Phase Change in Hedera helix: Stabilization of the Mature Form with Abscisic Acid and Growth Retardants

Applications of ABA to the mature form of Hedera helix stabilize its morphological characteristics and prevent GA₃ induced reversion to the juvenile form. Plants treated with GA₃ reverted to the juvenile form whereas those supplied with ABA in conjunction with GA₃ remained mature. When mature plants were treated with 5 nanomoles of GA₃ and 5 micromoles of ABA, reversion did not occur, but when the GA₃ dose was raised to 25 nanomoles with the same level of ABA, reversion did occur. This implies that the relative amounts of GA₃ and ABA applied are important in controlling growth form and not the absolute levels of these hormones. Applications of growth retardants (Chlormequat, Ancymidol, and SADH) stabilize the mature form by preventing spontaneous reversions induced under low light intensity. These two lines of evidence support the hypothesis that the mature morphological form can be stabilized by regulating the effective level of gibberellins in the plant and this can be accomplished by inhibition of gibberellin action or gibberellin biosynthesis.     

Phase Change in Hedera helix: Induction of the Mature to Juvenile Phase Change by Gibberellin A3

A sensitive and reproducible method to obtain GA₃ induced morphological reversion of mature Hedera helix to the juvenile form has been developed. Dose response experiments indicate that GA₃ stimulates reversion over a 50–100 fold range with a half maximal response at approximately 0.5 μg GA₃ per plant. The individual characteristics involved in phase change revert to the juvenile form in a sequential manner as GA₃ dose is increased. Variations in light intensity from 1.2–3.6 × 10⁴ lux and temperature from 15 to 26°C do not affect this hormonal response. Other growth regulators including indoleacetic acid, kinetin, abscisic acid and (2-chloroethyl)phosphonic acid (Ethephon) are inactive but other gibberellins (GA₁ and a mixture of A₄–A₇) are active in stimulating reversion. Therefore, the response is specific for gibberellins as a class of hormones but non-specific for a particular form of gibberellin. The significance of this response in relation to juvenility in woody plants is discussed.     

Phase Change in Hedera helix L.: III. THE EFFECTS OF GIBBERELLINS, ABSCISIC ACID AND GROWTH RETARDANTS ON JUVENILE AND ADULT IVY

Gibberellic acid, applied to delaminated petioles of rootedcuttings of juvenile and adult ivy initially induced internodeelongation and abnormal leaf development, and suppressed apicaldominance. Juvenile cuttings were affected only transientlyand soon reverted to normal growth. Adult cuttings, insteadof resuming normal growth after this initial response to GA₃,gradually developed many juvenile characteristics. Approximately16 weeks after treatment at 25 ?C nearly all shoots of adultcuttings had undergone complete rejuvenation. Lower temperaturereduced the speed of response to GA₃. A mixture of gibberellinsA₄ and A₇ had effects similar to those of GA₃ on the growthof juvenile and adult cuttings. Treatment of both phases ofivy with abscisic acid (ABA) induced no visible effects andwhen ABA was applied with GA₃ it did not reduce the responseof either phase to the gibberellin. CCC had a marked dwarfingeffect on juvenile ivy but did not induce pre-maturation. However,extraction of gibberellin-like substances from severely dwarfedplants suggested that CCC was not exerting its growth retardingeffect through an inhibition of gibberellin biosynthesis. AMO1618 did not retard growth of juvenile ivy cuttings.     

Physiological effects of temperature and growth regulators on foliar chlorophyll,soluble protein,and cold hardiness in citrus

Leaf chlorophyll (Chl, A, B) and total soluble protein were assayed in greenhouse-grown 1.5-year-old trees of 2 citrus types, trifoliate orange (Poncirus trifoliata (L.) Raf.) and sour orange (Citrus aurantium L.) exposed to 12 h (day/night) photoperiods in growth chambers under high (30°/21°C, day/night; noncold-hardening) and low (16°/5°C; cold-hardening) temperature regimes. Trees were sprayed 2 × per week for 5 weeks with one of the following solutions at 100 M: napthaleneacetic acid (NAA), paclobutrazol (2RS, 3RS)-1-(4-chlorophenyl-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol) (PPP333), benzyl-adenine (BA), abscisic acid (ABA), gibberellic acid (GA₃), minerals only (N, P, K, S, Ca, Mg) and BA (+) minerals. NAA, PP333, ABA and GA₃ decreased Chl A, B and soluble protein in both citrus types under cold-hardening conditions in contrast to increases with the use of BA and BA (+) minerals especially in trifoliate orange. Both BA and GA₃ increased Chl A, B and protein synthesis under high temperature in both citrus types. Under noncold-hardening temperatures, GA₃ enhanced Chl A, B but sharply reduced foliar protein concentration. Dieback of both cultivars following exposure to temperatures down to –6.7°C was decreased 7% by NAA sprays during noncold-hardening temperatures. Cold tolerance of noncoldhardened trifoliate orange trees was also improved with ABA and PP333. Foliar sprays of NAA (sour orange) and PP333 and BA (+) minerals (trifoliate) increased cold tolerance of cold-hardened trees by 8%. Results indicate that spray applications of growth regulators influence physiological factors associated with foliar functioning and cold tolerance in citrus during different temperature regimes.Summary Growth promoters (BA) and inhibitors (NAA) have the potential to promote cold hardines through either a strong stimulatory effect on foliar physiology or a marked inhibition of growth in general. This suggests that each growth regulator may possess an independent role in the cold-hardiness phenomenon and may also interact with physiological processes other than soluble protein and chlorophyll metabolism. The relationship between soluble protein levels in citrus foliage and the degree of cold hardiness remains uncertain and is essentially unresolved pending more specific qualitative research.University of Florida Agricultural Experiment Station Series No. 7446.This paper reports the results of research only. Mention of a trademark of a proprietary product does not constitute a recommendation for use by the U.S. Department of Agriculture to the exclusion of other products that may also be suitable.     

Effect of jasmonic acid on endogenous gibberellins and abscisic acid in rice under NaCl stress

Content of endogenous abscisic acid (ABA) increased in rice plants under salt stress. Pre- or post-treatment by jasmonic acid (JA) mostly further increased ABA content. In the presence of salt stress also content of gibberellins (GAs) mostly increased more after treatment by JA. Endogenous content of bioactive GA₁ was higher in post-treatment by JA than in pre-treatment by JA.This study was supported by the Korea Science and Engineering Foundation (2000-2-20100-001-3)     

Influence of growth regulator treatments on dry matter production,fruit abscission,and14C-assimilate partitioning in citrus

Experiments were performed to monitor (1) uptake and translocation of foliar-applied microdroplets of¹⁴C hormones and (2) effects of multiple growth regulator sprays on foliar and fruit growth variables and photosynthate partitioning in Valencia orange trees (Citrus sinensis (L.) Osbeck). The uptake of¹⁴C-sucrose,¹⁴C-paclobutrazol (PP333), and¹⁴C-napthaleneacetic acid (NAA) in 6-month-old greenhouse-grown trees exceeded that of¹⁴C-abscisic acid (ABA) and¹⁴C-benzyladenine (BA) 48 h after microdroplet application.¹⁴C-sucrose transport from the application site was much greater than any other source, especially¹⁴C-BA. In a second study, 2-year-old Valencia orange trees were maintained under field conditions and were sprayed to foliar runoff (3 × /week for 3 weeks) with BA, NAA, ABA, PP333, and gibberellic acid (GA₃) at 100 M during flowering and early fruit set. Select branches were then briefly exposed to¹⁴CO₂ and harvested 24 h later. Both GA₃ and BA sprays promoted foliar growth. BA also stimulated fruit growth, whereas GA₃ sharply increased fruit dry weight while fruit number decreased. BA and GA₃ enhanced¹⁴C assimilate export by the foliage to the developing fruit, and GA₃ was especially active in promoting fruit sink intensity (¹⁴C/dry wt). The other compounds (NAA, ABA, PP333) restricted foliar and fruit growth. They also inhibited transport of¹⁴C assimilate from the leaves to the fruit. Results indicate that foliar-applied growth regulators can influence source-sink relations in citrus early in reproductive development by manipulating photoassimilate production and partitioning.     

Effects of abscisic acid on the orientation and cold stability of cortical microtubules in epicotyl cells of the dwarf pea

Summary The effects of abscisic acid (ABA) on the orientation and cold stability of cortical microtubules (MTs) in epidermal cells of epicotyls of the dwarf pea,Pisum sativum L. cv. Little Marvel, were examined by immunofluorescence microscopy. The effect of ABA on the elongation of epicotyls and on the orientation of cortical MTs was opposite to that of gibberellin A₃ (GA₃). Treatment with ABA, which reduced the promotion of epicotyl elongation by GA₃, eliminated the GA₃-induced predominance of transverse MTs and resulted in a predominance of longitudinal MTs. The effect of ABA on the cold stability of cortical MTs was also opposite to that of GA₃. ABA increased the cold stability of MTs, while GA₃ decreased it. The predominance of longitudinal MTs brought about by ABA may have some relationship to ABA-induced inhibition of the elongation of the epicotyl. ABA may alter membrane proteins to stabilize cortical MTs and induce cold hardiness of plants.Abbreviations ABA abscisic acid - DMSO dimethylsulfoxide - FITC fluorescein isothiocyanate - GA₃ gibberellin A₃ - MT microtubule - PBS phosphate-buffered saline Dedicated to the memory of Professor Oswald Kiermayer     

Control of macaw palm seed germination by the gibberellin/abscisic acid balance

The hormonal mechanisms involved in palm seed germination are not fully understood. To better understand how germination is regulated in Arecaceae, we used macaw palm (Acrocomia aculeata (Jacq.) Lodd. Ex Mart.) seed as a model. Endogenous hormone concentrations, tocopherol and tocotrienol and lipid peroxidation during germination were studied separately in the embryo and endosperm. Evaluations were performed in dry (D), imbibed (I), germinated (G) and non‐germinated (NG) seeds treated (+GA₃) or not treated (control) with gibberellins (GA). With GA₃ treatment, seeds germinated faster and to a higher percentage than control seeds. The +GA₃ treatment increased total bioactive GA in the embryo during germination relative to the control. Abscisic acid (ABA) concentrations decreased gradually from D to G in both tissues. Embryos of G seeds had a lower ABA content than NG seeds in both treatments. The GA/ABA ratio in the embryo was significantly higher in G than NG seeds. The +GA₃ treatment did not significantly affect the GA/ABA ratio in either treatment. Cytokinin content increased from dry to germinated seeds. Jasmonic acid (JA) increased and 1‐aminocyclopropane‐1‐carboylic acid (ACC) decreased after imbibition. In addition, α‐tocopherol and α‐tocotrienol decreased, while lipid peroxidation increased in the embryo during germination. We conclude that germination in macaw palm seed involves reductions in ABA content and, consequently, increased GA/ABA in the embryo. Furthermore, the imbibition process generates oxidative stress (as observed by changes in vitamin E and MDA).     

Phytohormones Related to Host Plant Manipulation by a Gall-Inducing Leafhopper

The maize orange leafhopper Cicadulina bipunctata (Hemiptera: Cicadellidae) induces galls characterized by growth stunting and severe swelling of leaf veins on various plants of Poaceae. Previous studies revealed that galls are induced not on feeding site but on distant, newly extended leaves during the feeding, and strongly suggested that some chemicals injected by the leafhopper affect at the leaf primordia. To approach the mechanism underlying gall induction by C. bipunctata, we examined physiological response of plants to feeding by the leafhopper. We performed high-throughput and comprehensive plant hormone analyses using LC-ESI-MS/MS. Galled maize leaves contained higher contents of abscisic acid (ABA) and trans-Zeatin (tZ) and lower contents of gibberellins (GA₁ and GA₄) than ungalled maize leaves. Leafhopper treatment significantly increased ABA and tZ contents and decreased GA₁ and GA₄ contents in extending leaves. After the removal of leafhoppers, contents of tZ and gibberellins in extending leaves soon became similar to the control values. ABA content was gradually decreased after the removal of leafhoppers. Such hormonal changes were not observed in leafhopper treatment on leaves of resistant maize variety. Water contents of galled leaves were significantly lower than control leaves, suggesting water stress of galled leaves and possible reason of the increase in ABA content. These results imply that ABA, tZ, and gibberellins are related to gall induction by the leafhopper on susceptible variety of maize.     

Abscisic acid and apical dominance in Phaseolus coccineus L.

Abscisic acid (ABA) in lanolin, applied to the internode of decapitated runner bean plants enhances the outgrowth of lateral buds. The optimum concentration of the paste is 10^-5 M. The effect of ABA is counteracted by indoleacetic acid (IAA) but not by gibberellic acid (GA₃). There is no effect when ABA is applied to the apical bud or lateral buds of intact plants. However, 13.2 ng given to the lateral buds of decapitated plants stimulate their growth, whereas higher concentrations are inhibitory. Consequently, ABA enhances growth of lateral buds directly, but only when apical dominance is already weakened. The growth of the decapitated 2^nd internode was not affected by ABA. Radioactivity from [2-¹⁴C] ABA, applied to nonelongating 2^nd internode stumps of decapitated runner bean plants moves to the lateral buds, whereas [1-¹⁴C]IAA-and [³H]GA₁-translocation is much weaker. ABA transport is inhibited if IAA or [³H]GA₁ is applied simultaneously. In elongating internodes [¹⁴C]ABA is almost completely immobile. [¹⁴C]IAA-and [³H]GA₁-translocation is not affected by ABA. The amount of radioactivity from labelled ABA, translocated to the lateral buds, is highest during the early stages of bud outgrowth.Abbreviations ABA 2,4-cis, trans-(+)-abscisic acid - GA gibberellic acid - IAA indoleacetic acid - p.l. plain lanolin     

EFFECTS OF WATER STRESS,ABSCISIC ACID,AND GIBBERELLIC ACID ON FLOWER PRODUCTION AND DIFFERENTIATION IN THE CLEISTOGAMOUS SPECIES COLLOMIA GRANDIFLORA DOUGL. EX LINDL. (POLEMONIACEAE)

The effects of water stress, abscisic acid (ABA), and gibberellic acid (GA₃) on flower production and differentiation by Collomia grandiflora were investigated. An untreated plant typically produced both small, closed cleistogamous (CL) and large, open chasmogamous (CH) flowers. The larger corolla of CH flowers was due to a greater cell number and size. When plants were water-stressed or sprayed with ABA, both the percentage of CH flowers and the total number of flowers were reduced significantly. The corolla dimensions and epidermal cell numbers and sizes of CL flowers produced by water-stressed and ABA-sprayed plants did not differ from those of CL flowers produced by control plants. Application of GA₃ to both well-watered and water-stressed plants significantly increased the percentage of CH flowers formed compared to well-watered controls. In the absence of GA₃, water-stressed plants produced almost entirely CL flowers. GA₃-sprayed plants produced CH flowers whose corolla dimensions were intermediate between those of CL and CH flowers formed by control plants. Epidermal cells of these intermediate corollas were reduced only in number and not in size when compared to control CH flowers. Endogenous levels of ABA and gibberellins may control the type of flower produced by C. grandiflora and may mediate some of the observable effects of water stress on flowering.     

Phase Change in Hedera helix L: II. THE POSSIBLE BOLE OF ROOTS AS A SOURCE OF SHOOT GIBBERELLIN-LIKE SUBSTANCES

When synthesis was estimated by the agar diffusion techniqueboth basal and lateral adventitious roots of Hedera helix L.in the juvenile growth phase were shown to synthesize gibberellin-likesubstances. Seedlings and cuttings from juvenile ivy could begrown in water culture for several weeks. When roots were excisedfrom these plants shoot growth was reduced in comparison withthat of intact plants. The stems, apices, and leaves of derootedseedlings and cuttings contained lower levels of extractablegibberellin-like substances than comparable organs of intactplants. The major zone of gibberellin-like activity in intactplants co-chromatographed with gibberellins A₁ and A₃. Whenthese gibberellins were applied to plants grown in culture theywere found to promote growth of intact but not derooted plants.These findings are discussed in relation to the role of rootfactors and particularly gibberellins in phase change.     

Hormonal changes associated with fruit set and development in mandarins differing in their parthenocarpic ability

Satsuma [Citrus unshiu (Mak) Marc.] and Clementine [Citrus reticulata (Hort.) Ex. Tanaka, cv. Oroval] are two related species of seedless mandarins which differ in their tendency to set parthenocarpic fruits. Satsuma fruits naturally set parthenocarpically whereas Clementine mandarins show very low ability to set fruit in the absence of cross-pollination. The endogenous levels of gibberellins (GAs) and free and conjugated indole-acetic acid (IAA) and abscisic acid (ABA) throughout early stages of fruit development were investigated in seedless cultivars of both species. Analyses performed by full-scan combined gas chromatography-mass spectrometry (GC-MS) of extracts from ovaries at anthesis demonstrated the presence of GA₁₉, GA₂₀, GA₂₉, GA₁, GA₈, GA₃ and iso-GA₃ in Satsuma mandarin, whereas only GA₂₉, GA₃ and trace levels of GA₈ were detected in Clementine. At this developmental stage GA-like substances, as estimated by bioassay, reached their highest levels in Satsuma, while Clementine mandarins contained relatively lower levels. In both species the highest levels of free IAA were found at petal-fall stage at which time free ABA levels also peaked. Developing fruits of Clementine had higher amounts of both free IAA and ABA. In Satsuma, levels of conjugated IAA remained low throughout reproductive development whereas in Clementine they increased as the free form declined. In contrast, conjugated ABA was at low levels in Clementine but reached higher concentrations in Satsuma. These results suggest that in these mandarins the potential for setting parthenocarpic fruits is mainly influenced by the hormonal status of the fruit during the later stages of cell division and early stages of cell enlargement. Thus, the condition of low ability to set parthenocarpic fruits appears to be associated with lower levels of active GAs, lower capability to catabolize ABA to conjugated ABA and higher ability to conjugate IAA during this period.     

Interactions between abscisic acid, ethylene and gibberellin in internodal elongation in floating rice: the promotive effect of abscisic acid at low humidity

The enhancement of internodal elongation in floating or deepwater rice (Oryza sativa L. cv. Habiganj Aman II) by treatment with ethylene or gibberellic acid (GA₃) at high relative humidity (RH) is inhibited by abscisic acid (ABA). Here, we examined the interactive effects of ethylene, gibberellin (GA) and ABA at low RH on internodal elongation of deepwater rice stem segments. Although ethylene alone hardly promoted internodal elongation of stem sections at 30% RH, it enhanced the internodal elongation induced by GA₃. Application of ABA alone to stem segments had no effect on internodal elongation. However, in the presence of ethylene and GA₃ at 30% RH, ABA further promoted internodal elongation. This promotive effect of ABA was not found in the internodes of stem segments treated either with ethylene or with GA₃ at 30% RH or in the internodes of stem segments treated with ethylene and/or GA₃ at 100% RH.     

Fibre length and gibberellins A1 and A20 are decreased in Eucalyptus globules by acylcyclohexanedione injected into the stem

Trinexapacethyl (TriEt), an acylcyclohexanedionetype inhibitor of gibberellin (GA) biosynthesis, was applied to 3-year-old Eucalyptus globules saplings by localised injection near the base of each stem. The objective was to alter cambial region GA levels and to study the effects on secondary xylem fibre development. Seven weeks later wood samples, with bark and cambial region intact, were removed 10 and 30 cm above the point of injection. Fusiform cambial cell dimensions were compared with those of fibre-tracheids in the most recently formed 100 um of secondary xylem. Increasing TriEt applications from 5 to 5 000 mg active ingredient significantly reduced average fibre length, and to a lesser extent average fusiform cambial cell length. Also reduced was the number of cells in the cambial zone and the number of differentiating fibres with primary walls. However, no trends were evident for changes in fibre diameter, the proportion of vessel elements or the ratio of cambial ray cells to fusiform cambial cells. Two gibberellins (GA₁ and GA₂₀), indole-3-acetic acid (IAA) and abscisic acid (ABA) were quantified in cambial region tissues by gas chromatographymass spectrometry using stable isotope labelled internal standards. Increasing TriEt application reduced both GA₁ and GA₂₀ levels. Effects on IAA and ABA were not significant, although their levels tended to be lower at the highest TriEt application rate. The elongation of secondary xylem fibres was positively correlated with higher levels of endogenous GA₁ (r_s= 0.74, P < 0.01) and GA₂₀ (r_s= 0.72, P < 0.01). These results support a causal role for GA₁ in cambial cell division. They are also consistent with the hypothesis that the elongation of differentiating secondary xylem fibres in woody an–giosperms is dependent on GA₁ levels in the cambial region.     

Fungal endophyte Penicillium janthinellum LK5 improves growth of ABA-deficient tomato under salinity

An endophytic fungus was isolated from the roots of tomato (Solanum lycopersicum Mill) and identified as Penicillium janthinellum LK5. The culture filtrate (CF) of P. janthinellum significantly increased the shoot length of gibberellins (GAs) deficient mutant waito-c and normal Dongjin-beyo rice seedlings as compared to control. The CF of P. janthinellum contained GAs (GA₃, GA₄, GA₇ and GA₁₂). To assess endophyte-growth promoting and stress-tolerance potential, the CF along with the propagules of endophyte was applied to tomato-host and abscisic acid (ABA)-deficient mutant Sitiens plants under sodium chloride (NaCl) induced salinity stress. Sitiens plants had retarded growth under normal and salinity stress however its growth was much improved during P. janthinellum-association. The endophyte inoculation reduced the membrane injury by decreasing lipid peroxidation as compared to non-inoculated control under salinity. Endophyte-associated Sitiens plants have significantly higher catalase, peroxidase and glutathione activities as compared to control. Endophyte-infected host and Sitiens plants had low level of sodium ion toxicity and high calcium contents in its root as compared to control. P. janthinellum LK5 helped the Sitiens plants to synthesis significantly higher ABA and reduced the level of jasmonic acid to modulate stress responses. The results suggest that endophytes-association can resist salinity stress by producing gibberellins and activating defensive mechanisms of host and Sitiens plants to achieve improved growth.     

Gibberellins and Abscisic Acid Promote Carbon Allocation in Roots and Berries of Grapevines

Carbon allocation within grapevines may affect berry growth and development. The plant hormones gibberellins (GAs) and abscisic acid (ABA) control various processes across the plant life and both have been involved in assimilate production and transport in different species. Hence, this work examined the distribution of sugars (sucrose, fructose, and glucose) and starch in grapevines at veraison after foliar applications of GA₃, ABA, and an inhibitor of GA biosynthesis, paclobutrazol (PBZ). The results demonstrated that GA₃ increased total grapevine mass, with carbon allocated to the whole grapevine (as structural and soluble carbohydrates). Both GA₃ and ABA increased monosaccharide (glucose and fructose) levels in berries (up to tenfold) and roots (up to threefold). However, GA₃ increased the net carbon fixation whereas ABA did not. PBZ diminished most growth parameters except grapevine mass, and allocated more carbohydrates to roots (up to threefold more sucrose and starch). Such results indicate that GAs promote net carbon fixation and transport, whereas ABA as a stress signal only enhances sugar transport; notwithstanding the two hormones promoted carbon allocation toward roots and berries.     

The control of flower initiation by gibberellin in Helianthus annuus L. (sunflower), a non-photoperiodic plant

The involvement of gibberellins in the control of flowering of sunflower was studied by direct application of GA₃ to the apex of the plants, analysis of the endogenous levels of gibberellin-like substances at different plant ages, and indirectly by the application of paclobutrazol, an inhibitor of gibberellin synthesis. GA₃ speeded-up flower initiation and floral apex development. The time of GA₃ application was more critical than the amount of GA₃ applied. The endogenous levels of gibberellin-like compounds increased significantly by day 15 after sowing. The application of paclobutrazol markedly delayed floral initiation and this effect was also depedent on plant age. Both GA₃ and paclobutrazol had their greatest effects between 10 and 20 days after sowing suggesting that an increase in gibberellins in that time period plays a role in floral initiation.     

New perspectives of gibberellic acid production: a review

The gibberellins (GAs) are an important group of hormones which exert various effects on promoter and regulator of plant growth. Gibberellic acid (GA₃) is a natural plant hormone, with great economical and industrial importance. It affects stem elongation, germination, elimination of dormancy, flowering, sex expression, enzyme induction and leaf and fruit senescence. Despite its diverse applications, the use of GA₃ is limited due to its high production costs. The industrial process currently used for the production of GA₃ is based on submerged fermentation (SmF) techniques. As an alternative for its production, solid state fermentation (SSF) has also been investigated for its ability to increase the yields of GA₃ with the use of agro-industrial wastes as support/substrate, which contributes to the decreased production costs. This review describes GA₃’s physical, chemical and biological properties, its production by fermentation and new advances that are being carried out with special interest on the SSF technique.     

Determination of femtomol quantities of gibberellic acid by radioimmunoassay

A highly sensitive and specific radioimmunoassay which allows the detection of as little as 5 fmol (2 pg) of gibberellic acid (GA₃) in crude plant extracts is described. Antisera of high affinity and titer were obtained by immunizing rabbits with a conjugate of carboxyl-coupled GA₃ and bovine serum albumin. [¹²⁵I]Gibberellic acid-[N-(p-hydroxybenzyl) putrescine]amide of high specific activity, used as the immunotracer, is readily displaced by gibberellic acid methyl ester but not by free gibberellic acid. Thus, methylation of extracts prior to analysis is required. The assay is very specific; besides GA₃, only the closely related GA₇ is highly immunoreactive. Various gibberellins, related compounds, as well as other classes of plant hormones do not interfere with the assay. Levels of immunoreactive gibberellins (GA₃, GA₇) in actively growing tissues, among them cell suspension cultures of 33 different species, were determined.Abbreviations ABA abscisic acid - GC-MS gas chromatography-mass spectroscopy - TLC thin-layer chromatography - GA gibberellin Part 17 in the Series: Use of Immunoassay in Plant Science