Water-soluble and chlorophyll-binding protein that probably does not function as a chloroplast chlorophyll carrier and is not involved in photosynthesis (PubMed:11577184, PubMed:26160583). Involved in the control of cell death in the transmitting tract and septum epidermis during flower development. Binds and inhibits the activity of the cysteine protease RD21A as a pro-death protein (PubMed:26160583). May play a role in herbivore resistance activation during seedling greening (PubMed:26016527). Interacts with RD21A (PubMed:26160583, PubMed:26016527). Interacts with RD21B and RD21C (PubMed:26160583). Targeted to ER bodies. Expressed in vascular bundles of the carpels, the transmitting tract of the style and septum epidermis (PubMed:26160583). Expressed in etiolated seedlings (PubMed:26016527). During flower development, expressed in the transmitting tract of the septum from stage 12 to stage 15. No visible phenotype under normal growth conditions. Belongs to the protease inhibitor I3 (leguminous Kunitz-type inhibitor) family.