Regulating Water Uptake Research Articles

From swamp to field: how genes from mangroves and its associates can enhance crop salinity tolerance.

Salinity stress is a critical challenge in crop production and requires innovative strategies to enhance the salt tolerance of plants. Insights from mangrove species, which are renowned for their adaptability to high-salinity environments, provides valuable genetic targets and resources for improving crops. A significant hurdle in salinity stress is the excessive uptake of sodium ions (Na+) by plant roots, causing disruptions in cellular balance, nutrient deficiencies, and hampered growth. Specific ion transporters and channels play crucial roles in maintaining a low Na+/K+ ratio in root cells which is pivotal for salt tolerance. The family of high-affinity potassium transporters, recently characterized in Avicennia officinalis, contributes to K+ homeostasis in transgenic Arabidopsis plants even under high-salt conditions. The salt overly sensitive pathway and genes related to vacuolar-type H+-ATPases hold promise for expelling cytosolic Na+ and sequestering Na+ in transgenic plants, respectively. Aquaporins contribute to mangroves' adaptation to saline environments by regulating water uptake, transpiration, and osmotic balance. Antioxidant enzymes mitigate oxidative damage, whereas genes regulating osmolytes, such as glycine betaine and proline, provide osmoprotection. Mangroves exhibit increased expression of stress-responsive transcription factors such as MYB, NAC, and CBFs under high salinity. Moreover, genes involved in various metabolic pathways, including jasmonate synthesis, triterpenoid production, and protein stability under salt stress, have been identified. This review highlights the potential of mangrove genes to enhance salt tolerance of crops. Further research is imperative to fully comprehend and apply these genes to crop breeding to improve salinity resilience.

Soil-root interaction in the rhizosheath regulates the water uptake of wheat

The development of crops better adapted to endure weather extremes requires knowledge of the belowground traits that have potential to improve plant water uptake. Recent evidence has indicated that root induced modification of soil pore geometry of the rhizosheath is linked with drought tolerance of crops. Here we sought to understand whether the regulation of plant water uptake by rhizosheath is mediated through the rhizodeposits present at the soil-root interface. We compared eight wheat cultivars and demonstrated that cultivars with longer root hairs and greater rhizosheath mass and cover transpired more water. The wheat cultivars with less rhizosheath had the highest concentration of trehalose in the rhizosheath. Trehalose may increase the surface tension of soil water, which could further modify the transpiration of cultivars with less rhizosheath. Moreover, rhizosheath mass and cover had significant negative association with the bacterial abundance, indicating a link between metabolite concentration and bacterial abundance in the rhizosheath. We propose that the complex interactions of root, microbes and rhizodeposits in the rhizosheath have the potential to regulate water uptake by crops. The root and rhizosheath traits highlighted here can be targeted to develop crops with better ability to uptake water.

Effects of 5‐aminolevulinic acid on water uptake, ionic toxicity, and antioxidant capacity of Swiss chard (Beta vulgaris L.) under sodic‐alkaline conditions

AbstractSodic‐alkalinity may be more deleterious to plant growth than salinity. The objectives of this study were to determine whether 5‐aminolevulinic acid (ALA: an essential precursor for chlorophyll biosynthesis) foliar application could improve the sodic‐alkaline resistance of Swiss chard (Beta vulgaris L. subsp. cicla) by regulating water uptake, ionic homeostasis, photosynthetic capacity, and antioxidant metabolism. Eight‐week‐old uniform plants were grown in nutrient medium without and with a sodic‐alkaline regime generated by a mixture of NaHCO3 and Na2CO3 (NaHCO3 : Na2CO3 = 9:1 molar ratio) for 12 d, and leaves were sprayed daily with water or ALA. The Na+ and ALA concentrations were gradually increased to 60 mM and 120 μM, respectively. ALA foliar application alleviated the physiological damage from sodic‐alkalinity, as reflected by the increases in plant dry weight, relative growth rate, chlorophyll, Mg2+ concentration, and the decrease in Na+ concentration. However, ALA foliar application did not change the water uptake capacity or the concentration of K+, Fe3+, and endogenous ALA in leaf tissues under sodic‐alkaline conditions. ALA foliar application effectively mitigated damage from sodic‐alkalinity because of the increased activity of antioxidant enzymes (catalase and guaiacol peroxidase), particularly superoxide dismutase activity, which was maintained at the same level as for control plants. These results suggest that ALA foliar application alleviated sodic‐alkaline stress mainly owing to its antioxidant capacity, and superoxide dismutase has the main responsibility for reducing oxidative stress in Swiss chard.

Improving Plant Water Use Efficiency through Molecular Genetics

Improving crop performance under water-limiting conditions is essential for achieving environmentally sustainable food production. This requires significant progress in both the identification and characterization of key genetic and physiological processes involved in water uptake and loss. Plants regulate water uptake and loss through both developmental and environmental responses. These responses include: root morphology and architecture, cuticle development, stomatal development, and guard cell movements in response to the environment. Genes controlling root traits and stomatal development and guard cell movements strongly impact water use efficiency (WUE), and represent the best targets for molecular breeding programs. This article provides an overview of the complex networks of genes involved in water uptake and loss. These traits represent novel opportunities and strategies for genetic improvement of WUE and drought tolerance in crops.

A molecular dynamics study of water mass accommodation on condensed phase water coated by fatty acid monolayers

As the water uptake by particles and clouds influences the radiative balance of the Earth, it is desirable to understand the mechanisms and parameters, which regulate water uptake in these colloidal particles. In this work, molecular dynamics simulations were used to simulate scattering or accommodation of water vapor molecules impinging on a slab of water and slabs of water coated by monomolecular amphiphile films: octanoic acid (C-8) at surface densities of 29 and 18 angstrom(2) per molecule and myristic acid (C-14) at 29 angstrom(2) per molecule. The mass accommodation coefficient of near unity on a pure water slab is in agreement with values estimated using similar scattering simulations using other potentials for water. The addition of surface-active organic molecules in quantities corresponding to less than 1% of mass in a typical cloud droplet are predicted to reduce this mass accommodation coefficient by 70-100% in similar types of scattering simulations. The mass accommodation coefficient decreased monotonically with projected surface coverage of the hydrocarbon backbones, although the accommodation mechanisms differed by packing density and type of organic molecule. The mechanisms of interaction of the impinging water vapor molecules with the simulated organic films are discussed in the context of their chemical characteristics and physical structures (e.g., fatty acid chain orientation).

Cultivar differences in the deterioration of vase-life in cut-flowers of Anthurium andraeanum is determined by mechanisms that regulate water uptake

Vase-life, average daily water uptake rate and abaxial stomata density were evaluated in 17 anthurium ( Anthurium andraeanum Hort.) cultivars over two trials. There were significant cultivar differences for vase-life (14–49 days), 5-day average water uptake rate and abaxial stomata density, in both trials. A progressively stronger correlation coefficient between average daily water uptake rates during the period 25–50 days after initiation of experiment (DAI) and vase-life was observed, indicating that cultivars with longer vase-life were able to maintain above average water uptake rate over a longer period of time and hence delay symptoms of water stress. This was evident in the water uptake rate curves as an inflection, resulting in the levelling off of water uptake rates. The cultivars with long vase-lives achieved steady state water uptake levels faster, and maintained a high steady state water uptake rate for longer durations. The role of vascular occlusion and other senescence factors on water relations and vase-life is discussed.

Effect of Low Root Temperature on Hydraulic Conductivity of Rice Plants and the Possible Role of Aquaporins

The role of root temperature T(R) in regulating the water-uptake capability of rice roots and the possible relationship with aquaporins were investigated. The root hydraulic conductivity Lp(r) decreased with decreasing T(R) in a measured temperature range between 10 degrees C and 35 degrees C. A single break point (T(RC) = 15 degrees C) was detected in the Arrhenius plot for steady-state Lp(r). The temperature dependency of Lp(r) represented by activation energy was low (28 kJ mol(-1)) above T(RC), but the value is slightly higher than that for the water viscosity. Addition of an aquaporin inhibitor, HgCl(2), into root medium reduced osmotic exudation by 97% at 25 degrees C, signifying that aquaporins play a major role in regulating water uptake. Below T(RC), Lp(r) declined precipitously with decreasing T(R) (E(a) = 204 kJ mol(-1)). When T(R) is higher than T(RC), the transient time for reaching the steady-state of Lp(r) after the immediate change in T(R) (from 25 degrees C) was estimated as 10 min, while it was prolonged up to 2-3 h when T(R) < T(RC). The Lp(r) was completely recovered to the initial levels when T(R) was returned back to 25 degrees C. Immunoblot analysis using specific antibodies for the major aquaporin members of PIPs and TIPs in rice roots revealed that there were no significant changes in the abundance of aquaporins during 5 h of low temperature treatment. Considering this result and the significant inhibition of water-uptake by the aquaporin inhibitor, we hypothesize that the decrease in Lp(r) when T(R) < T(RC) was regulated by the activity of aquaporins rather than their abundance.

Variations of root hydraulic conductance of Fraxinus mandshurica seedlings in different concentrations of NH4NO3 solution

Absorbing water from soil by roots in vascular plants is an important physiological function and plays an essential role on their water balance. The root hydraulic conductance (L P) determined by radical water transport inside the root is a major influence on the shoot water status, plant growth, and development. However, a few studies have focused on the effect of different substances on L P of roots, and the role of radical water transport was poorly understood. Based on the pressure-flux approach, this study used the roots of Fraxinus mandshurica seedlings with different treatments, i.e., distilled water, NH4NO3 solution, and HgCl2 to determine the effect of various substances on L P of roots. The objectives are: 1) to evaluate the difference in L P occurred between distilled water and NH4NO3 solution with various concentrations; and 2) to examine the changes of L P under distilled water and NH4NO3 solution with various concentrations after HgCl2 treatment. The results showed that L P of roots were 18.85×10−8 m/(s·MPa) in distilled water, 31.25–34.15×10−8 m/(s·MPa) in four NH4NO3 solutions (2, 4, 8 and 16 mmol/L), 14.69×10−8 m/(s·MPa) in distilled water after HgCl2-treated, and 9.63–13.57×10−8 m/(s·MPa) in four NH4NO3 solutions after HgCl2-treated, respectively. Aquaporins play an important role in regulating water uptake and transport in roots. NH4 + and NO3 − could stimulate activity of aquaporins, and L P of roots in NH4NO3 solution was distinctly 77% higher than in distilled water. Nevertheless, Hg2+ can inhibit activity of aquaporins, and and L P of roots decreased 22% in distilled water and 68% in NH4NO3 solution after treatment by HgCl2 respectively. These evidences suggested that both Hg2+-sensitive aquaporins and ion channels existing in the protoplasm and vacuole membranes could regulate root water uptake, transport, and integral plant water balance.

Vertical stratification of soil water storage and release dynamics in Pacific Northwest coniferous forests

We characterized vertical variation in the seasonal release of stored soil moisture in old-growth ponderosa pine (OG-PP, xeric), and young and old-growth Douglas-fir (Y-DF, OG-DF, mesic) forests to evaluate changes in water availability for root uptake. Soil water potential ( ψ) and volumetric water content ( θ) were measured concurrently at 10 cm intervals to 1 m depth to create in situ soil water retention curves (SWRC) under drying conditions. Non-linear regression was used to fit SWRC specific to each depth and site. We also quantified root biomass, soil texture, and hydraulic redistribution (HR) of soil water by roots to identify factors affecting the seasonal dynamics of root water uptake and depletion from the soil profile. Soil θ measured at a particular ψ increased with soil depth, and was strongly dependent upon soil texture. For example, when ψ was −0.1 MPa, θ ranged from 13% at 20 cm to 35% at 100 cm for the OG-DF forest. Soil texture and bulk density accounted for 60–90% of the variation in the SWRC. As the summer drought progressed, water extraction shifted to the deeper layers, and recharge from HR approached 0.15 mm day −1 in the upper 60 cm for all sites. Total water use from the upper 2 m at all sites peaked between 1.5–2.5 mm day −1 in mid-July and then declined to 0.5–1.0 mm day −1 by the end of the dry season. Total fine root biomass in the upper 1 m was 0.77 kg m −2 (OG-PP), 1.08 kg m −2 (OG-DF) and 1.15 kg m −2 (Y-DF), with 40% (PP) to 60% (DF) of fine roots located in the upper 20 cm. However, the upper 20 cm only accounted for 20% of total water depletion from the upper 2 m at peak water uptake, declining to 4–6% later in the season, illustrating the contribution of deeper roots to water uptake. Nevertheless, daily water uptake from the entire 2 m profile was strongly dependent on water potential at 20 cm, indicating that fine roots in the upper soil may play an important role in regulating water uptake through hydraulic effects on stomatal conductance.

BARLEY ENZYMES AND MALTING POTENTIAL

The amylases of barley are of only indirect significance in the modification of the starchy endosperm. More directly concerned are: (a) the β-glucanase system (endo-β-glucanases, exo-β-glucanase, β-oligosaccharases); (b) pentosanases (endoxylanase, exoxylanase, xylo-oligosaccharases, arabinosidase); and (c) proteolytic enzymes, about which precise information is lacking. Contributions may also be made by phosphatases (including the complex system responsible for the hydrolysis of phytic acid) and Upases. The autolytic technique provides useful means for the study of these factors. Regarding the starch grains of the inner endosperm as being embedded in a matrix of β-glucan, araboxylan and protein, the whole being divided into cell-like units by walls of similar materials in high-molecular state, modification may be taken to involve a balanced attack of hemicellulases and proteases on substrates in reasonably accessible physical state. Since the hemicellulases and probably also the proteases are apparently produced in superabundance, the physical state of the hemicelluloses and proteins appears to be most significant, and this same property may also play an important part in regulating water uptake by the grain and, in particular, its distribution among the various tissues.