Gibberellin biosynthesis inhibitors: Comparing growth-retarding effectiveness on apple

The relative growth inhibitory activities of paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2(1,2,4-triazol-1-yl)pentan-3-ol]; XE-1019 [(E)-(1-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol]; flurprimidol [-(1-methylethyl)--[4-(trifluoromethyloxy)-phenyl]-5-pyrimidine-methanol]; and triadimefon (a fungicide) [1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl)-2-butanone] were evaluated and compared by treating the root zone of young greenhouse-grown tissue-culture-propagated Gala (Malus domestica Borkh.) trees. At 0.25 mg/plant, only XE-1019 significantly reduced new stem length and number, area, and dry weight of leaves after 115 days. Paclobutrazol and flurprimidol both significantly reduced growth compared to controls when applied at 0.5 mg/plant, but XE-1019 was more effective. All three gibberellin (GA) biosynthesis inhibitors effectively retarded growth at a dosage of 1 mg/plant. Triadimefon applied at 10 mg/plant had essentially no effect on growth, but at 50 and 100 mg/plant it caused significant but less dramatic growth retardation when compared with the GA inhibitors. Major differences in effectiveness among the triazole GA biosynthesis inhibitors may be due to longevity of effect as well as to extent of inhibition.The use of a company or product name does not constitute an endorsement by USDA nor imply approval to the exclusion of other suitable products.     

Interactive effects of GAs,CKs and growth retardants on the germination of celery seeds

The germination of whole seeds of celery (Apium graveolens L.) was inhibited by paclobutrazol, ancymidol and lower concentrations of uniconazole. The growth retardants daminozide, AMO 1618 and chlormequat chloride inhibited the germination of cut seeds only, indicating that the seed coat prevents the penetration of these compounds at the examined concentrations. Application of a mixture of the gibberellins A4 and A7 (GA 4/7) reversed the inhibition of all the examined growth retardants. Cytokinins (artificial or natural) had no effect when applied alone and did not interact with GA4/7 in the light. However, in the dark the cytokinins at some concentrations and GA4/7 had a synergistic effect in reversing the inhibition caused by growth retardants to whole seeds or in promoting the germination of whole seeds. It is therefore suggested that the major effect on seed of exogenous cytokinins when applied together with GA's is to increase the uptake of gibberellins by the seeds.Abbreviations AMO 1618 (2 isopropyl-5-methyl-4-trimethylammonium chloride-phenyl-1-Piperidinium-carboxylate - ancymidol -cyclopropyl-[4-methoxyphenyl]-5-pyrimidinemeth anol] - chlormequat chloride 2-chloroethyltrimethylommonium chloride - daminozide succinin acid 2,2-diamethyl hydrazide - paclobutrazol [2 RS, 3 RS]-1-(4-chlorophenyl)-4,4-dimethyl-2-(1 H-1,2,4-triazol-1-yl) pentan-3-ol - uniconazole (E)-1-(P-chlorophenyl)-4,4-dimethyl-2-(1,2,4 triazol-1-yl)-1 penten-3-ol     

Growth regulation of Eurasian watermilfoil with flurprimidol

Studies were conducted in 55-liter aquariums under controlled environment conditions to evaluate growth regulator effects of flurprimidol [-(1-methylethyl)--[4-(trifluoromethoxy) phenyl]-5-pyrimidinemethanol] on Eurasian watermilfoil (Myriophyllum spicatum L.). Treatments included flurprimidol concentrations ranging from 0 to 500 g L^-1, with exposure times varying from 0.25 to 28 days. Extending the flurprimidol contact time increased the growth inhibitory response. Flurprimidol-treated shoots were 14–64% shorter than untreated plants at 14 DAT (days after treatment). Growth inhibition persisted 56 DAT for plants exposed to 25 and 100 g L^-1 flurprimidol for 28 days or 200 g L^-1 flurprimidol for 10 days. Growth-inhibited plants accumulated starch in shoots and roots, whereas plants showing little or no growth suppression utilized available assimilate for growth. Treatments that most effectively suppressed shoot length accumulated up to 68% more total nonstructural carbohydrate compared with untreated plants. Shoot and root dry weight biomass were unaffected by flurprimidol.Abbreviations PGR(s) plant growth regulator(s) - TNC total non-structural carbohydrate - DAT days after treatment - PVC polyvinyl chloride - DW dry weight - BOD biological oxygen demand - DMSO dimethyl sulfoxide - LSD least significant difference     

The effect of flurprimidol on bud flush,shoot growth,and on endogenous gibberellins and abscisic acid of Douglas-fir seedlings

For 4-month-old Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings under 17-h photoperiods in controlled environment conditions, flurprimidol (-(1-methlyethyl--[4-(trifluoromethoxy)phenyl]-5-pyrimidine-methanol) decreased incidence of second flushing from 81 to 54% and significantly reduced height growth in the second year following low-temperature treatment, in comparison to untreated controls. For seedlings under 15-h photoperiods, flurprimidol had only limited early effects, but after a period of bud dormancy, shoot growth was reduced to one-third that of the untreated controls. Under both photoperiods flurprimidol significantly depressed abscisic acid levels and gibberellin-like bioactivity. These results suggest that growth reduction in this conifer by flurprimidol may well involve inhibition of gibberellin biosynthesis.Abbreviations GA gibberellin - ABA abscisic acid - FPP farnesyl pyrophosate - HPLC high performance liquid chromatography - GC-EC gas chromatography-electron capture - GC-MS gas chromatography-mass spectrometry     

Reversing the inhibitory effect of paclobutrazol on seed germination of Amaranthus paniculatus by GA3, ethephon or ACC

The germination of Amaranthus paniculatus seeds was inhibited by applying paclobutrazol, a specific inhibitor of gibberellin biosynthesis. This inhibition was markedly counteracted by gibberellin A₃ (GA₃), suggesting that endogenous gibberellins are required for germination in this species. The inhibitory effect of paclobutrazol was also overcome by ethephon (2-chloroethylphosphonic acid) or the precursor of ethylene biosynthesis, ACC (1-aminocyclopropane-l-carboxylic acid). Thus the physiological effect of gibberellin can be mimicked by ethylene released from ethephon or synthesised from exogenous ACC. It is suggested, that endogenous gibberellins are involved in germination of Amaranthus paniculatus seeds and that action of GA₃ can be substituted by ethylene.Abbreviations ACC 1-aminocyclopropane-l-carboxylic acid - AMO-1618 (2-isopropyl-5methyl-4-trimethylammoniumchloride)-phenyl-l-piperidinium-carboxylate - ancymidol -cyclopropyl--(4-methoxyphenyl)-5-pyrimidine methanol - chloromequat chloride (2-chloroethyl)trimethylammoniumchloride - ethephon 2-chloroethylphosphonic acid - GA gibberellin A₃ - paclobutrazol (2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-lyl)pentan-3-ol - Phosphon D 2,4,dichlorobenzyl-tributhylphosphoniumchloride - tetcyclacis 5,(4-chlorophenyl)-3,4,5,9,10-pentaaza-tetracyclo)5,4,1,0,Z,6,0^8,11 dodeca-3,9-diene     

Influence of method of application of paclobutrazol on soil residues and growth retardation in a ‘Starkrimson-Delicious’ apple orchard

A 3-year field study was conducted to determine the influence of mode of application of the gibberellin-inhibitor paclobutrazol (PP333), [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4 triazol-1-yl)pentan-3-ol], on PP333 soil residue levels and vegetative growth retardation of 10-year-old Starkrimson Delicious (Malus Domestica Borkh.) spur-type apple trees. Treatments were applied in March, 1986 and consisted of foliar or soil sprays (200 ppm, 7 × applications at petal fall (+) 2, 4, 6, 8, 10 and 12 weeks) or a single soil drench (8.2 g A.I./tree) applied to the collar at petal fall. Foliar sprays were applied with and without a plastic ground cover to evaluate the influence of foliar runoff on the degree of soil absorption and its subsequent effect on vegetative growth. PP333 was extracted over a 3 year period (1986–88) from 400 cm² soil patches located at the drip line of each tree, with the exception of soil drenches which were sampled near the collar. PP333 soil extracts were purified and quantitatively analyzed by HPLC. PP333 soil residue levels following foliar sprays were comparable to the soil spray treatment for each year and decreased at a rate of 50% per year from 1986–1988. Foliar sprays retarded terminal growth in the year of application, whereas the soil spray did not inhibit growth until the following year. PP333 residue levels were highest in the soil drench where growth retardation was evident in 1987 and 1988. The greatest carry-over effect occurred in the soil treatments, especially the soil drench application which resulted in the highest soil residue rates throughout the 3 year period.     

Promotion of root emergence in vitro from rhizome buds of Lapageria rosea cv. Nashcourt after proliferation in the presence of paclobutrazol

Medium components that may influence the emergence of adventitious root primordia in rhizome buds of Lapageria rosea (Ruiz et Pav.) cv. Nashcourt in vitro were examined. Sucrose was the only medium component tested that affected root emergence. Increasing the sucrose concentration in the medium from 10 to 30 g 1^-1 stimulated adventitious root emergence from rhizome buds that had been proliferated on a medium containing the gibberellin biosynthesis inhibitor paclobutrazol (5 M). Successful clonal propagation of L. rosea cv. Nashcourt can now be achieved by a rhizome bud proliferation stage(s) in the presence of paclobutrazol followed by an adventitious root emergence stage in the absence of paclobutrazol.     

Effect of paclobutrazol on accumulation of organic acids and total phenols in apple wood

Apple trees (Malus domestica Borkh Spartan grafted on MM 106 rootstock) planted in 1976 in an orchard at Beltsville, Maryland, were treated with paclobutrazol (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-1,2,4-triazol-1-yl-pentan-3-ol) using a foliage spray in 1982 and by trunk banding in 1983. Paclobutrazol did not inhibit shoot growth in 1983; however, shoot growth was significantly retarded in 1984. Increases in organic acids, including succinic, malic, citric, and quinic, and also in total phenols, occurred in wood produced in 1983 on paclobutrazol-treated trees when growth was not inhibited and in wood produced in 1984 when growth was inhibited. The organic acid content of both paclobutrazol-treated and untreated wood tended to decrease from the winter dormant period through growth resumption in the spring. However, the content of total phenols remained nearly the same throughout this sampling period.Mention of a trademark, proprietary product or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

The effect of paclobutrazol on in vitro rooting,transplant establishment and growth of fruit plants

The effect of paclobutrazol on in vitro rooting and growth of sour cherry (Prunus cerasus) rootstock CAB 11E clone, of S 749 × S 1490 (Prunus persica × Prunus kansuensis) hybrid rootstock, and of pear (Pyrus communis), cv. Abbé Fetel is reported.PP333 increased rooting of S 749 × S 1490 and of Abbé Fetel, particularly at a concentration of 0.5 mg/l (a.i.); moreover, it induced a rooting percentage as high as auxin in the former and hastened rooting of the latter. By contrast, paclobutrazol did not affect root production of 11 E.PP333-treated plants had shorter and thicker roots than controls but similar survival rates during acclimatization. Otherwise they grew less than controls during the first part of the acclimatization phase.Abbreviations used in text and tables BA = 6-benzyladenine - IBA = indole-3-butyric acid - PP333 = paclobutrazol = (2RS,3RS)-1-(-4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)pentan-3-ol Part of the results referring to S 749 × S 1490 (P. persica × P. kansuensis) rootstock were presented at the meeting on Controllo della fruttificazione delle piante da frutto, Bologna, Italy, June 1986, and were published in the Riv. Ortoflorofrutt. It. 70 (6)(1986). This research was funded in part by the Italian Ministry of Education (M.P.I. 60%).     

The preparation in vitro of chrysanthemum for transplantation to soil

Plantlets of Dendranthema grandiflora Pennine Reel were grown from nodal sections on Sorbarods saturated with liquid medium containing 0–3 mg 1^–1 of various growth retardants. After 4 weeks they were transferred to compost and maintained at a relative humidity of 42% at 27.5°C. Wilting was assessed over a period of 3 h. Plantlets treated with paclobutrazol, flurprimidol, triapenthenol, chlorphonium chloride, uniconazol and ancymidol showed dose-related reductions in wilting up to a concentration of 3 mg 1^–1. Responses to tetcyclacis and mepiquat chloride were weaker, and no responses to chlormequat chloride, BTS 44584 or diaminozide could be detected. These observations are compatible with an hypothesis that resistance to wilting derives from inhibited synthesis of gibberellins.     

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.     

Linking above- and belowground phenology of hybrid walnut growing along a climatic gradient in temperate agroforestry systems

Background and aims

Plant phenology is a sensitive indicator of plant response to climate change. Observations of phenological events belowground for most ecosystems are difficult to obtain and very little is known about the relationship between tree shoot and root phenology. We examined the influence of environmental factors on fine root production and mortality in relation with shoot phenology in hybrid walnut trees (Juglans sp.) growing in three different climates (oceanic, continental and Mediterranean) along a latitudinal gradient in France.

Methods

Eight rhizotrons were installed at each site for 21 months to monitor tree root dynamics. Root elongation rate (RER), root initiation quantity (RIQ) and root mortality quantity (RMQ) were recorded frequently using a scanner and time-lapse camera. Leaf phenology and stem radial growth were also measured. Fine roots were classified by topological order and 0–1 mm, 1–2 mm and 2–5 mm diameter classes and fine root longevity and risk of mortality were calculated during different periods over the year.

Results

Root growth was not synchronous with leaf phenology in any climate or either year, but was synchronous with stem growth during the late growing season. A distinct bimodal pattern of root growth was observed during the aerial growing season. Mean RER was driven by soil temperature measured in the month preceding root growth in the oceanic climate site only. However, mean RER was significantly correlated with mean soil water potential measured in the month preceding root growth at both Mediterranean (positive relationship) and oceanic (negative relationship) sites. Mean RIQ was significantly higher at both continental and Mediterranean sites compared to the oceanic site. Soil temperature was a driver of mean RIQ during the late growing season at continental and Mediterranean sites only. Mean RMQ increased significantly with decreasing soil water potential during the late aerial growing season at the continental site only. Mean root longevity at the continental site was significantly greater than for roots at the oceanic and Mediterranean sites. Roots in the 0–1 mm and 1–2 mm diameter classes lived for significantly shorter periods compared to those in the 2–5 mm diameter class. First order roots (i.e. the primary or parents roots) lived longer than lateral branch roots at the Mediterranean site only and first order roots in the 0–1 mm diameter class had 44.5% less risk of mortality than that of lateral roots for the same class of diameter.

Conclusions

We conclude that factors driving root RER were not the same between climates. Soil temperature was the best predictor of root initiation at continental and Mediterranean sites only, but drivers of root mortality remained largely undetermined.

     

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.     

Allelopathy in black walnut (Juglans nigra L.) alley cropping. I. Spatio-temporal variation in soil juglone in a black walnut–corn (Zea maysL.) alley cropping system in the midwestern USA

A study was conducted to quantify the spatial and temporal variation in soil juglone (5-hydroxy-1,4-naphthoquinone) in a 10-year-old black walnut (Juglans nigra L.)–corn (Zea mays L.) alley cropping system. Two treatments (root barrier and no barrier) were applied to determine if soil juglone in the alley can be minimized by preventing black walnut root growth into the alley. Although no significant seasonal variation in soil juglone existed, a distinct spatial pattern was observed. Juglone concentration decreased as much as 80% as the distance increased to 4.25 m from the tree row. Installation of polyethylene root barriers minimized juglone concentration to trace levels in the alley. However, this treatment increased juglone levels within the tree row as compared to the no barrier treatment, probably as a result of increased rooting density within a limited volume of soil.     

Sensitivity of the Entomogenous Fungus Beauveria bassiana to Selected Plant Growth Regulators and Spray Additives

Mefluidide was the only one of four plant growth regulators that caused little to no significant inhibition of in vitro germination and growth of the entomogenous fungus Beauveria bassiana. Silaid, paclobutrazol, and flurprimidol significantly inhibited germination and growth. Mortality of fall armyworm, Spodoptera frugiperda, resulting from B. bassiana was significantly reduced when larvae were exposed to conidia plus soil treated with paclobutrazol. Larval mortality resulting from conidia plus soil treated with mefluidide did not differ significantly from mortality resulting from untreated conidia. Triton CS-7 was the only one of eight spray adjuvants that significantly inhibited germination of B. bassiana conidia.     

The effect of long term CO2 enrichment on the growth,biomass partitioning and mineral nutrition of Sitka spruce (Picea sitchensis (Bong.) Carr.)

Sitka spruce [Picea sitchensis (Bong.) Carr.] seedlings were grown for 3 years in an outside control plot or in ambient (355 mol mol^-1) or elevated (ambient + 350 mol mol^-1) atmospheric CO₂ environments, within open top chambers (OTCs) at the Institute of Terrestrial Ecology, Edinburgh. Sequential harvests were carried out at the end of each growing season and throughout the 1991 growing season, five in all. Plants grown in elevated CO₂ had, (i) 35 and 10% larger root/shoot ratios at the end of the first and third season, respectively, (ii) significantly higher summer leader extension relative growth rates, which declined more rapidly in early autumn than ambient grown plants, (iii) after three growing seasons a significantly increased mean annual relative growth rate, (iv) consistently lower foliar nutrient concentrations, and (v) after two growing seasons smaller total projected needle areas. Plants grown inside OTCs were taller, heavier and had a smaller root/shoot ratio than those grown outside the chambers. There was no effect of CO₂ concentration on Sitka spruce leaf characteristics, although leaf area ratio, specific leaf area and leaf weight ratio all fell throughout the course of the 3 year experiment.     

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     

An in vitro microplant bioassay using clonal white ash to test for tall fescue allelopathy

Axillary shoots from three selected white ash (Fraxinus americana L.) clones were harvested from in vitro shoot cultures. Roots were initiated by pulsing excised shoots for eight days in the dark in MS medium supplemented with 2% sucrose, 0.7% agar, 5 M NAA, and 1 M IBA. Pulsed shoots were transferred to a root elongation medium consisting of 25% MS macrosalts, full-strength microsalts and organics, 1% sucrose, 0.7% agar and no auxins. When roots were visible (6–10 days after transfer to root elongation medium), microplants were transferred to vessels containing the same minimal medium and tall fescue (Festuca elatior var. arundinacea (Schreb.) Wimm.) leaf extracts, leaf leachates, or soil leachates from plant boxes with and without tall fescue sod. After four weeks in vitro, primary adventitious and secondary root growth was reduced by extracts obtained from 5 and 10 g ground leaves per 100 ml of medium. Leachates obtained from 5 g soaked leaves per 100 ml of medium stimulated primary root growth. Soil leachates from bare soil also stimulated primary root growth. Variation was observed among the clones for root growth when plantlets were grown in extracts or leachates from tall fescue.     

Principal directions of growth and the generation of cell patterns in wild-type and gib-1 mutant roots of tomato (Lycopersicon esculentum Mill.) grown in vitro

The patterns of cell growth and division characteristic of the apex of tomato roots grown in vitro were simulated by computer using a growth tensor (GT). The GT was used to clarify the basis of the altered cell patterns found within apices of roots whose gibberellin levels had been depressed by mutation (at the GIB-1 locus) or through application of the gibberellin-biosynthesis inhibitor, 2S,3S paclobutrazol. At the pole of wild-type roots, where the cell files of the cortex converge, there are commonly only one or two tiers of cortical cells sandwiched between the pole of the stele and the cap initials. By contrast, root apices of the gib-1 mutant contain additional tiers in this region. The development of these additional tiers is suppressed when roots of the mutant are grown in the presence of gibberellic acid (GA₃), but could be induced in wild-type roots when they are grown in 2S,3S paclobutrazol. The wild-type cell pattern can be simulated using the GT and by the application of appropriate rules that govern cell growth and division. The induced variations in cell pattern are interpreted as being due to displacements, within the apex, of the principal directions of growth (PDGs), which are represented, in part, by the set of periclines and anticlines seen in the cell wall network; these, in turn, are utilized in the specification of the GT. During normal (wild-type) root growth, the PDGs maintain a stable pattern and the corresponding cell pattern is also stable. However, in order to interpret the cellular behaviour found in wild-type roots grown in 2S, 3S paclobutrazol, simulation using the GT shows that, if the pattern of PDGs is destabilized and displaced distally along the root axis, the cell pattern reorganizes into that typical of gib-1 mutant roots. Conversely, the cell pattern of gib-1 roots, which reverts to wild-type upon exposure to GA₃, can be simulated if the PDGs are displaced proximally to the inside of the apex whereupon the number of cortical tiers at the root pole decreases. These results suggest a link between endogenous gibberellin level and the specification of the PDGs in the growing tomato root apex. Furthermore, the evidence of cell patterns from gib-1 roots suggests that, in order to achieve stability of PDGs with concomitant stable cellular patterning, an optimal gibberellin level is necessary. In practice, this can be attained by culturing the mutant roots in medium containing 1 M GA₃.Abbreviations GA₃ gibberellic acid - GT growth tensor - NCS natural coordinate system - PDG principal direction of growth - QC quiescent centre - RERG relative elemental rate of growth We are grateful to the former Agricultural and Food Research Council for financial support under the International Scientific Interchange Scheme to enable J.N. to work at Long Ashton Research Station, and to K. Kurczyski (Silesian University, Katowice, Poland) for help in writing a computer program for cell proliferation. Preparation of the model for growth and division was supported in part by a grant from the Committee for Scientific Research, Poland.     

XE-1019: Plant response,translocation, and metabolism

XE-1019 [(E)-1-(4-chlorophenyl)-4,4,-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol] was injected into bean plants (Phaseolus vulgaris L. Black Valentine) at doses of 0.1–1000 g/plant and caused reduced height growth, fresh weight, and leaf area 7 days after treatment. The sprout growth of California privet (Ligustrium ovalifolium Hassk.) was inhibited 52% by 10 g and growth was further suppressed as the dose was increased to 100 g, without injury. The shoot growth of American sycamore (Platanus occidentalis L.) and yellow-poplar (Liriodendron tulipifera L.) was progressively inhibited after 3 months as the injected dose of XE-1019 was increased from 2.5 to 240 mg/tree. Neither species was injured. Growth of 1-year-old trees of Golden Delicious apple (Malus domestica Borkh) was inhibited 28 days after injecting the stem with 2 mg of¹⁴C-labeled XE-1019. At this time, 2% of¹⁴C activity has been translocated into the new shoots and 3% was present in the xylem and phloem of the scion. From 96 to 99% of¹⁴C-activity found in the xylem and phloem and 92% in the new shoot tissue chromatographed with XE-1019. This indicates that little degradation of XE-1019 occurred during the initial inhibition period.