A protein found in large amounts in the sap-conducting sieve elements of phloem tissue in plants. It takes various forms in the mature sieve element, depending on plant species, ranging from a network of filaments to discrete crystalline bodies. One general property is its ability to form a gel, and it functions as a puncture repair substance, forming a plug at any site of damage in the sieve element, thus preventing loss of food materials being translocated by the phloem. In an intact functioning sieve element, the P-protein is mainly found lining the interior wall.
Subjects: Biological Sciences — Chemistry.