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International audience; Aquaporins are transmembrane water channels found in almost every living organism. Numerous studies have brought a good understanding of both water transport through their pores and the regulations taking place at the molecular level, but subtleties remain to be clarified. Recently, a voltage‐related gating mechanism involving the conserved arginine of the channel’s main constriction was captured for human aquaporins through molecular dynamics studies. With a similar approach, we show that this voltage‐gating could be conserved among this family and that the underlying mechanism could explain part of plant AQPs diversity when contextualized to high ionic concentrations provoked by drought. Finally, we identified residues as adaptive traits which constitute good targets for drought resistance plant breeding research.

Major Intrinsic Proteins (MIP) are a family of channels facilitating the diffusion of water and/or small solutes across cellular membranes. X Intrinsic Proteins (XIP) form the least characterized MIP subfamily in vascular plants. XIPs are mostly impermeable to water but facilitate the diffusion of hydrogen peroxide, urea and boric acid when expressed in heterologous expression systems. However, their transport capabilities in planta and their impact on plant physiology are still unknown. Here, we demonstrated that overexpression of NtXIP1;1 in Nicotiana tabacum by the En2pPMA4 or the 35S CaMV promoter and in Arabidopsis, which does not contain any XIP gene, by the 35S CaMV promoter, resulted in boron (B)‐deficiency symptoms such as death of the shoot apical meristem, infertile flowers, and puckered leaves. Leaf B concentrations in symptomatic tissues and B xylem sap concentrations were lower in the overexpressors than in control plants. Importantly, expression of NtXIP1;1 under the control of the AtNIP5;1 promoter complemented the B deficiency phenotype of the Atnip5;1 knockout mutant, defining its ability to act as a boric acid channel in planta. Protein quantification analysis revealed that NtXIP1;1 was predominantly expressed in young B‐demanding tissues and induced under B‐deficient conditions. Our results strongly suggest that NtXIP1;1 plays a role in B homeostasis and its tissue‐specific expression critically contributes to the distribution of B within tobacco.

Leaf hydraulic conductance (Kleaf) and capacitance (Cleaf) are among the key parameters in plant-water regulation. Understanding the responses of these hydraulic traits to drought conditions remains a challenge for describing comprehensive plant-water relationships. The ability of an organism to resist and/or tolerate embolism events, which may occur at high negative pressure caused by hydric stress, relies on how well it can sustain a hydraulic system in a dynamic equilibrium. Populus deltoides is a water-saving tree species with a stomatal conductance that declines rapidly with reduced water availability. Under unfavorable conditions, the stomatal control of transpiration is known to be closely coordinated with a loss of plant hydraulic functioning that can ultimately result in hydraulic failure through xylem embolism, notably in leaves. The effects of drought on leaf hydraulics are also related to regulation in water permeases such as the aquaporins. To describe the responses linked to leaf hydraulics under severe drought and rewatering conditions, water-stressed poplars were monitored daily on an ecophysiological and a molecular scale. A structural and expression analysis on a set of aquaporins was carried out in parallel by in situ hybridization analysis and quantitative PCR. In complement, water distribution in water-challenged leaves was investigated using X-ray microtomography. A general depression of leaf hydraulic conductance and relative water content occurred under drought, but was reversed when plants were rewatered. More interestingly, (i) extreme leaf water deficiency led to marked xylem and lamina embolism, but a degree of hydric integrity in the midrib extraxylem territories and the bundle sheath of the minor veins was maintained, and (ii) the sub-tissue water allocation correlated well with an over-accumulation of several PIP and TIP aquaporins. Our multi-facet molecular ecophysiological approach revealed that leaves were able to secure a certain level of hydric status, in particular in cell territories near the “living ribs”, which provided rapid hydric adjustment responses once favorable conditions were restored. These findings contribute to an integrated approach to leaf hydraulics, thus favoring a better understanding of the cell mechanisms involved in tree vulnerability to climate changes.

In the global change scenario, increased CO 2 may favour water use efficiency (WUE) by plants. By contrast, in arid and semiarid areas, salinity may reduce water uptake from soils. However, an elevated WUE does not ensure a reduced water uptake and upon salinity this fact may constitute an advantage for plant tolerance. In this work, we aimed to determine the combined effects of enhanced [CO 2 ] and salinity on the plant water status, in relation to the regulation of PIP aquaporins, in the root and leaf tissues of broccoli plants ( Brassica oleracea L. var Italica), under these two environmental factors. Thus, different salinity concentrations (0, 60 and 90 mM NaCl) were applied under ambient (380 ppm) and elevated (800 ppm) [CO 2 ]. Under non-salinised conditions, stomatal conductance ( G s ) and transpiration rate ( E ) decreased with rising [CO 2 ] whereas water potential ( Ψ ω ) was maintained stable, which caused a reduction in the root hydraulic conductance ( L 0 ). In addition, PIP1 and PIP2 abundance in the roots was decreased compared to ambient [CO 2 ]. Under salinity, the greater stomatal closure observed at elevated [CO 2 ] – compared to that at ambient [CO 2 ] – caused a greater reduction in G s and E and allowed plants to maintain their water balance. In addition, a lower decrease in L 0 under salt stress was observed at elevated [CO 2 ], when comparing with the decrease at ambient [CO 2 ]. Modifications in PIP1 and PIP2 abundance or their functionality in the roots is discussed. In fact, an improved water status of the broccoli plants treated with 90 mM NaCl and elevated [CO 2 ], evidenced by a higher Ψ ω , was observed together with higher photosynthetic rate and water use efficiency. These factors conferred on the salinised broccoli plants greater leaf area and biomass at elevated [CO 2 ], in comparison with ambient [CO 2 ]. We can conclude that, under elevated [CO 2 ] and salt stress, the water flow is influenced by the tight control of the aquaporins in the roots and leaves of broccoli plants and that increased PIP1 and PIP2 abundance in these organs provides a mechanism of tolerance that maintains the plant water status.

Members of the Brassicaceae are known for their contents of nutrients and health-promoting phytochemicals, including glucosinolates. The concentrations of these chemopreventive compounds (glucosinolate-degradation products, the bioactive isothiocyanates) may be modified under salinity. In this work, the effect of the aliphatic glucosinolate sinigrin (2-propenyl-glucosinolate) on plant water balance, involving aquaporins, was explored under salt stress. For this purpose, water uptake and its transport through the plasma membrane were determined in plants after NaCl addition, when sinigrin was also supplied. We found higher hydraulic conductance (L0 ) and water permeability (Pf ) and increased abundance of PIP2 aquaporins after the direct administration of sinigrin, showing the ability of the roots to promote cellular water transport across the plasma membrane in spite of the stress conditions imposed. The higher content of the allyl-isothiocyanate and the absence of sinigrin in the plant tissues suggest that the isothiocyanate is related to water balance; in fact, a direct effect of this nitro-sulphate compound on water uptake is proposed. This work provides the first evidence that the addition of a glucosinolate can regulate aquaporins and water transport: this effect and the mechanism(s) involved merit further investigation.

Due to the high market demand for off-season vegetables and the limited availability of arable land, vegetable seedlings are cultivated under changing environmental conditions which may induce stress. These conditions include cold, wet or dry environments, low or high radiation, etc. In addition, marginal water quality successive cropping can increase salinity and the incidence of pests and soil-borne diseases. Grafting is a horticultural technology, practiced for many years and in many parts of the world, in order to overcome many of these problems. The use of grafted plants in vegetable crop production is still rare compared to the use of grafting in tree crops. However, this technique is now being expanded greatly and the use of rootstocks can enhance plant yield through vigorous attainment of soil nutrients, avoidance of infection by soil pathogens and tolerance of low soil temperatures, salinity and wet-soil conditions. This review focuses on the physiological and biochemical aspects of the rootstock-scion interaction for both Solanaceae and Cucurbitaceae species, considering the mechanisms involved in graft compatibility, nutrient and water uptake, assimilation and translocation of solutes and the influence of the rootstock on the main physiological processes of the scion.

X-Intrinsic Proteins (XIP) were recently identified in a narrow range of plants as a full clade within the aquaporins. These channels reportedly facilitate the transport of a wide range of hydrophobic solutes. The functional roles of XIP in planta remain poorly identified. In this study, we found three XIP genes (HbXIP1;1, HbXIP2;1 and HbXIP3;1) in the Hevea brasiliensis genome. Comprehensive bioinformatics, biochemical and structural analyses were used to acquire a better understanding of this AQP subfamily. Phylogenetic analysis revealed that HbXIPs clustered into two major groups, each distributed in a specific lineage of the order Malpighiales. Tissue-specific expression profiles showed that only HbXIP2;1 was expressed in all the vegetative tissues tested (leaves, stem, bark, xylem and latex), suggesting that HbXIP2;1 could take part in a wide range of cellular processes. This is particularly relevant to the rubber-producing laticiferous system, where this isoform was found to be up-regulated during tapping and ethylene treatments. Furthermore, the XIP transcriptional pattern is significantly correlated to latex production level. Structural comparison with SoPIP2;1 from Spinacia oleracea species provides new insights into the possible role of structural checkpoints by which HbXIP2;1 ensures glycerol transfer across the membrane. From these results, we discuss the physiological involvement of glycerol and HbXIP2;1 in water homeostasis and carbon stream of challenged laticifers. The characterization of HbXIP2;1 during rubber tree tapping lends new insights into molecular and physiological response processes of laticifer metabolism in the context of latex exploitation.

MECA; The wall-associated kinases (WAKs) are a family of transmembrane proteins involved in pathogen responses and cell elongation in Arabidopsis. They belong to the major receptor-like kinase (RLK) family in plants. Given their architecture and connection to the cell wall, WAKs are thought to perceive and propagate extracellular signals. This study reports the characterization of the WAK family in a woody species based on the v3.0 genome assembly of Populus trichocarpa. In silico analysis revealed a total of 175 PtWAK sequences classified into four groups based on protein domains. Of the PtWAKs, 91.5 % were found in tandem-duplicated clusters contributing to the expansion of the family in poplar. Microarray and EST expression data mining revealed contrasting temporal and spatial expression patterns in stress treatments for several WAK members. The WAKs in poplar form the largest WAK family encountered to date in plants. The combination of phylogenetic and transcriptional data showed that members in nonexpanded clusters were mainly expressed in developmental processes, whereas PtWAKs that had evolved independently in a species-specific way were structured in clusters and were involved in resistance responses. This paper offers an overview of WAK family structure in P. trichocarpa, which will be useful for further functional analysis of the PtWAK family.

The aim of this study was to compare differences in water relations in the leaves of three broccoli cultivars and differential induction of the expression of PIP2 aquaporin isoforms under salt stress. Although broccoli is known to be moderately tolerant to salinity, scarce information exists about the involvement of leaf aquaporins in its adaptation to salinity. Thus, leaf water relations, leaf cell hydraulic conductivity (Lpc), gas exchange parameters and the PIP2 expression pattern were determined for short- (15 h) and long- (15 days) term NaCl treatments. In the long term, the lower half-time of water exchange in the cells of cv. Naxos, compared with Parthenon and Chronos, and its increased PIP2 abundance may have contributed to its Lpc maintenance. This unmodified Lpc in cv. Naxos under prolonged salinity may have diluted NaCl in the leaves, as suggested by lower Na(+) concentrations in the leaf sap. By contrast, the increase in the half-time of water exchange and the lower PIP2 abundance in cvs. Chronos and Parthenon would have contributed to the reduced Lpc values. In cv. Parthenon, there were no differences between the ε values of control and salt-stressed plants; in consequence, cell turgor was enhanced. Also, the increases in BoPIP2;2 and BoPIP2;3 expression in cv. Chronos for the short-term NaCl treatment suggest that these isoforms are involved in osmotic regulation as downstream factors in this cultivar, in fact, in the short-term, Chronos had a significantly reduced osmotic potential and higher PIP2 isoforms expression.

In the soil-plant-atmosphere continuum the major resistance to water flux is the leafatmosphere interface which determine the rate of transpiration for a specific evaporative demand. In this scenario, the hydraulic resistance of the different plant tissues is minor; however, the hydraulic conductivity of the whole plant is subjected to a tight physiological regulation in which the aquaporins role may result fundamental. The expression of a large number of aquaporins occurs predominantly in roots and different experimental procedures have demonstrated that aquaporins activity is linked to the hydraulics of some species during abiotic stress. However, the plants roots hydraulic properties also depend on the morphology and anatomy of roots and the length of the absorbing region in addition to the influence of aquaporins. These features change during the plant development and in response to environmental stimuli by altering the hydraulic conductivity of the root. To fully understand root system hydraulics and the contribution of native aquaporins, comprehensive studies at different scales are required. In this chapter the definitions used to describe the plant hydraulic resistances are mentioned and the influence of the root anatomy and morphology on hydraulic conductivity is reviewed. Also, the variations in the hydraulic resistances under different abiotic stresses and distinct environmental conditions have been explored. Finally, the different properties and characteristics among various measuring methods are reviewed.

Interest in nutrient absorption and accumulation is derived from the need to increase crop productivity by better nutrition and also to improve the nutritional quality of plants as foods and feeds. This review focuses on contrasting data on the importance for human health of food mineral nutrients (Ca, Mg, K, Na and P) and also the trace elements considered essential or beneficial for human health (Cr, Co, Cu, Fe, Mn, Mo, Ni, Se and Zn). In addition, environmental stresses such as salinity, drought, extreme temperatures and light conditions that affect mineral content were revised in the light that the effect of these factors depends on the species or cultivar, and the specific plant organ, as well as the intensity and duration of the stress. Differences between inorganic and organic fertilisation practices on the mineral levels were also analysed to evaluate the influence of external factors on the quality of plant-based foods.

Plasma membrane Intrinsic Proteins (PIPs), a subfamily of aquaporins, are ubiquitous membrane channel proteins that play a crucial role in water uptake in plants. The use of high-performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) analysis of peptides has previously shown to be a valuable tool to differentiate among PIP homologues sharing a high sequence homology and also to characterize their post-translational modifications (PTMs). The recent introduction of mass spectrometers able to measure peptide mass with high mass accuracy, together with new alternative ways of peptide fragmentation allows the identification and characterization of proteins from nonsequenced organisms, such as broccoli. In this study, we combined three endoproteases (trypsin, Glu-C and Lys-C) with HPLC-MS/MS analysis and two types of peptide fragmentations, CID (collision induced dissociation) and HCD (higher-energy C-trap dissociation), to identify PIP isoforms and PTMs from broccoli roots. After de novo sequencing analysis, eight peptides showing homology to Arabidopsis thaliana PIPs were identified. Although Arabidopsis nomenclature of PIP isoforms has not been defined for broccoli, our results agree with the occurrence of seven AtPIP isoforms (PIP 1;1, PIP 1;2, PIP 1;3 and PIP2;2, PIP 2;3, PIP2;1 and PIP2;7) in broccoli roots, as compared to the plant model A. thaliana. To our knowledge, these results represent the deepest characterization of the PIPs isolated from the roots of broccoli, a crop with increasing agronomical interest. © 2010 American Chemical Society., This work was funded by the CICYT (AGL2006-06499) and the ‘Consejerı ́a de Educacio ́n y Cultura de la Regio ́n de Murcia’ (‘BioCARM’ BIO-AGR 06/04-0008

International audience; Interest in nutrient absorption and accumulation is derived from the need to increase crop productivity by better nutrition and also to improve the nutritional quality of plants as foods and feeds. This review focuses on contrasting data on the importance for human health of food mineral nutrients (Ca, Mg, K, Na and P) and also the trace elements considered essential or beneficial for human health (Cr, Co, Cu, Fe, Mn, Mo, Ni, Se and Zn). In addition, environmental stresses such as salinity, drought, extreme temperatures and light conditions that affect mineral content were revised in the light that the effect of these factors depends on the species or cultivar, and the specific plant organ, as well as the intensity and duration of the stress. Differences between inorganic and organic fertilisation practices on the mineral levels were also analysed to evaluate the influence of external factors on the quality of plant-based foods.

In the context of global change, attention has been focused on the increases in CO2 and temperature, as well as a reduction in the global solar irradiance. In this chapter we have explored how components of global change such as CO2, temperature and radiation will affect water uptake by plants. We focus on how aquaporins will respond to these environmental factors in order to maintain water balance in plants according to the water demand. Plant growth may be stimulated directly by increasing CO2 concentration, through enhanced photosynthesis, or, indirectly, through induced plant water consumption. However, the fine regulation of aquaporins, also involved in CO2 transport through membranes, will be crucial in the control of H2O and CO2 diffusion. Raised temperatures may benefit some crops but disadvantage others through increased evapotranspiration and thermal damage. However, in general, plants can develop different adaptive mechanisms in order to avoid water-deficit stress and excess transpiration modulating the hydraulic conductance, which involve the expression and activity of aquaporins. In the same way, the response of plants to the amount of perceived radiation affects water balance. Therefore, the study of aquaporin regulation is necessary for establishing future adaptation of plants to global change.

Plant aquaporins belong to a large superfamily of conserved proteins called the major intrinsic proteins (MIPs). There is limited information about the diversity of MIPs and their water transport capacity in broccoli (Brassica oleracea) plants. In this study, the cDNAs of isoforms of Plasma Membrane Intrinsic Proteins (PIPs), a class of aquaporins, from broccoli roots have been partially sequenced. Thus, sequencing experiments led to the identification of eight PIP1 and three PIP2 genes encoding PIPs in B. oleracea plants. The occurrence of different gene products encoding PIPs suggests that they may play different roles in plants. The screening of their expression as well as the expression of two specific PIP2 isoforms (BoPIP2;2 and BoPIP2;3), in different organs and under different salt-stress conditions in two varieties, has helped to unravel the function and the regulation of PIPs in plants. Thus, a high degree of BoPIP2;3 expression in mature leaves suggests that this BoPIP2;3 isoform plays important roles, not only in root water relations but also in the physiology and development of leaves. In addition, differences between gene and protein patterns led us to consider that mRNA synthesis is inhibited by the accumulation of the corresponding encoded protein. Therefore, transcript levels, protein abundance determination and the integrated hydraulic architecture of the roots must be considered in order to interpret the response of broccoli to salinity.