Evidence for the plant-specific intercellular transport of the Arabidopsiscopper chaperone CCH

Arabidopsis copper chaperone (CCH) belongs to a family of eukaryotic protei ns that participates in intracellular copper homeostasis by delivering this metal to the secretory pathway. In this work we show that the CCH protein is mainly located along the vascular bundles of senescing leaves and petiol es, as shown by tissue prints and immunohistochemical detection. CCH protei n also accumulates in stem sieve elements and is collected in phloem exudat es. Accordingly, Arabidopsis CCH is the only member of the metallochaperone family described to function intercellularly to date. Moreover, the CCH pr otein remains stable when plants are subjected to excess copper that causes a rapid and specific decrease in its mRNA. These facts point to a role for CCH in copper mobilization from decaying organs towards reproductive struc tures, as a result of metalloprotein breakdown.