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Background and objective: Salicylic acid (SA) has keratolytic activities and it is used topically to treat dandruff and seborrheic dermatitis. The hydrotropic phenomenon in pharmaceutical preparations is utilized to enhance the solubility of water-insoluble drug molecules that promoted to prepare the salicylic acid as a hair gel for local effect and it can extend its keratolytic action for a longer period compared to the salicylic acid solution. Methods: Preformulation study was performed to exclude any unwanted chemical interaction between SA and excipients using Fourier-transform infrared spectroscopy (FTIR). The solubility of SA was determined separately in sodium acetate and sodium citrate solutions at a concentration of 1, 3, and 5 %w/v, using distilled water as a solvent. An optimum gel formulation was developed and it was used to prepare the SA gel formulation. Characterizations were performed in terms of physical appearance, viscosity, pH, and spreadability, in-vitro studies were performed in physiological pH, and ex-vivo diffusion studies were performed utilizing rats’ skin. Results: FTIR did not show any chemical interaction between the drug and sodium citrate. The hydrotropic solution of sodium citrate with a concentration of 5% w/v increased the solubility of SA by 28 folds, while the sodium acetate solutions with a concentration of 5% w/v increased the solubility of SA by 19 folds. The optimum gel formula (F1) with a drug content of 97% showed a slow dissolution rate and minimum diffusion through the skin. Conclusion: The hydrotropic solubilization technique significantly influenced the solubilization of salicylic acid in the water and the highest solubility rate was achieved from 5% w/v sodium citrate solution. The formulated hydrogels using carbopol 971P as gelling agent decreased the diffusion rate of SA.

SUMMARY: Plants partly optimize their water recruitment from the growth medium by directing root growth toward a moisture source, a phenomenon termed hydrotropism. The default mechanism of downward growth, termed gravitropism, often functions to counteract hydrotropism when the water‐potential gradient deviates from the gravity vector. This review addresses the identity of the root sites in which hydrotropism‐regulating factors function to attenuate gravitropism and the interplay between these various factors. In this context, the function of hormones, including auxin, abscisic acid, and cytokinins, as well as secondary messengers, calcium ions, and reactive oxygen species in the conflict between these two opposing tropisms is discussed. We have assembled the available data on the effects of various chemicals and genetic backgrounds on both gravitropism and hydrotropism, to provide an up‐to‐date perspective on the interactions that dictate the orientation of root tip growth. We specify the relevant open questions for future research. Broadening our understanding of root mechanisms of water recruitment holds great potential for providing advanced approaches and technologies that can improve crop plant performance under less‐than‐optimal conditions, in light of predicted frequent and prolonged drought periods due to global climate change. Significance Statement: Understanding the mechanisms that plant roots utilize to resist the strong tendency to grow downward in order to grow toward a moisture source, holds great potential for unveiling research approaches and technologies to improve crop performance. Herein, we assess the complex interplay between major regulators of root growth, development, and responses to myriad internal and external cues, that function to attenuate downward root growth, thereby enabling the root to reach water. [ABSTRACT FROM AUTHOR]

Plant roots exert hydrotropism in response to moisture gradients to avoid drought stress. The regulatory mechanism underlying hydrotropism involves novel regulators such as MIZ1 and GNOM/MIZ2 as well as abscisic acid (ABA), reactive oxygen species (ROS), and Ca2+ signaling. ABA, ROS, and Ca2+ signaling are also involved in plant responses to drought stress. Although the mechanism of moisture gradient perception remains largely unknown, the sensory apparatus has been reported to reside in the root elongation zone rather than in the root cap. In Arabidopsis roots, hydrotropism is mediated by the action of MIZ1 and ABA in the cortex of the elongation zone, the accumulation of ROS at the root curvature, and the variation in the cytosolic Ca2+ concentration in the entire root tip including the root cap and stele of the elongation zone. Moreover, root exposure to moisture gradients has been proposed to cause asymmetric ABA distribution or Ca2+ signaling, leading to the induction of the hydrotropic response. A comprehensive and detailed analysis of hydrotropism regulators and their signaling network in relation to the tissues required for their function is apparently crucial for understanding the mechanisms unique to root hydrotropism. Here, referring to studies on plant responses to drought stress, we summarize the recent findings relating to the role of ABA, ROS, and Ca2+ signaling in hydrotropism, discuss their functional sites and plausible networks, and raise some questions that need to be answered in future studies. [ABSTRACT FROM AUTHOR]

Hydrotropism is an important adaptation of plant roots to the uneven distribution of water, with current research mainly focused on Arabidopsis thaliana. To examine hydrotropism in tomato (Solanum lycopersicum) primary roots, we used RNA sequencing to determine gene expression of root tips (apical 5 mm) on dry and wet sides of hydrostimulated roots grown on agar plates. Hydrostimulation enhances cell division and expansion on the dry side compared with the wet side of the root tip. In hydrostimulated roots, the abscisic acid (ABA) biosynthesis gene ABA4 was induced more on the dry than the wet side of root tips. The ABA biosynthesis inhibitor Fluridone and the ABA‐deficient mutant notabilis (not) significantly decreased hydrotropic curvature. Wild‐type, but not the ABA biosynthesis mutant not, root tips showed asymmetric H+ efflux, with greater efflux on the dry than on the wet side of root tips. Thus, ABA mediates asymmetric H+ efflux, allowing the root to bend towards the wet side to take up more water. Summary statement: ABA regulates asymmetric H+ efflux, which is required for the root hydrotropic bending. [ABSTRACT FROM AUTHOR]

The MIZ1 play an important role in root hydrotropism. However, the relationship between MIZ1-regulated hydrotropism and amyloplast-mediated gravitropism remain largely unclear. Here, we generated the miz1/pgm1 double mutants by crossing the non-hydrotropic miz1 mutant with the amyloplast-defective pgm1 mutant, which lacks gravitropic response. Our results showed that the miz1/pgm1 mutants exhibited a significant reduction in amyloplast and gravitropic bending, while maintaining a similar ahydrotropic phenotype as the miz1 single mutant. These findings suggest that MIZ1 plays a role in hydrotropism downstream of PGM1. Understanding the mechanisms of interaction between hydrotropism and gravitropism is crucial for comprehending the rooting patterns of plants in natural conditions. The counteracting relationship between root hydrotropism and gravitropism in the miz1 mutant should receive attention in this field, particularly considering the interference from gravitropism on Earth. • he miz1/pgm1 showed a substantial reduction in amyloplast and gravitropic responses, while it exhibited similar ahydrotropic phenotype to miz1 single mutant. • The miz1/pgm1 exhibited similar ahydrotropic phenotype to miz1 single mutant. • MIZ1 plays a role in root hydrotropism downstream of PGM1. [ABSTRACT FROM AUTHOR]

Keywords: Auxin; gravitropism; hydrotropism; phototropism; roots EN Auxin gravitropism hydrotropism phototropism roots 4892 4895 4 09/15/23 20230913 NES 230913 When exposed to one-sided blue light, the roots of plants such as I Arabidopsis thaliana i exhibit negative phototropism and curve away from the light. Transgenic I GNOMpro:GNOM-GFP i roots showed perfect phototropism, identical to wild-type roots, but transgenic I SMBpro:GNOM-GFP i and I SCRpro:GNOM-GFP i roots showed reduced phototropism. Overall, the study shows that MIZ1 acts in the cortex of the Arabidopsis root elongation zone not only in hydrotropism but also in phototropism (Fig. [12] found out that the same tissues in Arabidopsis roots involved in MIZ1- and GNOM/MIZ2-regulated hydrotropism are also required for phototropism. [Extracted from the article]

In response to unilateral blue light illumination, roots of some plant species such as Arabidopsis thaliana exhibit negative phototropism (bending away from light), which is important for light avoidance in nature. MIZU-KUSSEI1 (MIZ1) and GNOM/MIZ2 are essential for positive hydrotropism (i.e. in the presence of a moisture gradient, root bending towards greater water availability). Intriguingly, mutations in these genes also cause a substantial reduction in phototropism. Here, we examined whether the same tissue-specific sites of expression required for MIZ1- and GNOM/MIZ2-regulated hydrotropism in Arabidopsis roots are also required for phototropism. The attenuated phototropic response of miz1 roots was completely restored when a functional MIZ1–green fluorescent protein (GFP) fusion was expressed in the cortex of the root elongation zone but not in other tissues such as root cap, meristem, epidermis, or endodermis. The hydrotropic defect and reduced phototropism of miz2 roots were restored by GNOM/MIZ2 expression in either the epidermis, cortex, or stele, but not in the root cap or endodermis. Thus, the sites in root tissues that are involved in the regulation of MIZ1- and GNOM/MIZ2-dependent hydrotropism also regulate phototropism. These results suggest that MIZ1- and GNOM/MIZ2-mediated pathways are, at least in part, shared by hydrotropic and phototropic responses in Arabidopsis roots. [ABSTRACT FROM AUTHOR]

Hydrotropism is the movement or growth of a plant towards water. It is a type of tropism, or directional growth response, that is triggered by water. Plants are able to detect water through various stimuli, including changes in moisture levels and changes in water potential. The purpose of this study is to provide an overview of how root movement towards water and plant water uptake are stabilized. The impact of hydrotropism on plants can be significant. It can help plants to survive in environments where water is scarce, and it can also help them to grow more efficiently by directing their roots towards the most nutrient-rich soil. To make sure that plant growth and water uptake are stabilized, plants must sense water. Flowing down the roots, being absorbed by roots, and evaporating from the leaves are all processes that are governed by plant physiology and soil science. Soil texture and moisture affect water uptake. Hydraulic resistances can impede plants' water absorption, while loss of water and water movement can change plants' water potential gradients. Growth causes water potential gradients. Plants respond to gradient changes. Stomata and aquaporins govern water flow and loss. When water is scarce, stomatal closure and hydraulic conductance adjustments prevent water loss. Plants adapt to water stream changes by expanding their roots towards water and refining the architecture of their roots. Our study indicates that water availability, or gradients, are impacted by systemic and local changes in water availability. The amount of water available is reflected in plant turgor. There is still a lot of work to be done regarding the study of how the loss and availability of water affect plant cells, as well as how biophysical signals are transformed in a certain way during their transmission into chemical signals so that pathways such as abscisic acid response or organ development can be fed with information. [ABSTRACT FROM AUTHOR]

In recent years, with the abnormal global climate change, the problem of desertification has become more and more serious. The vegetation pattern is accompanied by desertification, and thus, the study of the vegetation pattern is helpful to better understand the causes of desertification. In this work, we reveal the influences of hydrotropism on the vegetation pattern based on a vegetation–water system in the form of reaction–diffusion equations. Parameter ranges for the steady-state mode obtained by analyzing the system show the dynamic behavior near the bifurcation point. Furthermore, we found that vegetation hydrotropism not only induces spatial pattern generation but also promotes the growth of vegetation itself in this area. Therefore, through the study of vegetation patterns, we can take corresponding preventive measures to effectively prevent land desertification and improve the stability of the ecosystem in the region.

Root gravitropism affects root hydrotropism. The interference intensity of root gravitropism with root hydrotropism differs among plant species. However, these differences have not been well compared within a single plant species. In this study, we compared root hydrotropism in various natural variants of Arabidopsis under stationary conditions. As a result, we detected a range of root hydrotropism under stationary conditions among natural Arabidopsis variants. Comparison of root gravitropism and root hydrotropism among several Arabidopsis natural variants classified natural variants that decreased root hydrotropism into two types; namely one type that expresses root gravitropism and root hydrotropism weaker than Col-0, and the other type that expresses weaker root hydrotropism than Col-0 but expresses similar root gravitropism with Col-0. However, root hydrotropism of all examined Arabidopsis natural variants was facilitated by clinorotation. These results suggested that the interference of root gravitropism with root hydrotropism is conserved among Arabidopsis natural variants, although the intensity of root gravitropism interference with root hydrotropism differs. [ABSTRACT FROM AUTHOR]

Drought limits crop performance worldwide. Plant roots' ability to grow toward moisture, termed hydrotropism, is considered one strategy for optimizing water recruitment from the growth medium. Based on the sequence of the hydrotropism-indispensable MIZ1 protein in Arabidopsis thaliana, we identify hydrotropism and drought-responsive genes in tomato. We utilized CRISPR/Cas9 genome-editing technology for targeted mutagenesis of three hydrotropism-associated loci (MIZ1-like) in tomato (Solanum lycopersicum). We show that the three tomato MIZ1-like genes are drought-responsive and two of them are hydrostimulation-responsive. Examination of the root hydrotropic response of triple and double mutants indicated the gene SlMIZ1-1 as indispensable for tomato root hydrotropism. Moreover, expression of the SlMIZ1-1 gene in the Arabidopsis miz1 mutant effectively complemented the lost MIZ1 functionality, including root hydrotropic bending and generation of hydrotropic Ca 2+ signals. Transcriptome analysis of hydrostimulated tomato root tips under control gravity and continuous clinorotation conditions was performed to identify gravitropism- and hydrotropism-responsive genes. This analysis suggested the involvement of ethylene and ABA signalling in modulating the interplay between hydrotropism and gravitropism. Unveiling the molecular mechanisms that underlie hydrotropism and drought response holds great potential for improving crop performance under limiting water availability due to global climate changes., (© 2024 The Author(s). Plant, Cell & Environment published by John Wiley & Sons Ltd.)

Hydrotropism facilitates the orientation of plant roots towards regions of elevated water potential, enabling them to absorb adequate water. Although calcium signaling plays a crucial role in plant response to water tracking, the exact regulatory mechanisms remain a mystery. Here, we employed the Arabidopsis (Arabidopsis thaliana) hydrotropism-specific protein MIZU-KUSSEI1 (MIZ1) as bait and found that calcium-dependent protein kinases4/5/6/11 (CPK4/5/6/11) interacted with MIZ1 in vitro and in vivo. The cpk4/5/6/11 mutant exhibited increased sensitivity to water potential and enhanced root tip curvature. Furthermore, CPK4/5/6/11 primarily phosphorylated MIZ1 at Ser14/36 residues. Additionally, CPK-mediated phosphorylation of MIZ1 relieved its inhibitory effect on the activity of the endoplasmic reticulum-localized Ca2+ pump ECA1, altering the balance between cytoplasmic Ca2+ inflow and outflow, thereby negatively regulating the hydrotropic growth of plants. Overall, our findings unveil the molecular mechanisms by which the CPK4/5/6/11-MIZ1 module functions in regulating plant hydrotropism responses and provide a theoretical foundation for enhancing plant water use efficiency and promoting sustainable agriculture., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Society of Plant Biologists. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

We designed and validated a test system that simulates a growth environment for Zea mays L. maize seedlings under conditions of low moisture gradient in darkness. This system allowed us to simultaneously measure mesocotyl elongation and the primary root hydrotropic response in seedlings before the emergence phase in a collection of maize hybrids. We found great variation in these two traits with statistically significant reduction of their elongations under the low moisture gradient condition that indicate the richness of maize genetic diversity. Hence, the objective of designing a new test system that evaluates the association between these underground traits with the potential use to measure other traits in maize seedlings related to early vigor was achieved.

Hydrotropes are a class of amphiphilic molecules that significantly increase the solubility of organic compounds in water. However, it cannot form well-organized structures, such as micelles by surfactants. Hydrotropes are extremely water-soluble surface-active organic salts which increase the solubility of practically insoluble or sparingly soluble organic compounds in water by almost 200 times. The fundamental physico-chemical properties of hydrotropes, hydrotropic mechanism, and interactions of the compounds with hydrotropes are well elaborated earlier. However, the use of hydrotropes in organic transformation fascinated new attention. This is the first review which explores various organic transformations comprising utilization hydrotropes. [ABSTRACT FROM AUTHOR]

The enzyme activity of the plasma membrane (PM) proton pump, well known as arabidopsis PM H+-ATPase (AHA) in the model plant arabidopsis (Arabidopsis thaliana), is controlled by phosphorylation. Three different classes of phytohormones, brassinosteroids (BRs), abscisic acid (ABA), and auxin regulate plant growth and responses to environmental stimuli, at least in part by modulating the activity of the pump through phosphorylation of the penultimate Thr residue in its carboxyl terminus. Here, we review the current knowledge regarding this tripartite hormonal AHA regulation and highlight mechanisms of activation and deactivation, as well as the significance of hormonal crosstalk. Understanding the complexity of PM H+-ATPase regulation in plants might provide new strategies for sustainable agriculture. Plasma membrane (PM) H+-ATPases regulate pH homeostasis and cellular membrane potential in fungi and plants. Modulation of PM H+-ATPase activity plays a critical role in plant physiology. The acid growth theory has received additional support from hormonal studies that found that brassinosteroids (BRs), auxin, and abscisic acid (ABA) regulate the PM H+-ATPase activity by phosphorylation/dephosphorylation of the penultimate residue, Thr. [ABSTRACT FROM AUTHOR]

Root hydrotropism refers to root directional growth toward soil moisture. Cortical microtubule arrays are essential for determining the growth axis of the elongating cells in plants. However, the role of microtubule reorganization in root hydrotropism remains elusive. Here, we demonstrate that the well-ordered microtubule arrays and the microtubule-severing protein KATANIN (KTN) play important roles in regulating root hydrotropism in Arabidopsis. We found that the root hydrotropic bending of the ktn1 mutant was severely attenuated but not root gravitropism. After hydrostimulation, cortical microtubule arrays in cells of the elongation zone of wild-type (WT) Col-0 roots were reoriented from transverse into an oblique array along the axis of cell elongation, whereas the microtubule arrays in the ktn1 mutant remained in disorder. Moreover, we revealed that abscisic acid (ABA) signaling enhanced the root hydrotropism of WT and partially rescued the oryzalin (a microtubule destabilizer) alterative root hydrotropism of WT but not ktn1 mutants. These results suggest that katanin-dependent microtubule ordering is required for root hydrotropism, which might work downstream of ABA signaling pathways for plant roots to search for water. [ABSTRACT FROM AUTHOR]

Roots exhibit hydrotropism in response to moisture gradients, with the hydrotropism-related gene Mizu-kussei1 (MIZ1) playing a role in regulating root hydrotropism in an oblique orientation. However, the mechanisms underlying MIZ1-regulated root hydrotropism are not well understood. In this study, we employed obliquely oriented experimental systems to investigate root hydrotropism in Arabidopsis. We found that the miz1 mutant displays reduced root hydrotropism but increased root gravitropism following hydrostimulation, as compared to wild-type plants. Conversely, overexpression of AtMIZ1 leads to enhanced root hydrotropism but decreased root gravitropism following hydrostimulation, as compared to wild-type plants. Using co-immunoprecipitation followed by mass spectrometry (IP-MS), we explored proteins that interact with AtMIZ1, and we identified PGMC1 co-immunoprecipitated with MIZ1 in vivo. Furthermore, the miz1 mutant exhibited higher expression of the PGMC1 gene and increased phosphoglucomutase (PGM) activity, while AtMIZ1 overexpressors resulted in lower expression of the PGMC1 gene, reduced amyloplast amount, and reduced PGM activity in comparison to wild-type roots. In addition, different Arabidopsis natural accessions having difference in their hydrotropic response demonstrated expression level of PGMC1 was negatively correlated with hydrotropic root curvature and AtMIZ1 expression. Our results provide valuable insights into the role of amyloplast in MIZ1-regulated root hydrotropism. • MIZ1 is negatively correlated with amyloplast to regulate root hydrotropism. • MIZ1 is negatively correlated with PGMC1 gene expression. • MIZ1 is negatively correlated with PGM activity. [ABSTRACT FROM AUTHOR]

We hereby show that root systems adapt to a spatially discontinuous pattern of water availability even when the gradients of water potential across them are vanishingly small. A paper microfluidic approach allowed us to expose the entire root system of Brassica rapa plants to a square array of water sources, separated by dry areas. Gradients in the concentration of water vapor across the root system were as small as 10-4·mM·m-1 (~4 orders of magnitude smaller than in conventional hydrotropism assays). Despite such minuscule gradients (which greatly limit the possible influence of the well-understood gradient-driven hydrotropic response), our results show that 1) individual roots as well as the root system as a whole adapt to the pattern of water availability to maximize access to water, and that 2) this adaptation increases as water sources become more rare. These results suggest that either plant roots are more sensitive to water gradients than humanmade water sensors by 3-5 orders of magnitude, or they might have developed, like other organisms, mechanisms forwater foraging that allow them to findwater in the absence of an external gradient in water potential. [ABSTRACT FROM AUTHOR]

Hydrotropism is the directed growth of roots toward the water found in the soil. However, mechanisms governing interactions between hydrotropism and gravitropism remain largely unclear. In this study, we found that an air system and an agar–sorbitol system induced only oblique water-potential gradients; an agar–glycerol system induced only vertical water-potential gradients; and a sand system established both oblique and vertical water-potential gradients. We employed obliquely oriented and vertically oriented experimental systems to study hydrotropism in Arabidopsis and tomato plants. Comparative analyses using different hydrotropic systems showed that gravity hindered the ability of roots to search for obliquely oriented water, whilst facilitating roots' search for vertically oriented water. We found that the gravitropism-deficient mutant aux1 showed enhanced hydrotropism in the oblique orientation but impaired root elongation towards water in the vertical orientation. The miz1 mutant exhibited deficient hydrotropism in the oblique orientation but normal root elongation towards water in the vertical orientation. Importantly, in contrast to miz1 , the miz1 / aux1 double mutant exhibited hydrotropic bending in the oblique orientation and attenuated root elongation towards water in the vertical orientation. Our results suggest that gravitropism is required for MIZ1-regulated root hydrotropism in both the oblique orientation and the vertical orientation, providing further insight into the role of gravity in root hydrotropism. [ABSTRACT FROM AUTHOR]

Summary: Recent studies mainly in Arabidopsis have renewed interest and discussion in some of the key issues in hydrotropism of roots, such as the site of water sensing and the involvement of auxin. We examined hydrotropism in maize (Zea mays) primary roots.We determined the site of water sensing along the root using a nonintrusive method. Kinematic analysis was conducted to investigate spatial root elongation during hydrotropic response. Indole‐3‐acetic acid (IAA) and other hormones were quantified using LC–MS/MS. The transcriptome was analyzed using RNA sequencing.Main results: The very tip of the root is the most sensitive to the hydrostimulant. Hydrotropic bending involves coordinated adjustment of spatial cell elongation and cell flux. IAA redistribution occurred in maize roots, preceding hydrotropic bending. The redistribution is caused by a reduction of IAA content on the side facing a hydrostimulant, resulting in a higher IAA content on the dry side. Transcriptomic analysis of the elongation zone prior to bending identified IAA response and lignin synthesis/wall cross‐linking as some of the key processes occurring during the early stages of hydrotropic response.We conclude that maize roots differ from Arabidopsis in the location of hydrostimulant sensing and the involvement of IAA redistribution. [ABSTRACT FROM AUTHOR]

Dwindling fresh water resources and climate change poses serious threats to rice production. Roots play crucial role in sensing water gradient and directing growth of the plant towards water through a mechanism called hydrotropism. Since very little information is available on root hydrotropism in major food crops, this study was carried out to clone and characterize an ortholog of Arabidopsis MIZU-KUSSEI1 (MIZ1) from rice. Contrasting rice genotypes for drought and salt tolerance were selected based on phenotyping for root traits. Nagina 22 and CR-262-4 were identified as most tolerant and Pusa Sugandh 5 and Pusa Basmati 1121 were identified as most susceptible varieties for both drought and salt stresses. Allele mining of MIZ1 in these varieties identified a 12 bp Indel but did not show specific allelic association with stress tolerance. Analysis of allelic variation of OsMIZ1 in 3024 rice genotypes of 3K genome lines using Rice SNP-Seek database revealed 49 InDels. Alleles with the 12 bp deletions were significantly prevalent in indica group as compared to that of japonica group. Real-time RT-PCR analysis revealed that OsMIZ1 expression levels were upregulated significantly in tolerant cv. Nagina 22 and CR-262-4 under osmotic stress, while under salt stress, it was significantly upregulated only in CR-262-4 but maintained in Nagina 22 under salt stress. However, in the roots of susceptible genotypes, OsMIZ1 expression decreased under both the stresses. These results highlight the possible involvement of OsMIZ1 in drought and salt stress tolerance in rice. Furthermore, expression studies using publically available resources showed that enhanced expression of OsMIZ1 is regulated in response to disease infections, mineral deficiency, and heavy metal stresses and is also expressed in reproductive tissues in addition to roots. These findings indicate potential involvement of MIZ1 in developmental and stress response processes in rice. [ABSTRACT FROM AUTHOR]

Roots display directional growth toward moisture in response to a water potential gradient. Root hydrotropism is thought to facilitate plant adaptation to continuously changing water availability. Hydrotropism has not been as extensively studied as gravitropism. However, comparisons of hydrotropic and gravitropic responses identified mechanisms that are unique to hydrotropism. Regulatory mechanisms underlying the hydrotropic response appear to differ among different species. We recently performed molecular and genetic analyses of root hydrotropism in Arabidopsis thaliana. In this review, we summarize the current knowledge of specific mechanisms mediating root hydrotropism in several plant species. [ABSTRACT FROM AUTHOR]

Mizu-kussei1 (MIZ1) plays a crucial role in root hydrotropism, but it is still unclear whether auxin-mediated gravitropism is involved in MIZ1 -modulated root hydrotropism. This study aimed to investigate whether the hydrotropism of the Arabidopsis miz1 mutants could be restored through pharmacological inhibition of auxin transport or genetic modification in root gravitropism. Our findings indicate that the hydrotropic defects of miz1 mutant can be partly recovered by using an auxin transport inhibitor. Furthermore, miz1/pin2 double mutants exhibit more pronounced defects in root gravitropism compared to the wild type, while still displaying a normal hydrotropic response similar to the wild type. These results suggest that the elimination of gravitropism enables miz1 roots to become hydrotropically responsive to moisture gradients. [ABSTRACT FROM AUTHOR]

Understanding how plants respond to spaceflight and extraterrestrial environments is crucial to develop life-support systems intended for long-term human explorations. Gravity is a main factor influencing root development and orientation, typically masking other tropisms. Considering that reduced levels of gravity affect many plant responses in space, the interaction of other tropic stimuli in microgravity represents the frontier to be investigated aiming at life-support systems optimization. In this paper we report on MULTITROP (Multiple-Tropism: interaction of gravity, nutrient and water stimuli for root orientation in microgravity), an experiment performed on the International Space Station during the Expedition 52/53. Scientific aim of the experiment was to disentangle hydrotropism from chemotropism for root orientation in absence of the gravity stimulus. Among several species relevant to space farming, Daucus carota was selected for the experiment because of its suitability with the experimental hardware and setup. At launch site, carrot seeds were placed between two disks of inert substrate (one imbibed with water and the other with a disodium phosphate solution) and integrated into a hardware developed, refurbished and flight-certificated by Kayser Italia. Post-flight, a Ground Reference Experiment was performed. Root development and orientation of seedlings grown in microgravity and at 1g condition were measured through 3D-image analysis procedures after imaging with X-ray microtomography. Radicle protruded preferentially from the ventral side of the seed due to the asymmetric position of the embryo. Such a phenomenon did not prevent the achievement of MULTITROP scientific goal but should be considered for further experiments on radicle growth orientation in microgravity. The experiment conducted in space verified that the primary root of carrot shows a positive chemotropism towards disodium phosphate solution in the absence of the gravity stimulus. On Earth, the positive chemotropism was masked by the dominant effect of gravity and roots developed downward regardless of the presence/absence of nutrients in the substrate. Taking advantage of altered gravity conditions and using other chemical compounds, further studies should be performed to deepen our understanding of root chemotropic response and its interaction with other tropisms.

Maize illustrates one of the most complex cases of embryogenesis in higher plants that results in the development of early embryo with distinctive organs such as the mesocotyl, seminal and primary roots, coleoptile, and plumule. After seed germination, the elongation of root and mesocotyl follows opposite directions in response to specific tropisms (positive and negative gravitropism and hydrotropism). Tropisms represent the differential growth of an organ directed toward several stimuli. Although the life cycle of roots and mesocotyl takes place in darkness, their growth and functions are controlled by different mechanisms. Roots ramify through the soil following the direction of the gravity vector, spreading their tips into new territories looking for water; when water availability is low, the root hydrotropic response is triggered toward the zone with higher moisture. Nonetheless, there is a high range of hydrotropic curvatures (angles) in maize. The processes that control root hydrotropism and mesocotyl elongation remain unclear; however, they are influenced by genetic and environmental cues to guide their growth for optimizing early seedling vigor. Roots and mesocotyls are crucial for the establishment, growth, and development of the plant since both help to forage water in the soil. Mesocotyl elongation is associated with an ancient agriculture practice known as deep planting. This tradition takes advantage of residual soil humidity and continues to be used in semiarid regions of Mexico and USA. Due to the genetic diversity of maize, some lines have developed long mesocotyls capable of deep planting while others are unable to do it. Hence, the genetic and phenetic interaction of maize lines with a robust hydrotropic response and higher mesocotyl elongation in response to water scarcity in time of global heating might be used for developing more resilient maize plants.

Understanding how plants respond to spaceflight and extraterrestrial environments is crucial to develop life-support systems intended for long-term human explorations. Gravity is a main factor influencing root development and orientation, typically masking other tropisms. Considering that reduced levels of gravity affect many plant responses in space, the interaction of other tropic stimuli in microgravity represents the frontier to be investigated aiming at life-support systems optimization. In this paper we report on MULTITROP (Multiple-Tropism: interaction of gravity, nutrient and water stimuli for root orientation in microgravity), an experiment performed on the International Space Station during the Expedition 52/53. Scientific aim of the experiment was to disentangle hydrotropism from chemotropism for root orientation in absence of the gravity stimulus. Among several species relevant to space farming, Daucus carota was selected for the experiment because of its suitability with the experimental hardware and setup. At launch site, carrot seeds were placed between two disks of inert substrate (one imbibed with water and the other with a disodium phosphate solution) and integrated into a hardware developed, refurbished and flight-certificated by Kayser Italia. Post-flight, a Ground Reference Experiment was performed. Root development and orientation of seedlings grown in microgravity and at 1g condition were measured through 3D-image analysis procedures after imaging with X-ray microtomography. Radicle protruded preferentially from the ventral side of the seed due to the asymmetric position of the embryo. Such a phenomenon did not prevent the achievement of MULTITROP scientific goal but should be considered for further experiments on radicle growth orientation in microgravity. The experiment conducted in space verified that the primary root of carrot shows a positive chemotropism towards disodium phosphate solution in the absence of the gravity stimulus. On Earth, the positive chemotropism was masked by the dominant effect of gravity and roots developed downward regardless of the presence/absence of nutrients in the substrate. Taking advantage of altered gravity conditions and using other chemical compounds, further studies should be performed to deepen our understanding of root chemotropic response and its interaction with other tropisms. [ABSTRACT FROM AUTHOR]

[Display omitted] • The preferential solvation of two perichromic probes was studied in binary mixtures with an ionic liquid (IL). • Frequently observed synergism occurred in mixtures where the two components had similar probe polarities. • A parallel was drawn between the observed synergism and the phenomenon of hydrotropism, both caused by ILs. • More generally, ILs are characterized as solvatotropes in solutions of perichromic dyes in binary mixtures. • Solvatotropic ILs form aggregates with the dye and the solvent, leading to synergism and a "hyperpolar" medium. The preferential solvation of two perichromic dyes, 4-amino- N -methylphthalimide (4-AMP) and Nile Red (NR) in binary mixtures of an ionic liquid ([bmim][X], where X = BF 4 , PF 6 , Tf 2 N and DCA) with a protic or non-protic solvent, was investigated, in search of examples of a synergetic or "hyperpolar" behavior. Synergism was generally observed in those mixtures where the two pure components had similar polarity values, according to the employed probe. A parallel was drawn between the observed synergism in these IL mixtures and the phenomenon of hydrotropism, also observed with organic solutes in aqueous IL mixtures. More generally, in binary mixtures with organic solvents, ionic liquids can act as solvatotropes, promoting the dye solvation by formation of solute-specific aggregates with all species present in the mixture. By stabilizing the dipolar excited state of 4-AMP or NR through hydrogen-bonds and electrostatic interactions in these aggregates, a "hyperpolar" milieu is generated, which surpasses the polarities of the two pure components. Solvatotropism seems to offer a more realistic picture than the solvent-exchange model, originally developed for simpler systems, to the phenomenon of preferential solvation in binary mixtures with ionic liquids. [ABSTRACT FROM AUTHOR]

Ever since Darwin postulated that the tip of the root is sensitive to moisture differences and that it "transmits an influence to the upper adjoining part, which bends towards the source of moisture" [Darwin C, Darwin F (1880) The Power of Movement in Plants, pp 572-574], the signal underlying this tropic response has remained elusive. Using the FRET-based Cameleon Ca2+ sensor in planta, we show that a water potential gradient applied across the root tip generates a slow, long-distance asymmetric cytosolic Ca2+ signal in the phloem, which peaks at the elongation zone, where it is dispersed laterally and asymmetrically to peripheral cells, where cell elongation occurs. In addition, the MIZ1 protein, whose biochemical function is unknown but is required for root curvature toward water, is indispensable for generating the slow, long-distance Ca2+ signal. Furthermore, biochemical and genetic manipulations that elevate cytosolic Ca2+ levels, including mutants of the endoplasmic reticulum (ER) Ca2+-ATPase isoform ECA1, enhance root curvature toward water. Finally, coimmunoprecipitation of plant proteins and functional complementation assays in yeast cells revealed that MIZ1 directly binds to ECA1 and inhibits its activity. We suggest that the inhibition of ECA1 by MIZ1 changes the balance between cytosolic Ca2+ influx and efflux and generates the cytosolic Ca2+ signal required for water tracking. [ABSTRACT FROM AUTHOR]

This work shows that autophagy plays a key role in the hydrotropic curvature of Arabidopsis thaliana roots. An analysis of GFP-ATG8a transgenic plants showed that autophagosomes accumulated in the root curvature 2 h after the transfer of seedlings to Normal Medium-Water Stress Medium (NM-WSM). Autophagy flux was required for root bending. Remarkably, several atg mutants did not show hydrotropic curvature in NM-WSM or the splitting-agar system. Hyper, an H 2 O 2 sensor showed that H 2 O 2 preferentially accumulated in the root curvature at a similar rate as the autophagosomes did during hydrotropic response. Peroxidase and ROBH activity inhibition affected, negatively or positively root curvature. This data suggested H 2 O 2 balance was required for root bending. Malondialdehyde, a metabolite used as an indicator of oxidative stress, accumulated at the same rate during the development of the curvature in NM-WSM. These results suggest that autophagy is required for the hydrotropic response in NM-WSM. We discuss the possible regulatory role of H 2 O 2 on autophagy during the hydrotropic response that might relieve oxidative stress provoked by water stress. NM-WSM is water stress system suitable for studying hydrotropic responses on a short-term basis. [ABSTRACT FROM AUTHOR]

Fresh water is an increasingly scarce resource for agriculture. Plant roots mediate water uptake from the soil and have developed a number of adaptive traits such as hydrotropism to aid water foraging. Hydrotropism modifies root growth to respond to a water potential gradient in soil and grow towards areas with a higher moisture content. Abscisic acid (ABA) and a small number of genes, including those encoding ABA signal transducers, MIZ2/GNOM, and the hydrotropism-specific MIZ1, are known to be necessary for the response in Arabidopsis thaliana, whereas the role of auxin in hydrotropism appears to vary depending on the plant species. This review will describe recent progress characterizing the hormonal regulation of hydrotropism. Recent advances in identifying the sites of hydrotropic perception and response, together with its interaction with gravitropism, will also be discussed. Finally, I will describe putative mechanisms for perception of the water potential gradient and a potential role for hydrotropism in acclimatizing plants to drought conditions. [ABSTRACT FROM AUTHOR]

While fast plant movements are spectacular but rare, almost all plants exhibit relatively slow, growth-mediated tropic movements that are key to their survival in the natural world. In this brief review, we discuss recent insights into the molecular mechanisms underlying phototropism, gravitropism, hydrotropism, and autostraightening. Careful molecular genetic and physiological studies have helped confirm the importance of lateral auxin gradients in gravitropic and phototropic responses. However, auxin signaling does not explain all tropisms: recent work has shown that abscisic acid signaling mediates root hydrotropism and has implicated mechanosensing in autostraightening, the organ straightening process recently modeled as a proprioceptive response. The interactions between distinct tropic signaling pathways and other internal and external sensory processes are also now being untangled. [ABSTRACT FROM AUTHOR]

We report synthesis of chromeno[2,3- c]pyrazolyl-pyrazolol(s) with anti-infective potential in aq. sodium p-toluenesulfonate (NaPTS) hydrotropic solution under ultrasound irradiation at room temperature. Salicylaldehyde (1 mmol), on reaction with 1-phenyl-3-methyl-5-pyrazolone (2 mmol), yielded chromeno[2,3- c]pyrazolyl-pyrazolol(s). Knoevenagel reaction, Michael reaction, intramolecular cyclization, followed by dehydration are key steps involved in the present synthetic protocol. The synthesized compounds were screened for their antimicrobial potential, and molecular docking studies were performed to establish their possible mode of action. Graphical Abstract: [ABSTRACT FROM AUTHOR]

In cucumber seedlings, gravitropism interferes with hydrotropism, which results in the nearly complete inhibition of hydrotropism under stationary conditions. However, hydrotropic responses are induced when the gravitropic response in the root is nullified by clinorotation. Columella cells in the root cap sense gravity, which induces the gravitropic response. In this study, we found that removing the root tip induced hydrotropism in cucumber roots under stationary conditions. The application of auxin transport inhibitors to cucumber seedlings under stationary conditions suppressed the hydrotropic response induced by the removal of the root tip. To investigate the expression of genes related to hydrotropism in de-tipped cucumber roots, we conducted transcriptome analysis of gene expression by RNA-Seq using seedlings exhibiting hydrotropic and gravitropic responses. Of the 21 and 45 genes asymmetrically expressed during hydrotropic and gravitropic responses, respectively, five genes were identical. Gene ontology (GO) analysis indicated that the category auxin-inducible genes was significantly enriched among genes that were more highly expressed in the concave side of the root than the convex side during hydrotropic or gravitropic responses. Reverse transcription followed by quantitative polymerase chain reaction (RT-qPCR) analysis revealed that root hydrotropism induced under stationary conditions (by removing the root tip) was accompanied by the asymmetric expression of several auxin-inducible genes. However, intact roots did not exhibit the asymmetric expression patterns of auxin-inducible genes under stationary conditions, even in the presence of a moisture gradient. These results suggest that the root tip inhibits hydrotropism by suppressing the induction of asymmetric auxin distribution. Auxin transport and distribution not mediated by the root tip might play a role in hydrotropism in cucumber roots. [ABSTRACT FROM AUTHOR]

One of the greatest challenges of terrestrial vegetation is to acquire water through soil-grown roots. Owing to the scarcity of high-quality water in the soil and the environment’s spatial heterogeneity and temporal variability, ranging from extreme flooding to drought, roots have evolutionarily acquired tremendous plasticity regarding their geometric arrangement of individual roots and their three-dimensional organization within the soil. Water deficiency has also become an increasing threat to agriculture and dryland ecosystems due to climate change. As a result, roots have become important targets for genetic selection and modification in an effort to improve crop resilience under water-limiting conditions. This review addresses root plasticity from different angles: Their structures and geometry in response to the environment, potential genetic control of root traits suitable for water-limiting conditions, and contemporary and future studies of the principles underlying root plasticity post-Darwin’s ‘root-brain’ hypothesis. Our increasing knowledge of different disciplines of plant sciences and agriculture should contribute to a sustainable management of natural and agricultural ecosystems for the future of mankind.

Roots of higher plants change their growth direction in response to moisture, avoiding drought and gaining maximum advantage for development. This response is termed hydrotropism. There have been few studies of root hydrotropism in grasses, particularly in maize. Our goal was to test whether an enhanced hydrotropic response of maize roots correlates with a better adaptation to drought and partial/lateral irrigation in field studies. We developed a laboratory bioassay for testing hydrotropic response in primary roots of 47 maize elite DTMA ( D rought T olerant M aize for A frica) hybrids. After phenotyping these hybrids in the laboratory, selected lines were tested in the field. Three robust and three weak hybrids were evaluated employing three irrigation procedures: normal irrigation, partial lateral irrigation and drought. Hybrids with a robust hydrotropic response showed growth and developmental patterns, under drought and partial lateral irrigation, that differed from weak hydrotropic responders. A correlation between root crown biomass and grain yield in hybrids with robust hydrotropic response was detected. Hybrids with robust hydrotropic response showed earlier female flowering whereas several root system traits, such as projected root area, median width, maximum width, skeleton width, skeleton nodes, average tip diameter, rooting depth skeleton, thinner aboveground crown roots, as well as stem diameter, were considerably higher than in weak hydrotropic responders in the three irrigation procedures utilized. These results demonstrate the benefit of intensive phenotyping of hydrotropism in primary roots since maize plants that display a robust hydrotropic response grew better under drought and partial lateral irrigation, indicating that a selection for robust hydrotropism might be a promising breeding strategy to improve drought avoidance in maize. [ABSTRACT FROM AUTHOR]

Roots of land plants show gravitropism and hydrotropism in response to gravity and moisture gradients, respectively, for controlling their growth orientation. Gravitropism interferes with hydrotropism, although the mechanistic aspects are poorly understood., Here, we differentiated hydrotropism from gravitropism in cucumber roots by conducting clinorotation and spaceflight experiments. We also compared mechanisms regulating hydrotropism and auxin-regulated gravitropism., Clinorotated or microgravity (μG)-grown cucumber seedling roots hydrotropically bent toward wet substrate in the presence of moisture gradients, but they grew straight in the direction of normal gravitational force at the Earth's surface (1G) on the ground or centrifuge-generated 1G in space. The roots appeared to become hydrotropically more sensitive to moisture gradients under μG conditions in space. Auxin transport inhibitors significantly reduced the hydrotropic response of clinorotated seedling roots. The auxin efflux protein Cs PIN5 was differentially expressed in roots of both clinorotated and μG-grown seedlings; with higher expression in the high-humidity (concave) side than the low-humidity (convex) side of hydrotropically responding roots., Our results suggest that roots become hydrotropically sensitive in μG, and Cs PIN5-mediated auxin transport has an important role in inducing root hydrotropism. Thus, hydrotropic and gravitropic responses in cucumber roots may compete via differential auxin dynamics established in response to moisture gradients and gravity. [ABSTRACT FROM AUTHOR]

The Caatinga biome, characterized by a species-rich seasonally dry tropical forest, but highly disturbed covers most of Brazil's Northeast. Endemic to this biome is the multipurpose tree Spondias tuberosa Arr., which forms numerous root tubers to resist drought stress. In order to develop improved soil management for reforestation with S. tuberosa the response of its root system to different soil amendments was studied with 52 seedlings, using goat manure, clay substrate, biochar as soil amendments, and mineral fertilizer. The default root architecture of three-year-old S. tuberosa and the relation between soil physical parameters and fine root dry matter (≤2 mm), root length density, root tuber volume, root tuber fresh weight, and shoot-root ratio were analyzed. Seedlings still formed a tap root with a maximum rooting depth of 63 cm and a maximum horizontal extent of 35 cm, developing 2–4 root tubers per seedling. Fine root dry matter in 3000 cm 3 soil samples differed significantly, ranging from 0.23 g in the control to 0.03 g in the treatment combining manure with biochar and mineral fertilizer. According to the orthogonal contrast, manure was the pivotal soil amendment affecting fine root dry matter negatively. Simultaneously, manure application led to increased soil water content compared to treatments without . The shoot-root ratio increased by 32% compared to the control, when S. tuberosa was grown in wet soils. Root tuber growth was significantly enhanced by manure addition. This effect is attributed to a reduction of soil bulk density as root tuber volume exhibited a negative correlation with soil bulk density. There was no statistical relationship between root tuber volume and seedling survival during the field experiment. Compared with the control, neither clay, biochar nor solely mineral fertilization significantly affected root growth. Soil management focused on improving water availability is suspected of hampering fine root growth of S. tuberosa seedlings, whereas reducing soil bulk density enables better root tuber development and could, therefore, be a promising measure to increase S. tuberosa drought resistance in the long term for more successful reforestation. Disregarding its negative impact on fine root growth, we assume manure is the most promising amendment among the tested treatments, due to its positive effect on root tuber growth. [ABSTRACT FROM AUTHOR]

The direction of auxin transport changes in gravistimulated roots, causing auxin accumulation in the lower side of horizontally reoriented roots. This study found that auxin was similarly involved in hydrotropism and gravitropism in rice and pea roots, but hydrotropism in Lotus japonicus roots was independent of both auxin transport and response. Application of either auxin transport inhibitors or an auxin response inhibitor decreased both hydrotropism and gravitropism in rice roots, and reduced hydrotropism in pea roots. However, Lotus roots treated with these inhibitors showed reduced gravitropism but an unaltered or an enhanced hydrotropic response. Inhibiting auxin biosynthesis substantially reduced both tropisms in rice and Lotus roots. Removing the final 0.2 mm (including the root cap) from the root tip inhibited gravitropism but not hydrotropism in rice seedling roots. These results suggested that modes of auxin involvement in hydrotropism differed between plant species. In rice roots, although auxin transport and responses were required for both gravitropism and hydrotropism, the root cap was involved in the auxin regulation of gravitropism but not hydrotropism. Hydrotropism in Lotus roots, however, may be regulated by a novel mechanism that is independent of both auxin transport and the TIR1/AFBs auxin response pathway. [ABSTRACT FROM AUTHOR]

Effects of a hydrotropic salt, sodium salicylate (NaSal), on the dynamic behavior of cationic dodecyltrimethylammonium bromide (DTAB) micelles as studied using dynamic light scattering (DLS) and quasielastic neutron scattering (QENS) techniques are reported here. DLS study showed that the addition of NaSal leads to a decrease in the apparent diffusion coefficient of the whole micelle indicating micellar growth. QENS data analysis suggested that observed dynamics involves two distinct motions, lateral motion of the surfactant over the curved micellar surface and localized segmental motion of the surfactant. It is found that the addition of NaSal slows down the lateral motion of DTAB while the localized segmental motion of the DTAB chain is not affected much. An atomistic molecular dynamics (MD) simulation was performed to gain further insight into the underlying phenomena. MD simulation results are found to be consistent with the experimental observations. MD simulation revealed that location of the salicylate ions on the micellar surface and their strong electrostatic association with their oppositely charged surfactant headgroup are the major factors in slowing down the lateral motion of the DTAB molecule. In the present work, a quantitative description of the effects of NaSal on the nanoscopic dynamics of DTAB micelles and its correlation with the microstructure of the micelle is provided. [ABSTRACT FROM AUTHOR]

Because water is essential to life, organisms have evolved a wide range of strategies to cope with water limitations, including actively searching for their preferred moisture levels to avoid dehydration. Plants use moisture gradients to direct their roots through the soil once a water source is detected, but how they first detect the source is unknown. We used the model plant Pisum sativum to investigate the mechanism by which roots sense and locate water. We found that roots were able to locate a water source by sensing the vibrations generated by water moving inside pipes, even in the absence of substrate moisture. When both moisture and acoustic cues were available, roots preferentially used moisture in the soil over acoustic vibrations, suggesting that acoustic gradients enable roots to broadly detect a water source at a distance, while moisture gradients help them to reach their target more accurately. Our results also showed that the presence of noise affected the abilities of roots to perceive and respond correctly to the surrounding soundscape. These findings highlight the urgent need to better understand the ecological role of sound and the consequences of acoustic pollution for plant as well as animal populations. [ABSTRACT FROM AUTHOR]

Hydrotropism is the directional root growth response determined by water stimulus. In a water potential gradient system (WPGS) the roots of the Arabidopsis wild type have a diminished root growth compared to normal medium (NM). In contrast, the altered hydrotropic response1 ( ahr1 ) mutant roots maintain their robust growth in the same WPGS. The aims of this work were to ascertain how ahr1 roots could sustain growth in the WPGS, with a special focus on the integration of cellular processes involved in the signaling that determines root growth during abiotic stress and their relation to hydrotropism. Cellular analysis of the root apical meristem of ahr1 mutant contrary to the wild type showed an absence of changes in the meristem length, the elongation zone length, the length of fully elongated cells, and the cell cycle duration. The robust and steady root growth of ahr1 seedlings in the WPGS is explained by the mutant capacity to maintain cell production and cell elongation at the same level as in the NM. Analysis of auxin response at a transcriptional level showed that roots of the ahr1 mutant had a lower auxin response when grown in the WPGS, compared to wild type, indicating that auxin signaling participates in attenuation of root growth under water stress conditions. Also, wild type plants exhibited a high increase in proline content while ahr1 mutants showed minimum changes in the Normal Medium → Water Stress Medium (NM → WSM), a lower water potential gradient system than the WPGS. Accordingly, in this condition, gene expression of Δ 1-6 Pyrroline-5-Carboxylate Synthetase1 ( P5CS1) involved in proline synthesis strongly increased in wild type but not in ahr1 seedlings. The ahr1 phenotype shows unique features since the mutant root cells continue to proliferate and grow in the presence of a progressively negative water potential gradient at a level comparable to wild type growing in the NM. As such, it represents an exceptional resource for understanding hydrotropism. [ABSTRACT FROM AUTHOR]

High air temperature (HAT) and natural soil drought (NSD) have seriously affected crop yield and frequently take place in a HAT-NSD combination. Maize (Zea mays) is an important crop, thermophilic but not heat tolerant. In this study, HAT, NSD, and HAT-NSD effects on maize inbred line Huangzao4 -were characterized. Main findings were as follows: H 2 O 2 and O- accumulated much more in immature young leaves than in mature old leaves under the stresses. Lateral roots were highly distributed near the upper pot mix layers under HAT and near root tips under HAT-NSD. Saccharide accumulated mainly in stressed root caps (RC) and formed a highly accumulated saccharide band at the boundary between RC and meristematic zone. Lignin deposition was in stressed roots under NSD and HAT-NSD. Chloroplasts increased in number and formed a high-density ring around leaf vascular bundles (VB) under HAT and HAT-NSD, and sparsely scattered in the peripheral area of VBs under NSD. The RC cells containing starch granules were most under NAD-HAT but least under HAT. Under NSD and HAT-NSD followed by re-watering, anther number per tassel spikelet reduced to 3. These results provide multiple clues for further distinguishing molecular mechanisms for maize to tolerate these stresses. • Effects of high air temperature (HAT), natural soil drought (NSD), and HAT-NSD on maize were characterized. • Stress-caused ROS occurs mainly in immature young rather than mature leaves under stresses. • There are some differences in microstructure changes caused by different stresses. • A high saccharide band exists between root caps and meristematic zones under HAT-NSD. • Chloroplasts are highly concentrated around leaf vascular bundles under HAT-NSD. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effect of hydrotrope as a pretreatment process on rice straw for bioethanol production. Sodium cumene sulfonate and sodium xylene sulfonate (Na–X) were used as hydrotropes to delignify rice straw. Effects of biomass loading, time, temperature and hydrotrope concentration were studied for both the hydrotropes. There was no loss of cellulose & hemicellulose in the hydrotrope solution. Sodium cumene sulfonate could remove more than 50% of lignin from rice straw with 5% biomass loading at 121 °C for 1 h. Reusability of aqueous hydrotrope solution was demonstrated. Enzymatic digestibility of the hydrotrope pretreated rice straw was studied and evaluated for subsequent bioethanol production. The use of the hydrotrope for biomass pretreatment has the potential to mitigate the environmental impact of chemical pretreatment. [ABSTRACT FROM AUTHOR]