Radioactive gibberellin a(5) and its metabolism in dwarf peas

Radioactive gibberellin A₅ (³H-GA₅) was synthesized from gibberellic acid. When it was applied to dwarf peas grown in the dark, an average of 3% was converted to another acid gibberellin within 48 hours. The biological activity of the metabolite did not account for the response to applied GA₅. GA₅ is therefore assumed to be biologically active per se.³H-GA₅ did not appear to form a stable complex with a macromolecule in pea shoots. When injected into dwarf pea pods, ³H-GA₅ was readily metabolized by maturing seed to more water-soluble substances and to two other acidic compounds. This metabolism continued even throughout germination of the seed without reconversion of the metabolites to GA₅. It is concluded that “bound” GA₅ plays no part in the germination of dwarf pea seeds.     

Gibberellic Acid-Promoted Lignification and Phenylalanine Ammonia-lyase Activity in a Dwarf Pea (Pisum sativum)

The effects of gibberellic acid on lignification in seedlings of a dwarf and a tall cultivar of pea (Pisum sativum) grown under red or white light or in the darkness, were studied. Gibberellic acid (10⁻⁶-10⁻⁴ m) promoted stem elongation in both light and dark and increased the percentage of lignin in the stems of the light-grown dwarf pea. The gibberellin had no effect on the lignin content of the tall pea although high concentrations (10⁻⁴ m) promoted growth of the tall plants. Time course studies indicated that the enhanced lignification in the gibberellin-treated dwarf plants occurred only after a lag period of several days. It was concluded that gibberellic acid-enhanced ligmification had no direct relation to gibberellic acid-promoted growth. The activity of phenylalanine ammonia-lyase (E.C. 4.3.1.5) was higher in gibberellin-treated dwarf plants grown under white or red light than in untreated dwarf plants. Gibberellic acid had no detectable effect on the activity of this enzyme when the plants were grown in darkness, just as it had no effect on lignification under dark conditions. The data suggest that in gibberellin-deficient peas the activity of phenylalanine ammonia-lyase is one of the limiting factors in lignification.     

Shoot elongation in Lathyrus odoratus L.: Gibberellin levels in light- and dark-grown tall and dwarf seedlings

The levels of gibberellin A₁ (GA₁), GA₂₀, GA₁₉, GA₈, GA₂₉ and GA₈₁ (2-epiGA₂₉) were measured in tall (L-) and dwarf (ll) sweet-pea plants grown in darkness and in light. In both environments the apical portions of dwarf plants contained less GA₁; GA₈ and GA₁₉, but more GA₂₀, GA₂₉, and GA₈₁ than did those of tall plants. It is concluded that the partial block in 3β-hydroxylation of GA₂₀ to GA₁ is imposed by allele l in darkness as well as in the light. Furthermore, darkness does not appear to enhance elongation in sweet pea by increasing GA₁ levels. The reduction of the pool size of GA₁₉ in dwarf plants supports recent theories on the regulation of GA biosynthesis, formulated on the basis of observations in monocotyledonous species. Darkness results in decreased GA₂₀, GA₂₉, and GA₈₁ levels in the apical portions of tall and dwarf plants and possible reasons for this are discussed.     

Induction of Secondary Dormancy in Chenopodium bonus-henricus L. Seeds by Osmotic and High Temperature Treatments and Its Prevention by Light and Growth Regulators

Factors controlling the establishment and removal of secondary dormancy in Chenopodium bonus-henricus L. seeds were investigated. Unchilled seeds required light for germination. A moist-chilling treatment at 4 C for 28 to 30 days removed this primary dormancy. Chilled seeds now germinated in the dark. When chilled seeds were held in the dark in −8.6 bars polyethylene glycol 6000 solution at 15 C or in water at 29 C a secondary dormancy was induced which increased progressively with time as determined by subsequent germination. These seeds now failed to germinate under the condition (darkness) which previously allowed their germination. Continuous light or daily brief red light irradiations during prolonged imbibition in polyethylene glycol solution at 15 C or in water at 29 C prevented the establishment of the secondary dormancy and caused an advancement of subsequent germination. Far red irradiations immediately following red irradiation reestablished the secondary dormancy indicating phytochrome participation in “pregerminative” processes. The growth regulator combination, kinetin + ethephon + gibberellin A₄+A₇ (GA₄₊₇), and to a relatively lesser extent GA₄₊₇, was effective in preventing the establishment of the secondary dormancy and in advancing the germination or emergence time. Following the establishment of the secondary dormancy by osmotic or high temperature treatments the regulator combination was relatively more active than light or GA₄₊₇ in removing the dormancy. Prolonged dark treatment at 29 C seemed to induce changes that were partially independent of light or GA₄₊₇ control. The data presented here indicate that changes during germination preventing dark treatment determine whether the seed will germinate, show an advancement effect, or will become secondarily dormant. These changes appear to be modulated by light and hormones.     

Gibberellic-acid-induced cell elongation in pea epicotyls: Effect on polyploidy and DNA content

In gibberellic-acid(GA₃)-treated epicotyls of dwarf peas (Pisum sativum L.) grown in the light, DNA (per cell and per epicotyl) is followed. Histofluorometric DNA determinations show that GA₃-promoted cell elongation is not accompanied by increased endomitosis, but chemical estimations show an increased DNA content per epicotyl. This difference must therefore be the result of increased mitotic activity in the GA₃-treated tissue. Epicotyls of seedlings grown with or without cotyledons under continuous light with GA₃ are tetraploid, as are those of ecotylized embryos grown in darkness. These epicotyls reach no more than half the length of octaploid epicotyls of seedlings grown in darkness. This result provides evidence for a relationship between polyploidy and final possible cell length.     

Stem growth,flower formation,and endogenous gibberellins in a normal and a dwarf strain of Silene armeria

The physiological basis of dwarfism in a single-gene, recessive mutant of Silene armeria L. was investigated through comparison with a normal strain. Exposure of the normal strain to long days led to stem growth and flower formation while similar exposure of the dwarf strain led only to flowering, with very little stem growth. Application of gibberellin A₃ or A₄₊₇ in short days promoted stem elongation in the normal strain, but had a much lesser effect in the dwarf strain. Upon extraction and chromatographic fractionation of the endogenous gibberellins (GAs) in the normal strain of S. armeria, three zones of GA activity were found. An increase in one zone of activity was found in both strains after 1 long day. Neither the quality nor the quantity of the extractable GAs differed greatly between the dwarf and the normal strain. Vegetative dwarf scions, grafted onto fully induced, normal stocks formed flowers, but their growth habit was not changed. Thus, the lack of stem growth in response to long days in the dwarf strain appears to result from a lack of GA sensitivity in the stem tissue of these plants. However, during flower formation dwarf plants did exhibit elongation of the peduncles. This response was suppressed by the growth retardant 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine-carboxylate methyl chloride (AMO-1618), and applied GA₃ could partially overcome this inhibition. Thus, peduncle elongation in the dwarf strain appears to be regulated by endogenous GAs.Abbreviations AMO-1618 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine-carboxylate methyl chloride - GA(s) gibberellin(s) - LD long day(s) - SD short day(s)     

Comparison of endogenous gibberellins and of the fate of applied radioactive gibberellin a(1) in a normal and a dwarf strain of Japanese morning glory

The effect of application of GA₃ on hypocotyl growth, the endogenous GAs, and the metabolism of applied ³H-GA₁ were investigated in relation to dwarfism and light-mediated growth inhibition in the normal (tall) strain Violet and the dwarf strain Kidachi of Japanese morning glory (Pharbitis nil). GA₃ applied in a wide concentration range (10⁻⁹ to 10⁻³m) to 4-day-old seedlings caused great extension of the hypocotyls in light-grown plants of both the normal and the dwarf strain. However, the dwarf strain did not attain the same length as the normal one at any given GA₃ concentration, even when saturation was reached. Dark-grown plants of the dwarf strain responded to GA₃, although relatively much less than light-grown ones; dark-grown plants of the normal strain showed no GA₃ response at all.     

Evidence for Phytochrome Regulation of Gibberellin A(20) 3beta-Hydroxylation in Shoots of Dwarf (lele) Pisum sativum L

The effect of light on the dwarfing allele, le, in Pisum sativum L. was tested as the growth response to gibberellins prior to or beyond the presumed block in the gibberellin biosynthetic pathway. The response to the substrate (GA₂₀), the product (GA₁), and a nonendogenous early precursor (steviol) was compared in plants bearing the normal Le and the deficient lele genotypes in plants made low in gibberellin content genetically (nana lines) or by paclobutrazol treatment to tall (cv Alaska) and dwarf (cv Progress) peas. Both genotypes responded to GA₁ under red irradiation and in darkness. The lele plants grew in response to GA₂₀ and steviol in darkness but showed a much smaller response when red irradiated. The Le plants responded to GA₂₀ and steviol in both light and darkness. The red effects on lele plants were largely reversible by far-red irradiation. It is concluded that the deficiency in 3β-hydroxylation of GA₂₀ to GA₁ in genotype lele is due to a Pfr-induced blockage in the expression of that activity.     

Localization of Stem Elongation Control in Cucumis sativus L

Reciprocal grafts, and applications of gibberellin (GA) and indoleacetic acid (IAA) were used to localize the site of control for stem elongation in cucumber (Cucumis sativus L.). Dwarf and tall plants were reciprocally grafted to determine influence of stems and roots on stem elongation. At 21 days there were no significant differences in length between stems grafted to their own roots and those grafted to roots of the other type. GA₃, GA₄₊₇, and IAA were applied to seedlings with and without live apical buds. Seedlings with live apical buds responded to level of added GA, but not to added IAA. GA₄₊₇ was more effective than GA₃. Hypocotyls of tall plants responded more to both GA treatments than did those of the dwarves when both types had live apical buds. When either GA₄₊₇ or IAA was applied to seedlings with dead apical buds, elongation of the hypocotyl responded to level of the growth regulator, but there was no difference in response between the dwarf and tall plants.     

Ultrastructure ofDigitalis lanata tissue cultures

Summary The anatomy of twoDigitalis lanata tissue culture strains, S-1 and S-2, has been studied. The cardenolide accumulating cell aggregates consisted of highly vacuolated cells with very lobed nuclei in the periphery and a central part of meristematic cells. Sieve tube elements and companion cells and tracheids were observed in some of the cultures. The effect of gibberellic acid (GA₃) and SAN 9789 on the ultrastructure of the cultures was most apparent as regards the plastids and the amounts of mitochondria and ER. The content of starch seemed to be highest in the cardenolide accumulating strain S-2 grown in darkness (S-2 D) with or without GA3, but considerable amounts were also found in S-1 grown in darkness (S-1 D) with or without GA₃, which did not accumulate cardenolides. The amount of plastoglobuli was increased in S-1 by SAN treatment. It was also higher in S-2 D and S-2 D+GA₃ than in S-1 D and S-1 D+GA₃; i.e., it was high in tissues with blocked carotene synthesis. Many large plastoglobuli were also observed in apparently degenerating cells. The amount of ER seemed relatively high in cardenolide producing cultures. The amount of mitochondria was highly variable, but no correlation with cardenolide accumulation could be found.Abbreviations D dictyosome - ER endoplasmic reticulum - M mitochondrion - N nucleus - P plastid - PG plastoglobule - S starch grain - SC sieve cell - V vacuole - W cell wall - GA₃ gibberellic acid - S-1D strain S-1 cultured in darkness - S-1 L strain S-1 cultured in light - S-2 D strain S-2 cultured in darkness - S-2L8 strain S-2 previously cultured in darkness followed by 8 days in light in the present study - SAN SAN 9789 (Norflurazon) 4-chloro-5-(methylamino)-2-(,,,-trifluoro-m-tolyl)-3(2H)-pyridazinone     

Effect of temperature regimes on gibberellin levels in thermosensitive dwarf apple trees

Orchard-grown dwarf apple (Malus domestica Borkh.) trees selected from a hybrid population were propagated by tissue culture but had a growth pattern similar to standard cv. Golden Delicious plants when grown at constant 27°C instead of the expected dwarf pattern of growth. Shoot elongation was markedly reduced, with or without gibberellin A₁ (GA₁) or GA₄ treatment, when trees were grown in an environment where day temperature was maintained at 35°C for 2 h in a ramped regime (night 20°C day ramped to 35°C, held for 2 h and ramped down to 20°C night over a 14-h photoperiod). Application of GA₁ or GA₄ partially overcame growth retardation resulting from prior paclobutrazol treatment of both standard and dwarf trees grown at constant 27°C and of standard trees grown in the ramped environment. However, these GAs had no effect on paclobutrazol-treated or untreated dwarfs grown in the ramped regime. Gas chromatography-mass spectrometry with labelled internal standards was used to quantify GA₁, GA₃, GA₈, GA₁₉, GA₂₀ and GA₂₉ in extracts from standard and dwarf plants grown either at a constant 27°C or in a 20-30-20°C ramped temperature regime. Standard plants, which elongate quite rapidly in either environment, had similar levels of these GAs in both temperature regimes. The slowly growing dwarfs in the ramped temperature environment contained three times more GA₁₉ than the rapidly elongating dwarfs grown at 27°C. The concentrations of the other GAs were reduced to ca 40% or less in plants grown in the ramped temperature regime compared with those grown at 27°C. These data suggest that shoot elongation of dwarf plants is sensitive to elevated temperatures both as a result of reduced responsiveness to GAs and because of a reduction in the concentration of GA₁, apparently as a result of a lower rate of conversion of GA₁₉ to GA₂₀. It is possible that the altered GA metabolism may be a consequence of the change in GA sensitivity.     

Gibberellins and the photosensitivity of isolated embryos from non-stratified apple seeds

Summary The phytochrome system is responsible for the photosensitivity of dormant, isolated apple embryos in culture. Maximum photosensitivity occurs on the second day of culture and it is unaffected by gibberellins (GAs) in concentrations below 10^-4M. Higher concentrations of GA decrease the photosensitivity.The endogenous quantities of GA₄ and GA₇ were determined in embryos grown at white light, in darkness and in darkness following an exposure to red light. The GA₇ level remained unaffected by the light conditions, whereas the amount of GA₄ was three times higher in light or red-light-treated cultures than in the dark grown ones.Similar experiments were done using AMO-1618, an inhibitor of GA biosynthesis, which is also a strong inhibitor of apple seed germination. In this case the level of both GA₄ and GA₇ was light-independent. These experiments suggest that the phytochrome system participates in the regulation of GAs biosynthesis by mediating one of the last steps of GA₄ formation.     

Cell elongation and cell division in elongating lettuce hypocotyl sections

The roles of cell division and cell elongation in the growth of sections excised from hypocotyls of lettuce (Lactuca sativa L. cv. Arctic) were investigated. Elongation of sections incubated in the light is inhibited compared to dark-grown sections and this inhibition is reversed by gibberellic acid (GA₃). The elongation of both dark-grown and GA₃-treated, light-grown sections can be enhanced by 10mM KCl. Under all conditions of incubation, elongation growth is greatest in the uppermost quarter of the hypocotyl section while the basal quarter does not elongate. In darkness the two apical segments of sections marked into four equal parts grow at the same rate, while in light, growth of the apical segment exceeds that of the second segment. Cell division in cortical or epidermal cells, as measured by mitotic index or cell number, is not affected by illumination conditions nor by GA₃ or KCl treatments. Although -irradiation and FUDR pretreatment eliminate or cause a marked reduction in cell division in the excised hypocotyl, sections from seeds irradiated with -rays or incubated in 5-fluorodeoxyuridine elongate in response to GA₃ and KCl treatment as do sections from non-pretreated controls. Therefore, since neither GA₃ nor darkness affect celldivision activity and since treatments which eliminate or significantly reduce cell division do not affect growth, we conclude that the effect of GA₃ and darkness in this material is to increase cell elongation.Abbreviations FUDR 5-fluorodeoxyuridine - GA(s) gibberellin(s) - GA₃ gibberellic acid     

Synergism between Gibberellin and Auxin in the Growth of Intact Tomato

Gibberellin A_4&7 was more effective than gibberellic acid in increasing shoot elongation when applied to the apex of intact Lycopersicum esculentum seedlings of Tiny Tim, a dwarf cultivar, and Winsall, a tall cultivar. After 14 days, gibberellic acid and gibberellin A_4&7 stimulated growth of the dwarf more than the tall tomato. In tall tomato the application of indole-3-acetic acid alone (6.1 μg/plant) showed an inhibitory growth effect, but when applied with 17.5 μg per plant of gibberellic acid, it had a synergistic effect at 7 days but not at 14 days. When the auxin concentration was reduced to 0.61 μg per plant a synergistic effect was observed on tall plants at 7 and 14 days between indole-3-acetic acid and gibberellic acid. Application of gibberellin A_4&7 with auxin did not give a synergistic response in tall or dwarf tomato.     

Isolation of Acidic Growth Inhibitors in Dwarf Peas

Fumaric, palmitic, oleic and abscisic acids and methyl and ethyl hydrogen succinates were isolated from seedlings of dwarf pea (Pisum sativum L., var. Progress No. 9), grown under red light, as growth inhibitors which interfered with the responses of these plants to GA₃. Of the six compounds, fumaric acid did not show any inhibitory effect on stem elongation in the absence of GA₃.     

Biological activity of gibberellin analogues

In order to determine the significance of the C-6 carboxyl group for the biological activity gibberellin A₃, 6-epigibberellin A₃, 7-norgibberellin A₃, 6-methyl-7-norgibberellin A₃, and 7-homogibberellin A₃ were studied using dwarf pea, dwarf maize, dwarf rice, dwarf barley and -amylase bioassays. All gibberellin A₃(GA₃)derivatives tested were considerably less active than GA₃. In all biossays, 6-epi-GA₃ showed a low activity of the same order, whereas 6-methyl-7-nor-GA₃ was inactive. Surprisingly, 7-nor-GA₃ had some activity in the dwarf rice (root application), dwarf barley, and -amylase bioassay, in contrary to its low potency in the dwarf pea, dwarf maize, and dwarf rice (micro drop) bioassay. 7-Homo-GA₃ was primarily active in the dwarf maize, dwarf barley and dwarf rice bioassay. It also caused antigibberellin effects in dwarf rice. The results demonstrate that the C-6 carboxyl group is not absolutely essential for biological activity of gibberellins. The different activities of 7-nor-GA₃ observed in the various test systems may indicate that the C-6 carboxyl group is a structural requirement more for uptake and/or transport processes than for receptor affinity.Abbreviation GA₃ gibberellic acid     

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     

Seed Germination in Chenopodium album L: Relationships between Nitrate and the Effects of Plant Hormones

Effects of ethylene, gibberellins, and kinetin on the germination of two lots of Chenopodium album L. seeds, collected from the field in 1982 and 1983, were studied in relation to the availability of nitrate. The experiments were conducted in darkness and at temperatures ranging from 12 to 32°C. Ethylene induced over 75% germination in the 1983 seed but had little effect on the 1982 seed. Nitrate was only slightly promotive in either of the two seed lots. A combination of ethylene and nitrate, however, acted synergistically on 1982 seed, resulting in as much germination as that induced in 1983 seed by ethylene alone. In 1983 seed, a combination of ethylene and nitrate was only marginally more effective than ethylene. A similar relationship was observed in the effects of gibberellic acid₄₊₇ (GA₄₊₇) and nitrate on seeds from the two lots. The 1982 seed, which responded synergistically to combinations of nitrate with ethylene or GA₄₊₇ was found to contain an extremely low endogenous level of nitrate as compared to 1983 seed. Thus, high levels of either endogenous or applied nitrate appeared to enhance the germination response to ethylene or GA₄₊₇.

Kinetin had no effect on 1982 seed and only a small promotive effect on 1983 seed. There was no synergism between kinetin and nitrate in either of the seed lots.

     

CHARACTERIZATION OF VEGETATIVE GROWTH OF DWARF SOYBEAN GENOTYPES INCLUDING A GIBBERELLIN-INSENSITIVE GENOTYPE WITH IMPAIRED CELL DIVISION

The response of normal soybean (Glycine max [L.] Merrill) cultivars to gibberellins (GAs) and to an inhibitor of GA biosynthesis indicated that, as in other species, endogenous GAs are involved in controlling internode length. The responses to GA of several pairs of isogenic dwarf and normal genotypes (isolines) were compared. Dwarf genotypes T209, T244, T256, and M64–503-Duddy apparently are not dwarfed by lesions in the biosynthetic pathway similar to the well-studied mutations in pea and corn. Although these genotypes responded to GA₃, their growth as a percentage of initial shoot length was less than that of the normal isolines following GA₃ treatment. Dwarf genotype T210 responded to GA₃ treatment with a much smaller increase in stature than the other dwarf genotypes. Roots of T210 seedlings were of normal size, which indicated that the mutation in T210 primarily affects shoot growth. Transport and metabolism of GA₃ were equivalent in T210 and its non-dwarf isoline, Lincoln. The slight response in shoot length of T210 to GA₃ was accounted for by cell elongation, which GA₃ promoted to at least the same extent as in Lincoln. Gibberellin A₃ had no effect on cell number in T210, although GA₃ increased cell number in Lincoln by 53%. Thus, T210 is dwarfed by an inability to carry out GA-promoted cell division.     

<Emphasis Type="Italic">In vitro</Emphasis> stem elongation of stemless carline thistle

In vitro culture of stemless carline thistle was established using immature zygotic embryos. A satisfactory bud multiplication was achieved on MS medium supplemented with BAP (1 mg L^–1) and IAA (0.2 mg L^–1). Maximum rooting of buds was induced upon short cultivation (4 or 8 days) on an auxin-supplemented medium. Highest number of roots was obtained with NAA in the medium while the longest roots developed on the IAA-supplemented medium. Plantlets that subsequently developed were in rosette form if grown in light (16/8 h light to darkness photoperiod) and with elongated stems if raised in darkness. Light grown plantlets treated with GA₃ showed dose dependent stem increase in length, reaching maximum at the concentration of 10^–4 M. This was correlated with the length and the average number of internodes. If cultivated in the presence of ancymidol, dark grown plantlets showed reduced stem length. However, the inhibitory effect of the growth retardant on stem elongation was completely overcome by the addition of GA₃.