Radial and axial water transport in the sugar beet storage root

AMODEO GABRIELA, DORR RICARDO, VALLEJO AUGUSTO, SUTKA MOIRA, PARISI MARIO

JOURNAL OF EXPERIMENTAL BOTANY

Oxford University press

Lugar: Oxford; Año: 1999 vol. 50 p. 509 - 516

0022-0957

To evaluate the contribution of transcellular, apoplastic and symplastic pathways to water movements, horizontal (axial pathway) and vertical (radial pathway) sugar beet root (Beta vulgaris L.) slices were studied. Volume flows (Jv) were measured under hydrostatic and/or osmotic gradients, using a computer-based data-acquisition system. When tissues were tested under hydrostatic gradients (0.3 MPa.m-1) a much more important permeability was observed in the axial pathway, as compared with the radial one. Negative pressure gradients (tensions) were as effective as positive ones in order to induce a net water movement. After the establishment of a concentration gradient in the radial pathway (obtained by adding 300 M . m-3 mannitol to the employed solution) an osmotic flux, sensitive to HgCl2, was observed. The inhibitory effect of mercurial compounds was reverted by bmercaptoethanol while [14C] mannitol unidirectional fluxes were not affected by mercurial agents. In the axial pathway, the presence of a mannitol gradient did not developed a sustained osmotic flux. After an initial Jv in the expected direction, the Jv reverted and moved in the opposite one. It is concluded that, in the sugar beet root, water channels play a significant role in water transfers in the radial pathway. On the other side, water and solutes are transported by a hydrostatic gradient in the xylem vessels. In general, these results extend and adapt to a storage root the “composite transport model” first proposed by Steudle et al. (Plant Physiol. (1993) 103, 353-349).