Aquaporin-facilitated water uptake in barley (Hordeum vulgare L.) roots

It is not known to what degree aquaporin-facilitated water uptake differs between root developmental regions and types of root. The aim of this study was to measure aquaporin-dependent water flow in the main types of root and root developmental regions of 14- to 17-d-old barley plants and to identify candidate aquaporins which mediate this flow. Water flow at root level was related to flow at cell and plant level. Plants were grown hydroponically. Hydraulic conductivity of cells and roots was determined with a pressure probe and through exudation, respectively, and whole-plant water flow (transpiration) determined gravimetrically in response to the commonly used aquaporin inhibitor HgCl2. Expression of aquaporins was analysed by real-time PCR and in situ hybridization. Hydraulic conductivity of cortical cells in seminal roots was largest in lateral roots; it was smallest in the fully mature zone and intermediate in the not fully mature ‘transition’ zone along the main root axis. Adventitious roots displayed an even higher (3- to 4-fold) cortical cell hydraulic conductivity in the transition zone. This coincided with 3- to 4-fold higher expression of three aquaporins (HvPIP2;2, HvPIP2;5, HvTIP1:1). These were expressed (also) in cortical tissue. The largest inhibition of water flow (83–95%) in response to HgCl2 was observed in cortical cells. Water flow through roots and plants was reduced less (40–74%). It is concluded that aquaporins contribute substantially to root water uptake in 14- to 17-d-old barley plants. Most water uptake occurs through lateral roots. HvPIP2;5, HvPIP2;2, and HvTIP1;1 are prime candidates to mediate water flow in cortical tissue

Aquaporines tonoplastiques chez Arabidopsis (expression tissulaire, localisation intracellulaire et mutants d'expression)

Les aquaporines constituent une superfamille de canaux facilitant la diffusion d'eau et de petits solutés au travers des membranes biologiques. Les protéines intrinsèques du tonoplaste (TIP) représentent une sous-famille d'aquaporines dont la localisation prouvée, ou supposée, est le tonoplaste. Dix gènes TIP sont présents dans le génome d'Arabidopsis thaliana. Le patron d'expression racinaire des TIP d Arabidopsis et leur localisation intracellulaire ont été étudiés à l aide de fusions avec la GFP. Huit isoformes sont exprimées dans la racine où toutes, sauf une, sont intégrées au tonoplaste. L isoforme AtTIP1;1 est notamment abondante dans les zones de contact entre tonoplastes de vacuoles adjacentes. Les AtTIP ne sont pas exprimées dans le méristème racinaire ce qui indique qu elles ne participent pas aux étapes précoces de la biogenèse des vacuoles. Elles sont fortement exprimées dans la zone pilifère ce qui suggère leur implication dans le transport radial d eau et de petits solutés par la voie transcellulaire. Des mutants knockout pour les isoformes les plus exprimées ont été caractérisés. Ils ne présentent pas d altérations phénotypiques dans des conditions optimales de culture. Les AtTIP ne sont donc pas, à titre individuel, indispensables au développement et à la physiologie d Arabidopsis. Ces protéines agissent probablement de façon redondante pour faciliter les flux d eau et de solutés au travers du tonoplaste. Cependant, lorsque qu un mutant AtTIP1;1 est cultivé en présence de glycérol, un phénotype racinaire est observé. Ce résultat indique que cette isoforme pourrait être impliquée dans le transport du glycérol au travers du tonoplaste.Aquaporins constitute a superfamily of channel proteins that facilitate the transport of water and small solutes across biological membranes. Tonoplast intrinsic proteins (TIPs) represent a subfamily of aquaporins which are named in accordance with their proven or putative subcellular localization, i.e. the tonoplast. Ten TIP genes are found in the genome of Arabidopsis thaliana. The root expression pattern and intracellular localization of Arabidopsis TIPs were characterized using AtTIP:GFP fusions. Eigth AtTIPs are expressed in the root. All but one are targeted to the tonoplast and the AtTIP1;1 isoform was shown to be concentrated in contact zones of tonoplasts from adjacent vacuoles. AtTIPs are not expressed in meristem cells indicating that they are not needed for the early stages of vacuole biogenesis that occur in these cells. However, AtTIPs are strongly expressed in all cell types of the maturation zone. This result suggests that AtTIPs contribute to radial water and solute transport in the root through the transcellular pathway. Knockout mutants for the highly-expressed isoforms were characterized. No phenotypic alteration was found under optimal growth conditions indicating that AtTIPs are not individually essential for Arabidopsis physiology and development, and that members of the TIP subfamily may act redundantly to facilitate water and solute flow across the tonoplast. However, a conditional root phenotype was observed when an AtTIP1;1 mutant was grown on a glycerol-containing medium suggesting that this isoform may contribute to glycerol transport across the tonoplast.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

Simulating bathymetric changes in reservoirs due to sedimentation

Currently sedimentation is one of the major issues to deal with, for professionals, as it causes continuous loss of storage and hinder the intended purposes of a dam. More research and case-specific studies are required to understand the behavior of sediment transport mechanism in order to propose remedial measures. Sakuma dam on Tenryu River in Japan is one of the largest dams in Japan and it is rapidly losing its storage capacity due to sedimentation. The dam started its operations in 1957. To study the bathymetric changes upstream of the dam, a mathematical modeling approach was selected using HEC RAS to simulate the existing changes and predict future trends. Before going into the detailed modeling, a literature review has been made about different sediment-related studies on the river and Sakuma dam to get deeper insight and to build a conceptual model. Then a reach of about 32 km of Tenryu River, from Hiraoka dam to Sakuma dam was modeled. Google Earth and AutoCAD were used to extract the geometrical data of Tenryu River to be used as input in HEC-RAS. Other data about flow and sedimentation were obtained from the Department of Civil Engineering, University of Tokyo. As necessary, simplifications and assumptions were also made, and sometimes data was extracted indirectly. After initial data input, it was required to do calibration and validation of the model from 1957 to 2004, when the data were available. Once the model was validated, prediction of future bathymetric changes was also made through model simulation. For this prediction it was assumed that the existing flow data could be recycled. Predictive simulation shows that the dam would probably not serve its intended purpose after year 2035 ± 5. Therefore it is recommended to employ some suitable remedial measures to remove sediment and to prevent loss of storage in order to increase the useful age of the dam. Some prospective study options are also identified at the end

Assessment of the requirement for aquaporins in the thylakoid membrane of plant chloroplasts to sustain photosynthetic water oxidation

International audienc

Identification of tonoplast aquaporins in chloroplast membranes with role in photosynthesis

International audienc

Mapping of tonoplast intrinsic proteins in maturing and germinating Arabidopsis seeds reveals dual localization of embryonic TIPs to the tonoplast and plasma membrane

We have mapped the expression of the tonoplast intrinsic protein (TIP) gene family members in Arabidopsis seeds by fluorescent protein tagging of their genomic sequences and confocal microscopy. Three isoforms (TIP1;1, TIP2;1, and TIP2;2) have distinct patterns of expression in maternal tissues (outer integument and placento-chalazal region). Two isoforms, TIP3;1 and the previously uncharacterized TIP3;2, are the only detectable TIPs in embryos during seed maturation and the early stages of seed germination. Throughout these developmental stages, both isoforms co-locate to the tonoplast of the protein storage vacuoles, but also appear to label the plasma membrane. Plasma membrane labeling is specific to TIP3;1 and TIP3;2, is independent of the position of the fluorescent protein tag, and appears to be specific to early seed maturation and early germination stages. We discuss these results in the context of the predicted distribution of aquaporins in Arabidopsis seeds

Plastids of Marine Phytoplankton Produce Bioactive Pigments and Lipids

International audienc

Tonoplast intrinsic proteins and vacuolar identity

TIPs (tonoplast intrinsic proteins) have been traditionally used as markers for vacuolar identity in a variety of plant species and tissues. In the present article, we review recent attempts to compile a detailed map of TIP expression in Arabidopsis, in order to understand vacuolar identity and distribution in this model species. We discuss the general applicability of these findings. We also review the issue of the intracellular targeting of TIPs and propose key emerging questions relative to the cell biology of this protein family

The Arabidopsis thylakoid transporter PHT4;1 influences phosphate availability for ATP synthesis and plant growth.

The Arabidopsis phosphate transporter PHT4;1 was previously localized to the chloroplast thylakoid membrane. Here we investigated the physiological consequences of the absence of PHT4;1 for photosynthesis and plant growth. In standard growth conditions, two independent Arabidopsis knockout mutant lines displayed significantly reduced leaf size and biomass but normal phosphorus content. When mutants were grown in high-phosphate conditions, the leaf phosphorus levels increased and the growth phenotype was suppressed. Photosynthetic measurements indicated that in the absence of PHT4;1 stromal phosphate was reduced to levels that limited ATP synthase activity. This resulted in reduced CO2 fixation and accumulation of soluble sugars, limiting plant growth. The mutants also displayed faster induction of non-photochemical quenching than the wild type, in line with the increased contribution of DeltapH to the proton-motive force across thylakoids. Small-angle neutron scattering showed a smaller lamellar repeat distance, whereas circular dichroism spectroscopy indicated a perturbed long-range order of photosystem II (PSII) complexes in the mutant thylakoids. The absence of PHT4;1 did not alter the PSII repair cycle, as indicated by wild-type levels of phosphorylation of PSII proteins, inactivation and D1 protein degradation. Interestingly, the expression of genes for several thylakoid proteins was downregulated in the mutants, but the relative levels of the corresponding proteins were either not affected or could not be discerned. Based on these data, we propose that PHT4;1 plays an important role in chloroplast phosphate compartmentation and ATP synthesis, which affect plant growth. It also maintains the ionic environment of thylakoids, which affects the macro-organization of complexes and induction of photoprotective mechanisms