Ye, Qing , Holbrook, Noel M. , Zwieniecki, Maciej A. .
The nature of the xylem-epidermis hydraulic connection in Tradescantia fluminensis (Vell. Conc.) leaves.
A steady supply of water is indispensable for leaves to fulfil their metabolic function as photosynthetic machines. Hence, understanding water movement in leaves, especially water flux from the xylem to the epidermis and the mechanisms that regulate this flux, is of crucial importance. Here the hydraulic linkage between xylem and epidermis, as well as the porous nature of the veins, were studied in Tradescantia fluminensis leaves. Using a cell pressure probe, we determined that the halftime for water exchange (Tm1/2) did not differ significantly between cells located at the leaf base (2.5s), middle (2.6s) and tip (2.5s), indicating that epidermal cell hydraulic properties are similar along the length of the leaf. To determine the hydraulic linkage between xylem and epidermis, epidermal cell turgor pressure (Pt) was monitored in response to a 0.2 MPa step change in xylem pressure applied at the leaf petiole. Halftimes of Pt changes (Tx1/2) were 10 to 30 times greater than cell membrane Tm1/2, suggesting that cell-to-cell water transport constitutes a significant part of the leaf hydraulic path from xylem to epidermis. Furthermore, perfusion of H2O2 prior to experiment resulted in increases of both Tm1/2 and Tx1/2 by a factor of 2.5, indicating that aquaporins may play a role in the xylem-to-epidermis hydraulic link. Following the pressure application (0.2 MPa), Pt changed by 0.12, 0.06 and 0.04 MPa for epidermal cells at the base, middle and the tip of the leaf, respectively. This suggests that pressure dissipation between xylem and epidermis is significant, and that the pressure drop along the vein may be due to its structural similarities to a porous pipe, an idea which was further supported by measurements of xylem hydraulic resistance using a perfusion technique.
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Direct measurements of cell turgor and cell membrane water permeability with intact plant cells - the cell pressure probe technique
1 - Harvard University, Organismic and Evolutionary Biology, 16 Divinity Ave., Cambridge, MA, 02138, USA
2 - Harvard University, Arnold Arboretum, 16 Divinity Ave., Cambridge, MA, 02138, USA
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM