Pattern of Carbohydrate Breakdown in Sweet Potato Roots Infected With Ceratocystis fimbriata

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Abstract
Experiments using glucose-1-C14 and -6-C14 indicated that the catabolism of glucose was enhanced even by cutting, and that catabolism was presumably mediated chiefly by the pentose phosphate pathway. A much greater alteration was induced in the infected root tissue and increase in glucose catabolism was observed throughout the infection period. In the initial stage of infection the pattern seemed to be similar to that of the cut root tissue, that is, the pentose phosphate pathway contributed predominantly. But a rather marked change occurred in the later stage when an increase in the relative contribution of the glycolytic-TCA pathway was indicated as evidenced by a larger C6/C1 ratio. Experiments using specifically labelled acetate showed that as infection developed, acetate breakdown via TCA cycle was greatly promoted. The addition of ipomeamarone to diseased tissue at an early infection stage (24 hours) gave C6/C1 and C2/C1 ratio apparently identical to those at the later infection stage. Thus, the alteration of the metabolic pathway appeared to be partly due to the uncoupling action of ipomeamarone in the tissue adjacent to the infected region. However, from a previous analytical study on ipomeamarone synthesis this seems to be a more plausible explanation for a susceptible variety. In the inner healthy root tissue adjacent to the infected region of a resistant variety, the metabolic alteration is believed to be occurring independent of ipomeamarone action.