AOBPreview originally published online on October 8, 2003
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Annals of Botany 92: 767-770, 2003
© 2003 Annals of Botany Company
Roots of Pisum sativum L. Exhibit Hydrotropism in Response to a Water Potential Gradient in Vermiculite
,11 Faculty of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan, 2 Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi 980-8577, Japan and 3 Faculty of International Agriculture and Food Studies, Tokyo University of Agriculture, Setagaya, Tokyo 156-8502, Japan
* For correspondence. Fax +81 (0)42 360 8830, e-mail hirasawa{at}cc.tuat.ac.jp Present address: National Agricultural Research Center for Hokkaido Region, Kasaigun, Hokkaido 082-0071, Japan
Received: 31 March 2003; Returned for revision: 3 June 2003; Accepted: 22 August 2003 Published electronically: 8 October 2003
In the present study, root hydrotropism in an agravitropic mutant of Pisum sativum L. grown in vermiculite with a steep water potential gradient was examined. When wet and dry vermiculite were placed side by side, water diffused from the wet (–0·04 MPa) to the dry (–1·2 MPa) and a steep water potential gradient became apparent in the dry vermiculite close to the boundary between the two. The extent and location of the gradient remained stable between the fourth and sixth day after filling a box with vermiculite, and the steepest gradient (approx. 0·02 MPa mm–1) was found in the initially dry vermiculite between 60 and 80 mm from the boundary. When seedlings with 25–35 mm long roots were planted in the initially dry vermiculite near where the gradient had been established, each of the main roots elongated toward the wet vermiculite, i.e. toward the high water potential. Control roots elongated without curvature in both the wet and the dry vermiculite, in which no water potential gradient was detectable. These results show that pea roots respond to the water potential gradient around them and elongate towards the higher water potential. Therefore, positive hydrotropism occurs in vermiculite just as it does in air. Hydrotropism in soil may be significant when a steep water potential gradient is apparent, such as when drip irrigation is applied.
Key words: Hydrotropism, pea, Pisum sativum L., root elongation, vermiculite.