Root Signal Research Articles

A nitrogen-responsive cytokinin oxidase/dehydrogenase regulates root response to high ammonium in rice.

Plant root system is significantly influenced by high soil levels of ammonium nitrogen, leading to reduced root elongation and enhanced lateral root branching. In Arabidopsis, these processes have been reported to be mediated by phytohormones and their downstream signaling pathways, while the controlling mechanisms remain elusive in crops. Through a transcriptome analysis of roots subjected to high/low ammonium treatments, we identified a cytokinin oxidase/dehydrogenase encoding gene, CKX3, whose expression is induced by high ammonium. Knocking out CKX3 and its homologue CKX8 results in shorter seminal roots, fewer lateral roots, and reduced sensitivity to high ammonium. Endogenous cytokinin levels are elevated by high ammonium or in ckx3 mutants. Cytokinin application results in shorter seminal roots and fewer lateral roots in wild-type, mimicking the root responses of ckx3 mutants to high ammonium. Furthermore, CKX3 is transcriptionally activated by type-B RR25 and RR26, and ckx3 mutants have reduced auxin content and signaling in roots under low ammonium. This study identified RR25/26-CKX3-cytokinin as a signal module that mediates root responses to external ammonium by modulating of auxin signaling in the root meristem and lateral root primordium. This highlights the critical role of cytokinin metabolism in regulating rice root development in response to ammonium.

The impact of alternative recycled and synthetic phosphorus sources on plant growth and responses, soil interactions and sustainable agriculture - lettuce (Lactuca sativa) as a case model

This research assesses the efficacy of two phosphorus (P) adsorbents as alternative fertilizers in promoting lettuce growth. A synthetic Mg/Al-layered double hydroxide (LDH) and an iron-based recycled water treatment residual (Fe-WTR), both enriched with P from dairy wastewater and added at three dosage levels. We hypothesized that the adsorbents' physicochemical nature will overshadow the biological efforts in the plant ecosystem to increase P solubility, impacting plant growth, nutritional composition, and metabolite profiles.Fe-WTR significantly enhanced lettuce biomass compared to LDH. Yet, elemental analysis revealed higher or equal P concentrations in the low-biomass LDH plants relative to other treatments. Phosphorus uptake appears to influence the assimilation of other nutrients that divided into two groups: calcium, magnesium, zinc, and copper with notable correlations to P and nitrogen, iron, aluminum, vanadium and manganese with low correlations to P. Conversely, P retained poor correlation with most metabolites whereas iron showed a higher correlation with numerous metabolites. Analysis of metabolites, encompassing carbohydrates, the Krebs cycle, amino acids, nucleic acids, and stress and regulatory pathways, revealed diminished levels in the LDH treatments. Overall, carbon assimilation (plant growth) was more effectively predicted by soil P availability (adsorbent type and dose) rather than by cellular P concentration, suggesting root signaling was at play, influencing carbohydrate translocation to the roots. Diminished levels of cellular sugars further affect metabolic pathways and iron uptake, thus restricting photosynthesis. The results illustrate the substantial influence of the P source on the plant's metabolic processes and soil biogeochemistry. The synthetic LDH adsorbent with high sorption capacity, tightly binds its substantial P pool, rendering it inaccessible and potentially disrupting rhizosphere biogeochemical interactions. In contrast, the chemical nature of Fe-WTR enabled efficient nutrients acquisition bioactivity. The study highlights Fe-WTR as a promising sustainable alternative to conventional fertilizers, emphasizing its potential scalability and adaptability in agricultural contexts.

Root Signaling Substances Regulate Carbon Allocation Mechanism in the Plant and Soil of Peatlands under Permafrost Degradation

Root Signaling Substances Regulate Carbon Allocation Mechanism in the Plant and Soil of Peatlands under Permafrost Degradation

ЗАСТОСУВАННЯ ФІЛЬТРА ЧАСТОЧОК ДО ЗАДАЧ САМОЛОКАЛІЗАЦІЇ ЛИШЕ ЗА ВІДСТАННЮ ДО ДЖЕРЕЛ РАДІОСИГНАЛІВ

This work is aimed at searching for a relatively accurate and computationally efficient algorithm for range-only self-localization. Key requirement to the data sources is cost effectiveness. The radio signal strength indicator (RSSI)-based distance estimation model was chosen, due to wide availability of hardware and cost effectiveness. Key requirements to the algorithm are robustness towards noise introduced by RSSI-based distance estimation errors and flexibility to introduce additional data sources. Particle filter algorithm was chosen, because it satisfies both requirements, although it has bigger computational costs comparing to Kalman filter. A simulation environment was created to conduct experiments with assumed transmitted signal strength of 1W and square root signal decay law. A Particle filter-based actor was implemented. Actor starts by translating geo-spatial coordinates of beacons into relative planar cartesian coordinates, generates particles around beacons. Particles are placed with uniform distribution within a torus with co-planar circular axis radius equal to distance estimation. In each experiment, simulation software walks actor through a pre-defined path, compares obtained position estimates with expected state and calculates MAE and RMSE. Obtained results were satisfactory, in some cases showing MAE=2.5981 and RMSE=2.8474 after short stabilization period of few iterations. This period exists due to suboptimal initial particles placement. A Kalman filter-based actor was implemented as a comparison. A reference Kalman filter-based implementation showed slightly worse overall results with MAE=12.5199 and RMSE=13.2238. This can be explained by a lack of input from IMU. Further research will be directed towards UAV swarm self-localization and collision avoidance.

Evolution of endosymbiosis-mediated nuclear calcium signaling in land plants

The ability of fungi to establish mycorrhizal associations with plants and enhance the acquisition of mineral nutrients stands out as a key feature of terrestrial life. Evidence indicates that arbuscular mycorrhizal (AM) association is a trait present in the common ancestor of land plants,1,2,3,4 suggesting that AM symbiosis was an important adaptation for plants in terrestrial environments.5 The activation of nuclear calcium signaling in roots is essential for AM within flowering plants.6 Given that the earliest land plants lacked roots, whether nuclear calcium signals are required for AM in non-flowering plants is unknown. To address this question, we explored the functional conservation of symbiont-induced nuclear calcium signals between the liverwort Marchantia paleacea and the legume Medicago truncatula. In M.paleacea, AM fungi penetrate the rhizoids and form arbuscules in the thalli.7 Here, we demonstrate that AM germinating spore exudate (GSE) activates nuclear calcium signals in the rhizoids of M.paleacea and that this activation is dependent on the nuclear-localized ion channel DOES NOT MAKE INFECTIONS 1 (MpaDMI1). However, unlike flowering plants, MpaDMI1-mediated calcium signaling is only required for the thalli colonization but not for the AM penetration within rhizoids. We further demonstrate that the mechanism of regulation of DMI1 has diverged between M.paleacea and M.truncatula, including a key amino acid residue essential to sustain DMI1 in an inactive state. Our study reveals functional evolution of nuclear calcium signaling between liverworts and flowering plants and opens new avenues of research into the mechanism of endosymbiosis signaling.

OsRR26, a type-B response regulator, modulates salinity tolerance in rice via phytohormone-mediated ROS accumulation in roots and influencing reproductive development.

OsRR26 is a cytokinin-responsive response regulator that promotes phytohormone-mediated ROS accumulation in rice roots, regulates seedling growth, spikelet fertility, awn development, represses NADPH oxidases, and negatively affects salinity tolerance. Plant two-component systems (TCS) play a pivotal role in phytohormone signaling, stress responses, and circadian rhythm. However, a significant knowledge gap exists regarding TCS in rice. In this study, we utilized a functional genomics approach to elucidate the role of OsRR26, a type-B response regulator in rice. Our results demonstrate that OsRR26 is responsive to cytokinin, ABA, and salinity stress, serving as the ortholog of Arabidopsis ARR11. OsRR26 primarily localizes to the nucleus and plays a crucial role in seedling growth, spikelet fertility, and the suppression of awn development. Exogenous application of cytokinin led to distinct patterns of reactive oxygen species (ROS) accumulation in the roots of both WT and transgenic plants (OsRR26OE and OsRR26KD), indicating the potential involvement of OsRR26 in cytokinin-mediated ROS signaling in roots. The application of exogenous ABA resulted in varied cellular compartmentalization of ROS between the WT and transgenic lines. Stress tolerance assays of these plants revealed that OsRR26 functions as a negative regulator of salinity stress tolerance across different developmental stages in rice. Physiological and biochemical analyses unveiled that the knockdown of OsRR26 enhances salinity tolerance, characterized by improved chlorophyll retention and the accumulation of soluble sugars, K+ content, and amino acids, particularly proline.

Strigolactones Might Regulate Ovule Development after Fertilization in Xanthoceras sorbifolium.

Strigolactones (SLs) were recently defined as a novel class of plant hormones that act as key regulators of diverse developmental processes and environmental responses. Much research has focused on SL biosynthesis and signaling in roots and shoots, but little is known about whether SLs are produced in early developing seeds and about their roles in ovule development after fertilization. This study revealed that the fertilized ovules and early developing pericarp in Xanthoceras sorbifolium produced minute amounts of two strigolactones: 5-deoxystrigol and strigol. Their content decreased in the plants with the addition of exogenous phosphate (Pi) compared to those without the Pi treatment. The exogenous application of an SL analog (GR24) and a specific inhibitor of SL biosynthesis (TIS108) affected early seed development and fruit set. In the Xanthoceras genome, we identified 69 potential homologs of genes involved in SL biological synthesis and signaling. Using RNA-seq to characterize the expression of these genes in the fertilized ovules, 37 genes were found to express differently in the fertilized ovules that were aborting compared to the normally developing ovules. A transcriptome analysis also revealed that in normally developing ovules after fertilization, 12 potential invertase genes were actively expressed. Hexoses (glucose and fructose) accumulated at high concentrations in normally developing ovules during syncytial endosperm development. In contrast, a low ratio of hexose and sucrose levels was detected in aborting ovules with a high strigolactone content. XsD14 virus-induced gene silencing (VIGS) increased the hexose content in fertilized ovules and induced the proliferation of endosperm free nuclei, thereby promoting early seed development and fruit set. We propose that the crosstalk between sugar and strigolactone signals may be an important part of a system that accurately regulates the abortion of ovules after fertilization. This study is useful for understanding the mechanisms underlying ovule abortion, which will serve as a guide for genetic or chemical approaches to promote seed yield in Xanthoceras.

Exogenous abscisic acid induces the formation of a suberized barrier to radial oxygen loss in adventitious roots of barley (Hordeum vulgare).

Internal root aeration is essential for root growth in waterlogged conditions. Aerenchyma provides a path for oxygen to diffuse to the roots. In most wetland species, including rice, a barrier to radial oxygen loss (ROL) allows more of the oxygen to diffuse to the root tip, enabling root growth into anoxic soil. Most dryland crops, including barley, do not form a root ROL barrier. We previously found that abscisic acid (ABA) signalling is involved in the induction of ROL barrier formation in rice during waterlogging. Although rice typically does not form a tight ROL barrier in roots in aerated conditions, an ROL barrier with suberized exodermis was induced by application of exogenous ABA. Therefore, we hypothesized that ABA application could also trigger root ROL barrier formation with hypodermal suberization in barley. Formation of an ROL barrier was examined in roots in different exogenous ABA concentrations and at different time points using cylindrical electrodes and Methylene Blue staining. Additionally, we evaluated root porosity and observed suberin and lignin modification. Suberin, lignin and Casparian strips in the cell walls were observed by histochemical staining. We also evaluated the permeability of the apoplast to a tracer. Application of ABA induced suberization and ROL barrier formation in the adventitious roots of barley. The hypodermis also formed lignin-containing Casparian strips and a barrier to the infiltration of an apoplastic tracer (periodic acid). However, ABA application did not affect root porosity. Our results show that in artificial conditions, barley can induce the formation of ROL and apoplastic barriers in the outer part of roots if ABA is applied exogenously. The difference in ROL barrier inducibility between barley (an upland species) and rice (a wetland species) might be attributable to differences in ABA signalling in roots in response to waterlogging conditions.

Hormonal and epigenetic regulation of root responses to salinity stress

Salinity stress is a major environmental stress affecting crop productivity, and its negative impact on global food security is only going to increase, due to current climate trends. Salinity tolerance was present in wild crop relatives but significantly weakened during domestication. Regaining it back requires a good understanding of molecular mechanisms and traits involved in control of plant ionic and ROS homeostasis. This review summarizes our current knowledge on the role of major plant hormones (auxin, cytokinins, abscisic acid, salicylic acid, and jasmonate) in plants adaptation to soil salinity. We firstly discuss the role of hormones in controlling root tropisms, root growth and architecture (primary root elongation, meristematic activity, lateral root development, and root hairs formation). Hormone-mediated control of uptake and sequestration of key inorganic ions (sodium, potassium, and calcium) is then discussed followed by regulation of cell redox balance and ROS signaling in salt-stressed roots. Finally, the role of epigenetic alterations such as DNA methylation and histone modifications in control of plant ion and ROS homeostasis and signaling is discussed. This data may help develop novel strategies for breeding and cultivating salt-tolerant crops and improving agricultural productivity in saline regions.

Physiological, molecular, and genetic mechanism of action of the biostimulant Quantis™ for increased thermotolerance of potato (Solanum tuberosum L.)

BackgroundRaising global temperatures limit crop productivity and new strategies are needed to improve the resilience of thermosensitive crops such as potato (Solanum tuberosum L.). Biostimulants are emerging as potential crop protection products against environmental stress, however their mechanism of action remains largely unknown, hindering their wider adoption. We used comprehensive physiological, molecular, and mass spectrometry approaches to develop understanding of the mechanism of plant thermotolerance exerted by the biostimulant, Quantis™, under heat stress. Using orthologues gene mutations in Arabidopsis thaliana we report heat-defence genes, modified by Quantis™, which were also investigated for potential overlapping functions in biotic stress defence to Sclerotinia sclerotiorum and Rhizoctonia solani.ResultsQuantis™ enhanced PSII photochemical efficiency and decreased thermal dissipation of potato grown under heat stress. These effects were associated with upregulation of genes with antioxidant function, including PR10, flavonoid 3′‐hydroxylase and β-glucosidases, and modulation of abscisic acid (ABA) and cytokinin (CK) activity in leaves by Quantis™. The biostimulant modulated the expression of the heat-defence genes, PEN1, PR4 or MEE59, with functions in leaf photoprotection and root thermal protection, but with no overlapping function in biotic stress defence. Protective root growth under heat stress, following the biostimulant application, was correlated with enhanced CK signalling in roots. Increased endogenous concentrations of ABA and CK in potato leaves and significant upregulation of StFKF1 were consistent with tuberisation promoting effects. Quantis™ application resulted in 4% tuber weight increase and 40% larger tuber size thus mitigating negative effects of heat stress on tuber growth.ConclusionsQuantis™ application prior to heat stress effectively primed heat tolerance responses and alleviated temperature stress of S. tuberosum L. and A. thaliana by modulating the expression and function of PR4 and MEE59 and by regulating CK activity above and below ground, indicating that the mechanism of action of the biostimulant is conserved, and will be effective in many plant species. Thus, a biostimulant application targeting the most susceptible crop developmental stages to heat disorders can be effectively integrated within future agronomy practices to mitigate losses in other thermosensitive crops.Graphical

Physiological Responses Revealed Static Magnetic Fields Potentially Improving the Tolerance of Poplar Seedlings to Salt Stress

Magnetic fields play an important role in regulating plant growth and development, especially in improving plant stress tolerance. However, the physiological mechanism underlying the magnetic effects is still unclear. Here, we examined changes in reactive oxygen species (ROS) levels and ion flux in poplar (Populus × deltoides ‘Lulin-2’) seedling roots under salt stress in a static magnetic field (SMF). SMF treatment significantly increased seedling growth and mitigated the effects of salt stress on root growth. Furthermore, SMF treatment activated ROS and calcium signals in poplar roots. Relative to the SMF treatment group, control plants had significantly higher levels of cytoplasmic free Ca2+ ([Ca2+]cyt) and ROS following exposure to high salt concentrations. Under salt conditions, SMF treatment reduced increases in Na+ concentrations and maintained stable K+ and Ca2+ concentrations and K+/Na+ and Ca2+/Na+ ratios. NMT analysis suggests that SMF treatment may drive cation effluxes in poplar seedling roots. Susceptibility tests of Na+-transport inhibitors indicated that SMF treatment contributed to Na+ repulsion and H+ uptake under salt stress. Moreover, SMF exposure allowed roots to retain the ability to reduce salt-induced K+ and Ca2+ root effluxes, and qRT-PCR results demonstrate that SMF treatment can increase the expression of stress-responsive genes such as PtrRBOHF, PtrNHX1 and PtrHA5 in poplar seedlings. Therefore, we conclude that treating poplar seedlings with SMF can help them establish a stable tolerance to salt stress by regulating ROS, [Ca2+]cyt, and their regulatory networks. This study examined the physiological responses of poplar to SMF exposure under salt stress, providing insights into plant magnetobiological effects.

Straining the root on and off triggers local calcium signalling.

A fundamental function of an organ is the ability to perceive mechanical cues. Yet, how this is accomplished is not fully understood, particularly in plant roots. In plants, the majority of studies dealing with the effects of mechanical stress have investigated the aerial parts. However, in natural conditions roots are also subjected to mechanical cues, for example when the root encounters a hard obstacle during its growth or when the soil settles. To investigate root cellular responses to root compression, we developed a microfluidic system associated with a microvalve allowing the delivery of controlled and reproducible mechanical stimulations to the root. In this study, examining plants expressing the R-GECO1-mTurquoise calcium reporter, we addressed the root cell deformation and calcium increase induced by the mechanical stimulation. Lateral pressure applied on the root induced a moderate elastic deformation of root cortical cells and elicited a multicomponent calcium signal at the onset of the pressure pulse, followed by a second one at the release of the pressure. This indicates that straining rather than stressing of tissues is relevant to trigger the calcium signal. Although the intensity of the calcium response increases with the pressure applied, successive pressure stimuli led to a remarkable attenuation of the calcium signal. The calcium elevation was restricted to the tissue under pressure and did not propagate. Strain sensing, spatial restriction and habituation to repetitive stimulation represent the fundamental properties of root signalling in response to local mechanical stimulation. These data linking mechanical properties of root cells to calcium elevation contribute to elucidating the pathway allowing the root to adapt to the mechanical cues generated by the soil.

Foliar application of strigolactones improves the desiccation tolerance, grain yield and water use efficiency in dryland wheat through modulation of non-hydraulic root signals and antioxidant defense

Non-hydraulic root signals (nHRS) are affirmed as a unique positive response to soil drying, and play a crucial role in regulating water use efficiency and yield formation in dryland wheat production. Strigolactones (SLs) can enhance plant drought adaptability. However, the question of whether strigolactones enhance grain yield and water use efficiency by regulating nHRS and antioxidant defense systems in dryland wheat remains unanswered. In this study, pot experiments were conducted to investigate the effects of strigolactones on nHRS, antioxidant defense system, and grain yield and water use efficiency in dryland wheat. The results showed that external application of SLs increased drought-induced abscisic acid (ABA) accumulation and activated an earlier trigger of nHRS at 73.4% field capacity (FC), compared to 68.5% FC in the control group (CK). This phenomenon was mechanically associated with the physiological mediation of SLs. The application of SLs significantly enhanced the activities of leaf antioxidant enzymes, reduced ROS production, and mitigated oxidative damage to lipid membrane. Additionally, root biomass, root length density, and root to shoot ratio were increased under strigolactone treatment. Furthermore, exogenous application of SLs significantly increased grain yield by 34.9% under moderate drought stress. Water use efficiency was also increased by 21.5% and 33.3% under moderate and severe drought conditions respectively, compared to the control group (CK). The results suggested that the application of strigolactones triggered earlier drought-sensing mechanism and improved the antioxidant defense ability, thus enhancing grain yield and water use efficiency in dryland wheat production.

Three-dimensional magnetic resonance neurography aids in detection of brachial plexus nerve root signal and size alterations in patients with amyotrophic lateral sclerosis: a case-control study.

Since previous histopathological studies have shown a distal to proximal gradient of axonal damage in peripheral nerves of patients with amyotrophic lateral sclerosis (ALS), it would be worthwhile to evaluate consequence of such changes on magnetic resonance imaging (MRI). The aim of this study was to assess proximal-distal longitudinal signal and size alterations of brachial plexus nerve roots in ALS patients using 3-dimensional (3D) magnetic resonance neurography (MRN). A total of 21 ALS patients and 19 controls were evaluated. The diameters and signal-to-noise (SNR) ratio values of C5-C8 roots were measured at five points from proximal to distal sites. Student's t-test was performed to compare the differences at each point between two groups. Linear regression was performed for each nerve root, and the differences in linear regression slopes between two groups were analyzed. Receiver operating characteristic (ROC) analysis was performed for the diameter and SNR value ratio of the distal to the proximal points. Interobserver agreement was excellent [intraclass correlation coefficient (ICC): 0.802-0.913]. The diameters and SNR values of C5-C8 roots showed a significant decrease (P<0.05) from proximal to distal except SNR value of C5 root in controls. The slope values of diameters in ALS were -0.01924 for C5, -0.04404 for C6, -0.06228 for C7, and -0.06464 for C8. The slope values of SNR values in ALS were -10.14 for C5, -12.86 for C6, -15.99 for C7, and -19.06 for C8. The slope of nerve diameters and SNR values for ALS patients were more negatively sloped than controls (P<0.05) except SNR values of C5 and C7 roots. The ROC analysis confirmed that the diameter and SNR value ratio could differentiate ALS patients from controls with high accuracy. The cutoff values of diameter ratio were 0.7418 for C5, 0.6952 for C6, 0.6431 for C7, and 0.7147 for C8. The cutoff values of SNR value ratio were 0.5989 for C5, 0.6516 for C6, 0.6065 for C7, and 0.6758 for C8. Proximal-distal longitudinal diameters and SNR values decreased significantly for brachial plexus nerve roots in ALS patients with larger differences in slopes compared to controls. These results reflect pathophysiological changes of ALS and may be helpful in improving the diagnosis of ALS.

Imaging of the electrical activity in the root zone under limited-water-availability stress: a laboratory study for Vitis vinifera

Abstract. Understanding root signals and their consequences for the whole plant physiology is one of the keys to tackling the water-saving challenge in agriculture. The implementation of water-saving irrigation strategies, such as the partial root zone drying (PRD) method, is part of a comprehensive approach to enhance water use efficiency. To reach this goal tools are needed for the evaluation of the root's and soil water dynamics in time and space. In controlled laboratory conditions, using a rhizotron built for geoelectrical tomography imaging, we monitored the spatio-temporal changes in soil electrical resistivity (ER) for more than a month corresponding to eight alternating water inputs cycles. Electrical resistivity tomography (ERT) was complemented with electrical current imaging (ECI) using plant-stem-induced electrical stimulation. To estimate soil water content in the rhizotron during the experiment, we incorporated Archie's law as a constitutive model. We demonstrated that under mild water stress conditions, it is practically impossible to spatially distinguish the limited-water-availability effects using ECI. We evidenced that the current source density spatial distribution varied during the course of the experiment with the transpiration demand but without any significant relationship to the soil water content changes. On the other hand, ERT showed spatial patterns associated with irrigation and, to a lesser degree, to RWU (root water uptake) and hydraulic redistribution. The interpretation of the geoelectrical imaging with respect to root activity was strengthened and correlated with indirect observations of the plant transpiration using a weight monitoring lysimeter and direct observation of the plant leaf gas exchanges.

Genome-wide identification of QTLs associated with iron deficiency tolerance in soybean reveals GATA12 as the integrator of iron signaling in roots

Genome-wide identification of QTLs associated with iron deficiency tolerance in soybean reveals GATA12 as the integrator of iron signaling in roots

A high-yielding recipe: Cytokinin signaling in soybean roots affects phosphorus uptake efficiency and crop production.

A high-yielding recipe: Cytokinin signaling in soybean roots affects phosphorus uptake efficiency and crop production.

Promotion of Ca2+ Accumulation in Roots by Exogenous Brassinosteroids as a Key Mechanism for Their Enhancement of Plant Salt Tolerance: A Meta-Analysis and Systematic Review.

Brassinosteroids (BRs), the sixth major phytohormone, can regulate plant salt tolerance. Many studies have been conducted to investigate the effects of BRs on plant salt tolerance, generating a large amount of research data. However, a meta-analysis on regulating plant salt tolerance by BRs has not been reported. Therefore, this study conducted a meta-analysis of 132 studies to elucidate the most critical physiological mechanisms by which BRs regulate salt tolerance in plants from a higher dimension and analyze the best ways to apply BRs. The results showed that exogenous BRs significantly increased germination, plant height, root length, and biomass (total dry weight was the largest) of plants under salt stress. There was no significant difference between seed soaking and foliar spraying. However, the medium method (germination stage) and stem application (seedling stage) may be more effective in improving plant salt tolerance. BRs only inhibit germination in Solanaceae. BRs (2 μM), seed soaking for 12 h, and simultaneous treatment with salt stress had the highest germination rate. At the seedling stage, the activity of Brassinolide (C28H48O6) was higher than that of Homobrassinolide (C29H50O6), and post-treatment, BRs (0.02 μM) was the best solution. BRs are unsuitable for use in the germination stage when Sodium chloride is below 100 mM, and the effect is also weakest in the seedling stage. Exogenous BRs promoted photosynthesis, and antioxidant enzyme activity increased the accumulation of osmoregulatory and antioxidant substances and reduced the content of harmful substances and Na+, thus reducing cell damage and improving plant salt tolerance. BRs induced the most soluble protein, chlorophyll a, stomatal conductance, net photosynthetic rate, Glutathione peroxidase, and root-Ca2+, with BRs causing Ca2+ signals in roots probably constituting the most important reason for improving salt tolerance. BRs first promoted the accumulation of Ca2+ in roots, which increased the content of the above vital substances and enzyme activities through the Ca2+ signaling pathway, improving plant salt tolerance.

Arabidopsis root apical meristem survival during waterlogging is determined by phytoglobin through nitric oxide and auxin.

Over-expression of phytoglobin mitigates the degradation of the root apical meristem (RAM) caused by waterlogging through changes in nitric oxide and auxin distribution at the root tip. Plant performance to waterlogging is ameliorated by the over-expression of the Arabidopsis Phytoglobin 1 (Pgb1) which also contributes to the maintenance of a functional RAM. Hypoxia induces accumulation of ROS and damage in roots of wild type plants; these events were preceded by the exhaustion of the RAM resulting from the loss of functionality of the WOX5-expressing quiescent cells (QCs). These phenotypic deviations were exacerbated by suppression of Pgb1 and attenuated when the same gene was up-regulated. Genetic and pharmacological studies demonstrated that degradation of the RAM in hypoxic roots is attributed to a reduction in the auxin maximum at the root tip, necessary for the specification of the QC. This reduction was primarily caused by alterations in PIN-mediated auxin flow but not auxin synthesis. The expression and localization patterns of several PINs, including PIN1, 2, 3 and 4, facilitating the basipetal translocation of auxin and its distribution at the root tip, were altered in hypoxic WT and Pgb1-suppressing roots but mostly unchanged in those over-expressing Pgb1. Disruption of PIN1 and PIN2 signal in hypoxic roots suppressing Pgb1 initiated in the transition zone at 12h and was specifically associated to the absence of Pgb1 protein in the same region. Exogenous auxin restored a functional RAM, while inhibition of the directional auxin flow exacerbated the degradation of the RAM. The regulation of root behavior by Pgb1 was mediated by nitric oxide (NO) in a model consistent with the recognized function of Pgbs as NO scavengers. Collectively, this study contributes to our understanding of the role of Pgbs in preserving root meristem function and QC niche during conditions of stress, and suggests that the root transition zone is most vulnerable to hypoxia.

Functional analysis of auxin derived from a symbiotic mycobiont.

The biosynthesis of auxin or indole-3-acetic acid by microorganisms has a major impact on plant-microbe interactions. Several beneficial microbiota are known to produce auxin, which largely influences root development and growth in the host plants. Akin to findings in rhizobacteria, recent studies have confirmed the production of auxin by plant growth-promoting fungi too. Here, we show that Penicillium citrinum isolate B9 produces auxin as deduced by liquid chromatography tandem-mass spectrometry analysis. Such fungal auxin is secreted and contributes directly to enhanced root and shoot development and overall plant growth in Arabidopsis thaliana. Furthermore, auxin production by P. citrinum likely involves more than one tryptophan-dependent pathway. Using auxin biosynthesis inhibitor L-Kynurenine, we show that the indole-3-pyruvate pathway might be one of the key biosynthetic routes involved in such auxin production. Confocal microscopy of the DR5rev:GFP Arabidopsis reporter line helped demonstrate that P. citrunum B9-derived auxin is biologically active and is able to significantly enhance auxin signaling in roots during such improved root growth and plant development. Furthermore, the phenotypic growth defects arising from impaired auxin signaling in Arabidopsis taa1 mutant or upon L-Kynurenine treatment of wild-type Arabidopsis seedlings could be significantly alleviated by fungus B9-derived auxin, thus suggesting its positive role in plant growth promotion. Collectively, our results provide clear evidence that the production of auxin is one of the main mechanisms involved in induction of the beneficial plant growth by P. citrinum.