The effect of aflatoxins on the electron transport chain of chloroplasts from Zea mays L. and Pisum sativum L.

The influence of aflatoxins B1, B2, G1, and G2 was studied on the electron transport chain (from water to methyl viologen) of freshly lysed chloroplasts from maize (Zea mays L.) and peas (Pisum sativum L.). A partially purified extract containing all four toxins was added to a chloroplast suspension. Basal, phosphorylating, and uncoupled electron transport were assessed immediately after its addition and 4 min later. In maize chloroplasts, all three types of electron transport were inhibited by the mixture. The inhibition did not increase with time. The basal electron transport of pea chloroplasts was inhibited very slightly (20%) by the aflatoxin mixture. Commercially purified aflatoxins B1, B2, G1, and G2 were tested individually. Only aflatoxins B1 and B2 showed effects on the chloroplasts of both species. With 16 microM/ml of aflatoxin B2 in the assay medium, the three kinds of electron transport were drastically inhibited both in maize (75%) and pea (60%) chloroplasts. Aflatoxin B1 showed no effect on maize chloroplasts; however, a slight increase (31%) was observed on the electron transport rate of pea chloroplasts. Differential response between electron transport rate in maize and pea could be related to the toxin's chemical structure, with a slight difference between molecules resulting in enormous differences in activity.