Plant Aquaporins by François Chaumont & Stephen D. Tyerman

Author:François Chaumont & Stephen D. Tyerman
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

1.1 Regulation of Plant Hydraulic Conductance

Water flow along the soil-plant-atmosphere continuum (SPAC) is driven by hydrostatic negative pressure. Generally, plant hydraulic conductance has two aspects: axial conductance and radial conductance. Axial conductance (from the roots to the leaves) is mainly determined by vascular anatomy (i.e., tracheid diameter, cell wall composition, pit structure, and the presence of embolisms) and does not involve membrane selectivity mechanisms. Radial conductance controls the rate at which water enters the roots (known as root hydraulic conductivity, LPr; reviewed by Maurel et al. 2010) and the radial water outflux through the leaf, i.e., from xylem vessels toward the evaporation sites on the mesophyll cell walls (known as leaf hydraulic conductance, K leaf) reviewed by (Sack and Holbrook 2006). In addition, parenchymatic cells, old (nonfunctional) xylem vessels, and apoplastic spaces along the length of the stem vascular system may serve as reservoirs of water, supporting the transpiration stream through the radial transfer of water to it.

Rapid and dynamic valve-like behavior has been observed for both K leaf (Cochard et al. 2007; Levin et al. 2007) and L Pr (Maggio and Joly 1995; Carvajal et al. 1996; Clarkson et al. 2000; Tournaire-Roux et al. 2003; Gorska et al. 2008; Bramley et al. 2010). Radial conductance responds rapidly to ambient signals. For example, reducing Arabidopsis root water potential to −0.8 MPa leads to a rapid reduction in leaf turgor [the signal transfer rate was higher than 40 cm/min; (Christmann et al. 2013)]. Another study revealed that the opposite direction signal (shoot to root) was also very rapid. In that study, grapevine shoot injury reduced root hydraulic conductance within a few minutes (Vandeleur et al. 2014). Other ambient signals (e.g., light, temperature) and internal signals such as the stress phytohormone abscisic acid (ABA) have also been shown to regulate plant hydraulic conductance (Sack and Holbrook 2006; Shatil-Cohen et al. 2011; Aroca et al. 2012; Pantin et al. 2013; Sade et al. 2015 b).

It has been suggested that the leaf bundle sheath (BS) and root endodermis (as well as other parenchymal cells surrounding the xylem) may act as hydraulic control centers in the regulation of K leaf and L Pr, respectively (Sack and Holbrook 2006; Shatil-Cohen et al. 2011; Shatil-Cohen and Moshelion 2012; Prado et al. 2013; Sade et al. 2014 c) (see also chapters “Aquaporins and Root Water Uptake” and “Aquaporins and Leaf Water Relations”). It was recently shown that Kleaf is dynamically controlled by the permeability of the membranes of BS cells to water, with the osmotic permeability coefficient (Pf) likely reflecting the regulated activity of AQPs in BS cells (Shatil-Cohen et al. 2011). The endodermis is a layer of root inner cortex cells that tightly encases the stele of vascular plants. Its hydrophobic Casparian strip (Steudle and Peterson 1998), which separates the stele from passive apoplastic diffusion (Moon et al. 1986; Alassimone et al. 2010), has a major effect on the radial transport of water and ions. Thus, the endodermis (together with other xylem-surrounding cells) represents the most critical boundary along the apoplastic route, markedly limiting plant radial water uptake (Alassimone et al.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.