Role of plasma membrane redox activities in elongation growth in plants

Abstract

Comparing isolated plasma membrane vesicles and excised hypocotyl segments from etiolated seedlings of soybean [Glycine max (L.) Merr. cv. Williams], certain antiproliferative agents that inhibited growth inhibited plasma membrane redox activities. Additionally, auxins that stimulated growth stimulated plasma membrane redox activities. Hormone stimulation was restricted to NADH oxidase (determined from disappearance of NADH) and was given both by isolated plasma membranes and by a soluhilizedenzyme preparation. Comparing IAA, the native auxin regulator, and 2,4‐D, a synthetic regulator, stimulation was observed, hut the dose‐response curves were different. Yet, the dose‐response relationships of both stimulation of auxin growth and stimulation of NADH oxidase were parallel. Inhibition of auxin‐induced growth by antiproliferative drugs was more complex. Some, like actinomycin D, preferentially inhibited NADH oxidase (EC 1.6.99.2) but inhibited NADH‐ferricya‐nide oxido‐reductase (EC 1.6.99.3) as well. Others, like adriamycin, inhibited primarily the NADH‐ferricyanide oxido‐reductase. Therefore, growth control by auxin appeared to involve NADH oxidase as a rate‐limiting terminal oxidase to link electron flow from NADH to oxygen. This observation may provide a fundamental difference from animal cells. With the latter, impermeant electron acceptors such as diferric transferrin or ferricyanide fulfill such a role. In plants, these impermeant electron acceptors were without effect on growth or were growth inhibitory.

The Hormone-responsive NADH Oxidase of the Plant Plasma Membrane Has Properties of a NADH:Protein Disulfide Reductase

“…Within the error of the determinations the 2,4-D-stimulated decrease in NADH accounts quantitatively for the auxin-stimulated disappearance of disulfides of membrane proteins and for a twoelectron transfer to account for appearance of thiols of membrane proteins (Table VI). DISCUSSION An NADH oxidative activity of unknown function has been observed in plasma membrane of soybeans as an activity with a 2,4-D-responsive component (1,2). A component of the basal activity was first thought to represent an NADH-ascorbate free radical oxidoreductase (13).…”

“…A logarithmic dependence on concentration of auxin was obtained. The optimum auxin concentrations of 1-10 M corresponded to the concentrations optimal for stimulation of NADH oxidation and of plant cell elongation (2).…”

“…The activity was unaffected by benzoic acid and the structurally related but inactive auxin analogs 2,3-dichlorophenoxyacetic acid (2,3-D) and ␤-naphthaleneacetic acid (␤-NAA) (2). Subsequently, the activity was correlated with plant cell elongation using thiol reagents as inhibitors of both auxin-induced cell elongation and the auxin-stimulated oxidation of NADH (3).…”