Lipopeptide production by Bacillus atrophaeus strain B44 and its biocontrol efficacy against cotton rhizoctoniosis

OBJECTIVES

An assay was conducted to show the comparisons the effects of nine metal ions on antagonistic metabolites (lipopeptides, siderophores and gibberellins) by Bacillus atrophaeus strain B44 using well-diffusion assays, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis, chrome azurol S plus mannitol salt agar (CAS-MSA) tests, and reversed-phase high-performance liquid chromatography (RP-HPLC) analysis. This assay is also designed to demonstrate the biocontrol efficacy of B44 against cotton rhizoctoniosis using pot culture tests.

RESULTS

Both the lipopeptide yield and the antimicrobial activity of B44 increase with the MnSO₄, MgSO₄, CaCO₃, and CuSO₄ treatments and either have no effect or decreased lipopeptide yield and antimicrobial activity with the FeSO₄, K₂HPO₄, KCl, KH₂PO₄ and ZnSO₄ treatments. The medium containing MgSO₄ has no significant effect on either the lipopeptide yield or antimicrobial activity. MALDI-TOF-MS analysis shows a broad range of m/z peaks, indicating that strain B44 produces a complex mixture of iturin, surfactin, and fengycin lipopeptides. Gibberellin production by strain B44 varies greatly depending on the culture medium, and the siderophore production is not significantly affected by the culture medium. Pot tests show that lipopeptide production affects the disease control efficacy of strain B44.

CONCLUSION

The biocontrol efficacy of B. atrophaeus strain B44 is related to the lipopeptide yield. Moreover, B. atrophaeus strain B44 significantly increases the size of cotton seedlings, which is related to the GA₃ concentration.

One-pot sample preparation approach for profiling spatial distribution of gibberellins in a single shoot of germinating cereal seeds

Sample preparation remains a bottleneck in the rapid and reliable quantification of gibberellins (GAs) for obtaining an insight into the physiological processes mediated by GAs. The challenges arise from not only the extremely low content of GAs in complex plant matrices, but the poor detectability of GAs by mass spectrometry (MS) in negative ion mode. In an effort to solve these urgent difficulties, we present a spatial-resolved analysis method to investigate the distribution of GAs in tiny plant tissues based on a simplified one-pot sample preparation approach coupled with ultrahigh-performance liquid chromatography-tandem MS. By integrating extraction and derivatization into one step, target GAs were effectively extracted from plant materials and simultaneously reacted with N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide, the sample preparation time was largely shortened, the probability of sample loss was minimized and the detection sensitivity of MS was also greatly improved compared with underivatized GAs. Under optimal conditions, the method was validated from the quantification linearity, limits of detection and limits of quantification in the presence of plant matrices, recoveries, and precision. With the proposed method, 15 endogenous GAs were detected and, among these, 11 GAs could be quantified in 0.50 mg fresh weight (FW) wheat shoot samples, and five GAs were quantified in only 0.15 mg FW developing seed samples of Arabidopsis thaliana. The distribution patterns of GAs along both the non-13-hydroxylation pathway and the early 13-hydroxylation pathway in a single shoot of germinating wheat, rice and maize seeds were finally profiled with a spatial resolution down to approximately 1 mm² .

Current advances in gibberellic acid (GA3) production, patented technologies and potential applications

Gibberellic acid is a plant growth hormone that promotes cell expansion and division. Studies have aimed at optimizing and reducing production costs, which could make its application economically viable for different cultivars. Gibberellins consist of a large family of plant growth hormones discovered in the 1930s, which are synthesized via the terpenes route from the geranylgeranyl diphosphate and feature a basic structure formed by an ent-gibberellane tetracyclic skeleton. Among them, only four have biological activity, including gibberellic acid (GA₃), which acts as a natural plant growth regulator, especially for stem elongation, seed germination, and increased fruit size. It can be obtained from plants, fungi, and bacteria. There are also some reports about microalgae GA₃ producers. Fungi, especially Gibberella fujikuroi, are preferred for GA₃ production via submerged fermentation or solid-state fermentation. Many factors may affect its production, some of which are related to the control and scale-up of fermentation parameters. Different GA₃ products are available on the market. They can be found in liquid or solid formulations containing only GA₃ or a mixture of other biological active gibberellins, which can be applied on a wide variety of cultivars, including crops and fruits. However, the product's cost still limits its large and continuous application. New low-cost and efficient GA₃ production alternatives are surely welcome. This review deals with the latest scientific and technological advances on production, recovery, formulation, and applications of this important plant growth hormone.

Biotransformation of ent-kaur-16-ene and ent-trachylobane 7β-acetoxy derivatives by the fungus Gibberella fujikuroi (Fusarium fujikuroi)

Candol A (7β-hydroxy-ent-kaur-16-ene) (6) is efficiently transformed by Gibberella fujikuroi into the gibberellin plant hormones. In this work, the biotransformation of its acetate by this fungus has led to the formation of 7β-acetoxy-ent-kaur-16-en-19-oic acid (3), whose corresponding alcohol is a short-lived intermediate in the biosynthesis of gibberellins and seco-ring ent-kaurenoids in this fungus. Further biotransformation of this compound led to the hydroxylation of the 3β-positions to give 7β-acetoxy-3β-hydroxy-ent-kaur-16-en-19-oic acid (14), followed by a 2β- or 18-hydroxylation of this metabolite. The incubation of epicandicandiol 7β-monoacetate (7β-acetoxy-18-hydroxy-ent-kaur-16-ene) (10) produces also the 19-hydroxylation to form the 18,19 diol (20), which is oxidized to give the corresponding C-18 or C-19 acids. These results indicated that the presence of a 7β-acetoxy group does not inhibit the fungal oxidation of C-19 in 7β-acetoxy-ent-kaur-16-ene, but avoids the ring B contraction that leads to the gibberellins and the 6β-hydroxylation necessary for the formation of seco-ring B ent-kaurenoids. The biotransformation of 7β-acetoxy-ent-trachylobane (trachinol acetate) (27) only led to the formation of 7β-acetoxy-18-hydroxy-ent-trachylobane (33).

Simultaneous determination of different endogenetic plant growth regulators in common green seaweeds using dispersive liquid-liquid microextraction method

A simple and rapid HPLC-based method was developed for simultaneous determination of major classes of plant growth regulators (PGRs) in Monostroma and different species of Ulva. The plant growth regulators determined included gibberellic acid (GA(3)), indole-3-acetic acid (IAA), abscisic acid (ABA), indole-3-butyric acid (IBA), salicylic acid and kinetin riboside (KR) and their respective elution time was 2.75, 3.3, 3.91, 4.95, 5.39 and 6.59 min. The parameters optimized for distinct separation of PGRs were mobile phase (60:40 methanol and 0.6% acetic acid in water), column temperature (35°C) and flow rate (1ml/min). This method presented an excellent linearity (0.2-100μg/ml) with limit of detection (LOD) as 0.2μg/ml for ABA, 0.5μg/ml for KR and salicylic acid, and 1μg/ml for IAA, IBA and GA(3). The precision and accuracy of the method was evaluated after inter and intra day analysis in triplicates. The effect of plant matrix was compensated after spiking and the resultant recoveries estimated were in the range of 80-120%. Each PGR thereby detected were further characterized by ESI-MS analysis. The method optimized in this study determined IBA along with IAA for the first time in the seaweed species investigated except Ulva linza where the former was not detected. In all the species studied, ABA level was detected to be the highest while kinetin riboside was the lowest. In comparison to earlier methods of PGR analysis, sample preparation and analysis time were substantially reduced while allowing determination of more classes of PGRs simultaneously.

Plant growth promotion and Penicillium citrinum

BACKGROUND

Endophytic fungi are known plant symbionts. They produce a variety of beneficial metabolites for plant growth and survival, as well as defend their hosts from attack of certain pathogens. Coastal dunes are nutrient deficient and offer harsh, saline environment for the existing flora and fauna. Endophytic fungi may play an important role in plant survival by enhancing nutrient uptake and producing growth-promoting metabolites such as gibberellins and auxins. We screened roots of Ixeris repenes (L.) A. Gray, a common dune plant, for the isolation of gibberellin secreting endophytic fungi.

RESULTS

We isolated 15 endophytic fungi from the roots of Ixeris repenes and screened them for growth promoting secondary metabolites. The fungal isolate IR-3-3 gave maximum plant growth when applied to waito-c rice and Atriplex gemelinii seedlings. Analysis of the culture filtrate of IR-3-3 showed the presence of physiologically active gibberellins, GA1, GA3, GA4 and GA7 (1.95 ng/ml, 3.83 ng/ml, 6.03 ng/ml and 2.35 ng/ml, respectively) along with other physiologically inactive GA5, GA9, GA12, GA15, GA19, GA20 and, GA24. The plant growth promotion and gibberellin producing capacity of IR-3-3 was much higher than the wild type Gibberella fujikuroi, which was taken as control during present study. GA5, a precursor of bioactive GA3 was reported for the first time in fungi. The fungal isolate IR-3-3 was identified as a new strain of Penicillium citrinum (named as P. citrinum KACC43900) through phylogenetic analysis of 18S rDNA sequence.

CONCLUSION

Isolation of new strain of Penicillium citrinum from the sand dune flora is interesting as information on the presence of Pencillium species in coastal sand dunes is limited. The plant growth promoting ability of this fungal strain may help in conservation and revegetation of the rapidly eroding sand dune flora. Penicillium citrinum is already known for producing mycotoxin citrinin and cellulose digesting enzymes like cellulase and endoglucanase, as well as xylulase. Gibberellins producing ability of this fungus and the discovery about the presence of GA5 will open new aspects of research and investigations.

Introduction to time-of-flight secondary ion mass spectrometry application in chromatographic analysis

New on-line analytical system coupling thin layer chromatography (TLC) and high selective identification unit-time of flight secondary ion mass spectrometry (TOF-SIMS) is introduced in this article. Chromatographic mixture separation and analyte surface deposition followed with surface TOF-SIMS analysis on-line allows to identify the analytes at trace and ultratrace levels. The selected analytes with different detectability and identification possibility were analysed in this hyphenated unit (Methyl Red indicator, Terpinolen and Giberrelic acid). Here, the chromatographic thin layer plays a universal role: separation unit, analyte depositing surface and TOF-SIMS interface, finally. Two depositing substrates and TOF-SIMS compatible interfaces were tested in above-mentioned interfacing unit: modified aluminium backed chromatographic thin layer and monolithic silica thin layer. The sets of positive and negative ions TOF-SIMS spectra obtained from different SIMS modes of analysis were used for analyte identification purposes. SIMS enables analyte detection with high mass resolution at the concentration level that is not achieved by other methods.

Involvement of endogenous gibberellins in potato tuber dormancy and early sprout growth: a critical assessment

The role of endogenous gibberellins (GAs) in the regulation of potato (Solanum tuberosum) tuber dormancy was examined by determining: 1. changes in endogenous GA levels during natural dormancy progression, 2. the effects of GA biosynthesis inhibitors on tuber dormancy duration and 3. the dormancy status and tuber GA levels in a dwarf mutant of potato. The tubers (cv. Russet Burbank) used in these studies were still completely dormant after 98 days of storage. Between 98 and 134 days of storage, dormancy began to end and tubers exhibited limited (< 2 mm) sprout growth. Tuber dormancy weakened with further storage and tubers exhibited greater rates of sprout growth after 187 days of storage. Tubers stored for 212 days or longer were completely non-dormant and exhibited vigorous sprout growth. Immediately after harvest, the endogenous contents of GA19, GA20, and GA1 were relatively high (0.48-0.62 ng g fresh weight(-1)). The content of these GAs declined between 33 and 93 days of storage. Internal levels of GA19, GA20, and GA, rose slightly between 93 and 135 days of storage reaching levels comparable to those found in highly dormant tubers immediately after harvest. Levels of GA19, GA20, and GA1 continued to increase as sprout growth became more vigorous. Neither GA4 nor GA8 was detected in any tuber sample regardless of dormancy status. Dormant tubers exhibited a time-dependent increase in apparent GA sensitivity. Freshly harvested tubers were completely insensitive to exogenous GAs. As postharvest storage continued, exogenous GAs promoted premature dormancy release with GA1 and GA20 eliciting the greatest response. Injection of up to 5 microg tuber(-1) of kaurene, GA12, GA19 or GA8 had no effect on dormancy release. Sprout growth from non-dormant tubers was also promoted by exogenous GA in the following sequence of activity: GA1 = GA20 > GA19. Kaurene, GA12, and GA8 were inactive. Continuous exposure of developing tubers to inhibitors of GA biosynthesis (AMO-1618, ancymidol, or tetcyclasis) did not extend tuber dormancy but rather hastened dormancy release. Comparison of tuber dormancy and GA1 content in tubers of a wild-type and dwarf mutant of S. tuberosum ssp. andigena revealed a near-identical pattern of dormancy progression in spite of the absence of detectable levels of GA1 in tubers of the dwarf sibling at any time during dormancy progression. Collectively, these results do not support a role for endogenous GA in potato tuber dormancy release but are consistent with a role for GAs in the regulation of subsequent sprout growth.

Cytokinins and gibberellins in sap exudate of the oil palm

Exudates were collected from stumps of pre-anthesis inflorescences of oil palm and analysed for cytokinin and gibberellin content using combined HPLC-ELISA techniques. Three antisera, for zeatin-type, dihydrozeatin-type and isopentenyladenine-type cytokinins, were used in ELISAs to identify members of these three groups of cytokinins. Ribotides, 9-glucosides, free bases and ribosides were detected for each of the groups with zeatin riboside the most abundant cytokinin identified in the exudate. Isopentenyladenine-type and dihydrozeatin-type cytokinins were also identified but at lower levels. In addition, two monoclonal antibodies were used in the development of novel ELISAs for members of the 13-hydroxylated and non-13-hydroxylated families of gibberellins. The new ELISAs allow the determination of gibberellins in smaller amounts of tissue than are required for GC-MS. The most abundant gibberellins identified in exudates were GA19 and GA44, as well as other members of the early 13-hydroxylation pathway. Gibberellins were confirmed by GC-MS. The presence of these types of growth regulators in exudate supplying immature inflorescences suggest they have a role in growth and development of these structures.

Isolation and identification of antheridiogens in the ferns, Lygodium microphyllum and Lygodium reticulatum

Antheridiogens in culture media of 6-week-old prothallia of two species of Schizaeaceous ferns, Lygodium microphyllum and Lygodium reticulatum, were analyzed by gas chromatography-mass spectrometry. In both species, the gibberellin A73 methyl ester (GA73-Me) was identified as the most abundant antheridiogen, and the methyl esters of GA9 and of several monohydroxy-GA73 derivatives were also detected. Since both species produced antheridiogens at a high level, they were classified into high-antheridiogen-producing ferns. The response to GA73-Me of gametophytes of both species is also discussed.

Identification of endogenous gibberellins in strawberry, including the novel gibberellins GA123, GA124 and GA125

Extracts of carboxylic acids from immature fruits of strawberry (Fragaria x ananassa Duch. cv. Elsanta) were analysed for gibberellins by combined gas chromatography-mass spectrometry. The following previously characterised gibberellins were identified by comparison of their mass spectra and Kovats retention indices (KRIs) with those of standards or published data: GA1, GA3, GA5, GA8, GA12, GA17, GA19, GA20, GA29, GA44, GA48, GA49, GA53, GA77, GA97, GA111 and GA112. Evidence for endogenous 1-epi GA61 (GA119) and 11alpha-OH-GA12 was also obtained. In addition, a number of putative GAs were detected. Of these, three were shown to be 12alpha-hydroxy-GA53, 12alpha-hydroxy-GA44, and 12alpha-hydroxy-GA19 by comparison with authentic compounds prepared by rational synthesis, and have been allocated the descriptors GA123, GA124 and GA125, respectively.

Synthesis and confirmation of structure for a new gibberellin, 2 beta-hydroxy-GA12 (GA110), from spinach and oil palm

The identity of a new gibberellin (GA) in spinach and oil palm sap has been confirmed as 2 beta-hydroxy-GA12 (GA110) by comparisons of GC-mass spectral data obtained for the trimethylsilyl ether methyl ester derivatives with those of a synthetic sample prepared by means of a 24 step sequence from gibberellic acid; 2 beta-hydroxy-GA24 was also prepared. Experimental details for the latter part of the syntheses are described.

[Separation and determination of plant growth regulators by capillary micellar electrokinetic chromatography]

It is important for separation and determination of plant growth regulators in the research of plant physiology. A study of the separation of five plant growth regulators, such as abscisic acid (ABA), gibberellic acid (GA), indole-butyric acid (IBA), indole acetic acid (IAA) and naphthaleneacetic (NAA) by micellar electrokinetic chromatography (MEKC) is presented. The effects of pH, SDS concentration, applied voltage and organic additives on migration behavior were investigated. Results showed that satisfactory separation was achieved on optimization of electrophoretic condition: 80 mmol/L SDS, 10 mmol/L borate-phosphate, 5% isopropanol, 18 kV applied voltage, pH 8.0. The SDS concentration and organic additives played an important role in separating plant growth regulators, and the applied voltage and pH gave less effect. The detection limit of ABA, GA, IBA, IAA and NAA were 5.0 x 10(-3), 3.0 x 10(-3), 5.8 x 10(-4), 1.5 x 10(-4) and 1.4 x 10(-4) g/L respectively. Increasing of the SDS concentration or organic additives would change separation factor (alpha) and result an improvement of the resolution of difficult separation pairs ABA-GA and IAA-NAA.

Endogenous gibberellins in Arabidopsis thaliana and possible steps blocked in the biosynthetic pathways of the semidwarf ga4 and ga5 mutants

Twenty gibberellins (GAs) have been identified in extracts from shoots of the Landsberg erecta line of Arabidopsis thaliana by full-scan gas chromatography-mass spectrometry and Kovats retention indices. Eight of them are members of the early-13-hydroxylation pathway (GA53, GA44, GA19, GA17, GA20, GA1, GA29, and GA8), six are members of the early-3-hydroxylation pathway (GA37, GA27, GA36, GA13, GA4, and GA34), and the remaining six are members of the non-3,13-hydroxylation pathway (GA12, GA15, GA24, GA25, GA9, and GA51). Seven of these GAs were quantified in the Landsberg erecta line of Arabidopsis and in the semidwarf ga4 and ga5 mutants by gas chromatography-selected ion monitoring (SIM) using internal standards. The relative levels of the remaining 13 GAs were compared by the use of ion intensities only. In comparison with the Landsberg erecta line, the ga4 mutant had reduced levels of the 3-hydroxy- and 3,13-dihydroxy-GAs, and it accumulated the 13-hydroxy-GAs, except GA53, and the non-3,13-hydroxy-GAs, except GA12. The GA4 gene encodes, therefore, a protein with 3 beta-hydroxylation activity. The ga5 mutant had reduced levels of the C19-GAs, which indicates that the product of the GA5 gene catalyzes the elimination of C-20 at the aldehyde level. The ga5 mutant also had increased levels of certain C20-GAs, which indicates existence of an additional control, possibly hydroxylation of C-20. The growth-response data, as well as the accumulation of GA9 in the ga4 mutant, indicate that GA9 is not active in Arabidopsis, but it must be 3 beta-hydroxylated to GA4 to become bioactive. It is concluded that the reduced levels of the 3 beta-hydroxy-GAs, GA1 and GA4, are the cause of the semidwarf growth habit of both mutants.

Biosynthesis of gibberellins in Gibberella fujikuroi. Gibberellin A47

Two minor radioactive products in cultures of G. fujikuroi strain ACC917 supplemented with labeled gibberellin A4 have been identified as the 2alpha-hydroxy derivative, gibberellin A47, and the hydrate, gibberellin A2. In addition, evidence was obtained by combined gas chromatography--mass spectrometry for the formation of 3-O-acetylgibberellin A1,3-O-acetylgibberellin A3, and gibberellin A20 by the culture. The time course of gibberellin synthesis in defined and complex media, as well as changes in the relative amounts of radioactive gibberellins formed when [4C]gibberellin A4 was added to cultures at different ages, suggest that the composition of the gibberellin mixture produced is determined by the balance between synthesis and decay of key enzymes in the branching pathway.

Isolation of novel conjugated gibberellins from Cucumis sativus seed

Neutral and n-butanol fractions of a methanol extract of mature seeds of a monoecious line of Cucumis sativus (cucumber) were found to contain novel gibberellins. A β-D-glucoside was isolated from the n-butanol fraction and partially characterized by thin-layer chromatography as a derivative of gibberellin A1. The n-propyl ester of GA3 was isolated from the neutral fraction and the n-propyl ester of GA1 was tentatively identified as a second component of that fraction.

Improved methods for preparing pure gibberellins from cultures of Gibberella fujikuroi. Isolation by adsorption or partition chromatography on silicic acid and by partition chromatography on Sephadex columns

Procedures have been developed for the separation of closely related gibberellins on a preparative scale by partition chromatography on columns of Sephadex. This technique simplifies the isolation of gibberellins which have previously been difficult to obtain, or have been overlooked. It has particular value in preparing radiochemically pure gibberellins after biosynthetic labeling. Selective fermentations were used to promote the formation of required gibberellins by Gibberella fujikuroi. These gave enriched mixtures which, after an initial fractionation by silicic acid chromatography, were conveniently separated by Sephadex partition chromatography to yield pure compounds.