Storage of defense metabolites in the leaves of Myrtaceae: news of the eggs in different baskets

This issue of Tree Physiology presents a surprising finding of specialization of within-leaf secondary compound storage and synthesis in eucalypts by Goodger et al. (2018). The following commentary first tackles the general issue of why plants need storage structures for secondary metabolites, then discusses the evidence of within-leaf specialization of storage of different secondary chemicals, and ultimately addresses the implications of metabolically completely different secretory structures within the eucalypt leaves discovered by Goodger et al. (2018). While metabolic specialization in surface storage structures, in different types of glandular trichomes, is well recognized, much less is known of variation in within-leaf storage structures and the new methodology for isolation of intact secretory cavities developed by Goodger et al. (2018) opens up new vistas to start resolving spatial, temporal and genetic controls on secondary metabolism in species having storage structures embedded within the leaf mesophyll.