Rapid changes in root HvPIP2;2 aquaporins abundance and ABA concentration are required to enhance root hydraulic conductivity and maintain leaf water potential in response to increased evaporative demand

Abstract

http://www.publish.csiro.au/nid/102.htm Functional Plant BiologyRapid changes in root HvPIP2;2 aquaporins abundance and ABA concentration are 1 required to enhance root hydraulic conductivity and maintain leaf water potential in 2 response to increased evaporative demand 3 4 Abstract. To address the involvement of abscisic acid (ABA) in regulating transpiration and root 14 hydraulic conductivity (Lp Root ) and their relative importance for maintaining leaf hydration, the 15 ABA-deficient barley mutant Az34 and its parental wild-type (WT) genotype (cv. Steptoe) were 16 grown in hydroponics and exposed to changes in atmospheric vapour pressure deficit (VPD) 17 imposed by air warming. WT plants were capable of maintaining leaf water potential (Ψ L ) that 18 was likely due to increased Lp Root enabling higher water flow from the roots, which increased in 19 response to air warming. The increased Lp Root and immunostaining for HvPIP2;2 aquaporins 20 correlated with increased root ABA content of WT plants when exposed to increased air 21 temperature. The failure of Az34 to maintain Ψ L during air warming may be due to lower Lp Root 22 than WT plants, and an inability to respond to changes in air temperature. The correlation 23 between root ABA content and Lp Root was further supported by increased root hydraulic 24 conductivity in both genotypes when treated with exogenous ABA (10 -5 M). Thus the ability of 25 the root system to rapidly regulate ABA levels (and thence aquaporin abundance and hydraulic 26 conductivity) seems important to maintain leaf hydration. 28Additional keywords: Hordeum vulgare L., absicisic acid, tissue hydration, water relations. 29 Page 2 of 24 http://www.publish.csiro.au/nid/102.htm Functional Plant Biology 54 lasting effects on plant hydraulic properties and aquaporin activity in maize (Parent et al. 2009) 55 and tomato (Thompson et al. 2007) plants. However, the role of ABA in regulating plant water 56 relations is likely to be most critical in response to abrupt step-changes in environmental 57 conditions. Thus we compared leaf water relations, AQPs abundance and ABA content and 58 localization in roots of the ABA deficient barley mutant (Az34) and its parental line cv. Steptoe 59in response to air heating (that increased evaporative demand). The goal of the work was to 60 check the ability of the root system to rapidly regulate ABA levels (and thence hydraulic 61 conductivity) and its importance to maintain leaf hydration. 63Material and Methods

Zinc treatment of hydroponically grown barley plants causes a reduction in root and cell hydraulic conductivity and isoform‐dependent decrease in aquaporin gene expression

“…HvPIP2;5 , but not HvPIP2;2, was one of the three PIP genes which was reduced in gene expression by high Zn in the present study. Veselov et al () observed for barley plants, which were exposed to an increased vapour pressure deficit and transpirational demand, that an increase in root Lp was accompanied by a large increase in protein level of HvPIP2;2, while protein levels of HvPIP2;1 and HvPIP2;5 did not change. Katsuhara et al () studied changes in root Lp and gene transcript and protein level of HvPIP2;1 during day/night and concluded that HvPIP2;1 plays a key role in the diurnal root water uptake and plant transpiration response of barley.…”

Role of Pea LTPs and Abscisic Acid in Salt-Stressed Roots

“…Five millimeter root segments were fixed for 12 h in a solution of 4% N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (Merck, Darmstadt, Germany) prepared in 0.1 M phosphate buffer (pH 7.2-7.4). Carbodiimide not only fixes proteins, but also conjugates ABA with tissue proteins [16,17]. Then, root tissues were placed in a mixture of 4% paraformaldehyde (Riedel de Haen, Seelze, Germany) and 0.1% glutaraldehyde (Sigma) for 12 h. After fixation, plant tissues were washed for 1 h in phosphate buffer and successively kept for 30 min in ethanol dilutions for their dehydration.…”

Potential involvement of root auxins in drought tolerance by modulating nocturnal and daytime water use in wheat

“…Such possibility is supported by findings of Kudoyarova et al . (2011) on durum wheat and Veselov et al . (2018) on barley, indicating that high VPD triggers leaf ABA export to the root to regulate root hydraulic conductivity, as a way to maintaining leaf hydration as increases.…”

“…Currently, there is evidence supporting the idea that whole-plant TR response to VPD involves an interaction between ‘local’ (i.e., leaf-based) and ‘non-local’ (root-based) mechanisms mobilizing long-distance hydraulic signals that involve a combination of root anatomical traits and a dynamic control over radial water flow mediated by aquaporins (Vandeleur et al ., 2014; Vadez, 2014; Maurel et al ., 2016; Sivasakthi et al ., 2017). However, other investigations point to a role played by a shoot-to-root hormonal signal, namely abscisic acid (ABA) in coordinating TR with root hydraulic conductivity in response to increasing VPD (Kudoyarova et al ., 2011; Veselov et al ., 2018).…”