This proposal deals with the synthesis of 3-deoxyanthocyanidin phytoalexins in sorghum. It involves characterization of an enzyme suspected to be involved in deoxyanthocyanidin synthesis, determination of the timing of initiation of the synthetic pathway by analysis of pathway intermediates by 14C labeling, the appearance of mRNA specific to genes regulating phenylpropanoid and flavonoid synthesis, and comparison of juvenile and mature stages of plants to determine differences in their ability to express resistance. The phytoalexins are synthesized in a site specific manner within vesicle-like inclusions in cells that are under fungal attack. The deoxyanthocyanidins are both fungitoxic and phytotoxic and they accumulate specifically within the immediate area of the infection site at an exceptionally early time in the disease interaction. Three hours prior to the onset of accumulation there is a marked increase in the level of extractable chalcone synthase enzyme activity in the host tissue. As these compounds are phytotoxic they are themselves toxic to the cells that produce them. It is hypothesized that the synthesis of the phytoalexins occurs in a compartmentalized fashion that protects the host tissue from their toxic effects and in a manner that allows for their directed synthesis and release at the site of fungal perturbation. These studies will help to elucidate natural mechanisms of plant resistance to pests with important implications for agricultural applications.//
