Figure 6.

Comparison of in situ analyses of different enzymatic activities in Arabidopsis inflorescent stems using two different substrates. XXXG-β-Res substrate visualizes the xyloglucanase (XEH, EC 3.2.1.151) activity, whereas GG-β-Res substrate reveals cellulase (endoglucanase, EC 3.2.1.4; or cellobiohydrolase) and β-glucosidase activities (EC 3.2.1.21). A, The fluorescence signal from resorufin (yellow) is superimposed on the transmitted light signal to visualize the anatomy of the stem. The reaction product can be seen in secondary cell walls of xylem (x) and interfacscicular fibers (if). B, A sequence of fluorograms taken at successive time points during the incubation of fresh sections of stems with the substrates. Note that the release of resorufin by the enzymes present in the stem tissues is much slower in the case of xyloglucanases compared to cellulases/glucosidases. C, Control sections that were heated at 95°C to inactivate enzymatic activities prior to incubation with the substrates. Scale bar = 50 μm. It should be noted that XXXG-β-Res is not enzyme isoform specific, and thus may detect enzymes with XEH activity and pH optima distinct from TmNXG1, vide infra.