Polysaccharide synthesis in the Golgi apparatus is considered a multistep reaction that requires the cooperative and orchestrated action of several enzymes, mostly glycosyltransferases (GTs). The organisation of such biosynthetic machinery determines the properties of the polysaccharide made: its size, substitution degree and pattern, translating into specific rheological behaviour, defining the polysaccharide function. The mechanism of synthesis is poorly understood; not only is very little known about the specificity of the GTs, but even less about their interaction or the identity of other types of proteins involved. Studies towards determining all the machinery components and their abundances are therefore of high importance. In order to obtain such insight we explored three different quantitative proteomic approaches. Firstly, the LOPIT technique led to the localisation of nearly 200 proteins in the Golgi apparatus, 79 of which have not been previously reported [1]. We found, unexpectedly, a number of novel putative GT families which will extend the base for understanding polysaccharide synthesis. Further analysis on multiple LOPIT experiments enabled an even greater list of Golgi residents, with confident assignment of over 500 proteins. This list can be further extended to nearly 1000 proteins by the addition of homologues, and thus possibly comprise the complete Golgi proteome and a finite list of GTs and other synthetic components. Secondly, the label-free approach (MS e and IMS-MS e) allowed ranking of the Golgi proteins by their abundances along three orders of magnitude, led to novel hypotheses on polysaccharide synthesis. Lastly, a targeted absolute quantitation method (SRM) was employed for precise measurement of the abundances of the xylan synthetic enzymes and their stoichiometry. These different proteomics techniques led to a fuller insight into the Golgi proteome composition and organisation, specifically into the control of xylan structure and function. [1] N. Nikolovski et al. (2012) Plant Physiol., 160, 1037-1051.