Oxidation of NADH by intact segments of soybean hypocotyls and stimulation by 2,4-D.

Intact sections of soybean cut from regions of cell elongation of hypocotyls of etiolated soybean seedlings oxidized externally supplied NADH (NADH is an impermeant substrate). The oxidation of NADH by 1-cm intact sections was stimulated by the plant growth factor 2,4-dichlorophenoxyacetic acid (2,4-D). The optimum concentration of 2,4-D for stimulation was about 1 microM. Stimulations also were given by the naturally occurring 2,4-D analog, indole-3-acetic acid (IAA), but not by the growth inactive 2,4-D analog 2,3-dichlorophenoxyacetic acid (2,3-D). The findings confirm studies comparing inside-out and right side-out vesicles that show the 2,4-D-stimulated NADH oxidase to be located at the external cell surface. Since plant cells are unlikely to encounter NADH at their external cell surface, functions of the oxidase in reactions other than oxidation of NADH are discussed.