Role of Auxin-Induced Reactive Oxygen Species in Root Gravitropism

Abstract

We report our studies on root gravitropism indicating that reactive oxygen species (ROS) may function as a downstream component in auxin-mediated signal transduction. A transient increase in the intracellular concentration of ROS in the convex endodermis resulted from either gravistimulation or unilateral application of auxin to vertical roots. Root bending was also brought about by unilateral application of ROS to vertical roots pretreated with the auxin transport inhibitor N-1-naphthylphthalamic acid. Furthermore, the scavenging of ROS by antioxidants (N-acetylcysteine, ascorbic acid, and Trolox) inhibited root gravitropism. These results indicate that the generation of ROS plays a role in root gravitropism.Since Cholodny (1926) and Went (1926) discovered that directional auxin transport occurs upon gravistimulation, the mechanism of auxin transport is well established. According to the mechanism, the gravitropic stimulation induces asymmetric auxin movement, and the localized auxin in turn causes gravitropic curvature (Young et al., 1990; Dolan, 1998; Rosen et al., 1999). These results indicate that auxin is indeed essential for gravitropism. Several lines of evidence suggest that the second messengers, Ca 2ϩ and inositol 1,4,5-triphosphate (IP 3 ), are involved in root gravitropism (Lee et al., 1983; Perera et al., 1999). However, the relationship between auxin and second messengers is still unknown.Although reactive oxygen species (ROS) such as superoxide anions and H 2 O 2 are generally considered to be toxic byproducts of respiration, recent evidence suggests that the production of ROS might be an integral component of intracellular signaling (Krieger-Brauer and Kather, 1992; Finkel, 1998; Rhee et al., 2000). In mammalian cells, a variety of extracellular stimuli have been shown to induce a transient increase in the intracellular concentration of ROS, and specific inhibition of the ROS generation results in a complete blockage of stimulus-dependent signaling (Sundaresan et al., 1995; Bae et al., 1997). Also, several lines of evidence suggest that ROS serve as signaling molecules in plants. It has been shown that ROS mediate systemic signal networks for plant defense (Chen et al

Phytotoxicity of multi-walled carbon nanotubes on red spinach (Amaranthus tricolor L) and the role of ascorbic acid as an antioxidant

“…6j-k) compared to control respectively. AsA is a membrane-permeable ROS scavenger [46] that 19 suppresses ROS accumulation in plants; AsA treatment protects roots from salt stress-induced tomato root death and associated oxidative damage and also inhibits ROS-dependent root gravitropism [47] and [48]. In our study, AsA treatment significantly suppressed the production of DAB polymerization (Fig.…”

Glutathione – linking cell proliferation to oxidative stress

“…The Arabidopsis genome has ten AtRboh genes (AtRbohA-AtRbohJ) that encode NADPH oxidases (59). The activity of NADPH oxidases is required for root growth and for root hair development (60).Auxininduced ROS production is mediated at least in part by the activation of RbohD (58,(60)(61)(62)(63) but RbohC is involved in the control of root hair tip growth(64), a process that also involves the transcriptional Mediator subunits, PFT1/MED25 by activating a subset of hydrogen peroxide-producing class III peroxidases (65). As discussed below, the regulated activities of both NADPH oxidases and peroxidases are required for the orchestration of root development.…”

ARL2, ARG1 and PIN3 define a gravity signal transduction pathway in root statocytes

“…Lateral redistribution of auxin in roots can be detected by following the movement of radio-labeled auxin (Young et al, 1990), or visualizing the expression of reporter genes driven by the auxin-responsive DR5 promoter Ottenschlä ger et al, 2003;Rashotte et al, 2001). Additionally, the auxin-dependent production of reactive oxygen species, as monitored by dihydro-rhodamine-123 fluorescence, can be detected asymmetrically along the lower flank of gravi-stimulated corn roots (Joo et al, 2001). The development of auxin asymmetry is thought to derive from redirection of auxin through the root tip toward the new lower flank of the root cap, followed by basipetal transport to the elongation zone (Blancaflor and Masson, 2003;Swarup et al, 2005).…”

“…Basipetal auxin transport may also be regulated by molecules affecting the activity, expression and subcellular localization of auxin transporters in the lateral cell files of the root (as reviewed by Muday and Rahman, 2007). In addition to auxin, other hormones or signaling molecules such as cytokinins (Aloni et al, 2004), reactive oxygen species (Joo et al, 2001), flavonoids and ethylene (Buer and Muday, 2004;Buer et al, 2006) may be involved in the growth response phase of gravitropism through control of differential elongation, either in parallel with auxin or as regulators of the auxin-mediated signaling pathway.…”