Effect of paclobutrazol on water stress-induced abscisic Acid in apple seedling leaves

Abscisic acid (ABA) was quantitated by enzyme-linked immunosorbent assay (ELISA) in water-stressed leaves from control apple seedlings, and also from apple seedlings treated for 28 days with paclobutrazol ([2RS, 3RS]-1-[4-chlorophenyl]-4,4-dimethyl-2-[1,2,4-triazol-1-yl] pentan-3-ol). The ELISA quantitative estimates were also validated by gas chromatography-electron capture detector and lettuce seed germination inhibition bioassay. Paclobutrazol treatment reduced endogenous ABA levels by about one-third, and prevented the marked accumulation of water-stress-induced ABA that occurred in untreated seedlings. The presence of ABA in the apple leaf extracts was confirmed by gas chromatography-mass spectrometry.     

Controlling plant growth via the gibberellin biosynthesis system – I. Growth parameter alterations in apple seedlings

'York Imperial' apple seedlings ( Malus domestica Borkh.) were continuously supplied via the roots with paclobutrazol [(2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol)], a triazole GA biosynthesis inhibitor, at 0.68 μ M in a nutrient solution. In comparison to controls, seedlings treated with paclobutrazol for 66 days showed a 91% reduction in shoot length, a 66% reduction in leaf area but only a 17% reduction in leaf number. This effect could be reversed by GA₃ applied to the foliage at 71.4 μ M 0, 19 or 35 days after paclobutrazol was initially supplied and leaf area values for paclobutrazol-treated seedlings given both treatments did not differ significantly from controls. Plots of growth data indicate linearity of shoot longitudinal growth of GA₃-treated seedlings. Leaf area increase was non-linear after GA₃ treatment up to approximately 30 days, when the rate dropped. On a per shoot basis, leaf weight closely followed leaf area but on a per unit area basis, paclobutrazol-treated leaves were heavier than controls; GA₃ applications temporarily reversed this trend.     

Effect of paclobutrazol on membrane lipids in apple seedlings

The effect of paclobutrazol [( 2RS, 3RS )-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2, 4-triazol-1-yl) pentan-3-ol] on the fatty acid composition of polar lipids and on the sterol content in apple ( Malus domestica Borkh. cv. York Imperial) seedlings was determined. Polar lipids isolated from leaves, stems and roots included mono- and digalactosyldiglycerides and the phospholipids phosphatidylinositol, phosphatidylcholine, phosphatidylglycerol and phosphatidylethanolamine. The predominant fatty acids in membrane polar lipids were palmitic (C16:0), linolnic (C18:2) and linolenic (C18:3). The predominant sterol, both free and esterified, was β-sitosterol. There were no significant alterations in the fatty-acid composition of glyco- and phospholipids from paclobutrazol-treated apple seedlings. In contrast, a significant decrease in the content of β-sitosterol and campesterol occurred in treated tissues. The decline in sterol content continued with increasing duration of paclobutrazol treatment, and was most pronounced in the root tissue.     

Translocation of paclobutrazol, a gibberellin biosynthesis inhibitor, in apple seedlings

The [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1- yl)-pentan-3-ol] (paclobutrazol, PP333) measured in apple seedlings (`York Imperial' Malus domestica Borkh) was confirmed by gas chromatography-mass spectrometry. Data showed that paclobutrazol was taken up through roots and transported primarily in the xylem through the stems and accumulated in leaves. No detectable basipetal movement of paclobutrazol in apple seedlings was found.     

The role of abscisic acid and plant growth regulators in tissue culture-induced rejuvenation of strawberry ex vitro

Plant growth regulators applied in vitro affected strawberry plant performance ex vitro for a period of up to 4 months. Benzyl-adenine and gibberellin enhanced juvenile characteristics; in general, more runners and monofoliolate leaves were produced, net photosynthesis was reduced, leaf diffusive resistance was increased and, on occasion, flowering was delayed. In contrast, abscisic acid and a gibberellin biosynthesis inhibitor, paclobutrazol, resulted in a more adult phenotype; specifically, flowering was earlier, net photosynthesis and leaf diffusive resistance rates were equal to those of adult plants, and fewer leaves were monofoliolate. Tissue culture-produced plants reacquire the adult phenotype earlier than seedlings mature. Abscisic acid application to seedlings also resulted in earlier and increased flowering.Endogenous abscisic acid concentrations were greater in adult plants and less in tissue culture and seedling plants at 3 and 7 weeks ex vitro, after germination or after adult runner propagation. No flowering occurred at 3 weeks in any propagation type and only runner-produced plants flowered at 7 weeks. At 15 weeks, no statistical difference in abscisic acid concentrations existed among propagation treatments and all propagation types flowered. The endogenous concentrations of abscisic acid in plants propagated by all three methods were much higher at three weeks compared to concentrations at 7 or 15 weeks.Abbreviations ABA +cis, trans-abscisic acid - BA benzyl-adenine - GC-SIM-MS combined gas chromatography-selected ion monitoring mass spectrometry - GA gibberellin A₃ - RS leaf diffusive resistance in sec cm^-1 - MS Murashige & Skoog medium devoid of plant growth regulators - Pn net photosynthesis in mol CO₂ fixed m^-2 sec^-1 - paclo paclobutrazol as 50WP - TC-plants plants produced from tissue culture - Tween20 polyoxyethylene-sorbitan monolaurate - RP runner plants - SDLG selfed seedlings     

Effect of paclobutrazol on water stress-induced ethylene biosynthesis and polyamine accumulation in apple seedling leaves

Ethylene biosynthesis and polyamine content were determined in [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol] (paclobutrazol) pre-treated and non-treated water-stressed apple seedling leaves. Paclobutrazol reduced water loss, and decreased endogenous putrescine spermidine content. Gibberellic acid (GA) counteracted the inhibitory effect of paclobutrazol on polyamine content. Paclobutrazol also prevented accumulation of water stress-induced 1-aminocyclopropane-1-carboxylic acid (ACC), 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC), ethylene production and polyamines in apple leaves. α-Difluoromethylarginine (DFMA), but not α-difluoromethylornithine (DFMO), inhibited the rise of putrescine and spermidine in stressed leaves. S-Adenosylmethionine (SAM) was maintained at a steady state level even when ethylene and the polyamines were actively synthesized in stressed apple seedling leaves. The conversion of ACC to ethylene did not appear to be affected by paclobutrazol treatment.     

Growth Responses and Allocation of Assimilates of Rice Seedlings by Paclobutrazol and Gibberellin Treatment

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)methyl-4,4-dimethyl-2-(1h-1,2,4-trizol-1-yl)penten-3-ol] effectively decreased vegetative growth of rice (Oryza sativa L.) seedlings and increased the chlorophyll content. The number of veins in a leaf, the calculated number of stomata per leaf, and the length of guard cells were not altered by the paclobutrazol treatment, suggesting an effect on cell elongation. The allocation pattern of carbohydrates was changed by either gibberellin (GA) or paclobutrazol treatment. GA₃ induced more shoot growth and less accumulation of starch than the control and paclobutrazol-treated seedlings. Photosynthetic ability was not affected by either paclobutrazol or GA₃ treatment. Paclobutrazol-treated plants allocated a smaller amount of photosynthates for vegetative shoot growth and stored more as starch in the crowns than the control and GA₃-treated plants. The same starch degrading activity in the crown tissue of paclobutrazol-treated seedlings as in control plants suggests that the accumulated starch is utilized in a normal activity for growth including leaf emergence, tiller formation, and root production, resulting in improved seedling quality. Received May 30, 1996; accepted December 10, 1996     

Effect of paclobutrazol and chilling on leaf membrane lipids in cucumber seedlings

The effects of paclobutrazol on the leaf membrane lipid composition of seedlings of cucumber ( Cucumis sativus L. cv. Victory) subjected to chilling temperatures were assessed. At a non-injurious temperature (12.5°C), there was no difference in the polar lipid fatty acid composition or in the glycolipid, phospholipid or free sterol content of leaves from treated vs untreated seedlings, regardless of whether paclobutrazol was administered 1 or 7 days prior to analysis. In the latter case (7 days pretreatment), there were clear effects of the bioregulator on plant growth and morphology as well as on leaf chlorophyll content. At an injurious chilling temperature (5°C), desaturation of leaf polar lipid fatty acids was markedly reduced in both treated and untreated seedlings. Chilling at 5°C resulted in losses of fresh weight and membrane lipids in leaves of both groups of plants. These losses were either reversible or irreversible, depending upon the duration of chilling and of pretreatment with paclobutrazol. Seedlings pretreated with 10 μg ml⁻¹ paclobutrazol generally sustained less chilling injury than untreated controls, as judged by the extent of wilting, necrosis and desiccation. This correlated with reduced losses of leaf fresh Weight and membrane lipids.     

Growth and photosynthesis of sweet orange plants treated with paclobutrazol

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan3-ol], formulated as GFU 265, applied at 100, 250, and 500 mg plant^–1 to the soil of container-grown sweet orange [Citrus sinensis (L.) Osbeck cv. Valencia], suppressed plant weight, stem height, leaf size, and total leaf area. At the 500-mg dosage, total plant dry weight was reduced by 61%, stem height by 74%, and both leaf biomass and area by 80%, as compared to control plants. All paclobutrazol dosages induced fibrous root thickening and increased their soluble sugar and starch content. Fresh root biomass was 14 to 40% higher and root:shoot ratios were increased three- to sixfold for treated plants. Paclobutrazol applications of 250 and 500 mg plant^–1 reduced leaf photosynthetic rate, ribulose bisphosphate carboxylase activity, total nonstructural carbohydrates, and dark respiration 70 to 80% of the control plants. Reductions of leaf photosynthetic rate, carboxylase activity, and photosynthate by paclobutrazol contributed to biomass reduction in treated sweet orange.Mention of a trademark, warranty, proprietary product, or vendor does not constitute a guarantee by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable.     

Enhancement of extractable ethylene at light/dark transition in primary leaves of paclobutrazol-treated Phaseolus vulgaris seedlings

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol], a triazole growth retardant, increased the 1-aminocyclopropane-1-carboxylic acid (ACC) level and resulted in reduced ethylene production, estimated as ethylene release in a closed system or by vacuum-extraction, in the primary leaves of Phaseolus vulgaris L. cv. Juliska seedlings exposed to light. At the light/dark transition, a definite enhancement of the endogenous ethylene level was observed by vacuum-extraction of primary leaves of treated plants and the ethylene deficiency of retardant-treated leaves ceased. The concentration of ACC after the light/dark transition followed the pattern for ethylene, and the increase in ACC content was paralleled by a decrease in malonyl-ACC.
It is concluded that the internal level of ethylene is not necessarily lower in the primary leaves of paclobutrazol-treated bean plants, but under special environmental conditions in vivo it may reach that of the control.     

Low-Density Releases of Neoseiulus Fallacis Provide for Rapid Dispersal and Control of Tetranychus Urticae (Acari: Phytoseiidae, Tetranychidae) on Apple Seedlings

Releases of Neoseiulus fallacis (Garman) at 1500--6000 per ha when prey were at 0.1-0.3 per leaf provided seasonal control of Tetranychus urticae Koch (all stages) at 1-2 per leaf in an apple seedling rootstock nursery. Predaceous mites (all stages) increased to 0.3-0.4 per leaf after releases and predator prey ratios of < or = 1:3-7 provided pest regulation thereafter. Such low-density releases were thought to be effective because multiple dispersal bouts allowed predators to locate widely distributed spider mites (on 2-6% of leaves). A random-diffusion model simulating predator dispersal (incorporating wind speed and direction parameters) adequately explained movement and pest control patterns. An upright, dense, uniform planting of apple seedlings was an effective producer and recipient for dispersing predators and these attributes seemed to explain why biological control was so effective. Low-density releases of N. fallacis for control of T. urticae are predicted to be less effective on other crops with less prominent profiles and soil coverage.     

PP333对离体苹果苗的生长及其生理的影响

在生根培养基中加入0.5或2.0PPm PP333, 明显地减少了苹果离体新梢的鲜重和干重、叶片鲜重和叶面积,增加了比叶重、根的鲜重和干重及根梢鲜重和干重比,并促进了根的形成。PP333对单位叶重量的叶绿素含量没有影响,而增加了单位叶面积的叶绿素含量。经PP333处理后,叶片中的淀粉含量、过氧化物酶活性、蛋白质和游离氨基酸的含量均明显高于对照,可溶性糖与对照差异不明显。     

Effects of gibberellic acid,ethephon, and 1-aminocyclopropane-1-carboxylic acid on germination ofAmaranthus caudatus seeds inhibited by paclobutrazol

The specific inhibitor of gibberellin biosynthesis, (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol (paclobutrazol), inhibited germination ofAmaranthus caudatus L. seeds. Addition of gibberellic acid (GA₃), 2-chloroethylphosphonic acid (ethephon), or 1-aminocyclopropane-1-carboxylic acid (ACC) effectively antagonized inhibition. Ethephon was found to be the most efficient antagonist. The transfer of seeds after 1 day's incubation in paclobutrazol to solutions of GA₃ or ethephon reversed the inhibition, the effect increasing with increasing concentration of GA₃ or ethephon. Seeds incubated in paclobutrazol for 5 days decreased sensitivity to GA₃ and ethephon.     

PP_(333)对离体苹果苗的生长及其生理的影响

在生根焙养基中加入0.5或2.0ppm PP_333,明显地减少了苹果离体新梢的鲜重和干重、叶片鲜重和叶面积,增加了比叶重、根的鲜重和干重及根梢鲜重和干重比,并促进了根的形成。PP_333对单位叶重量的叶绿素含最没有影响,而增加了单位叶面积的叶绿素含量。经PP_333处理后,叶片中的淀粉含量、过氧化物酶活性、蛋白质和游离氨基酸的含量均明显离于对照,可溶性糖与对照差异不明显。     

Changes of polyamines and ethylene in cucumber seedlings in response to chilling stress

Cucumber ( Cucumis sativus L. cv. Victory) seedlings were exposed to chilling at 5°C and endogenous levels of polyamines and 1-aminocyclopropane-1-carboxylic acid (ACC) were measured after chilling and after warming at 20°C. The level of spermidine was higher in the chilled seedlings than in the non-chilled seedlings. Treatment with a plant bioregulator, (2RS,3RS)-1-(4-cholorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol (paclobutrazol), reduced the chilling injury and the levels of spermidine in the chilled seedlings. The levels of ACC and production of ethylene showed sharp increases after warming following exposure to chilling. These increases were suppressed by the application of aminooxyacetic acid (AOA). However, AOA treatment did not reduce chilling injury or affect the levels of polyamines in the tissue. These data indicate that the increase in ACC and ethylene is a response of the tissue to the chilling exposure and is not a cause of the injury. The data also suggest that the syntheses of polyamines and ethylene are not competitive with each other even under chilling stress conditions.     

Paclobutrazol affects the extension growth and the levels of endogenous IAA of almond seedlings

The effect of paclobutrazol on plant height and the concentration of free indole-3-acetic acid (IAA) in almond seedlings grown in 0.5 L pots with moist perlite and subjected to 15°C and photoperiod of 16 hours was studied.In the first two experiments the paclobutrazol was applied as a drench at 0, 0.5, 1.5 and 5 mg/pot. Seven and sixteen days respectively after application a gradual decrease in the growth rate and concentration of free IAA in the tops of the growing shoots of almond seedlings on which paclobutrazol was applied, was observed. Furthermore, a gradual increase in the concentration of free IAA in the four younger leaves at the time of application was also detected.In the third experiment the effect of paclobutrazol (5 mg/pot) on plant height and the concentration of free IAA measured over 10 day period was studied. From the 4th day following application differences in the height of seedlings and in the concentration of free IAA in the growing tops between the control and treated seedlings were observed.Abbreviations IAA Indoleacetic acid - GA₃ Gibberellic acid - CCC 2 Chloroethanephosphonic acid - B-995 N-dimethyl aminosuccinamic acid     

Influence of paclobutrazol in the soil on growth,nutrient elements in the leaves,and flood/freeze tolerance of citrus rootstock seedlings

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3ol] was applied to soil at 0, 100, or 250 mg/3.78-liter pot containing seedlings of Swingle citrumelo, Carrizo citrange, Cleopatra mandarin, sour orange, rough lemon, and Sun Chu Sha. All cultivars were sensitive to paclobutrazol, which caused a proliferation of shorter/thicker roots, and top growth showed shorter internodes and lower dry weight. Induced changes resulted in greater root/shoot ratios, and paclobutrazol treatments showed higher concentrations of nitrogen, calcium, boron, iron, and manganese in the leaves of different cultivars. Paclobutrazol-treated seedlings did not show a greater ability to tolerate flooded soil for 60 continuous days under greenhouse conditions nor survive-6.7°C controlled freeze tests. Paclobutrazol is a potentially useful plant growth regulator to dwarf citrus, but it apparently is not a strong candidate for increasing flooding and freezing tolerance in citrus rootstock seedlings.Abbreviations PPFD photosynthetic photon flux density - ANOVA analysis of variance     

The occurrence of nitrate reductase in apple leaves

Nitrate reductase utilizing NADH or reduced flavin mononucleotide (FMNH₂) as electron donor was extracted from the leaves, stems and petioles, and roots of apple seedlings. Successful extraction was made possible by the use of insoluble polyvinylpyrrolidone (Polyclar AT) which forms insoluble complexes with polyphenols and tannins. The level of nitrate reductase per gram fresh weight was highest in the leaf tissue although the nitrate content of the roots was much higher than that of the leaves. Nitrite reductase activity was detected only in leaf extracts and was 4 times higher than nitrate reductase activity. Nitrate was found in all parts of young apple trees and trace amounts were also detected in mature leaves from mature trees. Nitrate reductase was induced in young leaves of apple seedlings and in mature leaves from 3 fruit-bearing varieties. An inhibitor of polyphenoloxidase, 2-mercaptobenzothiazole was used in both the inducing medium and the extracting medium in concentrations from 10⁻³ to 10⁻⁵m with no effect upon nitrate reductase activity.     

多效唑对紫穗槐生长及生理特性的影响

采用盆栽试验的方法研究了土施不同浓度多效唑(1、5、10、15、20 mg/L)对紫穗槐(Amorpha fruticosa Linn.)生长及生理特性的影响,以探明多效唑对紫穗槐的作用机制和最佳处理方式。结果显示:随着多效唑处理浓度(1~20 mg/L)的增加,紫穗槐幼苗株高、单叶面积和主根长呈下降趋势,基径、叶片长宽比、根鲜重和根冠比呈上升趋势;多效唑各处理均使紫穗槐幼苗叶片的相对含水量、叶绿素、可溶性糖和可溶性蛋白含量显著升高,POD活性显著增加,MDA含量和相对电导率显著下降。采用隶属函数法对各项生长、生理指标进行综合评价,结果发现20 mg/L多效唑处理下紫穗槐幼苗的抗性最强。说明多效唑可通过调节紫穗槐幼苗的生物量分配、水分状况、细胞渗透性和抗氧化性等,有效改善其生长、生理特性及提高抗逆性。本研究结果为多效唑在边坡植被建成和恢复中的应用提供了理论依据。     

盐胁迫下番茄砧木对嫁接苗生物量、氨基酸含量和活性氧代谢的影响

为探讨砧木对提高番茄嫁接苗耐盐性的作用机理,以耐盐性较敏感的‘中杂9号’(S)为接穗,耐盐性较强的‘OZ-006’(R)为砧木,采用劈接法形成嫁接苗(RS)以及接穗自嫁接苗(SS)、砧木自嫁接苗(RR)3个试验材料,在175 mmol·L^-1 NaCl处理下测定植株生长、Na⁺积累、氨基酸含量和活性氧代谢的变化。结果表明: NaCl胁迫导致番茄幼苗的盐害指数和Na⁺含量均显著提高,幼苗生长速率和叶绿素含量显著降低,但不同嫁接苗的类型差异显著,在盐害表型上表现为SS>RS>RR的规律。NaCl胁迫诱导嫁接苗的叶片和根系总氨基酸含量显著提高,其中RR、RS叶片有9种、根系有8种氨基酸含量显著高于对照,以脯氨酸含量变化最为显著,而SS叶片中仅有2种、根系中仅有4种氨基酸含量显著高于对照;幼苗间的氨基酸含量呈现RR>RS>SS的规律,RR、RS叶片的氨基酸含量分别比SS叶片上升了32.8%、16.6%,根系分别比SS上升了53.1%和32.5%。NaCl胁迫造成活性氧代谢的变化,幼苗叶片和根系的抗氧化酶活性、超氧阴离子产生速率、丙二醛含量均显著提高,以RR叶片和根系中抗氧化酶活性的增幅最大,其次为RS;SS和抗氧化酶活性的增幅最小,品种间活性氧水平表现为SS>RS>RR。综上,砧木通过抑制Na⁺向上运输、提高氨基酸水平和抗氧化酶活性缓解了盐胁迫对嫁接苗的伤害,但不同砧穗组合的耐盐性差异较大,以RR的耐盐性最强,其次为RS,SS最弱。因此,番茄嫁接苗的耐盐性主要受砧木耐盐性的影响,其次为接穗,同时,其与番茄体内的氨基酸和活性氧代谢调控密切相关。