Figure 3.

Graphical representation of the density of expansin binding sites in the surface lamella of a plant cell wall. The image is an atomic force micrograph of a primary cell wall from onion scale, showing single cellulose microfibrils and microfibril bundles (arrows), decorated with red ellipses representing the density, but not the actual locations, of expansin binding sites in the surface lamella. This graphic was produced by transforming the binding isotherms of McQueen-Mason and Cosgrove (1995) into the maximum number of binding sites per µm of cellulose microfibril, assuming an 18-chain microfibril (Cosgrove, 2014). The density of microfibrils in the surface lamella was based on the AFM image. The image illustrates that expansins bind to limited sites on cellulose microfibrils. Micrograph adapted from Zhang et al. 2014, copyright Springer Verlag, used with permission.