A newly discovered structure where mouth-puckering compounds called tannins form inside plant cells. Plants from oak trees to corn make tannins, which discourage nibbling insects and reduce damage from UV light. Tannosomes are tiny organelles that arise in chloroplasts, structures that capture light energy. There, sacs of green pigment break into little spheres.
The chloroplast membrane creates a pocket around clusters of these spheres, and the pocket eventually breaks loose and shuttles to the cell’s large fluid-filled vacuole. During the shuttle ride, tannosomes earn their name by filling with tannins, researchers report in the Oct. 6 Annals of Botany. Learning how plants build tannins feeds the dream of tweaking flavor in wine, tea, chocolate or other tannin-containing pleasures.