Plasma Membrane Aquaporins Play a Significant Role during Recovery from Water Deficit

Abstract

The role of plasma membrane aquaporins (PIPs) in water relations of Arabidopsis was studied by examining plants with reduced expression of PIP1 and PIP2 aquaporins, produced by crossing two different antisense lines. Compared with controls, the double antisense (dAS) plants had reduced amounts of PIP1 and PIP2 aquaporins, and the osmotic hydraulic conductivity of isolated root and leaf protoplasts was reduced 5-to 30-fold. The dAS plants had a 3-fold decrease in the root hydraulic conductivity expressed on a root dry mass basis, but a compensating 2.5-fold increase in the root to leaf dry mass ratio. The leaf hydraulic conductance expressed on a leaf area basis was similar for the dAS compared with the control plants. As a result, the hydraulic conductance of the whole plant was unchanged. Under sufficient and under water-deficient conditions, stomatal conductance, transpiration rate, plant hydraulic conductance, leaf water potential, osmotic pressure, and turgor pressure were similar for the dAS compared with the control plants. However, after 4 d of rewatering following 8 d of drying, the control plants recovered their hydraulic conductance and their transpiration rates faster than the dAS plants. Moreover, after rewatering, the leaf water potential was significantly higher for the control than for the dAS plants.From these results, we conclude that the PIPs play an important role in the recovery of Arabidopsis from the water-deficient condition.Water transport through cellular membranes is facilitated by aquaporins, proteins that form waterselective channels. The presence of aquaporins in a membrane can increase the osmotic hydraulic conductivity of the membrane (L P , meters per second per megapascal) by 10-to 20-fold (Preston et al., 1992). In plants, the physiological importance of aquaporins is currently mainly inferred from their widespread occurrence (Johansson et al., 2000) and the use of HgCl 2 , a nonspecific inhibitor (Tyerman et al., 2002). Aquaporins, which are found in almost all types of tissues (Maurel, 1997), have changed the way we think about plant water relations (Maurel and Chrispeels, 2001).Water movement through a living organ such as a root or a leaf can take an apoplastic route, which has a low resistance to flow, or a transcellular route, which has a higher resistance because water has to move through lipid bilayer membranes . Bulk water flow associated with the transpiration stream is mostly apoplastic, except in the root exo-and endodermis (Zimmermann et al., 2000) and in the leaf bundle sheath (Koroleva et al., 2002), where apoplastic barriers (Casparian band, suberin lamellae, and secondary cell wall thickening) restrict the apoplastic path. Other important processes such as cell enlargement, refilling of embolized vessels, and movement of guard cells and pulvini may require rapid transport of water across membranes. Furthermore, the considerable growth-associated water potential difference (0.1-0.3 MPa) found in most growing organs of herbaceous plants (e.g. Nonami and Boyer, 1...

Expression and functional analysis of the rice plasma-membrane intrinsic protein gene family

“…Different research groups reached different conclusions on the function of PIP proteins. It has previously been reported that OsPIP1-1 and OsPIP1-3 had ability to transport water in the Xenopus oocytes [30,32], but other studies showed that only PIP2 proteins showed a rapid water transport activity, whereas PIP1s had no or a low water transport activity in the Xenopus oocytes [28,39]. Our data indicated that the transgenic plants over-expressing OsPIP1-1 or Os-PIP2-2 showed high tolerance to mild salt stress ( Figure 6C and 6D), suggesting that OsPIP genes play important roles in regulating water homeostasis, and that both OsPIP1-1 and OsPIP2-2 could possibly have intrinsic water transport ability in planta, which needs to be further confirmed biochemically in vivo.…”

Members of the aquaporin family in the developing pea seed coat include representatives of the PIP, TIP, and NIP subfamilies

“…First, it may be noted that the amino acid residues predicted to border the selectivity filter are the same in PIP1 and PIP2 members (exemplified in Table 1 for PsPIP1-1 and PsPIP2-1). Secondly, recent studies in which the expression of PIP1 members was either impaired or enhanced have provided strong evidence that PIP1 members function in cellular and whole-plant water relations (Siefritz et al, 2002;Martre et al, 2002;Aharon et al, 2003).…”

Temperate forest trees and stands under severe drought: a review of ecophysiological responses, adaptation processes and long-term consequences

“…Diurnal changes in root hydraulic conductance have been ascribed to changes in plasmalemna or tonoplast aquaporins that act as water channels controlling water fluxes between cells [96,129]. At leaf level, irradiance dependence of K L was found to be also driven by aquaporins or hydrogel effect on extravascular (and/or vascular) tissues [145].…”