The Effect of Naphthazarin on the Growth, Electrogenicity, Oxidative Stress, and Microtubule Array in Z. mays Coleoptile Cells Treated With IAA

Abstract

Naphthazarin (5,8-dihydroxy-1,4-naphthoquinone, DHNQ) is a naturally occurring 1,4-naphthoquinone derivative. In this study, we focused on elucidating the toxic effect of this secondary metabolite on the growth of plant cells. The dose–response curves that were obtained for the effects of DHNQ on endogenous and IAA-induced growth in maize coleoptile segments differ in shape; in the first case, it is linear, while in the presence of auxin it is bell-shaped with the maximum at 1 μM. It was found that DHNQ at almost all concentrations studied, when added to the incubation medium inhibited endogenous growth (excluding naphthazarin at 0.001 μM) as well as growth in the presence of IAA. Simultaneous measurements of the growth and external medium pH of coleoptile segments indicated that DHNQ diminished or eliminated proton extrusion at all of the concentrations that were used. Interestingly, the oxidative stress in maize coleoptile cells, which was measured as hydrogen peroxide (H2O2) production, catalase activity, redox activity and malondialdehyde (MDA) content, increased at the lower concentrations of DHNQ (<1 μM), thus suggesting a specific character of its action. It was also found that naphthazarin at concentration higher than 0.1 μM caused the depolarization of the membrane potential (Em). An analysis of the organization and anisotropy of the cortical microtubules showed that naphthazarin at all of the concentrations that were studied changed the IAA-induced transverse microtubule reorientation to an oblique reorientation. Our results indicate that naphthazarin diminished the growth of maize coleoptile cells by a broad spectrum of its toxic effects, thereby suggesting that naphthazarin might be a hypothetical component of new bioherbicides and biopesticides.

Some New Methodological and Conceptual Aspects of the “Acid Growth Theory” for the Auxin Action in Maize (Zea mays L.) Coleoptile Segments: Do Acid- and Auxin-Induced Rapid Growth Differ in Their Mechanisms?

“…To the best of our knowledge, the growth, medium pH and membrane potential have never been measured simultaneously. Generally, the characteristic IAA-induced changes in the membrane potential of the coleoptile cells that were observed here (the initial, transient depolarisation followed by the hyperpolarisation of the membrane) are in good agreement with other authors [ 22 , 23 , 24 , 25 , 42 , 57 , 58 ]. However, taking into account our experimental conditions (membrane potential was measured simultaneously with the growth and medium pH), it should be pointed out that these characteristic changes differed in their kinetics compared to those in the articles cited above.…”

Effects of Naphthazarin (DHNQ) Combined with Lawsone (NQ-2-OH) or 1,4-Naphthoquinone (NQ) on the Auxin-Induced Growth of Zea mays L. Coleoptile Segments

“…The organisation of the cortical microtubules was also analysed, and it was shown that naphthazarin changed the IAA-induced microtubule reorientation. These results suggest that naphthazarin decreased the growth of maize coleoptile cells via a broad spectrum of effects [44].…”

“…For the combination of naphthazarin with lawsone or 1,4-naphthoquinone, it should be pointed out that the inhibitory effect on the auxin-induced growth and proton extrusion of the maize coleoptile segments was stronger compared to the individual action of any of the naphthoquinones that were tested (see [38,44]). This synergetic effect was significantly more visible at a concentration of 1 nM, particularly when naphthazarin was combined with 1,4-naphthoquinone.…”

“…This process is crucial for the interaction of AUX/IAA with the SCF-TIR1 and its degradation [65,66,67,68]. Furthermore, it was found that secondary metabolites such as juglone and naphthazarin [44] exhibit a high level of toxicity by affecting the polymerisation of the cortical microtubules, which are involved in the elongation of plant cells [69,70,71].…”

Reorientation of Cortical Microtubule Arrays in the Hypocotyl of Arabidopsis thaliana Is Induced by the Cell Growth Process and Independent of Auxin Signaling

“…Formerly, Laskowki proposed that the longitudinal reorientation of microtubules follows growth rate decline, but that it must be triggered by factors distinct from the change of elongation rate [45]. More recently, the idea that a direct and rapid longitudinal reorientation of microtubules by auxin is part of the mechanism by which auxin inhibits growth (akin to Hypothesis A, recall Figure 1) has been a matter of debate [8,46,47]. Based on this recent discussion and on the findings presented here, we recognize that the reorientation of microtubules into longitudinal arrays is not likely to be a direct prerequisite for inhibition of root cell elongation by auxin.…”