Affect Root Growth Research Articles

Phosphorus Limitation Improved Salt Tolerance in Maize Through Tissue Mass Density Increase, Osmolytes Accumulation, and Na+ Uptake Inhibition.

Low phosphorus (P) availability and salt stress are two major constraints for maize (Zea mays L.) growth in north China. A combination of salinity and high P rather than low P is more detrimental to the growth of maize. However, little is known about the mechanisms by which P nutrition modifies the salt tolerance and P uptake of maize. The present study aimed to investigate the combined effects of salinity and P on maize growth and P uptake, and to address the physiological mechanisms of salt tolerance influenced by P availability in maize. Seedlings of a local maize cultivar XY335 were grown hydroponically for 35 days under low (5 μM) or sufficient P supply (200 μM) with or without 100 mM NaCl. Root morphological traits, tissue mass density, leaf osmolytes (sugars and proline) accumulation, and Na+/K+ ratio were measured to allow evaluation of the combined effects of salinity and P on maize growth and P uptake. Both P deficiency and salinity markedly reduced the growth of maize. However, P deficiency had a more pronounced effect on shoot growth while salinity affected root growth more prominently. Combined effects of P deficiency and salinity on total root length, root surface area, and average root diameter were similar to that of plants grown under salt stress. The combination of P deficiency and salinity treatments had a more pronounced effect on tissue mass density, leaf proline and soluble sugars compared to individual treatment of either low P or NaCl. When exposed to salt stress, maize plants of sufficient P accumulated greater amount of Na+ than those under P deficit, but similar amounts of K+ were observed between the two P treatments. Salt stress significantly increased shoot P concentration of maize with sufficient P (P < 0.01), but not for P-deficient plants. In sum, shoots and roots of maize exhibited different responses to P deficiency and salinity, with more marked effect of P deficiency on shoots and of salinity on roots. P deficiency improved salt tolerance of maize plants, which was associated with the increase of tissue mass density, accumulation of osmolytes, reduction of Na+ accumulation, and selective absorption of K+ over Na+.

Phytotoxicity of colloidal solutions of stabilized and non-stabilized nanoparticles of essential metals and their oxides

Abstract Advances in nanotechnology in various fields of human activity contribute to increase of their production, improved properties and wider implementation of nanomaterials. However, increasing use may enhance their release into the environment and can lead to affecting human health. The toxicity of colloidal solutions of metal nanoparticles (Cu, Mn) and their oxides, obtained in the absence and presence of a stabilizer, was examined and compared with the use of the standard test system of Allium cepa L.. The phytotoxicity of the experimental solutions was evaluated according to the growth response of the onion roots; the cyto- and genotoxicity were estimated due to the proliferative activity of the root meristem cells. It was established that solutions of stabilized metal nanoparticles were at given concentration toxic to Allium cepa L. according to the integral index of roots growth, however, were not cytotoxic. Difference in the phytotoxicity of stabilized and non-stabilized metal nanoparticles and their oxides depended on their phase composition and affected root growth.

Auxin-jasmonate crosstalk in Oryza sativa L. root system formation after cadmium and/or arsenic exposure

Soil pollutants may affect root growth through interactions among phytohormones like auxin and jasmonates. Rice is frequently grown in paddy fields contaminated by cadmium and arsenic, but the effects of these pollutants on jasmonates/auxin crosstalk during adventitious and lateral roots formation are widely unknown. Therefore, seedlings of Oryza sativa cv. Nihonmasari and of the jasmonate-biosynthetic mutant coleoptile photomorphogenesis2 were exposed to cadmium and/or arsenic, and/or jasmonic acid methyl ester, and then analysed through morphological, histochemical, biochemical and molecular approaches.In both genotypes, arsenic and cadmium accumulated in roots more than shoots. In the roots, arsenic levels were more than twice higher than cadmium levels, either when arsenic was applied alone, or combined with cadmium. Pollutants reduced lateral root density in the wild -type in every treatment condition, but jasmonic acid methyl ester increased it when combined with each pollutant. Interestingly, exposure to cadmium and/or arsenic did not change lateral root density in the mutant. The transcript levels of OsASA2 and OsYUCCA2, auxin biosynthetic genes, increased in the wild-type and mutant roots when pollutants and jasmonic acid methyl ester were applied alone. Auxin (indole-3-acetic acid) levels transiently increased in the roots with cadmium and/or arsenic in the wild-type more than in the mutant. Arsenic and cadmium, when applied alone, induced fluctuations in bioactive jasmonate contents in wild-type roots, but not in the mutant. Auxin distribution was evaluated in roots of OsDR5::GUS seedlings exposed or not to jasmonic acid methyl ester added or not with cadmium and/or arsenic. The DR5::GUS signal in lateral roots was reduced by arsenic, cadmium, and jasmonic acid methyl ester. Lipid peroxidation, evaluated as malondialdehyde levels, was higher in the mutant than in the wild-type, and increased particularly in As presence, in both genotypes.Altogether, the results show that an auxin/jasmonate interaction affects rice root system development in the presence of cadmium and/or arsenic, even if exogenous jasmonic acid methyl ester only slightly mitigates pollutants toxicity.

Relationship between photosynthesis, bleeding-sap mass, and bleeding components in maize hybrids and corresponding parents in northern China

Currently, the main maize production areas in northeastern China are facing soil fertility loss, which severely affects root growth and limits photosynthesis. It is widely acknowledged that physiological conditions of the root system are closely related to the photosynthetic capacity; therefore, we evaluated whether there are certain differences in root bleeding sap characteristics and photosynthetic capacity between the hybrids and their parents. The results showed that heterosis of the photosynthetic capacity occurred at the milk-ripe stage; however, heterosis of bleeding-sap mass (BSM) and organic biomass occurred during the whole growth period. Photosynthetic rate correlated positively with BSM and the bleeding components; a similar trend was also observed between BSM and bleeding components. These data suggested that appropriate water and fertilizer supply can improve the photosynthesis-related parameters and yield of maize.

Changes of Cinnamomum camphora root characteristics and soil properties under ozone stress in South China.

High O3 exposure affects the forest growth and soil characteristics. Although there is substantial evidence that O3 does impose a stress on forest trees, the effects of O3 on roots and soil of evergreen broad-leaved tree species in South China remain unknown. The effects of ozone (O3) fumigation on the root biomass, root morphology, root nutrient, soil physical, and chemical properties were examined in Cinnamomum camphora seedlings grown under four O3 treatments (charcoal-filtered air (CF) or O3 at 1×, 2× and 4× ambient concentration). O3 significantly decreased root biomass and root carbon (C). Regardless of O3 level, elevated O3 significantly resulted in reduced root surface area, volume, number of forks, and specific root length (SRL). The percentages of fine to total root in terms of root surface area and root volume of seedlings under the CF and 1 × O3 treatments were significantly higher than those of seedlings under the 4 × O3 treatment, indicating that high O3 level impaired the growth performance of fine roots. O3 affected root growth and structures, which increased soil bulk density and reduced soil total porosity and void ratio. The soil pH under all O3 fumigation treatments significantly increased compared with CF treatment, whereas the organic matter significantly decreased. In conclusion, although the increased O3 level enhanced root N and P under 2 and 4 × O3 treatments compared with 1 × O3 treatment as compensation mechanisms to prevent O3-induced decrease in root C gain and root functions, O3 still decreased the root biomass and root tips, and changed the soil physical and chemical properties.

Carbohydrate content and season collection of cuttings from ‘Roxo de Valinhos’ fig tree

Choosing the best season collection of cuttings is essential to have success with propagation, due mainly to carbohydrate content, since is a source of energy for roots and shoots development. In literature, there are no papers that associate the collection season of cuttings with carbohydrate contents in figs. Therefore, the current study aimed to evaluate carbohydrate contents and season collection of cuttings to propagate ‘Roxo de Valinhos’ fig tree. The experiment was conducted in a greenhouse; cuttings were collected in the first week of the following months: June, July, August and September. The design was in completely randomized blocks, with four replicates of 30 cuttings collected per season. The following traits were evaluated: carbohydrate content; percentage of root cuttings, bud cuttings, cuttings without bud and root; number of buds, leaves and roots per cutting; length of the largest root and bud; bud diameter; bud and root dry mass; and root volume. Results indicated high carbohydrate content in cuttings that were collected in August; therefore, the best month to collect cuttings of ‘Roxo de Valinhos’ fig tree in the city of São Manuel, state of São Paulo. This result is due to high percentage of rooted cuttings and better development. Furthermore, carbohydrate content mainly affects root growth; besides that, reducing sugars are the most important feature in the development of cuttings.

Overexpression of Nitrate Transporter OsNRT2.1 Enhances Nitrate-Dependent Root Elongation.

Root morphology is essential for plant survival. NO3− is not only a nutrient, but also a signal substance affecting root growth in plants. However, the mechanism of NO3−-mediated root growth in rice remains unclear. In this study, we investigated the effect of OsNRT2.1 on root elongation and nitrate signaling-mediated auxin transport using OsNRT2.1 overexpression lines. We observed that the overexpression of OsNRT2.1 increased the total root length in rice, including the seminal root length, total adventitious root length, and total lateral root length in seminal roots and adventitious roots under 0.5-mM NO3− conditions, but not under 0.5-mM NH4+ conditions. Compared with wild type (WT), the 15NO3− influx rate of OsNRT2.1 transgenic lines increased by 24.3%, and the expressions of auxin transporter genes (OsPIN1a/b/c and OsPIN2) also increased significantly under 0.5-mM NO3− conditions. There were no significant differences in root length, ß-glucuronidase (GUS) activity, and the expressions of OsPIN1a/b/c and OsPIN2 in the pDR5::GUS transgenic line between 0.5-mM NO3− and 0.5-mM NH4+ treatments together with N-1-naphthylphalamic acid (NPA) treatment. When exogenous NPA was added to 0.5-mM NO3− nutrient solution, there were no significant differences in the total root length and expressions of OsPIN1a/b/c and OsPIN2 between transgenic plants and WT, although the 15NO3− influx rate of OsNRT2.1 transgenic lines increased by 25.2%. These results indicated that OsNRT2.1 is involved in the pathway of nitrate-dependent root elongation by regulating auxin transport to roots; i.e., overexpressing OsNRT2.1 promotes an effect on root growth upon NO3− treatment that requires active polar auxin transport.

Effect of Salinity on Wheat Genotypes during Germination Stage

Salinity is a major abiotic stress that adversely affects wheat production in many regions of the world. Salinity stress limits wheat growth, development, and yield. Identification of salinity tolerant genotypes is critical for yield improvement. Therefore, a series of control environment experiments were carried out to evaluate the response of two spring wheat and two winter wheat cultivars (Triticum aestivum L.) to different levels of salinity. The experiments were designed in a randomized complete block design (RCBD) with five replications. Twenty seeds of each genotype were placed on pre-moistened filter paper in Petri dishes and placed in an incubator at 20 °C. The seeds were subjected to 4 levels of salinity 0, 50, 100, and 150 mM NaCl. Seedlings were harvested after 8 days, and data on final germination percentage, rate of germination, mean daily germination, shoot and root length, and seedling fresh and dry weight were recorded. The results indicated that winter and spring wheat genotypes differed significantly for germination percentages, rate of germination, mean daily germination, shoot and root lengths, and seedling fresh and dry weight. The results showed that salinity did not affect final germination percentage until salinity level reached to 100 mM NaCl; whereas seeds subjected to 100 and 150 mM NaCl retarded germination by 1 and 2 days of spring wheat, and 2-3 days of winter wheat respectively, as compared with 0 and 50 mM NaCl treatment. The data also showed that increasing salinity level significantly decreased shoot and root length, however, the study found that salinity affected root growth more severely than shoot growth of seedlings. Significantly, root length and dry weight of root ranked genotypes in the same order as their salt-tolerance. Therefore, the study concluded that the measurements of root growth would be effective criteria for screening wheat genotypes for salt tolerance at seedling stages.

Influences of plant spacing on root tensile strength of Schefflera arboricola and soil shear strength

Mechanical root reinforcement depends not only on root biomechanical properties but also on root biomass. Although it is known that plant spacing can affect root growth, it is not clear how it affects root tensile strength. We interpreted a set of field data to study the effects of spacing of Schefflera arboricola on root area ratio (RAR), root tensile strength and their combined effects on soil shear strength (also termed root cohesion). S. arboricola was transplanted into compacted silty sand at a spacing of 0.5 m, 0.8 m and 1.1 m. After 20 months of growth in the field, the root systems were excavated for root tensile testing and post-test trait measurements. Plant spacing affected the growth and tensile strength of roots. More closely spaced plants had higher RAR but lower root tensile strength, especially for roots 0.5–2 mm in diameter. According to the existing root breakage and fibre bundle models used in this study, which calculate root cohesion as the product of RAR and root tensile strength, the effects of plant spacing on root cohesion were minimal for most soil depths apart from 0.4- to 0.5-m depth.

Response Kailan Plants (Brassica oleraceae L.) to the Immersion Plant Growth Regulator (GA3) with Various Types Growing Media

Gibberellin are hormones that accelerate the germination of seeds, buds sprout, stem elongation, leaf growth, stimulate flowering, fruit development, affecting root growth and differentiation. The research aims to determine the response kailan plants (Brassica oleraceae L.) against immersion PGR gibberellin (GA3) with various types growing media have been conducted in Ciparanje Jatinangor since March 2015 to May 2015. Using a randomized block design (RAK) factorial design with three replications consisting of two factors. The first factor is the provision of PGR gibberellin (GA3) which consists of: (1) 0 ppm (2) 25 ppm (3) 50 ppm (4) 75 ppm (5) 100 ppm. The second factor is the type of growing media consisting of: (1) land (2) husk (3) cocopeat, with observation parameters plant height, leaf number, fresh plant weight, dry plant weight and dashed root. The results showed that the use of PGR gibberellin (GA3) with a concentration of (g2) 50 ppm and the type of soil planting medium (m1) of the most influential in improving growth and yield of kailan plant.

Effects hydrogen sulfide on the antioxidant system and membrane stability in mitochondria of Malus hupehensis under NaCl stress

Salt stress is one of the most critical environmental factors limiting plant growth, and hydrogen sulfide (H2S) can play a role in plant responses to this stress. To investigate the effects of H2S on mitochondrial functions under salt stress, we treated Malus hupehensis Rehd. var. pingyiensis germinating seeds with an 85 mM NaCl solution with or without an H2S donor sodium hydrosulfide (NaHS) and H2S scavenger hypotaurine (HT). Then, hydrogen peroxide (H2O2) content and antioxidant enzyme activities were measured in mitochondria of seedling roots. Our results show that the application of 0.05 mM NaHS rescued an NaCl-induced inhibition of root elongation, decreased H2O2 content, and enhanced superoxide dismutase (SOD), guaiacol peroxidase (POD), and catalase (CAT) activities in the mitochondria compared to NaCl treatment alone. It was also found that 0.05 mM NaHS significantly decreased the mitochondrial permeability transition pore and increased mitochondrial membrane fluidity, mitochondrial membrane potential, and cytochrome c/a ratio under NaCl stress. However, 0.02 mM NaHS did not affect root growth, antioxidant enzyme activities, and mitochondrial function under NaCl stress, whereas high concentrations of NaHS (more than 0.2 mM) had a weaker or negative effects. Moreover, 15 µM HT eliminated the beneficial effects of NaHS under NaCl stress. Our results suggest that H2S protected plants against salt stress by decreasing H2O2 accumulation and by regulating membrane stability and antioxidant system in mitochondria.

基于容器分区处理探究黑麦草生长对喀斯特不同土壤生境和水分的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 基于容器分区处理探究黑麦草生长对喀斯特不同土壤生境和水分的响应 DOI: 10.5846/stxb201805121045 作者: 作者单位: 三峡库区生态环境教育部重点实验室,三峡库区生态环境教育部重点实验室,三峡库区生态环境教育部重点实验室,三峡库区生态环境教育部重点实验室,三峡库区生态环境教育部重点实验室,三峡库区生态环境教育部重点实验室,三峡库区生态环境教育部重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31500399）；教育部第49批留学回国人员科研启动基金项目 Growth response of Lolium perenne L. under different soil habitats and water conditions based on container partition in a karst area Author: Affiliation: Key Laboratory of Eco-environments in Three Gorges Reservoir Region Ministry of Education,Chongqing Key Laboratory of Plant Ecology and Resources Research in Three Gorges Reservoir Region,School of Life Sciences,Southwest University,Key Laboratory of Eco-environments in Three Gorges Reservoir Region Ministry of Education,Chongqing Key Laboratory of Plant Ecology and Resources Research in Three Gorges Reservoir Region,School of Life Sciences,Southwest University,Key Laboratory of Eco-environments in Three Gorges Reservoir Region Ministry of Education,Chongqing Key Laboratory of Plant Ecology and Resources Research in Three Gorges Reservoir Region,School of Life Sciences,Southwest University,Key Laboratory of Eco-environments in Three Gorges Reservoir Region Ministry of Education,Chongqing Key Laboratory of Plant Ecology and Resources Research in Three Gorges Reservoir Region,School of Life Sciences,Southwest University,Key Laboratory of Eco-environments in Three Gorges Reservoir Region Ministry of Education,Chongqing Key Laboratory of Plant Ecology and Resources Research in Three Gorges Reservoir Region,School of Life Sciences,Southwest University,Key Laboratory of Eco-environments in Three Gorges Reservoir Region Ministry of Education,Chongqing Key Laboratory of Plant Ecology and Resources Research in Three Gorges Reservoir Region,School of Life Sciences,Southwest University,Key Laboratory of Eco-environments in Three Gorges Reservoir Region Ministry of Education,Chongqing Key Laboratory of Plant Ecology and Resources Research in Three Gorges Reservoir Region,School of Life Sciences,Southwest University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了探究不同水分条件下喀斯特地区分布不均、厚薄不一土壤小生境对禾本科草本植物生长的影响，用3种不同深度的容器（对照深度CK，深土D和浅土S）两两组合为6种复合容器（CK-CK、CK-S、CK-D、D-D、S-D和S-S）以实现容器分区，研究了黑麦草的根系生长、生物量积累及其分配特征。结果表明：1）在水分充足（W0）条件下，组合了浅土容器和深土容器的处理中，黑麦草的根系生长（根长、根直径、根表面积和根生物量）均低于对照容器（CK-CK），且有浅土容器的组合处理（S-S，S-D，CK-S）受抑制程度大于有深土容器的组合处理（CK-D，D-D）；当水分含量降低后，即中水（W1）和低水（W2）条件下，有深土容器的组合[D-D和（或）CK-D]根系生长与对照相比显著增加，而有浅土容器的组合[S-S和（或）CK-S]根系生长与对照相比显著降低。2）对比同一处理不同容器分区中黑麦草生长指标发现，在水分充足情况下，深土容器和浅土容器均会抑制植物生长，而当水分减少，S区根系生长被严重抑制，但D区根系增长优势明显。3）水分充足条件下，根冠比未受到显著影响；当水分降低时，组合了深土容器的处理根冠比均有升高的趋势，组合了浅土容器的处理根冠比有降低趋势。由此可见，不同土壤生境带来的物理空间限制会影响植物根系生长和生物量积累与分配，但水分的减少会改变根系生长及生物量积累对不同土壤生境的响应：在水分充足时，土壤物理空间是影响根系生长和生物量积累与分配的主要因子，黑麦草主要发展浅层根系。而当水分减少时，黑麦草根系在浅层土壤中无法获取供给生长代谢活动的足量水分，更倾向于将有限的有机物分配给根，通过根系伸长、表面积和体积增大、直径增粗等策略加强水分吸收，从而增强对干旱的抗逆性，提高对土壤和水分异质性的适应。 Abstract:Bare rock, uneven soil thickness, and drought have resulted in a harsh habitat in karst areas. Therefore, plant growth in these areas requires more advanced adaptation strategies. To explore the effect of unique soil habitats on herbaceous plant (Gramineae) growth under different water conditions in a karst area, we selected three container types[control (CK), deep (D), and shallow (S)] for six soil treatments in the following combinations:CK-CK, CK-S, CK-D, D-D, S-D, and S-S. Root growth, biomass accumulation, and root spatial distribution of Lolium perenne L. in different water levels (W0, W1, and W2) were observed. The results showed 1) with sufficient water (W0), the root length, diameter, surface area, and biomass of L. perenne in the compound containers that contained S or D were lower than that of the control (CK-CK). The degree of inhibition of L. perenne in treatment combined with shallow soil containers (S-S, S-D, CK-S) was greater than that in treatment combined with deep soil containers (CK-D, D-D). The root growth in treatments containing S (S-S, S-D, CK-S) were more inhibited than those in the treatments containing D (CK-D, D-D). With reduced water content (W1 and W2), root growth in the compound containers that contained D (D-D and/or CK-D) was significantly higher than that of the control, whereas it was significantly lower in the containers containing S (S-S/CK-S). 2) Comparing root growth in two sides of one compound container, we found that under W0, both deep and shallow soil inhibited plant growth. Under W1 and W2, root growth of the S sides was inhibited severely. However, root growth occurred in the D sides. 3) Under W0, the root-to-shoot ratio was not affected by soil space. With decrease in the water content, the root-to-shoot ratio increased in the D compound containers, whereas it decreased significantly in the S compound containers. Thus, the physical space limitation of different soil habitats affected plant root growth and biomass accumulation and distribution; however, the decrease of water content could change these responses:with sufficient water, soil physical space was the main factor affecting root growth and biomass accumulation and distribution. Correspondingly, L. perenne mainly developed shallow roots. However, when water was reduced, L. perenne roots could not obtain enough moisture in the shallow soil to supply metabolic growth activity. Therefore, L. perenne generally distributed limited organic matter to the roots and strengthened water absorption through root elongation, surface area and volume increase, and diameter thickening, to enhance drought resistance and improve adaptability to shallow soil and drought. 参考文献 相似文献 引证文献

Rosmarinic acid induces programmed cell death in Arabidopsis seedlings through reactive oxygen species and mitochondrial dysfunction.

Phytotoxic potential of rosmarinic acid (RA), a caffeic acid ester largely found in aromatic species, was evaluated on Arabidopsis through metabolomic and microscopic approaches. In-vitro bioassays pointed out that RA affected root growth and morphology, causing ROS burst, ROS scavengers activity inhibition and consequently, an alteration on cells organization and ultrastructure. In particular, RA-treatment (175 μM) caused strong vacuolization, alteration of mitochondria structure and function and a consistent ROS-induced reduction of their transmembrane potential (ΔΨm). These data suggested a cell energy deficit also confirmed by the metabolomic analysis, which highlighted a strong alteration of both TCA cycle and amino acids metabolism. Moreover, the increase in H2O2 and O2− contents suggested that RA-treated meristems underwent oxidative stress, resulting in apoptotic bodies and necrotic cells. Taken together, these results suggest that RA inhibits two of the main ROS scavengers causing high ROS accumulation, responsible of the alterations on mitochondrial ultrastructure and activity through ΔΨm dissipation, TCA-cycle alteration, cell starvation and consequently cell death on Arabidopsis seedlings. All these effects resulted in a strong inhibition on root growth and development, which convert RA in a promising molecule to be explored for further use in weed management.

MEDIATOR18 modulates viability of root initial cells.

MEDIATOR18 modulates viability of root initial cells.

An investigation of genotype-phenotype association in a festulolium forage grass population containing genome-spanning Festuca pratensis chromosome segments in a Lolium perenne background.

Alien chromosome introgression is used for the transfer of beneficial traits in plant breeding. For temperate forage grasses, much of the work in this context has focused on species within the ryegrasses (Lolium spp.) and the closely related fescues (Festuca spp.) particularly with a view to combining high forage quality with reliability and enhanced environmental services. We have analysed a L. perenne (perennial ryegrass) population containing the majority of a F. pratensis (meadow fescue) genome as introgressed chromosome segments to identify a) marker-trait associations for nutrient use and abiotic stress response across the family, and b) to assess the effects of introgression of F. pratensis genomic regions on phenotype. Using container-based assays and a system of flowing solution culture, we looked at phenotype responses, including root growth, to nitrogen and phosphorus status in the growing medium and abiotic stresses within this festulolium family. A number of significant marker/trait associations were identified across the family for root biomass on chromosomes 2, 3 and 5 and for heading date on chromosome 2. Of particular interest was a region on chromosome 2 associated with increased root biomass in phosphorus-limited conditions derived from one of the L. perenne parents. A genotype containing F. pratensis chromosome 4 as a monosomic introgression showed increased tiller number, shoot and root growth and genotypes with F. pratensis chromosome segment introgressions at different ends of chromosome 4 exhibited differential phenotypes across a variety of test conditions. There was also a general negative correlation between the extent of the F. pratensis genome that had been introgressed and root-related trait performances. We conclude that 1) the identification of alleles affecting root growth has potential application in forage grass breeding and, 2) F. pratensis introgressions can enhance quantitative traits, however, introgression can also have more general negative effects.

Nitric Oxide Affects Rice Root Growth by Regulating Auxin Transport Under Nitrate Supply.

Nitrogen (N) is a major essential nutrient for plant growth, and rice is an important food crop globally. Although ammonium (NH4+) is the main N source for rice, nitrate (NO3-) is also absorbed and utilized. Rice responds to NO3- supply by changing root morphology. However, the mechanisms of rice root growth and formation under NO3- supply are unclear. Nitric oxide (NO) and auxin are important regulators of root growth and development under NO3- supply. How the interactions between NO and auxin in regulating root growth in response to NO3- are unknown. In this study, the levels of indole-3-acetic acid (IAA) and NO in roots, and the responses of lateral roots (LRs) and seminal roots (SRs) to NH4+ and NO3-, were investigated using wild-type (WT) rice, as well as osnia2 and ospin1b mutants. NO3- supply promoted LR formation and SR elongation. The effects of NO donor and NO inhibitor/scavenger supply on NO levels and the root morphology of WT and nia2 mutants under NH4+ or NO3- suggest that NO3--induced NO is generated by the nitrate reductase (NR) pathway rather than the NO synthase (NOS)-like pathway. IAA levels, [3H] IAA transport, and PIN gene expression in roots were enhanced under NO3- relative to NH4+ supply. These results suggest that NO3- regulates auxin transport in roots. Application of SNP under NH4+ supply, or of cPTIO under NO3- supply, resulted in auxin levels in roots similar to those under NO3- and NH4+ supply, respectively. Compared to WT, the roots of the ospin1b mutant had lower auxin levels, fewer LRs, and shorter SRs. Thus, NO affects root growth by regulating auxin transport in response to NO3-. Overall, our findings suggest that NO3- influences LR formation and SR elongation by regulating auxin transport via a mechanism involving NO.

A broadly conserved NERD genetically interacts with the exocyst to affect root growth and cell expansion.

The exocyst, a conserved, octameric protein complex, helps mediate secretion at the plasma membrane, facilitating specific developmental processes that include control of root meristem size, cell elongation, and tip growth. A genetic screen for second-site enhancers in Arabidopsis identified NEW ENHANCER of ROOT DWARFISM1 (NERD1) as an exocyst interactor. Mutations in NERD1 combined with weak exocyst mutations in SEC8 and EXO70A1 result in a synergistic reduction in root growth. Alone, nerd1 alleles modestly reduce primary root growth, both by shortening the root meristem and by reducing cell elongation, but also result in a slight increase in root hair length, bulging, and rupture. NERD1 was identified molecularly as At3g51050, which encodes a transmembrane protein of unknown function that is broadly conserved throughout the Archaeplastida. A functional NERD1-GFP fusion localizes to the Golgi, in a pattern distinct from the plasma membrane-localized exocyst, arguing against a direct NERD1-exocyst interaction. Structural modeling suggests the majority of the protein is positioned in the lumen, in a β-propeller-like structure that has some similarity to proteins that bind polysaccharides. We suggest that NERD1 interacts with the exocyst indirectly, possibly affecting polysaccharides destined for the cell wall, and influencing cell wall characteristics in a developmentally distinct manner.

Distribution of Endogenous NO Regulates Early Gravitropic Response and PIN2 Localization in Arabidopsis Roots.

High-resolution and automated image analysis of individual roots demonstrated that endogenous nitric oxide (NO) contribute significantly to gravitropism of Arabidopsis roots. Lowering of endogenous NO concentrations strongly reduced and even reversed gravitropism, resulting in upward bending, without affecting root growth rate. Notably, the asymmetric accumulation of NO along the upper and lower sides of roots correlated with a positive gravitropic response. Detection of NO by the specific DAF-FM DA fluorescent probe revealed that NO was higher at the lower side of horizontally-oriented roots returning to initial values 2 h after the onset of gravistimulation. We demonstrate that NO promotes plasma membrane re-localization of PIN2 in epidermal cells, which is required during the early root gravitropic response. The dynamic and asymmetric localization of both auxin and NO is critical to regulate auxin polar transport during gravitropism. Our results collectively suggest that, although auxin and NO crosstalk occurs at different levels of regulation, they converge in the regulation of PIN2 membrane trafficking in gravistimulated roots, supporting the notion that a temporally and spatially coordinated network of signal molecules could participate in the early phases of auxin polar transport during gravitropism.

Rooted in physics

Roots are fundamental to a plant’s survival, but some of their behaviour at a cellular level remains a mystery to scientists. Jess Wade talks to Giovanni Sena, who is particularly interested in how electric fields can affect root growth and regeneration

Structural and ultrastructural variations in roots of Calopogonium mucunoides Desv. treated with phenolic compounds from Urochloa humidicola (Rendle) Morrone & Zuloaga and phenolic commercial standards

Urochloa humidicola (Rendle) Morrone & Zuloaga is an exotic forage grass cultivated in Brazil. Previous studies have identified different phenolic compounds produced by this species, including flavonoids and p-coumaric acid, which have been well-known as allelochemical compounds. We evaluated the morphology, anatomy and ultrastructure of Calopogonium mucunoides roots exposed to phenolic compounds found in U. humidicola. Leaves of U. humidicola were dried, crushed and submitted to extraction in methanol solution, which was fractionated through partition using organic solvents. In the bioassays, the hydromethanolic leaf extract of U. humidicola, commercial standard solutions of phenols and a control were all tested against the germination and seedling growth of C. mucunoides. The seedlings of C. mucunoides were measured, morphologically described, and the roots were processed according to standard techniques for plant anatomy and electron microscopy. Urochloa humidicola leaf extract inhibited root development, although they stimulated shoot elongation. The p-coumaric acid strongly inhibited plant development, caused root tip necrosis and decreased production of lateral roots, as well as changes in anatomy. Seedlings treated with quercitrin, luteolin and fisetin showed greater lengths, whereas kaempferol negatively affected root growth. Also, U. humidicola extract, p-coumaric acid and kaempferol caused marked changes in root cell ultrastructure. These results suggest a potential phytotoxic effect caused by U. humidicola leaf compounds isolated against C. mucunoides seedlings, although the association of these compounds is suggested to be antagonistic.