Auxin response, but not its polar transport, plays a role in hydrotropism of Arabidopsis roots

Abstract

Plants are sessile in nature, and need to detect and respond to many environmental cues in order to regulate their growth and orientation. Indeed, plants sense numerous environmental cues and respond via appropriate tropisms, and it is widely accepted that auxin plays an important role in these responses. Recent analyses using Arabidopsis have emphasized the importance of polar auxin transport and differential auxin responses to gravitropism. Even so, the involvement of auxin in hydrotropism remains unclear. To clarify whether or not auxin is involved in the hydrotropic response, Arabidopsis seedlings were treated with inhibitors of auxin influx (3-chloro-4-hydroxyphenylacetic acid), efflux (1-naphthylphthalemic acid and 2,3,5-triiodobenzoic acid), and response (p-chlorophenoxyisobutylacetic acid), and their effects were examined on both hydrotropic and gravitropic responses. In agreement with previous reports, gravitropism was inhibited by all the chemicals tested. By contrast, only an inhibitor of the auxin response (p-chlorophenoxyisobutylacetic acid) reduced hydrotropism, whereas inhibitors for influx or efflux of auxin had no effect. These results suggest that auxin response, apart from its polar transport, plays a definite role in hydrotropic response, and will evoke a new concept for the auxin-mediated regulation of tropisms.

RICE SALT SENSITIVE3 Forms a Ternary Complex with JAZ and Class-C bHLH Factors and Regulates Jasmonate-Induced Gene Expression and Root Cell Elongation

“…The spatial distribution of roots, including primary and lateral roots, largely depends on environmental signals, such as water availability, gravity, and light, which are perceived by the root apex (Kiss et al, 2002(Kiss et al, , 2003Kobayashi et al 2007) and modulate regional cell elongation rates via mechanisms that involve auxins (Swarup et al, 2005;Kaneyasu et al, 2007).…”

GNOM-Mediated Vesicular Trafficking Plays an Essential Role in Hydrotropism of Arabidopsis Roots

“…On the other hand, our recent demonstration showed that polar auxin transport is not essential for root hydrotropism in Arabidopsis. Namely, Arabidopsis roots treated with inhibitors of auxin efflux, TIBA or NPA, showed normal hydrotropic response, while their gravitropic response was substantially reduced (Kaneyasu et al, 2007). Also, hydrotropic response of pin2/wav6-52 mutant roots in which polar auxin transport and gravitropism were altered, did not differ from that of wild-type roots (Takahashi et al, 2002).…”

“…Further complementation analyses were performed as described previously . Treatment with BFA was performed as previously described (Kaneyasu et al, 2007), with the exception that the stock solution of BFA (Sigma Chemicals) was prepared at a concentration of 1,0003 in dimethyl sulfoxide. As a control, an equivalent volume of dimethyl sulfoxide was added to the culture medium.…”

How amyloplasts, water deficit and root tropisms interact?

“…2A and B). An inhibitor of auxin response reduced hydrotropism, 12 and also inhibited auxin-dependent DR5::GUS expression. 15 However, a decrease of DR5::GUS in wt root tips was not an impediment for developing an hydrotropic response.…”

“…4 Furthermore, current pharmacological studies using inhibitors also indicated that both auxin influx and efflux are not required for hydrotropic response whereas auxin response is necessary for it. 12 These authors suggested a novel mechanism for auxin in root hydrotropism. Here, we analyzed whether asymmetric auxin distribution takes place across hydrotropicallystimulated roots using transgenic plants carrying a responsive auxin promoter (DR5) driving the expression of ß-glucuronidase (GUS) or green fluorescent protein (GFP) 13,14 in wt and nhr1 backgrounds.…”