Effects of growth retardants on gibberellin biosynthesis inGibberella fujikurai and on growth of wheat seedlings

2-chloroethylphosphonic acid, unlike chlorocholinechloride, does not suppress gibberellin biosynthesis inGibberella fujikuroi cultures, and nullifies the effect of applied gibberellin A₃ on wheat seedling growth. Presented at the International Symposium “Plant Growth Regulators” on June 18 – 22, 1984 at Liblice, Czechoslovakia.     

Effect of gibberellin biosynthesis inhibitors on shoot regeneration from hypocotyl explants of Albizzia julibrissin

Summary Hypocotyl explants of Albizzia julibrissin were placed on Gamborg's B5 medium supplemented with various levels of paclobutrazol, uniconazole, prohexadione calcium, or GA₃. Callus formation was evident within one week after placement of the explants on the culture media. Green nodule-like structures protruded from the distal end of the explants within 10 days and developed into shoots within a month. These shoots readily formed adventitious roots when placed on fresh culture medium. All three of the gibberellin biosynthesis inhibitors increased shoot formation compared to the control. The number of shoots per explants was increased 107, 79, and 168% by 0.3–0.4 μM paclobutrazol, uniconazole, and prohexadione calcium, respectively. In contrast to the gibberellin biosynthesis inhibitors, GA₃ decreased shoot formation. These results indicate that modification of gibberellin status can have a strong impact on the number of shoots formed.     

Gibberellin and ethylene control endoreduplication levels in the Arabidopsis thaliana hypocotyl

We have previously shown that endoreduplication levels in hypocotyls of Arabidopsis thaliana (L.) Heynh. are under negative control of phytochromes. In this study, the hormonal regulation of this process was analysed using a collection of A. thaliana mutants. The results show that two hormones in particular, gibberellin (GA) and ethylene, play distinct roles. Hypocotyl cells of the GA-deficient mutant ga1-11 grown in the dark did not elongate and showed a greatly reduced endoreduplication. Normal endoreduplication could be restored by supplying 10⁻⁹ M of the gibberellin GA₄₊₇, whereas the restoration of normal cell growth required 100-fold higher concentrations. The GA-insensitive mutant gai showed reduced cell elongation but normal ploidy levels. We conclude that (i) GA₄₊₇ has a global positive effect on endoreduplication and (ii) that endoreduplication is more sensitive to GA₄₊₇ than cell elongation. Ethylene had a completely different effect. It induced an extra round of endoreduplication both in light- and dark-grown seedlings and acted mainly on discrete steps rather than having a global effect on endoreduplication. The genes EIN2 and CTR1, components of the ethylene signal transduction pathway were both involved in this process. Received: 27 February 1999 / Accepted: 21 May 1999     

The effects of IAA and tetcyclacis on tuberization in potato (Solanum tuberosum L.) shoot cultures in vitro

Potato (Solanum tuberosum cv. Désirée) shoots grown in vitro in continuous darkness or in long days (LDs), were used to investigate indole-3-acetic acid (IAA) effects on stolon initiation and tuber formation, combining IAA with increased or decreased gibberellin levels. An increased gibberellin (GA) level was achieved by the applying 1 μM GA₃, while decreased gibberellin level was presumably realized by the adding 3 μM tetcyclacis (Tc). About 15% of potato shoots developed stolons both in LDs and in darkness. Stolon initiation was stimulated by GA₃ in darkness and by Tc in LDs. Tuber formation was strongly inhibited in LDs and by GA₃ both in light and darkness, but stimulated in darkness at low GA level. Exceptionally, tuber formation occurred in LDs at the highest Tc concentrations, in about 25% of explants. Indole-3-acetic acid alone stimulated stolon formation in LDs, both in the presence or absence of GA₃. IAA alone also stimulated tuber formation in dark-grown shoots, but could not overcome the inhibitory effect of LDs. Indications that, depending on their concentration ratio, IAA may interact with GA₃ in different tuberization phases, have been discussed. Radomir Konjević—Deceased in July 2006.     

Thermomorphogenic and Photomorphogenic Control of Stem Elongation in Fuchsia Is Not Mediated by Changes in Responsiveness to Gibberellins

Stem elongation in Fuchsia × hybrida was influenced by cultivation at different day and night temperatures or in different light qualities. Internode elongation of plants grown at a day (25°C) to night (15°C) temperature difference (DIF+10) in white light was almost twofold that of plants grown at the opposite temperature regime (DIF−10). Orange light resulted in a threefold stimulation of internode elongation compared with white light DIF−10. Surprisingly, internode elongation in orange light was similar for plants grown at DIF−10 and DIF+10. Flower development was accelerated at DIF−10 compared with DIF+10 in both white and orange light. To examine whether the effects of DIF and light quality on shoot elongation were related to changes in gibberellin metabolism or plant sensitivity to gibberellins (GAs), the stem elongation responses of paclobutrazol-treated plants to applied gibberellins were determined. In the absence of applied gibberellins paclobutrazol (>0.32 μmol plant⁻¹) strongly retarded shoot elongation. This inhibition was nullified by the application of about 10–32 nmol of GA₁, GA₄, GA₉, GA₁₅, GA₁₉, GA₂₀, GA₂₄, or GA₄₄. The results are discussed in relation to possible effects of DIF and light quality on endogenous gibberellin levels and gibberellin sensitivity of fuchsia and their effects on stem elongation. Received October 4, 1997; accepted December 17, 1997     

Persistence of [14C] gibberellin A3 and [3H] gibberellin A1 in senescing,ethylene treated Citrus and tomato fruit

The fate of [¹⁴C] gibberellin A₃ and [³H] gibberellin A₁ was examined in senescing fruit of Shamouti orange (Citrus sinensis L. Osbeck) and tomato (Lycopersicon esculentum Mill.). Gibberellin A₃ was highly persistent in Citrus peel (t 1/2=18 days) and to a lesser degree in tomato (t 1/2=5.5 days). Ethylene and ethephon caused a slight enhancement of gibberellin A₃ metabolism in Citrus and tomato fruit, respectively. Gibberellin A₁ was metabolized by Citrus peel at a relatively high rate (t 1/2 < 24 h) and ethylene slightly reduced this rate. It is concluded that the ethylene-induced enhancement of senescence does not involve major effects on the deactivation of applied gibberellins.Abbreviations GA₃ gibberellin A₃ - GA₁ gibberellin A₁     

Structure Elucidation of Gibberellin A32 and Its Acetonide

The structures of two gibberellin-like substances isolated from the immature seeds of Prunus persica, tentatively named PG–I and PG–II, were elucidated. PG–I was an ammonium salt of a novel gibberellin, ent-3α,10,12β,13,15α-pentahydroxy-20-norgibberella-l,16-diene-7,19-dioic-19,10-lactone (1), to which gibberellin number A₃₂ was allocated. PG–II was shown to be gibberellin A₃₂ acetonide (7), and concluded to be an artifact produced from gibberellin A₃₂ in the isolation process.     

A study on floral biology of seedlings in vitro in Orychophragmus violaceus: Induction of flowers in seedlings of O. violaceus cultured in vitro

Seedlings of O. violaceus were cultured on MS media and treated at low temperature. Cold treatment at 5–7 °C for more than 7 days was needed for flower induction of seedlings in vitro originated from germinated seeds. When cultured on MS media supplemented with 2.5 mg l⁻¹ zeatin and 2 mg l⁻¹ gibberellin (GA₃), seedlings in vitro did initiate flowers without cold treatment. When MS media was used with a reduced amount of NH₄NO₃, flower induction of seedlings in vitro could be accelerated. This revised version was published online in June 2006 with corrections to the Cover Date.     

Molecular cloning and expression analysis of a novel <Emphasis Type="Italic">CONSTANS</Emphasis>-like gene from potato

A full-length cDNA of a StCONSTANS-like (StCOL) gene was cloned from potato (Solanum tuberosum L.) by RTPCR and RACE. The predicted amino acid sequence of this cDNA has a high degree of identity with other homologous members of the CO or COL family. Analysis of mRNA levels for StCOL shows that it is highly expressed in leaves and becomes weaker during tuberization; moreover, is independent of gibberellin A₃ and sucrose. Published in Russian in Biokhimiya, 2007, Vol. 72, No. 11, pp. 1525–1531.     

Effect of triterpenoid glycosides on α- and β-amylase activity and total protein content in wheat seedlings

Influence of the aleanolic acid glycosides from Silphium perfoliatum L. (silphioside B, C, E and G) and their progenins on the amylase activity and total protein content in wheat seedlings was studied. Treatment of the Triticum aestivum L. seeds with 1–10 μM water solutions of mono- and diglycosides (mono- and bisdesmosines) elevated the α-amylase and total amylase activities in seedlings. Silphioside E containing three glucose moieties in its molecule did not change α-amylase activity, but it did if bis-triglycoside acetylated carbohydrate (as in silphioside C). Effects of 5–10 μM solutions of the active glycosides was comparable with that of exogenous gibberellin A₃ and 6-benzylaminopurine.     

The mode of action of a morphactin,fluoren-9-carboxylic acid

Fluoren-9-carboxylic acid acts not only as an auxin but also as an gibberellin-antagonist. In the standard pea straight test (S₅ section) for auxin it stimulated elongation, the optimum concentration being 10 mg/l. On the other hand, it inhibited elongation at 0.1 mg/l. This inhibitory effect was more marked when younger tissue (S₁ section) which also responds to gibberellin was used. Interaction of FCA and IAA in the S₅ section has shown that at higher concentration of IAA there seemed to be a suppraoptimal effect, indicating that FCA acted as an auxin. However, in the S₁ section, the stimulating effect of GA₃ was markedly inhibited by 0.1 mg/l FCA; 10 mg/l FCA was either additive or less than additive to GA₃. In the cucumber hypocotyl test FCA itself was inactive up to 100 μg/plant, but it inhibited the GA₃-induced elongation. This inhibition was overcome by increasing the dosage of GA₃. In the same material, the IAA-induced elongation was not affected by FCA. These results indicate that whether FCA acts as an auxin or a gibberellin-antagonist depends on whether the tissue is sensitive to gibberellin and/or auxin.     

PHOTOINHIBITION OF STEM ELONGATION BY FULL SOLAR RADIATION

Lockhart , James A. (U. Hawaii, Honolulu.) Photoinhibition of stem elongation by full solar radiation. Amer. Jour. Bot. 48(5): 387–392. Illus. 1961.—Stem growth response of ‘Pinto’ bean (Phaseolus vulgaris) to full solar radiation and to various degrees of shading has been studied. Maximum stem elongation occurred at light intensities of approximately 40,000 lux, under the conditions used here. Lower growth rates were found when light intensities were greater or less than this level. When the plants are saturated with gibberellin A₃, stem growth is maximum at the highest light intensity, and less at all lower light intensities. Sucrose sprays promoted growth at low light intensities. Apparently, slower growth at low light intensities is due to a deficiency of photosynthetic products, while growth inhibition at high intensities is due to a deficiency of gibberellin. Growth of ‘Alaska’ peas, which are more nearly saturated with endogenous gibberellin, is much less inhibited by high light—or much less promoted by partial shading. This appears to be a general relationship. Dwarf Zea mays (d₁), which is very deficient in gibberellin, responds markedly to shading, but the normal segregate (D₁) responds little to shading. When the dwarfs are saturated with gibberellin they, too, respond little to shading. Experiments are presented indicating that the high-intensity light inhibition of stem growth and low-energy red light inhibition act on the same step in the gibberellin system.     

The Effects of Gibberellin4+7 on the Vase Life and Flower Quality of Alstroemeria Cut Flowers

Leaf yellowing is a major problem in Alstroemeria and absence of leaf senescence symptoms is an important quality attribute. Two Alstroemeria cultivars ‘Yellow King’ and ‘Marina’ were sourced from a commercial farm and harvested when sepals began to reflex. Stems were re-cut under water and kept in vase solutions of gibberellin A₄₊₇ (0, 2.5, 5.0, 7.5, 10.0, 12.5 or 15.0 mg l⁻¹ [Provide^r]). Treatments and cultivars were combined in a factorial fashion and arranged in a completely randomised design. Application of GA₄₊₇ in the holding solution at 2.5–10.0 mg l⁻¹ significantly delayed the onset of leaf senescence by around 7 days and significantly increased days to 50% petal fall by ca. 2 days. Additionally, these GA₄₊₇ concentrations resulted in higher retention of leaf nitrogen, leaf chlorophyll and also increased leaf water content, while reducing leaf dry weight, all relative to untreated controls. Cultivar ‘Yellow King’ had significantly longer vase life and a better retention of leaf quality than ‘Marina’. Our results suggest that a concentration of 10 mg l⁻¹ GA₄₊₇ can be used to prolong vase life, delay leaf senescence and enhance post-harvest quality of Alstroemeria cut flowers during their transport to market.     

Interactions between Abscisic Acid, Gibberellins and Cytokinins in Grand Rapids Lettuce Seeds Germination

Experiments with Grand Rapids lettuce seeds (Lactuca sativa L.) maintained in darkness or irradiated with red light have shown that the inhibition of germination induced by low concentrations of ABA (2, 4, 6 μM) could be overcome by gibberellins (GA₃ or GA₄). The same results were obtained, although to a lesser extent, under the influence of two out of the four cytokinins tested (K and BAP) for seeds maintained in darkness. To suppress the block induced by higher concentrations of ABA (for example 8 μM), it was necessary to apply a cytokinin (K, BAP, Z or 2iP) and a gibberellin (GA₄ or GA₃) simultaneously, or a cytokinin following a red light treatment. Experiments conducted in darkness in which ABA (8 μM) was applied together with a cytokinin (BAP) and a gibberellin (GA₄) showed that the gibberellin and the cytokinin played similar roles towards each other and towards ABA.     

The role of endogenous gibberellins in the formation of α-amylase by aleurone layers of germinating barley caryopses

Using sensitive and selective immunological assays we have shown that in germinating caryopses of Hordeum vulgare L. cv. Himalaya, the level of gibberellin A₄ (GA₄) rises approximately 18-to 20-fold shortly (2–4 h) before -amylase activity increases. Gibberellin A₄ is the predominant immunoreactive gibberelin during these developmental stages and reaches a peak amount of approximately 9 pmol per caryopsis about 48 h after imbibition. Isolated aleurone layers produce GA₄ in the presence of an exogenous gibberellin, such as GA₁, which is not a biosynthetic precursor for GA₄. Experiments with inhibitors of gibberellin biosynthesis indicate that gibberellin synthesis is required in this tissue for the induction of -amylase. The inductive effect of exogenously applied GA₁ is indirect and appears to be mediated by GA₄. Embryos form predominantly GA₁; however, very little of this material is released by isolated embryos into the incubation medium. The results presented make it unlikely that the role of the embryo in the process of -amylase induction in aleurone layers is to provide gibberellins or gibberellin precursors.Abbreviations ABA abscisic acid - GA gibberellin - GA₃ gibberellic acid - RIA radioimmunoassay - TLC thin-layer chromatography     

Inhibition of growth by ancymidol and tetcyclacis in the gibberellin-deficientdwarf-5 mutant ofZea mays L. and its prevention by exogenous gibberellin

Leaf sheath length and shoot dry matter of the gibberellin-deficientdwarf-5 mutant ofZea mays L. were further reduced by micromolar concentrations of two putative gibberellin biosynthesis inhibitors, ancymidol [-cyclopropyl--(p-methoxyphenyl)-5-pyrimidine methyl alcohol] and tetcyclacis [5-(4-chlorophenyl)-3,4,5,9,10-pentaazatetracyclo-5,4,1,0^2,6,0^8,11-dodeca-3,9-diene]. Growth retardant action was prevented by the subsequent application of gibberellin (GA₄₊₇). Plants treated with both gibberellin and growth retardants were identical in all outward respects to those treated with gibberellin alone. Although thedwarf-5 mutant is blocked in the synthesis ofent-kaurene and does not contain detectable quantities of gibberellin, the above results are consistent with the interpretation that biologically active levels of endogenous gibberellin are present in the dwarf which can be decreased by biosynthesis inhibitors.Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the United States Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

QUANTITATIVE CHANGES IN GIBBERELLIN AND RNA CORRELATED WITH SENESCENCE OF THE SHOOT APEX IN THE ‘ALASKA’ PEA

Senescence of shoot apices of Pisum sativum L. ‘Alaska’ as measured by cessation of stem elongation was delayed by removal of flowers and by treatment with gibberellin A₃ and was hastened by treatment with AMO-1618 (2 isopropyl-4-dimethylamino-5-methylphenyl-1-piperi-dinecarboxylate methyl chloride). Ontogenetic changes in relative endogenous gibberellin levels and in capability of gibberellin biosynthesis in deflowered and control plants were determined indirectly by studying time-course changes in the sensitivity, as indicated by the growth response, of these plants to applied gibberellin and AMO-1618. The results of these experiments suggest that the endogenous gibberellin level varies directly with the growth rate. Analyses of total RNA and protein in shoot tips of deflowered and control plants revealed that the levels of these substances also vary directly with growth rate throughout ontogeny. It is concluded that decreases in endogenous gibberellin, RNA and protein are factors correlated with senescence of the shoot apex.     

Regulation of Medicago sativa L. somatic embryos regeneration by gibberellin A3 and abscisic acid in relation to starch content and α-amylase activity

Somatic embryo quality is an important factor decisive for the efficiency of somatic embryogenesis. Addition gibberellic acid (GA₃) at a concentration of 1 μM to germination medium improved the regeneration of alfalfa somatic embryos. Inhibitory effect of ancymidol, an inhibitor of gibberellin biosynthesis, on germination and conversion may indicate that those processes require endogenous GAs. Since fluridone, an ABA biosynthetic inhibitor, at a concentration of 1 μM, had a slight stimulatory effect on germination of somatic embryos, it may be presumed that embryos contain a too high level of residual ABA after maturation phase (20 μM ABA is used at that phase). The observed improvement of regeneration of somatic embryos by GA₃ was correlated with acceleration of starch hydrolysis through α-amylase activity enhancement by GA₃. In contrast, the inhibitory effect of ABA on the above processes was probably related to inhibition of α-amylase activity and, in consequence, to delayed starch hydrolysis. It is suggested that α-amylase activity can be considered a good marker of the quality of Medicago sativa L. somatic embryos.     

In vitro propagation of caper (Capparis spinosa L.)

Summary A twenty fold multiplication per twenty days of caper was achieved by culturing nodal shoot segments in the presence of BAP (4 μM) plus IAA (0.3 μM) and GA₃ (0.3 μM). The use of a modified MS medium facilitated this response. Plantlet regeneration was induced on single shoots taken from proliferating clusters subcultured for 20 days on a reduced BAP (2 μM) without auxin and gibberellin Higher rooting responses (70%) were obtained after a 20-day incubation period in darkness on solid half-strength MS1 medium plus IAA (30 μM), followed by a subsequent 20 day culture period on half-strength MSI basal medium. Proliferation was mainly due to axillary shoot-bud development as revealed by histological studies. The extensive meristematic activities observed indicated the enormous morphological potential of this species.