Phytohormones in the formation of crown gall tumors

Probing into the unique relationship between a soil bacterium, Pseudomonas putida AKMP7 and Arabidopsis thaliana: A case of "conditional pathogenesis"

Plant growth-promoting rhizobacteria (PGPR) are beneficial soil bacteria that colonise the rhizosphere and help plants in growth, development, and stress tolerance. While there is a significant body of research elucidating their benefits to plants, studies on the "abnormal" or "unexpected" behavior of these bacteria are almost non-existent. One such study from our laboratory has previously reported a unique situation in which a certain strain of drought and thermo-tolerant PGPR, namely, Pseudomonas putida AKMP7, becomes pathogenic towards Arabidopsis thaliana under drought conditions, but not under normal (well-watered) conditions. In this study, we have probed deeper into this phenomenon of "conditional pathogenesis". We found that, AKMP7 imparts an enhancement in plant growth under well-watered conditions, while, causing a deterioration in plant health under drought conditions. In an attempt to understand the underlying reasons for this phenomenon, we analysed the phytohormones released by Pseudomonas putida AKMP7 using LC-ESI-MS/MS technique. We identified that AKMP7 releases zeatin (a cytokinin), the auxin derivative -indole acetamide and amino acid-conjugates of auxin (indole-3-acetyl-L-alanine, indole-3-acetyl-L-phenylalanine and indole-3-acetyl-L-aspartate) in the growth medium. By treating the plants with commercially obtained forms of these phytohormones, individually or in combination with AKMP7, we identified that zeatin and auxin derivative indole acetamide can play a crucial role in the conditional pathogenesis exhibited by this bacterium on A. thaliana under drought conditions. Our work lays a foundation for further understanding the precise molecular mechanisms involved in this unique phenomenon of conditional/opportunistic pathogenesis.

Regulation of flavonoid metabolism in ginkgo leaves in response to different day-night temperature combinations

Flavonoids are the most important secondary metabolites in ginkgo (Ginkgo biloba L.) leaves that determine its medicinal quality. Studies have suggested that secondary metabolism is strongly affected by temperature in other plant species, but little is known about ginkgo. In this study, we investigated the effects of different day-night temperature combinations (15/10, 25/20, and 35/30 °C (day/night)) on key enzyme activity, growth regulator concentrations, and flavonoid accumulation in ginkgo leaves. We found that phenylalanine ammonia-lyase (PAL) activity was enhanced and inhibited at 15/10 and 35/30 °C, respectively. Cinnamate-4-hydroxylase (C4H) activity was relatively stable under the three temperature conditions, and the p-coumarate CoA ligase (4CL) activity showed different trends under the three temperature conditions. The concentrations of flavonoid constituents (quercetin, kaempferol, and isorhamnetin) were decreased and increased under the 35/30 and 15/10 °C conditions, respectively. Low temperature promoted soluble sugar accumulation, while temperature had a limited impact on the accumulation of soluble protein. The pattern of change in the total flavonoid concentration was not always in agreement with PAL activity due to its complex pathway. Indoleacetic acid (IAA) and gibberellin (GA) changes shared similar patterns and had limited effects on flavonoid accumulation, while abscisic acid (ABA) acted as a promotor of flavonoid accumulation under high-temperature conditions. The total flavonoids achieved the highest content under the 15/10 °C treatment on the 40th day. Therefore, the lower temperature (15/10 °C) is more favorable for flavonoid accumulation and will provide a theoretical basis for further study.

Metabolic changes in Agrobacterium tumefaciens-infected Brassica rapa

Agrobacterium has the ability to transfer its genetic material, T-DNA, into the plant genome. The unique interaction between the bacterium and its host plant has been well studied at the transcriptome, but not at the metabolic level. For a better understanding of this interaction it is necessary to investigate the metabolic changes of the host plant upon infection with Agrobacterium tumefaciens. This study investigated the metabolic response of Brassica rapa to infection with disarmed and tumor-inducing strains of A. tumefaciens using (1)H nuclear magnetic resonance spectroscopy combined with multivariate data analysis. The partial least square-discriminant analysis (PLS-DA) of two varieties of B. rapa showed that there was a clear differentiation in the metabolite profiles of B. rapa leaves infected with the disarmed strain LBA4404 and with tumor-inducing octopine and nopaline strains, particularly in the flavonoid, phenylpropanoid, sugar and free amino/organic acid contents. However, individual PLS-DA of each type of infection suggests that, in general, some flavonoids and phenylpropanoids were suppressed as a consequence of these infections. The results obtained in this study indicate that the disarmed strain LBA4404 and tumor-inducing strains have different effects on the metabolite profile of B. rapa.

Biosynthesis and bioactivity of trichosanthin in cultured crown gall tissues of Trichosanthes kirilowii Maximowicz

Trichosanthin (TCS) from Trichosanthes kirilowii Maximowicz (T. kirilowii) can be used to treat choriocarcinoma. In this work, we established a novel system to produce TCS in crown gall tissues of T. kirilowii infected by Agrobacterium tumefaciens C58 (A. tumefaciens). In the crown gall tissues, a nopaline synthase (NOS) gene of A. tumefaciens was identified by polymerase chain reaction (PCR), and nopaline accumulation was confirmed by a high-voltage filter paper electrophoresis. Furthermore, we optimized conditions to culture the crown gall tissues able to grow fast and produce TCS in an auxin-free medium, and found that a fungal elicitor of Armillaria mellea was capable of stimulation of TCS secretion into the medium. Moreover, we identified that the TCS purified from the crown gall tissues could induce gastric cancer cell death. These data underscore the usefulness of our system as an inexpensive and virtually unlimited source of TCS.

Nuclear localization and interaction of RolB with plant 14-3-3 proteins correlates with induction of adventitious roots by the oncogene rolB

The rooting-locus gene B (rolB) on the T-DNA of the root-inducing (Ri) plasmid in Agrobacterium rhizogenes is responsible for the induction of transformed adventitious roots, although the root induction mechanism is unknown. We report here that the RolB protein of pRi1724 (1724RolB) is associated with Nicotianatabacum14-3-3-like protein omegaII (Nt14-3-3 omegaII) in tobacco bright yellow (BY)-2 cells. Nt14-3-3 omegaII directly interacts with 1724RolB protein. Green fluorescent protein (GFP)-fused 1724RolB is localized to the nucleus. GFP-fused mutant 1724RolB proteins having a deletion or amino acid substitution are unable to interact with Nt14-3-3 omegaII and also show impaired nuclear localization. Moreover, these 1724RolB mutants show decreased capacity for adventitious root induction. These results suggest that adventitious root induction by 1724RolB protein correlates with its interaction with Nt14-3-3 omegaII and the nuclear localization of 1724RolB protein.

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.

A single amino acid substitution beyond the C2H2-zinc finger in Ros derepresses virulence and T-DNA genes in Agrobacterium tumefaciens

Ros is a chromosomally-encoded repressor containing a novel C2H2 zinc finger in Agrobacterium tumefaciens. Ros regulates the expression of six virulence genes and an oncogene on the Ti plasmid. Constitutive expression of these genes occurs in the spontaneous mutant 4011R derived from the octopine strain Ach-5, resulting in T-DNA processing in the absence of induction, and in the biosynthesis of cytokinin. Interestingly, the mutation in 4011R is an Arg to Cys conversion at amino acid residue 125 near the C-terminus well outside the zinc finger of Ros. Yet, Ros bearing this mutation is unable to bind to the Ros-box and is unable to complement other ros mutants.

The never ripe mutant provides evidence that tumor-induced ethylene controls the morphogenesis of agrobacterium tumefaciens-induced crown galls on tomato stems

We confirm the hypothesis that Agrobacterium tumefaciens-induced galls produce ethylene that controls vessel differentiation in the host stem of tomato (Lycopersicon esculentum Mill.). Using an ethylene-insensitive mutant, Never ripe (Nr), and its isogenic wild-type parent we show that infection by A. tumefaciens results in high rates of ethylene evolution from the developing crown galls. Ethylene evolution from isolated internodes carrying galls was up to 50-fold greater than from isolated internodes of control plants when measured 21 and 28 d after infection. Tumor-induced ethylene substantially decreased vessel diameter in the host tissues beside the tumor in wild-type stems but had a very limited effect in the Nr stems. Ethylene promoted the typical unorganized callus shape of the gall, which maximized the tumor surface in wild-type stems, whereas the galls on the Nr stems had a smooth surface. The combination of decreased vessel diameter in the host and increased tumor surface ensured water-supply priority to the growing gall over the host shoot. These results indicate that in addition to the well-defined roles of auxin and cytokinin, there is a critical role for ethylene in determining crown-gall morphogenesis.

Phenotype and hormonal status of transgenic tobacco plants overexpressing the rolA gene of Agrobacterium rhizogenes T-DNA

The rolA gene of the TL-DNA of Agrobacterium rhizogenes Ri-plasmid plays a major role in establishing the hairy root syndrome in transgenic plants. Transgenic tobacco plants (Nicotiana tabacum L.) expressing constitutively the rolA gene under the transcriptional control of the 35S RNA promoter show pronounced phenotypical alterations. P35S-rolA transgenic tobacco plants are characterized by stunted growth, dark green wrinkled leaves with an altered length-to-width ratio, condensed influorescences, retarded onset of flowering, a reduced number of flowers and shortened styles. To investigate whether the pleiotropic alterations of growth and development are linked to an altered hormonal status we have compared the immunoreactive content of indole-3-acetic acid, cytokinins, abscisic acid, gibberellin and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) of seedlings and different tissues of P35S-rolA transgenic plants, transgenic plants expressing the rolA gene under control of its own phloem-specific promoter and wild-type plants. Multiple tissue-specific alterations of phytohormone concentrations are the consequence of rolA gene activity. Changes of phytohormonal content can explain part of the rolA-induced phenotypic alterations. Most strikingly, in young and fully developed leaves of rolA and P35S-rolA transgenic clones a 40-60% reduction of immunoreactive gibberellin A1 was found, as compared to wild-type leaves. Treatment of wild-type tobacco plants with inhibitors of gibberellin biosynthesis phenotypic alterations similar to those of rolA transgenic plants. This suggests that the reduction of gibberellic acid content is indirectly but causally involved in rolA-induced alterations of stem elongation and planar leaf blade growth.

A functional analysis of T-DNA gene 6b: the fine tuning of cytokinin effects on shoot development

The physiological function in planta of T-DNA gene 6b was studied under various experimental conditions. For this purpose the coding region of gene 6b was cloned behind the 1'-promoter of the TR-DNA to enhance expression of the gene product in transformed plant cells. Expression of the recombinant gene in leaf discs of Nicotiana tabacum altered the capacity for shoot formation of the discs, induced by exogenous (i.e. BAP in the growth medium or agrobacterial trans-zeatin produced under control of gene tzs) or endogenous cytokinins (i.e. isopentenyladenosine produced under control of T-DNA gene 4). The data obtained indicate a reduction of cytokinin activity within the plant cells by the product of T-DNA gene 6b.

Expression of an Agrobacterium Ti plasmid gene involved in cytokinin biosynthesis is regulated by virulence loci and induced by plant phenolic compounds

The nopaline-type Ti plasmid T37 of Agrobacterium tumefaciens carries two distinct genes that encode enzymes involved in cytokinin biosynthesis. In this report, we show that the level of expression of one of these genes was increased dramatically by culture conditions that increased the expression of Ti plasmid virulence genes, including coculture with plant cells or treatment with acetosyringone, a plant phenolic compound. When this nopaline-type Ti plasmid gene was introduced into Agrobacterium strains containing an octopine-type Ti plasmid, similar induction of expression by culture conditions was observed, and analysis of virulence region mutants demonstrated that this induction was under the control of the virA and virG regulatory loci. We further show that induction was strongly pH dependent in octopine strains but, under the conditions examined, pH independent in nopaline strains.

Immunoassay and ultrastructural localization of isopentenyladenine and related cytokinins using monoclonal antibodies

Two hybridoma cell lines, J40-IV-A1 and J40-IV-C4 were obtained from a fusion of spleen cells of Balb/c mice immunized against an isopentenyladenosine-bovine serum albumin conjugate with X63. Ag 8.653 myeloma cells. These hybrids secrete monoclonal antibodies of the immunoglobulin G (IgG) class and share high affinities and specificities to isopentenyladenine and isopentenyladenosine suitable for the detection of femtomole amounts of these cytokinins in plant extracts by enzyme-linked immunosorbent assay (ELISA). One of the monoclonal antibodies (J40-IV-C4) has been employed to localize isopentenyladenine immunoreactivity in a cytokinin-over-producing mutant of the moss, Physcomitrella patens. After fixation and embedding at low temperature, immunoreactivity was visualized in protonemal filaments of the moss mutant by the use of indirect immunogold labelling. In the mutant, the labelling was predominantly in the wall of the protonemal cells. Neither the wild-type nor control treatments showed any labelling. The signficance of these observations is discussed with respect to the applicability of immunocytochemical techniques for the localization of low-molecular-weight compounds in plant tissue.

A quantitative fluorescence enzyme immunoassay for plant cytokinins

An enzyme-linked immunosorbent assay (ELISA) which used 4-methylumbelliferyl phosphate as an enzyme substrate was used to quantify two plant cytokinins. This assay detected as little as 0.03 pmol (approximately 10 pg) of cytokinin in microplate wells coated with a cytokinin-ovalbumin conjugate. The method measured competition between free cytokinin and the bound conjugate for reaction with monoclonal anticytokinin antibodies and used a standard curve prepared by use of known amounts of free cytokinin to quantify hormone levels in unknown samples. Standard curves which consisted of logit/log plots of fluorescence units versus picomoles of competing cytokinin measured from 0.03 to 256 pmol (approximately 10-85,000 picograms) of zeatin riboside (ZR) or isopentenyl adenosine. The fluorescence ELISA was compared with radioimmunoassay for the quantification of ZR in wheat (Triticum aestivum L., cultivar Stephens) seed samples. This fluorescence ELISA method is recommended for use in combination with a fractionation method, such as HPLC, to quantify cytokinins present in plant extracts.

Changes in membrane permeability and mineral, phytohormone and polypeptide composition in rice suspension cells during growth and under the influence of the growth retardant tetcyclacis

The plant growth retardant tetcyclacis inhibits cell division growth in rice suspension cultures at concentrations above 10(-6) M. Tracer experiments with rice cells revealed that tetcyclacis reduced the incorporation of mevalonic acid into terpenoids after 30 min, the uptake of leucine, uridine and thymidine after 2 h and their incorporation into the corresponding macromolecules after 3-7 h. The changes in membrane permeability concluded to have been caused by an influence on phytosterol biosynthesis are probably also the explanation for alterations of tetcyclacis-treated cells in the content of macro- and microelements.As shown by immunoassay, tetcyclacis did not modify the levels of endogenous gibberellins (Grossmann et al. 1985), cytokinins and indole acetic acid during a growth cycle of 15 d. However, a clear rise in the abscisic acid (ABA) level occurred during the first 5 d of treatment. In untreated cells such a rise coincided only with the aging of the cell culture in the stationary growth phase. Investigations of the cell polypeptide pattern using sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed that the ABA increase following tetcyclacis treatment seems not to be a consequence of advanced cell aging.

Mass-spectrometric quantification of cytokinin nucleotides and glycosides in tobacco crown-gall tissue

the cytokinins of tobacco crown-gall tissue have been analysed by quantitative mass spectrometry using (2)H2-labelled cytokinin riboside 5'-monophosphates and (15)N4-labelled cytokinin glycosides as internal standards. The principal endogenous cytokinin of this tissue is zeatin riboside 5'-monophosphate. The biologically inactive 7-glucoside of zeatin is the most abundant basic cytokinin in the tissue. These findings expose the limitations of previously reported analyses of similar tissues, which were restricted to biologically active basic cytokinins. The present study demonstrates that the endogenous cytokinins of tobacco crowngall tissue show a clear correspondence to the range of metabolites formed when exogenous cytokinins are supplied to nontumorous tobacco cells.

The T-region of Ti plasmids codes for an enzyme synthesizing indole-3-acetic acid

Gene 2 from the T region of Ti plasmids appears to be expressed both in eucaryotic and in procaryotic systems. In transformed plant cells it participates in auxin-controlled growth and differentiation, and in bacteria it is expressed into a defined protein of Mr 49000. We investigated the possibility that it codes for an enzyme involved in auxin biosynthesis. Only extracts from Escherichia coli cells expressing gene 2 hydrolyzed indole-3-acetamide into a substance which was unambiguously identified as indole-3-acetic acid. The same reaction was found in Agrobacteria containing gene 2, but not in strains lacking the gene. Extracts from tobacco crown gall cells, but not from non-transformed cells, showed the same enzyme activity, and the reaction product was also identified as indole-3-acetic acid. The results indicate that gene 2 of the T region, which participates in tumorous growth of plant cells, codes both in bacteria and in plants for an amidohydrolase involved in the biosynthesis of the plant hormone indole-3-acetic acid.

Isolation and quantitation of isopentenyladenosine in an anise cell culture by single-ion monitoring, radioimmunoassay and bioassay

Using three different techniques, isopentenyladenosine was identified and quantitated in an anise cell line (Pimpinella anisum L.), growing on a medium without cytokinin. A method to quantitate cytokinins was developed which utilizes extraction of cytokinins in the presence of a deuterated reference compound and subsequent quantitation of the cytokinins by single-ion monitoring on a gas chromatography-mass spectrometry system. The results were compared with those obtained by radioimmunoassay as well as a bioassay. Quantitations by gas chromatography-mass spectrometry and radioimmunoassay correlated well, whereas the estimates by the bioassay gave considerably lower values.

Isolation and identification of a new, naturally occurring cytokinin (6-benzylaminopurineriboside) from an anise cell culture (Pimpinella anisum L.)

A new, naturally occurring cytokinin was isolated from a cell culture of anise (Pimpinella anisum L.). Its structure was determined as 6-benzylaminopurine riboside by the use of gas chromatography and mass spectrometry. Quantitation of this new plant hormone was accomplished by single-ion-monitoring measurements.

Cytoplasmic male sterility in barley : 12. Associations between disease resistance and restoration of msm1 fertility in the wild progenitor of barley

The associations between seedling reactions to three fungal pathogens (Puccinia hordei, Pyrenophora teres, and Rhynchosporium secalis) or between adult plant reaction to Rh. secalis and the male fertility restoration ability of msml cytoplasm were studied in about 100 accessions of Hordeum spontaneum. Significant differences in the severity of infection between classes of restoration ability were observed with two cultures of P. hordei (751 and 7,649) and with Rh. secalis on adult plants in the field. The cultures 7,432, 751 and 7,649 of P. hordei showed significant positive correlations between infection severity and restoration percentage. The culture 7,620 of P. hordei displayed a significant negative correlation. Rh. secalis (cultures 492A and 531 combined) on seedlings and the natural field infection in the 1978 season showed significant positive correlations. The accession class with the partial restoration ability of 0.1 to 5.0% of the four arbitrary classes (0.0, 0.1-5.0, 5.1-55.0, and 90.1-100%), displayed the lowest mean severity of infection in six of the eleven tests. Some frequently appearing races of these pathogens may operate as selective agents in the maintenance of restoration ability in the original spontaneum populations.

Radioimmunoassay for pmol-quantities of indole-3-acetic acid for use with highly stable [(125)I]- and [ (3)H]IAA derivatives as radiotracers

A radioimmunoassay for the detection of as little as 0.5-1 pmol indole-3-acetic acid (IAA) in unpurified or partially purified plant extracts is described. The assay makes use of either IAA[(125)I]tyrosine methyl ester or [(3)H]IAA methyl ester as radioactive antigens and IAA methyl ester as the assay standard (measuring range: 1-200 pmol). Levels of extractable IAA in a number of biological samples have been estimated.

Levels of indole-3-acetic acid in intact and decapitated coleoptiles as determined by a specific and highly sensitive solid-phase enzyme immunoassay

A specific solid-phase enzyme immunoassay for the detection of as little as 3-4 pg of indole-3-acetic acid (IAA) is described. The assay involves minimal procedural efforts and requires only standard laboratory equipment. Up to 50 samples in triplicate, processed simultaneously, can be assayed and evaluated in 2.5 h. As little as 1 mg oat coleoptile tissue is sufficient for a quantitative IAA analysis and little or no extract purification is necessary. Using this assay, levels of IAA have been determined in coleoptiles of maize and oat. The distribution of IAA within single coleoptiles was quantitated and the production of IAA during the regeneration of the physiological tip in Avena coleoptiles was investigated. The changes in levels of IAA and other major phytohormones were quantitated during the growth of oat coleoptiles.