (Diospyros kaki L.) fruit pericarp were sequentially extracted with 0.05 M rra«5-l,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA), 0.05 M Na^CO, (1°C) and Na.CO, (20°C) and the carbohydrate composition and metabolism during development determined. Young persimmon fruits contained a large proportion of pectins, 46% by dry weight, that decreased to 20% with ripening. This decrease occurred in the CDTA and NajCO^ (TC) fractions, mainly composed of uronic acids, and represents a net loss of uronic acids, arabinose and galactose. The amount of non-cellulosic neutral sugars was especially high in the Na.CO, (20°C) fraction. The loss of pectins was also accompanied by a depolymerisation of the polysaccharides extracted in the three pectic fractions. However, none of these changes can be attributed to the action of polygalacturonase activity. Proteins were extracted from the pericarp tissue, but endopolygalacturonase (EC 3.2.1.15) activity, determined as a decrease in viscosity of polygalacturonic acid, was not observed in the extract. Determination of exopolygalacturonase (EC 3.2.1.67) activity by measuring the release of reducing groups from polygalacturonic acid was also negative. The results presented indicate that polygalacturonase is not responsible for the metabolism of pectins during persimmon fruit ripening.-' '••<-'

Hemicellulosic polysaccharides from persimmon fruit (Diospyros kaki L.) pericarp were extracted from depectinated cell walls with 0.5, 1 and 4 M KOH at different stages of development: (I) maximal growth corresponding to the first sigmoidal growth phase; (II) cessation of growth corresponding to the lag between the first and the second sigmoidal phases; (III) maximal growth corresponding to the second sigmoidal phase; and (IV) cessation of growth when the fruit had reached its maximum size and the change in colour (green to red) had taken place. During fruit development the amount of total hemicelluloses per unit dry mass cell wall decreased twofold. Xyloglucan was present in the three hemicellulosic fractions, and also decreased with fruit age, although its amount relative to other hemicelluloses increased. The amount of xyloglucan was especially high in the hemicelluloses extracted with 4 M KOH, representing more than 50% at stages III and IV. The average molecular mass of xyloglucan increased from stage I through stage II (0.5 M hemicellulosic fraction) or through stage III (I and 4 M hemicellulosic fractions) and decreased after that. The xyloglucan endotransglycosylase (XET: EC 2.4.1.‐) activity was measured as the incorporation of [3H]XXXGol (reduced xyloglucan heptasaccharide labelled at position 1 of the glucitol moiety) into partially purified persimmon fruit xyloglucan. XET specific activity increased greatly between stages I and II. The importance of this enzyme during fruit ripening is discussed.

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The growth-promoting effect of xyloglucan-derived oligosaccharides was investigated using a bioassay with entire pea (Pisum safivum L., var Alaska) shoots. After a 24-h incubation period at 25T, xyloglucan oligosaccharide (XGO) solutions with concentrations of 10-6 M notably increased the growth rate of pea shoots, whereas the same oligosaccharides at 1 O-' M were less effective. To investigate the possible correlation between growth rate changes in the XCO-treated shoots and changes in the wall mechanical properties of their growing regions (third internodes), we used a shortterm creep assay. l h e promotion of elongation by XCOs was reflected in an enhancement of the viscoelasticity of the growing regions of the shoots. To show whether this effect on wall viscoelastic properties was the cause or a consequence of their growth promotion, we tested the effect of XGOs on the long-term extension of isolated cell walls. We characterized an acid-induced extension i n isolated cell walls from pea shoots that was not inhibited by preincubation in neutral buffers. Exogenously added XGOs did not alter the pattern of pea segment extension at any pH tested, indicating that XCOs have no direct effect on cell wall viscoelasticity. Finally, preincubation of pea segments in neutral buffers with XCOs enhanced their capacity to extend under acidic conditions. This finding suggests that XCOs at a neutral pH can act via transglycosylation, weakening the wall matrix and making the wall more responsive to other mechanisms of acid-induced extension as an expansin-mediated extension.

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