The Response to Gibberellin in Pisum sativum Grown under Alternating Day and Night Temperature

The application of gibberellins (GA) reduces the difference in stem elongation observed under a low day (DT) and high night temperature (NT) combination (negative DIF) compared with the opposite regime, a high DT/low NT (positive DIF). The aim of this work was to investigate possible thermoperiodic effects on GA metabolism and tissue sensitivity to GA by comparing the response to exogenously applied GA (in particular, GA₁ and GA₃) in pea plants (Pisum sativum cv. Torsdag) grown under contrasting DIF. Control plants not treated with growth inhibitors or additional GA were 38% shorter under negative (DT/NT 13/21°C) than positive DIF (DT/NT 21/13°C) because of shorter internodes. Additional GA₁ or GA₃ decreased the difference between positive and negative DIF. In pea plants dwarfed with paclobutrazol, which inhibits GA biosynthesis at an early step, the response to GA₁ was reduced more strongly by negative compared with positive DIF than the response to GA₃. The induced stem elongation by GA₁₉ and GA₂₀ did not deviate significantly from the response to GA₁. Plants treated with prohexadione-calcium, an inhibitor of both the production and the inactivation of GA₁, grew equally tall under the two temperature regimes in response to both GA₁ and GA₃. We hypothesize that the reduced response to GA₁ compared with GA₃ in paclobutrazol-treated plants grown under negative DIF is caused by a higher rate of 2β-hydroxylation of GA₁ into GA₈ under negative than positive DIF. This contributes to lower levels of GA₁ and consequently shorter stems and internodes in pea plants grown under negative than positive DIF. Differences in tissue sensitivity to GA alone cannot account for this specific thermoperiodic effect on stem elongation. Received May 28, 1998; accepted May 29, 1998     

The hormonal control of betacyanin synthesis in Amaranthus caudatus

Gibberellic acid (GA₃) inhibits amaranthin synthesis whereas the growth retardant, phosphon D, enhances pigment levels in A. caudatus seedlings exposed to light. No effect was observed on chlorophyll and carotenoid synthesis. Radioactive tyrosine and DOPA were incorporated into amaranthin. The specific activity of amaranthin synthesised in the presence of ¹⁴C-tyrosine or ¹⁴C-DOPA in seedlings treated with GA₃ is higher than water controls. The specific activity of pigment from phosphon D treated tissue is relatively low. GA₃ treated tissue has lower active tyrosine and DOPA pools compared to phosphon treated seedlings. Tyrosine and DOPA-oxidase activity increases in GA₃ treated and H₂O control seedlings exposed to light. Kinetin stimulates the synthesis of amaranthin in dark-grown seedlings and this is not overcome by simultaneous GA₃ application. Dark-grown seedlings treated with different kinetin concentrations and incubated in ¹⁴C-tyrosine synthesise radioactive amaranthin of similar specific activity. Kinetin treatment of dark-grown seedlings brings about an increased tyrosine and DOPA-oxidase activity. The results indicate that GA₃ controls the production and/or availability of tyrosine whereas kinetin can mimic light treatment and controls the utilisation of tyrosine probably by bringing about the synthesis or activation of tyrosine and DOPA-oxidase protein.     

外源GA3对紫斑牡丹幼苗叶片解剖结构与光合特性及内源激素含量的影响

以1年生紫斑牡丹幼苗为试验材料,采用不同浓度(0、100、300、500 mg/L)赤霉素(GA_3)喷施叶片处理,通过透射电镜、扫描电镜、光学显微镜观察幼苗叶片解剖结构,光合仪测定幼苗光合参数并以酶联免疫吸附法测叶片内源激素含量,探究外源GA_3对紫斑牡丹幼苗叶片解剖结构、光合特性和内源激素水平的影响。结果表明:(1)低浓度GA_3处理的紫斑牡丹叶肉细胞增大,栅栏组织外层细胞中叶绿体数量增加,高浓度GA_3处理则与之相反;GA_3处理叶片的栅栏组织/海绵组织比值(P/S)、组织结构紧密度(CTR)均下降,而其组织结构疏松度(SR)增加;GA_3处理的幼苗叶片的叶肉细胞内各叶绿体大小显著大于对照,随着GA_3处理浓度增加,紫斑牡丹叶肉细胞内叶绿体的体积趋于增大,类囊体垛叠凝聚逐渐松散,叶绿体上淀粉颗粒在300 mg/L GA_3处理中较明显;叶片气孔长度、宽度、气孔器大小、气孔开度和气孔密度随着GA_3浓度升高先升高后下降,同时叶片上表皮角质层厚度随GA_3浓度的升高而增加。(2)紫斑牡丹叶片净光合速率(P_n)、气孔导度(Cond)、蒸腾速率(T_r)、水分利用率(WUE)在100和300 mg/L GA_3处理下大都显著高于对照,且300 mg/L GA_3处理显著高于其余处理,而其在500 mg/L GA_3处理下显著低于对照。(3)紫斑牡丹叶片脱落酸(ABA)和吲哚乙酸(IAA)含量均在500 mg/L GA_3下显著高于对照,而在其余浓度处理下不同程度低于对照,叶片内源玉米素核苷(ZR)和GA_3含量均在300 mg/L GA_3处理下显著高于其余处理和对照,而其余处理相比对照均无显著变化;叶片的ZR/ABA、ZR/IAA、ZR/GA_3和(IAA+GA_3+ZR)/ABA比值都在300 mg/L GA_3处理下显著高于其他处理,叶片的IAA/ABA和ABA/GA_3比值均在500 mg/L GA_3处理下显著高于其他处理。研究发现,适宜浓度外源GA_3处理,能显著提高紫斑牡丹幼苗叶片光合速率、水分利用效率及蒸腾速率,调节植物体内源激素的含量及平衡,从而使叶片能合成较多有机物,促进幼苗生长。     

Uptake and metabolism of radioactive gibberellins by barley aleurone layers

Summary When aleurone layers were treated with labeled gibberellin A₁ (³H-GA₁), gibberellin A₅ (³H-GA₅) and the methyl ester of ³H-GA₅ (³H-GA₅-ME), radioactivity was accumulated by the tissue for a period of 20–30 h. After this time, radioactivity was released into the medium. Concomitantly, ribonuclease was also liberated by the tissue. The radioactivity accumulated by aleurone layers was associated with polar metabolites of the respective GAs, and the extent of extent of accumulation was a function of the degree of GA metabolism (GA₅-ME>GA₅>GA₁). Accumulation of radioactivity was inhibited in the cold and by the metabolic poisons NaF and dinitrophenol. This was thought to be due to inbition of GA metabolism. The accumulation of ³H-GA₁ in aleurone tissue did not reach saturation when unlabeled GA₃ up to 10^-2 M was added to the incubation medium.Abbreviations GA gibberellin - GA₅ ME, gibberellin A₅ methyl ester - RNase ribonuclease     

Localization of ATPase in the endoplasmic reticulum and golgi apparatus of barley aleurone

Summary The cytochemical localization of adenosine triphosphatase (ATPase) was studied in the aleurone layer of barley (Hordeum vulgare L. cv. Himalaya). Isolated barley aleurone layers secrete numerous enzymes having acid phosphatase activity, including ATPase. The secretion of these enzymes was stimulated by incubation of the aleurone layer in gibberellic acid (GA₃). ATPase was localized using the metal-salt method in tissue incubated in CaCl₂ with and without GA₃. In sections of tissue incubated without GA₃, cytochemical staining was confined to a narrow band of cytoplasm adjacent to the starchy endosperm and to the cell wall of the innermost tier of aleurone cells. Cytochemical staining was absent from the organelles of tissues not treated with GA₃. In tissue incubated in the presence of GA₃, cytochemical staining was evident throughout the cytoplasm and cell walls of the tissue. In the cell wall, electron-dense deposits were found only in digested channels. The cell-wall matrix of GA₃-treated aleurone did not stain, indicating that it does not permit diffusion of enzyme. In the cytoplasm of GA₃-treated aleurone, all organelles except microbodies, plastids, and spherosomes stained for ATPase activity; endoplasmic reticulum (ER), Golgi apparatus, and mitochondria showed intense deposits of stain. The ER of the aleurone is a complex system made up of flattened sheets of membrane, which may be associated with both the Golgi apparatus and the plasma membrane. The dictyosome did not stain uniformly for ATPase activity; rather there was a gradation in staining of the cisternae from thecis (lightly stained) to thetrans (heavily stained) face. Vesicles associated with dictyosome cisternae also stained intensely as did the protein bodies of GA₃-treated aleurone cells.     

Gibberellic acid-induced changes in glutathione metabolism and anthocyanin content in plant tissue

Literature data point to a possible link between gibberellic acid (GA₃) and glutathione metabolism in plant tissue, as both are connected to dormancy breakage. In order to study the influence of GA₃ on glutathione metabolism, we treated an anthocyanin accumulating cell culture of periwinkle (Catharanthus roseus) and a shoot differentiated culture of pea (Pisum sativum) with GA₃. Glutathione reductase (GR; E.C. 1.6.4.2) activity increased to 135% and 190% of the control in C. roseus and P. sativum, respectively. The level of oxidized glutathione (GSSG) decreased to 60% of the control in the C. roseus culture while no change in GSSG was observed in the P. sativum culture. No changes in the tissue concentration of total glutathione was observed in the cultures after GA₃ treatment. Concomitant to the changes in GSSG and GR, an increase in anthocyanin accumulation was observed in the C. roseus culture in association with a strong increase in phenylalanine ammonia-lyase (PAL; E.C. 4.3.1.5) activity in response to GA₃. These data strongly suggest a link between GA₃ and glutathione metabolism.     

Enzyme formation and release by isolated barley aleurone layers

Aleurone layers, with testa attached, were prepared from degermed, decorticated barley with the aid of a fungal enzyme preparation. The preparations appeared intact under the scanning electron microscope. By using antibiotics only in an early stage preparations were obtained uncontaminated by micro-organisms and which, when incubated under optimal conditions with gibberellic acid, GA₃, produced near-maximal amounts of α-amylase. The enzyme accumulated in the tissue before it was released into the incubation medium. Daily replacement of the incubation medium, containing GA₃, depressed the quantity of α-amylase produced. α-Amylase was also produced in response to gibberellins GA₁, GA₄ and GA₇ and, to a much lesser extent, helminthosporol and helminthosporic acid. A range of other substances, reported elsewhere to induce α-amylase formation, failed to do so in these trials. At some concentrations, glutamine marginally enhanced the quantity of enzyme formed during prolonged incubations. It is confirmed that α-glucosidase occurs in the aleurone layer and embryo of ungerminated barley, and increases in amount during germination. GA₃ is shown to enhance this increase. When embryos arc burnt, to prevent gibberellin formation, no rise in α-glucosidase levels occurs unless GA₃ is supplied to the grains. As the activity of α-glucosidase and other enzymes have been determined as ‘α-amylase’ by some assay methods, their alterations in activity in response to GA₃ necessitates a re-evaluation of the evidence for de novo) synthesis of α-amylase in aleurone tissue.     

C]GA(12)-Aldehyde, [C]GA(12), and [H]- and [C]GA(53) Metabolism by Elongating Pea Pericarp

Gibberellins (GAs) are either required for, or at least promote, the growth of the pea (Pisum sativum L.) fruit. Whether the pericarp of the pea fruit produces GAs in situ and/or whether GAs are transported into the pericarp from the developing seeds or maternal plant is currently unknown. The objective of this research was to investigate whether the pericarp tissue contains enzymes capable of metabolizing GAs from [¹⁴C]GA₁₂-7-aldehyde ([¹⁴C]GA₁₂ald) to biologically active GAs. The metabolism of GAs early in the biosynthetic pathway, [¹⁴C]GA₁₂ and [¹⁴C]GA₁₂ald, was investigated in pericarp tissue isolated from 4-day-old pea fruits. [¹⁴C]GA₁₂ald was metabolized primarily to [¹⁴C]GA₁₂ald-conjugate, [¹⁴C]GA₁₂, [¹⁴C]GA₅₃, and polar conjugate-like products by isolated pericarp. In contrast, [¹⁴C]GA₁₂ was converted primarily to [¹⁴C]GA₅₃ and polar conjugate-like products. Upon further investigations with intact 4-day-old fruits on the plant, [¹⁴C]GA₁₂ was found to be converted to a product which copurified with endogenous GA₂₀. Lastly, [²H]GA₂₀ and [²H]GA₁ were recovered 48 hours after application of [²H]- and [¹⁴C]GA₅₃ to pericarp tissue of intact 3-day-old pea fruits. These results demonstrate that pericarp tissue metabolizes GAs and suggests a function for pericarp GA metabolism during fruit growth.     

In vitro and in vivo modification of sugar transport and translocation in celery by phytohormones

In an attempt to address the controversy in the literature as to whether phytohormones have any direct effect on phloem loading of sucrose, we investigated the effect of gibberellic acid (GA₃) and indoleacetic acid (IAA) on sugar transport and translocation in celery (Apium graveolens L. cv. Utah 5270). Both hormones enhanced sucrose uptake into isolated vascular bundles and phloem tissue of celery and enhanced the export of ¹⁴C assimilates from leaves of intact plants in vivo. The hormone-induced increase of uptake into isolated vascular bundles or phloem was specific for sucrose and mannitol which are translocated in phloem. Furthermore, the hormone-induced increase in translocation was not due to an increase in sink demand, since neither glucose nor sucrose uptake rates were affected in the storage parenchyma tissue discs (sink region) in the presence of GA₃ or IAA. The evidence suggests that phytohormones may have a direct effect on phloem loading of sucrose. The possibility of short-term GA₃ and IAA effects on processes resulting in membrane transport of sugars in celery is discussed.     

Exogenously applied GA4 is converted to GA1 in seedlings of Salix

Gibberellin A₄ (GA₄) is biologically active in Salix pentandra and is able to induce stem elongation in seedlings grown under short day (SD) conditions, as well as in seedlings grown under long day (LD) conditions and treated with a growth retardant BX-112. [³H₂]GA₄ and [²H₂]GA₄ were applied to seedlings and leaf and stem explants of S. pentandra, and metabolites were studied using HPLC and GC-MS. After application of [³H₂]GA₄ to seedlings of S. pentandra, one of the three main radioactive metabolites in the free acid fraction had retention properties similar to GA₁. Using [²H₂]GA₄, this compound was identified by GC-MS with SIM as [²H₂]GA₁ both from short day-grown and BX-112-treated seedlings, as well as in leaf and stem explants. After injection of GA₄ into a mature leaf, GA₁ was mainly found in the elongating stem tissue. Thus, the possibility that the biological activity of GA₄ in Salix is due to its conversion to GA₁ cannot be excluded.     

Regulation of Growth in Avena Stem Segments by Gibberellic Acid and Kinetin

Kinetin at physiological concentrations causes significant reduction of GA₃-promoted growth in excised Avena stem segments. Kinetin is therefore considered to be a gibberellin-antagonist in this system. A Lineweaver-Burke plot reveals that kinetin acts non-competitively with GA₃. The kinetin inhibition of GA₃-promoted growth can be seen within 6 hours. It was found that soluble protein is markedly increased by kinetin in the tissue during the first 3 hours, thus preceding the inhibition of GA₃-promoted growth by several hours. At the cellular level, kinetin negated the blocking effect of GA₃ on cell division in the intercalary meristem portions of these segments. In fact, kinetin promotes both lateral and longitudinal cell divisions in intercalary meristem cells.     

Calmodulin stimulation of unidirectional calcium uptake by the endoplasmic reticulum of barley aleurone

The role of calmodulin (CaM) in gibberellic acid (GA₃)-stimulated Ca²⁺ uptake was investigated in endomembranes isolated from aleurone cells of barley (Hordeum vulgare L.). Unidirectional Ca²⁺ -uptake activity of endoplasmic reticulum (ER) was higher in membranes isolated from aleurone layers treated for 16 h with GA₃ and Ca²⁺ compared with those isolated from layers incubated in Ca²⁺ alone. However, the level of uptake from Ca²⁺-treated tissue could be stimulated to that of the GA₃-treated cells by applying exogenous CaM which increased the V _max of the Ca²⁺ transporter approximately threefold. Calcium uptake in ER from GA₃-treated tissue was inhibited by the CaM antagonist W7 in 50% of experiments, whereas the activity in membranes from non-GA₃-treated tissue was unaffected. Treatment with GA₃ also led to a twofold increase in CaM levels in aleurone layers within 4–6 h, paralleling the time course of the stimulation of Ca²⁺ uptake and preceding the stimulation of α-amylase secretion. We propose that the elevation of Ca²⁺ uptake into the ER induced by GA₃ may be coordinated and regulated by elevated levels of membrane-associated CaM and this may regulate Ca²⁺-dependent α-amylase synthesis in the lumen of the ER.     

Control of protein synthesis in barley aleurone layers by the plant hormones gibberellic acid and abscisic acid

The patterns of protein synthesis in barley aleurone layers treated with gibberellic acid (GA₃) and abscisic acid (ABA) are compared with the patterns observed in wheat germ in vitro translation assays directed by RNA isolated from similarly treated layers. When used alone, GA₃ and ABA both induce the formation of new translatable mRNAs and cause new proteins to be synthesized. The effects of GA₃ are more dramatic than those of ABA. In GA₃-treated tissues, overall protein synthesis is redirected to produce large quantities of α-amylase and a few other GA₃-induced proteins, while other protein synthesis is reduced or stopped. Large amounts of new translatable mRNA for α-amylase are also induced such that the dominant in vitro translation product is α-amylase. These changes are blocked by the simultaneous addition of ABA to the tissue. In GA₃ plus ABA-treated layers, few changes in protein synthesis in vivo are observed when compared to protein synthesis in untreated tissue, although the induction of mRNA for α-amylase and the other GA₃-induced mRNAs does occur. This indicates that ABA does not interfere with GA₃ induction of translatable mRNAs but prevents the translation of these mRNAs in vivo. Thus ABA and potentially GA₃ regulate the translation of proteins in vivo in barley aleurone layers.     

The influence of dwarfing interstocks on the distribution and metabolism of xylem-applied [h]gibberellin a(4) in apple

The influence of an interstock of the dwarfing cultivar M9 and the nondwarfing cultivar MM115 on the distribution and metabolism of labeled gibberellic acid A₄ ([³H]GA₄) of high specific radioactivity (5.18 × 10¹⁰ becquerel per millimole) applied to the xylem of the rootstock in grafted apple (Malus × domestica Borkh.) trees was compared. Free [³H] GA-like metabolites of [³H]GA₄, including putative GA₁, GA₂, GA₃, and GA₃₄, as well as various ³H-putative GA glucosyl conjugates were detected in stem segments from both cultivars. M9 interstocks reduced the total uptake of [³H]GA₄ and decreased the proportion of ³H metabolites transported to the shoots and leaves of scions. The M9 interstock tissue and adjacent rootstock and scion tissue retained a much greater amount and a higher proportion of the label than did comparable tissue of the nondwarfing MM115 interstock. In addition, the amount and proportion of free [³H]GAs was higher, and the proportion of putative [³H]GA glucosyl conjugates lower, in M9 interstocks compared to MM115. These effects of the dwarfing interstock on GA distribution and metabolism indicate a significant role for GAs in any satisfactory explanation of the dwarfing mechanism in apple.     

Effects of Abscisic Acid on Phenolic Content and Lignin Biosynthesis in Tobacco Tissue Culture

A significant depression of callus growth resulted from low concentrations of abscisic acid (ABA) added to the medium recommended by Linsmaier and Skoog. Low concentrations also decreased the chlorogenic acid and lignin content of the callus, and generally decreased amounts of scopolin and scopoletin in the tissue. Gibberellic acid (GA₃) stimulated callus growth in a low concentration (0.1 mg/1) and inhibited growth at a high concentration (10.0 mg/1). Both levels of GA₃ increased scopoletin accumulation in tobacco callus. A high concentration of GA₃ increased the accumulation of scopolin and chlorogenic acids, whereas a low concentration decreased the amounts of these two phenolic compounds. In comparison with the control, lignin synthesis was stimulated by a low GA₃ concentration, but a high GA₃ concentration did not have a significant effect. Both low and high concentrations of GA₃ overcame ABA inhibition of growth and lignin synthesis, and partially reversed ABA inhibition of scopoletin production. However, GA₃ did not reverse the inhibitory effect of ABA on scopolin production. The low concentration of GA₃ overcame the inhibition of chlorogenic acid production resulting from a 0.01 mg/1 concentration of ABA, but this was the only reversal of chlorogenic acid inhibition resulting from addition of GA₃ to the medium.     

<Emphasis Type="Italic">In vitro</Emphasis> effects of GA<Subscript>3</Subscript> on morphogenesis of CIP potato explants and acclimatization of plantlets in field

Improvement of potato has been accomplished using conventional and non-conventional approaches coupled with numerous tissue culture procedures. The aim of the present study was to assess the efficacy of gibberellic acid (GA₃) on the morphogenesis of International Potato Center (CIP) potato explants and acclimatization of plantlets in the field. Nodal segments as an explant source (1–1.5 cm) were isolated from 31 CIP potato plantlets and were inoculated into Murashige and Skoog (MS) medium supplemented with 0.0 (control), 0.1, 0.5, or 1.0 mg L^?1of GA₃. The variation in growth parameters of the cultivars was then observed. The highest shoot induction occurred in MS medium containing 1.0 mg L^?1 GA₃ with an increase in the inter-nodal distance between nodes as compared to other treatments. Higher concentration (1.0 mg L^?1) of GA₃ significantly increased plant height and root length in the treated germplasm however; this concentration was inhibitory to the number of nodes and roots per plant. The number of leaves was significantly increased in plants receiving GA₃ treatment at lower concentration (0.1 mg L^?1). The 31 CIP genotypes were transplanted to the field and checked for yield quality traits. It was concluded from the results that GA₃ had significant effects on morphogenesis and was effective in the acclimatization of CIP potato plantlets in field.     

The role of gibberellins A1 and A3 in fruit growth of Pisum sativum L. and the identification of gibberellins A4 and A7 in young seeds

Gibberellins A₁ and A₃ are the major physiologically active gibberellins (GAs) present in young fruit of pea (Pisum sativum L.). The relative importance of these GAs in controlling fruit growth and their biosynthetic origins were investigated in cv. Alaska. In addition, the non-13-hydroxylated active GAs, GA₄ and GA₇, were identified for the first time in young seeds harvested 4 d after anthesis, although they are minor components and are not expected to play major physiological roles. The GA₁ content is maximal in seeds and pods at 6 d after anthesis, the time of highest growth-rate of the pod (Garcia-Martinez et al. 1991, Planta 184: 53–60), whereas gibberellic acid (GA₃), which is present at high levels in seeds 4–8 d after anthesis, has very low abundance in pods. Gibberellins A₁₉, A₂₀ and A₂₉ are most concentrated in seeds at, or shortly after, anthesis and their abundance declines rapidly with development, concomitant with the sharp increase in GA₁ and GA₃ content. Application of GA₁ or GA₃ to the leaf subtending an emasculated flower stimulated parthenocarpic fruit development. Measurement of the GA content of the pods at 4 d after anthesis indicated that only 0.002–0.5% of the applied GA was transported to the fruit, depending on dose. There was a linear relationship between GA₁ content and pod weight up to about 2 ng · (g FW)⁻¹, whereas no such correlation existed for GA₃ content. The concentration of endogenous GA₁ in pods from pollinated ovaries is just sufficient to give the maximum growth response. It is concluded that GA₁, but not GA₃, controls pod growth in pea; GA₃ may be involved in early seed development. The distribution of GAs within the seeds at 4 d post anthesis was also investigated. Most of the GA₁, GA₈, GA₁₉, GA₂₀ and GA₂₉ was present in the testa, whereas GA₃ was distributed equally between testa and endosperm and GA₄ was localised mainly in the endosperm. Of the GAs analysed, only GA₃ and GA₂₀ were detected in the embryo. Metabolism experiments with intact tissues and cell-free fractions indicated compartmentation of GA biosynthesis within the seed. Using ¹⁴C-labelled GA₁₂, GA₉, 2,3-didehydroGA₉ and GA₂₀ as substrates, the testa was shown to contain 13-hydroxylase and 20-oxidase activities, the endosperm, 3β-hydroxylase and 20-oxidase activities. Both tissues also produced 16,17-dihydrodiols. However, GA₁ and GA₃ were not obtained as products and it is unlikely that they are formed via the early 13-hydroxylation pathway. [¹⁴C]gibberellin A₁₂, applied to the inside surface of pods in situ, was metabolised to GA₁₉, GA₂₀, GA₂₉, GA₂₉-catabolite, GA₈₁ and GA₉₇, but GA₁ was not detected. Gibberellin A₂₀ was metabolised by this tissue to GA₂₉ and GA₂₉-catabolite. Received: 23 July 1996 / Accepted: 2 September 1996     

Metabolism of Tritiated Gibberellins in d-5 Dwarf Maize: I. In Excised Tissues and Intact Dwarf and Normal Plants

Metabolism of [³H]gibberellin A₁ ([³H]GA₁) was followed in intact seedlings and excised apices and leaf tissue of both dwarf and normal (tall) plants of d-5 maize (Zea mays L.). The three metabolites produced were tentatively identified as [³H]GA_s, [³H]GA_s-glucoside ([³H]GA_s-glu), and [³H]GA₁-X, an unknown.     

Effects of gibberellic acid and uniconazole on the activities of some enzymes of anthocyanin biosynthesis in carrot cell cultures

Gibberellic acid (GA₃) inhibition of anthocyanin accumulation by carrot cell-suspension cultures was reversed by supplying dihydroquercitin or naringenin to the culture and not by supplying 4-coumaric acid or malonic acid. This suggested that gibberellic acid was inhibiting chalcone synthase, chalcone isomerase, or acetyl CoA carboxylase. Acetyl-CoA-carboxylase specific activity was the same in GA₃-treated and untreated cultures and was not detected in cultures treated with uniconazole, an inhibitor of gibberellic acid biosynthesis. Chalcone-isomerase specific activity was lower in GA₃-treated cultures than in untreated cultures and was lower in uniconazole-treated cultures than in the GA₃-treated cultures. The total chalcone synthase activity in extracts from GA₃- and from uniconazole-treated cells was not significantly different from that in extracts of untreated tissue. When these extracts were chromatographed on a Mono Q column, three peaks of chalcone synthase activity were found in extracts of nontreated cells, whereas only two of these peaks were detected in extracts of GA₃-treated cells. The extracts from GA₃-treated cells did not contain the peak of chalcone synthase activity that, in untreated cells, preceded the main peak. The correlation between the absence of this peak and the inhibition of anthocyanin accumulation suggests that this form of chalcone synthase is responsible for anthocyanin synthesis and that GA₃ prevents this form from appearing in the cells.     

Stem elongation and gibberellins in alpine and prairie ecotypes of Stellaria longipes

The potential for gibberellins (GAs) to control stem elongation and itsplasticity (range of phenotypic expression) was investigated inStellaria longipes grown in long warm days. Gibberellinmetabolism and sensitivity was compared between a slow-growing alpine dwarfwithlow stem elongation plasticity and a rapidly elongating, highly plastic prairieecotype. Both ecotypes elongated in response to exogenous GA₁,GA₄ or GA₉, but surprisingly, the alpine dwarf wasrelatively unresponsive to GA₃. Endogenous GA₁,GA₃, GA₄, GA₅, GA₈, GA₉and GA₂₀ were identified and quantified in stem tissue harvested atcommencement, middle and end of the period of most rapid elongation. Theconcentration of GAs which might be expected to promote shoot elongation washigher during rapid elongation than toward its end for both ecotypes. Whilethere was a trend for certain GAs (GA₃, GA₄,GA₉, GA₂₀) to be higher in stems of the alpine ecotypeduring rapid elongation, that result does not explain the slower growth of thealpine ecotype and the faster growth of the prairie ecotype under a range ofconditions. To determine if the two ecotypes metabolized GA₂₀differently, plants were fed [²H]- or[³H]-GA₂₀. The metabolic products identified included[²H₂]-GA₁, -GA₈, -GA₂₉,-GA₆₀, -3-epi-GA₁, GA₁₁₈(-1-epi-GA₆₀) and -GA₇₇. The concentration of[²H₂]-GA₁ also did not differ between the twoecotypes and metabolism of [²H₂]- or[³H]-GA₂₀ was also similar. In the same experiments thepresence of epi-GA₁, GA₂₉, GA₆₀,GA₁₁₈ and GA₇₇ was indicated, suggesting that these GAsmay also occur naturally in S. longipes, in addition tothose described above. Collectively, these results suggest that while stemelongation within ecotypes is likely regulated by GAs, differences in GAcontent, sensitivity to GAs (GA₃ excepted), or GA metabolism areunlikely to be the controlling factor in determining the differences seen ingrowth rate between the two ecotypes under the controlled environmentconditionsof this study. Nevertheless, further study is warranted especially underconditions where environmental factors may favour a GA:ethylene interaction.