Two Auxinic Herbicides Affect Brassica napus Plant Hormone Levels and Induce Molecular Changes in Transcription

With the introduction of the new auxinic herbicide halauxifen-methyl into the oilseed rape (Brassica napus) market, there is a need to understand how this new molecule interacts with indigenous plant hormones (e.g., IAA) in terms of crop response. The aim of this study was to investigate the molecular background by using different growth conditions under which three different auxinic herbicides were administered. These were halauxifen-methyl (Hal), alone and together with aminopyralid (AP) as well as picloram (Pic). Three different hormone classes were determined, free and conjugated indole-3-acetic acid (IAA), aminocyclopropane carboxylic acid (ACC) as a precursor for ethylene, and abscisic acid (ABA) at two different temperatures and growth stages as well as over time (2–168 h after treatment). At 15 °C growth temperature, the effect was more pronounced than at 9 °C, and generally, the younger leaves independent of the developmental stage showed a larger effect on the alterations of hormones. IAA and ACC showed reproducible alterations after auxinic herbicide treatments over time, while ABA did not. Finally, a transcriptome analysis after treatment with two auxinic herbicides, Hal and Pic, showed different expression patterns. Hal treatment leads to the upregulation of auxin and hormone responses at 48 h and 96 h. Pic treatment induced the hormone/auxin response already after 2 h, and this continued for the other time points. The more detailed analysis of the auxin response in the datasets indicate a role for GH3 genes and genes encoding auxin efflux proteins. The upregulation of the GH3 genes correlates with the increase in conjugated IAA at the same time points and treatments. Also, genes for were found that confirm the upregulation of the ethylene pathway.

The chemical compound 'Heatin' stimulates hypocotyl elongation and interferes with the Arabidopsis NIT1-subfamily of nitrilases

Temperature passively affects biological processes involved in plant growth. Therefore, it is challenging to study the dedicated temperature signalling pathways that orchestrate thermomorphogenesis, a suite of elongation growth-based adaptations that enhance leaf-cooling capacity. We screened a chemical library for compounds that restored hypocotyl elongation in the pif4-2-deficient mutant background at warm temperature conditions in Arabidopsis thaliana to identify modulators of thermomorphogenesis. The small aromatic compound 'Heatin', containing 1-iminomethyl-2-naphthol as a pharmacophore, was selected as an enhancer of elongation growth. We show that ARABIDOPSIS ALDEHYDE OXIDASES redundantly contribute to Heatin-mediated hypocotyl elongation. Following a chemical proteomics approach, the members of the NITRILASE1-subfamily of auxin biosynthesis enzymes were identified among the molecular targets of Heatin. Our data reveal that nitrilases are involved in promotion of hypocotyl elongation in response to high temperature and Heatin-mediated hypocotyl elongation requires the NITRILASE1-subfamily members, NIT1 and NIT2. Heatin inhibits NIT1-subfamily enzymatic activity in vitro and the application of Heatin accordingly results in the accumulation of NIT1-subfamily substrate indole-3-acetonitrile in vivo. However, levels of the NIT1-subfamily product, bioactive auxin (indole-3-acetic acid), were also significantly increased. It is likely that the stimulation of hypocotyl elongation by Heatin might be independent of its observed interaction with NITRILASE1-subfamily members. However, nitrilases may contribute to the Heatin response by stimulating indole-3-acetic acid biosynthesis in an indirect way. Heatin and its functional analogues present novel chemical entities for studying auxin biology.

Different Roles of Auxins in Somatic Embryogenesis Efficiency in Two Picea Species

The effects of auxins 2,4-D (2,4-dichlorophenoxyacetic acid), NAA (1-naphthaleneacetic acid) or picloram (4-amino-3,5,6-trichloropicolinic acid; 9 µM) and cytokinin BA (benzyloadenine; 4.5 µM) applied in the early stages of somatic embryogenesis (SE) on specific stages of SE in Picea abies and P. omorika were investigated. The highest SE initiation frequency was obtained after 2,4-D application in P. omorika (22.00%) and picloram application in P. abies (10.48%). NAA treatment significantly promoted embryogenic tissue (ET) proliferation in P. abies, while 2,4-D treatment reduced it. This reduction was related to the oxidative stress level, which was lower with the presence of NAA in the proliferation medium and higher with the presence of 2,4-D. The reduced oxidative stress level after NAA treatment suggests that hydrogen peroxide (H2O2) acts as a signalling molecule and promotes ET proliferation. NAA and picloram in the proliferation medium decreased the further production and maturation of P. omorika somatic embryos compared with that under 2,4-D. The quality of the germinated P. abies embryos and their development into plantlets depended on the auxin type and were the highest in NAA-originated embryos. These results show that different auxin types can generate different physiological responses in plant materials during SE in both spruce species.

Exogenous Auxin Induces Transverse Microtubule Arrays Through TRANSPORT INHIBITOR RESPONSE1/AUXIN SIGNALING F-BOX Receptors

Auxin plays a central role in controlling plant cell growth and morphogenesis. Application of auxin to light-grown seedlings elicits both axial growth and transverse patterning of the cortical microtubule cytoskeleton in hypocotyl cells. Microtubules respond to exogenous auxin within 5 min, although repatterning of the array does not initiate until 30 min after application and is complete by 2 h. To examine the requirements for auxin-induced microtubule array patterning, we used an Arabidopsis (Arabidopsis thaliana) double auxin f-box (afb) receptor mutant, afb4-8 afb5-5, that responds to conventional auxin (indole-3-acetic acid) but has a strongly diminished response to the auxin analog, picloram. We show that 5 µm picloram induces immediate changes to microtubule density and later transverse microtubule patterning in wild-type plants, but does not cause microtubule array reorganization in the afb4-8 afb5-5 mutant. Additionally, a dominant mutant (axr2-1) for the auxin coreceptor AUXIN RESPONSIVE2 (AXR2) was strongly suppressed for auxin-induced microtubule array reorganization, providing additional evidence that auxin functions through a transcriptional pathway for transverse patterning. We observed that brassinosteroid application mimicked the auxin response, showing both early and late microtubule array effects, and induced transverse patterning in the axr2-1 mutant. Application of auxin to the brassinosteroid synthesis mutant, diminuto1, induced transverse array patterning but did not produce significant axial growth. Thus, exogenous auxin induces transverse microtubule patterning through the TRANSPORT INHIBITOR 1/AUXIN F-BOX (TIR1/AFB) transcriptional pathway and can act independently of brassinosteroids.

The pea branching RMS2 gene encodes the PsAFB4/5 auxin receptor and is involved in an auxin-strigolactone regulation loop

Strigolactones (SLs) are well known for their role in repressing shoot branching. In pea, increased transcript levels of SL biosynthesis genes are observed in stems of highly branched SL deficient (ramosus1 (rms1) and rms5) and SL response (rms3 and rms4) mutants indicative of negative feedback control. In contrast, the highly branched rms2 mutant has reduced transcript levels of SL biosynthesis genes. Grafting studies and hormone quantification led to a model where RMS2 mediates a shoot-to-root feedback signal that regulates both SL biosynthesis gene transcript levels and xylem sap levels of cytokinin exported from roots. Here we cloned RMS2 using synteny with Medicago truncatula and demonstrated that it encodes a putative auxin receptor of the AFB4/5 clade. Phenotypes similar to rms2 were found in Arabidopsis afb4/5 mutants, including increased shoot branching, low expression of SL biosynthesis genes and high auxin levels in stems. Moreover, afb4/5 and rms2 display a specific resistance to the herbicide picloram. Yeast-two-hybrid experiments supported the hypothesis that the RMS2 protein functions as an auxin receptor. SL root feeding using hydroponics repressed auxin levels in stems and down-regulated transcript levels of auxin biosynthesis genes within one hour. This auxin down-regulation was also observed in plants treated with the polar auxin transport inhibitor NPA. Together these data suggest a homeostatic feedback loop in which auxin up-regulates SL synthesis in an RMS2-dependent manner and SL down-regulates auxin synthesis in an RMS3 and RMS4-dependent manner.

Induction of somatic embryogenesis in explants of shoot cultures established from adult Eucalyptus globulus and E. saligna × E. maidenii trees

A reproducible procedure for induction of somatic embryogenesis (SE) from adult trees of Eucalyptus globulus Labill. and the hybrid E. saligna Smith × E. maidenii has been developed for the first time. Somatic embryos were obtained from both shoot apex and leaf explants of all three genotypes evaluated, although embryogenic frequencies were significantly influenced by the species/genotype, auxin and explant type. Picloram was more efficient for somatic embryo induction than naphthaleneacetic acid (NAA), with the highest frequency of induction being obtained in Murashige and Skoog medium containing 40 µM picloram and 40 mg l(-1) gum Arabic, in which 64% of the shoot apex explants and 68.8% of the leaf explants yielded somatic embryos. The embryogenic response of the hybrid was higher than that of the E. globulus, especially when NAA was used. The cultures initiated on picloram-containing medium consisted of nodular embryogenic structures surrounded by a mucilaginous coating layer that emerged from a watery callus developed from the initial explants. Cotyledonary somatic embryos were differentiated after subculture of these nodular embryogenic structures on a medium lacking plant growth regulators. Histological analysis confirmed the bipolar organization of the somatic embryos, with shoot and root meristems and closed procambial tissue that bifurcated into small cotyledons. The root pole was more differentiated than the shoot pole, which appeared to be formed by a few meristematic layers. Maintenance of the embryogenic lines by secondary SE was attained by subculturing individual cotyledonary embryos or small clusters of globular and torpedo embryos on medium with 16.11 µM NAA at 4- to 5-week intervals. Somatic embryos converted into plantlets after being transferred to liquid germination medium although plant regeneration remained poor.

The transcriptional regulator BBX24 impairs DELLA activity to promote shade avoidance in Arabidopsis thaliana

In response to canopy shade, plant vegetative structures elongate to gain access to light. However, the mechanism that allows a plastic transcriptional response to canopy shade light is not fully elucidated. Here we propose that the activity of PIF4, a key transcription factor in the shade signalling network, is modulated by the interplay between the BBX24 transcriptional regulator and DELLA proteins, which are negative regulators of the gibberellin (GA) signalling pathway. We show that GA-related targets are enriched among genes responsive to BBX24 under shade and that the shade-response defect in bbx24 mutants is rescued by a GA treatment that promotes DELLA degradation. BBX24 physically interacts with DELLA proteins and alleviates DELLA-mediated repression of PIF4 activity. The proposed molecular mechanism provides reversible regulation of the activity of a key transcription factor that may prove especially relevant under fluctuating light conditions.

Enhanced biosynthesis of withanolides by elicitation and precursor feeding in cell suspension culture of Withania somnifera (L.) Dunal in shake-flask culture and bioreactor

The present study investigated the biosynthesis of major and minor withanolides of Withania somnifera in cell suspension culture using shake-flask culture and bioreactor by exploiting elicitation and precursor feeding strategies. Elicitors like cadmium chloride, aluminium chloride and chitosan, precursors such as cholesterol, mevalonic acid and squalene were examined. Maximum total withanolides detected [withanolide A (7606.75 mg), withanolide B (4826.05 mg), withaferin A (3732.81 mg), withanone (6538.65 mg), 12 deoxy withanstramonolide (3176.63 mg), withanoside IV (2623.21 mg) and withanoside V (2861.18 mg)] were achieved in the combined treatment of chitosan (100 mg/l) and squalene (6 mM) along with 1 mg/l picloram, 0.5 mg/l KN, 200 mg/l L-glutamine and 5% sucrose in culture at 4 h and 48 h exposure times respectively on 28^th day of culture in bioreactor. We obtained higher concentrations of total withanolides in shake-flask culture (2.13-fold) as well as bioreactor (1.66-fold) when compared to control treatments. This optimized protocol can be utilized for commercial level production of withanolides from suspension culture using industrial bioreactors in a short culture period.

Diurnal dependence of growth responses to shade in Arabidopsis: role of hormone, clock, and light signaling

We investigated the diurnal dependence of the hypocotyl-growth responses to shade under sunlight-night cycles in Arabidopsis thaliana. Afternoon shade events promoted hypocotyl growth, while morning shade was ineffective. The lhy-D, elf3, lux, pif4 pif5, toc1, and quadruple della mutants retained the response to afternoon shade and the lack of response to morning shade while the lhy cca1 mutant responded to both morning and afternoon shade. The phyB mutant, plants overexpressing the multidrug resistance-like membrane protein ABCB19, and the iaa17/axr3 loss-of-function mutant failed to respond to shade. Transient exposure of sunlight-grown seedlings to synthetic auxin in the afternoon caused a stronger promotion of hypocotyl growth than morning treatments. The promotion of hypocotyl growth by afternoon shade or afternoon auxin required light perceived by phytochrome A or cryptochromes during the previous hours of the photoperiod. Although the ELF4-ELF3-LUX complex, PIF4, PIF5, and DELLA are key players in the generation of diurnal hypocotyl-growth patterns, they exert a minor role in the control of the diurnal pattern of growth responses to shade. We conclude that the strong diurnal dependency of hypocotyl-growth responses to shade relates to the balance between the antagonistic actions of LHY-CCA1 and a light-derived signal.

Compositional changes in cell wall polysaccharides from apple fruit callus cultures modulated by different plant growth regulators

The cell wall composition of apples callus cultures showed changes in the presence of 5 mg l(-1) of three different plant growth regulators (PGRs), namely picloram, abscisic acid and gibberellic acid. Although the structural functions of cell walls do not generally allow for pronounced variations of the total pectin and matrix glycan content, this work provides evidence that the addition of these plant growth regulators can rule, at least partly, cell wall metabolism in apple callus cultures. The chelator- and carbonate-extracts always had the analytical characteristics of pectins, with high proportions of uronic acids, arabinose and galactose as the main monosaccharides, and a significant proportion of rhamnose, but the cross-linking glycan fractions were still rich in RG-I-like material. The application of PGRs produced shifts of uronic acid and neutral sugars between fractions. Arabinose was the neutral sugar exhibiting more variations in apple callus cell wall. Picloram and abscisic acid produced an increase of the uronic acid contents of the cell walls. The AIRs obtained from calluses treated with different PGRs did not show large amounts of high molecular weight products, as determined by size-exclusion chromatography. For the carbonate-extract only the callus treated with picloram displayed two separated peaks for products of different molecular weights. The chromatographic profiles for the 4% KOH-extract displayed two peaks for all the treatments, one very sharp with high molecular weight, and another one wider of smaller molecular weight, whereas the difference between treatments can only be appraised through the areas of the peaks. This is the first report on cell wall composition from fruit calluses supplemented with different PGRs.

Agrobacterium-mediated transformation of durum wheat (Triticum turgidum L. var. durum cv Stewart) with improved efficiency

An efficient Agrobacterium-mediated durum wheat transformation system has been developed for the production of 121 independent transgenic lines. This improved system used Agrobacterium strain AGL1 containing the superbinary pGreen/pSoup vector system and durum wheat cv Stewart as the recipient plant. Acetosyringone at 400 microM was added to both the inoculation and cultivation medium, and picloram at 10 mg l(-1) and 2 mg l(-1) was used in the cultivation and induction medium, respectively. Compared with 200 microM in the inoculation and cultivation media, the increased acetosyringone concentration led to significantly higher GUS (beta-glucuronidase) transient expression and T-DNA delivery efficiency. However, no evident effects of acetosyringone concentration on regeneration frequency were observed. The higher acetosyringone concentration led to an improvement in average final transformation efficiency from 4.7% to 6.3%. Furthermore, the concentration of picloram in the co-cultivation medium had significant effects on callus induction and regeneration. Compared with 2 mg l(-1) picloram in the co-cultivation medium, increasing the concentration to 10 mg l(-1) picloram resulted in improved final transformation frequency from 2.8% to 6.3%, with the highest frequency of 12.3% reached in one particular experiment, although statistical analysis showed that this difference in final transformation efficiency had a low level of significance. Stable integration of foreign genes, their expression, and inheritance were confirmed by Southern blot analyses, GUS assay, and genetic analysis. Analysis of T(1) progeny showed that, of the 31 transgenic lines randomly selected, nearly one-third had a segregation ratio of 3:1, while the remainder had ratios typical of two or three independently segregating loci.

Somatic embryogenesis in peach palm using the thin cell layer technique: induction, morpho-histological aspects and AFLP analysis of somaclonal variation

BACKGROUND AND AIMS

The thin cell layer (TCL) technique is based on the use of very small explants and has allowed enhanced in vitro morphogenesis in several plant species. The present study evaluated the TCL technique as a procedure for somatic embryo production and plantlet regeneration of peach palm.

METHODS

TCL explants from different positions in the shoot apex and leaf sheath of peach palm were cultivated in MS culture medium supplemented with 0-600 microM Picloram in the presence of activated charcoal. The production of primary calli and embryogenic calli was evaluated in these different conditions. Histological and amplified fragment length polymorphism (AFLP) analyses were conducted to study in vitro morphogenetic responses and genetic stability, respectively, of the regenerated plantlets.

KEY RESULTS

Abundant primary callus induction was observed from TCLs of the shoot meristem in culture media supplemented with 150-600 microM Picloram (83-97%, respectively). The production of embryogenic calli depends on Picloram concentration and explant position. The best response observed was 43% embryogenic callus production from shoot meristem TCL on 300 microM Picloram. In maturation conditions, 34+/-4 somatic embryos per embryogenic callus were obtained, and 45.0+/-3.4% of these fully developed somatic embryos were converted, resulting in plantlets ready for acclimatization, of which 80% survived. Histological studies revealed that the first cellular division events occurred in cells adjacent to vascular tissue, resulting in primary calli, whose growth was ensured by a meristematic zone. A multicellular origin of the resulting somatic embryos arising from the meristematic zone is suggested. During maturation, histological analyses revealed bipolarization of the somatic embryos, as well as the development of new somatic embryos. AFLP analyses revealed that 92% of the regenerated plantlets were true to type. The use of TCL explants considerably improves the number of calli and somatic embryos produced in comparison with previously described protocols for in vitro regeneration of peach palm.

CONCLUSIONS

The present study suggests that the TCL somatic embryogenesis protocol developed is feasible, although it still requires further optimization for in vitro multiplication of peach palm, especially the use of similar explants obtained from adult palm trees.

Optimization of Agrobacterium-mediated transformation conditions in mature embryos of elite wheat

Immature embryos have been used frequently as target tissues in the genetical transformation of wheat. However, obtaining a large number of high quality immature embryos throughout the year is a laborious and delicate process, because of the need to cultivate the plants under controlled conditions. To circumvent this, we have employed mature embryos rather than immature ones as starter explants for Agrobacterium-mediated transformation of an elite wheat (Triticum aestivum L.) cultivar EM12. The neomycin phosphotransferase II, (npt II) and beta-glucuronidase (gus) genes were used as selectable and screenable marker genes, respectively, to assess and optimize the performance of T-DNA delivery. With the aid of an orthogonal design, the effect of four factors in combination on transfer DNA (T-DNA) delivery was studied. These factors were preculture duration, different kinds of inoculation, length of inoculation and co-culture condition. Optimal conditions for T-DNA delivery were obtained for mature embryos precultured for 14 days, followed by immersing in inoculation suspension with full strength Murashige and Skoog (MS) salts in darkness at 23-25 degrees C for 3 h, and then co-culturing with Agrobacterium under desiccating condition in the dark at 23-24 degrees C for 2-3 days. Complete analysis of transgene insertion demonstrated that the optimized method for Agrobacterium-mediated transformation of mature embryos of wheat was efficient and practicable.

Picloram resistance in transgenic tobacco expressing an anti-picloram scFv antibody is due to reduced translocation

Picloram resistance exhibited by transgenic tobacco (Nicotiana tabacum) plants expressing an anti-picloram single-chain variable fragment (scFv) antibody was investigated through the study of homozygous lines expressing the antibody. Dose-response bioassays, using foliar application of picloram, showed that these homozygous transgenic plants were resistant to at least 5 g of ai ha-1 picloram and grew normally to produce seed, whereas wild-type plants did not survive. Although these lines had improved resistance compared with those previously reported, significant improvements are still required to achieve field-level resistance. Uptake and translocation studies demonstrated that [14C]picloram translocation from treated leaves to the apical meristem was reduced in transgenic versus wild-type plants. The presence of [14C]picloram visualized by autoradiography and quantified by liquid scintillation spectrometry, demonstrated the distribution of more picloram in the treated leaf and less in the apical meristem of transgenic plants when compared to wild-type plants. No differences between transgenic and wild-type plants were found in the distribution of [14C]clopyralid, a herbicide with structural similarity to picloram as well as the same mechanism of action. No differences were found in the metabolism of [14C]picloram. Taken together, these results suggest that reduced translocation to the site of action is a major mechanism responsible for picloram resistance in tobacco plants expressing this anti-picloram antibody.

Visual selection and maintenance of the cell lines with high plant regeneration ability and low ploidy level in Dianthus acicularis by monitoring with flow cytometry analysis

Efficient plant regeneration system from cell suspension cultures was established in D. acicularis (2n=90) by monitoring ploidy level and visual selection of the cultures. The ploidy level of the cell cultures closely related to the shoot regeneration ability. The cell lines comprising original ploidy levels (2C+4C cells corresponding to DNA contents of G1 and G2 cells of diploid plant, respectively) showed high regeneration ability, whereas those containing the cells with 8C or higher DNA C-values showed low or no regeneration ability. The highly regenerable cell lines thus selected consisted of compact cell clumps with yellowish color and relatively moderate growth, suggesting that it is possible to select visually the highly regenerable cell lines with the original ploidy level. All the regenerated plantlets from the highly regenerable cell cultures exhibited normal phenotypes and no variations in ploidy level were observed by flow cytometry (FCM) analysis.

Carbon source dependent somatic embryogenesis and plant regeneration in cotton, Gossypium hirsutum L. cv. SVPR2 through suspension cultures

Highly reproducible and simple protocol for cotton somatic embryogenesis is described here by using different concentrations of maltose, glucose, sucrose and fructose. Maltose (30 g/l) is the best carbon source for embryogenic callus induction and glucose (30 g/l) was suitable for induction, maturation of embryoids and plant regeneration. Creamy white embryogenic calli of hypocotyl explants were formed on medium containing MS basal salts, myo-inositol (100 mg/l), thiamine HCI (0.3 mg/l), picloram (0.3 mg/l), Kin (0.1 mg/l) and maltose (30 g/l). During embryo induction and maturation, accelerated growth was observed in liquid medium containing NH3NO4 (1 g/l), picloram (2.0 mg/l), 2 ip (0.2 mg/l), Kin (0.1 mg/l) and glucose (30 g/l). Before embryoid induction, large clumps of embryogenic tissue were formed. These tissues only produced viable embryoids. Completely matured somatic embryos were germinated successfully on the medium fortified with MS salts, myo-inositol (50 mg/l), thiamine HCl (0.2 mg/l), GA3 (0.2 mg/l), BA (1.0 mg/l) and glucose (30 g/l). Compared with earlier reports, 65% of somatic embryo germination was observed. The abnormal embryo formation was highly reduced by using glucose (30 g/l) compared to other carbon sources. The regenerated plantlets were fertile but smaller in height than the seed derived control plants.

Increasing expression of an anti-picloram single-chain variable fragment (ScFv) antibody and resistance to picloram in transgenic tobacco (Nicotiana tabacum)

Systematic research involving four chimeric gene constructions designed to express the same anti-picloram single-chain variable fragment (scFv) antibody is described. Agrobacterium-mediated transformation produced at least 25 transgenic tobacco plants with each of these, and the number of T-DNA loci in each plant was determined using kanamycin-resistance segregation assays. The relative amounts of active and total scFv in each plant were evaluated using quantitative enzyme-linked immunosorbent assay and immunoblot technologies, respectively. No significant differences in scFv activity were found among the four groups of single-locus plants, although the 35S/M construct was found to produce significantly more total anti-picloram scFv than the other three constructs. A dose-response bioassay involving T(1) seedlings from several of the highest expressers of active scFv demonstrated resistance to a constant exposure of picloram at 5 x 10(-)(8) M. Other approaches for increasing antibody-based herbicide resistance are discussed, as further improvements are needed before practical application of this technology.

Hemoglobin promotes somatic embryogenesis in peanut cultures

Critical parameters influencing somatic embryogenesis include growth regulators and oxygen supply. Consequently, the present investigation has focused on optimization of a somatic embryogenic system for peanut (Arachis hypogaea L.) through media supplementation with the auxin, picloram. The latter at 30 mg L(-1) was optimal for inducing regeneration of somatic embryos from cultured explants of zygotic embryos. In contrast, somatic embryogenesis did not occur in the absence of this growth regulator. An assessment has also been made of the beneficial effect on somatic embryogenesis and plant regeneration of the commercial hemoglobin (Hb) solution, Erythrogen. Hemoglobin at 1:50 and 1:100 (v:v) stimulated increases in mean fresh weight (up to a maximum of 57% over control), mean number of explants producing somatic embryos (15%) and mean number of somatic embryos per explant (29%).

Evaluation of haemoglobin (erythrogen): for improved somatic embryogenesis and plant regeneration in cotton (Gossypium hirsutum L. cv. SVPR 2)

Somatic embryogenesis in cotton (Gossypium hirsutum L.) is accelerated when the plant regeneration medium is supplemented with haemoglobin (erythrogen). In cotton SVPR 2 lines, a higher frequency of embryoid formation was observed when the medium contained 400 mg/l haemoglobin. Fresh weight of the callus, rate of embryoid induction, number of embryoids formed and the percentage of plant regeneration from somatic embryos were increased. Among the two different cultivars tested, MCU 11 showed no response to the presence of haemoglobin when compared to SVPR 2, and embryogenic callus formation was completely absent in the former. Medium containing MS salts, 100 mg/l myo-inositol , 0.3 mg/l thiamine-HCL, 0.3 mg/l Picloram (PIC), 0.1 mg/l kinetin and 400 mg/l haemoglobin effected a better response with respect to embryogenic callus induction. After 8 weeks of culture, a high frequency of embryoid induction was observed on medium containing MS basal salts, 100 mg/l myo-inositol, 0.3 mg/l PIC , 0.1 mg/l isopentenyl adenine, 1.0 g/l NH4NO3 and 400 mg/l haemoglobin. Plant regeneration was observed in 75.8% of the mature somatic embryos, and whole plant regeneration was achieved within 6-7 months of culture. The regenerated plantlets were fertile and similar to in vivo-grown, seed-derived plants except that they were phenotypically smaller. A positive influence of haemoglobin was observed at concentrations up to 400 mg/l at all stages of somatic embryogenesis. The increase in the levels of antioxidant enzyme activities, for example superoxide dismutase and peroxidase, indicated the presence of excess oxygen uptake and the stressed condition of the plant tissues that arose from haemoglobin supplementation. This increased oxygen uptake and haemoglobin-mediated stress appeared to accelerate somatic embryogenesis in cotton.

Inheritance of resistance to clopyralid and picloram in yellow starthistle (Centaurea solstitialis L.) is controlled by a single nuclear recessive gene

The noxious weed yellow starthistle (Centaurea solstitialis L.) can be controlled effectively at the seedling stage with foliar application of the auxinic herbicides picloram or clopyralid. Although resistance to these herbicides is rare, a yellow starthistle biotype resistant to picloram and cross-resistant to clopyralid was observed in 1989 near Dayton, WA, in a pasture that had been subjected to intensive picloram selective pressure. Our objective was to determine the mode of inheritance for this resistance trait. Transmission of the resistant phenotype was monitored in reciprocal F(1) crosses between susceptible (SCI) and resistant (RDW) plants, their testcross and pseudo-F(2) progeny. Progeny from all crosses, as well as RDW and SCI seedlings of original populations, were sprayed with picloram or clopyralid to distinguish between susceptible and resistant individuals. All F(1) progeny were susceptible to both herbicides, indicating that the resistance trait was of nuclear origin and recessive in nature. Segregation of the resistant phenotype among pseudo-F(2) and testcross progeny of F(1) genotypes demonstrated monofactorial inheritance (P >.25) for resistance to both herbicides. The conclusion that resistance is conferred by a single recessive allele is consistent with the observation that no other picloram-resistant yellow starthistle populations have been identified in the area since picloram selection pressure was abated.

Proteome-level differences between auxinic-herbicide-susceptible and -resistant wild mustard (Sinapis arvensis L.)

To identify proteins that may be involved in mediating auxinic herbicide resistance (i.e., resistance to dicamba, picloram, 2,4-D), we compared the proteomes of an auxinic-herbicide-susceptible (S) and -resistant (R) wild mustard (Sinapis arvensis L.) biotype at different developmental stages. Using two-dimensional electrophoresis and mass spectrometry, we identified 11 seedling and leaf proteins that showed reproducible differences in expression between the S and the R wild mustard biotype following application of dicamba. Our proteome-level studies revealed the increased expression of the enzyme peptidylprolyl cis-trans isomerase (PPIase), which has recently been implicated in auxin signal transduction. Juglone, an inhibitor of PPIase, interfered with the normal ability of R seeds to germinate in the presence of dicamba, whereas S seeds did not germinate in the presence of dicamba or dicamba plus juglone. When R and S plants (3-4 leaf stage) were treated with dicamba, S showed typical auxinic herbicide effects (e.g., epinasty) whereas R did not. However, the concomitant application of dicamba and juglone to greenhouse-grown R plants produced morphological changes that were consistent with known auxinic-herbicide-induced symptoms. This is the first report suggesting the potential involvement of differential expression of PPIase in mediating auxinic herbicide resistance.

Regeneration of flowering plants from difficile lily protoplasts by means of a nurse culture

The regeneration of difficile lily protoplasts isolated from suspension cells of the Oriental hybrid lily ( Lilium L.) cultivars Casablanca, Siberia and Acapulco was achieved by using the nurse-culture method. The divided protoplasts grew into colonies with nurse cells that have no regeneration ability, and developed to visible calli on a medium containing picloram. Many plantlets were formed on the calli after transfer of the proliferated calli to hormone-free medium. We were able to transplant the plantlets to soil in pots without acclimatization, and the plantlets grew in a greenhouse until flowering 2 years later.

Electrophoretic monitoring of pollutants: effect of cations and organic compounds on protein interactions monitored by native gel electrophoresis

We describe how the interaction between actin and its protein ligands can be used to evaluate the presence of certain metal (Cd, Cu, Hg, Zn) ions and organic compounds (2,4-dioxin or Picloram) which are common components of environmental pollution. The assay detects the high-affinity binding of actin to actin-binding proteins (ABPs), cofilin or DNase I. The actin-ABP complex was analyzed using native polyacrylamide gel electrophoresis and quantified by scanning densitometry. These proteins are widely distributed in animals and plant cells. The assay involves allowing the proteins to form an actin-ABP complex into which increasing amounts of pollutants are titrated. Thus, the assay directly tests for inhibition of protein-protein interaction. It is sensitive to common pollutants using concentration ranges over which they are known to exert a biological toxicity. A convenient feature of the assay is the fact that all the proteins can be stored in freeze-dried form, and can be purchased commercially. We suggest that if this molecular assay is sensitive to a wide range of environmental pollutants, it could be used as a rapid and convenient assay of the environment in combination with currently available tests.

Comparison of flash-induced light-scattering transients and proton efflux from auxinic-herbicide resistant and susceptible wild mustard protoplasts: a possible role for calcium in mediating auxinic herbicide resistance

Comparison of flash-induced light-scattering signals from protoplasts of auxinic herbicide-resistant ('R') and -susceptible ('S') wild mustard biotypes suggest that ATP-dependent activity manifested as a conformational change differs between the biotypes. The signal obtained from R protoplasts is unaffected by 50 microM picloram, an auxin analogue. In comparison, the signal amplitude from the S protoplasts decreases 40% in 20 microM picloram and is abolished in 50 microM picloram. Signal amplitude from the R protoplasts can be decreased by simultaneous incubation with 50 microM picloram and 50 microM verapamil, a calcium channel blocker. Incubation of the S protoplasts with the calcium ionophore A23187 in the presence of 0.5 mM calcium reduced the inhibitory effect of picloram. Absorbance spectrophotometry using acridine orange as a pH indicator suggests that picloram affects the proton flux in the S biotype only. Based on these results, we hypothesize that picloram affects the calcium and hydrogen dynamics in the S biotype. Because the scattering characteristics of S protoplasts incubated with picloram can be nearly reproduced in the R protoplasts by simultaneous incubation with picloram and verapamil, calcium may have a significant role in modulating auxinic herbicide resistance. To our knowledge, this is the first report to implicate such a role for calcium.

Identification of the hepatic cytochrome P-450 isozymes induced and decreased by picloram

Microsomes from male rats treated with picloram (100 mg/kg/day) for 7 days showed a 48% decrease in 16 alpha-hydroxylase activity when incubated with (4-14C) androstenedione. These data are consistent with the assertion that picloram decreases the titer of hepatic male specific cytochrome P-450h. Several lines of evidence suggested that picloram is an inducer of hepatic cytochrome P-450 in male rats. First, SDS polyacrylamide gel electrophoresis revealed an intensified hepatic microsomal polypeptide (MW 54,000) following picloram pretreatment. This polypeptide co-migrated with protein bands which were correspondingly intensified after pretreatment with known inducers of cytochrome P-450d (3-methylcholanthrene and isosafrole). Second, no increase in the binding of metyrapone to picloram treated microsomes was noted compared with controls, suggesting no increase in phenobarbital-inducible forms of cytochrome P-450. Third, hepatic microsomes from picloram treated rats activated 2-amino-3-methylimidazo [4,5-f] quinoline (a cytochrome P-450d mediated catalysis) causing a 5-fold increase in the number of induced Salmonella typhimurium TA98 revertant colonies formed compared with control microsomes. Fourth, the binding of n-octylamine to hepatic microsomes from picloram-treated rats showed, like microsomes from 3-methylcholanthrene-treated rats, an increase in the proportion of high-spin cytochrome P-450 present. Cytochrome P-450d is known to be a high spin haemoprotein.

Effects of picloram on xenobiotic biotransformation in rat liver

1. The effect of picloram on model xenobiotic substrate biotransformation in vivo was studied in female and male rat liver. 2. Treatment with picloram had little effect on epoxide hydratase and glutathione S-transferase activity, but caused a dose-dependent increase in ethoxyresorufin-O-deethylase activity and a concomitant decrease in aldrin epoxidase activity in male rats. 3. Treatment of male rats with equivalent doses of 2-acetylaminofluorene, 2-amino-anthracene and picloram induced ethoxyresorufin-O-deethylase activity to the same degree. 4. Treatment of female rats with picloram resulted in dose-dependent increases in ethoxyresorufin and ethoxycoumarin-O-deethylation without decreasing aldrin epoxidase activity. 5. Picloram binds to liver microsomal preparations from rats pretreated with phenobarbitone and/or 3-methylcholanthrene, giving a type I spectrum. 6. The results indicate that picloram is a 3-methylcholanthrene-type inducer, and the implications are discussed.

[Ultrastructural changes caused by a herbicide, picloram in technical dosage (70,4%), in a plankton alga, Dunaliella bioculta (Volvocales)]

A study on the effects of an auxin-like herbicide-picloram (techinical grade 70,4%)--was carried out on a planktonic green Alga, Dunaliella bioculata. At concentrations about 250 mug/ml, the cellular growth decreases while at 400 mug/ml it is completely inhibited. Concentrations of 250-300 mug/ml induce the fall of flagella and an increase of the cellular volume; granulous inclusions-nuclear bodies-are observed inside the nucleus; Golgi apparatus is abnormally developed. The vascuolar system is particularly disturbed: its volume increases; vesicles, cytoplasmic and membrane fragments and osmiophilic granulations can be observed inside vacuoles under the electron microscope.