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Understanding how root system architecture (RSA) adapts to changing nitrogen and water availability is important for improving acquisition. A sand rhizotron system was developed to study RSA in a porous substrate under tightly regulated nutrient supply. The RSA of Arabidopsis seedlings under differing nitrate (NO3) and water supplies in agar and sand was described. The hydraulic conductivity of the root environment was manipulated by using altered sand particle size and matric potentials. Ion‐selective microelectrodes were used to quantify NO3 at the surface of growing primary roots in sands of different particle sizes. Differences in RSA were observed between seedlings grown on agar and sand, and the influence of NO3 (0.1–10.0 mm ) and water on RSA was determined. Primary root length (PRL) was a function of water flux and independent of NO3. The percentage of roots with laterals correlated with water flux, whereas NO3 supply was important for basal root (BR) growth. In agar and sand, the NO3 activities at the root surface were higher than those supplied in the nutrient solution. The sand rhizotron system is a useful tool for the study of RSA, providing a porous growth environment that can be used to simulate the effects of hydraulic conductivity on growth.  相似文献   

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Phytohormone brassinosteroids (BRs) are essential for plant growth and development, but the mechanisms of BR‐mediated pollen development remain largely unknown. In this study, we show that pollen viability, pollen germination and seed number decreased in the BR‐deficient mutant d^im, which has a lesion in the BR biosynthetic gene DWARF (DWF), and in the bzr1 mutant, which is deficient in BR signaling regulator BRASSINAZOLE RESISTANT 1 (BZR1), compared with those in wild‐type plants, whereas plants overexpressing DWF or BZR1 exhibited the opposite effects. Loss or gain of function in the DWF or BZR1 genes altered the timing of reactive oxygen species (ROS) production and programmed cell death (PCD) in tapetal cells, resulting in delayed or premature tapetal degeneration, respectively. Further analysis revealed that BZR1 could directly bind to the promoter of RESPIRATORY BURST OXIDASE HOMOLOG 1 (RBOH1), and that RBOH1‐mediated ROS promote pollen and seed development by triggering PCD and tapetal cell degradation. In contrast, the suppression of RBOH1 compromised BR signaling‐mediated ROS production and pollen development. These findings provide strong evidence that BZR1‐dependent ROS production plays a critical role in the BR‐mediated regulation of tapetal cell degeneration and pollen development in Solanum lycopersicum (tomato) plants.  相似文献   

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In multicellular organisms, the balance between cell division and differentiation determines organ size, and represents a central unknown in developmental biology. In Arabidopsis roots, this balance is mediated between cytokinin and auxin through a regulatory circuit converging on the IAA3/SHORT HYPOCOTYL 2 (SHY2) gene. Here, we show that crosstalk between brassinosteroids (BRs) and auxin occurs in the vascular transition zone to promote root meristem development. We found that BR increases root meristem size by up‐regulating expression of the PINFORMED 7 (PIN7) gene and down‐regulating expression of the SHY2 gene. In addition, BES1 could directly bind to the promoter regions of both PIN7 and SHY2, indicating that PIN7 and SHY2 mediate the BR‐induced growth of the root meristem by serving as direct targets of BES1. Moreover, the PIN7 overexpression and loss‐of‐function SHY2 mutant were sensitive to the effects of BR and could partially suppress the short‐root phenotypes associated with deficient BR signaling. Interestingly, BRs could inhibit the accumulation of SHY2 protein in response to cytokinin. Taken together, these findings suggest that a complex equilibrium model exists in which regulatory interactions among BRs, auxin, and cytokinin regulate optimal root growth.  相似文献   

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Using a high‐resolution (40 × 40 km) chemical transport model coupled with the Regional Emission inventory in Asia (REAS), we simulated surface ozone concentrations ([O3]) and evaluated O3‐induced wheat production loss in China and India for the years 2000 and 2020 using dose–response functions based on AOT40 (accumulated [O3] above 40 ppb) and PODY (phytotoxic O3 dose, accumulated stomatal flux of O3 above a threshold of Y nmol m?2 s?1). Two O3 dose metrics (90 days AOT40 and POD6) were derived from European experiments, and the other two (75 days AOT40 and POD12) were adapted from Asian studies. Relative yield loss (RYL) of wheat in 2000 was estimated to be 6.4–14.9% for China and 8.2–22.3% for India. POD6 predicted greater RYL, especially for the warm regions of India, whereas the 90 days AOT40 gave the lowest estimates. For the future projection, all the O3 dose metrics gave comparable estimates of an increase in RYL from 2000 to 2020 in the range 8.1–9.4% and 5.4–7.7% for China and India, respectively. The lower projected increase in RYL for India may be due to conservative estimation of the emission increase in 2020. Sensitivity tests of the model showed that the PODY‐based estimates of RYL are highly sensitive to perturbations in the meteorological inputs, but that the estimated increase in RYL from 2000 to 2020 is much more robust. The projected increase in wheat production loss in China and India in the near future is substantially larger than the uncertainties in the estimation and indicates an urgent need for curbing the rapid increase in surface [O3] in these regions.  相似文献   

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The growth and development of roots in plants depends on the specification and maintenance of the root apical meristem. Here, we report the identification of CBL, a gene required for embryo and root development in Arabidopsis, and encodes cystathionine beta‐lyase (CBL), which catalyzes the penultimate step in methionine (Met) biosynthesis, and which also led to the discovery of a previous unknown, but crucial, metabolic contribution by the Met biosynthesis pathway. CBL is expressed in embryos and shows quiescent center (QC)‐enriched expression pattern in the root. cbl mutant has impaired embryo patterning, defective root stem cell niche, stunted root growth, and reduces accumulation of the root master regulators PLETHORA1 (PLT1) and PLT2. Furthermore, mutation in CBL severely decreases abundance of several PIN‐FORMED (PIN) proteins and impairs auxin‐responsive gene expression in the root tip. cbl seedlings also exhibit global reduction in histone H3 Lys‐4 trimethylation (H3K4me3) and DNA methylation. Importantly, mutation in CBL reduces the abundance of H3K4me3 modification in PLT1/2 genes and downregulates their expression. Overexpression of PLT2 partially rescues cbl root meristem defect, suggesting that CBL acts in part through PLT1/2. Moreover, exogenous supplementation of Met also restores the impaired QC activity and the root growth defects of cbl. Taken together, our results highlight the unique role of CBL to maintain the root stem cell niche by cooperative actions between Met biosynthesis and epigenetic modification of key developmental regulators.  相似文献   

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Despite the obvious importance of roots to agro‐ecosystem functioning, few studies have attempted to examine the effects of warming on root biomass and distribution, especially under different tillage systems. In this study, we performed a field warming experiment using infrared heaters on winter wheat, in long‐term conventional tillage and no‐tillage plots, to determine the responses of root biomass and distribution to warming. Soil monoliths were collected from three soil depths (0–10, 10–20, and 20–30 cm). Results showed that root biomass was noticeably increased under both till and no‐till tillage systems (12.1% and 12.9% in 2011, and 9.9% and 14.5% in 2013, in the two tillage systems, respectively) in the 0–30 cm depth, associated with a similar increase in shoot biomass. However, warming‐induced root biomass increases occurred in the deeper soil layers (i.e., 10–20 and 20–30 cm) in till, while the increase in no‐till was focused in the surface layer (0–10 cm). Differences in the warming‐induced increases in root biomass between till and no‐till were positively correlated with the differences in soil total nitrogen (R2 = .863, < .001) and soil bulk density (R2 = .853, < .001). Knowledge of the distribution of wheat root in response to warming should help manage nutrient application and cycling of soil C‐N pools under anticipated climate change conditions.  相似文献   

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To determine how root‐to‐shoot abscisic acid (ABA) signalling is regulated by vertical soil moisture gradients, root ABA concentration ([ABA]root), the fraction of root water uptake from, and root water potential of different parts of the root zone, along with bulk root water potential, were measured to test various predictive models of root xylem ABA concentration [RX‐ABA]sap. Beans (Phaseolus vulgaris L. cv. Nassau) were grown in soil columns and received different irrigation treatments (top and basal watering, and withholding water for varying lengths of time) to induce different vertical soil moisture gradients. Root water uptake was measured at four positions within the column by continuously recording volumetric soil water content (θv). Average θv was inversely related to bulk root water potential (Ψroot). In turn, Ψroot was correlated with both average [ABA]root and [RX‐ABA]sap. Despite large gradients in θv, [ABA]root and root water potential was homogenous within the root zone. Consequently, unlike some split‐root studies, root water uptake fraction from layers with different soil moisture did not influence xylem sap (ABA). This suggests two different patterns of ABA signalling, depending on how soil moisture heterogeneity is distributed within the root zone, which might have implications for implementing water‐saving irrigation techniques.  相似文献   

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Glucose functions as a hormone‐like signalling molecule that modulates plant growth and development in Arabidopsis thaliana. However, the role of glucose in root elongation remains elusive. Our study demonstrates that high concentrations of glucose reduce the size of the root meristem zone by repressing PIN1 accumulation and thereby reducing auxin levels. In addition, we verified the involvement of ABA INSENSITIVE 5 (ABI5) in this process by showing that abi5‐1 is less sensitive to glucose than the wild type, whereas glucose induces ABI5 expression and the inducible overexpression of ABI5 reduces the size of the root meristem zone. Furthermore, the inducible overexpression of ABI5 in PIN1::PIN1‐GFP plants reduces the level of PIN1‐GFP, but glucose reduces the level of PIN1‐GFP to a lesser extent in abi5‐1 PIN1::PIN1‐GFP plants than in the PIN1::PIN1‐GFP control, suggesting that ABI5 is involved in glucose‐regulated PIN1 accumulation. Taken together, our data suggest that ABI5 functions in the glucose‐mediated inhibition of the root meristem zone by repressing PIN1 accumulation, thus leading to reduced auxin levels in roots.  相似文献   

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Phosphatidylinositol 4,5‐bisphosphate [PtdIns(4,5)P2] serves as a subcellular signal on the plasma membrane, mediating various cell‐polarized phenomena including polar cell growth. Here, we investigated the involvement of Arabidopsis thaliana PCaP2, a plant‐unique plasma membrane protein with phosphoinositide‐binding activity, in PtdIns(4,5)P2 signaling for root hair tip growth. The long‐root‐hair phenotype of the pcap2 knockdown mutant was found to stem from its higher average root hair elongation rate compared with the wild type and to counteract the low average rate caused by a defect in the PtdIns(4,5)P2‐producing enzyme gene PIP5K3. On the plasma membrane of elongating root hairs, the PCaP2 promoter‐driven PCaP2–green fluorescent protein (GFP), which complemented the pcap2 mutant phenotype, overlapped with the PtdIns(4,5)P2 marker 2xCHERRY‐2xPHPLC in the subapical region, but not at the apex, suggesting that PCaP2 attenuates root hair elongation via PtdIns(4,5)P2 signaling on the subapical plasma membrane. Consistent with this, a GFP fusion with the PCaP2 phosphoinositide‐binding domain PCaP2N23, root hair‐specific overexpression of which caused a low average root hair elongation rate, localized more intense to the subapical plasma membrane than to the apical plasma membrane similar to PCaP2–GFP. Inducibly overexpressed PCaP2–GFP, but not its derivative lacking the PCaP2N23 domain, replaced 2xCHERRY‐2xPHPLC on the plasma membrane in root meristematic epidermal cells, and suppressed FM4‐64 internalization in elongating root hairs. Moreover, inducibly overexpressed PCaP2 arrested an endocytic process of PIN2–GFP recycling. Based on these results, we conclude that PCaP2 functions as a negative modulator of PtdIns(4,5)P2 signaling on the subapical plasma membrane probably through competitive binding to PtdIns(4,5)P2 and attenuates root hair elongation.  相似文献   

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Although nitric oxide (NO) is known to regulate root growth, the factor(s) modulating NO during this process have not yet been elucidated. Here, we identified Arabidopsis WD40‐REPEAT 5a (WDR5a) as a novel factor that functions in root growth by modulating NO accumulation. The wdr5a‐1 mutant accumulated less NO and produced longer roots than the wild type, whereas the WDR5a overexpression lines had the opposite phenotype. The role of NO was further supported by our observation that the NO donor sodium nitroprusside (SNP) and the NO scavenger 2‐(4‐carboxyphenyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide (cPTIO) rescued the root meristem growth phenotypes of the wdr5a‐1 and WDR5a overexpression lines, respectively. The regulation of root growth by WDR5a was found to involve auxin because the auxin levels were similar in SNP‐treated wdr5a‐1 and wild‐type roots, but higher in untreated wdr5a‐1 roots than in wild‐type roots. In addition, the wdr5a‐1 mutant had higher production and activity levels of the auxin biosynthetic enzyme TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS1 (TAA1), in contrast to its reduced expression and activity in the WDR5a overexpression lines, and the increased root meristem growth in wdr5a‐1 was suppressed by treatment with l ‐kynurenine, which inhibits TAA1, as well as by mutating TAA1. WDR5a therefore functions in root meristem growth by maintaining NO homeostasis, and thus TAA1‐mediated auxin biosynthesis.  相似文献   

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Root hairs elongate in a highly polarized manner known as tip growth. Overexpression of constitutively active Rho of Plant (ROP)/RAC GTPases mutants induces swelling of root hairs. Here, we demonstrate that Atrop11CA‐induced swelling of root hairs depends on the composition of the growth medium. Depletion of ammonium allowed normal root hair elongation in Atrop11CA plants, induced the development of longer root hairs in wild‐type plants and suppressed the effect of Atrop11CA expression on actin organization and reactive oxygen species distribution, whereas membrane localization of the protein was not affected. Ammonium at concentrations higher than 1 mM and the presence of nitrate were required for induction of swelling. Oscillations in wall and cytoplasmic pH are known to accompany tip growth in root hairs, and buffering of the growth medium decreased Atrop11CA‐induced swelling. Fluorescence ratio imaging experiments revealed that in wild‐type root hairs, the addition of NH4NO3 to the growth medium induced an increase in the amplitude of extracellular and intracellular pH oscillations and an overall decrease in cytoplasmic pH at the cell apex. Based on these results, we suggest a model in which ROP GTPases and nitrogen‐dependent pH oscillations function in parallel pathways, creating a positive feedback loop during root hair growth.  相似文献   

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Auxin acts synergistically with cytokinin to control the shoot stem‐cell niche, while both hormones act antagonistically to maintain the root meristem. In aluminum (Al) stress‐induced root growth inhibition, auxin plays an important role. However, the role of cytokinin in this process is not well understood. In this study, we show that cytokinin enhances root growth inhibition under stress by mediating Al‐induced auxin signaling. Al stress triggers a local cytokinin response in the root‐apex transition zone (TZ) that depends on IPTs, which encode adenosine phosphate isopentenyltransferases and regulate cytokinin biosynthesis. IPTs are up‐regulated specifically in the root‐apex TZ in response to Al stress and promote local cytokinin biosynthesis and inhibition of root growth. The process of root growth inhibition is also controlled by ethylene signaling which acts upstream of auxin. In summary, different from the situation in the root meristem, auxin acts with cytokinin in a synergistic way to mediate aluminum‐induced root growth inhibition in Arabidopsis.  相似文献   

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The Arabidopsis thaliana AGD1 gene encodes a class 1 adenosine diphosphate ribosylation factor‐gtpase‐activating protein (ARF‐GAP). Previously, we found that agd1 mutants have root hairs that exhibit wavy growth and have two tips that originate from a single initiation point. To gain new insights into how AGD1 modulates root hair polarity we analyzed double mutants of agd1 and other loci involved in root hair development, and evaluated dynamics of various components of root hair tip growth in agd1 by live cell microscopy. Because AGD1 contains a phosphoinositide (PI) binding pleckstrin homology (PH) domain, we focused on genetic interactions between agd1 and root hair mutants altered in PI metabolism. Rhd4, which is knocked‐out in a gene encoding a phosphatidylinositol‐4‐phosphate (PI‐4P) phosphatase, was epistatic to agd1. In contrast, mutations to PIP5K3 and COW1, which encode a type B phosphatidylinositol‐4‐phosphate 5‐kinase 3 and a phosphatidylinositol transfer protein, respectively, enhanced the root hair defects of agd1. Enhanced root hair defects were also observed in double mutants to AGD1 and ACT2, a root hair‐expressed vegetative actin isoform. Consistent with our double‐mutant studies, targeting of tip growth components involved in PI signaling (PI‐4P), secretion (RABA4b) and actin regulation (ROP2), were altered in agd1 root hairs. Furthermore, tip cytosolic calcium ([Ca2+]cyt) oscillations were disrupted in root hairs of agd1. Taken together, our results indicate that AGD1 links PI signaling to cytoskeletal‐, [Ca2+]cyt?, ROP2‐, and RABA4b‐mediated root hair development.  相似文献   

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