Root System Response Research Articles

Cover crops and a devigorating rootstock can impart substantial agroecosystem services to high-resource vineyards: A multi-year study

In vineyards, cover crops typically grow concurrently with grapevines and can impart a multitude of agroecosystem services; yet concerns over potential disservices might limit adoption. Reductions in yield and vegetative growth are key disservices of concern, but at sites with high soil resources, reducing excessive vegetative growth is often considered beneficial, if the yield is not strongly penalized. To optimize agroecosystem services provided by cover crops, it is crucial to examine above- and belowground plant responses over multiple years. Documentation of the responses of fruit crop root systems to cover crops may clarify potential benefits for long-term agroecosystem services associated with aboveground growth and soil resources. In 2016, we established a perennial grass under young vines (full floor cover) to examine if agroecosystem services imparted by an under-vine cover crop change in the first five years of vineyard production and depend on rootstock vigor. Overall, cover crop reduced grapevine vegetative growth between 13% and 30% across all years and with a trend of more substantial reductions in the first two years. In contrast, yield was reduced in only three of the five years, between 9% and 25%, depending on the rootstock. Furthermore, neither cover crop nor differences in rootstock vigor resulted in relevant or consistent changes in fruit chemistry during the study. Overall, we found that in a relatively fertile, young vineyard, combining a lower vigor rootstock with a perennial, under-vine cover crop imparts substantial agroecosystem services in comparison to the more common practices of using a medium vigor rootstock and spraying herbicide under the vines. These services included improved crop load (ratio of fruit to vegetative mass), increased soil phosphorus availability, increased deep soil water content, and presumably lower labor and other costs associated with vineyard maintenance. Studies on a decadal timescale are needed to further clarify whether these services persist, accumulate with time, or if competition from the cover crop eventually leads to unacceptable decreases in vine nutrient status, growth, and production.

Arbuscular Mycorrhizal Fungi Alleviate Low Phosphorus Stress in Maize Genotypes with Contrasting Root Systems.

Soil available phosphorus (P) is one of the main factors limiting plant growth and yield. This study aimed to determine the role of arbuscular mycorrhizal fungi (AMF) in P-use efficiency in two maize genotypes with contrasting root systems in response to low P stress. Maize genotypes small-rooted Shengrui 999 and large-rooted Zhongke 11 were grown in rhizoboxes that were inoculated with or without AMF (Funneliformis mosseae) under low P (no added P) or optimal P (200 mg kg-1) for 53 days. Low P stress significantly inhibited shoot and root growth, photosynthesis, tissue P content, and root P concentration in both genotypes. Shengrui 999 was more tolerant to P stress with less reduction of these traits compared to Zhongke 11. Shengrui 999 had a higher AMF infection rate than Zhongke 11 at both P levels. Under P deficit, inoculation with AMF significantly promoted plant growth and P uptake in both genotypes with more profound effects seen in Zhongke 11, whilst Shengrui 999 was more dependent on AMF under optimal P. Low P stress inhibited the growth and physiological attributes of both genotypes. The small-rooted Shengrui 999 was more tolerant to low P than Zhongke 11. Inoculation with AMF alleviates low P stress in both genotypes with a more profound effect on Zhongke 11 at low P and on Shengrui 999 at high P conditions.

Root System Architecture and Omics Approaches for Belowground Abiotic Stress Tolerance in Plants

Plant growth and productivity is negatively affected by several abiotic stresses. To overcome the antagonistic effect of a changing environment, plants have evolved several modifications at the physiological as well as molecular levels. Besides being a vital organ for a plant’s nutrient uptake, roots also plays a significant role in abiotic stress regulation. This review provides insight into changing Root System Architecture (RSA) under varying environmental stimuli using high-throughput omics technologies. Several next-generation and high-throughput omics technologies, such as phenomics, genomics, transcriptomics, proteomics, and metabolomics, will help in the analysis of the response of root architectural traits under climatic vagaries and their impact on crop yield. Various phenotypic technologies have been implied for the identification of diverse root traits in the field as well as laboratory conditions, such as root-box pinboards, rhizotrons, shovelomics, ground-penetrating radar, etc. These phenotypic analyses also help in identifying the genetic regulation of root-related traits in different crops. High-throughput genomic as well as transcriptome analysis has led researchers to unravel the role of the root system in response to these environmental cues, even at the single-cell level. Detailed analysis at the protein and metabolite levels can provide a better understanding of the response of roots under different abiotic stresses. These technologies will help in the improvement of crop productivity and development of resistant varieties.

Integration of mRNA and microRNA analysis reveals the molecular mechanisms underlying drought stress tolerance in maize (Zea mays L.).

Drought is among the most serious environmental issue globally, and seriously affects the development, growth, and yield of crops. Maize (Zea mays L.), an important crop and industrial raw material, is planted on a large scale worldwide and drought can lead to large-scale reductions in maize corn production; however, few studies have focused on the maize root system mechanisms underlying drought resistance. In this study, miRNA–mRNA analysis was performed to deeply analyze the molecular mechanisms involved in drought response in the maize root system under drought stress. Furthermore, preliminary investigation of the biological function of miR408a in the maize root system was also conducted. The morphological, physiological, and transcriptomic changes in the maize variety “M8186” at the seedling stage under 12% PEG 6000 drought treatment (0, 7, and 24 h) were analyzed. With prolonged drought stress, seedlings gradually withered, the root system grew significantly, and abscisic acid, brassinolide, lignin, glutathione, and trehalose content in the root system gradually increased. Furthermore, peroxidase activity increased, while gibberellic acid and jasmonic acid gradually decreased. Moreover, 32 differentially expressed miRNAs (DEMIRs), namely, 25 known miRNAs and 7 new miRNAs, and 3,765 differentially expressed mRNAs (DEMRs), were identified in maize root under drought stress by miRNA-seq and mRNA-seq analysis, respectively. Through combined miRNA–mRNA analysis, 16 miRNA–target gene pairs, comprising 9 DEMIRs and 15 DEMRs, were obtained. In addition, four metabolic pathways, namely, “plant hormone signal transduction”, “phenylpropane biosynthesis”, “glutathione metabolism”, and “starch and sucrose metabolism”, were predicted to have important roles in the response of the maize root system to drought. MiRNA and mRNA expression results were verified by real-time quantitative PCR. Finally, miR408a was selected for functional analysis and demonstrated to be a negative regulator of drought response, mainly through regulation of reactive oxygen species accumulation in the maize root system. This study helps to elaborate the regulatory response mechanisms of the maize root system under drought stress and predicts the biological functions of candidate miRNAs and mRNAs, providing strategies for subsequent mining for, and biological breeding to select for, drought-responsive genes in the maize root system.

Root system response to salt stress in grapevines (Vitis spp.): A link between root structure and salt exclusion

Accessing freshwater resources for agriculture becomes more complex due to increasing demands and declining water quality. Alternative water sources, such as saline water, require ad hoc solutions. Therefore, understanding roots' response to saline water is crucial for future agriculture. We examined the response of three grapevine rootstocks (Paulsen 1103, Richter 110 and SO4) to salt stress. The rootstocks were subjected to two salinity treatments: 10 mM and 30 mM NaCl (EC = 2 and 4 ds/m, respectively). Root and shoot samples were taken at the end of the experiment for morphologic and ionomic analyses. The specific root area (SRA) increased in response to salinity for all three rootstocks due to root tissue density and average root diameter reductions. Salinity also led to increased root Na+ and Cl- contents and reduced root K+/Na+ ratio, parallel to increased leaf Cl- but not Na+ contents. SO4 showed improved chloride and sodium exclusion, concomitant with its highest SRA, resulting from the increase in its thin roots' contribution to the total root system surface area. We suggest that enhanced SRA combined with decreased root tissue density and diameter may improve grapevines' salt exclusion by less salt uptake from the soil.

Effects of variable temperature and moisture conditions on respiration and nonstructural carbohydrate dynamics of tree roots

• Low soil moisture lowered the root respiration rate of boreal Scots pines. Root respiration was clearly higher in warm and dry than cool and moist year. • Root respiration peaked after the aboveground growth began to decrease. • The root fructose and glucose contents correlated negatively with soil moisture. The method used to determine root respiration should be selected carefully. In warming climates, soil water content (SWC) may act as an important factor in determining belowground carbon dynamics in boreal forests. Here, we estimated the respiration and nonstructural carbohydrate (NSC) concentrations of tree roots in a mature Scots pine ( Pinus sylvestris L.) stand in southern Finland during two growing seasons with contrasting weather conditions. Root respiration was estimated with four different methods: 1) incubating excised roots, 2) partitioning forest floor respirations with root exclusion, or 3) based on temperature response functions and 4) modelling with the whole-tree carbon model ‘CASSIA’. In addition, we conducted a drought experiment in a greenhouse to determine the effect of reduced soil-water availability on respiration by incubating soil and roots of Scots pine saplings. We observed that the respiration of incubated roots of Scots pine saplings and soil decreased with drying after excluding the effect of temperature on respiration (R RES ), soil being more sensitive to drought than roots. Similarly, R RES of incubated roots in the field was significantly decreased by lowered SWC, whereas respiration of the entire root system estimated with other methods was clearly higher in dryer and warmer than moister and cooler year. Nevertheless, incubated roots excavated from the topsoil are most affected by drying soil, which might not reflect the response of the entire root system. R RES of incubated roots was negatively associated with root fructose and glucose concentrations. At the same time, root fructose, glucose and sucrose concentrations were negatively associated with SWC due to their role in osmoregulation. Thereby it seems that R RES does not directly follow the changes in NSCs despite the apparent correlation. Our study highlights the responsive nature of root carbon dynamics in varying weather events that should be taken into account in estimating and modelling the impacts of warming climate.

Effects of Combined Abiotic Stresses Related to Climate Change on Root Growth in Crops

Climate change is a major threat to crop productivity that negatively affects food security worldwide. Increase in global temperatures are usually accompanied by drought, flooding and changes in soil nutrients composition that dramatically reduced crop yields. Against the backdrop of climate change, human population increase and subsequent rise in food demand, finding new solutions for crop adaptation to environmental stresses is essential. The effects of single abiotic stress on crops have been widely studied, but in the field abiotic stresses tend to occur in combination rather than individually. Physiological, metabolic and molecular responses of crops to combined abiotic stresses seem to be significantly different to individual stresses. Although in recent years an increasing number of studies have addressed the effects of abiotic stress combinations, the information related to the root system response is still scarce. Roots are the underground organs that directly contact with the soil and sense many of these abiotic stresses. Understanding the effects of abiotic stress combinations in the root system would help to find new breeding tools to develop more resilient crops. This review will summarize the current knowledge regarding the effects of combined abiotic stress in the root system in crops. First, we will provide a general overview of root responses to particular abiotic stresses. Then, we will describe how these root responses are integrated when crops are challenged to the combination of different abiotic stress. We will focus on the main changes on root system architecture (RSA) and physiology influencing crop productivity and yield and convey the latest information on the key molecular, hormonal and genetic regulatory pathways underlying root responses to these combinatorial stresses. Finally, we will discuss possible directions for future research and the main challenges needed to be tackled to translate this knowledge into useful tools to enhance crop tolerance.

Root system responses to phosphate nutrition involve plasma membrane H+-ATPases in Arabidopsis thaliana

Root system responses to phosphate nutrition involve plasma membrane H+-ATPases in Arabidopsis thaliana

Root System Response of Selected Rabi Sorghum Genotypes to Varied Soil Moisture Regimes

Root System Response of Selected Rabi Sorghum Genotypes to Varied Soil Moisture Regimes

Root growth and architecture of Tamarix chinensis in response to the groundwater level in the Yellow River Delta

AimsInvestigate the growth adaptation law of the Tamarix chinensis root system in response to the groundwater level in a muddy coastal zone. MethodsThe high groundwater level (0.7–0.9 m), medium groundwater level (1.1–1.3 m) and low groundwater level (1.5–1.7 m) T. chinensis forests on the beaches of the Yellow River Delta were used as the research objects. Full excavation methods were used to excavate root systems with different groundwater levels; then, the aboveground biomass, root biomass, root spatial distribution, root topological structure and fractal characteristics of T. chinensis response characteristics to groundwater level were measured and analysed. ResultsThe results showed that with the decrease in the groundwater level, the soil water content and soil salt content showed upward trends. At high groundwater levels, T. chinensis reduced root biomass allocation to reduce the damage to roots caused by salinity. At low groundwater levels, T. chinensis strengthened the development of root systems, which greatly enhanced the ability of T. chinensis to balance its water intake. The root biomass at the high groundwater level was 43.06% lower than that at the low groundwater level. The relationship between root and shoot growth of T. chinensis at high groundwater levels and medium groundwater levels indicated allometric growth, and at low groundwater levels, roots and shoots grew uniformly. The root distribution of T. chinensis tended to be shallow at the different groundwater levels, showing the characteristics of a horizontal root type. At high groundwater levels, the root topological structure tended to be dichotomous, and the fractal dimension and fractal abundance values were both large, at 1.31 and 2.77, respectively. The branch complexity increased to achieve spatial expansion and increase plant stability. However, the topological structure of the medium and low groundwater level T. chinensis tended to be herringbone-like, the fractal dimension and fractal abundance values were small, the second branch was limited, and the structure was simple. The topological structure and fractal characteristics of the T. chinensis root system responded to different groundwater levels in a coordinated manner. ConclusionsBased on the differences in the growth and architecture of the T. chinensis root system, the T. chinensis root system has strong phenotypic plasticity to the heterogeneous water-salt habitat of the groundwater-soil system, and the T. chinensis root system shows strong root adaptability to water and salt stress.

Comparative Proteomic Analysis by Isobaric Tags for the Relative and Absolute Quantification Reveals the Responses of Tobacco (Nicotiana tabacum L.) Roots to Different Soil Types.

Tobacco (Nicotiana tabacum) root affects the yield and quality of tobacco leaves. To gain insight into the responses of the tobacco root system to different soil types, we integrated morphological characteristics, the physiological index, the metabolic pathways of the root system, and the aboveground biomass of tobacco cultivated in limestone soil (LS), paddy soil (PS), and red soil (RS). Compared with plants growing in LS and PS, the chemical composition of tobacco leaves in RS tended to be coordinated. Red soil facilitated the accumulation of aboveground and belowground biomass of flue-cured tobacco and had the most significant effect on the dry matter quality of the roots. In addition, it promoted an increased root length, root surface area (RSA), root volume, and a higher number of root forks and improved root vigor and nitrate reductase (NR) activity; however, the activities of superoxide dismutase (SOD) and peroxidase (POD) were decreased. We studied differentially the abundant proteins (DAPs) of the flue-cured tobacco roots cultivated in different soil types by isobaric tags for the relative and absolute quantification (iTRAQ) of the proteomic profiles of cultivar. In total, 699, 650, and 569 differentially abundant proteins (DAPs) were identified from limestone soil (LS) vs. PS, LS vs. RS, and PS vs. RS, respectively, including 412/287, 291/359, and 323/246 up-/downregulated proteins, respectively. These DAPs were mainly involved in starch and sucrose metabolism, phenylalanine metabolism, the biosynthesis of secondary metabolites, microbial metabolism in different environments, and ribosomes. The parallel reaction monitoring (PRM) and quantitative reverse transcription PCR (qRT-PCR) analysis showed that the results of the iTRAQ proteomics were reliable. Overall, our study facilitates a new understanding of the responses of tobacco roots to different soil types at the protein level.

Metabolomics analysis reveals the physiological mechanism underlying growth restriction in maize roots under continuous negative pressure and stable water supply

Metabolomics analysis was used to elucidate the mechanism underlying response of the maize root system to continuous negative pressure and stable water supply. Results showed a significant reduction in continuous negative pressure and stable water supply (NPI) relative to intermittent positive pressure water supply (DI), maize root dry matter accumulation and root shoot ratio in NPI was 20.22%, 34.15% and lower than DI, respectively, yield was 44.10% higher than DI, and superoxide anion, malonic dialdehyde, osmotic adjustment substance content, and antioxidant enzyme activity was reduced. Next, we applied liquid chromatography-mass spectrometry, gas chromatography-mass spectrometry, and nuclear magnetic resonance to perform non-targeted metabolomics analysis with the aim of elucidating the physiological basis of root redundant growth restriction. Results revealed presence of 33 different metabolites in NPI, belonging to different categories, including organic acids and their derivatives, nucleosides, nucleotides and their corresponding analogues, lipids and lipid-like molecules, as well as organic oxygen compounds. Moreover, all these were enriched in 44 metabolic pathways, relative to DI. Notably, metabolic pathways, biosynthesis of secondary metabolites, starch and sucrose metabolism, plant hormones biosynthesis, and biosynthesis of plant secondary metabolites might restrict maize roots growth. In NPI was, Trehalose, 2’-deoxyadenosine, isoleucine and ajmaline were 0.34-, 0.05-, 0.004- and 0.17-fold lower than DI, whereas glutamic acid, glutamine and zeatin were 4.62,4.26,4.06 times higher than DI. This might inhibit root redundant growth. In summary, continuous negative pressure and stable water supply inhibited maize root redundant growth restriction by suppressing sugar metabolism and protein synthesis via genetic information transmission.

Response of Wheat Root System and its Mineralization to Chemical Inputs, Plant Genotype and Phenotypic Plasticity

Response of Wheat Root System and its Mineralization to Chemical Inputs, Plant Genotype and Phenotypic Plasticity

Belowground consequences of converting broadleaf to conifer forest: Comparing the fine root systems of European beech and Scots pine

Planted forests of Scots pine (P. sylvestris L.) and other Pinus species extend over >1.7 million hectares in the Pleistocene lowlands of northern Germany, replacing former broadleaf forests (primarily European beech, Fagus sylvatica L.). This transformation belongs to the world’s largest broadleaf-conifer forest conversions; yet, the belowground consequences of this species shift are poorly studied. Based on root coring, an ingrowth core study and root morphological analyses, we compared (i) the bio- and necromass, productivity and morphology of fine roots in pairs of beech and pine stands and (ii) analyzed the species’ fine root system response to variation in soil properties and climatic conditions across a climate continentality gradient. Fine root biomass was on average 6.5 times higher (237 vs. 37 g m−2) and fine root productivity 1.9 times greater (147 vs. 77 g m−2 yr−1, difference not significant) in beech than pine stands. Beech responded with considerable plasticity in fine root system size and fine root morphology to variation in soil acidity and soil fertility and to the contrasting growing conditions in organic layer and mineral soil, but was not responsive to the climatic gradient. In contrast, pine modified fine root biomass and root morphology in response to precipitation and temperature, but did not respond to soil chemistry and fertility. Pine had a somewhat higher mean fine root diameter and also higher specific fine root surface area than beech, while its fine root tip abundance and mean fine root lifespan were lower than in beech (4 vs. 13 months). We conclude that the conversion of broadleaf (beech) to coniferous (pine) forest is accompanied by marked root system changes, notably the reduction of standing fine root biomass and productivity and an apparently contrasting belowground responsiveness to climatic and edaphic changes, with possible consequences for the trees’ susceptibility to climate-warming and drought.

Choices of ectomycorrhizal foraging strategy as an important mechanism of environmental adaptation in Faxon fir (Abies fargesii var. faxoniana)

Faxon fir (Abies fargesii var. faxoniana) is endemic to the cool and moist subalpine region of Southwest China, where the occurrence of warmer and drier climate may impose uncertain environmental constraints to its population stability and community scuccession. Here we determine the role of root-mycorrhizal symbiosis in the adaptability of Faxon fir to varying environmental conditions. The traits and foraging behaviors of the ectomycorrhizal (ECM) associations in Faxon fir were investigated along elevational gradient in three representative natural distributional areas of the species. Soil and Faxon fir root samples were collected from varying elevations in three study areas, namely Wolong Nature Reserve, Miyaluo Nature Reserve, and Wanglang Nature Reserve, in Sichuan province, Southwest China, using point-centered quarter sampling method, with 32 samples for each elevational site. Measurements were made on fine root biomass, ECM morphological diversity and soil exploration types, density and superficial area of ECM root tips, and soil chemistry. Values for selective climatic variables were derived from the national grid-datasets of meteorology of China. Principle component analysis (PCA), redundancy analysis (RDA) and linear regressions were performed to determine the inter-relationships of ECM root traits with climatic and soil factors, and the variations of the ECM root traits with elevation. We found that the biomass of absorptive fine roots and ECM morphological diversity decreased with rising elevations and increasing soil water content or precipitation and soil C:N ratio. The foraging ability of ECM roots, inferred by the soil exploration type of ECM symbionts, and density and superficial area of ECM root tips, were weakened by warming and drying. Under conditions of low N availability, both the frequency of contact exploration type and ECM root tip density prevailed, whilst the frequency of both short-distance and medium-distance exploration types tended to decline, suggesting conservative carbon cost of ECM root systems in low fertility soil. Overall, our findings suggest that the ECM symbionts in Faxon fir adopt the strategy of C investment in root systems in response to warming and drying while relying on the functional efficiency of the ECM root tips toward the colder and more humid environments, and that Faxon fir may sustain moderate changes in the regional climate and maintain population stability, partially owning to adjustment of the ECM foraging strategies.

The Effect of Salinity on Root Architecture in Forage Pea (Pisum sativum ssp. arvense L.)

Background: Plants face different abiotic stresses such as salinity that affect their normal development, growth and survival. Forage pea is an important legume crop for herbage production in ruminants. Its agronomy requires high levels of irrigation and fertilization. This study aimed to evaluate the effect of salinity on seedling root system development in forage pea under semi-hydroponics conditions.Methods: Different treatment of NaCl doses (0, 50, 100, 150, 200, 250 and 300 mM) on root architecture was investigated in two different forage pea cultivars (Livioletta and Ulubatlý) with contrasting root structures under controlled conditions. The experimental design was completely randomized design with three replications and nine plants per replication.Result: Salinity affects root and shoot development differently on these cultivars. Despite the salinity, Livioletta produced more shoot (0.71 g) and root biomass (0.30 g) compared to Ulubatlý (0.52 g and 0.25 g for Root and Shoot biomass, respectively) at 150 mM and all other salinity levels. Livioletta developed a better root system and tolerated salt to a higher dose than Ulubatlý. Understanding root system responses of forage pea cultivars may allow breeding and selecting salinity tolerant cultivars with better rooting potential.

A 3D-printed Arabidopsis thaliana root imaging platform.

High-resolution live imaging promises new insights into the cellular and molecular dynamics of the plant root system in response to external cues. Microfluidic platforms are valuable analytical tools that combine the precise spatial and temporal control of culture conditions with live-imaging capabilities. However, complexity in the fabrication and operations of current plant microfluidic platforms limits their use to a few technologically-focused laboratories. Here, we design and characterize an easy-to-implement 3D printed open microfluidic platform for Arabidopsis thaliana roots. Our biocompatibility study identified a suitable material for the platform production and an established drought stress assay validates the reliability of our stereolithography (SLA)-based next generation RootChip.

Drought response of European beech (Fagus sylvatica L.)—A review

European beech (Fagus sylvatica) is the dominant tree species of Central Europe’s natural forests and one of the continent’s most important timber species. This highly competitive species is known to be drought-sensitive and thus may increasingly be threatened by climate change-related heat waves and drought in part of its distribution range. Tree responses and tolerance to drought are complex processes that are best understood by adopting a multi-level analysis spanning from the molecular physiological to the tree and stand levels. Here I review recent progress in our understanding of beech drought responses in all relevant fields of research, notably adjustments in cellular biochemistry, responses of photosynthesis, stomatal regulation and leaf water status, the vulnerability of the hydraulic and phloem systems, adaptive responses of the fine root system, leaf area adjustments, long-term declines in radial growth, and drought-induced tree mortality. A special focus is on population differences in drought tolerance as the basis for the selection of drought-hardier provenances. The evidence from the different research fields is brought together with the aim to develop a multi-disciplinary perception of beech drought response, to identify weak components in the species’ drought response strategy, and to suggest future research efforts to close knowledge gaps.

Responses of root physiological characteristics of different drought-tolerant cotton varieties to drought

In order to explore the physiological responses of root system of different drought-resistant cotton varieties to drought and their relationships with biomass, we examined the effects of drought stress on root vigor, antioxidant enzyme activities and anatomic structure (duct diameter, number) and biomass of different drought-tolerant varieties, including the drought-inolerant variety 'Xinluzao 17' (L17) and the drought-tolerant variety 'Xinluzao 22' (L22). Both varieties were grown under soil column cultivation conditions, with conventional irrigation (CK), mild drought (W1) and moderate drought (W2) treatments. The results showed that drought stress caused significant reductions in soluble protein (SP) content, root vigor (RV), the number of cork layers, the number of rhizome ducts, the diameter of the ducts in both varieties. The higher root MDA content, CAT, POD and SOD activities in response to drought led to reduction of aboveground dry mass. Compared with that of L17, SP content, 0-40 cm and 80-120 cm soil layer RV, the number of cork layers, the number of rhizome ducts, the diameter of ducts, and the aboveground dry mass of L22 all signi-ficantly increased. Under the W2 treatment, the RV decrease of L22 was 26.2% lower than that of L17, and CAT, POD, SOD activities and the thickness of cortex were 43.6%, 6.9%, 25.4%, 19.9% higher than that of L17. There were positive correlations between dry mass and RV, SOD, POD, the number of cork layers, the diameter and number of rhizome ducts. Therefore, cotton variety with strong drought tolerance could maintain higher root activity, cork layer number, the diameter of rhizome ducts, and number under drought conditions, and thus promote the accumulation of aboveground biomass, which was the physiological mechanism for their stronger drought tolerance.

Abscisic acid-nitric oxide and auxin interaction modulates salt stress response in tomato roots

Integrated signaling network involving abscisic acid (ABA), nitric oxide (NO), and indole-acetic acid (IAA) controls root morphogenesis during salt stress by a mechanism still poorly understood. The present data unveiled an ABA-NO-IAA interaction underlying radicular morphological responses to salinity. Three Solanum lycopersicum genotypes were analyzed: wild type, ABA-insensitive mutant (sitiens), and auxin-responsive (DR5::GUS) plants. Nitric oxide fluorescence, nitrate reductase activity, auxin signaling, and some molecular analyses were performed. Pharmacological inhibitors and NO donor sodium nitroprusside were also used to evaluate NaCl-induced root morphological responses. Sodium nitroprusside inhibited primary root length, increased lateral root emergence, and rescued salt inhibited lateral root growth. The results showed that NO integrates the ABA-IAA signaling network of root system responses under salt stress, involving: (a) ABA and molybdenum-dependent enzymes as responsible for salt-induced NO production; (b) modulations of the plasma membrane H+-ATPase coupling and isoforms differential expression; and (c) ABA-mediated and NO-dependent antioxidative enzymes activities.