Triazole Plant Growth Regulators Research Articles

Transcriptomic and metabolomic analyses reveal the mechanism of uniconazole inducing hypocotyl dwarfing by suppressing BrbZIP39-BrPAL4 module mediating lignin biosynthesis in flowering Chinese cabbage.

Uniconazole, a triazole plant growth regulator, is widely used to regulate plant height and prevent the overgrowth of seedlings. However, the underlying molecular mechanism of uniconazole in inhibiting the hypocotyl elongation of seedlings is still largely unclear, and there has been little research on the integration of transcriptomic and metabolomic data to investigate the mechanisms of hypocotyl elonga-tion. Herein we observed that the hypocotyl elongation of flowering Chinese cabbage seedings was significantly inhibited by uniconazole. Interestingly, based on combined transcriptome and metabolome analyses, we found that the "phenylpropanoid biosynthesis" pathway was significantly affected by uniconazole. In this pathway, only one member of the portal enzyme gene family, named BrPAL4, was remarkably downregulated, which was related to lignin biosynthesis. Furthermore, the yeast one-hybrid and dual-luciferase assays showed that BrbZIP39 could directly bind to the promoter region of BrPAL4 and activate its transcript. The virus-induced gene silencing system further demonstrated that BrbZIP39 could positively regulate hypocotyl elongation and the lignin biosynthesis of hypocotyl. Our findings provide a novel insight into the molecular regulatory mechanism of uniconazole inhibiting hypocotyl elongation in flowering Chinese cabbage and confirm, for the first time, that uniconazole decreases lignin content through repressing the BrbZIP39-BrPAL4 module-mediated phenylpropanoid biosynthesis, which leads to the hypocotyl dwarfing of flowering Chinese cabbage seedlings.

Effects of triazole plant growth regulators on molting mechanism in Chinese mitten crab (Eriocheir sinensis)

Rice crab co-culture is a new integrated farming model in China. The application of triazole plant growth regulators (PRGs) is often used as an advantageous option to combat rice lodging. However, there is still a gap regarding the toxicity of these PRGs on the growth and development of the Chinese mitten crab (Eriocheir sinensis, E. sinensis). Here the effect of triazoles (paclobutrazol and uniconazole) on the molting mechanism of E. sinensis was investigated. Monitoring of regulatory genes associated with molting showed that the two PRGs were found to inhibit the expression of ecdysteroid hormone (EH), ecdysteroid receptors gene (EcR), and retinoid X receptors gene (RXR) and induce secretion of molt-inhibiting hormone (MIH) gene. In addition, the activities of chitinase (CHIA) and N-acetyl-β-d-aminoglucosidase (β-NAGase) were also inhibited by exposure to PRGs. Exposure to PRGs also elevated the mRNA expression of the growth-related myostatin gene (MSTN). These results revealed that there is a long-term risk of exposure to triazoles PRGs that may inhibit molting and affect normal development and immune system of E. sinensis.

Effects of Triazole Plant Growth Regulators on Molting Mechanism in Chinese Mitten Crab (Eriocheir Sinensis)

Effects of Triazole Plant Growth Regulators on Molting Mechanism in Chinese Mitten Crab (Eriocheir Sinensis)

Chiral enantiomers of the plant growth regulator paclobutrazol selectively affect community structure and diversity of soil microorganisms

Paclobutrazol is a triazole plant growth regulator with a wide range of applications in crop and fruit tree production. Paclobutrazol is used as a racemic mixture in agriculture. However, the effects of paclobutrazol enantiomers on soil microbial community structure and diversity are unclear. In the present study, Illumina high-throughput sequencing was used to study the enantioselective effects of two paclobutrazol enantiomers on soil microbial community. S-paclobutrazol was more persistent than R-paclobutrazol. The half-lives of the S- and R-isomers were 80 d and 50 d, respectively. No interconversion between the two isomers occurred in soils. In addition, the enantiomers had significant enantiomeric effects on soil microbial community and the paclobutrazol degradation was probably attributed to the presence of Pseudomonas and Mycobacterium. Notably, the relative abundance of Fusarium, a genus of filamentous fungi producing gibberellins, could be enantioselectively affected by the chiral enantiomers. Paclobutrazol enantiomers exhibited greater effects on the fungal community structure than bacterial community structure due to the fungicidal activity of paclobutrazol. Finally, R-paclobutrazol had a significant effect on the microbial networks. The findings of the present study suggest that the use of S-paclobutrazol may accomplish both plant growth regulation and the minimization of effects of paclobutrazol on soil microbial communities.

Triazole sprays induce diffuse browning disorder in ‘Cox's Orange Pippin’ apples in controlled atmosphere storage

The inclusion of triazole chemicals in orchard spray programmes was investigated as a possible cause of a physiological storage disorder (diffuse browning disorder or DBD) that has seriously affected commercial consignments of ‘Cox's Orange Pippin’ apples ( Malus domestica Borkh.) since 2000. In 2006, spray regimes that included or excluded the triazole plant growth regulator paclobutrazol and triazole fungicides myclobutanil and penconazole were compared in each of nine commercial ‘Cox’ orchards. In 2007 the number of orchards was reduced to eight but the number of treatments was increased in order to compare the effects of paclobutrazol separately from those of the triazole fungicides. Apples were stored in controlled atmosphere (CA) conditions of 1.2 kPa O 2 and <1 kPa CO 2 at 3.5 °C for 5 months and assessed for presence of DBD after a further 7 d at 20 °C. In 2007 additional samples were subjected to a delayed cooling (7 d at 20 °C) or postharvest treatment with diphenylamine (DPA) or 1-methylcyclopropene (1-MCP). In both years DBD did not develop where triazole chemicals were omitted from the spray programmes, whereas the inclusion of triazole chemicals resulted in DBD development in fruit from 67% and 71% of orchards in 2006 and 2007, respectively. Fungicide application was more conducive to DBD development than application of paclobutrazol but, in combination, induced the highest incidence of DBD. Triazole (fungicides + paclobutrazol) application generally increased the respiration rate of CA-stored fruit but ethylene production rates were not affected. The development of DBD was not affected by post harvest application of DPA or 1-MCP or a delayed cooling of the fruit.

EFFECTS OF PACLOBUTRAZOL ON GROWTH AND FRUITING CHARACTERISTICS OF ´PITANGA´ ORNAMENTAL PEPPER

Two experiments using container-grown ornamental pepper (Capsicum chinense ‘Pitanga’), were conduced to determine effects of paclobutrazol on growth and fruiting responses. In experiment 1, paclobutrazol was sprayed on the canopy at concentrations of 0; 30; 60; 90; 120 and 150 mg ai⋅L. In experiment 2, paclobutrazol drenches were applied at 0, 5, 10, 15, 30 and 60 mg ai⋅L. Increasing paclobutrazol concentration decreased plant height, plant diameter and plant dry mass but increased leaf chlorophyll content in both experiments. Severe height retardation of plants was evident at 30 and 60 mg ai⋅L in the second experiment, also exhibiting phytotoxicity symptoms. Paclobutrazol treated plants exhibited greener leaves compared to untreated plants. Increasing paclobutrazol foliar application concentrations, the fruit diameter was increased and the fruit weight was unaffected. Considerations of growth and fruiting response should be balanced when using paclobutrazol in ‘Pitanga’ ornamental pepper pot production. INTRODUCTION Brazil has a large genetic diversity of wild peppers but more scientific research is needed to undertanding the growth cycles and cultural requirements of those plants. The use of peppers as ornamental potted plants exhibit advantages like easy seed propagation, short cycle production, heat and drought tolerance, fruit production and excellent postharvest performance (Harbaugh and Waters, 1979). A new genetic access ‘Pitanga’ pepper (Capsicum chinense), catalogued in Germoplasm Bank of Federal University of Vicosa, has potential as an ornamental pot plant, if the growth can be controlled. Application of growth retardants is a common practice for commercial growers to achieve attractive compact pot-grown plants. Researchers have reported that paclobutrazol, a triazole plant growth regulator, is effective in controlling vegetative growth and promoting compactness in the production of a number of ornamental plants including Chrysanthemum morifolium (Barret, 1982; Zalewska, 1989), Lilium longiflorum (Jiao et al. 1986), Euphorbia pulcherrima (Goulston and Shearing, 1985) and Tulips (McDaniel, 1990). Starman (1993) investigated the effects of different concentrations of uniconazole, another triazole plant growth regulator, on controlling growth and fruiting of ‘Holiday Cheer’ Capsicum annuum. Concentrations ranging from 5.0 to 15.0 mg•L gave adequade height control. Triazoles are generally more effective in retarding growth when applied to the soil or directly to stems compared to foliar applications (Davis et al., 1988). However, foliar and drench paclobutrazol applications have been studied on growth control of ornamental plant production (Anderson and Hartley, 1990; Banon et al., 2002). Despite the use of paclobutrazol in the industry of potted plants, few studies have been published concerning paclobutrazol efficacy for ornamental peppers. Also, evaluation of the effect of paclobutrazol on growth and fruiting characteristics of ‘Pitanga’ ornamental pepper has not been reported. The objective of this study was to investigate the effects of paclobutrazol on growth and fruiting characteristics of ‘Pitanga’ ornamental pepper. Proc. V IS on New Flor. Crops Eds.: A.F.C. Tombolato and G.M. Dias-Tagliacozzo Acta Hort. 683, ISHS 2005

Cultivar, Planting Density, and Plant Growth Regulator Effects on Growth and Fruiting of Tissue-cultured Apple Trees

Tissue-culture (TC)-propagated `Gala' and Triple Red `Delicious' apple trees grown at three planting densities were not treated (CON) or treated with plant growth regulators (PGRs) starting the third or fourth season to control tree size and maximize fruiting. `Gala' and `Delicious' trees budded on M.7a rootstock (BUD) were also included as controls. `Gala' trees were larger than `Delicious' after the first three growing seasons but `Delicious' were larger than `Gala' at the end of 9 years. BUD trees were larger than CON trees the first few seasons hut final trunk cross-sectional area (TCSA) of CON trees averaged 43% greater than BUD trees. Paclobutrazol and uniconazole treatments more readily controlled the growth of `Gala' than `Delicious' and uniconazole was more effective than paclobutrazol in controlling tree size. Daminozide + ethephon sprays (D+E-S) did not influence tree size. Tree size of both cultivars was inversely related to planting density and both triazole PGRs were more effective in controlling tree size as planting density increased. The trees had fewer flowers as planting density increased and BUD trees generally had more Bowers than CON. Triazole PGRs had little effect on the flowering pattern of `Gala' trees but tended to stimulate flowering of young `Delicious' TC trees, although the increases were not sustained. The D+E-S treatment increased flowering of `Gala' trees the last 3 years of the experiment and consistently increased flowering of `Delicious' TC trees. Fruit yields were higher for young `Gala' compared to `Delicious' trees and the final cumulative yield per tree for `Gala' was also greater. Yield per tree decreased as tree density increased and was the same for BUD and CON trees. D+E-S increased cumulative per tree yield of `Delicious' but not of `Gala'. Cumulative yields per tree for triazole-treated TC trees were the same as, or significantly lower than, CON trees. Increasing tree density did not increase yield/ha. Yield efficiency of `Gala' trees was increased by three, and of `Delicious' trees by one, of the triazole treatments, because they reduced TCSA proportionally more than they reduced per tree yield. There was less bienniality with `Gala' than `Delicious' and no difference between BUD and CON trees. Bienniality indices were higher for paclobutrazol-treated `Gala' trees compared with CON `Gala' but only uniconazole applied as a trunk paint increased the bienniality index of `Delicious' trees. Chemical names used: succinic acid-2,2-dimethyl hydrazide (daminozide), (2-chloroethyl) phosphonic acid (ethephon), (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-01 (paclobutrazol), (E)-(l-chlorophenyl)-4,4-dimethyl-2-(I,2,4-triazol-l-yl)-1-penten-3-ol (uniconazole).

Paclobutrazol-induced Tolerance of Wheat Leaves to Paraquat May Involve Increased Antioxidant Enzyme Activity

The damage caused by active oxygen generated by paraquat was investigated in two wheat cultivars, Triticum aestivum L. Frederick and Glenlea, which differed in their sensitivity to heat and chilling stress. Application of paraquat induced photoinhibition and loss of fresh mass, protein, and membrane integrity in the leaves. The photosynthetic pigments were lost after paraquat treatment, with Chl b declining the least and carotenoids declining the most. Paclobutrazol, a triazole plant growth regulator, reduced these symptoms and induced a 2-fold increase in paraquat tolerance in both cultivars. This study tested the hypothesis that paclobutrazol protects wheat from oxidative stress by enhancing antioxidant enzyme activity. The enzymes investigated were superoxide dismutase, ascorbate peroxidase, glutathione reductase, as well as cytosolic catalase and guaiacol peroxidase. Paclobutrazol stimulated an overall increase in antioxidant enzyme activities on both a fresh-mass and protein basis in the winter wheat cultivar Frederick, but only on a fresh-mass basis in Glenlea. The spring wheat, Glenlea, which is more sensitive to temperature stress, had lower antioxidant enzyme activity than the tolerant winter cultivar Frederick. Irrespective of the natural difference in the two cultivars to stress, paclobutrazol elevated the plants to a higher level of oxidative stress tolerance.

Triazole Plant Growth Regulator Binding to Native and Detergent-Solubilized Plant Microsomal Cytochrome P450

BAS 111..W, a triazole which retards plant growth, is an inhibitor of cytochrome P450 monooxygenase enzymes in the gibberellic acid biosynthetic pathway. Microsomal membranes isolated from endosperm of immature pumpkin (Cucurbita maxima L. cv. Big Max) seeds at a developmental stage corresponding to 15-45% cotyledon fill were found to be enriched in cytochrome P450 and exhibited spectral characteristics that indicate binding of BAS 111..W to cytochrome P450. Magnesium-dependent density shifts on equilibrium sucrose gradients demonstrated that NADPH:cytochrome c reductase, total dithionite-reducible cytochrome P450, and BAS 111..W-binding cytochrome P450 were localized exclusively in the endoplasmic reticulum in endosperm cells of developing C. maxima seed. Binding competition experiments between ent-kaurene and BAS 111..W were not conclusive, but suggested that the substrate and inhibitor compete for binding at the same site on the ent-kaurene oxidase cytochrome P450. We used the detergent (3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate) to solubilize the BAS 111..W-binding cytochrome P450 from seed endosperm microsomes. Detergent-solubilized C. maxima microsomal cytochrome P450 retained high-affinity triazole-binding characteristics observed with microsomes, but had reduced affinity for ent-kaurene.

Variable increases in cold hardiness induced in winter rape by plant growth regulators

Triazole and conventional growth regulators were tested for their ability to extend cold hardiness and improve the winter survival of winter rape (Brassica napus L.). Winter rape plants were grown in the field (Ottawa 45°23′ N) and in growth cabinets. Plant growth regulators (PGRs) were applied during the early vegetative stage and the plants were allowed to cold harden. Cold-hardened plants from the field and cabinet were subjected to freezing and ice encasement tests in the laboratory. Some of the triazole PGRs reduced plant size by limiting cell expansion and increasing cell numbers. While cold hardiness and ice encasement tolerance were increased by some growth regulators, these effects were not consistent with time nor were they reflected in increased winter survival. Natural cold hardening may have eclipsed the PGR-induced hardening.

Growth and organogenesis in moth bean callus cultures as influenced by triazole growth regulators and gibberellic acid

The triazole plant growth regulators, paclobutrazol and uniconazole, reduced in vitro growth of moth bean callus by 20–25% when added to the culture medium at 1 mg/L (3.4 μM). The addition of 10 mg/L (29 μM) gibberellic acid (GA3) to the culture medium in combination with the triazoles restored callus growth to a level equivalent to that of the untreated control. GA3 alone had little effect on callus growth. When added to a regeneration medium at 1 mg/L both paclobutrazol and uniconazole reduced the percentage of cultures that formed roots, as well as the mean number of roots per culture. In contrast, GA3 increased root formation and counteracted the inhibitory effects of the triazoles on rooting. The addition of triazoles or GA3 to the regeneration medium reduced the formation of green meristematic nodules, which are precursors of shoots in moth bean callus. When callus was grown in the presence of either paclobutrazol or uniconazole, subsequent root and green meristematic nodule formation were reduced upon transfer to a growth regulator-free regeneration medium. The results of this study indicate that exposure of moth bean callus tissue to micromolar concentrations of triazoles or GA3 can significantly alter in vitro growth and differentiation.

Influence of a Triazole Plant Growth Regulator on Root and Shoot Development and Nitrogen Utilisation of Oilseed Rape (Brassica napus L.)

AbstractA factorial experiment with 3 nitrogen (N) levels and 4 application rates of the triazole type plant growth regulator (PGR), BAS 111 W = l‐phenoxy‐3‐(1H‐1,2,4‐triazol‐1‐yl)‐4‐hydroxy‐5,5‐dimethylhexane, was conducted in hydroponics to study the influence on N uptake and morphological changes of oilseed rape. The following results were obtained:–Increased N level of the nutrient solution increased plant height and root and shoot weight. Enhanced N uptake caused a higher N concentration of root and shoot.–Increasing PGR application rates reduced plant height and shoot biomass production; this reaction was stronger at higher doses of N.–Root weight, root length, root diameter and root surface area were increased by N application. None of these parameters was significantly altered by the PGR. This resulted in increased root‐shoot‐ratios at higher PGR rates.–As a consequence of reduced shoot production PGR application resulted in increased concentrations of N. The root reacted similarly but to a lesser degree.

Anatomy ofZea mays andGlycine max seedlings treated with triazole plant growth regulators

Soil drenches containing 250 μg of paclobutrazol or uniconazol (50 ml of a 17 μM solution) reduced the height of both corn (Zea mays L. cv. How.Sweet It Is) and soybean (Glycine max (L.) Merr. cv. A2) seedlings. With corn, uniconazol was considerably more active than paclobutrazol in reducing height whereas with soybean both compounds had similar dwarfing effects. The compounds increased foliar chlorophyll content and leaf thickness in soybean but had no effect on these parameters in corn. The increase in leaf thickness with soybean was due primarily to an increase in the thickness of the palisade cell layer. Chloroplast size and ultrastructure of both species were unaffected by the compounds. The growth regulators increased root diameter in both corn and soybean because of increased size of cortical parenchyma cells and particularly in soybean because of radial rather than longitudinal growth of the first few layers of the cortical parenchyma.

Endogenous Gibberellins and Shoot Growth and Development in Brassica napus

Greenhouse-grown oilseed rape (Brassica napus, annual Canola variety ;Westar') plants were harvested at six dates from the vegetative phase until the early pod (silique)-fill/late flowering stage. Endogenous gibberellin (GA)-like substances were extracted from stems, purified, and chromatographed on silica gel partition columns prior to bioassay in serial dilution using the ;Tan-ginbozu' dwarf rice microdrop assay. The concentrations of total endogenous GA-like substances were low during vegetative stages (1 nanogram GA(3) equivalents/gram dry weight), and rose 300-fold by the time of floral initiation. After floral initiation the concentration of GA-like substances fell, then rose again during bolting to maximal levels during the early pod-fill stage (940 nanograms per gram dry weight). The qualitative profiles of GA-like substances varied across harvests, with higher proportions of a GA(1)-like substance at the early pod-fill stage. In a second study stems were similarly harvested at eight dates and the concentrations of endogenous GA(1), the principal bioactive native GA of oilseed rape, were determined by gas chromatography-selected ion monitoring using [17,17-(2)H]GA(1) as a quantitative internal standard. The concentration of GA(1) increased at about the time of floral initiation and then subsequently fell, thus confirming the pattern noted above for total GA-like substances. The exogenous application of paclobutrazol (PP333), a persistent triazole plant growth regulator (PGR) which blocks GA biosynthesis, or another triazole, triapenthenol (RSW0411), prevented flowering as well as bolting; plants remained at the vegetative rosette stage. These results imply a causal role for endogenous GA, in the control of bolting, which normally precedes anthesis. Further, the rise in the concentration of total endogenous GA-like substances, including GA(1), which was associated with floral initiation, and the prevention of visable floral development by the triazole PGRs, also indicates a role for endogenous GAs in the regulation of flowering in B. napus.

Efficacy of triapenthenol as a safener against metribuzin injury in soybean (Glycine max) cultivars

Triapenthenol or RSW 0411 (B(-cyclohexalmethylene)-gamma-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol), a triazole plant growth regulator, applied preemergence as a separate broadcast application, protected tolerant and midtolerant soybean cultivars from metribuzin (4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one)-induced necrotic injury, and stabilized seedling fresh weight and dry weight loss to herbicide treatment. Soybean yields were not significantly reduced by triapenthenol treatment alone, but 1.12 kg ai/ha metribuzin and a 0.56 kg ai/ha triapenthenol plus 1.12 kg ai/ha metribuzin combination reduced crop yield averaged across cultivars.

Sterol requirements and paclobutrazol inhibition of a celery cell culture

The triazole plant growth regulator paclobutrazol was an effective inhibitor of growth of a celery cell suspension culture. Exposure of the celery cells to paclobutrazol caused inhibition of sterol biosynthesis at the 14α-demethylation step and there was an accumulation of several 14α-methylsterols [obtusifoliol, cycloeucalenol, cycloartenol, 14α,24-dimethylcholest-8-en-3β-ol and 14α,24-dimethylcholesta-8,24(28)-dien-3β-ol] with an accompanying decrease in the sitosterol and stigmasterol content of the cells. There was a marked fall in the stigmasterol: sitosterol ratio. Addition of paclobutrazol during the linear phase of growth (day 6) caused a rapid cessation of cell division. Obtusifoliol, added on day six to the growing celery cultures at low concentrations (0.05 to 5 μM), also stopped cell division but at the lowest concentration an increase in dry weight continued to day 10 before starting to decline. 14α-Methylcholest-9(11)-en-3β-ol was an effective inhibitor of cell growth but other 14α-methylsterols possessing a 4β-methyl group and/or a 9β,19-cyclopropane ring (lanosterol, dihydrolanosterol, cycloartenol, cycloeucalenol) had little or no effect on cell growth. The inhibition of celery cell growth by paclobutrazol could be partially reversed by addition of 50 μM cholesterol to the growth medium. Complete restoration of growth was achieved by addition of 50 μM stigmasterol or by 50 μM cholesterol plus a low concentration (0.05 μM to 5 μM) of stigmasterol. Stigmasterol alone at these low concentrations was ineffective in promoting growth of the paclobutrazol treated cells. These results reveal that the celery cells have two requirements for sterols. One is for relatively large amounts of sterol and may be associated with membrane elaboration. The other essential role, termed ‘trigger’, requires trace amounts of sterol with a 24α-ethyl side chain such as stigmasterol. Thus, plants have sterol requirements for cell proliferation which resemble those demonstrated for fungi. The significance of these results in relation to the mode of action of azole plant growth regulators is discussed.

Modification of Root‐Shoot‐Ratio of Sunflower (Helianthus annuus, L.) by Nitrogen Supply and a Triazole‐Type Plant Growth Regulator

AbstractA factorial nutrient solution experiment with 3 N levels and 4 plant growth regulator (PGR) rates with sunflower (Helianthus annuus, L., cv. Sorex) was conducted to investigate the effect of both variables on shoot and root development. Nitrogen shortage resulted in reduced shoot and root growth throughout the experiment, but root growth was less affected than the shoot PGR treatments drastically reduced shoot biomass production. Root growth was promoted. Both reduced nitrogen supply and application of a triazole plant growth regulator (BAS 111. W) increased the proportion of roots relative to the shoot.