Uptake of 3-o-Methylglucose by Healthy and Hypomyces-infected Squash Hypocotyls

Rates of uptake of 3-o-methylglucose (MeG) by squash (Cucurbita maxima) hypocotyl sections from above lesions caused by Hypomyces solani f. sp. cucurbitae, race 1, are 2-fold greater than uptake by comparable tissues from healthy plants. Kinetic analyses indicate (i) that a single (constitutive) carrier system, with a Michaelis constant (Km) of 25 to 30 mm, mediates the transport of MeG into healthy hypocotyl cells and (ii) that an additional (inducible) system with a much lower Km (ca. 2 mm) is present in diseased hypocotyls. In both systems MeG uptake is inhibited competitively by glucose. The inducible transport system (s) in diseased tissues has a higher temperature coefficient, greater sensitivity to metabolic inhibitors and larger accumulation capacity than the one in healthy plants. While the nature of the constitutive system is ambiguous, the inducible carrier mechanism is a typical active transport system. These results indicate that increased rates of uptake and accumulation of metabolites by diseased tissues can be caused by new transport systems.