Maize Roots In Response Research Articles

Multi-Omics Analysis Reveals the Transcriptional Regulatory Network of Maize Roots in Response to Nitrogen Availability

Nitrogen (N) availability determines higher plant productivity and yield. However, the molecular mechanisms governing N acquisition and utilization remain largely unknown in maize. In this study, ATAC-seq, RNA-seq, and Ribo-seq analyses were conducted in maize roots under different N supply conditions. A set of differentially expressed genes enriched in N and phenylpropanoid metabolisms at both the transcription and translation levels were highlighted. Interestingly, less than half of low-N responsive genes were shared between transcription and translation. The alteration of translational efficiency (TE) is also an important mechanism by which maize responds to LN. In addition, we identified low-N-induced open chromatin regions (OCRs) and observed an enrichment of transcription factor (TF) binding motifs. Furthermore, we constructed a transcriptional regulatory network for maize roots subjected to low-N. These findings extend our understanding of N availability response and provide new insights for improving N use efficiency (NUE).

Integrated Transcriptomic and Metabolomic Analysis of Exogenous NAA Effects on Maize Seedling Root Systems under Potassium Deficiency.

Auxin plays a crucial role in regulating root growth and development, and its distribution pattern under environmental stimuli significantly influences root plasticity. Under K deficiency, the interaction between K+ transporters and auxin can modulate root development. This study compared the differences in root morphology and physiological mechanisms of the low-K-tolerant maize inbred line 90-21-3 and K-sensitive maize inbred line D937 under K-deficiency (K+ = 0.2 mM) with exogenous NAA (1-naphthaleneacetic acid, NAA = 0.01 mM) treatment. Root systems of 90-21-3 exhibited higher K+ absorption efficiency. Conversely, D937 seedling roots demonstrated greater plasticity and higher K+ content. In-depth analysis through transcriptomics and metabolomics revealed that 90-21-3 and D937 seedling roots showed differential responses to exogenous NAA under K-deficiency. In 90-21-3, upregulation of the expression of K+ absorption and transport-related proteins (proton-exporting ATPase and potassium transporter) and the enrichment of antioxidant-related functional genes were observed. In D937, exogenous NAA promoted the responses of genes related to intercellular ethylene and cation transport to K-deficiency. Differential metabolite enrichment analysis primarily revealed significant enrichment in flavonoid biosynthesis, tryptophan metabolism, and hormone signaling pathways. Integrated transcriptomic and metabolomic analyses revealed that phenylpropanoid biosynthesis is a crucial pathway, with core genes (related to peroxidase enzyme) and core metabolites upregulated in 90-21-3. The findings suggest that under K-deficiency, exogenous NAA induces substantial changes in maize roots, with the phenylpropanoid biosynthesis pathway playing a crucial role in the maize root's response to exogenous NAA regulation under K-deficiency.

Weed-induced changes in the maize root transcriptome reveal transcription factors and physiological processes impacted early in crop-weed interactions.

A new paradigm suggests weeds primarily reduce crop yield by altering crop developmental and physiological processes long before the weeds reduce resources through competition. Multiple studies have implicated stress response pathways are activated when crops such as maize are grown in close proximity with weeds during the first 4-8 weeks of growth-the point at which weeds have their greatest impact on subsequent crop yields. To date, these studies have mostly focused on the response of above-ground plant parts and have not examined the early signal transduction processes associated with maize root response to weeds. To investigate the impact of signals from a below-ground competitor on the maize root transcriptome when most vulnerable to weed pressure, a system was designed to expose maize to only below-ground signals. Gene set enrichment analyses identified over-represented ontologies associated with oxidative stress signalling throughout the time of weed exposure, with additional ontologies associated with nitrogen use and transport and abscisic acid (ABA) signalling, and defence responses being enriched at later time points. Enrichment of promoter motifs indicated over-representation of sequences known to bind FAR-RED IMPAIRED RESPONSE 1 (FAR1), several AP2/ERF transcription factors and others. Likewise, co-expression networks were identified using Weighted-Gene Correlation Network Analysis (WGCNA) and Spatiotemporal Clustering and Inference of Omics Networks (SC-ION) algorithms. WGCNA highlighted the potential roles of several transcription factors including a MYB 3r-4, TB1, WRKY65, CONSTANS-like5, ABF3, HOMEOBOX 12, among others. These studies also highlighted the role of several specific proteins involved in ABA signalling as being important for the initiation of the early response of maize to weeds. SC-ION highlighted potential roles for NAC28, LOB37, NAC58 and GATA2 transcription factors, among many others.

Variable responses of maize roots at the seedling stage to artificial biopores in noncompacted and compacted soil

Variable responses of maize roots at the seedling stage to artificial biopores in noncompacted and compacted soil

Film mulching affects root growth and function in dryland maize-soybean intercropping

• Maize roots morphological behaviors respond to soybean roots presence in dry and wet conditions. • Intercropped maize roots were shallower compared to sole maize. • More active root-diameter strategy for intercropped maize to adapt to varied water conditions. • Film mulching improved the overlap of interspecific roots. • Film mulching greatly increased maize grain yield with a lesser decline of soybean grain yield relative to sole soybean. Understanding the morphological response of maize roots in the presence of soybeans in fields under varied water conditions is vital for identifying maize-dominant intercropping systems suitable for climate change. In this study, two maize-soybean intercropping systems (maize with and without film mulching) were compared with maize and soybean sole crops in rainfed farmland on the Loess Plateau. Different features, including the maize root morphological traits, root vertical distribution, shoot traits, interspecific root overlap, and grain yield of intercrops, were determined after silking in 2017 (dry year) and 2018 (wet year). The intercropped maize (without film mulching) employed a thin root system under dry conditions and a profuse root system under wet conditions, with shallow roots and active root-diameter strategy to adapt to varied water conditions. These features resulted in higher grain yield in per unit area for the intercropped maize (16.97 % overyielding) than sole maize without film mulching. Film mulching of intercropped maize modified the roots with confined growth under dry conditions and inhibited the roots with excessive growth under wet conditions; as a consequence, the two morphologies of intercropped maize root system were reshaped into the optimal one (less profuse but not thin), with S-type vertical distribution (1 m soil profile) for root length and more beneficial root-diameter strategy. Besides, film mulching improved interspecific root interaction through an evident increase in root length or mass in the interspecific overlap regions. Finally, film mulching improved the maize overyielding dramatically (84 %) due to high leaf adaptability and efficient root-shoot synergy in maize plants. Importantly, the maize mulching did not decrease intercropped soybean yield significantly when compared with sole soybean due to the benefits from interspecific facilitation, while it enhanced total grain yield (10.67 %) for the intercropping system. Thus, film mulching improved maize root morphology and balanced soil resource exploitation and shoot development, consequently strengthening the attainable grain yield in the intercropping system. To conclude, the research elucidates the plant root mechanisms (root morphological changes) underlying overyielding of intercropped maize in varied water conditions. It identifies film mulching of maize as a strategy to optimize root growth and function for higher intercropping yield advantage in dryland.

Proteomic responses of maize roots to the combined stress of sulphur deficiency and chromium toxicity

Sulphur (S) metabolism plays a crucial role in response to heavy metal stress. It has been well demonstrated that the deficiency of S is a limiting factor to plant capability to cope with chromium (Cr) stress. However, little is known about the plant response to S-deficiency and Cr stress at the proteome level. In the present study, a hydroponic experiment was conducted to examine the role of S supply on Cr-induced proteomic alterations in the roots of maize seedlings. Maize seedlings were exposed to Cr (0 and 100 μM) and different S concentrations (0 and 1 mM) for seven days. Biomass accumulation (fresh and dry weights) was significantly decreased by Cr stress (100 μM), and this decrease was more pronounced under S-deficiency condition. Analysis of proteins on gels detected 54 proteins that exhibited differential expression patterns, out of which 38 were identified by matrix-assisted laser desorption ionization time-of-flight/ time-of-flight (MALDI-TOF/TOF) mass spectrometry. Of these, 21 proteins were up-regulated and 17 proteins were down-regulated by >1.5-fold S-deficiency and/or under Cr stress. The majority of the proteins functioned in stress defence, protein metabolism, and energy metabolism. Our results show that S supplementation enhanced the tolerance to Cr stress by increasing the abundance of stress defence-related proteins including pathogenesis-related protein 10, glutathione peroxidase, superoxide dismutase [Mn], glutathione S-transferase 3, proteasome subunit alpha type 6, IN2–1 protein, and ABA-responsive protein. This study may provide new insights into the proteomic response mechanisms of maize seedlings under Cr stress and/or S-deficiency.

Insufficient and excessive N fertilizer input reduces maize root mass across soil types

Quantifying maize root response to nitrogen (N) fertilizer, soil texture, and weather is crucial to understand complex soil-root-plant processes. We performed a 2-year x 4 locations (sand content range: 5–95%) x N treatments (range: 0 to 336 kg N ha−1) field experiment in Iowa, U.S. to (1) determine the response of root traits to N fertilizer, and (2) develop generalized functions to aid understanding and prediction of root mass and root to shoot (R:S) ratio. Deep root samples (0−210 cm, increments of 30 cm) were collected using the soil core approach at early to middle grain fill period and quantified root mass, length, and N and C concentrations. In addition, yield and shoot biomass was measured. Root traits and yield had different responses to N fertilizer input. Root mass was maximized at 168 kg N ha−1; zero and excessive N fertilization decreased root mass by 33 and 17 %, respectively. Nitrogen fertilizer significantly affected root traits only in the top 30 cm soil layer. Soil texture affected root traits in a dry year (root mass was positively associated with silt and clay), but not in a wet year, suggesting that soil moisture overwhelms the effect of texture. The combined data (N rates x locations x years) revealed a negative relationship between R:S ratio and yield. This resulted in a new set of equations (e.g., upper bound R:S = e(–1.5 – 0.04*yield)) that can replace the constant R:S approach used in the literature. Yield, which is commonly measured, integrates the effects of environment, management, and genetic variation; hence the proposed equations can be widely applied. This study provides evidence that different plant traits are maximized at different levels of mineral N nutrition. Results can enhance biophysical models and prediction of R:S ratio.

Quantitative proteomic analysis reveals altered enzyme expression profile in Zea mays roots during the early stages of colonization by Herbaspirillum seropedicae.

The use of plant growth-promoting bacteria as agricultural inoculants of plants should be encouraged because of their prominent role in biological nitrogen fixation, the increase of nutrient uptake by roots, abiotic stress mitigation, and disease control. The complex mechanisms underlying the association between plant and beneficial bacteria have been increasingly studied, and proteomic tools can expand our perception regarding the fundamental molecular processes modulated by the interaction. In this study, we investigated the changes in protein expression in maize roots in response to treatment with the endophytic diazotrophic Herbaspirillum seropedicae and the activities of enzymes related to nitrogen metabolism. To identify maize proteins whose expression levels were altered in the presence of bacteria, a label-free quantitative proteomic approach was employed. Using this approach, we identified 123 differentially expressed proteins, of which 34 were upregulated enzymes, in maize roots cultivated with H. seropedicae. The maize root colonization of H. seropedicae modulated the differential expression of enzymes involved in the stress response, such as peroxidases, phenylalanine ammonia-lyase, and glutathione transferase. The differential protein profile obtained in the inoculated roots reflects the effect of colonization on plant growth and development compared with control plants.

Strigolactones and Auxin Cooperate to Regulate Maize Root Development and Response to Nitrate.

In maize, nitrate regulates root development thanks to the coordinated action of many players. In this study, the involvement of strigolactones (SLs) and auxin as putative components of the nitrate regulation of lateral root (LR) was investigated. To this aim, the endogenous SL content of maize root in response to nitrate was assessed by liquid chromatography with tandem mass Spectrometry (LC-MS/MS) and measurements of LR density in the presence of analogues or inhibitors of auxin and SLs were performed. Furthermore, an untargeted RNA-sequencing (RNA-seq)-based approach was used to better characterize the participation of auxin and SLs to the transcriptional signature of maize root response to nitrate. Our results suggested that N deprivation induces zealactone and carlactonoic acid biosynthesis in root, to a higher extent if compared to P-deprived roots. Moreover, data on LR density led to hypothesize that the induction of LR development early occurring upon nitrate supply involves the inhibition of SL biosynthesis, but that the downstream target of SL shutdown, besides auxin, also includes additional unknown players. Furthermore, RNA-seq results provided a set of putative markers for the auxin- or SL-dependent action of nitrate, meanwhile also allowing to identify novel components of the molecular regulation of maize root response to nitrate. Globally, the existence of at least four different pathways was hypothesized: one dependent on auxin, a second one mediated by SLs, a third deriving from the SL-auxin interplay, and a last one attributable to nitrate itself through further downstream signals. Further work will be necessary to better assess the reliability of the model proposed.

Science behind biostimulant action of seaweed extract on growth and crop yield: insights into transcriptional changes in roots of maize treated with Kappaphycus alvarezii seaweed extract under soil moisture stressed conditions

Seaweed extracts have been reported to be effective crop biostimulants having low carbon foot print. However, the mechanism of their action on crops has remained elusive due to dearth of studies. Kappaphycus alvarezii seaweed extract (K-sap) has been found to increase the yield of several crops as well as impart drought tolerance. Here, an attempt was made to get a global view of the transcriptome response of maize roots when subjected to soil drench application of K-sap under normally irrigated and drought conditions. mRNA were sequenced using high-throughput RNA sequencing employing Illumina platform and transcriptome mapping was carried out. K-sap applied plants under drought, when compared to its control, recorded several differentially expressed genes involved in RNA-, protein-, cell wall–, signaling-, transport-, stress-, development-, cell-, secondary metabolism–, hormone metabolism–, DNA-, lipid metabolism–, major and minor CHO metabolism–, redox-, metal handling–, amino acid metabolism–, nucleotide metabolism–, TCA-, and N metabolism–related pathways. Up-regulation was observed in the genes coding towards enhancement of root growth, gibberellic acid and auxin signaling, seed development, nitrogen metabolism, transport, and antioxidant activity like glutathione S-transferase and peroxidases. On the other hand, down-regulation of starch and sucrose degradation–related transcripts was apparent. These related well to our morphological observations on improved root growth, grain yield, and higher nutrient content of the roots under drought stress owing to application of K-sap. The study gives a comprehensive insight of several biological processes being modulated and opens up avenues for further targeted mechanistic studies.

Morphological and Physiological Characteristics of Maize Roots in Response to Controlled‐Release Urea under Different Soil Moisture Conditions

Core Ideas We investigated the impacts of CRU on summer maize root growth under different soil water conditions.We clarified the interaction of water and CRU on summer maize grain yield.We found an optimized amount of CRU for each water level for summer maize grain yield. Controlled‐release urea (CRU) is being promoted in Chinese maize (Zea mays L.) planting to improve nitrogen (N) use efficiency, yield and reduce N losses, but its impacts vary widely depending on the soil moisture condition. There has been little study on the effects of CRU on the morphological and physiological characteristics of maize roots under different soil moisture conditions. We conducted three soil moistures (severe stress, mild stress, and adequate condition) and four levels of CRU (0, 105, 210, and 315 kg N ha−1) in a specially designed soil column experiment. Results revealed that CRU regulated plant growth by affecting root morphology and activity under different soil moistures, and ultimately influenced yield. Drought limited root and shoot dry matter accumulation, and decreased root length and root length density, which significantly reduced root active absorption area; leaf area index (LAI), chlorophyll content, and net photosynthetic rate (Pn) were also inhibited. Increasing CRU application did not counteract the inhibition of root and shoot growth under severe water stress, but did counteract this effect under mild water stress. An application of CRU beyond the optimal N rate did not consistently promote maize root growth or increase yield under adequate soil moisture. The CRU application of 210 kg N ha−1 under adequate moisture was the best treatment combination, and was associated with superior root morphology and activity during the grain‐filling period, which could transport more water and nutrients to aboveground plant, improved LAI, chlorophyll content, and Pn, ultimately increased yield. Based on the yield and cost, the CRU application of 315 kg N ha−1 was optimal under mild drought stress, and selecting the lower CRU application of 210 kg N ha−1 under adequate soil moisture condition is recommended to promote root growth and increase grain yield in maize production.

Architectural and anatomical responses of maize roots to agronomic practices in a semi‐arid environment

AbstractRoot architecture and anatomy are important determinants of nitrogen (N) and water acquisition, but they are also environmentally plastic to adapt to N and water availability. Therefore, understanding the relationship between root traits and environmental factors is essential for improving N and water acquisition. A field experiment was conducted in the semi‐arid region of the Loess Plateau in northwestern China to quantify the architectural and anatomical root traits of maize (Zea mays L.) in response to plastic film mulching and N fertilization. We compared four treatments: non‐mulching with and without N supply as well as plastic film mulching with and without N supply. Variation existed for all root architecture and anatomy traits within maize root crowns. Crown and brace root angles to the soil line decreased in response to film mulching and N fertilization. Crown roots under plastic film mulching showed a significantly decreased distance to branching, reduced lateral root length, and overall increased root diameter. Similarly, N application significantly decreased the distance to branching, yet induced more compact and denser crown roots, and increased the root diameter. Brace roots exhibited an increased distance to branching, greater lateral root length and density, as well as a larger root diameter in response to plastic film mulching and N fertilization. Additionally, the accumulated number of nodal roots increased greatly under plastic film mulching and N treatments. At the anatomical level, N application reduced the proportion of the root cortical aerenchyma area. In contrast, aerenchyma area, cortex cell size, and late metaxylem vessel diameter were increased as a result of plastic film mulching. These results demonstrate root architectural and anatomical traits respond to mulching practices and N fertilization.

The Control of Zealactone Biosynthesis and Exudation is Involved in the Response to Nitrogen in Maize Root.

Nitrate acts as a signal in regulating plant development in response to environment. In particular nitric oxide, auxin and strigolactones (SLs) were supposed to cooperate to regulate the maize root response to this anion. In this study, a combined approach based on liquid chromatography-quadrupole/time-of-flight tandem mass spectrometry and on physiological and molecular analyses was adopted to specify the involvement of SLs in the maize response to N. Our results showed that N deficiency strongly induces SL exudation, likely through stimulating their biosynthesis. Nitrate provision early counteracts and also ammonium lowers SL exudation, but less markedly. Exudates obtained from N-starved and ammonium-provided seedlings stimulated Phelipanche germination, whereas when seeds were treated with exudates harvested from nitrate-provided plants no germination was observed. Furthermore, our findings support the idea that the inhibition of SL production observed in response to nitrate and ammonium would contribute to the regulation of lateral root development. Moreover, the transcriptional regulation of a gene encoding a putative maize WBC transporter, in response to various nitrogen supplies, together with its mRNA tissue localization, supported its role in SL allocation. Our results highlight the dual role of SLs as molecules able to signal outwards a nutritional need and as endogenous regulators of root architecture adjustments to N, thus synchronizing plant growth with nitrogen acquisition.

Growth and Distribution of Maize Roots in Response to Nitrogen Accumulation in Soil Profiles after Long-Term Fertilization Management on a Calcareous Soil

The replacement of inorganic fertilizer nitrogen by manure is highlighted to have great potential to maintain crop yield while delivering multiple functions, including the improvement of soil quality. However, information on the dynamics of root distributions in response to chemical fertilizers and manure along the soil profile is still lacking. The aim of this study was to investigate the temporal-spatial root distributions of summer maize (Zea mays L.) from 2013 to 2015 under four treatments (unfertilized control (CK), inorganic fertilizer (NPK), manure + 70% NPK (NPKM), and NPKM + straw (NPKMS)). Root efficiency for shoot N accumulation was increased by 89% in the NPKM treatment compared with the NPK treatment at V12 (the emergence of the twelfth leaf) of 2014. Root growth at 40–60 cm was consistently stimulated after manure and/or straw additions, especially at V12 and R3 (the milk stage) across three years. Root length density (RLD) in the diameter <0.2 mm at 0–20 cm was significantly positively correlated with soil water content and negatively with soil mineral N contents in 2015. The RLD in the diameter >0.4 mm at 20–60 cm, and RLD <0.2 mm, was positively correlated with shoot N uptake in 2015. The root length density was insensitive in response to fertilization treatments, but the variations in RLD along the soil profile in response to fertilization implies that there is a great potential to manipulate N supply levels and rooting depths to increase nutrient use efficiency. The importance of incorporating a manure application together with straw to increase soil fertility in the North China Plain (NCP) needs further studies.

Early development of apoplastic barriers and molecular mechanisms in juvenile maize roots in response to La2O3 nanoparticles

The increasing occurrence of engineered nanoparticles (NPs) in soils may decrease water uptake in crops, followed by lower crop yield and quality. As one of the most common rare earth oxide NPs, lanthanum oxide (La2O3) NPs may inhibit the relative expressions of aquaporin genes, thus reduce water uptake. In the present study, maize plants were exposed to different La2O3 NPs concentrations (0, 5, 50 mg L−1) for 72 h and 144 h right after the first leaf extended completely. Our results revealed that water uptake was reduced by La2O3 NPs through accelerating the development of apoplastic barriers in maize roots. The level of abscisic acid, determined by using ultra high performance liquid chromatography-tandem mass spectrometry, was increased upon La2O3 NPs exposure. Furthermore, ZmPAL, ZmCCR2 and ZmCAD6, the core genes specific for biosynthesis of lignin, were up-regulated by 3–13 fold in roots exposed to 50 mg L−1 La2O3 NPs. However, ZmF5H was suppressed, indicating that lignin with S units could be excluded for the formed lignin in apoplastic barriers upon La2O3 NPs exposure. The level of essential component of apoplastic barriers - lignin was increased by 1.5-fold. The early development of apoplastic barriers was observed, and stomatal conductance and transpiration rate of La2O3 NPs-treated plants were significantly decreased by 63%–83% and 42%–86%, respectively, as compared to the control. The lignin enriched apoplastic barriers in juvenile maize thus led to the reduction of water uptake, subsequently causing significant growth inhibition. This is the first study to show early development of root apoplastic barriers upon La2O3 NPs exposure. This study will help us better understand the function of apoplastic barriers in roots in response to NPs, further providing fundamental knowledge to develop safer and more efficient agricultural nanotechnology.

Correction to: Root-colonizing bacteria enhance the levels of (E)-β-caryophyllene produced by maize roots in response to rootworm feeding.

Unfortunately, family name of author "Xavier Chiriboga M" was incorrectly identified in the original publication and the same is corrected here. The original article has been corrected.

Root-colonizing bacteria enhance the levels of (E)-β-caryophyllene produced by maize roots in response to rootworm feeding.

When larvae of rootworms feed on maize roots they induce the emission of the sesquiterpene (E)-β-caryophyllene (EβC). EβC is attractive to entomopathogenic nematodes, which parasitize and rapidly kill the larvae, thereby protecting the roots from further damage. Certain root-colonizing bacteria of the genus Pseudomonas also benefit plants by promoting growth, suppressing pathogens or inducing systemic resistance (ISR), and some strains also have insecticidal activity. It remains unknown how these bacteria influence the emissions of root volatiles. In this study, we evaluated how colonization by the growth-promoting and insecticidal bacteria Pseudomonas protegens CHA0 and Pseudomonas chlororaphis PCL1391 affects the production of EβC upon feeding by larvae of the banded cucumber beetle, Diabrotica balteata Le Conte (Coleoptera: Chrysomelidae). Using chemical analysis and gene expression measurements, we found that EβC production and the expression of the EβC synthase gene (tps23) were enhanced in Pseudomonas protegens CHA0-colonized roots after 72h of D. balteata feeding. Undamaged roots colonized by Pseudomonas spp. showed no measurable increase in EβC production, but a slight increase in tps23 expression. Pseudomonas colonization did not affect root biomass, but larvae that fed on roots colonized by P. protegens CHA0 tended to gain more weight than larvae that fed on roots colonized by P. chlororaphis PCL1391. Larvae mortality on Pseudomonas spp. colonized roots was slightly, but not significantly higher than on non-colonized control roots. The observed enhanced production of EβC upon Pseudomonas protegens CHA0 colonization may enhance the roots' attractiveness to entomopathogenic nematodes, but this remains to be tested.

Water-extractable humic substances speed up transcriptional response of maize roots to nitrate

Humic substances are known to positively influence plant growth and nutrition. In particular, the water-extractable fraction of humic substances (WEHS) has been shown to enhance nitrate acquisition, increasing the activity of high affinity nitrate uptake system. However, molecular bases of this physiological response are not clarified so far.Thus, in the present work, the physiological effect of WEHS on nitrate acquisition in maize roots was correlated with changes in the root transcriptomic profile.Results confirmed that WEHS caused a faster induction of a higher capacity to take up nitrate in maize roots. Comparing the root transcriptomic profile of Nitrate- and Nitrate + WEHS-treated plants with Control (-N) ones, more than 2000 transcripts appeared to be modulated only in the presence of WEHS. Among these, genes involved in nitrate transport and assimilation (NRT1s, NRT2s, NAR2.1, NR, GS, GOGAT, CNX, UPM) were strongly modulated by WEHS. Furthermore, also some genes known to be linked to the nitrogen limitation responses were affected by WEHS, as transcripts coding for transcription factors (as LBD37, NIN-like protein, NFY-A, GRF5) and enzymes of hormones’ metabolism. The modulation of these transcripts might play a crucial role in coordinating the induction to nitrate, favouring its uptake and assimilation in WEHS-treated plants. The overexpression of nitrogen assimilatory genes by WEHS might led to an early feedback regulation of the high affinity nitrate transport system, as being operated by N-metabolites.Results of the present work shed further light on the contribution of the organic soil component to the nitrogen use efficiency in crops.

Synergy between root hydrotropic response and root biomass in maize (Zea mays L.) enhances drought avoidance

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

Growth and metabolic responses of maize roots to straw biochar application at different rates

Biochar application in soil has been increasingly suggested as an option to improve soil ecosystem functions and optimize agricultural systems. The main goal of the present work was to explore the effects of straw biochar application at different dosages on the growth and metabolic processes of maize plants, especially roots. Field and pot experiments were conducted independently, in which maize plants were grown in soil amended with straw-biochar at dosages of 0%, 1%, 3%, 5%, 15% and 30% (w/w). Metabolic profiling in both leaves and roots were analyzed by nuclear magnetic resonance. Biochar application at rates from 1% to 5% caused growth and physiological changes of maize plants including increases in plant height and stem diameter, and improvements of chlorophyll content and net photosynthetic rate, which led to an increase in grain and straw yield. The root growth in maize seedlings was stimulated at a BC dose of 5% and was inhibited up to a dose of 30%, which was characterized by changes in root elongation, root thickening, lateral root branching and root cell viability. A wide range of metabolic responses, including changes in metabolomic profile, and metabolism of sugars and amino acids, may also contribute to the observed stimulation of plant growth following BC application at an optimum dosage of 5%. The present results provided a better understanding of the mechanism underlying the enhanced plant productivity and its relationship with biochar application rates.