Significant Root Growth Inhibition Research Articles

A putative Na+/H+ antiporter BpSOS1 contributes to salt tolerance in birch

White birch (Betula platyphylla Suk.) is an important pioneer tree which plays a critical role in maintaining ecosystem stability and forest regeneration. The growth of birch is dramatically inhibited by salt stress, especially the root inhibition. Salt Overly Sensitive 1 (SOS1) is the only extensively characterized Na+ efflux transporter in multiple plant species. The salt-hypersensitive mutant, sos1, display significant inhibition of root growth by NaCl. However, the role of SOS1 in birch responses to salt stress remains unclear. Here, we characterized a putative Na+/H+ antiporter BpSOS1 in birch and generated the loss-of-function mutants of the birch BpSOS1 by CRISPR/Cas9 approach. The bpsos1 mutant exhibit exceptional increased salt sensitivity which links to excessive Na+ accumulation in root, stem and old leaves. We observed a dramatic reduction of K+ contents in leaves of the bpsos1 mutant plants under salt stress. Furthermore, the Na+/K+ ratio of roots and leaves is significant higher in the bpsos1 mutants than the wild-type plants under salt stress. The ability of Na+ efflux in the root meristem zone is found to be impaired which might result the imbalance of Na+ and K+ in the bpsos1 mutants. Our findings indicate that the Na+/H+ exchanger BpSOS1 plays a critical role in birch salt tolerance by maintaining Na+ homeostasis and provide evidence for molecular breeding to improve salt tolerance in birch and other trees.

Effects of acid and aluminum stress on seed germination and physiological characteristics of seedling growth in Sophora davidii

ABSTRACT Sophora davidii, a vital forage species, predominantly thrives in the subtropical karst mountains of Southwest China. Its resilience to poor soil conditions and arid environments renders it an ideal pioneer species for ecological restoration in these regions. This study investigates the influence of acidic, aluminum-rich local soil on the germination and seedling growth physiology of S. davidii. Experiments were conducted under varying degrees of acidity and aluminum stress, employing three pH levels (3.5 to 5.5) and four aluminum concentrations (0.5 to 2.0 mmol·L−1). The results showed that germination rate, germination index, and vigor index of S. davidii seeds were decreased but not significantly under slightly acidic conditions (pH 4.5–5.5), while strong acid (pH = 3.5) significantly inhibited the germination rate, germination index, and vigor index of white spurge seeds compared with the control group. Aluminum stress (≥0.5 mmol·L−1) significantly inhibited the germination rate, germination index, and vigor index of S. davidii seed. Moreover, the seedlings’ root systems were sensitive to the changes of aluminum concentration, evident from significant root growth inhibition, characterized by root shortening and color deepening. Notably, under aluminum stress (pH = 4.3), the levels of malondialdehyde and proline in S. davidii escalated with increasing aluminum concentration, while antioxidant enzyme activities demonstrated an initial increase followed by a decline. The study underscores the pivotal role of cellular osmoregulatory substances and protective enzymes in combating aluminum toxicity in S. davidii, a key factor exacerbating growth inhibition in acidic environments. These findings offer preliminary theoretical insights for the practical agricultural utilization of S. davidii in challenging soil conditions.

Application of Long-Chained Auxin Conjugates Influenced Auxin Metabolism and Transcriptome Response in Brassica rapa L. ssp. pekinensis.

Auxin amino acid conjugates are considered to be storage forms of auxins. Previous research has shown that indole-3-acetyl-L-alanine (IAA-Ala), indole-3-propionyl-L-alanine (IPA-Ala) and indole-3-butyryl-L-alanine (IBA-Ala) affect the root growth of Brassica rapa seedlings. To elucidate the potential mechanism of action of the conjugates, we treated B. rapa seedlings with 0.01 mM IAA-, IPA- and IBA-Ala and investigated their effects on the auxin metabolome and transcriptome. IBA-Ala and IPA-Ala caused a significant inhibition of root growth and a decrease in free IAA compared to the control and IAA-Ala treatments. The identification of free auxins IBA and IPA after feeding experiments with IBA-Ala and IPA-Ala, respectively, confirms their hydrolysis in vivo and indicates active auxins responsible for a stronger inhibition of root growth. IBA-Ala caused the induction of most DEGs (807) compared to IPA-Ala (417) and IAA-Ala (371). All treatments caused similar trends in transcription profile changes when compared to control treatments. The majority of auxin-related DEGs were found after IBA-Ala treatment, followed by IPA-Ala and IAA-Ala, which is consistent with the apparent root morphology. In addition to most YUC genes, which showed a tendency to be downregulated, transcripts of auxin-related DEGs that were identified (UGT74E2, GH3.2, SAUR, IAA2, etc.) were more highly expressed after all treatments. Our results are consistent with the hypothesis that the hydrolysis of conjugates and the release of free auxins are responsible for the effects of conjugate treatments. In conclusion, free auxins released by the hydrolysis of all auxin conjugates applied affect gene regulation, auxin homeostasis and ultimately root growth inhibition.

Physiological, Biochemical, and Transcriptomic Responses of Neolamarckia cadamba to Aluminum Stress.

Aluminum is the most abundant metal of the Earth’s crust accounting for 7% of its mass, and release of toxic Al3+ in acid soils restricts plant growth. Neolamarckia cadamba, a fast-growing tree, only grows in tropical regions with acidic soils. In this study, N. cadamba was treated with high concentrations of aluminum under acidic condition (pH 4.5) to study its physiological, biochemical, and molecular response mechanisms against high aluminum stress. High aluminum concentration resulted in significant inhibition of root growth with time in N. cadamba. The concentration of Al3+ ions in the root tip increased significantly and the distribution of absorbed Al3+ was observed in the root tip after Al stress. Meanwhile, the concentration of Ca, Mg, Mn, and Fe was significantly decreased, but P concentration increased. Aluminum stress increased activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase from micrococcus lysodeiktic (CAT), and peroxidase (POD) in the root tip, while the content of MDA was decreased. Transcriptome analysis showed 37,478 differential expression genes (DEGs) and 4096 GOs terms significantly associated with treatments. The expression of genes regulating aluminum transport and abscisic acid synthesis was significantly upregulated; however, the genes involved in auxin synthesis were downregulated. Of note, the transcripts of several key enzymes affecting lignin monomer synthesis in phenylalanine pathway were upregulated. Our results shed light on the physiological and molecular mechanisms of aluminum stress tolerance in N. cadamba.

Assessing Domestic Wastewater Effluent with a Battery of Bioassays after Treatment with a Specific Consortium of Microalgae and Different Flocculation Methods

Wastewater stabilization ponds (WSP) are a common method to treat wastewater before release. The purpose of the current study was to find the most inexpensive coagulation and flocculation reagents to use during harvesting of WSP algae from effluent so that water without algae can be generated for irrigation purposes. In the study, the toxicity of effluent from the algae-based WSP system after treatment with alum and chitosan was investigated. The chemical composition of the resultant supernatants was tested in conjunction with a battery of bioassays (Daphnia magna, Allium cepa, Lactuca sativa and Triticum aestivum). The bioindicator organisms were exposed to varying concentrations of the supernatant resulting from harvesting the algae biomass with chitosan (0.368 g/L chitosan) and aluminium sulphate (9.96 g/L powder). Alum was lethal to D. magna, while chitosan did not seem to affect the Daphnia test specimens. Undiluted chitosan supernatant and 100% alum resulted in minimal inhibition of the rate of T. aestivum seed germination, while both resulted in significant inhibition of the L. sativa seed germination rates. Similarly, minimal effects were found for the root growth in T. aestivum, with significant root growth inhibition observed in L. sativa and A. cepa. In A. cepa, clear differences were observed in the inhibition of root growth when the two reagents were compared. The alum and chitosan supernatants had a total carbon, iron and sulphate concentration of 327.78 mg/L, 0.12 mg/L and 68.44 mg/L and 182.04 mg/L, 0.16 mg/L and 166.80 mg/L, respectively. Based on the test specimens’ response, chitosan as flocculation method was less toxic when compared with alum coagulation, even though both algae harvesting methods changed the chemical composition of the algae-treated water.

Effects of crude ethanolic extract of <i>Gloriosa superba</i> L. tuber, on root growth and root tip mitosis, of <i>Allium sativum</i> L.

Colchicine is an alkaloid produced by some members of the Liliaceae family which include Gloriosa superba L. Apart from its other medicinal uses, it is used for both cytological and plant breeding studies. Absence of pure colchicine in Nigeria has retarded research progress in the above-mentioned areas of research. In this study, the genotoxic and cytotoxic effect of ethanolic crude extract of G. superba tubers, obtained by freeze-drying method, on Allium sativum meristematic roots were examined; to explore the possibility of using it, in research, in the absence of pure colchicine. The mitotic index of the roots treated with aqueous crude extract concentrations of 500mg/L, 1000mg/L and 2000mg/L for 3, 6, 12 and 24 hours, showed that there was significant reduction in the number of dividing cells with time. There were evidences of disturbed mitotic phases, C-metaphase, precocious chromosome movement and anaphase bridges, which increased as concentration and duration of treatment increased. Distilled water and 8-hydroxyquinoline were used as negative and positive controls. A. sativum roots exposed to the crude extract concentrations for 3, 6, 12, 24, 48 and 72 hours showed significant inhibition of root growth which increased with concentration and duration of treatment. The results obtained from this study indicate that the crude colchicine contained in G. superba , is an effective tubulin binder, which can arrest cells at the metaphase stage and is therefore recommended for cytological studies in Nigeria and other underdeveloped economies, in the absence of pure colchicine. Keywords: Root growth, root tip, mitosis, Gloriosa superba , Allium sativum , colchicine

FERONIA mutation induces high levels of chloroplast-localized Arabidopsides which are involved in root growth.

The FERONIA (FER) signaling pathway is known to have diverse roles in Arabidopsis thaliana, such as growth, reproduction, and defense, but how this receptor kinase is involved in various biological processes is not well established. In this work, we applied multiple mass spectrometry techniques to identify metabolites involved in the FER signaling pathway and to understand their biological roles. A direct infusion Fourier transform ion cyclotron resonance (FT-ICR)-MS approach was used for initial screening of wild-type and feronia (fer) mutant plant extracts, and Arabidopsides were found to be significantly enriched in the mutant. As Arabidopsides are known to be induced by wounding, further experiments on wounded and non-wounded leaf samples were carried out to investigate these oxylipins as well as related phytohormones using a quadrupole-time-of-flight (Q-TOF) MS by direct injection and LC-MS/MS. In a root growth bioassay with Arabidopside A isolated from fer mutants, the wild-type showed significant root growth inhibition compared with the fer mutant. Our results therefore implicated Arabidopsides, and Arabidopside A specifically, in FER functions and/or signaling. Finally, matrix-assisted laser desorption/ionization MS imaging (MALDI-MSI) was used to visualize the localization of Arabidopsides, and we confirmed that Arabidopsides are highly abundant at wounding sites in both wild-type and fer mutant leaves. More significantly, five micron high-spatial resolution MALDI-MSI revealed that Arabidopsides are localized to the chloroplasts where many stress signaling molecules are made.

Effects of new derivatives of 2-amino-5-benzylthiazole of genotoxicity and acute toxicity in Allium bioassays

We have found that new derivatives of 2-amino-5-benzylthiazole possess cytotoxic action towards human tumor cells (Finiuk et al., Biopolym. Cell, 2017; Finiuk et al., Ukr. Biochem. J., 2018). A release of the chemotherapeutic drugs into the environment may cause adverse effects towards ecosystems. To promote further these derivatives as potential anticancer agents, it was necessary to evaluate their genotoxicity and acute toxi­city, namely in plants that have an important trophic level in ecosystems. To do that, we used towards plant bioassays for new derivatives of N-(5-benzyl-1,3-thiazol-2-yl)-3,5-dimethyl-1-benzofuran-2-carboxamide (compound 1 ) and 2,8-dimethyl-7-(3-trifluoromethyl-benzyl)pyrazolo[4,3-e]thiazolo[3,2-a]pyrimidin-4-one (compound 2 ). Allium cepa ana-telophase assay was applied to monitor the genotoxicity of the studied compounds. Besides, the acute toxic effects such as inhibition of cell division, seed germination and growth of Allium roots were estimated. The compound 1 (10 mM) in concentration equal to the IC 50 for tumor cells, and compound 2 in 1 mM (1´ concentration, equal to the IC 50 for tumor cells) and 10 mM (10´ concentration) did not possess acute toxicity towards Allium cepa. A significant inhibition of root growth and seed germination effects were detected at using the compound 1 only in dose that is 10 times higher than the IC 50 for tumor cells. The ana-telophase assay did not reveal the genotoxic effect of the compounds 1 (10 mM) and 2 (1 and 10 mM). The compounds 1 (10 mM) and 2 (1 and 10 mM) did not affect the mitotic and phase (prophase, metaphase, anaphase, telophase) indices. A commercial anticancer drug Doxorubicin (0.1 and 1 mM) possessed a significant inhibitory effect on root growth and seed germination, mitotic index and enhanced a level of chromosomal aberrations in Allium cepa . The compound 1 at 10 mM and compound 2 at 1 mM and 10 mM did not possess a significant acute toxicity (inhibition of cell division, seed germination and growth of Allium roots), did not demonstrated the genotoxic effects (induction of chromosomal aberrations) in Allium bioassay. These results give primary evidence about a possibility of using the synthetic 2-amino-5-benzylthiazole derivatives – compounds 1 and 2 – as novel antineoplastic agents that will have no negative side effects in the treated plant organism. Additional experiments should be performed in order to evaluate the adverse effects of new derivatives of 2-amino-5-benzylthiazole in a vide spectrum of the concentrations for the prediction of environmental toxicity and genotoxicity of chemicals.

Effect of sugar concentration on ginsenoside biosynthesis in hairy root cultures of Panax quinquefolium cultivated in shake flasks and nutrient sprinkle bioreactor

The study assessed the influence of sugar concentration (10, 20, 30, 50, 70, 100, 120 g l−1) on growth and ginsenoside biosynthesis in Panax quinquefolium hairy roots cultivated in shake flasks and a nutrient sprinkle bioreactor. The highest growth rate was achieved in medium containing 3–5 % sucrose. More than 70 g l−1 or less than 20 g l−1 sugar content in the medium induces significant inhibition of root growth when cultivated in shake flasks. The saponin content was determined using HPLC. The maximum yield (above 9 mg g−1 d.w.) of the sum of six examined ginsenosides (Rb1, Rb2, Rc, Rd, Re and Rg1) in hairy roots cultivated in shake flasks was obtained with 30 g l−1 sucrose in the medium. The sucrose concentration in the medium was found to correlate with saponin content in bioreactor-cultured specimens. A higher level of protopanaxadiol derivatives was found for lower (20 and 30 g l−1) sucrose concentrations; higher sucrose concentrations (50 and 70 g l−1) in the medium stimulated a higher level of Rg group saponins.

Auxin signalling is involved in cadmium-induced glutathione-S-transferase activity in barley root

Transient exposure of barley roots to Cd, IAA or H2O2 for 30 min resulted in a significant root growth inhibition. Cd significantly increased the GST activity of roots 6 h after the end of short-term treatment. This increase was more relevant in root segment containing differentiation zone than in root segment just immediately behind the root apex. In contrast to Cd treatment, the short-term exposure of barley roots to IAA resulted in a significant increase of GST activity along the whole root tip and this increase was detectable already 3 h after the treatment with 10 μM IAA. Similarly to IAA, exogenously applied 10 mM H2O2 for 30 min caused significant increase of GST activity along the whole root tip 6 h after the treatment. This increase was already detectable 3 h after the exposure, but only in the differentiation zone of root tip. Auxin influx or signalling inhibitor considerable decreased the Cd- or IAA-induced GST activity in barley root tips. The strong activation of GST even after a brief exposure of barley roots to Cd support the crucial role of GST in the Cd-induced stress response in which presumably IAA and H2O2 play an important signalling role including the activation of GST.

Trichilone, a New C21 Steroid from Trichilia Connaroides

Phytochemical investigation of the leaves of Trichilia connaroides led to the isolation of a new pregnane, trichilone (1), featuring a 2-methoxycyclopent-2-enone moiety, along with a related known compound, 3beta,4alpha-dihydroxypregnane-16-one (2). The structure of 1 was established on the basis of extensive spectroscopic analysis. Compound 1 showed significant root-growth inhibition activity against Amaranthus. mangostanus with an IC50 value of 23.1 ppm.

Impact of short-term cadmium treatment on catalase and ascorbate peroxidase activities in barley root tips

The aim of this study was to analyse the relationship between root growth inhibition and alterations in catalase (CAT) and ascorbate peroxidase (APX) contents and activities in barley root tips during the recovery after short-term Cd stress. Significant root growth inhibition was observed after a relatively short-term (30 min) exposure of barley roots to low 15 μM Cd concentration. In seedlings treated with 30 μM Cd root growth was renewed 8-9 h after Cd treatment. By contrast, seedlings exposed to 60 μM Cd failed to restore root growth. The CAT activity increased after 15 μM Cd treatment, whereas, higher Cd concentrations inhibited CAT activity. However, APX activity was not affected by Cd treatment. The content of APX1 transcript increased while content of APX2 decreased 3 h after short-term treatment in a concentration dependent manner. While the expression of CAT1 was upregulated after 15 and 30 μM Cd treatment, it was strongly downregulated by 60 μM Cd. By contrast, CAT2 was upregulated in a concentration dependent manner. These results suggest that increased CAT activity is crucial for restoration of root growth after moderate Cd stress while at severe Cd stress its inhibition may lead to the irreversible damages.

Transcriptional and posttranscriptional regulation of chloroplast gene expression by heavy metals in barley seedlings

The effects of Cd, Cu, and Ni ions on chloroplast gene expression were studied in 7-day-old barley (Hordeum vulgare L.) seedlings. Toxicity of heavy metals (HM) was estimated from their effects on root and shoot growth and from the accumulation of HM in roots and leaves of seedlings grown in roll culture. Root growth was affected by HM to a higher extent than shoot growth. A statistically significant inhibition of root growth was observed at concentrations of all studied HM ≥100 μM. Leaf growth was inhibited by Cu and Ni at concentrations ≥400 μM, while the inhibitory effect of Cd on leaf growth was observed at concentrations ≥100 μM. The translocation of Cu from roots to shoots of barley seedlings proceeded slower than the accumulation of Cu in roots. Unlike Cu, Ni was actively accumulated by shoots in addition to its strong absorption by roots. Using the run-on transcription and RT-PCR (reverse transcription-polymerase chain reaction), we showed that HM at a concentration of 100 μM regulated the expression of individual chloroplast genes. The presence of either Cd, Cu, or Ni ions in the plant growth solution enhanced transcription of rpl16, rpl23, and rpl12 genes encoding ribosomal proteins, and of ndhA encoding the subunit 1 of plastid NADH-plastoquinone oxidoreductase. Transcription of sixteen other studied plastid genes was not affected by HM. The activation of transcription of the studied genes was not always accompanied by an increase in the transcript copy number. Northern blot analysis showed that Cd impaired the splicing of rpl16, a chloroplast gene that contains an intron. Thus, this study proves that HM regulate not only the transcriptional activity of chloroplast genes but also the splicing of rpl16 transcripts.

Abiotic stress–induced inhibition of root growth and ascorbic acid oxidase activity in barley root tip is associated with enhanced generation of hydrogen peroxide

Using short-term treatments, the aim of this study was to analyze the role of hydrogen peroxide in the regulation of AAO activity during Cd, Cu or IAA treatments in barley root tips. For analysis individual barley root segments were obtained by the gradual cutting of each root from the tip to the base 1, 2, 3 or 6 h after short-term treatments. Already a short 30 min exposure of barley roots to Cd induced significant root growth inhibition in a Cd concentration dependent manner, which was accompanied by a marked reduction of AAO activity. At Cu concentration which had no effect on the root growth a significant increase in AAO activity was observed. This increased AAO activity was detected only in ionically-bound CW fraction. In contrast, Cu at higher concentration and IAA inhibited both ionically-bound CW AAO isozymes. Prompt inhibition of AAO activity immediately after short-term treatment was observed only in the case of H2O2 treatment suggesting that H2O2 may act as an inhibitor of AAO. This was further supported by the observation that all Cd-, Cu- or IAA-induced root growth and AAO activity inhibition in barley roots was connected with an elevated production of H2O2.

Phytotoxicity tests with higher plants for environmental risk assessment

Phytotoxicity test were performed to evaluate their application in environmental monitoring on different substrates e.g. commercial detergents (D1, D2) and surface water from the dismissed Cu and Fe mine of Libiola (NW Italy), respectively. Seeds of Vicia faba were grown in 0, 10, 30, 60, 100 g/l of D1 and D2. Number of germinated seeds and root length, Germination iNDEX (G1) and growth inhibition (EC50) were considered. The Vicia test showed no significant differences between D1 and D2, with an EC50 of 13 g/l (11-15 95% C1) for D1 and 16 g/l (14-19 95% C1) for D2. These data were confirmed by G1<50% at 18, 26, 30, 60 and 100 g/l. Onion bulbs of Allium cepa, were tested at 0, 6 12, 25, 50 and 100% of mine water. Root length inhibition (EC50) and Mitotic Index (MI) were evaluated. The Allium test showed a statistically significant inhibition of root growth at 50% and 100%. The root growth percentage decreased in a dose-related manner, with an EC50 of 87%. The MI decreased significantly only at 100% (undiluited mine water). Both phytotoxicity tests should be considered as valid ecotoxicological indicators for health and environment.

Short-term aluminium-induced changes in barley root tips

The short-term exposure of barley roots to low Al concentration caused significant root growth inhibition and radial swelling of roots. During Al treatment, the radial expansion of root cells occurred in root tissues representing elongation zone and meristem. Both low pH and Al treatments caused significant disruption of cell membranes in swollen roots. In contrast to Evans blue uptake callose formation was observed only at higher Al concentrations and was detected in both swollen and adjacent root areas. Similarly to Al, exogenous short-term application of indole-3-acetic acid, polar transport inhibitor triiodobenzoic acid, ethylene precursor 1-aminocyclopropane-1-carboxylic acid or H(2)O(2) evoked root growth inhibition and radial cell expansion in barley root tip too.

A crop tolerating oxidative stress induced by excess lead: maize

Two 14-day-old seedlings of maize (Zea mays L.) cultivars (3223 and Vero) were exposed to different concentrations of lead [0, 2, 5 and 8 mM Pb(NO3)2·4H2O] for 8 days. Exposure of maize cultivars to excess Pb resulted in a significant root growth inhibition though shoot growth and absolute water content remained less affected. The results of chlorophyll a fluorescence indicated that the highly toxic Pb level affected photochemical efficiency in 3223, while no significant effect was observed in the Vero. At the highly toxic Pb concentration, higher membrane leakage was observed in 3223 leaves than that of Vero. This result was related to the accumulation of Pb. On the other hand, the results suggested that there were similar responses in total soluble POD and GR activities with increasing Pb concentrations between both cultivars. But APX activity significantly decreased at highly toxic Pb level in the Vero while a significant increase observed in the 3223. However, SOD activity in 3223 significantly decreased at the highly toxic Pb concentration compared with that at 2 mM Pb concentration. The results of the present study indicated that, Vero withstands excess Pb with its higher Pb accumulation capacity in roots and better upregulated protective mechanisms compared to 3223. Therefore, Vero is more tolerant to Pb toxicity compared to 3223 which was found to be a less tolerant cultivar.

Inhibition of Root Growth and Polyamine Metabolism in Sunflower (Helianthus annuus) Seedlings Under Cadmium and Copper Stress

Although sunflower is usually regarded as a highly tolerant crop, impairment of root growth at initial stages of plant development may result in poor crop establishment and higher susceptibility to pathogen attack. In order to evaluate if Cd2+ and Cu2+ may impact on sunflower germination and initial root development, a pot experiment under controlled conditions was carried out. Possible involvement of polyamine metabolism in sunflower response to these stressors was also investigated. Although Cd2+ and Cu2+ treatments affect neither seed germination nor radical emergence, sunflower seedlings grown in the presence of these heavy metals showed significant inhibition of root growth, being this inhibition greater for Cd2+. Both metals caused significant increases in proline contents at the highest concentrations tested (0.5 and 1 mM), and these increments were more pronounced for Cd2+ treatments, especially between days 3 and 10. Metals also increased putrescine (Put) contents at all concentrations assayed from the seventh day onward, causing no variations on this polyamine time-course pattern. Spermine and spermidine contents, however, were increased only by 1 mM Cd2+. Arginine decarboxylase seems to have been the enzyme responsible for Put increases under both metal treatments. This work demonstrates that initial root growth of sunflower seedlings may be significantly impaired in Cd2+ or Cu2+ contaminated soils. It also shows that polyamines are key biological compounds, which are probably involved in signaling pathways triggered under stress environmental conditions.

Three oxidative metabolites of indole-3-acetic acid from Arabidopsis thaliana

Three metabolites of indole-3-acetic acid (IAA), N-(6-hydroxyindol-3-ylacetyl)-phenylalanine (6-OH-IAA-Phe), N-(6-hydroxyindol-3-ylacetyl)-valine (6-OH-IAA-Val), and 1- O-(2-oxoindol-3-ylacetyl)-β- d-glucopyranose (OxIAA-Glc), were found by a liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS)-based search for oxidative IAA metabolites during the vegetative growth of Arabidopsis. Their structures were confirmed by making a comparison of chromatographic characteristics and mass spectra between naturally occurring compounds and synthetic standards. An incorporation study using deuterium-labeled compounds showed that 6-OH-IAA-Phe and 6-OH-IAA-Val were biosynthesized from IAA-Phe and IAA-Val, respectively, which strongly suggested the formation of these amino acid conjugates of IAA in plants. Both 6-OH-IAA-Phe and 6-OH-IAA-Val were inactive as auxins, as indicated by no significant root growth inhibition in Arabidopsis. Quantitative analysis demonstrated that OxIAA-Glc was present in the largest amount among the metabolites of IAA in Arabidopsis, suggesting that the conversion into OxIAA-Glc represents the main metabolic process regarding IAA in Arabidopsis.

Aluminium stimulated hydrogen peroxide production of germinating barley seeds

In spite of the localisation of Al in the root tips and loss of cell viability, the presence of Al (2–8 mM) during the first day of germination had no effect on germination capability and on the growth of emerging roots of barley seeds. At this stage of germination, considerable increase of hydrogen peroxide production was observed in Al-treated germinated seeds in comparison to control non-treated seeds. During the second day of germination, further Al uptake and loss of cell viability continued and significant root growth inhibition was observed. On the other hand, production of H 2O 2 decreased in comparison to the first day production, however was still higher than in control seedlings. Superoxide production and superoxide dismutase activity were inhibited by Al both 24 and 48 h after the onset of germination. The role of hydrogen peroxide and superoxide in relation to the seed germination, root growth, and cell viability during Al stress is discussed.