Plasticity of the Tannosome Ontogenesis in the Tracheophyta

Abstract

The tannosome, an organelle producing condensed tannins in the chlorophyllous organs of the Tracheohyta, is formed from the unstacked granal thylakoids by pearling into tiny spheres [1]. Other variants of intraplastidial ontogenesis of the tannosomes were investigated in the Tracheophyta by transmission electron microscopy. The “pearl necklace” model consists in the formation of vaguely ellipsoidal loculi by inflation of the intrathylakoidal lumen in which emerge, bound to the inner face of the lumen, “pear necklace”-shaped suites of osmiophilic spheres (30 nm); once filled with tannins, these loculi can be described as giant tannosomes bound by a single thylakoidal membrane. In the “snail” model, the granal thylakoids whirl upon themselves while pearling tannosomes which remain, in the stroma, aggregated in vaguely spherical osmiophilic structures. While in the former model [1], numerous isolated tannosomes are packed in a shuttle, the aggregated tannosomes (“pearl necklace” and “snail” models) are ejected from the chloroplast by budding into shuttles.