Chemical hormesis in cell growth: a molecular target at the cell surface

Abstract

A multifunctional ubiquinol (NADH) oxidase with protein disulfide-thiol interchange activity of the cell surface, abbreviated as NOX, is described as a molecular target for chemical hormesis of cell growth. The activity of the NOX correlates with rate of cell enlargement, which helps to determine how rapidly cells will divide. When NOX activity is inhibited, cells fail to enlarge following division and the result is a population of small cells unable to reach the minimum size required for them to divide again. In plants, cells fail to enlarge when NOX activity is inhibited. When NOX activity is stimulated or constitutively activated, as in cancer, cells enlarge more rapidly and the rate of cell division also is enhanced. Both cell growth and NOX activity are sometimes stimulated by low concentrations of normally inhibitory molecules. These properties define chemical hormesis, making the NOX molecule a molecular target to explain hormetic growth responses and to utilize hormetic principles to increase, for example, crop yields with plants. The NOX activity at the cell surface oscillates with a temperature-compensated 24-min ultradian (<24 h) periodicity. The indicated function of the NOX protein as a time-keeping mechanism adds to its potential importance as a molecular target for chemical hormesis.

Herbicides can stimulate plant growth

“…Synthetic auxins are known to increase cell elongation in both roots and shoots, though at different concentrations (Cobb, 1992b), and have been used to study the mechanisms behind auxin‐induced hormesis (Allender et al. , 1997; Morré, 2000). The increased root:shoot ratio in MCPA‐treated plants indicate that both root and leaf MCPA exposure primarily stimulated root growth.…”

“…Only a few studies have tried to investigate the mechanisms behind the growth stimulation; for those that did, the results were largely inconclusive (Allender et al. , 1997; Morré, 2000; Appleby, 2001). Any sceptic could therefore, with good reason, claim that the biphasic dose–response curves reported in plant science are either a result of poorly growing controls or of trade‐offs between traits.…”

The Occurrence of Hormesis in Plants and Algae

“…Plants have hormones just as animals, and it is possible that some of the hormetic responses stem from induction of plant hormonal systems at low chemical concentrations. This is demonstrated by the synthetic auxins, which have shown to induce hormetic responses in several studies (Morré, 2000;Allender et al, 1997). If low doses of chemicals therefore stimulated the production or activity of natural auxins or other plant hormone systems (Weyers and Paterson, 2001), hormetic responses in some plant traits could be expected.…”

Improved empirical models describing hormesis

“…Evidence is accumulating that stimulatory responses to low levels of stress probably are the rule rather than the exception [1][2][3]. Stimulations have been shown for various population growth parameters, such as individual growth, longevity, and number of eggs produced in insects and crustacean [1,[4][5][6], but physiological and biochemical parameters, such as gene expression, enzyme activity, and tumor formation, have shown hormetic behavior as well [7][8][9][10]. Hormetic responses are found in all organisms, from animals and plants to microbiota.…”