Second-order Lateral Roots Research Articles

Regulation of maize root growth by local phosphorus availability, sucrose metabolism, and partitioning.

Understanding how maize roots proliferate in phosphorus (P)-rich soil patches is critical for improving nutrient acquisition and crop productivity. This study explores the mechanisms of root adaptation to heterogeneous P availability, focusing on sucrose metabolism and the role of local P signals. A split-root system with chambers of differing Pi concentrations (0 and 500 μM) was used to examine maize root responses. Various physiological and biochemical parameters, including root growth, sucrose partitioning, enzyme activities, and gene expression, were measured to elucidate the underlying mechanisms. Root proliferation, particularly of second-order lateral roots, was markedly enhanced in P-rich patches. Sucrose was preferentially allocated to the Pi-supplied side, as confirmed by Fourier-transform infrared (FTIR) microscopy. Sucrose content in these roots decreased, indicating active metabolism. Higher activities of cell-wall invertase and sucrose synthase were observed in the Pi-supplied roots, supporting enhanced carbohydrate utilization. Local P availability triggers significant adjustments in sucrose metabolism and allocation, enhancing the sink capacity of maize roots in P-rich patches. These changes facilitate efficient lateral root proliferation and Pi utilization, highlighting the critical role of local P signals in nutrient acquisition strategies. This research provides deeper insights into the adaptive responses of maize to heterogeneous P environments, offering potential strategies for improving crop nutrient efficiency.

Mycorrhizal Symbiosis Enhances P Uptake and Indole-3-Acetic Acid Accumulation to Improve Root Morphology in Different Citrus Genotypes

Arbuscular mycorrhizal fungi (AMF) are known to enhance plant growth via stimulation of root system development. However, the extent of their effects and underlying mechanisms across different citrus genotypes remain to be fully elucidated. This study investigates the impact of Funneliformis mosseae (F. mosseae) inoculation on plant growth performance, root morphology, phosphorus (P), and indole-3-acetic acid (IAA) concentrations, as well as the expression of related synthesis and transporter genes in three citrus genotypes: red tangerine (Citrus tangerine ex. Tanaka), kumquat (Fortunella margarita L. Swingle), and fragrant citrus (Citrus junos Sieb. ex. Tanaka). Following 12 weeks of inoculation, significant improvements were observed in plant height, shoot and root biomass, total root length, average root diameter, second-order lateral root development, root hair density, and root hair length across all genotypes. Additionally, F. mosseae inoculation significantly increased root P and IAA concentrations in the three citrus genotypes. Notably, phosphatase activity was enhanced in F. margarita but reduced in C. tangerine and C. junos following inoculation. Gene expression analysis revealed a universal upregulation of the P transporter gene PT5, whereas expressions of the auxin synthesis gene YUC2, transporter gene LAX2, and phosphatase gene PAP1 were commonly downregulated. Specific to genotypes, expressions of YUC5, LAX5, PIN2, PIN3, PIN6, and expansin genes EXPA2 and EXPA4 were significantly upregulated in C. tangerine but downregulated in F. margarita and C. junos. Principal component analysis and correlation assessments highlighted a strong positive association between P concentration, P and auxin synthesis, and transporter gene expressions with most root morphology traits, except for root average diameter. Conversely, IAA content and phosphatase activities were negatively correlated with these root traits. These findings suggest that F. mosseae colonization notably enhances plant growth and root system architecture in citrus genotypes via modifications in P transport and IAA accumulation, indicating a complex interplay between mycorrhizal symbiosis and host plant physiology.

An advanced three-dimensional phenotypic measurement approach for extracting Ginkgo root structural parameters based on terrestrial laser scanning.

The phenotyping of plant roots is essential for improving plant productivity and adaptation. However, traditional techniques for assembling root phenotyping information are limited and often labor-intensive, especially for woody plants. In this study, an advanced approach called accurate and detailed quantitative structure model-based (AdQSM-based) root phenotypic measurement (ARPM) was developed to automatically extract phenotypes from Ginkgo tree root systems. The approach involves three-dimensional (3D) reconstruction of the point cloud obtained from terrestrial laser scanning (TLS) to extract key phenotypic parameters, including root diameter (RD), length, surface area, and volume. To evaluate the proposed method, two approaches [minimum spanning tree (MST)-based and triangulated irregular network (TIN)-based] were used to reconstruct the Ginkgo root systems from point clouds, and the number of lateral roots along with RD were extracted and compared with traditional methods. The results indicated that the RD extracted directly from point clouds [coefficient of determination (R 2) = 0.99, root-mean-square error (RMSE) = 0.41cm] outperformed the results of 3D models (MST-based: R 2=0.71, RMSE = 2.20cm; TIN-based: R 2=0.54, RMSE = 2.80cm). Additionally, the MST-based model (F1=0.81) outperformed the TIN-based model (F1=0.80) in detecting the number of first-order and second-order lateral roots. Each phenotyping trait fluctuated with a different cloud parameter (CP), and the CP value of 0.002 (r = 0.94, p < 0.01) was found to be advantageous for better extraction of structural phenotypes. This study has helped with the extraction and quantitative analysis of root phenotypes and enhanced our understanding of the relationship between architectural parameters and corresponding physiological functions of tree roots.

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

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

Plasticity of the Root System Architecture and Leaf Gas Exchange Parameters Are Important for Maintaining Bottle Gourd Responses under Water Deficit.

The evaluation of root system architecture (RSA) development and the physiological responses of crop plants grown under water-limited conditions are of great importance. The purpose of this study was to examine the short-term variation of the morphological and physiological plasticity of Lagenaria siceraria genotypes under water deficit, evaluating the changes in the relationship between the root system architecture and leaf physiological responses. Bottle gourd genotypes were grown in rhizoboxes under well-watered and water deficit conditions. Significant genotype-water regime interactions were observed for several RSA traits and physiological parameters. Biplot analyses confirmed that the drought-tolerant genotypes (BG-48 and GC) showed a high net CO2 assimilation rate, stomatal conductance, transpiration rates with a smaller length, and a reduced root length density of second-order lateral roots, whereas the genotypes BG-67 and Osorno were identified as drought-sensitive and showed greater values for average root length and the density of second-order lateral roots. Consequently, a reduced length and density of lateral roots in bottle gourd should constitute a response to water deficit. The root traits studied here can be used to evaluate bottle gourd performance under novel water management strategies and as criteria for breeding selection.

Heterogeneous phosphate supply influences maize lateral root proliferation by regulating auxin redistribution.

Roots take up phosphorus (P) as inorganic phosphate (Pi). Enhanced root proliferation in Pi-rich patches enables plants to capture the unevenly distributed Pi, but the underlying control of root proliferation remains largely unknown. Here, the role of auxin in this response was investigated in maize (Zea mays). A split-root, hydroponics system was employed to investigate root responses to Pi supply, with one (heterogeneous) or both (homogeneous) sides receiving 0 or 500 μm Pi. Maize roots proliferated in Pi-rich media, particularly with heterogeneous Pi supply. The second-order lateral root number was 3-fold greater in roots of plants receiving a heterogeneous Pi supply than in roots of plants with a homogeneous Pi supply. Root proliferation in a heterogeneous Pi supply was inhibited by the auxin transporter inhibitor 1-N-naphthylphthalamic acid (NPA). The proliferation of lateral roots was accompanied by an enhanced auxin response in the apical meristem and vascular tissues at the root tip, as demonstrated in a DR5::RFP marker line. It is concluded that the response of maize root morphology to a heterogeneous Pi supply is modulated by local signals of Pi availability and systemic signals of plant P nutritional status, and is mediated by auxin redistribution.

Abscisic Acid Coordinates Dose-Dependent Developmental and Hydraulic Responses of Roots to Water Deficit.

Root water uptake is influenced by root system architecture, which is determined by root growth and branching and the hydraulics of root cells and tissues. The phytohormone abscisic acid (ABA) plays a major role in the adaptation of plants to water deficit (WD). Here we addressed at the whole-root level in Arabidopsis (Arabidopsis thaliana) the regulatory role of ABA in mechanisms that determine root hydraulic architecture. Root system architecture and root hydraulic conductivity (Lpr) were analyzed in hydroponically grown plants subjected to varying degrees of WD induced by various polyethylene glycol (PEG) concentrations. The majority of root traits investigated, including first- and second-order lateral root production and elongation and whole-root hydraulics, had a bell-shaped dependency on WD, displaying stimulation under mild WD conditions (25 g PEG L-1) and repression under more severe conditions. These traits also showed a bell-shaped dependency on exogenous ABA, and their regulation by WD was attenuated in genotypes altered in ABA biosynthesis and response. Thus, we propose that ABA acts as a coordinator and an integrator of most root responses to mild and moderate WD, whereas responses to strong WD (150 g PEG L-1) are largely ABA independent. We also found that roots exhibit different growth responses to both WD and ABA depending on their rank and age. Taken together, our results give further insights into the coordinated water acquisition strategies of roots deployed in relation to WD intensity.

Changes in Root Anatomy of Peanut (Arachis hypogaea L.) under Different Durations of Early Season Drought

Changes in the anatomical structure of peanut roots due to early season drought will likely affect the water acquiring capacity of the root system. Yet, as important as these changes are likely to be in conferring drought resistance, they have not been thoroughly investigated. The objective of this study was to investigate the effects of different durations of drought on the root anatomy of peanut in response to early season drought. Plants of peanut genotype ICGV 98305 were grown in rhizoboxes with an internal dimension of 50 cm in width, 10 cm in thickness and 120 cm in height. Fourteen days after emergence, water was withheld for periods of 0, 7, 14 or 21 days. After these drought periods, the first and second order roots from 0–20 cm below soil surface were sampled for anatomical observation. The mean xylem vessel diameter of first- order lateral roots was higher than that of second- order lateral roots. Under early season drought stress root anatomy changes were more pronounced in the longer drought period treatments. Twenty-one days after imposing water stress, the drought treatment and irrigated treatment were clearly different in diameter, number and area of xylem vessels of first- and second-order lateral roots. Plants under drought conditions had a smaller diameter and area of xylem vessels than did the plants under irrigated control. The ability of plants to change root anatomy likely improves water uptake and transport and this may be an important mechanism for drought tolerance. The information will be useful for the selection of drought durations for evaluation of root anatomy related to drought resistance and the selection of key traits for drought resistance.

Tobacco Growth Responses and Soil Properties to Rice-straw Biochar Applied on Yellow-brown Soil in Central China

Pot experiments were conducted to study the effect of straw biochar application on tobacco growth and soil fertility. The growth of ground parts of tobacco was promoted by biochar application at appropriate levels (0.2-1.0%), while it was inhibited by high-level (5%) biochar application. The growth of root system was promoted more extensively by biochar application at all levels tested than was the growth of the aboveground organs, with 5% biochar addition resulting in the highest root-shoot ratio, which also delayed the senility of the root system, including of lateral roots. The taproot length, the first- and second-order lateral roots and the root-shoot ratio of tobacco increased during the early growth stage but decreased at latter growth stage in all treatments. Moreover, with the increasing amount of biochar applied, soil pH and soil nutritional indicators including organic carbon, alkali-hydrolysable N, available P and available K increased with the highest value was observed in the 5% biochar treatment. Our results suggested that straw biochar application at appropriate levels (0.2-1.0%) would lead to an increase in soil fertility and promote tobacco growth. The field experiments are required to test the effect of biochar application on tobacco growth and soil environment with different soil types in tobacco planting area in China.

PROMOTION OF LATERAL ROOT GROWTH AND LEAF QUALITY OF FLUE-CURED TOBACCO BY THE COMBINED APPLICATION OF HUMIC ACIDS AND NPK CHEMICAL FERTILIZERS

SUMMARYIn this study, the effects of HA combined with NPK fertilizer (HANPK) on root growth and leaf quality of tobacco plants were investigated in tobacco fields. Results indicated that the application of HA alone did not enhance the growth of tobacco obviously, while HANPK increased tobacco biomass by 36.9% and stimulated the growth of lateral roots significantly. The number of the second-order lateral roots was increased by 89.3% compared with the control. Furthermore, HANPK raised the ratio of root biomass in 0–20 cm soil layer over the whole soil layer and increased the proportion of fine roots over the total roots. Tobacco leaf yield, output value, and benefit of HANPK were 12.2%, 29.4% and 35.5% higher than those of the control, respectively. The above results suggest that the combined application of HA and NPK chemical fertilizer is an economical pattern for improving tobacco growth.

Mycorrhiza alters the profile of root hairs in trifoliate orange

Root hairs and arbuscular mycorrhiza (AM) coexist in root systems for nutrient and water absorption, but the relation between AM and root hairs is poorly known. A pot study was performed to evaluate the effects of four different AM fungi (AMF), namely, Claroideoglomus etunicatum, Diversispora versiformis, Funneliformis mosseae, and Rhizophagus intraradices on root hair development in trifoliate orange (Poncirus trifoliata) seedlings grown in sand. Mycorrhizal seedlings showed significantly higher root hair density than non-mycorrhizal seedlings, irrespective of AMF species. AMF inoculation generally significantly decreased root hair length in the first- and second-order lateral roots but increased it in the third- and fourth-order lateral roots. AMF colonization induced diverse responses in root hair diameter of different order lateral roots. Considerably greater concentrations of phosphorus (P), nitric oxide (NO), glucose, sucrose, indole-3-acetic acid (IAA), and methyl jasmonate (MeJA) were found in roots of AM seedlings than in non-AM seedlings. Levels of P, NO, carbohydrates, IAA, and MeJA in roots were correlated with AM formation and root hair development. These results suggest that AMF could alter the profile of root hairs in trifoliate orange through modulation of physiological activities. F. mosseae, which had the greatest positive effects, could represent an efficient AM fungus for increasing fruit yields or decreasing fertilizer inputs in citrus production.

Nitrate Starvation Induced Changes in Root System Architecture, Carbon:Nitrogen Metabolism, and miRNA Expression in Nitrogen-Responsive Wheat Genotypes.

Improvement of nutrient use efficiency in cereal crops is highly essential not only to reduce the cost of cultivation but also to save the environmental pollution, reduce energy consumption for production of these chemical fertilizers, improve soil health, and ultimately help in mitigating climate change. In the present investigation, we have studied the morphological (with special emphasis on root system architecture) and biochemical responses (in terms of assay of the key enzymes involved in N assimilation) of two N-responsive wheat genotypes, at the seedling stage, under nitrate-optimum and nitrate-starved conditions grown in hydroponics. Expression profile of a few known wheat micro RNAs (miRNAs) was also studied in the root tissue. Total root size, primary root length, and first- and second-order lateral root numbers responded significantly under nitrate-starved condition. Morphological parameters in terms of root and shoot length and fresh and dry weight of roots and shoots have also been observed to be significant between N-optimum and N-starved condition for each genotypes. Nitrate reductase (NR), glutamine synthatase (GS), and glutamate dehydrogenase (GDH) activity significantly decreased under N-starved condition. Glutamine oxoglutarate amino transferase (GOGAT) and pyruvate kinase (PK) activity was found to be genotype dependent. Most of the selected miRNAs were expressed in root tissues, and some of them showed their differential N-responsive expression. Our studies indicate that one of the N-responsive genotype (NP-890) did not get affected significantly under nitrogen starvation at seedling stage.

Potassium deficiency inhibits lateral root development in tobacco seedlings by changing auxin distribution

Potassium deficiency (LK) is a common abiotic stress that affects plant root development. We aimed to identify the role of auxin in LK effects on root growth. We investigated the effects of LK on the formation and elongation of first- and second-order lateral roots (LRs), auxin concentration, DR5::GUS expression, [3H]IAA transport and the expressions of six PIN genes in roots of tobacco plants. We also examined the effects of exogenous auxin (NAA) and a transport inhibitor (NPA) on LR growth and DR5::GUS expression. Potassium deficiency reduced root growth, mostly by impairing the formation and elongation of first-order LRs. Indole acetic acid (IAA) concentration and DR5::GUS expression levels decreased in leaves and roots subjected to LK, indicating that LK affected auxin distribution. [3H]IAA transport and the expression levels of PIN genes were reduced by LK, showing that auxin polar transport was inhibited by LK. Application of NAA to LK-treated plants increased first-order LR formation and elongation to levels similar to the control, an outcome that was consistent with the similarity in DR5::GUS expression levels between treatments. NPA acted in a converse manner. Potassium deficiency inhibited LR formation and elongation in tobacco plants by shifting auxin distribution.

Effects of nano-ZnO on the agronomically relevant Rhizobium–legume symbiosis

The impact of nano-ZnO (nZnO) on Rhizobium–legume symbiosis was studied with garden pea and its compatible bacterial partner Rhizobium leguminosarum bv. viciae 3841. Exposure of peas to nZnO had no impact on germination, but significantly affected root length. Chronic exposure of plant to nZnO impacted its development by decreasing the number of the first- and the second-order lateral roots, stem length, leaf surface area, and transpiration. The effect of nZnO dissolution on phytotoxicity was also examined. Results showed that Zn2+ had negative impact on plant development. Exposure of R. leguminosarum bv. viciae 3841 to nZnO brought about morphological changes by rendering the microbial cells toward round shape and damaging the bacterial surface. Furthermore, the presence of nZnO in the rhizosphere affected root nodulation, delayed the onset of nitrogen fixation, and caused early senescence of nodules. Attachment of nanoparticles on the root surface and dissolution of Zn2+ are important factors affecting the phytotocity of nZnO. Hence, the presence of nZnO in the environment is potentially hazardous to the Rhizobium–legume symbiosis system.

Variation in Nitrogen Rate and Local Availability Alter Root Architecture Attributes at the Onset of Storage Root Initiation in ‘Beauregard’ Sweetpotato

This study characterized the influence of nitrogen (N) rates and variation in local availability on root architecture as measured by lateral root (LR) development attributes during the onset of the storage root (SR) initiation stage in ‘Beauregard’ sweetpotato adventitious roots (ARs). In N rate experiments, plants grown without fertilizer N showed significantly lower values for all measured LR attributes compared with fertilized plants. Total first- (1LR) and second-order LR (2LR) length increased by 78% and 2873%, respectively, as N was increased from 0 to 50 kg·ha−1. Total 1LR and 2LR number increased by 32% and 1465%, respectively. Increasing the N rates to 100 and 200 kg·ha−1 did not result in further increases for all LR attributes measured. There were no differences in AR number between untreated controls and plants fertilized with 50 kg N/ha. However, the number of ARs increased by 65% when fertilizer N was increased from 50 to 100 kg·ha−1. Increasing the rate to 200 kg·ha−1 did not result in further increases in AR number. In split-root experiments, roots grown in the compartment with 50 kg N/ha had 135% and 2916% increase in total 1LR and 2LR length, respectively, compared with roots grown in the compartment without fertilizer N. Total 1LR and 2LR number increased by 110% and 2114%, respectively. There were 111% more ARs in the fertilized compartment relative to the unfertilized compartment. There were no differences in LR attributes and AR number between compartments that received similar fertilizer N rates. In fertilizer placement experiments, there were no differences in LR attributes between pre-mixing fertilizer N and placement of fertilizer ≈4 cm below the surface of the growth substrate. There were also no differences between the unfertilized control and placement of fertilizer ≈4 cm from the bottom of the pot. Plants grown in substrate with pre-mixed N showed 38% and 342% increase in 1LR and 2LR length, respectively, relative to the bottom placement of N. Total number of 1LR and 2LR in the growth substrate with pre-mixed N increased by 30% and 312%, respectively, relative to the bottom placement of N. These results represent the first evidence for the association between sweetpotato root architectural attributes and variation in N rate and localized availability. These results are also consistent with findings in model systems in which local N presence is necessary for LR development. This information can be used to further optimize SR yield by helping to ensure the availability of N at the optimum rate across time and space.

Aeromonas punctata PNS-1: a promising candidate to change the root morphogenesis of Arabidopsis thaliana in MS and sand system

A model system of sand, comprising Arabidopsis plants inoculated with Aeromonas punctata PNS-1 strain, was used to evaluate the bacterial effect in modulation of plant root structure at second-order lateral root level. In MS media, the root morphogenesis was changed only at first-order lateral root level when inoculated with PNS-1 strain. Inoculation with PNS-1 strain was subjected to significant (P < 0.01) increase in primary root length and lateral root density in both MS and sand system. However, this strain modulated the root structure in the sand environment in a complex manner that may be helpful for incitation of the plant–microbe interaction close to natural environment. In order to determine whether this change in root morphology was due to bacterial auxin, Arabidopsis transgenic line (DR5:GUS) was used to reveal the change in homeostasis of endogenous auxin. In PNS-1 inoculated transgenic seedlings of Arabidopsis plant (DR5:GUS), endogenous auxin in primary root apices and lateral roots was enhanced. For confirmation, PNS-1 was evaluated for auxin production in vitro, showed an increase in auxin production after supplementation of l-tryptophan. The presence of ACC deaminase activity in PNS-1 showed its possible involvement in primary root elongation. In the present study Aeromonas punctata PNS-1 is the potential candidate for triggering the change in root morphogenesis of Arabidopsis thaliana with the involvement of auxin and ACC deaminase production.

Influence of limited soil on the root distribution and anchorage of Vitex negundo L.

Field pull-out and laboratory tests were applied to investigate the effect of metal bolts and wire netting on plant root distribution and anchorage characteristics of 9-year-old Vitex negundo L. growing on a weakly weathered rocky slope (38°). Root number, length and diameter were recorded and single root specimens were classified and tested for tensile strength. The results show that root anchorage is different between the two constructions by bolts and wire. Under limited soil condition, root anchorage ability is 80% lower than when there is sufficient soil due to the reduction of the diameter and number of all second-order lateral roots, as well as the reduction of the tensile strength of the embedded second-order and first-order lateral roots on limited soil. We conclude that the distribution and anchorage of Vitex negundo L. is affected by limited soil availability on rocky slopes.

Anatomical observation of polyphenol changes in epidermal cells during the development of Quercus acutissima–Scleroderma verrucosum ectomycorrhizae

Quercus acutissima seedlings were cultivated in growth pouches and inoculated with Scleroderma verrucosum in order to assess the changes in polyphenol contents in epidermal cells during ECM development. Semithin sections stained with metachromatic Toluidine Blue O (TBO) were compared among non-inoculated lateral roots, early mantled lateral roots, and mycorrhizal roots with a mature mantle. Hyphae adhered closely or were embedded in mucilage-like materials on the epidermis. Epidermal cells and root hairs of the non-inoculated second-order lateral roots developing from the taproot harbored polyphenolic compounds that were stained by TBO. At non-inoculated stage, the average numbers of epidermal cells stained entirely (PC2), stained partially (PC1) or remaining unstained (PC0) were 16.5 ± 0.7, 0 ± 0, and 0 ± 0, respectively. At the early mantled stage, the numbers were 6.5 ± 1.6, 5.2 ± 1.4, and 4.2 ± 1.0, and at the mycorrhizal stage, it was 0 ± 0, 0 ± 0, and 32.8 ± 1.3 for PC2, PC1, and PC0, respectively. Total phenolic content in the root tips at each developmental stage declined with ECM development. The early mantled stage involved a dynamic process of polyphenol localization. However, some epidermal cells and endodermal cells of the proximal zone accumulated polyphenols. Eventually, polyphenolic compounds, which were found abundantly in the epidermal cells and root hairs of the non-inoculated lateral roots of the host, disappeared at the mycorrhization process with the symbiont.

Developmental Changes in Peanut Root Structure during Root Growth and Root-structure Modification by Nodulation

Basic information about the root and root nodule structure of leguminous crop plants is incomplete, with many aspects remaining unresolved. Peanut (Arachis hypogaea) forms root nodules in a unique process. Structures of various peanut root types were studied with emphasis on insufficiently characterized lateral roots, changes in roots during their ontogenesis and root modification by nodule formation. Peanut plants were grown in the field, in vermiculite or in filter paper. The taproot, first-order and second-order lateral roots and root nodules were analysed using bright-field and fluorescence microscopy with hand sections and resin sections. Three root categories were recognized. The primary seminal root was thick, exhibiting early and intensive secondary thickening mainly on its base. It was tetrarch and contained broad pith. First-order lateral roots were long and thin, with limited secondary thickening; they contained no pith. Particularly different were second- and higher-order lateral roots, which were anatomically simple and thin, with little or no secondary growth. Unusual wall ingrowths were visible in the cells of the central part of the cortex in the first-order and second-order lateral roots. The nodule body was formed at the junction of the primary and lateral roots by the activity of proliferating cells derived originally from the pericycle. Two morphologically and anatomically distinct types of lateral roots were recognized: long, first-order lateral roots, forming the skeleton of the root system, and thin and short second- and higher-order lateral roots, with an incomplete second state of endodermal development, which might be classified as peanut 'feeder roots'. Formation of root nodules at the base of the lateral roots was the result of proliferating cell divisions derived originally from the pericycle.

Influence of slope on root system anchorage of Pinus yunnanensis

In southwestern China, Yunnan pines ( Pinus yunnanensis) have been extensively cultivated on barren hills for reforestation and ecological engineering. The objective of this work is to study the influences of slope gradient on anchorage of root systems of P. yunnanensis. Pulling experiments were carried out at low (5–6°), moderate (25–26°) and high gradient (42–43°) by using selected 15-year-old P. yunnanensis. The results showed that the anchorage resistances induced by the slope gradient were significantly ( P < 0.01) different from each other and followed in the order of high slope > moderate slope > low slope. Anchorage strength of upslope-grown roots increased with size and length of first-order lateral roots as well as the number of second-order lateral roots. Contributions of upslope-grown roots for preventing plants from overturning varied considerably between those from different slopes. The contribution of roots growing on upslope side on high slope to the anchorage of root system reached 50%, whereas those on moderate and low slopes were about 44% and 37%, respectively. It was concluded that the anchorage resistance was closely related to slope gradient and root distribution, while upslope-grown roots were positively related to anchorage resistance.