Pearl millet (Pennisetum glaucum) contrasting for the transpiration response to vapour pressure deficit also differ in their dependence on the symplastic and apoplastic water transport pathways

2018 ◽  
Vol 45 (7) ◽  
pp. 719 ◽  
Author(s):  
Murugesan Tharanya ◽  
Kaliamoorthy Sivasakthi ◽  
Gloria Barzana ◽  
Jana Kholová ◽  
Thiyagarajan Thirunalasundari ◽  
...  

Genotypic differences in transpiration rate responses to high vapour pressure deficit (VPD) was earlier reported. Here we tested the hypothesis that this limitation could relate to different degrees of dependence on the apoplastic (spaces between cells), and symplastic water transport pathways (through cells via aquaporin-facilitated transport), which are known to have different hydraulic conductivities. The low transpiration rate (Tr) genotype PRLT 2/89/33 either restricted its transpiration under high VPD, or was more sensitive to VPD than H77/833-2, when grown hydroponically or in soil. The slope of the transpiration response to an ascending series of VPD was lower in whole plants than in de-rooted shoots. In addition, the transpiration response of detached leaves to moderately high VPD (2.67 kPa), normalised against leaves exposed to constant VPD (1.27 kPa), was similar in low and high Tr genotypes. This suggested that roots hydraulics were a substantial limitation to water flow in pearl millet, especially under high VPD. The dependence on the apoplastic and symplastic water transport pathways was investigated by assessing the transpiration response of plants treated with inhibitors specific to the AQP-mediated symplastic pathway (AgNO3 and H2O2) and to the apoplastic pathway (precipitates of Cu(Fe(CN)6) or Cu(CuFe(CN)6)). When CuSO4 alone was used, Cu ions caused an inhibition of transpiration in both genotypes and more so in H77/833-2. The transpiration of high Tr H77/833-2 was decreased more by AQP inhibitors under low VPD (1.8 kPa) than in PRLT 2/89/33, whereas under high VPD (4.2 kPa), the transpiration of PRLT 2/89/33 was decreased more by AQP inhibitors than in H77/833-2. The transpiration rate of detached leaves from H77/833-2 when treated with AgNO3 decreased more than in PRLT 2/89/33. Although the root hydraulic conductivity of both genotypes was similar, it decreased more upon the application of a symplastic inhibitor in H77/833-2. The transpiration of low Tr PRLT 2/89/33 was decreased more by apoplastic inhibitors under both low and high VPD. Then the hydraulic conductivity decreased more upon the application of an apoplastic inhibitor in PRLT 2/89/33. In conclusion, both pathways contributed to water transport, and their contribution varied with environmental conditions and genotypes. Roots were a main source of hydraulic limitation in these genotypes of pearl millet, although a leaf limitation was not excluded. The similarity between genotypes in root hydraulic conductivity under normal conditions also suggests changes in this conductivity upon changes in the evaporative demand. The low Tr genotype depended more on the apoplastic pathway for water transport, whereas the high Tr genotype depended on both pathway, may be by ‘tuning-up’ the symplastic pathway under high transpiration demand, very likely via the involvement of aquaporins.

2020 ◽  
Author(s):  
Alexandre Grondin ◽  
Pablo Affortit ◽  
Christine Tranchant-Dubreuil ◽  
Carla de la Fuente Cantó ◽  
Cédric Mariac ◽  
...  

AbstractPearl millet is a key cereal for food security in arid and semi-arid regions but its yield is increasingly threatened by water stress. Physiological mechanisms consisting in saving water or increasing water use efficiency can alleviate that stress. Aquaporins (AQP) are water channels contributing to plant hydraulic balance that are supposedly involved in these mechanisms by mediating root water transport. However, AQP remain largely uncharacterized in pearl millet. Here, we studied AQP function in root water transport in two pearl millet lines contrasting for water use efficiency (WUE). We observed that these lines were also contrasting for root hydraulic conductivity (Lpr) and AQP contribution to Lpr, the line with lower WUE showing significantly higher AQP contribution to Lpr. To investigate the AQP isoforms contributing to Lpr, we developed genomic approaches to first identify the entire AQP family in pearl millet and second study the plasma membrane intrinsic proteins (PIP) gene expression profile. We identified and annotated 33 AQP genes in pearl millet among which ten encoded PIP isoforms. PgPIP1-3 and PgPIP1-4 were significantly more expressed in the line showing lower WUE, higher Lpr and higher AQP contribution to Lpr. Overall, our study suggests that AQP from the PIP1 family are the main contributor of Lpr in pearl millet and are possibly associated to whole plant water use mechanisms. This study paves the way for further investigations on AQP functions in pearl millet hydraulics and adaptation to environmental stresses.The newly sequenced nucleotide sequences reported in this article have been submitted to GenBank under the submission number 2333840 (TPA grp467567). Assignment of GenBank accession number is in process.


PLoS ONE ◽  
2020 ◽  
Vol 15 (10) ◽  
pp. e0233481
Author(s):  
Alexandre Grondin ◽  
Pablo Affortit ◽  
Christine Tranchant-Dubreuil ◽  
Carla de la Fuente-Cantó ◽  
Cédric Mariac ◽  
...  

2018 ◽  
Vol 45 (2) ◽  
pp. 143 ◽  
Author(s):  
Dmitry S. Veselov ◽  
Guzel V. Sharipova ◽  
Stanislav Yu. Veselov ◽  
Ian C. Dodd ◽  
Igor Ivanov ◽  
...  

To address the involvement of abscisic acid (ABA) in regulating transpiration and root hydraulic conductivity (LpRoot) and their relative importance for maintaining leaf hydration, the ABA-deficient barley mutant Az34 and its parental wild-type (WT) genotype (cv. Steptoe) were grown in hydroponics and exposed to changes in atmospheric vapour pressure deficit (VPD) imposed by air warming. WT plants were capable of maintaining leaf water potential (ψL) that was likely due to increased LpRoot enabling higher water flow from the roots, which increased in response to air warming. The increased LpRoot and immunostaining for HvPIP2;2 aquaporins (AQPs) correlated with increased root ABA content of WT plants when exposed to increased air temperature. The failure of Az34 to maintain ψL during air warming may be due to lower LpRoot than WT plants, and an inability to respond to changes in air temperature. The correlation between root ABA content and LpRoot was further supported by increased root hydraulic conductivity in both genotypes when treated with exogenous ABA (10−5 M). Thus the ability of the root system to rapidly regulate ABA levels (and thence aquaporin abundance and hydraulic conductivity) seems important to maintain leaf hydration.


1994 ◽  
Vol 345 (1312) ◽  
pp. 137-152 ◽  

The evolution of the stele was studied under the functional aspect of water transport problems by using a numerical approach. The underlying mathematical model describes the behaviour of a fluid-filled porous medium and is based on the coupling of Hooke’s law and Darcy’s law including a dynamic permeability approach which leads to a self-organization of the considered structure according to the resulting fluid- pressure field. Calculations dealing with two problems were performed. The essential demand of a water conducting system for a plant was demonstrated quantitatively. As soon as the plant shows an upright habit, the need for efficient water transport occurring through a highly porous apoplastic pathway becomes evident. In a second approach, the evolution of the protostele was simulated using the concept of dynamic permeability. The simulations of structures with self-regulating hydraulic conductivity yielded two strategies according to the pressure-permeability relationship. Increasing hydraulic conductivity with increasing negative fluid pressure results in peripheral layers of the conducting tissues, whereas the inverse pressure-permeability relationship yields a central position of the conducting tissues. The latter arrangement corresponds to the protostelar construction of early vascular plants.


Molecules ◽  
2020 ◽  
Vol 26 (1) ◽  
pp. 3
Author(s):  
Maite Olaetxea ◽  
Veronica Mora ◽  
Roberto Baigorri ◽  
Angel M. Zamarreño ◽  
Jose M. García-Mina

Some studies have reported that the capacity of humic substances to improve plant growth is dependent on their ability to increase root hydraulic conductivity. It was proposed that this effect is directly related to the structural conformation in solution of these substances. To study this hypothesis, the effects on root hydraulic conductivity and growth of cucumber plants of a sedimentary humic acid and two polymers—polyacrylic acid and polyethylene glycol—presenting a molecular conformation in water solution different from that of the humic acid have been studied. The results show that whereas the humic acid caused an increase in root hydraulic conductivity and plant growth, both the polyacrylic acid and the polyethylene glycol did not modify plant growth and caused a decrease in root hydraulic conductivity. These results can be explained by the different molecular conformation in water solution of the three molecular systems. The relationships between these biological effects and the molecular conformation of the three molecular systems in water solution are discussed.


1988 ◽  
Vol 109 (4) ◽  
pp. 465-471 ◽  
Author(s):  
C. P. ANDERSEN ◽  
A. H. MARKHART ◽  
R. K. DIXON ◽  
E. I. SUCOFF

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