Differential responses of grapevine rootstocks to water stress are associated with adjustments in fine root hydraulic physiology and suberization

Abstract

Water deficits are known to alter fine root structure and function, but little is known about how these responses contribute to differences in drought resistance across grapevine rootstocks. The ways in which water deficit affects root anatomical and physiological characteristics were studied in two grapevine rootstocks considered as low-medium (101-14Mgt) and highly (110R) drought resistant. Rootstocks were grown under prolonged and repeated drying cycles or frequent watering ('dry' and 'wet' treatments, respectively), and the following parameters were evaluated: root osmotic and hydrostatic hydraulic conductivity (Lp os and Lp hyd, respectively), suberization, steady-state root pressure (P rs), sap exudation rates, sap osmotic potential, and exosmotic relaxation curves. For both rootstocks, the 'dry' treatment reduced fine root Lp, elicited earlier root suberization and higher sap osmotic potential, and generated greater P rs after rewatering, but the rootstocks responded differently under these conditions. Lp os, Lp hyd, and sap exudation rates were significantly higher in 110R than in 101-14Mgt, regardless of moisture treatment. Under 'dry' conditions, 110R maintained a similar Lp os and decreased the Lp hyd by 36% compared with 'wet' conditions, while both parameters were decreased by at least 50% for 101-14Mgt under 'dry' conditions. Interestingly, build-up of P rs in 110R was 34% lower on average than in 101-14Mgt, suggesting differences in the development of suberized apoplastic barriers between the rootstocks as visualized by analysis of suberization from fluorescence microscopy. Consistent with this pattern, 110R exhibited the greatest exosmotic Lp os (i.e. Lp os of water flowing from roots to the soil) as determined from relaxation curves under wet conditions, where backflow may have limited its capacity to generate positive xylem pressure. The traits studied here can be used in combination to provide new insights needed for screening drought resistance across grapevine rootstocks.

Mechanical Failure of Fine Root Cortical Cells Initiates Plant Hydraulic Decline during Drought

“…The root system was carefully removed from the pot, and fine roots were excised under water at approximately 10 cm from the tip. Lp r was measured osmotically (Gambetta et al, 2012) to prevent the collapsing of potential air-spaces in the root tissue that may have formed under drought, as would be the case by pressuring the root to obtain a hydrostatic Lp r (Barrios-Masias et al, 2015). The proximal-open end of the root was connected to a glass microcapillary (0.25-mm i.d.…”

“…The resistance differential between radial and axial pathways persists or increases in magnitude as fine Lp r decreases under mild to moderate drought stress. While decreased fine root permeability under drought has been attributed to root shrinkage (Passioura, 1988;Nobel and Cui, 1992), changes in membrane permeability via aquaporins (Maurel et al, 2015;Aroca et al, 2012;North, 2004), development of suberized apoplastic barriers over longer periods of drought (Barrios-Masias et al, 2015;North and Nobel, 1991), or mechanical damage in cortical cells (i.e. lacunae formation; North and Nobel, 1991), the integration of these responses particularly under mild stress is still lacking.…”

Water uptake can occur through woody portions of roots and facilitates localized embolism repair in grapevine

“…The radial hydraulic properties of woody roots remain largely unknown, whereas hydraulics of nonwoody roots have been studied extensively (e.g. Steudle & Peterson, 1998;Knipfer & Fricke, 2011;Gambetta et al, 2012Gambetta et al, , 2013Barrios-Masias et al, 2015;Cuneo et al, 2016). In general, it is known that the hydraulic resistance per unit root length decreases toward the tip (Meyer & Ritchie, 1980), but it has been modeled that half of the water absorbed in Barley roots occurs in older suberized regions (Sanderson, 1983).…”

“…The rate of this transition varies across species, and can be impacted by abiotic and biotic factors. Deposition of suberin and lignin in the apoplast occurs as a normal developmental process in maturing roots, but this process can be hastened by drought stress and is partially responsible for reducing the permeability of these roots (see also Passioura, 1988;North & Nobel, 1991;Nobel & Cui, 1992;North, 2004;Ranathunge et al, 2004;Schreiber et al, 2005;Aroca et al, 2011;Gambetta et al, 2013;Barrios-Masias et al, 2015;Cuneo et al, 2016). During secondary growth, the activity of the vascular and cork cambium produces bark tissue that is composed of inner bark (i.e.…”

Grapevine adaptations to water stress: new perspectives about soil/plant interactions

“…Soil texture and structure have therefore a major role to play in the root system architecture and depth, regardless of the genotype (Barrios-Masias et al 2015). However in similar soil types both the scion and the rootstock genotypes were shown to have an impact on root development in grafted vines.…”