GUS is used as a tag to address nuclear localization whereas GFP is more versatile. GFP is detectable directly in living cells, GUS is only detected indirectly by staining of fixed tissue which may lead to artifacts or may obscure problems with protein solubility. In this protocol, protein localization is routinely assayed after particle-mediated transient transformation of onion epidermal cells. With this method it can be determined rapidly whether a given fusion protein is active and....