Root Elongation Of Seedlings Research Articles

Phytotoxic Isocassadiene-Type Diterpenoids from Tomato Fusarium Crown and Root Rot Pathogen Fusarium oxysporum f. sp. radicis-lycopersici.

Fusarium crown and root rot (FCRR) has emerged as a highly destructive soil-borne disease, posing a significant threat to the safe cultivation of tomatoes in recent years. The pathogen of tomato FCRR is Fusarium oxysporum f. sp. radicis-lycopersici (Forl). To explore potential phytotoxins from Forl, eight undescribed diterpenoids namely fusariumic acids A-H (1-8) were isolated. Their structures were elucidated by using spectroscopic data analyses, quantum chemical calculations, and X-ray crystallography. Fusariumic acids A (1) and C-H (3-8) were typical isocassadiene-type diterpenoids, while fusariumic acid B (2) contained a cage-like structure with an unusual 7,8-seco-isocassadiene skeleton. A biosynthetic pathway of 2 was proposed. Fusariumic acids A (1) and C-H (3-8) were further assessed for their phytotoxic effects on tomato seedlings at 200 μg/mL. Among them, fusariumic acid F (6) exhibited the strongest inhibition against the hypocotyl and root elongation of tomato seedlings, with inhibitory rates of 61.3 and 45.3%, respectively.

CALMODULIN-LIKE16 and PIN-LIKES7a cooperatively regulate rice seedling primary root elongation under chilling.

Low-temperature sensitivity at the germination stage is a challenge for direct seeding of rice in Asian countries. How Ca2+ and auxin (IAA) signaling regulate primary root growth under chilling remains unexplored. Here, we showed that OsCML16 interacted specifically with OsPILS7a to improve primary root elongation of early rice seedlings under chilling. OsCML16, a subgroup 6c member of the OsCML family, interacted with multiple cytosolic loop regions of OsPILS7a in a Ca2+-dependent manner. OsPILS7a localized to the endoplasmic reticulum membranes and functioned as an auxin efflux carrier in a yeast growth assay. Transgenics showed that presence of OsCML16 enhanced primary root elongation under chilling, whereas the ospils7a knockout mutant lines showed the opposite phenotype. Moreover, under chilling conditions, OsCML16 and OsPILS7a-mediated Ca2+ and IAA signaling and regulated the transcription of IAA signaling-associated genes (OsIAA11, OsIAA23, and OsARF16) and cell division marker genes (OsRAN1, OsRAN2, and OsLTG1) in primary roots. These results show that OsCML16 and OsPILS7a cooperatively regulate primary root elongation of early rice seedlings under chilling. These findings enhance our understanding of the crosstalk between Ca2+ and IAA signaling and reveal insights into the mechanisms underlying cold-stress response during rice germination.

Physical Conditions That Limit Chickpea Root Growth and Emergence in Heavy-Textured Soil

The tillage method determines several soil physical parameters that affect the emergence of post-rice chickpea (Cicer arietinum L.) in the Indo-Gangetic Plain of South Asia. Mechanised row-sowing with minimum soil disturbance and crop residue retention in medium-to-heavy-textured soils will alter the seedbed when compared to that prepared after traditional full tillage and broadcast sowing. Whilst minimum soil disturbance and timely sowing may alleviate the soil water constraint to crop establishment, other soil physical properties such as soil strength, bulk density, and aggregate size may still inhibit seedling emergence and root elongation. This study’s objective was to determine the limitations to chickpea crop establishment with increasing bulk density and soil strength, and different aggregate sizes below and above the seed. In two growth cabinet studies, chickpea seed was sown in clay soil with (i) a bulk density range of 1.3–1.9 Mg m−3 (Experiment 1) and (ii) the combination of bulk densities (1.3 and 1.8 Mg m−3) and aggregate sizes (<2 mm and >4 mm) above and below the seed (Experiment 2). Root length was significantly reduced with increasing bulk density (>1.4 Mg m−3), and soil strength impeded early root growth at >1 MPa. Where main root growth was impeded due to high bulk density and soil strength, a greater proportion of total root growth was associated with the elongation of lateral roots. The present study suggests that the soil above the seed needs to be loosely compacted (<1.3 Mg m−3) for seedling emergence to occur. Further research is needed to determine the size of the soil aggregates, which optimise germination and emergence. We conclude that soil strength values typical of field conditions in the Indo-Gangetic Plain at sowing will impede the root growth of chickpea seedlings. This effect can be minimised by changing tillage operations to produce seedbed conditions that are within the limiting thresholds of bulk density and soil strength.

Exogenous IAA enhances low potassium tolerance of sweetpotato by regulating root response strategy

ABSTRACT Plant roots are sensitive to potassium (K+) deficiency signals. Therefore, regulating root growth by exogenous methods is a vital strategy to improve low K+ tolerance of sweetpotato. We studied the effects of exogenous indole-3-acetic acid (IAA) on growth, K+ absorption, and root characteristics in sweetpotato exposed to low K+ treatment (LK). LK significantly inhibited dry mass, K+ concentration and accumulation, as well as the root elongation (length) and branching (forks and crossings) in sweetpotato seedlings. However, exogenous IAA increased the length, ratio, and density of lateral roots and promoted absorption and accumulation of K+, which effectively alleviated the inhibitory effect of low K+. Exogenous IAA also increased the expression levels of auxin synthesis (IbYUC6 and IbTAR2) and transport (IbPIN1, IbPIN3, and IbPIN8) genes in leaves and roots, which promoted the increase of endogenous IAA content. Furthermore, exogenous IAA was more effective on low-K-tolerant variety (XS32) than low-K-sensitive variety (NZ1) under LK stress, depending on their different IAA synthesis and transport strategies. These results indicated that exogenous IAA enhanced root responsiveness of sweetpotato to low K+ stress by modulating auxin biosynthesis and transport, thereby improving the tolerance of sweetpotato to low K+ stress.

Effects of Coating with Different Doses of Boron Compound on Germination Parameters of Cotton Seeds

In this study, seeds of cotton plants were coated with different boron concentrations and their effect on seedling growth was investigated. The experiment was carried out at Muş Alparslan University, Faculty of Applied Sciences, Department of Plant Production and Technologies, under laboratory and greenhouse conditions, according to the Randomized Plots Trial Design with 4 in laboratory and 3 in greenhouse replications, respectively. In the study, Di-sodium tetraborate decahydrate (Na2B4O7.10H20) (M=381.37 g mol-1) with a minimum purity of 99% boron compound have been used in different doses; 0 (control), 250, 500, 750, 1000, 1250, 1500, 1750, 2000, 2250 and 2500 mg kg-1. According to the results of the regression analysis, it was determined that as the boron dose in the application increased, the root length was positively correlated and other parameters were negatively correlated. In terms of the parameters examined, 250 mg kg-1 Kaolin+liquid K-Humate (15% HA) 400 ml kg-1 (U3) boron application under laboratory conditions showed better results, and 1000 ml kg-1 Kaolin+liquid boron application under greenhouse conditions. It was determined that the application of K-Humate (15% HA) 400 ml kg-1 (U6) promoted growth. In addition, it was found that the results were confirmed in the grouping of the relationships between applications and parameters with heat map clustering and PCA graphs. As a result, it was determined that the toxic range of boron applications applied to the seed in the cotton plant was very narrow, and that it promoted seedling development and root elongation in the U6 application, but it was concluded that the study should also be studied in field trials in order to make more decisive decisions.

Zn nutrients-loaded chitosan nanocomposites and their efficacy as nanopriming agents for maize (Zea mays) seeds.

Recent breakthroughs in agro-inputs research have led to the development of nanomaterials that can promote precision agriculture and better environmental security. The agricultural sector is increasingly facing the negative impacts of changing climates due to various stress conditions. To curb this scenario, economical and low-risk practices such as decreasing fertilizer inputs and seed priming have been promoted. In the current study, the H. odoratissimum aqueous extract was used to nucleate the Zn ionic species and grow the zinc oxide nanoparticles (ZnO NPs). The developed nanocomposites and their ionic zinc precursor were then integrated into tripolyphosphate (TPP)-crosslinked chitosan (CS/TPP) nanostructures by ionic gelation. Advanced physicochemical characterization techniques (SEM, EDS, TEM, DLS, FTIR, TGA, and XPS) were exploited to report the morphology, hydrodynamic size, surface charge, and structural organization of the developed nanomaterials. These revealed positively charged particles with hydrodynamic size in the 149-257nm range. The NPs were used as priming agents for Zea mays seeds. At 0.04%, the ZnO-loaded CS/TPP NPs achieved higher root and shoot elongation in 10-day old seedlings compared to other treatments. The pristine CS/TPP NPs, Zn(II)-laden CS/TPP NPs, and ZnO-loaded CS/TPP NPs at 0.01% significantly promoted the early seedling development of seeds under salt stress. This represents the first report showing ZnO integrated chitosan nanocomposites as an auspicious nanopriming agent for stimulating the seed germination of maize. The study envisages offering perspectives on utilizing green nanotechnology to improve the early seedling development of maize. Furthermore, it has the potential to contribute towards UN SDG 2, thus addressing the threats to global food insecurity and doubling agricultural productivity by 2030.

Beneficial aluminium immobilizing microorganisms inhabiting the rhizosphere of pea

Acid soils contain elevated concentrations of mobile aluminium (Al) ions which are toxic for plants. Plants form symbioses with the rhizosphere microorganisms stimulating plant growth and affecting Al availability. Here, for the first time the approach based on the ability to immobilize Al in soil was applied for initial selection of beneficial rhizosphere microorganisms. Al-Immobilizing yeast Rhodotorula sp. AL1 and 12 bacterial strains assigned to various genera and species were isolated from the rhizosphere of pea cultivated in acid soils. Immobilization of Al was related to the increased pH of the environment and the formation of insoluble Al phosphates in soil. The strains differed in possessing beneficial properties such as modulation of the nutrient element (Ca, Fe, K, Mg, Mn, P) concentrations in soil, production of phytohormones (auxins, abscisic and gibberellic acids, ethylene), utilization of 1-aminocyclopropane-1-carboxylic acid and organic components typical for root exudates, acetylene reduction and antifungal activities. Eight strains promoted root elongation of radish seedlings by 30÷50 % with a maximal effect exerted by Cupriavidus basilensis strain D39. Taking together, the selected microorganisms are promising models to study the mechanisms of plant-microbe interactions in the presence of toxic Al and improving Al tolerance of plants in acid soils.

Self-DNA Early Exposure in Cultivated and Weedy Setaria Triggers ROS Degradation Signaling Pathways and Root Growth Inhibition.

The accumulation of fragmented extracellular DNA reduces conspecific seed germination and plantlet growth in a concentration-dependent manner. This self-DNA inhibition was repeatedly reported, but the underlying mechanisms are not fully clarified. We investigated the species-specificity of self-DNA inhibition in cultivated vs. weed congeneric species (respectively, Setaria italica and S. pumila) and carried out a targeted real-time qPCR analysis under the hypothesis that self-DNA elicits molecular pathways that are responsive to abiotic stressors. The results of a cross-factorial experiment on root elongation of seedlings exposed to self-DNA, congeneric DNA, and heterospecific DNA from Brassica napus and Salmon salar confirmed a significantly higher inhibition by self-DNA as compared to non-self-treatments, with the latter showing a magnitude of the effect consistent with the phylogenetic distance between the DNA source and the target species. Targeted gene expression analysis highlighted an early activation of genes involved in ROS degradation and management (FSD2, ALDH22A1, CSD3, MPK17), as well as deactivation of scaffolding molecules acting as negative regulators of stress signaling pathways (WD40-155). While being the first exploration of early response to self-DNA inhibition at molecular level on C4 model plants, our study highlights the need for further investigation of the relationships between DNA exposure and stress signaling pathways by discussing potential applications for species-specific weed control in agriculture.

Root elongation test on seeds of Sinapis alba reveals toxicity of extracts from thirteen colour forms of the Asian multi‐coloured ladybird, Harmonia axyridis

AbstractLadybirds (Coleoptera: Coccinellidae) use toxic compounds such as alkaloids in their hemolymph to defend against predators and pathogens. Direct measurement of their toxicity to predators is unavailable as predators show various avoidance reactions without eating the beetles. Because inhibition by harmonine – the alkaloid of the alien invasive ladybird Harmonia axyridis (Pallas) – was observed in many organisms, its toxicity can also be tested on various non‐target organisms. This is the first study examining ladybird alkaloid toxicity to plants. We used a quick, inexpensive, and easy‐to‐perform method to quantify the phytotoxicity of 13 strains of H. axyridis, representing natural colour forms and spontaneous laboratory mutations. We used the seed germination rate and root elongation of seedlings of Sinapis alba L. (Brassicaceae). Following a logistic curve, root length decreased with increasing concentration of the extract from adult beetles. The effect of extracts from the cowpea weevil, Callosobruchus maculatus (Fabricius) (Coleoptera: Chrysomelidae) (negative control) did not differ from the control (water). Extract from the lesser mealworm Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae) (positive control) decreased the root length to about half of that of the negative control. Extract from young ladybirds (1 week old) decreased the root length to about one‐third of the control and the extract from 3‐month‐old ladybirds to one‐10th. Differences in toxicity among all 13 strains were minor and not consistent for the two age cohorts.

Plant growth-enhancing traits of rhizobacteria isolated from brinjal, okra, and leaf mustard

Exploring new plant-associated rhizobacteria and reintroducing them to the crop-soil environment is among the strategies to reverse the declining quality of the agricultural soil environment. A total of 340 isolates were recovered from the rhizospheres of okra (Abelmoschus esculentus), leaf mustard (Brassica juncea), and brinjal (Solanum melongena). From among the total, 155 isolates (45.59%) were diazotrophs, and 122 (35.88%) and 127 (37.35%) were isolates with the solubilising activity of phosphate and potassium, respectively. Thirteen of the most promising isolates were identified by gas chromatography for their cellular fatty acid methyl esters: Escherichia vulneris (TC19), Klebsiella pneumoniae (BA5, SA19, SB22), Pantoea ananatis (TC22), Pseudomonas aeruginosa (BA46), Pseudomonas putida (BA29, BA37, SC5, SC14), Salmonella bongori (BC17), Salmonella enterica (BB2), and Shigella dysenteriae (BA16). Three Pseudomonas strains viz. P. aeruginosa BA46 and P. putida BA37 and SC5 were selected after enhancing root elongation and vigour of lettuce seedlings. The American lettuce growth performance in the non-circulating hydroponic system was established. The inoculation with rhizobacteria strains, SC5 and BA46, stimulated shoot and root biomass over uninoculated control plants. The inoculation of lettuce plants with isolates BA37, BA46 and SC5, produced significantly longer roots compared to uninoculated control plants. This study indicates the potential use of the strains BA46 and SC5 as candidates for the formulation and production of hydroponic nutrient solution fortified with beneficial bacteria.

Potential of the rhizobacterium Ensifer meliloti for the phytoremediation of mixed PAH–heavy metal contamination

The potential of the rhizobial strain Ensifer meliloti P221 as a bacterium capable of degrading phenanthrene in the presence of a heavy metal (nickel) and exhibiting plant-growth promoting activity toward Sorghum bicolor under mixed contamination condition was studied. It was shown that nickel at a concentration of 0.1 mM inhibited the microbial growth and phenanthrene degradation by 43 and 34%, respectively. Analysis of the enzymes involved in the phenanthrene degradation by the rhizobium revealed the activity of the phenanthrenequinone reductase (PQR) and protocatechuate 2,3-dioxigenase (2,3-PCD). It was found that nickel at concentrations up to 0.2 mM did not affect significantly the PQR activity, but inhibited it by 30% when the metal concentration increased to 5 mM. Nickel at concentrations up to 5.0 mM did not affect significantly on the activity of 2,3-PCD. E. meliloti promoted elongation of sorghum seedling roots by 69% in medium co-contaminated with phenanthrene and nickel. The results obtained assume that the rhizobial strain studied can exhibit its PAH-degrading and plant-growth promoting activities in the environment co-contaminated with nickel and phenanthrene. This microorganism may be promising for bioremediation and phytoremediation of mixed PAH–heavy metal contamination.

Cadmium-resistant Streptomyces stimulates phytoextraction potential of Crotalaria juncea L. in cadmium-polluted soil

This work evaluated the competence of two strains of cadmium (Cd)-resistant Streptomyces, namely Streptomyces rapamycinicus K5PN1, an indole-3-acetic acid (IAA) producer, and Streptomyces cyaneus 11-10SHTh, a siderophore producer on promoting Cd phytoextraction by sunn hemp. The results showed that S. rapamycinicus improved root elongation of sunn hemp seedlings under Cd stress conditions. S. rapamycinicus and S. cyaneus were colonized on the root surface of sunn hemp at concentrations of 2.3 × 104 and 6.4 × 103 CFU g−1 root fresh weight, respectively. The results of pot-culture experiments showed that S. rapamycinicus increased the root and shoot lengths, and dry biomass of sunn hemp planted in high Cd-contaminated soil. The Cd concentration in the leaves of sunn hemp inoculated with S. cyaneus (73.82 ± 2.20 mg kg−1 plant dry wt) was higher than that of plants with S. rapamycinicus inoculation and the uninoculated control. The phytoextraction of Cd by sunn hemp was significantly increased with Cd-resistant Streptomyces inoculation. In conclusion, both strains of Cd-resistant Streptomyces had potential on enhancing Cd phytoextraction efficiency of sunn hemp. Our study suggests the application of Cd-resistant Streptomyces can improve Cd phytoextraction by sunn hemp for restoration of Cd-polluted sites.

Insights on mechanisms of aluminum phytotoxicity mitigation by canola straw biochars from different regions

To better understand the amendment effects and mechanisms of aluminum (Al(III)) phytotoxicity mitigation by different regional crop straw biochars, wheat seedling root elongation trials were conducted. The contributions of liming effect, oxygen-containing surface functional group adsorption, and oxyanions precipitation to Al(III) phytotoxicity mitigation by Ca(OH)2, pristine and ash-free canola straw biochar were evaluated. The results indicated that biochars derived from canola straw collected from four different regions (Yingtan, Xuancheng, Nanjing, and Huaiyin) caused 22–70% wheat seedling root elongation, which might be linked to liming effect. Incorporation of the corresponding ash-free biochars caused 15–30% elongation, which could be attributed to the surface functional group adsorption. About 0–60% of changes could be explained by Al(III) precipitation with inorganic oxyanions. These findings provide new insights into the physicochemical properties, potential applications, efficiencies, and underlying mechanisms of crop straw biochar in alleviating Al(III) phytotoxicity, which is dependent on the cultivation soil, and indicate similar application of crop straw biochar for acidic soil amelioration, contaminated soil remediation, and arable soil improvement.Graphical

Tomato SlYTH1 encoding a putative RNA m6A reader affects plant growth and fruit shape

N6-methyladenosine (m6A), the most abundant and common modification on eukaryotic mRNA, plays crucial roles in multiple biological processes through controlling endogenous gene activity in organisms. The m6A reader specifically recognizes the m6A mark to mediate the regulation of m6A on mRNA, and determines the fate of its target mRNA. In plants, the currently confirmed m6A readers are YTH (YT521B homology) domain-containing proteins. We previously reported that tomato contains 9 YTH genes, of which SlYTH1 has the strongest expression. The present study reports the functional characterization of SlYTH1 in tomato. SlYTH1 mutants generated via CRISPR/Cas9 technology exhibited pleiotropic phenotypes, including low seed germination rate, shortened seedling root, retarded plant growth and development during vegetative development, and elongated and longitudinally flattened fruit with reduced the locule number. SlYTH1 knockout reduced GA3 content and downregulated the expression of related genes in gibberellin biosynthesis pathway. Moreover, exogenous GA3 application could partially restore the phenotypic defects caused by SlYTH1 mutations. SlYTH1 knockout could alleviate the inhibition of seedling root elongation by exogenous GA3 application at relatively low concentration. These facts indicated SlYTH1 is involved in regulating gibberellin biosynthesis and plays important roles in multiple physiological processes in tomato.

Transcription Factor AtOFP1 Involved in ABA-Mediated Seed Germination and Root Growth through Modulation of ROS Homeostasis in Arabidopsis.

Ovate family proteins (OFPs) are valued as a family of transcription factors that are unique to plants, and they play a pluripotent regulatory role in plant growth and development, including secondary-cell-wall synthesis, DNA repair, gibberellin synthesis, and other biological processes, via their interaction with TALE family proteins. In this study, CHIP-SEQ was used to detect the potential target genes of AtOFP1 and its signal-regulation pathways. On the other hand, Y2H and BIFC were employed to prove that AtOFP1 can participate in ABA signal transduction by interacting with one of the TALE family protein called AtKNAT3. ABA response genes are not only significantly upregulated in the 35S::HAOFP1 OE line, but they also show hypersensitivity to ABA in terms of seed germination and early seedling root elongation. In addition, the AtOFP1-regulated target genes are mainly mitochondrial membranes that are involved in the oxidative–phosphorylation pathway. Further qRT-PCR results showed that the inefficient splicing of the respiratory complex I subunit genes NAD4 and NAD7 may lead to ROS accumulation in 35S::HA-AtOFP1 OE lines. In conclusion, we speculated that the overexpression of AtOFP1 may cause the ABA hypersensitivity response by increasing the intracellular ROS content generated from damage to the intima systems of mitochondria.

Biopriming of maize seeds with plant growth-promoting bacteria isolated from the earthworm Aporrectodea molleri: effect on seed germination and seedling growth.

Earthworms have become a potential source of multi-beneficial bacteria and effective bioinoculants. Seed biopriming is an efficient inoculation method to apply bacteria prior to sowing, which enhances the chances of bacterial candidates to colonize the rhizosphere and/or establish a liaison with the plant. In this study, we evaluated plant growth-promoting traits of bacterial strains isolated from the earthworm's Aporrectodea molleri chloragogenous tissue. In addition, we investigated their prospective use as biopriming agents to enhance Zea mays germination and seedling growth. Results were subjected to principal component analysis for potential correlations between the studied parameters. The bacterial strains displayed different in vitro plant growth-promoting characteristics and were efficient when applied in vivo as they significantly increased maize germination rate (26-78%), root elongation (67-84%), seedlings fresh weight and dry weight. Aeromonas encheleia TC22 was the most significant strain to influence germination due to its high ability to produce indole-3-acetic acid, and along with Pseudomonas azotoformans TC1, they were the most proficient at enhancing seedling root elongation and biomass, which was significantly correlated with their in vitro plant growth-promoting traits. Our findings indicate that isolates TC22 and TC1 are potent bio-primers for maize seeds and should be tested further for their use as biopriming inoculants.

Comparative Toxicity Assessment of Eco-Friendly Synthesized Superparamagnetic Iron Oxide Nanoparticles (SPIONs) in Plants and Aquatic Model Organisms

This study aimed to evaluate the toxicity of superparamagnetic iron oxide nanoparticles (SPIONs) synthesized by biogenic (BS) and chemical (CH) routes. The nanoparticles were characterized by X-ray diffraction (XRD), X-ray spectroscopy (XPS), atomic force microscopy (AFM), vibrating-sample magnetometry (VSM-SQUID), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The toxicity of SPIONs was evaluated using Artemia salina as model aquatic organisms and Raphanus sativus and Lactuca sativa as model plants to evaluate their phytotoxicity. The results obtained from XRD, XPS, and AFM confirmed the formation of spherical nanoparticles of 41.9 ± 1.00 nm (BS route) and 19.8 ± 0.47 nm (CH route). VSM-SQUID demonstrated the superparamagnetic behavior of both nanoparticles, and FT-IR provided evidence of the differences in the surface of SPIONs, suggesting the presence of phenolic compounds on the surface of BS-SPIONs. For the assays with Artemia salina, the results demonstrated (i) nonsignificant differences of BS-SPIONs in mortality rates, and (ii) significant toxicity (p < 0.05) was observed for CH-SPIONs at 300 and 400 mg L−1. The Raphanus sativa plant assay tests showed (i) BS-SPIONs and CH-SPIONs improved the root elongation of seedlings. However, BS-SPIONs demonstrated significant activity on root seedling elongation (p < 0.05) in the range of 300 mg L−1 to 600 mg L−1. To the best of our knowledge, this is the first report to compare the toxicity of chemically and biogenically synthesized SPIONs. In conclusion, although BS-SPIONs and CH-SPIONs present similar structures, their characteristics of magnetic saturation and surface structure are nonidentical, providing differences in their biological activity.

Ultraviolet-B Radiation Represses Primary Root Elongation by Inhibiting Cell Proliferation in the Meristematic Zone of Arabidopsis Seedlings.

In Arabidopsis thaliana plants, exposure to UV-B induces an inhibition of primary root elongation. Different mutants have been isolated that are deficient in this response; however, little is known about the cellular and molecular mechanisms that regulate inhibition of root elongation in seedlings exposed to UV-B. In this work, we investigated the effect UV-B irradiation of different organs on primary root elongation. Our results demonstrate that irradiation of the leaves and shoots only induce a partial inhibition of primary root elongation, while when only roots are exposed to this radiation, primary root inhibition is similar as that measured when the complete seedling is irradiated. The consequences of exposure at different root developmental stages and times after the end of the treatment was also studied. We here show that inhibition of primary root elongation is a consequence of a decrease in cell proliferation in the meristematic zone of the primary roots, while the elongation zone size is not affected by the treatment. The decrease in cell number after UV-B exposure is partially compensated by an increase in cell length in the root meristem; however, this compensation is not enough to maintain the meristem size. We also here demonstrate that, similarly as what occurs in developing leaves, GROWTH REGULATING FACTOR 3 (GRF3) transcription factor regulates cell proliferation in UV-B irradiated roots; however, and in contrast to what occurs in the leaves, this response does not depend on the presence of MITOGEN ACTIVATED PROTEIN KINASE 3 (MPK3). Inhibition of primary root elongation by UV-B under our experimental conditions is also independent of the UV-B photoreceptor UV RESISTANT LOCUS 8 (UVR8) or ATAXIA TELANGIECTASIA MUTATED (ATM); but a deficiency in ATM AND RAD3-RELATED (ATR) expression increases UV-B sensitivity in the roots. Finally, our data demonstrate that UV-B affects primary root growth in various Arabidopsis accessions, showing different sensitivities to this radiation.

Inuloxin A Inhibits Seedling Growth and Affects Redox System of Lycopersicon esculentum Mill. and Lepidium sativum L.

Allelochemicals are considered an environment-friendly and promising alternative for weed management, although much effort is still needed for understanding their mode of action and then promoting their use in plant allelopathy management practices. Here, we report that Inuloxin A (InA), an allelochemical isolated from Dittrichia viscosa, inhibited root elongation and growth of seedlings of Lycopersicon esculentum and Lepidium sativum at the highest concentrations tested. InA-induced antioxidant responses in the seedlings were investigated by analysing the contents of glutathione (GSH) and ascorbate (ASC), and their oxidized forms, dehydroascorbate (DHA), and glutathione disulphide (GSSG), as well as the redox state of thiol-containing proteins. An increase in ASC, DHA, and GSH levels at high concentrations of InA, after 3 and 6 days, were observed. Moreover, the ASC/DHA + ASC and GSH/GSSG + GSH ratios showed a shift towards the oxidized form. Our study provides the first insight into how the cell redox system responds and adapts to InA phytotoxicity, providing a framework for further molecular studies.

Effect of Prunus serotina Ehrh. Volatile Compounds on Germination and Seedling Growth of Pinus sylvestris L.

In temperate European forests invaded by Prunus serotina Ehrh. (black cherry), a reduction in the spontaneous regeneration capacity of Pinus sylvestris L. (Scots pine) is observed. It could be caused by various factors, including allelopathic properties of this invasive plant. In this study the phytotoxic effect of P. serotina volatile compounds on P. sylvestris and the seasonal variation in this effect were assessed. Simple assays showed that volatiles emitted from P. serotina leaves significantly inhibited root growth of P. sylvestris seedlings. Their negative effect on stem growth was much weaker. The strongest phytotoxic effect on Scots pine seedlings was caused by the volatiles emitted from the youngest black cherry leaves. In fresh foliage of P. serotina, nineteen volatile organic compounds were identified by gas chromatography–mass spectrometry (GC–MS). The dominant compound was benzaldehyde. On the basis of tests of linalool alone, it was found that this monoterpene present in the volatile fraction has a strong allelopathic potential and inhibits germination, root elongation and shoot elongation of pine seedlings. The results of our research suggest that volatile compounds from P. serotina leaves could limited survival of P. sylvestris individuals in the seedling phase.