SUPEROXIDE, HYDROGEN-PEROXIDE, AND THE RESPIRATORY BURST OF FUNGALLY INFECTED-PLANT CELLS

The principal route of oxygen utilization in the respiratory burst of fungally infected plants was determined from stoichiometries of the up take and electronic reduction of oxygen in cotton cells exposed to Asp ergillus flavus walls. Using 2,2'-azino-di-(3-ethyl-benzothiazoline-6- sulfonic acid) and epinephrine as redox reagents to manipulate oxygen transitions, we found that oxygen consumption doubled when superoxide disproportionation was abolished and was abolished when disproportiona tion doubled. Of four possible pathways for oxygen consumption, only m onovalent reduction of molecular oxygen to superoxide was consistent w ith this inversely proportional relationship. According to the observe d rate of oxygen consumption in this pathway and in the absence of com petition to disproportionation of superoxide, infected cells are capab le of generating intracellular concentrations of 1 M hydrogen peroxide in 13 min.