Unsung and understudied: plastids involved in secondary growth.

Plastids represent the only subcellular compartment where aromatic amino acid precursors for lignin can be synthesized during secondary growth in vascular plants. Despite this, aside from a general shared understanding that plastid-localized metabolism occurs during secondary growth, virtually no research has been performed on understanding their biology. Of particular importance will be insight into their ontogeny, morphology and ultrastructure, and (given the complex cytonuclear communication required) their nuclear-encoded and organellar-encoded regulation. Updating and integrating this knowledge will contribute to our fundamental understanding of a ubiquitous developmental process in vascular plants, and a major terrestrial carbon sink, as well as carbon-related plant biotechnology. Given available evidence, we propose a new name for a distinct plastid derivative-the 'xyloplast', is required.