Fig. 8.

Pathways of storage xyloglucan catabolism in the cotyledon of a developing seedling of Hymenaea courbaril. These steps are considered together as ‘xyloglucan degradation’. The figure also shows some of the events that occur in the hypocotyl and developing leaves. The entire process that includes xyloglucan degradation, sucrose production, and transport through the hypocotyl towards the leaves is termed xyloglucan mobilization. The names of the enzymes are shown in italics. Hypothetically the following correlations between enzymes and genes exist: XTH=HcXTH1, hcbetagal=HcBGAL1, invertase=HcAlkIN1, and sucrose synthase=HcSUS1. Note that there are several points at which feedback control is present. The figure illustrates the points which are thought to control xyloglucan mobilization according to the experiments with application of NPA, top shoot excision, and presence or absence of light. Question marks were added to indicate hypothetical pathways that need further experiments. phy, phytochrome; cry, cryptochrome; Gal, galactose; Glc, glucose; Xyl, xylose.