Individual Root Research Articles

A microchannel device for root hair isolation and behavior analysis

Despite the active development of microchannel devices for cell manipulation, there are few reports on such devices for plants than those for animal cells, including human cells. This paper presents root-hair isolation and observation methods for Arabidopsis thaliana roots by using a microchannel device. Specifically, to facilitate observation, the height and width of the channel were optimized so that only one A. thaliana root hair could pass through. As A. thaliana is a model organism for plant research, in this study, it was used in a experiment with the expectation that its application will expand in the future. In typical in vitro experimental systems, a gel-like medium is used; however, as this is difficult to introduce into the micron-order narrow space of a microchannel device, a liquid medium was used in this study. We established a protocol unique to microchannel devices and succeeded in isolating root hairs at channel heights and widths of at least 10 μm and 10–14 μm, respectively. Root-hair elongation was confirmed in the microchannel, and the deceleration of root-hair elongation rate was confirmed quantitatively. In a future work, based on the findings of this study, we intend to analyze the behavior of individual root hairs and clarify the correlation with repellent substances by exploiting the characteristics of microchannel devices. This research can potentially serve as a basis for future applied research of agricultural chemicals.

Interactive effects of soil water content and nutrients on root exudation in two Mediterranean tree species

Root exudation is affected by the soil water content (SWC) and availability of nutrients, but the impact of the interaction between these abiotic factors is unclear. Understanding the combined effect of these factors is vital for all ecosystems, including Mediterranean forests, where droughts are increasing. A greenhouse experiment was established with a drought treatment (control versus drought) and the subsequent recovery, factorially combined with four nutrient treatments (control, nitrogen (N) addition, phosphorus (P) addition, and both N and P addition). N was added as ammonium nitrate at a rate of 50 kg N ha−1 and P was added as calcium phosphate at a rate of 25 kg P ha−1. Exudation of total organic carbon (TOC) was measured from the roots of 64 saplings of each of two important tree species that coexist in montane Mediterranean regions, Pinus sylvestris (Scots pine) and Quercus ilex (holm oak). The amount of TOC released from individual roots of the saplings was measured to estimate root exudation per gram of root mass. Chlorophyll fluorescence (Fv/Fm) was also monitored to check for treatment effects on leaf performance. Chlorophyll fluorescence was not affected by SWC or nutrient addition in either species, but root exudation was, and varied between the two species. SWC was positively correlated with the amount of TOC released during the drought period for Q. ilex but had no effect on P. sylvestris. The addition of P increased root exudation in Q. ilex. The amount of TOC released in the recovery period for both species with no added nutrients was weakly negatively correlated with SWC during the drought period, potentially indicating a delayed positive effect of the earlier water stress. During recovery, SWC positively affected the amount of TOC collected from the roots when P was added for both species and when N was added for P. sylvestris. Our results indicate that the impacts of drought on root exudation will likely vary between species and will depend on the availability of soil nutrients.

Getting to the root of the problem: improving measurements of mangrove belowground production and carbon sequestration.

This article is a Commentary on Arnaud et al. (2021), 232: 1591–1602.

ALLOMETRIC EQUATIONS FOR BELOWGROUND BIOMASS AND CARBON CONTENT OF Pinus patula SCHL. et CHAM.

Allometric equations are essential tools for estimating biomass and carbon fixation in forest ecosystems. Published information is limited for belowground biomass of forests, mainly due to the methodological challenges of its determination. With the aim of contributing to the study of this important carbon store, in the present study allometric equations were developed for the estimation of belowground biomass of Pinus patula Schiede ex Schldl. et Cham. in its main natural distribution area: the states of Hidalgo, Puebla and Veracruz, Mexico. Seven Pinus patula trees with varying dimensions were selected and torn down at various sites; their diameter at breast height (DBH), total height (H), and crown diameter (CD) were measured. The totality of fine and coarse roots was extracted; the aboveground biomass was quantified by census, by sampling or by means of an allometric equation. Equations were developed for belowground biomass and carbon content, both total and by components, aswell as for individual root, both total and by components. The average root/ shoot ratio was 0.20 and the proportion of belowground in relation to the total biomass ranged from 12.1 to 21.2 %. The data on belowground biomass and carbon content at the tree level better fitted the Schumacher and Hall model that included both DBH and H as independent variables, which explained 99 % of the variation of belowground biomass and carbon. It was concluded that it is possible to use allometric equations to estimate the belowground biomass and carbon of Pinus patula trees from DBH and H, or even using only DBH.

Biomass accumulation of Schlumbergera truncata (Haw.) Moran (Thanksgiving cactus) grown under high pot density

The growth of most pot-grown succulents offered by the ornamental industry is limited mainly by water, nutrients, photoperiod, and temperature manipulation, while other decisions, such as: plant density at pot cropping are often based on the grower’s experience. In the present study, to optimize the biomass accumulation of Schlumbergera truncata under high pot density, we performed an experimental design that included different numbers of initials phylloclades and spraying or not with the synthetic cytokinin 6-benzylaminopurine (BAP). The highest biomass accumulation on a fresh weight basis and highest stem area expansion were recorded in pots with five initial phylloclades and BAP-sprayed plants. The decrease in individual biomass accumulation and the expansion of steam area were related to an increase in pot density. Since shading effect can be discard, responses to photo-assimilate uptake and distribution more associated with mechanical constraints on pot roots rather than with a competition between individual roots. Our results suggest that, when Schlumbergera truncata is grown in pots, the number of initial phylloclades may be higher than the usually recommended number per pot.

Time Course of Root Axis Elongation and Lateral Root Formation in Perennial Ryegrass (Lolium perenne L.).

Grasses have a segmental morphology. Compared to leaf development, data on root development at the phytomer level are scarce. Leaf appearance interval was recorded over time to allow inference about the age of segmental sites that later form roots. Hydroponically grown Lolium perenne cv. Aberdart tillers were studied in both spring and autumn in increasing and decreasing day length conditions, respectively, and dissected to define the development status of roots of known age on successive phytomers basipetally on the tiller axis. Over a 90-day observation period spring and autumn tillers produced 10.4 and 18.1 root bearing phytomers (Pr), respectively. Four stages of root development were identified: (0) main axis elongation (~0–10 days), (1) primary branching (~10–18 days), (2) secondary branching (~18–25 days), and (3) tertiary and quaternary branching without further increase in root dry weight. The individual spring roots achieved significantly greater dry weight (35%) than autumn roots, and a mechanism for seasonal shift in substrate supply to roots is proposed. Our data define a root turnover pattern likely also occurring in field swards and provide insight for modelling the turnover of grass root systems for developing nutrient efficient or stress tolerant ryegrass swards.

Stability of Stretched Root Systems, Root Posets and Shards

Inspired by the infinite families of finite and affine root systems, we define a "stretching" operation on general crystallographic root systems which, on the level of Coxeter diagrams, replaces a vertex with a path of unlabeled edges. We embed a root system into its stretched versions using a similar operation on individual roots. For a fixed root, we describe the long-term behavior of two associated structures as we lengthen the stretched path: the downset in the root poset and Reading's arrangement of shards. We show that both eventually admit a uniform description, and deduce enumerative consequences: the size of the downset is eventually a polynomial, and the number of shards grows exponentially.

Proximity of mandibular third molar root(s) to surrounding cortical bone: cone beam computed tomography (CBCT) and panoramic findings.

We evaluated the relationship between mandibular third molar roots (M3Ms) and surrounding cortical bone using cone beam computed tomography (CBCT) and panoramic findings. We studied (a) the location of mandibular third molar roots in relation with cortical bone in terms of contact, penetration, and perforation on CBCT; (b) the relationship between characteristics of a root in panoramic findings and the CBCT image (entire and segmentally); and (c) the relationship of the root plane in panoramic findings vs. CBCT. One hundred five teeth with 224 roots of mandibular third molar from 73 patients were evaluated by using cone beam computed tomography and panoramic image. The relationships were assessed using 105 images of impacted M3Ms: 104/105 (99%) showed cortical bone involvement (30.4% penetration and 68.6% perforation). The more apical the segment, the higher the proportion of perforation. Most (79.9%) of the M3M roots involved a lingual cortex with 46.9% penetration and 49.2% perforation. The panoramic signs of segmental root images-viz. clear and blurred-were not associated with cortical penetration or perforation. Panoramic signs of individual root images-in the same and different planes-could be used to predict root plane M3M roots. The same appearance in the panoramic image was significantly related to the same plane of the root in CBCT (p-value 0.048). These findings could contribute to enhanced radiological assessment and surgical planning.

SIGNIFICANCE OF SEDIMENTATION SIGN OF MAGNETIC RESONANCE IMAGING (MRI) IN LUMBAR CANAL STENOSIS

Lumbar spinal stenosis (LSS) is common sequelae of degenerative disorders of spine. Spinal canal stenosis is a narrowing in the spinal canal or neural foramina, causing compression on the spinal cord, cauda equina, or individual nerve roots, and it may be congenital or acquired. The acquired causes for Spinal canal stenosis are frequently occurring and can result from: facet osteoarthritis, ligamentum flavum hypertrophy, degenerative bulging disc, or osteophyte formation. The nerve root sedimentation (NRS) sign is a new radiological sign first reported by Barzet al.In the normal person during supine position, the nerve roots would sink posteriorly in the dural sac due to gravity. In those patients with LSS, the nerve root would not be able to sink but disperse ventrally. The NRS sign has been shown to discriminate well between patients with and without LSS and reported to be 94% sensitive and 100% specific. However, the sign is not widely used probably due to its limited reliability study. A positive sedimentation sign was defined as the absence of nerve root sedimentation in at least 1 axial MRI scan, at a level above or below, disregarding the location of the scan within the level and its proximity to the maximal stenosis.The only exception from this is the two nerve roots leaving the dural sac one segmental level below the stenosis. If there are nerve roots in the ventral part of the dural sac except for the ones exiting the dural sac, the sedimentation sign is positive.

Transthoracic echocardiographic reference values of the aortic root: results from the Hamburg City Health Study

Here we generate up-to-date reference values of transthoracic echocardiographic aortic root dimensions matched by sex, age, and body surface area (BSA) derived from the population-based Hamburg City Health Study (HCHS) cohort. In 1687 healthy subjects (mean age 57.1 ± 7.7, 681 male and 1006 female), derived from the first prospectively-recruited 10,000 HCHS participants, dimensions of the aortic root were measured in systole and diastole using state-of-the-art 2-dimensional transthoracic echocardiography. Diameters were assessed at four levels: aortic annulus, Sinus of Valsalva, sinotubular junction, and ascending aorta. Female sex was associated with significantly smaller absolute aortic root dimensions, while indexing for BSA resulted in a reverse effect at all levels. There was a strong age dependency of all aortic root diameters as well as aortic annulus/sinotubular junction ratio for both sexes. Multivariate analysis revealed age, sex, weight, height, and BSA to be significant determinants of aortic root size. Finally, formulas were generated for the calculation of individual aortic root reference values considering age, sex, weight, and height. We provide population-based reference values of aortic root diameters based on a standardized transthoracic echocardiographic protocol of the population-based HCHS which may support the diagnosis, monitoring, and treatment of aortic root disease.

Unstable Phase Response Curves Shown by Spatiotemporal Patterns in the Plant Root Circadian Clock.

Phase response curves (PRCs) play important roles in the entrainment of periodic environmental cycles. Measuring the PRC is necessary to elucidate the relationship between environmental cues and the circadian clock. Conversely, the PRCs of plant circadian clocks are unstable due to multiple factors such as biotic/abiotic noise, individual differences, changes in amplitude, growth stage, and organ/tissue specificity. However, evaluating the effect of each factor is important because PRCs are commonly obtained by determining the response of many individuals, which include different amplitude states and organs. The plant root circadian clock spontaneously generates a spatiotemporal pattern called a stripe pattern, whereby all phases of the circadian rhythm exist within an individual root. Therefore, stimulating a plant root expressing this pattern enables phase responses at all phases to be measured using an individual root. In this study, we measured PRCs for thermal stimuli using this spatiotemporal pattern method and found that the PRC changed asymmetrically with positive and negative temperature stimuli. Individual differences were observed for weak but not for strong temperature stimuli. The root PRC changed depending on the amplitude of the circadian rhythm. The PRC in the young root near the hypocotyl was more sensitive than those in older roots or near the tip. Simulation with a phase oscillator model revealed the effect of measurement and internal noises on the PRC. These results indicate that instability in the entrainment of the plant circadian clock involves multiple factors, each having different characteristics. These results may help us understand how plant circadian clocks adapt to unstable environments and how plant circadian clocks with different characteristics, such as organ, age, and amplitude, are integrated within individuals.

Aortic root dimensions as a correlate for aortic regurgitation\u2019s severity

To evaluate the prevalence of aortic regurgitation (AR) and associations between the individual aortic root components and AR severity in the general population. The study included the first 10,000 participants of the population-based Hamburg City Health Study (HCHS) of whom 8259 subjects, aged 62.23 ± 8.46 years (51.3% females), enrolled 2016–2018, provided echocardiographic data. 69 subjects with bicuspid valves and 23 subjects with moderate/severe aortic stenosis were excluded. Aortic root dimensions were measured using state-of-the-art cardiac ultrasound, including the aortic annulus, sinus of Valsalva, sinotubular junction (STJ), and ascending aorta, in diastole and systole. The distribution of AR was: 932 (11.4%) mild, 208 (2.5%) moderate, and 20 (0.24%) severe. Patients with moderate or severe AR were predominantly male at advanced age who had hypertension, coronary artery disease, atrial fibrillation, and renal dysfunction. Increasing AR severity correlated with higher absolute and indexed aortic root diameters (e.g., end-diastolic sinus of Valsalva for no-mild-moderate-severe AR in mm ± standard deviation: 34.06 ± 3.81; 35.65 ± 4.13; 36.13 ± 4.74; 39.67 ± 4.61; p < 0.001). In binary logistic regression analysis, all aortic root components showed significant associations with moderate/severe AR. Mid-systolic STJ showed the strongest association with moderate/severe AR (OR 1.33, 95% confidence interval 1.25–1.43, p < 0.001). AR was prevalent in 14.2%, of whom 2.8% showed moderate/severe AR. All assessed aortic root diameters correlated with the prevalence and severity of AR. STJ diameter had the strongest association with moderate/severe AR possibly reflecting the pathophysiological impact of an increasingly dilated STJ in the context of an ageing aorta.

Intrusion of maxillary molar roots into the maxillary sinus in a sample of the Egyptian population using cone beam computed tomography

BackgroundThe proximity of the maxillary sinus floor to the maxillary molar roots increases the probability of oroantral communication on conducting any surgical or endodontic procedure in the involved area. The aim of this study is to evaluate the relationship between each maxillary molar root and maxillary sinus floor using cone beam computed tomography. Predicting the probability of protrusion of each root into the sinus will consequently predict the probability of occurrence of the oroantral fistula in a sample of the Egyptian population.ResultsThe total number of roots located outside the sinus was 121 (35.3%), while those contacting the sinus floor were 80 (23.3%) and those intruded the sinus were 141 (41.2%). The percentage of root intrusion into the sinus in males (56.9%) was significantly (p = 0.01) higher than females (42.9%). The probability of root intrusion in the left molars (54.2%) was non-significantly (p = 0.067) higher than that of the right side (44.3%). As for the type of tooth, the second molar showed the highest probability of root intrusion into the sinus (55.3%) followed by the third molars (52.6%) then the first molars (40.9). According to the type of root, the mesiobuccal root showed the highest probability of intrusion into the sinus (50.9%) followed by the palatal root (49.1%) then the distobuccal root (47.4%). However, the difference in both type of tooth and type of root was statistically non-significant (p = 0.051 and 0.869 respectively). As for the individual root with the highest probability of intrusion, the mesio-buccal root of the right third molar is the most frequent root to intrude the sinus (71.4%) and the mesio-buccal root of the right first molar is the least frequent (22.7%).ConclusionsIn a sample of the Egyptian population, males exhibit higher probability of root protrusion into the sinus than females. The side and type of tooth are of higher impact on the probability of its intrusion into the sinus compared to the type of root. Left second molars are at a higher risk of oroantral communications on surgical or endodontic procedures compared to other molars due to its highest probability of intrusion into the sinus.

Development of grapevine plants under hydroponic copper-enriched solutions induced morpho-histological, biochemical and cytogenetic changes

Copper (Cu) is an essential micronutrient for plants, but when present in excess, it induces toxicity. In this study, cuttings of four wine-producing varieties of Vitis vinifera L. were used: ‘Tinta Barroca’, ‘Tinto Cão’, ‘Malvasia Fina’ and ‘Viosinho’. The grapevine cuttings were distributed by hydroponic solutions enriched with different Cu concentrations (1, 10, 25 and 50 μM) plus control. At the end of the experiment, the root growth was evaluated, and individual roots were collected, fixed, and used for histological sections and chromosome spreads preparation. The higher Cu concentrations induced toxicity and inhibited root growth. However, the grapevine varieties responded with the thickening of the root exodermis and endodermis. In the chromosome spreads, normal and abnormal interphase and mitotic cells were observed in all varieties and treatments. The increase of Cu concentration decreased the nucleolar activity, as seen by reducing the nucleolar number and area. It increased the frequency of interphase cells with anomalies (ICA), but it did not influence total soluble protein concentration. The augment of Cu concentration also decreased the mitotic index (MI) and increased the percentage of dividing cells with anomalies (DCA). Different types of chromosomal anomalies in all mitotic phases, treatments and varieties were found. Overall, the white wine varieties, ‘Malvasia Fina’ and ‘Viosinho’, appeared to be more tolerant to the Cu-induced stress because they showed higher root growth and mean MI and lower mean DCA than the red wine varieties.

Foliar application of fertilizers and biostimulant has a strong impact on the olive (Olea europaea) rhizosphere microbial community profile and the abundance of arbuscular mycorrhizal fungi

Many studies on biostimulants and nutrient-based fertilizers of olive trees have been focused on the ability of these products to increase olive productivity and ameliorate oil quality. However, little information is available on their effects on rhizosphere microbial communities; whereas it is well known that microorganisms associated with plants play a key role on the productivity and the health of their host. The aim of this study was to evaluate the effects of foliar application of a biostimulant and nutrient fertilizers on photosynthesis, carbohydrate profile of the roots and soil microbial community structure. Specific attention was paid to arbuscular mycorrhizal (AM) fungi. The phospholipid fatty acid (PLFA) 16:1ω5 and the neutral lipid fatty acid (NLFA)16:1ω5 in the roots (intraradical mycelium) and in the soil (extraradical mycelium) were used as biomarkers for AM fungi. Experimentation consists of the annual foliar application of six nutrient-based treatments during two successive growing seasons: TC (untreated trees), T1 (nitrogen-based fertilizer), T2 (biostimulant rich in boron, magnesium, sulfur, manganese and amino acids), T3 (products rich in phosphorus, potassium and boron), T4 (product rich in phosphorus, calcium and zinc), T12 (application of T1 and T2) and T1234 (application of T1, T2, T3 and T4). At the end of the experiment, statistical analysis revealed a significant modification of macronutrient and micronutrient profiles of olive leaves, which caused a significant increase of photosynthesis and induced quantitative changes in the most of individual root sugars, essentially the translocated forms of sugars (sucrose and mannitol). Foliar application of fertilizers and biostimulant increased the PLFA biomarkers indicative of Gram-positive bacteria (i15:0, i16:0), Gram-negative bacteria (16:1ω7, 16:1ω9, cy17:0, 18:1ω7 and cy19:0) and actinobacteria (10Me16:0). The level of NLFA 16:1ω5 in both the rhizosphere and roots, increased significantly under foliar fertilization, however the level of PLFA 16:1ω5 did not appear to be significantly influenced, suggesting that spore and vesicle formation was more sensitive to foliar fertilization than the hyphae development. The NLFA 16:1ω5/PLFA 16:1ω5 ratio, in the roots of olive trees, showed a significant increase, indicating that AM fungi allocated high carbon to storage structures following foliar fertilization. Our study provides evidence that foliar fertilization induces rapid changes in specific microbial groups, which in turn increase the rhizosphere carbon metabolism.

Optimizing the methodology for saphenous nerve somatosensory evoked potentials for monitoring upper lumbar roots and femoral nerve during lumbar spine surgery: technical note.

The demand for intraoperative monitoring (IOM) of lumbar spine surgeries has escalated to accommodate more challenging surgical approaches to prevent perioperative neurologic deficits. Identifying impending injury of individual lumbar roots can be done by assessing free-running EMG and by monitoring the integrity of sensory and motor fibers within the roots by eliciting somatosensory (SEP), and motor evoked potentials. However, the common nerves for eliciting lower limb SEP do not monitor the entire lumbar plexus, excluding fibers from L1 to L4 roots. We aimed to technically optimize the methodology for saphenous nerve SEP (Sap-SEP) proposed for monitoring upper lumbar roots in the operating room. In the first group, the saphenous nerve was consecutively stimulated in two different locations: proximal in the thigh and distal close to the tibia. In the second group, three different recording derivations (10-20 International system) to distal saphenous stimulation were tested. Distal stimulation yielded a higher Sap-SEP amplitude (mean ± SD) than proximal: 1.36 ± 0.9µV versus 0.62 ± 0.6µV, (p < 0.0001). Distal stimulation evoked either higher (73%) or similar (12%) Sap-SEP amplitude compared to proximal in most of the nerves. The recording derivation CPz-cCP showed the highest amplitude in 65% of the nerves, followed by CPz-Fz (24%). Distal stimulation for Sap-SEP has advantages over proximal stimulation, including simplicity, lack of movement and higher amplitude responses. The use of two derivations (CPz-cCP, CPz-Fz) optimizes Sap-SEP recording.

Simulating rhizodeposition patterns around growing and exuding root systems

Abstract In this study, we developed a novel model approach to compute the spatio-temporal distribution patterns of rhizodeposits around growing root systems in three dimensions. This model approach allows us to study the evolution of rhizodeposition patterns around complex three-dimensional root systems. Root systems were generated using the root architecture model CPlantBox. The concentration of rhizodeposits at a given location in the soil domain was computed analytically. To simulate the spread of rhizodeposits in the soil, we considered rhizodeposit release from the roots, rhizodeposit diffusion into the soil, rhizodeposit sorption to soil particles and rhizodeposit degradation by microorganisms. To demonstrate the capabilities of our new model approach, we performed simulations for the two example rhizodeposits mucilage and citrate and the example root system Vicia faba. The rhizodeposition model was parameterized using values from the literature. Our simulations showed that the rhizosphere soil volume with rhizodeposit concentrations above a defined threshold value (i.e. the rhizodeposit hotspot volume) exhibited a maximum at intermediate root growth rates. Root branching allowed the rhizospheres of individual roots to overlap, resulting in a greater volume of rhizodeposit hotspots. This was particularly important in the case of citrate, where overlap of rhizodeposition zones accounted for more than half of the total rhizodeposit hotspot volumes. Coupling a root architecture model with a rhizodeposition model allowed us to get a better understanding of the influence of root architecture as well as rhizodeposit properties on the evolution of the spatio-temporal distribution patterns of rhizodeposits around growing root systems.

PEG-Induced Osmotic Stress Alters Root Morphology and Root Hair Traits in Wheat Genotypes.

Wheat crop in drought-prone regions of Bangladesh suffers from osmotic stress. The objective of this study was to investigate the response of wheat genotypes with respect to root morphology and root hair traits under polyethylene glycol (PEG)-induced osmotic stress. A total of 22 genotypes of wheat were grown hydroponically and two treatments—0% and 10% PEG—were imposed at 14 days after germination. Plant growth was reduced in terms of plant height, number of live leaves per tiller, shoot dry weight, number of root-bearing phytomers, and roots per tiller. Notably, PEG-induced osmotic stress increased root dry weight per tiller by increasing length of the main axis and lateral roots, as well as the diameter and density of both lateral roots and root hairs of the individual roots. A biplot was drawn after a principal component analysis, taking three less-affected (high-yielding genotypes) and three highly affected (low-yielding genotypes and landrace) genotypes under 10% PEG stress, compared to control. Principal component 1 separated PEG-treated wheat genotypes from control-treated genotypes, with a high and positive coefficient for the density of lateral roots and root hairs, length and diameter of the main axis, and first-order lateral roots and leaf injury scores, indicating that these traits are associated with osmotic stress tolerance. Principal component 2 separated high-yielding and tolerant wheat genotypes from low-yielding and susceptible genotypes, with a high coefficient for root dry weight, density of root hairs and second-order lateral roots, length of the main axis, and first-order lateral roots. An increase in root dry weight in PEG-stress-tolerant wheat genotypes was achieved through an increase in length and diameter of the main axis and lateral roots. The information derived from this research could be exploited for identifying osmotic stress-tolerant QTL and for developing abiotic-tolerant cultivars of wheat.

Phosphatase activity and acidification in lupine and maize rhizosphere depend on phosphorus availability and root properties: Coupling zymography with planar optodes

Increase of phosphatase activity and rhizosphere acidification are two main physiological mechanisms of phosphorus mobilization by plants. To understand plant P-acquisition strategies, the spatial distribution of phosphatase activity and pH in the rhizosphere in response to P availability between legumes and cereals and along individual roots were investigated. Zymography of acid and alkaline phosphatase activities visualizing P hydrolysis potential was combined with planar optodes to localize pH changes in maize and lupine rhizosphere. Lupine was more adapted to P-deficiency than maize by increasing phosphatase activity (up to 30%), decreasing pH for 0.8 units in the rhizosphere and having larger hotspot areas compared to P addition. The P deficiency-induced increases of phosphatase activities and acidification were position-specific along taproot of lupine: acid phosphatase was highest while alkaline phosphatase was least at apical parts; pH was 1.7 units lower at the apical than at the basal part. The phosphatase activities and pH along lateral roots of lupine were independent on P availability but had specific distribution patterns: acid phosphatase activity declined from the root tips toward basal part, while the alkaline phosphatase activity was slightly increased from root tips; the pH was highest at the root tips (first 5 mm) and declined thereafter until stabilized after 20 mm. We conclude that 1) lupine is better adapted to P deficiency than maize by a stronger increase of phosphatase activities and facilitation of rhizosphere acidification; 2) The organic P mobilization by phosphatases and mineral P solubilization by acidification along individual roots were dependent on the root zone.

Single-cell transcriptome atlas and chromatin accessibility landscape reveal differentiation trajectories in the rice root

Root development relies on the establishment of meristematic tissues that give rise to distinct cell types that differentiate across defined temporal and spatial gradients. Dissection of the developmental trajectories and the transcriptional networks that underlie them could aid understanding of the function of the root apical meristem in both dicots and monocots. Here, we present a single-cell RNA (scRNA) sequencing and chromatin accessibility survey of rice radicles. By temporal profiling of individual root tip cells we reconstruct continuous developmental trajectories of epidermal cells and ground tissues, and elucidate regulatory networks underlying cell fate determination in these cell lineages. We further identify characteristic processes, transcriptome profiles, and marker genes for these cell types and reveal conserved and divergent root developmental pathways between dicots and monocots. Finally, we demonstrate the potential of the platform for functional genetic studies by using spatiotemporal modeling to identify a rice root meristematic mutant from a cell-specific gene cohort.