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The mechanism of root hydrotropism has been a mystery for many years, due to the complexity of the interactions between the external environment and plants themselves. To gain an engineering perspective, the time-dependent hydrotropism of a single root has been modeled, initially using a two-dimensional model. Based on the water and nutrient distribution in rhizosphere as computed with the conservation equations, together with a basic reaction-kinetics-type growth model and an intuitive root bending model, it has been found that the root already possesses the property of hydrotropism. For the first time, hydrotropism could be tracked by a process engineering model, which is a new idea based on chemical engineering concept, suggesting an alternative mechanism of hydrotropism. The effects of different initial root widths, lengths, and other growth/transport coefficients on root hydrotropism have then been explored. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1331-1346, 2016 [ABSTRACT FROM AUTHOR]

Hydrotropes are special class of amphiphilic molecules that have an ability to solubilize the insoluble or sparingly soluble molecules in water. To find out the mechanism of hydrotropic action of hydrotropes on hydrophobic molecules, we have carried out classical molecular dynamics simulation of hydrophobic solute di-t-butyl-methane (DTBM) and hydrotrope sodium cumene sulfonate (SCS) in water with a regime of SCS concentrations. Our study demonstrates that, above the minimum hydrotrope concentration (MHC), the self-aggregation of SCS starts, and it creates a micellar-like environment in which the hydrophobic tail part of SCS points inward while its hydrophilic sulfonate group points outward to make favorable contact with water molecules. The formation of the hydrophobic core of SCS cluster creates a hydrophobic environment where the hydrophobic DTBM molecules are encapsulated. Interestingly, the determination of average water-SCS hydrogen bonds further suggests that the aggregate formation of SCS molecules has a negligible influence on it. Moreover, the calculations of Flory-Huggins interaction parameters also reveal favorable interactions between hydrotrope SCS and solute DTBM molecules. The implications of these findings on the mechanism of hydrotrope assisted enhanced solubility of hydrophobic molecules are discussed. [ABSTRACT FROM AUTHOR]

Aims: Root hydrotropism has been widely studied in seedling radicles through artificial experiments that reduce the influence of gravity and soil. In this work we aimed to study hydrotropism of primary lateral and pivotal roots in developed root systems of desert plants under simulated natural conditions. Methods: We grew Bulnesia retama Griseb. (non phreatophyte), Prosopis flexuosa DC. (facultative phreatophyte) and Prosopis alpataco Phil.(obligate phreatophyte) seedlings in observation boxes with sand. Lateral and pivotal roots were stimulated by lateral water gradients and hydrotropic responses, root proliferation and root : shoot ratios were measured. Results: We found that 65 ± 15 % of lateral roots that grew in response to water gradients in B. retama, 84 ± 8 % in P. flexuosa and 88 ± 8 % in P. alpataco displayed hydrotropism. Conversely, pivotal roots did not show hydrotropic growth. This was accompanied by root proliferation inside water patches, and biomass partitioning to shoot growth. Conclusions: Our results provide evidence that root hydrotropism is a relevant response that could occur in nature. Lateral and pivotal roots manifest different hydrotropic responses under the conditions assayed. The combination of hydrotropism and precise root proliferation can shape root architecture, leading to optimum water patch exploration. [ABSTRACT FROM AUTHOR]

Highlights: [•] gnom emb30-1 rescued ahydrotropic phenotype of gnom miz2 , while gnom B4049 did not. [•] Requirement of GNOM function differs among the tropisms. [•] GNOM can regulate root phototropism independent of PIN2 polar targeting. [•] Auxin related defects of severe gnom mutants are fully recovered by gnom miz2 . [•] A novel GNOM function regulates root hydrotropism and phototropism. [ABSTRACT FROM AUTHOR]

Roots exhibit positive hydrotropism in response to soil moisture gradients in arid conditions. However, the mechanisms that regulate hydrotropism are yet to be elucidated. Ca2+ is involved in this response, but the molecular factors that interact with Ca2+ are currently unknown. To understand the role of Ca2+ in hydrotropism, as well as to identify proteins that are involved in this process, we examined the physiology of Arabidopsis thaliana seedlings cultured in Ca2+-free medium. Treatment with cytosolic and apoplastic Ca2+ chelators triggered an increase in hydrotropic root bending, which became more pronounced during the latter stages of the hydrotropic response. Furthermore, we found that the phenotypes of mutants defective in OSCA1.1, a mechanosensitive Ca2+ channel, resembled those of wild-type seedlings treated with Ca2+ chelators. Although treatment with Ca2+ chelators also affected root gravitropism, no significant differences in root gravitropism were observed in osca1 mutants, suggesting that OSCA1.1 has a specific function in root hydrotropism. Moreover, transcript level of MIZ1 in OSCA1.1 knockout mutant was higher than that of wild type, specifically at latter stages of the hydrotropic response. Double mutants that carry miz1–1 or miz2 alleles in addition to the osca1 knockout allele lacked hydrotropic response, the phenotypes of which were resembled those of miz1–1 or miz2 single mutants. Our results suggest that OSCA1.1 functions within the same signaling pathway as MIZ1 and MIZ2, and that OSCA1.1-mediated Ca2+ influx across the plasma membrane is required to regulate hydrotropic root bending by regulating MIZ1 expression at the latter stages. • Dysfunction of a mechanosensitive Ca2+ channel, OSCA1.1, enhances root hydrotropism. • Mutation in OSCA1.1 does not affect root gravitropism. • OSCA1.1 specifically functions within the same signaling pathway as MIZ1 and MIZ2. [ABSTRACT FROM AUTHOR]

Threepentyl and three aryl 1-O-monoglyceryl ethersprepared via a green catalytic route were investigated as hydrotropicsolvents. Their amphiphilicities were quantified by comparing theirso-called “fish” diagrams constructed with oils of increasinghydrophobicity (EACN). For the same number of carbon atoms, the presenceof a methyl substituent in β position makes the hydrotrope slightlymore hydrophobic, as evidenced by the more hydrophobic optimal oil.Branched isomers are also less efficient since they require higherconcentrations to get microemulsions. The presence of an aromaticmoiety within the hydrophobic chain increases the solubility of thehydrotrope in water in comparison to the alkyl derivative that hasthe same number of carbon atoms. It also modifies significantly theassociative behavior in oil/water systems: Benzylglycerol monoetheris able to form Winsor III systems, just as the pentyl derivatives,but with much more polar oils, whereas phenylglycerol is not. In oil/watersystems, all glycerol-derived amphiphiles exhibit a twice-lower temperature-sensitivitycompared to their ethyleneglycol counterparts. The pentyl and benzyl1-O-monoglyceryl ethers can be classified as amphiphilicsolvents, or “solvo-surfactants”, as regards to theirsurface-active properties and good solubilizing abilities. [ABSTRACT FROM AUTHOR]

Background and Aims Root hydrotropism is a response to water-potential gradients that makes roots bend towards areas of higher water potential. The gene MIZU-KUSSEI1 (MIZ1) that is essential for hydrotropism in Arabidopsis roots has previously been identified. However, the role of root hydrotropism in plant growth and survival under natural conditions has not yet been proven. This study assessed how hydrotropic response contributes to drought avoidance in nature. Methods An experimental system was established for the study of Arabidopsis hydrotropism in soil. Characteristics of hydrotropism were analysed by comparing the responses of the miz1 mutant, transgenic plants overexpressing MIZ1 (MIZ1OE) and wild-type plants. Key Results Wild-type plants developed root systems in regions with higher water potential, whereas the roots of miz1 mutant plants did not show a similar response. This pattern of root distribution induced by hydrotropism was more pronounced in MIZ1OE plants than in wild-type plants. In addition, shoot biomass and the number of plants that survived under drought conditions were much greater in MIZ1OE plants. Conclusions These results show that hydrotropism plays an important role in root system development in soil and contributes to drought avoidance, which results in a greater yield and plant survival under water-limited conditions. The results also show that MIZ1 overexpression can be used for improving plant productivity in arid areas. [ABSTRACT FROM PUBLISHER]

Abstract: Membrane potential and membrane conductance measurements have been carried out using Dowex-50Kynar membrane, sodium chloride and urea as a hydrotrope, mixture of varying composition to examine the hydrotrope effect on electrochemical character of the membrane. A significant change on membrane electrochemical character is observed in the presence of hydrotrope due to changed co-ion exclusion. The Donnan equilibrium has been incorporated to estimate the activity coefficient of counter ion, yp m, and solute, y± m in the membrane phase along with the parameter, so called Ф expressing non-ideality. Solute rejection performance of the membrane is examined when electrolyte concentration remains constant and hydrotrope concentration varies and vice-versa. In both cases, membrane specific conductance depends on NaCl and hydrotrope concentrations differently. Friction caused through the membrane by the variation in concentration of hydrotrope is greater than friction caused by the variation in concentration of NaCl. Zeta potential is sensitive to the variation of hydrotrope concentration but insensitive to the variation of electrolyte concentration. The membrane system shows the behavior of NF membrane because Pe≪1 is estimated in both cases. [Copyright &y& Elsevier]

Abscisic acid (ABA) signaling plays a critical role in regulating root growth and root system architecture. ABA-mediated growth promotion and root tropic response under water stress are key responses for plant survival under limiting water conditions. In this work, we have explored the role of Arabidopsis (Arabidopsis thaliana) PYRABACTIN RESISTANCE1 (PYR1)/PYR1-LIKE (PYL)/REGULATORY COMPONENTS OF ABA RECEPTORS for root ABA signaling. As a result, we discovered that PYL8 plays a nonredundant role for the regulation of root ABA sensitivity. Unexpectedly, given the multigenic nature and partial functional redundancy observed in the PYR/PYL family, the single pyl8 mutant showed reduced sensitivity to ABA-mediated root growth inhibition. This effect was due to the lack of PYL8-mediated inhibition of several clade A phosphatases type 2C (PP2Cs), since PYL8 interacted in vivo with at least five PP2Cs, namely HYPERSENSITIVE TO ABA1 (HAB1), HAB2, ABA-INSENSITIVE1 (ABI1), ABI2, and PP2CA/ABA-HYPERSENSITIVE GERMINATION3 as revealed by tandem affinity purification and mass spectrometry proteomic approaches. We also discovered that PYR/PYL receptors and clade A PP2Cs are crucial for the hydrotropic response that takes place to guide root growth far from regions with low water potential. Thus, an ABA-hypersensitive pp2c quadruple mutant showed enhanced hydrotropism, whereas an ABA-insensitive sextuple pyr/pyl mutant showed reduced hydrotropic response, indicating that ABA-dependent inhibition of PP2Cs by PYR/PYLs is required for the proper perception of a moisture gradient. [ABSTRACT FROM AUTHOR]

While water shortage remains the single-most important factor influencing world agriculture, there are very few studies on how plants grow in response to water potential, i.e., hydrotropism. Terrestrial plant roots dwell in the soil, and their ability to grow and explore underground requires many sensors for stimuli such as gravity, humidity gradients, light, mechanical stimulations, temperature, and oxygen. To date, extremely limited information is available on the components of such sensors; however, all of these stimuli are sensed in the root cap. Directional growth of roots is controlled by gravity, which is fixed in direction and intensity. However, other environmental factors, such as water potential gradients, which fluctuate in time, space, direction, and intensity, can act as a signal for modifying the direction of root growth accordingly. Hydrotropism may help roots to obtain water from the soil and at the same time may participate in the establishment of the root system. Current genetic analysis of hydrotropism in Arabidopsis has offered new players, mainly AHRI, NHR1, MIZ1, and MIZ2, which seem to modulate how root caps sense and choose to respond hydrotropically as opposed to other tropic responses. Here we review the mechanism(s) by which these genes and the plant hormones abscisic acid and cytokinins coordinate hydrotropism to counteract the tropic responses to gravitational field, light or touch stimuli. The biological consequence of hydrotropism is also discussed in relation to water stress avoidance. [ABSTRACT FROM AUTHOR]

Roots show positive hydrotropism in response to moisture gradients, which is believed to contribute to plant water acquisition. This article reviews the recent advances of the physiological and molecular genetic studies on hydrotropism in seedling roots of Arabidopsis thaliana. We identified M1ZU-KUSSEll (MIZ1) and MIZ2, essential genes for hydrotropism in roots; the former encodes a protein of unknown function, and the latter encodes an ARF-GEF (GNOM) protein involved in vesicle trafficking. Because both mutants are defective in hydrotropism but not in gravitropism, these mutations might affect a molecular mechanism unique to hydrotropism. MIZ1 is expressed in the lateral root cap and cortex of the root proper. It is localized as a soluble protein in the cytoplasm and in association with the cytoplasmic face of endoplasmic reticulum (ER) membranes in root cells. Light and ABA independently regulate MIZ1 expression, which influences the ultimate hydrotropic response. In addition, MIZ1 overexpression results in an enhancement of hydrotropism and an inhibition of lateral root formation. This phenotype is likely related to the alteration of auxin content in roots. Specifically, the auxin level in the roots decreases in the MIZ1 overexpressor and increases in the miz1 mutant. Unlike most gnom mutants, miz2 displays normal morphology, growth, and gravitropism, with normal localization of PIN proteins. It is probable that MIZ1 plays a crucial role in hydrotropic response by regulating the endogenous level of auxin in Arabidopsis roots. Furthermore, the role of GNOM/MIZ2 in hydrotropism is distinct from that of gravitropism. [ABSTRACT FROM AUTHOR]

Because of their sessile nature, plants evolved several mechanisms to tolerate or avoid conditions where water is scarce. The molecular mechanisms contributing to drought tolerance have been studied extensively, whereas the molecular mechanism underlying drought avoidance is less understood despite its importance. Several lines of evidence showed that the roots sense the moisture gradient and grow toward the wet area: so-called hydrotropism. We previously identified MIZU-KUSSEI (MIZ) 1 and MIZ2/GNOM as genes responsible for this process. To gain new insight into the molecular mechanism of root hydrotropism, we generated overexpressors of MIZ1 (MIZ1OEs) and analyzed their hydrotropic response. MIZ1OEs had a remarkable enhancement of root hydrotropism. Furthermore, a greater number of MIZ1OE root cells remained viable under hydrostimulated conditions than those of the wild type, which might contribute to retaining root growth under hydrostimulated conditions. Although overexpression of MIZ1 also caused a slight decrease in the root gravitropic response, it was not attributable to the enhanced hydrotropic response. In addition, miz2 mutation or the auxin response inhibitor nullified the enhanced hydrotropic response in MIZ1OEs. Furthermore, the expression of MIZ1 did not alter the expression of typical genes involved in drought tolerance. These results suggest that MIZ1 positively regulates hydrotropism at an early stage and its overexpression results in an enhancement of signal transduction unique to root hydrotropism to increase the degree of hydrotropic root bending. [ABSTRACT FROM AUTHOR]

Roots are highly plastic and can acclimate to heterogeneous and stressful conditions. However, there is little knowledge of the effect of moisture gradients on the mechanisms controlling root growth orientation and branching, and how this mechanism may help plants to avoid drought responses. The aim of this study was to isolate mutants of Arabidopsis thaliana with altered hydrotropic responses. Here, altered hydrotropic response 1 (ahr1), a semi-dominant allele segregating as a single gene mutation, was characterized. ahr1 directed the growth of its primary root towards the source of higher water availability and developed an extensive root system over time. This phenotype was intensified in the presence of abscisic acid and was not observed if ahr1 seedlings were grown in a water stress medium without a water potential gradient. In normal growth conditions, primary root growth and root branching of ahr1 were indistinguishable from those of the wild type (wt). The altered hydrotropic growth of ahr1 roots was confirmed when the water-rich source was placed at an angle of 45° from the gravity vector. In this system, roots of ahr1 seedlings grew downward and did not display hydrotropism; however, in the presence of cytokinins, they exhibited hydrotropism like those of the wt, indicating that cytokinins play a critical role in root hydrotropism. The ahr1 mutant represents a valuable genetic resource for the study of the effects of cytokinins in the differential growth of hydrotropism and control of lateral root formation during the hydrotropic response. [ABSTRACT FROM PUBLISHER]

Seedling roots display not only gravitropism but also hydrotropism, and the two tropisms interfere with one another. In Arabidopsis ( Arabidopsis thaliana) roots, amyloplasts in columella cells are rapidly degraded during the hydrotropic response. Degradation of amyloplasts involved in gravisensing enhances the hydrotropic response by reducing the gravitropic response. However, the mechanism by which amyloplasts are degraded in hydrotropically responding roots remains unknown. In this study, the mechanistic aspects of the degradation of amyloplasts in columella cells during hydrotropic response were investigated by analyzing organellar morphology, cell polarity and changes in gene expression. The results showed that hydrotropic stimulation or systemic water stress caused dramatic changes in organellar form and positioning in columella cells. Specifically, the columella cells of hydrotropically responding or water-stressed roots lost polarity in the distribution of the endoplasmic reticulum (ER), and showed accelerated vacuolization and nuclear movement. Analysis of ER-localized GFP showed that ER redistributed around the developed vacuoles. Cells often showed decomposing amyloplasts in autophagosome-like structures. Both hydrotropic stimulation and water stress upregulated the expression of AtATG18a, which is required for autophagosome formation. Furthermore, analysis with GFP-AtATG8a revealed that both hydrotropic stimulation and water stress induced the formation of autophagosomes in the columella cells. In addition, expression of plastid marker, pt-GFP, in the columella cells dramatically decreased in response to both hydrotropic stimulation and water stress, but its decrease was much less in the autophagy mutant atg5. These results suggest that hydrotropic stimulation confers water stress in the roots, which triggers an autophagic response responsible for the degradation of amyloplasts in columella cells of Arabidopsis roots. [ABSTRACT FROM AUTHOR]

ABSTRACT Plant roots undergo tropic growth in response to environmental cues, and each tropic response is affected by several environmental stimuli. Even its importance, molecular regulation of hydrotropism has not been largely uncovered. Tropic responses including hydrotropism were impacted by other environmental signal. We found that hydrotropism was reduced in dark-grown seedling. Moreover, we found that the expression of MIZ1, an essential gene for hydrotropism, was regulated by light signal. From our genetic analysis, phytochrome A (phyA)-, phyB- and HY5-mediated blue-light signalling play curial roles in light-mediated induction of MIZ1 and hydrotropism. In addition, we found that abscisic acid (ABA) also induced MIZ1 expression. ABA treatment could recover weak hydrotropism and MIZ1 expression level of hy5, and ABA synthesis inhibitor, abamineSG, further reduced hydrotropic curvature of hy5. In contrast, ABA treatment did not affect ahydrotropic phenotype of miz1. These results suggest that ABA signalling regulates MIZ1 expression independently from light signalling. Our results demonstrate that environmental signals, such as light and stresses mediated by ABA signalling, are integrated into MIZ1 expression and thus regulate hydrotropism. These machineries will allow plants to acquire sufficient amounts of water. [ABSTRACT FROM AUTHOR]

Aims: Because plants cannot change their environmental circumstances by changing their location, they must instead adapt to a wide variety of environmental conditions, especially soil conditions. One of the most effective ways for a plant to adapt to a given soil condition is by modifying its root system architecture. We aim to identify the genetic factors controlling root growth angle, a trait that affects root system architecture. Methods: The present study consisted of a genetic analysis of the seminal root growth angle in wheat; the parental varieties of the doubled haploid lines (DHLs) used in this study exhibited significantly different root growth directions. Using the 'basket' method, the ratio of deep roots (DRR; the proportion of total roots with GA > 45 degrees) was observed for evaluating deep rooting. Results: We were able to identify novel quantitative trait loci (QTLs) controlling the gravitropic and hydrotropic responses of wheat roots. Moreover, we detected one QTL for seminal root number per seedling (RN) on chromosome 5A and two QTLs for seminal root elongation rate (ER) on chromosomes 5D and 7D. Conclusions: Gravitropic and hydrotropic responses of wheat roots, which play a significant role in establishing root system architecture, are controlled by independent genetic factors. [ABSTRACT FROM AUTHOR]

An efficient synthesis of medicinally relevant bis(indolyl)methanes and 2-aryl benzimidazoles has been achieved in an aqueous hydrotropic solution at ambient temperature. Substantial enhancements in the rates of the reactions along with easy recovery of the products were noted. Additionally, the aqueous hydrotropic solution could be reused for several cycles with modest change in yields of products. [ABSTRACT FROM PUBLISHER]

Abstract: The use of riparian tree cuttings for river rehabilitation relies on a good understanding of cutting survival and growth responses to environmental variables. A series of experiments aimed at studying the effects of water table fluctuation induced by streamflow variability on the development of below-ground biomass of riparian tree cuttings was performed on the Thur River (Switzerland). White willow (Salix alba) cuttings were installed in gravel bar plots at various locations to develop an understanding of how topography and flow variability control cutting root development strategies, which in turn can lead to observed different vertical root density distributions in response to varying forms of tropism. In particular, we show that the transient root growth dynamics, eventually create a distribution reflecting the hydrologic conditions experienced towards the end of the growing season. A scaling relationship is presented that is useful to predict the expected depth with the highest root density as a function of soil topography and river discharge statistics. The results have implications for predicting cutting survival and growth, along with a corresponding strengthening of the alluvial sediment, in different flow regimes. This approach is therefore useful to incorporate in morphodynamic models covering the ecological and hydraulics responses of below-ground biomass to floods. [Copyright &y& Elsevier]

Abstract: MIZ1 is encoded by a gene essential for root hydrotropism in Arabidopsis. To characterize the property of MIZ1, we used transgenic plants expressing GFP-tagged MIZ1 (MIZ1-GFP) and mutant MIZ1 (MIZ1G235E-GFP) in a miz1-1 mutant. Although both chimeric genes were transcribed, the translational products of MIZ1G235E-GFP did not accumulate in roots. Moreover, MIZ1-GFP complemented the mutant phenotype but not MIZ1G235E-GFP. The signal corresponding to MIZ1-GFP was detected at high levels in cortical cells and lateral root cap cells and accumulated in compartments in cortical cells. MIZ1-GFP was fractionated into a soluble protein fraction and an endoplasmic reticulum (ER) membrane fraction, where it was bound to the surface of the ER membrane at the cytosolic side. [Copyright &y& Elsevier]

A drug administered in solution form immediately available for absorption and efficiently absorbed than the same amount of drug administered in a tablet or capsule form. Solubility is a most important parameter for the oral bioavailability of poorly soluble drugs. Dissolution of drug is the rate determining step for oral absorption of the poorly water soluble drugs, which can subsequently affect the in vivo absorption of drug. Currently only 8% of new drug candidates have both high solubility and permeability. Because of solubility problem of many drugs the bioavailability of them gets affected and hence solubility enhancement becomes necessary. It is now possible that to increase the solubility of poorly soluble drugs with the help of various techniques such as Physical method, Chemical method. Co-crystallisation, co-solvency solubilizing agents, molecular encapsulation with cyclodextrins, nanotechnology approaches and hydrotropy. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the present work was to compare the physiological responses to water stress and recovery of seedlings and saplings of three different Mediterranean species (Olea europaea var. sylvestris, Rhamnus alaternus and Cneorum tricoccon), pre-conditioning and aged in nursery and presenting different ages and pot sizes. Our hypothesis was that the ratio of plant size to soil volume (which constrains root development leading to low root-to-shoot ratios) rather than any of the two factors separately determines the seedling response to water stress. Seedlings (1-y) and saplings (3 to 4-y) were transplanted into pots bigger than those used during growth in the nursery and irrigation was stopped to each species×age/size combination. Leaf water potential (Ψ), net CO2 assimilation (A N), stomatal (g s) and mesophyll (g m) conductances, and the rate of photosynthetic electron transport (ETR) were determined every few days. Plants were re-watered when A N dropped below 70% of control values. Saplings of each species presented larger total leaf area (TLA) and reached lower Ψ than seedlings. Even under irrigation, saplings showed lower A N, which was not related to g s but to lower g m and ETR. During water stress, A N decreased slowly in seedlings due to stomatal limitations, while in saplings it decreased fast and mainly associated to non-stomatal limitations (g m and ETR). Upon re-watering, seedlings recovered maximum A N within a few days, while recovery was slow and incomplete in saplings. At the end of the experiment, significant leaf die-back occurred in saplings but not in seedlings except for Cneorum. The minimum Ψ achieved during water stress was strongly linearly related to TLA when pooling all species and ages, and leaf die-back was strongly dependent on Ψ and on the appearance of non-stomatal limitations to photosynthesis. Therefore, we conclude that the total amount of leaf area for a given volume of substrate (i.e., maximum water availability), rather than plants pre-conditioning in nurseries or plant age, determines seedling/sapling responses to water stress and re-watering in Mediterranean species. [Copyright &y& Elsevier]

Abstract: Root hydrotropism is the directional growth of roots toward a source of moisture in response to a water potential gradient. Root hydrotropism is therefore one of the most important factors for efficient water acquisition under water-limited conditions. However, the mechanisms underlying hydrotropism are not well understood. A previous study of the hydrotropism of primary roots in Arabidopsis thaliana identified the MIZU-KUSSEI (MIZ) 1 and MIZ2 genes as essential for this process. However, despite the important role of lateral roots in water acquisition under water deficient conditions, the mechanism of hydrotropism in lateral roots has not been investigated to date. The present study established an experimental system for the induction of lateral root hydrotropism in Arabidopsis and analyzed its characteristics in comparison with those of primary roots. Lateral roots were found to exhibit hydrotropism irrespective of their length. Expression of a pMIZ1::GUS fusion gene at the tip of lateral roots and assessment of lateral root hydrotropism in the ahydrotropic mutant miz1, which did not display hydrotropism, demonstrated that the lateral roots of Arabidopsis have the capacity to respond to water potential gradients, and that this activity is regulated by MIZ1. [Copyright &y& Elsevier]

Abstract: Earlier studies showed that water deficit reduces nitrogen (N) uptake and N nutrition index of grasses. So far, the main effect of water deficit on N uptake and N nutrition status was ascribed to the alteration of the transpiration-dependent transport of mineral N in the soil solution. A split-root experiment was performed to determine whether plant and/or solution water potential could alter N uptake and allocation, independently of N fluxes in the soil solution. The split-root experiment allowed to manipulate separately the water and the N status of the root environment and of the plant, by various combinations of addition of polyethylene glycol 6000 (PEG) and mineral N on half or on the entire root system. Tall fescue, Italian ryegrass and cocksfoot, known for their contrasted sensitivities to water deficit, were studied. The addition of PEG largely reduced water and N uptake of the roots on which it was applied (half or entire root system). A significant accumulation of N was observed on the roots to which PEG was added, particularly in cocksfoot and tall fescue, hypothetically contributing to the alteration of N uptake. Cocksfoot displayed a high plasticity in N allocation to leaves related to sheaths, allowing the maintenance of N concentration and therefore its N status despite the reduction in N uptake. By contrast, leaf N concentration and N status of tall fescue and Italian ryegrass was more sensitive to water deficit, similarly to observations of the effect of drought in field studies. Therefore, it is concluded that the effect of soil solution potential on N uptake and plant N allocation may also contribute to the observed effect of drought on N status of grass crops, additionally to the effect of drought on the transfer of mineral N in the soil solution to the root surface. However, the importance of this physiological effect varies among species. [Copyright &y& Elsevier]

Plant organ development is important for adaptation to a changing environment. Genetic and physiological studies have revealed that plant hormones play key roles in lateral root formation. In this study, we show that MIZU-KUSSEI1 (MIZ1), which was identified originally as a regulator of hydrotropism, functions as a novel regulator of hormonally mediated lateral root development. Overexpression of MIZ1 (MIZ1OE) in roots resulted in a reduced number of lateral roots being formed; however, this defect could be recovered with the application of auxin. Indole-3-acetic acid quantification analyses showed that free indole-3-acetic acid levels decreased in MIZ1OE roots, which indicates that alteration of auxin level is critical for the inhibition of lateral root formation in MIZ1OE plants. In addition, MIZ1 negatively regulates cytokinin sensitivity on r development. Application of cytokinin strongly induced the localization of MIZl-green fluorescent protein to lateral root primordia, which suggests that the inhibition of lateral root development by MIZ1 occurs downstream of cytokinin signaling. Surprisingly, miz2, a weak allele of gnom, suppressed developmental defects in MIZ1OE plants. Taken together, these re suggest that MIZ1 plays a role in lateral root development by maintaining auxin levels and that its function requires GNOM activity. These data provide a molecular framework for auxin-dependent organ development in Arabidopsis (Arabidopsis thaliana). [ABSTRACT FROM AUTHOR]

Background: Hydrotropic solubilization process involves cooperative intermolecular interaction with several balancing molecular forces, rather than either a specific complexation event or a process dominated by a medium effect, such as co-solvency or salting-in. Materials and Methods: In the present investigation, hydrotropic solution of 2 M niacinamide was employed as the solubilizing agent to solubilize the poorly water-soluble drug, indomethacin, from the capsule dosage form for spectrophotometric determination in ultraviolet region. Results: Hydrotropic agent used did not interfere in the spectrophotometric analysis. In preliminary solubility studies, it was found that there was more than fivefold enhancement in the aqueous solubility of indomethacin (poorly water-soluble drug) in 2 M niacinamide solution as compared to its aqueous solubility at 28 ± 1°C. Conclusion: The proposed method is new, simple, safe, environmentally friendly, economic, accurate and cost-effective and can be successfully employed in routine analysis. [ABSTRACT FROM AUTHOR]

Conventional furosemide tablets are practically insoluble in water, have slow onset of action (45-60 min) and poor bioavailability (39-53%), and therefore cannot be given in emergency clinical situations like hypertension or pulmonary edema. So purpose of research was to provide a fast dissolving oral dosage form of furosemide, which can provide quick onset of action by using concept of mixed hydrotropy. Initially solubility of furosemide was determined individually in 4 hydrotropic agents namely urea, sodium acetate, sodium benzoate, sodium citrate at concentration of 10, 20, 30 and 40% w/v solutions using purified water as solvent. Highest solubility was obtained in 40% sodium benzoate solution. Then different combinations of 2, 3 and 4 hydrotropic agents in different ratios were used to determine solubility, so that total concentration of hydrotropic agents was always 40%. Highest solubility was obtained in solution of urea+sodium benzoate+sodium citrate at optimum ratio of 15:20:5. This optimized combination was utilized in preparing solid dispersions by common solvent technique using distilled water as solvent. Solid dispersions were evaluated for flow properties, XRD, DSC, SEM and were also compressed to form tablets. Dissolution studies of conventional and prepared tablets were done using USP Type II apparatus. It was concluded that the concept of mixed hydrotropic solid dispersion is novel, safe and cost-effective technique for enhancing bioavailability of poorly water-soluble drugs by dissolving drug in non-ionized form. The magical enhancement in solubility of furosemide is clear indication of its potential to be used in future for other poorly water-soluble drugs in which low bioavailability is major concern. [ABSTRACT FROM AUTHOR]

Abstract: Because of their sessile nature, plants require appropriate strategies to adapt to the surrounding environment. Tropism is a directional growth in response to environmental stimulus that allows plants to adapt to changes in sunlight, nutrients and water. Plant roots display hydrotropism in response to a moisture gradient, and this phenomenon is believed to play an important role in the ability of the plant to obtain water. However, the molecular mechanism underlying hydrotropism has yet to be fully elucidated. To investigate the transcriptional changes associated with root hydrotropism, we performed a whole-genome microarray analysis of Arabidopsis to monitor the transcription levels of 22,810 genes during the early phase of the hydrotropic response. The transcript levels of 793 genes were significantly changed 1 or 2hours (h) after hydrotropic stimulation. A large number of genes responsive to abscisic acid (ABA) or water-stress were among the hydrostimulation-responsive genes. In contrast, there appeared to be little overlap in transcript abundance between hydrostimulation-responsive and gravistimulation-responsive genes. Our results suggest that ABA and water-stress responses are important signal transduction mechanisms involved in the root hydrotropic response, and that the signaling pathways involved in hydrotropism differ from those of gravitropism. [Copyright &y& Elsevier]

Abstract: Hydrotropy is a phenomenon where the presence of a large quantity of one solute enhances the solubility of another solute. The mechanism of this phenomenon remains elusive and a topic of debate. This study employed molecular dynamics simulation to investigate solute interactions of a model system consisting of a hydrotropic agent, caffeine (CAF), a poorly water-soluble solute, riboflavin (RBF), and water. The study demonstrates that CAF and RBF undergo molecular parallel stacking in the aqueous solution, a result correlating closely to the self-stacking of CAF under the same conditions. The correlations are found both structurally and dynamically, suggesting that the self-stacking of CAF is the primary effect, and incorporation of RBF is the secondary effect. The solute stacking gives rise to the partitioning of solutes and water, which helps restoring the normal water structure and drives down the system energy. The interactions between the solutes are found insignificant to the solute clustering. The dynamic data confirm that the solute stacks are dynamically active. These results suggest that hydrotropic effect of CAF may be attributed to solute parallel stacking. [ABSTRACT FROM AUTHOR]

The effect of hydrotropes potassium p-toluene sulfonate (KPTS), citric acid, and nicotinamide on the solubility and mass-transfer coefficient of 1,2-dihydroxy-9,10-anthraquinone (alizarin) was studied. Solubility studies were carried out under a wide range of hydrotrope concentrations (0 to 3.0 mol·L-1) and different system temperatures (303 to 333 K). It was observed that the solubility and mass-transfer coefficient of alizarin increases with an increase in hydrotrope concentration and system temperature. The maximum enhancement factor, the ratio of the value of solubility in the presence and absence of a hydrotrope, was determined for all experiments under study. The effectivity of hydrotropes was measured by the determination of the Setschenow constant, Ks. The order of effectiveness of various hydrotropes based on Ks values is potassium p-toluene sulfonate > citric acid > nicotinamide. [ABSTRACT FROM AUTHOR]

Various techniques are employed to enhance the aqueous solubility of poorly water-soluble drugs and hydrotropic solubilization is one of them. In the present investigation, hydrotropic solution of ibuprofen sodium (0.5M) was employed as solubilizing agent to solubilize the poorly water-soluble drug, ornidazole from fine power of its tablets for spectrophotometric determination. Ornidazole shows its maximum absorbance at 320 nm and Beer's law was obeyed in concentration range of 5-25 mcg/ml. Results of analysis were validated statistically and by recovery studies. The proposed method is new, simple, safe, environmentally friendly, accurate and cost-effective and can be successfully employed in routine to analyze ornidazole tablets. Hydrotropic agent and commonly used tablet additives did not interfere in the analysis. [ABSTRACT FROM AUTHOR]

Plants have evolved a variety of mechanisms for responding to environmental cues, which allows them to survive in the presence of limited resources or environmental stresses. One of the most significant growth adaptations plants have attained is tropism, a growth response that involves bending of plant organs toward or away from a stimulus. Roots exhibit hydrotropism in response to moisture gradients, which is thought to be critical in acquiring water and establishing their stand in the soil. However, the mechanism underlying hydrotropism remains unsolved. Here, we report that the no hydrotropic response ( nhr1) mutant of Arabidopsis, which is impaired in hydrotropism, is tolerant to drought. The no hydrotropic response phenotype of nhr1 was repressed by AbamineSG, an inhibitor of abscisic acid (ABA) biosynthesis, indicating that ABA negatively regulates hydrotropism. Furthermore, the content of ABA was higher in nhr1 compared to those of wild type (wt). However, the higher ABA levels in nhr1 plants were not due to higher transcript levels of 9- cis-epoxycarotenoid dioxygenase ( NCED3), since these were diminished compared to those of wt. Our results indicated that the root hydrotropic response of the nhr1 mutant is modulated by ABA and that the higher ABA levels of the mutant might confer it drought resistance. [ABSTRACT FROM AUTHOR]

Root hydrotropism is the phenomenon of directional root growth toward moisture under water-deficient conditions. Although physiological and genetic studies have revealed the involvement of the root cap in the sensing of moisture gradients, and those of auxin and abscisic acid (ABA) in the signal transduction for asymmetric root elongation, the overall mechanism of root hydrotropism is still unclear. We found that the promoter activity of the Arabidopsis phospholipase Dζ2 gene ( PLDζ 2) was localized to epidermal cells in the distal root elongation zone and lateral root cap cells adjacent to them, and that exogenous ABA enhanced the activity and extended its area to the entire root cap. Although pldζ 2 mutant root caps did not exhibit a morphological phenotype in either the absence or presence of exogenous ABA, the inhibitory effect of ABA on gravitropism, which was significant in wild-type roots, was not observed in pldζ 2 mutant roots. In root hydrotropism experiments, pldζ 2 mutations significantly retarded or disturbed root hydrotropic responses. A drought condition similar to that used in a hydrotropism experiment enhanced the PLDζ2 promoter activity in the root cap, as did exogenous ABA. These results suggest that PLDζ 2 responds to drought through ABA signaling in the root cap and accelerates root hydrotropism through the suppression of root gravitropism. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented discussing hydrotropism without requiring auxin redistribution.

Abstract: Plants are sessile in nature and must respond to various environmental cues to regulate their growth orientation. Root hydrotropism, a response to moisture gradients, has been considered to play an important role in drought avoidance. Nonetheless, the processes underlying hydrotropism in roots have remained obscure until recently because of the interfering effect of gravitropism. To shed light on root hydrotropism, we isolated and analyzed two Arabidopsis mutants, mizu-kussei (miz) 1 and 2, that have abnormal hydrotropic responses but normal responses to gravity. MIZ1 encodes a protein of unknown function with a conserved domain at its C-terminus. MIZ2 encodes a guanine-nucleotide exchange factor for ADP-ribosylation factor-type G proteins, which has been identified as GNOM. These findings suggest that roots possess molecular mechanisms essential for hydrotropism but independent of gravitropism. One of such mechanisms involves vesicle transport unique to hydrotropism in roots. Here we summarize recent progress on the molecular mechanism of root hydrotropism and the roles of MIZ1 and MIZ2. [Copyright &y& Elsevier]

The influence of soil fungi on soil organic carbon (OC) from surface residue was tested in outdoor plots in southern Ontario, Canada, 2004. Fungal hyphal length, soil aggregation, OC and light and heavy fractions of organic matter were compared with factors of plant growth (with or without oat [Avena sativa]) and surface residue (no residue, oat straw (low C:N) or corn (Zea mays) stalks (high C:N)) in a factorial arrangement. Significant increases were observed in soil OC from the oat plants, and from corn stalks compared to straw residue, in the growing season with very moist, high OC, sandy soil. In treatments with corn stalk residue, fungal hyphal length was increased with interaction from the oat plants and residue and was positively correlated with the heavy fraction organic matter along with soil OC. Fungal hyphae, plant roots and high C:N residue were all factors in soil OC increases. [ABSTRACT FROM AUTHOR]

In most soils, the spatial distribution of nutrients and water in the rooting zone of plants is heterogeneous and changes over time. To access localized resources more efficiently, plants induce foraging responses by modulating individual morphological root traits, such as the length of the primary root or the number and length of lateral roots. These adaptive responses require the integration of exogenous and endogenous nutrient- or water-related signals into the root developmental program. Recent studies corroborated a central role of auxin in shaping root architectural traits in response to fluctuating nutrient and water availabilities. In this review, we highlight current knowledge on nutrient- and water-related developmental processes that impact root foraging and involve auxin as a central player. A deeper understanding and exploitation of these auxin-related processes and mechanisms promises advances in crop breeding for higher resource efficiency. [ABSTRACT FROM AUTHOR]