THE ROLE OF THIONINS IN PLANT-PROTECTION

Thionins are a group of small (5000 Da), sulfur-rich plant proteins fo und mainly in cereals and mistletoes. Their three-dimensional structur es are very compact and amphipathic, stabilized by three or four disul fide bridges. Thionins are usually basic and exert toxicity in various biological systems by destroying membranes, Thionins are synthesized as preproproteins and secreted into vacuoles, protein bodies, and the cell wall. Their antibacterial and antifungal activities point to a ro le as plant defense proteins. Support for this possible function comes particularly from work on the leaf thionins of barley, showing that t hese proteins can be induced by several stress factors. Infection of b arley with mildew, one of its most devastating pathogens, leads to an incorporation of leaf thionins into papillae in incompatible interacti ons. The possible role of thionins to enhance the resistance of crop p lants by genetic engineering is discussed.