Hydrotropic Response and Expression Pattern of Auxin-Inducible Gene, CS-IAA1, in the Primary Roots of Clinorotated Cucumber Seedlings

Abstract

;Primary roots of cucumber seedlings showed positive hydrotropism when exposed to a moisture gradient and rotated on a two-axis clinostat. To examine the role of auxin in the differential growth of the hydrotropically responding roots, we first examined the expression of auxin-inducible genes, CS-AUX/IAAs, in cucumber roots. After auxin starvation, mRNA levels of CS-IAA1 and CS-IAA3 decreased in the roots. Applying auxin to the auxin-starved roots resulted in accumulation of CS-IAA1 and CS-IAA3 mRNA. The level of expression of these genes increased when the auxin concentration was increased. CS-IAA1 mRNA accumulated in response to 10 -8 M auxin, and the level increased further, depending on the dose. Auxin starvation did not result in a decrease in the level of CS-IAA2 mRNA; however, adding exogenous auxin at concentrations higher than 10 -7 M increased its accumulation. In the primary roots responding hydrotropically or gravitropically, CS-IAA1 expression was greater on the concave side of the curving roots than on the convex side. The difference could be detected 30 min following stimulation by gravity or a moisture gradient, and that difference increased with time. These results support the idea that asymmetry of localization of auxin is associated with differential growth in hydrotropically responding roots.

Plant Gravitropism. Unraveling the Ups and Downs of a Complex Process

“…Studies on the mechanisms underlying root hydrotropism have lagged behind those on gravitropism because of the influence that gravity, which is continuously present, has on the direction of root growth. To circumvent this problem, investigators have employed mutants that do not respond to gravity or clinostats that randomize the plant's orientation within the gravity field (Mizuno et al, 2002;Takahashi et al, 2002Takahashi et al, , 2003 to show that hydrotropism and gravitropism share some transducing steps, whereas other steps are pathway specific. For example, the expression pattern of an auxininducible gene in hydrotropically stimulated cucumber (Cucumis sativus) roots grown on a clinostat was similar to its expression pattern in gravistimulated roots (Mizuno et al, 2002).…”

Possible Involvement of CS-ACS1 and Ethylene in Auxin-induced Peg Formation of Cucumber Seedlings

“…Northern blot analysis was carried out according to Mizuno et al (2002). A CS-ACS1 cDNA fragment (corresponds to nucleotides 379-979 of GenBank accession number AB006805) was inserted into plasmid pGEM-T vector and was used to make probes .…”

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

“…However, investigators paid little attention to this phenomenon for much of the last century, due to the difficulty of separating hydrotropism from gravitropism; it was not until 1985 that Jaffe et al demonstrated a hydrotropic response, using an agravitropic pea mutant. Since that time, the roots of agravitropic mutant or of clinorotated seedlings have enabled hydrotropism to be separated from gravitropism in pea and cucumber (Jaffe et al, 1985;Takahashi and Suge, 1991;Takahashi et al, 1996;Mizuno et al, 2002). The results gained from these experimental systems suggest that gravitropism interferes with hydrotropism in these species.…”