A gene encoding a major Kunitz proteinase inhibitor of storage organs of winged bean is also expressed in the phloem of stems.

Winged bean Kunitz chymotrypsin inhibitor (WCI) accumulates abundantly in seeds and tuberous roots, and small amounts of the WCI protein and mRNA can also be detected in stems. In this study, we analyzed the localization of the WCI protein in stems of winged bean. The results demonstrated that the WCI protein was localized in sieve tubes. Furthermore, we showed that the 5' region of the WCI-3b gene, which exhibited strong transcriptional activity in developing seeds, also promoted transcription of a reporter gene in the phloem of stems of transgenic tobacco.