The tannosome: a new chloroplast-derived organelle

The tannosome: a new chloroplast-derived organelle
The tannosome: a new chloroplast-derived organelle

Condensed tannins (proanthocyanidins) are widely distributed amongst the vascular plants (Tracheophyta). Brillouet et al. use a variety of techniques to examine tannin-rich samples from various organs across a wide range of vascular plants and find that tannins are polymerized in a new thylakoid-derived chlorophyllous organelle, which they name the tannosome. These are formed by pearling of the thylakoids into 30-nm spheres, which are then encapsulated in a tannosome shuttle formed by budding from the chloroplast and bound by a membrane resulting from the fusion of both chloroplast envelopes. The shuttle conveys tannosomes through the cytoplasm to the vacuole, into which they are incorporated by invagination of the tonoplast. Finally, shuttles bound by a portion of tonoplast aggregate into tannin accretions, which are stored in the vacuole.