The Role of Plasma Membrane Intrinsic Protein Aquaporins in Water Transport through Roots: Diurnal and Drought Stress Responses Reveal Different Strategies between Isohydric and Anisohydric Cultivars of Grapevine  

Abstract

We report physiological and anatomical characteristics of water transport across roots grown in soil of two cultivars of grapevine (Vitis vinifera) differing in response to water stress (Grenache, isohydric; Chardonnay, anisohydric). Both cultivars have similar root hydraulic conductances (L o ; normalized to root dry weight) that change diurnally. There is a positive correlation between L o and transpiration. Under water stress, both cultivars have reduced minimum daily L o (predawn) attributed to the development of apoplastic barriers. Water-stressed and well-watered Chardonnay had the same diurnal change in amplitude of L o , while water-stressed Grenache showed a reduction in daily amplitude compared with well-watered plants. Hydraulic conductivity of root cortex cells (L pcell ) doubles in Chardonnay but remains unchanged in Grenache. Of the two most highly expressed plasma membrane intrinsic protein (PIP) aquaporins in roots (VvPIP1;1 and VvPIP2;2), only VvPIP2;2 functions as a water channel in Xenopus laevis oocytes. VvPIP1;1 interacts with VvPIP2;2 to induce 3-fold higher water permeability. These two aquaporins are colocated in the root from in situ hybridization and immunolocalization of VvPIP1 and VvPIP2 subfamily members. They occur in root tip, exodermis, root cortex (detected up to 30 mm), and stele. VvPIP2;2 mRNA does not change diurnally or with water stress, in contrast to VvPIP1;1, in which expression reflects the differences in L o and L pcell between cultivars in their responses to water stress and rewatering. VvPIP1;1 may regulate water transport across roots such that transpirational demand is matched by root water transport capacity. This occurs on a diurnal basis and in response to water stress that corresponds to the difference in drought tolerance between the cultivars. Root hydraulic conductance is usually lowest within the liquid component of the soil-plant-air continuum. The hydraulic conductance of roots can be highly variable in both time and space, which will affect soilwater extraction and shoot water status (Steudle and Peterson, 1998;Steudle, 2000aSteudle, , 2000b. Steudle (2000aSteudle ( , 2000b explains variation in root hydraulic conductivity (L p ; hydraulic conductance normalized to root surface area) in terms of the composite transport model based on the composite anatomical structure of roots, where water can move radially toward the xylem along three pathways: the apoplastic, symplastic, and transcellular. The symplastic and transcellular pathways are difficult to separate experimentally and are collectively considered as the cell-to-cell pathway (Steudle, 2000b). The extent to which water flow predominates in either pathway varies according to the relative hydraulic conductances of the pathways and the relative magnitude of hydrostatic versus osmotic gradients (Steudle, 2000a; Bramley et al., 2007b). Apoplastic flow can be altered irreversibly by anatomical changes, including Casparian bands and suberin lamellae (Steudle and Peterson, 1998). The conductance of the cell...

A Hydraulic Model Is Compatible with Rapid Changes in Leaf Elongation under Fluctuating Evaporative Demand and Soil Water Status

“…et al, 2013). The rapid phosphorylation events discussed above may also affect the plant hydraulic conductivity upon soil rehydration, although the latter tends to decrease rather than increase during water deficit (Vandeleur et al, 2009).…”

The Grapevine Root-Specific Aquaporin VvPIP2;4N Controls Root Hydraulic Conductance and Leaf Gas Exchange under Well-Watered Conditions But Not under Water Stress

“…1). Given that functional characterization of the VvPIP2;4 gene at the water transport ) and expression pattern (Vandeleur et al, 2009) levels was performed using GenBank accession EF364438, our gene represents a yet uncharacterized PIP2 from grapevine. To avoid confusion, we have used the name VvPIP2;4N for the gene we isolated from cv Nebbiolo.…”

“…Expression of some of these genes, belonging to the PIP and Tonoplast Intrinsic Protein subfamilies, has been studied in grape berry (Picaud et al, 2003;Fouquet et al, 2008;Choat et al, 2009) and vegetative tissues (Baiges et al, 2001;Vandeleur et al, 2009). The results of these studies suggest that aquaporins have important roles in facilitating water redistribution within the growing berry (Picaud et al, 2003;Fouquet et al, 2008;Choat et al, 2009) and in regulating adaptation to water stress (Vandeleur et al, 2009). However, these results, being based on correlations between the expression of aquaporin genes and morphological and physiological observations, lack reliable in vivo functional evidence.…”

“…species are well adapted to drought conditions and are thus expected to have developed efficient mechanisms to transfer water to their growing aerial organs and to limit negative effects of drought. Patterns of aquaporin expression and function are suspected to contribute significantly to this adaptation (Galmés et al, 2007;Vandeleur et al, 2009). Cultivated grapevine (Vitis vinifera) is traditionally a nonirrigated crop, and both yield and berry quality strongly depend on the vine adaptability to drought (for review of the molecular and physiological aspects of grapevine drought responses, see Lovisolo et al, 2010).…”

Rapid changes in root hydraulic conductivity and aquaporin expression in rice (Oryza sativaL.) in response to shoot removal – xylem tension as a possible signal

“…Water flow rate through AQPs, as an alternative signal regulating root AQP expression, could also explain diurnal changes in root AQP expression (e.g. Henzler et al, 1999;Lopez et al, 2003;Hachez et al, 2008;Vandeleur et al, 2009;Sakurai-Ishikawa et al, 2011). The question needs to be addressed of at which time scale protein levels of rice root AQPs change in response to shoot removal.…”