David R. Corbin

Studies on the mode of action of cholesterol oxidase on insect midgut membranes

Cholesterol oxidase (EC 1.1.3.6.) is an insecticidal protein known to have potent activity against the boll weevil, milder activity against a number of lepidopteran species, and virtually no activity against other insects. Several factors that could explain its species-dependent differential activity were examined. We compared cholesterol concentrations and rates of cholesterol oxidation in the midgut membranes from larvae of boll weevil (Anthonomus grandis grandis Boheman), southern corn rootworm (Diabrotica undecimpunctata howardi Barber), tobacco budworm (Heliothis virescens Fabricius), and yellow mealworm (Tenebrio molitor Linnaeus). Results showed that cholesterol concentration alone could not account for the differences in insecticidal activity and that midgut brush-border membranes of all species tested were generally susceptible to oxidation by cholesterol oxidase in vitro. We also demonstrated that cholesterol oxidase stability in the midgut environment was similar for the species tested and thus could not account for the differential activity. However, comparison of the pH of the insect midgut fluids with the pH optimum of cholesterol oxidase indicated that the lower sensitivity of lepidopteran larvae to the enzyme may be partially due to the alkaline nature of their midgut environments. In some species, oxidation caused significant changes in the activities of brush-border membrane alkaline phosphatase, and these changes did correlate with the susceptibility of the insect to cholesterol oxidase. Arch. Insect Biochem. Physiol. 34:429–442, 1997.

Agrobacterium tumefaciens-mediated plant transformation systems

Abstract The use of Agrobacterium tumefaciens in plant transformation is central to the recent rapid progress in plant molecular biology. The number of transformed species continues to grow rapidly. Many plants, particularly monocotyledons and legumes, are still not easily transformed by Agrobacterium , but significant progress in understanding the mechanism of transformation may lead to more widespread application of Agrobacterium in this area.