Bean Hypocotyls Research Articles

Differential Carbon Catabolite Repression and Hemicellulolytic Ability among Pathotypes of Colletotrichum lindemuthianum against Natural Plant Substrates.

Colletotrichum lindemuthianum is a phytopathogenic fungus that causes anthracnose in common beans (Phaseolus vulgaris) and presents a great diversity of pathotypes with different levels of virulence against bean varieties worldwide. The purpose of this study was to establish whether pathotypic diversity is associated with differences in the mycelial growth and secretion of plant-cell-wall-degrading enzymes (PCWDEs). We evaluated growth, hemicellulase and cellulase activity, and PCWDE secretion in four pathotypes of C. lindemuthianum in cultures with glucose, bean hypocotyls and green beans of P. vulgaris, and water hyacinth (Eichhornia crassipes). The results showed differences in the mycelial growth, hemicellulolytic activity, and PCWDE secretion among the pathotypes. Glucose was not the preferred carbon source for the best mycelial growth in all pathotypes, each of which showed a unique PCWDE secretion profile, indicating different levels of carbon catabolite regulation (CCR). The pathotypes showed a high differential hemicellulolytic capacity to degrade host and water hyacinth tissues, suggesting CCR by pentoses and that there are differences in the absorption and metabolism of different monosaccharides and/or disaccharides. We propose that different levels of CCR could optimize growth in different host tissues and could allow for consortium behavior in interactions with bean crops.

Exploring the impact of sulfocalcic solution and water glass on the synthesis of phytoalexins and antifungal activity against Cladosporium cladosporioides

The passion fruit production in Brazil stands out as an activity of significant interest, especially for small-scale farmers, due to the short cycle of the crop, high economic returns, and wide demand in the consumer market, encompassing both fresh consumption and industrial processing. However, despite these attractions, the crop faces considerable challenges due to its notable susceptibility to diseases. In this context, this study was conducted with the purpose of evaluating the effectiveness of sulfocalcic solution and water glass in two distinct aspects: (i) in the in vitro control of Cladosporium cladosporioides, the causal agent of Passion Fruit Scab; and (ii) in the induction of phytoalexin synthesis in soybean cotyledons and bean hypocotyls. Four distinct treatments were implemented: T1 as a control, T2 with water glass (1.25%), T3 with sulfocalcic solution (3.03%), and T4 with sulfocalcic solution (0.5%). Results revealed that the 3.03% sulfocalcic solution demonstrated significant efficacy in controlling mycelial growth, followed by the treatment with the same substance at 0.5%. Treatments 3 and 4 were equally effective in inhibiting germination and sporulation, reaching approximately 90%, while water glass showed no efficacy in the conducted tests. Regarding the induction of phytoalexins, none of the treatments resulted in the accumulation of these compounds in bean hypocotyls; however, the 3.03% sulfocalcic solution induced synthesis in soybean cotyledons. These findings underscore the potential of sulfocalcic solution as an effective control agent against C. cladosporioides.

Strigolactone inhibits hydrogen peroxide and plasma membrane H+-ATPase activities to downregulate adventitious root formation in mung bean hypocotyls

Strigolactones regulate root development and are known to inhibit adventitious root formation. However, the hormonal targets of strigolactones during adventitious rooting are yet to be determined. As a signal molecule, H2O2 stimulates adventitious rooting. On the other hand, plasma membrane H+-ATPase is involved in several hormonal signals that are linked to root development. This study evaluated the influence of a synthetic strigolactone (rac-GR24), H2O2, and plasma membrane H+-ATPase on adventitious root formation in mung bean hypocotyls. We also determined if H2O2 and plasma membrane H+-ATPases are possible hormonal targets in strigolactone-mediated inhibition of adventitious rooting. The results confirm the inhibitory role of strigolactones and the enhancing influence of H2O2 on adventitious rooting while also suggesting that plasma membrane H+-ATPase activity is necessary and may be employed to regulate adventitious rooting. Also, rac-GR24 diminished endogenous H2O2 content by inhibiting NOX and SOD activities while also inhibiting plasma membrane H+-ATPase activity. Therefore, we conclude that interference with H2O2 signaling and plasma membrane H+-ATPase activity may serve as a potent hormonal mechanism that may be employed by strigolactones to downregulate adventitious rooting in mung bean hypocotyls.

Phaseolin Induction on Common-Bean Cultivars and Biological Control of Colletotrichum lindemuthianum 89 Race by Baccharis trimera (Less.) Dc.

HIGHLIGHTS Baccharis trimera aqueous extracts can inhibit Colletotrichum lindemuthianun 89 race growth. C. lindemuthianum filtrate can be used as a phaseolin inductor on common bean. There is no evidence of phaseolin induction through application of aqueous extracts of B. trimera in common bean hypocotyls.

Histochemical changes induced by Trichoderma spp. and potassium phosphite in common bean (Phaseolus vulgaris) in response to the attack by Colletotrichum lindemuthianum

Induction of resistance in common bean (Phaseolus vulgaris) has been considered a promising alternative to control anthracnose. Among the changes generated in the induction of resistance, structural changes have been reported by several authors as an efficient form of resistance to the stress plants undergo. Histochemical analysis techniques have been used to investigate tissue changes triggered by induction of resistance. Thus, this study aims to investigate certain histochemical changes suffered by common bean plants induced with potassium phosphite and Trichoderma spp. in response to the attack by Colletotrichum lindemuthianum, aiming to determine the host response pattern in terms of structural changes, associating it to possible disease control. Treatments consisted of isolates T. harzianum (isolate TOD1) and T. virens (isolate TM4), leaf fertilizer potassium phosphite Fertilis®, and distilled water (control). Inducers were applied to common bean alone or associated, consisting of five treatments plus the control treatment. The six treatments were evaluated for the absence and presence of C. lindemuthianum in a factorial scheme (6×2). Treatments allowed evaluating the severity of anthracnose in common bean, location of H2O2, lignin deposition, and hypersensitivity response in common bean hypocotyl by histochemical staining. Potassium phosphite and combinations of T. virens and T. harzianum with potassium phosphite efficiently reduced disease severity under greenhouse conditions, reaching 68, 84, and 71%, respectively. Studies with hypocotyl showed that T. harzianum + potassium phosphite and T. virens + potassium phosphite accelerated the H2O2 accumulation process and lignin deposition at the pathogen penetration site, in addition to the hypersensitivity reaction through the resistance-inducing activity, contributing to the protection of common bean against anthracnose caused by C. lindemuthianum.

Nitric oxide donor improves adventitious rooting in mung bean hypocotyl cuttings exposed to cadmium and osmotic stresses

Exogenous application of a nitric oxide donor, sodium nitroprusside (SNP), improved the formation and growth of adventitious roots in mung bean hypocotyl cuttings. The combined applications of SNP and CdCl2 or mannitol partially overcame the negative effects of Cd and mannitol on adventitious rooting compared with Cd or mannitol alone. SNP significantly increased the endogenous NO level and the glutathione (GSH), ascorbic acid (ASA), polyphenol, and proline (Pro) levels during the root induction and/or initiation stages. However, the malondialdehyde (MDA) levels were significantly reduced by the SNP treatment during the entire time course. To unveil the role of NO in mediating the plant response to heavy metal and osmotic stresses during adventitious rooting, SNP together with CdCl2 or mannitol was applied in the experiments. The results obtained showed that the Cd- or mannitol-induced changes in the levels of GSH, ASA, polyphenol, Pro, and MDA and the activities of ascorbate peroxidase (APX), peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), and indole-3-acetic acid oxidase (IAAO) were completely or partially reversed by SNP supplementation in the SNP + Cd/mannitol treatments, suggesting that NO mediated the redox state via the regulation of antioxidative systems to prevent membrane lipid peroxidation in response to the stresses during adventitious rooting. Furthermore, the protective effects of NO on the cellular antioxidative systems under the stresses were similar to those of IBA, implying that auxin and NO shared common pathways to respond to the stresses and leading to adventitious rooting in mung bean hypocotyl cuttings under heavy metal and osmotic stresses. NO mediates the redox state and prevents membrane lipid peroxidation during adventitious rooting in plants exposed to abiotic stresses via the regulation of antioxidant levels and antioxidative enzyme activities. NO shares common signaling pathways with auxin or acts as a downstream mediator of auxin in response to abiotic stresses during adventitious rooting.

Induction of phytoalexins and proteins related to pathogenesis in plants treated with extracts of cutaneous secretions of southern Amazonian Bufonidae amphibians.

Cutaneous secretions produced by amphibians of the family Bufonidae are rich sources of bioactive compounds that can be useful as new chemical templates for agrochemicals. In crop protection, the use of elicitors to induce responses offers the prospect of durable, broad-spectrum disease control using the plant’s own resistance. Therefore, we evaluated the potential of methanolic extracts of cutaneous secretions of two species of amphibians of the family Bufonidae found in the Amazon biome—Rhaebo guttatus (species 1) and Rhinella marina (species 2)—in the synthesis of phytoalexins in soybean cotyledons, bean hypocotyls, and sorghum mesocotyls. Additionally, changes in the enzyme activity of β-1,3-glucanase, peroxidase (POX), and polyphenol oxidase (PPO) and in the total protein content of soybean cotyledons were determined. In the soybean cultivar ‘TMG 132 RR’, our results indicated that the methanolic extract of R. guttatus cutaneous secretions suppressed glyceollin synthesis and β-1,3-glucanase activity and increased POX and PPO activities at higher concentrations and total protein content at a concentration of 0.2 mg/mL. On the other hand, the methanolic extract of R. marina cutaneous secretions induced glyceollin synthesis in the soybean cultivars ‘TMG 132 RR’ and ‘Monsoy 8372 IPRO’ at 0.1–0.2 mg/mL and 0.2 mg/mL, respectively. The methanolic extract of R. marina cutaneous secretions also increased the specific activity of POX and PPO in ‘Monsoy 8372 IPRO’ and ‘TMG 132 RR’, respectively, and decreased the activity of β-1,3-glucanases in ‘Monsoy 8372 IPRO’. At 0.3 mg/mL, it stimulated phaseolin synthesis. The extracts did not express bioactivity in the synthesis of deoxyanthocyanidins in sorghum mesocotyls. The study in soybean suggests that the bioactivity in defense responses is influenced by cultivar genotypes. Therefore, these results provide evidence that extracts of cutaneous secretions of these amphibians species may contribute to the bioactivity of defense metabolites in plants.

Extrato etanólico de própolis verde na proteção de feijoeiro contra bacterioses

ABSTRACT: The aim of this study was to evaluate the ethanolic extract of green propolis (EEP) in the protection of common bean plants against two main bacterial cultures, bacterial blight (Xanthomonas axonopodis pv. phaseoli) and wildfire (Pseudomonas syringae pv. tabaci). Experiments on antimicrobial activity were performed, inducing phytoalexins, defense-related enzymes, and disease severity, under concentrations of 0, 0.5, 1.0, 2.5, and 5.0%. The EEP presented antimicrobial activity on both phytobacteria, causing a decrease in their development. It has also promoted a linear accumulation of phaseolin in bean hypocotyls according to the EEP concentration used. There was a reduction in the lesion area, which was caused by bacterial blight on bean leaves treated with EEP, and local and systemic effect were observed. Polyphenoloxidase was activated with 5% EEP, reaching the maximum activation time 62.5 h after application. An increase was observed in the activity of phenylalanine ammonia-lyase in plants treated with EEP, with local and systemic effect. Results indicated the potential of EEP in the control of these diseases.

The role of pH for ionic solute uptake by the non-aerial hypocotyl of mung bean plants

The non-aerial hypocotyl is an exceptional fast pathway for the uptake of soil-applied pre-emergent herbicides or systemic actives with soil mobility after release from coated seeds. The presence of charged groups at the interface of the non-aerial hypocotyl to the environment and its role for the penetration of likewise charged agrochemicals have not yet been investigated as a basis for the development of enhanced delivery systems. Recent work suggests pore-like structures having pore size diameters < 1.5 nm in mung bean hypocotyls, which is not associated with the existence of a real channel system having a continuous aqueous phase. The current work presents a detailed study on the role of pH for the sorption of ionic compounds by the non-aerial hypocotyl of mung bean plants. The presence of fixed dissociable charges on the surface of the non-aerial hypocotyl was characterized utilizing different methods, including local application of charged radiolabelled agrochemicals, incubation in osmotic solutions and differential dye staining experiments. The formation of a pH-dependent and continuous Donnan phase determined the adsorption or repulsion of compounds with opposite and equal ionic charge, which was shown for various ionic dyes and agrochemicals. Uptake via the non-aerial hypocotyl varied with the pH value of the test solution, indicating the presence of fixed charges in the membrane. This information is considered as essential for a better understanding of the transport properties through the non-aerial hypocotyl membrane.

ACCUMULATION OF PHYTOALEXINS IN BEANS, SOYBEANS AND SORGHUM BY FUNGAL FILTRATES

ABSTRACT The use of elicitors in plants for disease control is demonstrated by the accumulation of phytoalexins. Among these elicitors, metabolic products from fungi have been shown to be effective in the activation of mechanisms of induced resistance. Thus, this study aimed to evaluate the effects of filtrates from the saprobic fungi Curvularia inaequalis, Pseudobotrytis terrestris, Memnoniella echinata and Curvularia eragrostidis in inducing phaseolin, glyceolin and deoxyanthocyanidins. For this, fungal mycelial disks were liquid-subcultured in potato dextrose (BD) media and maintained in BOD at 25 °C and 12 h of light and darkness. After 20 days, the cultures were filtered and, the filtrates were used in the experiments. Phaseolin was measured in etiolated hypocotyls of bean. For glyceolin evaluation, cotyledons of soybean were used. The deoxyanthocyanidin accumulation was evaluated in etiolated mesocotyls of sorghum. The results were subjected to analysis of variance and compared by regression tests (p &lt; 0.05). The filtrates of the saprobic fungi C. eragrostidis, C. inaequalis, P. terrestris and M. echinata promoted 9, 8, 9 and 7% greater increases in the concentration of phaseolin accumulations, respectively. The glyceolin accumulation varied with the concentration of C. eragrostidis, C. inaequalis and P. terrestris by adjusting the behavior to a cubic model. The deoxyanthocyanidin accumulation increased with concentration, while the filtrates of M. echinata and C. eragrostidis promoted 2 to 3 times more increases than the application of water. The filtrates of P. terrestris, C. eragrostidis, C. inaequalis and M. echinata induced accumulations of phytoalexins in soybean, beans and sorghum.

English

Plant resistance induction against pathogens is an alternative disease control method, which involves the activation of the plant defense mechanisms, such as the phytoalexins induction. The eliciting molecules have the capacity of inducing and activating such responses and thus, techniques have searched to isolate and characterize fractions with eliciting aspect. This study aimed to purify, through ion exchange chromatography and gel filtration chromatography, eliciting molecules from phytopathogenic nematodes, and test them in the induction of phaseolin in bean hypocotyls and gliceolin in soybeans cotyledons. A Tris HCl 0.05 M (pH 6.8) buffer was used as control treatment and acibenzolar-S-methly (50 mg i.a. L-1) and Saccharomyces cerevisiae (20 mg m L-1) was used as induction standard treatment. Ion exchange chromatography (IEC) and gel filtration chromatography (GFC) were applied to separate power eliciting fractions from five hundred female root knot nematodes (Meloidogyne javanica). The purification of elicitors, through IEC, resulted in sixty glicidic fractions and six glycoprotein ones. They were classified according to their nature, being twenty-six glicidic fractions and thirty-seven glycoprotein ones, with molecular masses ranging from 29.19 to 2,989.25 kDa. From the purified fractions, eight of them presented phaseolin inducing effect potential, whereas fifteen fractions presented gliceolin inducing effect. Chromatography proved to be efficient in purifying the eliciting compounds. Compounds having gliceolin and phaseolin suppressing characteristics were verified in the bioassays. For those fractions obtained through IEC and posteriorly submitted to GFC that did not induce phytoalexin, it is suggested that the molecules need to act jointly so there is eliciting effect and thus induce a defense response in the plant. Key words: gel filtration chromatography, ion exchange chromatography, Meloidogyne javanica, phytoalexins, resistance induction.

Light piping driven photosynthesis in the soil: Low-light adapted active photosynthetic apparatus in the under-soil hypocotyl segments of bean (Phaseolus vulgaris)

Photosynthetic activity was identified in the under-soil hypocotyl part of 14-day-old soil-grown bean plants (Phaseolus vulgaris L. cv. Magnum) cultivated in pots under natural light-dark cycles. Electron microscopic, proteomic and fluorescence kinetic and imaging methods were used to study the photosynthetic apparatus and its activity. Under-soil shoots at 0–2cm soil depth featured chloroplasts with low grana and starch grains and with pigment-protein compositions similar to those of the above-soil green shoot parts. However, the relative amounts of photosystem II (PSII) supercomplexes were higher; in addition a PIP-type aquaporin protein was identified in the under-soil thylakoids. Chlorophyll-a fluorescence induction measurements showed that the above- and under-soil hypocotyl segments had similar photochemical yields at low (10–55μmolphotonsm−2s−1) light intensities. However, at higher photon flux densities the electron transport rate decreased in the under-soil shoot parts due to inactivation of the PSII reaction centers. These properties show the development of a low-light adapted photosynthetic apparatus driven by light piping of the above-soil shoot. The results of this paper demonstrate that the classic model assigning source and sink functions to above- and under-soil tissues is to be refined, and a low-light adapted photosynthetic apparatus in under-soil bean hypocotyls is capable of contributing to its own carbon supply.

Activity of seaweed extracts and polysaccharide-enriched extracts from Ulva lactuca and Padina gymnospora as growth promoters of tomato and mung bean plants

Although marine seaweeds have been used as biostimulants since the beginning of modern agriculture, studies have only recently focused on the ability of seaweed extracts and their polysaccharides to enhance growth of plants. In this work, two bioassays were carried out to study the growth-promoting activity of seaweed extracts and polysaccharide-enriched extracts from Ulva lactuca and Padina gymnospora, obtained in neutral and alkaline conditions. Initially, the effect of seaweed extracts and polysaccharide-enriched extracts on seed germination and growth-promoting activity on tomato (Solanum lycopersicum cv. Rio Grande) plants under in vitro conditions was studied. Half-strength Murashige-Skoog (MS) medium with or without sucrose was supplemented with different concentrations of seaweed extracts (2, 4, and 10 mg mL−1) or polysaccharide-enriched extracts (0.2, 0.4, and 1.0 mg mL−1). The parameters evaluated were germination percentage, radicle and shoot length, and dry weight. In a second experiment, polysaccharide-enriched extracts at 1.0 mg mL−1 and indole-3-butyric acid as the control were studied for root inducer activity in mung bean (Vigna radiata). The majority of seaweed extracts had an inhibitory effect on seed germination. However, a significant effect (P ≤ 0.05) on tomato seedling growth (except for dry weight) was shown with seaweed extracts at 2 mg mL−1 included in half-strength MS medium with sucrose (30 g L−1). Moreover, 10 mg mL−1 neutral and alkaline seaweed extracts had an inhibitory effect on the parameters evaluated. In contrast, polysaccharide-enriched extracts obtained from U. lactuca and P. gymnospora promoted germination and stimulated growth of tomato plants compared to the controls. Additionally, treatment of mung bean hypocotyl cuttings with polysaccharide-enriched extracts of U. lactuca and P. gymnospora induced rooting more rapidly and in greater number compared to the controls. These results provide evidence that polysaccharide-enriched extracts act as an effective growth-promoting treatment.

De Novo Characterization of the Mung Bean Transcriptome and Transcriptomic Analysis of Adventitious Rooting in Seedlings Using RNA-Seq.

Adventitious rooting is the most important mechanism underlying vegetative propagation and an important strategy for plant propagation under environmental stress. The present study was conducted to obtain transcriptomic data and examine gene expression using RNA-Seq and bioinformatics analysis, thereby providing a foundation for understanding the molecular mechanisms controlling adventitious rooting. Three cDNA libraries constructed from mRNA samples from mung bean hypocotyls during adventitious rooting were sequenced. These three samples generated a total of 73 million, 60 million, and 59 million 100-bp reads, respectively. These reads were assembled into 78,697 unigenes with an average length of 832 bp, totaling 65 Mb. The unigenes were aligned against six public protein databases, and 29,029 unigenes (36.77%) were annotated using BLASTx. Among them, 28,225 (35.75%) and 28,119 (35.62%) unigenes had homologs in the TrEMBL and NCBI non-redundant (Nr) databases, respectively. Of these unigenes, 21,140 were assigned to gene ontology classes, and a total of 11,990 unigenes were classified into 25 KOG functional categories. A total of 7,357 unigenes were annotated to 4,524 KOs, and 4,651 unigenes were mapped onto 342 KEGG pathways using BLAST comparison against the KEGG database. A total of 11,717 unigenes were differentially expressed (fold change>2) during the root induction stage, with 8,772 unigenes down-regulated and 2,945 unigenes up-regulated. A total of 12,737 unigenes were differentially expressed during the root initiation stage, with 9,303 unigenes down-regulated and 3,434 unigenes up-regulated. A total of 5,334 unigenes were differentially expressed between the root induction and initiation stage, with 2,167 unigenes down-regulated and 3,167 unigenes up-regulated. qRT-PCR validation of the 39 genes with known functions indicated a strong correlation (92.3%) with the RNA-Seq data. The GO enrichment, pathway mapping, and gene expression profiles reveal molecular traits for root induction and initiation. This study provides a platform for functional genomic research with this species.

Effect of Timing and Duration of Soil Saturation on Soilborne Pythium Diseases of Common Bean (Phaseolus vulgaris)

Understanding combined abiotic (waterlogging) and biotic (Pythium spp.) stress resistance remains an important challenge to improving common bean (Phaseolus vulgaris) productivity in disease-prone regions with irregular but intensive rainfall patterns. This study documented the effects of timing (1, 3, 5, 7, and 9 days after sowing) and duration (3, 6, 12, and 24 h) of soil saturation (waterlogging) on damping-off, as well as hypocotyl and root diseases of common bean caused by Pythium irregulare. There were significant effects of timing of waterlogging as well as the presence or absence of the pathogen on emergence of the three bean varieties tested; namely, 'Gourmet Delight', 'Brown Beauty', and 'Pioneer'. The interaction between time of waterlogging and variety was significant for both root and hypocotyl disease severities. In the presence of P. irregulare, waterlogging 1 day after sowing resulted in the least emergence (55.2 ± 5.6%), although plants that survived after 5 weeks had less hypocotyl and root disease (percent hypocotyl disease index [%HDI] ± standard deviation [SD] = 42.0 ± 2.1% and percent root disease index [%RDI] ± SD = 42.4 ± 2.1%, respectively) than nonwaterlogged plants (%HDI = 50.8 ± 2.1% and %RDI = 48.0 ± 2.1%, respectively). The most severe disease assessed 5 weeks after sowing occurred when plants were subjected to waterlogging 9 days after sowing (%HDI = 61.3 ± 2.1% and %RDI = 56.0 ± 2.1%). In general, both hypocotyl and root disease severity increased as the duration of waterlogging increased from 1 to 24 h, with %HDI increasing from 53.9 ± 3.2% to 70.9 ± 3.2%, while %RDI increased from 57.2 ± 1.5% to 73.7 ± 1.5%. Varieties responded differentially in terms of disease development after waterlogging, with the least hypocotyl and root disease on Gourmet Delight (%HDI = 51.4 ± 3.2 and %RDI = 60.1 ± 1.5, respectively) and greatest on Pioneer (%HDI = 66.2 ± 3.2 and %RDI = 64.9 ± 1.5, respectively). Despite being susceptible to hypocotyl and root disease, Pioneer had the greatest emergence and shoot dry weight overall among the three varieties, suggesting that this variety has a degree of tolerance to waterlogging, P. irregulare infection, and the combination of these two stresses. Although the resistance of Gourmet Delight could be exploited to breed bean varieties that exhibit less hypocotyl and root disease when waterlogging occurs, the tolerance to both P. irregulare infection and waterlogging observed for Pioneer could also be exploited to breed varieties that incur less damage from hypocotyl or root disease or waterlogging. Furthermore, this study demonstrated what appears to be independent resistance to hypocotyl versus root infection by P. irregulare, which offers an opportunity to combine resistance to both stresses to reduce the impact of damping-off and root rot in conditions conducive for P. irregulare.

Species of Pythium Associated with Seedling Root and Hypocotyl Disease on Common Bean (Phaseolus vulgaris) in Western Australia

The occurrence and distribution of Pythium spp. were determined by collecting isolates of Pythium from common bean (Phaseolus vulgaris) plants showing root or hypocotyl disease symptoms from different areas of Western Australia in 2012. Eight different Pythium species (Pythium conidiophorum, P. diclinum, P. intermedium, P. irregulare, P. lutarium, P. mamillatum, P. pachycaule, and P. perplexum) were isolated and identified according to molecular sequences. P. irregulare was the most widespread Pythium sp. All species, except P. perplexum, were pathogenic to the hypocotyl and root of common bean. We believe this is the first report of P. intermedium as a pathogen on common bean worldwide. This is also the first report of P. conidiophorum, P. intermedium, P. lutarium, P. mamillatum, P. pachycaule, and P. diclinum as pathogens on common bean in Australia and the first report of P. irregulare as a pathogen on common bean in Western Australia. P. intermedium was the most pathogenic species, causing the most severe disease on 'Gourmet Delight' (percent root disease index [%RDI] 75 ± 2.9 and percent hypocotyl disease index [%HDI] 59.2 ± 3.2) and 'Pioneer' (%RDI 75 ± 2.9 and %HDI 65.8 ± 3.2). That the relative susceptibility or resistance (the ability of a plant to reduce the extent of invasion by the pathogen) of a given bean variety to one Pythium sp. was, in general, similar across the other Pythium spp. was an important finding, because this opens up opportunities to utilize a single virulent isolate of one Pythium sp. to identify general resistance to a wider spectrum of Pythium spp.

Hydrogen Peroxide Is a Second Messenger in the Salicylic Acid-Triggered Adventitious Rooting Process in Mung Bean Seedlings

In plants, salicylic acid (SA) is a signaling molecule that regulates disease resistance responses, such as systemic acquired resistance (SAR) and hypertensive response (HR). SA has been implicated as participating in various biotic and abiotic stresses. This study was conducted to investigate the role of SA in adventitious root formation (ARF) in mung bean (Phaseolus radiatus L) hypocotyl cuttings. We observed that hypocotyl treatment with SA could significantly promote the adventitious root formation, and its effects were dose and time dependent. Explants treated with SA displayed a 130% increase in adventitious root number compared with control seedlings. The role of SA in mung bean hypocotyl ARF as well as its interaction with hydrogen peroxide (H2O2) were also elucidated. Pretreatment of mung bean explants with N, N’-dimethylthiourea (DMTU), a scavenger for H2O2, resulted in a significant reduction of SA-induced ARF. Diphenyleneiodonium (DPI), a specific inhibitor of membrane-linked NADPH oxidase, also inhibited the effect of adventitious rooting triggered by SA treatment. The determination of the endogenous H2O2 level indicated that the seedlings treated with SA could induce H2O2 accumulation compared with the control treatment. Our results revealed a distinctive role of SA in the promotion of adventitious rooting via the process of H2O2 accumulation. This conclusion was further supported by antioxidant enzyme activity assays. Based on these results, we conclude that the accumulation of free H2O2 might be a downstream event in response to SA-triggered adventitious root formation in mung bean seedlings.

Ferulic acid impairs rhizogenesis and root growth, and alters associated biochemical changes in mung bean (Vigna radiata) hypocotyls

The present study investigated the effect of ferulic acid (FA; 0–1000 µM) on early growth, and rhizogenesis in mung bean (Vigna radiata) hypocotyls and associated biochemical changes. FA severely affected the radicle elongation and number of secondary roots after 72 h. The root and shoot length, number and length of secondary roots, and seedling dry weight of one-week-old seedlings of mung bean were decreased by 64%. The rooting potential (percent rooting, number and length of adventitious roots) of mung bean hypocotyls under in vitro conditions was significantly inhibited in response to 1–100 µM FA. At 1000 µM there was complete cessation of rooting. FA caused a reduction in the contents of water-soluble proteins and endogenous total phenolics, whereas the activities of proteases, peroxidases, and polyphenol peroxidases increased. The study concludes that FA inhibits root growth and development, and in vitro rooting process in mung bean by interfering with biochemical processes that are crucial for root formation.

Teores de isoflavonas em grãos inteiros e nos componentes dos grãos de diferentes cultivares de soja (Glycine max (L.) Merrill)

Devido à maior concentração de isoflavonas nos hipocótilos dos grãos de soja, a indústria de alimentos tem utilizado esse componente do grão como matéria-prima. No presente trabalho, foram quantificados os teores de isoflavonas nas estruturas formadoras do grão de soja (hipocótilo, cotilédones e casca), analisadas por Cromatografia Líquida de Alta Eficiência (CLAE). Foram avaliadas quatro cultivares de sojas especiais: BRS 184, BRS 216, BRS 257 e BRS 267, desenvolvidas pela Embrapa Soja. Todas as cultivares apresentaram maior teor de isoflavonas totais no hipocótilo (média de 2029,32 mg.100 g-1). No grão inteiro (267,16 mg.100 g-1) e nos cotilédones (209,16 mg.100 g-1), os teores de isoflavonas foram cerca de dez vezes menores do que nos hipocótilos. A cultivar BRS 216 apresentou o teor maior de isoflavonas totais no hipocótilo (2583,20 mg.100 g-1). Embora a casca da soja não apresente isoflavonas, observou-se que esses compostos estavam presentes nessa parte do grão numa quantidade média de 105,58 mg.100 g-1, devido à presença de resíduos do hipocótilo e dos cotilédones provenientes do processo de descasque. Essa composição residual da casca favorece sua utilização como matéria-prima fonte de fibras, porque também fornece isoflavonas e outros compostos da soja.

Identification of the cellular location of internalized Escherichia coli O157:H7 in mung bean, Vigna radiata, by immunocytochemical techniques.

Escherichia coli O157:H7 has been associated with numerous outbreaks involving fresh produce. Previous studies have shown that bacteria can be internalized within plant tissue and that this can be a source of protection from antimicrobial chemicals and environmental conditions. However, the types of tissue and cellular locations the bacteria occupy in the plant following internalization have not been addressed. In this study, immunocytochemical techniques were used to localize internalized E. coli O157:H7 expressing green fluorescent protein in germinated mung bean (Vigna radiata) hypocotyl tissue following contamination of intact seeds. An average of 13 bacteria per mm(3) were localized within the sampled tissue. The bacteria were found to be associated with every major tissue and corresponding cell type (cortex, phloem, xylem, epidermis, and pith). The cortical cells located on the outside of the vascular bundles contained the majority of the internalized bacteria (61%). In addition, the bacteria were localized primarily to the spaces between the cells (apoplast) and not within the cells. Growth experiments were also performed and demonstrated that mung bean plants could support the replication of bacteria to high levels (10(7) CFU per plant) following seed contamination and that these levels could be sustained over a 12-day period. Therefore, E. coli O157:H7 can be internalized in many different plant tissue types after a brief seed contamination event, and the bacteria are able to grow and persist within the plant.