Second-harmonic imaging of plant polysaccharides.

The application of second-harmonic generation (SHG) microscopy to plant materials has been neglected hitherto even though it would seem to have promise for identification and characterization of biologically and commercially important plant polysaccharides. We find that imaging of cellulose requires rather high laser powers, which are above optimal values for live cell imaging. Starch, however, is easily imaged by the technique at laser fluences compatible with extended cell viability. This also has useful applications in imaging plant-derived starchy food products. Lignin in plant cell walls shows a strong three-photon excited fluorescence, which may be enhanced by resonance effects.