Cell-to-cell pathway dominates xylem-epidermis hydraulic connection in<Emphasis Type="Italic"> Tradescantia fluminensis</Emphasis>
(Vell. Conc.) leaves |
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Authors: | Qing Ye N Michele Holbrook Maciej A Zwieniecki |
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Institution: | (1) Arnold Arboretum, Harvard University, 16 Divinity Ave, Cambridge, MA 02138, USA;(2) Organismic and Evolutionary Biology, Harvard University, 16 Divinity Ave, Cambridge, MA 02138, USA |
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Abstract: | A steady supply of water is indispensable for leaves to fulfil their photosynthetic function. Understanding water movement
in leaves, especially factors that regulate the movement of water flux from xylem to epidermis, requires that the nature of
the transport pathway be elucidated. To determine the hydraulic linkage between xylem and epidermis, epidermal cell turgor
pressure (P
t) in leaves of Tradescantia fluminensis was monitored using a cell pressure probe in response to a 0.2 MPa step change in xylem pressure applied at the leaf petiole.
Halftime of P
t changes
were 10–30 times greater than that of water exchange across an individual cell membrane suggesting that cell-to-cell water transport constitutes a significant part of the leaf hydraulic path from xylem to epidermis.
Furthermore, perfusion of H2O2 resulted in increases of both and by a factor of 2.5, indicating that aquaporins may play a role in the xylem to epidermis hydraulic link. The halftime for
water exchange did not differ significantly between cells located at the leaf base (2.5 s), middle (2.6 s) and tip (2.5 s), indicating that
epidermal cell hydraulic properties are similar along the length of the leaf. Following the pressure application to the xylem
(0.2 MPa), P
t 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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Keywords: | Aquaporins Epidermis Leaf hydraulics Porous vein Pressure probe Xylem |
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