Changes in nitrogen metabolism in sweet potato with black rot

Abstract

Metabolic changes in proteins and amino acids of sweet potato root tissue in response to infection by Ceratocystis fimbriata were studied by the methods of immunochemistry, electrophoresis in starch-gel, and chromatography on modified cellulose columns. Some soluble proteins increased in tissue adjacent to the infection site; others decreased. Of special interest was the finding of new antigens in cells adjacent to the area invaded by the fungus which could not be detected before infection or were markedly increased in concentration as a result of the adjacent infection. Those new antigens or proteins produced in response to infection were more concentrated in tissue of the resistant Sunnyside variety than in the susceptible Orange Little variety. Resistance in both American and Japanese varieties of sweet potatoes seems to be correlated with the ability of the variety to form such proteins following the initial infection. One such antigenic component that is produced near the diseased tissue was identified as a peroxidase. Another component was concentrated by the methods of protein purification from 35-to 87-fold; its nature and function are unclear. Microsomes, especially the 73 S unit, were increased following infection. Resistance in such plants may be correlated with the ability of the host tissues to alter their protein metabolism in response to the infecting agent, and to then form proteins which cannot be detected or can be found at low levels before the infection.