Effects of exogenous gibberellins and paclobutrazol on floral stalk growth of tulip sprouts isolated from cooled and non-cooled tulip bulbs

The involvement of gibberellins (GAs) in the regulation of floral stalk elongation and flower development has been studied in tulip. The biological activity of GA₄ and GA₉, both endogenous in tulip bulb sprouts, and GA₁, was tested in vitro on sprouts of cooled and non-cooled tulip bulbs ( Tulipa gesneriana L. cv. Apeldoorn), in the presence or absence of the GA biosynthesis inhibitor paclobutrazol. At early starting dates of incubation, floral stalks from both cooled and non-cooled bulbs hardly showed any elongation in the absence of exogenous GA. Paclobutrazol had no effect on floral stalk elongation, and the response to GAs of sprouts from cooled bulbs was greater than that of sprouts from non-cooled bulbs. At later starts of incubation, considerable floral stalk elongation occurred without GA application. Paclobutrazol inhibited this floral stalk elongation, and the growth of sprouts from both cooled and non-cooled bulbs was stimulated by GA application. The effect of paclobutrazol was reversed by simultaneous application of GA₄ or GA₉. Application of GA with and without paclobutrazol resulted in the same elongation of the floral stalk, indicating the absence of substantial side effects of the inhibitor. The isolated sprouts did not develop a full-grown flower without the addition of GA. GA₄ was more effective than GA₉ in stimulating this flower development. The results demonstrate that both sprouts from cooled and non-cooled bulbs are responsive to exogenous GAs in vitro, and may be a site of GA biosynthesis.     

Role of endogenous gibberellins in germination of melon (Cucumis melo) seeds

The effect of the plant growth retardants ancymidol. mefluidide and uniconazole on germination of two melon accessions differing in their ability to germinate at 14°C was examined. The accessions were the cold sensitive Noy Yizre'el and the cold tolerant Persia 202. The three growth retardants were able to delay the germination of intact Noy Yizre'el seeds, but did not affect that of intact Persia 202 seeds. On the other hand germination of decoated seeds of both accessions was unaffected by these inhibitors at normal oxygen concentration, but was inhibited at 5% oxygen. When gibberellin-like activity was measured by a dwarf rice biological assay following HPLC fractionation, it was found that seeds of Persia 202 contained much more gibberellin-like activity than Noy Yizre'el seeds. Among the extracted compounds several endogenous gibberellins were identified by combined gas chromatography-mass spectrometry (GC-MS). They included GA₄, GA₂₀, GA₁ and GA₃ in Noy Yizre'el and GA₃₄, GA₂₀, GA₁ and GA₈ in Persia 202. It is suggested that the better germination of intact Persia 202 seeds, compared to Noy Yizre'el seeds at low temperature and low oxygen concentration, is due to a higher endogenous level of GA and a better seed coat permeability to oxygen.     

Gibberellin status and responsiveness in shoots of tall and dwarf genotypes of diploid rye (Secale cereale)

The recessive dwarfing alleles of rye ( Secale cereale L.), ct1 and ct2 , caused a 35–55% reduction in the length of leaf 2 compared with corresponding tall lines grown at both 10°C and 20°C. The dwarf lines were 45–50% as responsive to applied GA₃ as the tall lines at 20°C but the absolute GA-responsiveness of the dwarfs was greater at 10°C than at 20°C. There was no significant difference in the contents of GA₁₉, GA₂₀, GA₂₉, GA₁, GA₃ and GA₈ in the leaf extension zone of tall and dwarf seedlings grown at 20°C. It was concluded that the mechanism whereby GA homeostasis is maintained is functional in both tall and dwarf lines despite marked differences in leaf extension rate. The recessive rye mutations may cause loss of function late in the GA-cell elongation pathway or, alternatively, indirectly affect GA-responsiveness in vegetative tissues. The genetic and physiological evidence indicates that ct1 and ct2 are unrelated to the GA-insensitive Rht genes in hexaploid bread wheat.     

Gibberellins in relation to flowering in Polianthes tuberosa

Endogenous gibberellins (GAs) in corms of Polianthes tuberosa L. (cv. Double) were isolated and identified by high performance liquid chromatography, bioassay and combined capillary gas chromatography-mass spectrometry (GC-MS). Gibberellins A₁, A₁₉, A₂₀ and A₅₃ were quantified at the vegetative, early floral initiation and flower development stages. The identification of 13-hydroxylated GAs indicates the presence of the early 13-hydroxylation pathway in P. tuberosa corms. An increase in GA₁ and GA₂₀, and a decrease in GA₁₉ levels, coincided with the transition from the vegetative phase to the stages of early floral initiation and flower development. GA₅₃ stayed at constant levels at the 3 different growth stages. The absence of GA₁ in vegetative corms and its presence in corms at early floral initiation and flower development stages suggest that GA₁ is a causal factor in inducing floral initiation in P. tuberosa . When GA₁, GA₃, GA₄, GA₂₀ and GA₃₂ were applied to corms at the vegetative stage (plants about 5 cm in height), floral initiation was promoted by all of the GAs used, GA₃₂ being the most active. In contrast with the other GAs, GA₃₂ had no effect on stem elongation. Therefore, it is suggested that hydroxylated C-19 GAs play an important role in flower induction in P. tuberosa .     

Relation between relative growth rate, endogenous gibberellins, and the response to applied gibberellic acid for Plantago major

Relationships between relative growth rate (RGR), endogenous gibberellin (GA) concentration and the response to application of gibberellic acid (GA₃) were studied for two inbred lines of Plantago major L., which differed in RGR. A4, the fast-growing inbred line, had a higher free GA concentration than the slow-growing W9, as analyzed by enzyme immunoassay. GA₃ application increased total plant weight and RGR₃ particularly for the slow-growing line. Chlorophyll a content and photosynthetic activity per unit leaf area were decreased, while transpiration rate was unaffected by GA₃ application. The increase in RGR by GA₃ application was associated with an increased leaf weight ratio; specific leaf area and percentage of dry matter in the leaves were only temporarily affected. Root respiration rate per unit dry weight was unaffected.
The correlation between low RGR, low GA concentration and high responsiveness to applied GA₃ supports the contention that gibberellins are involved in the regulation of RGR. However, the transient influence of GA₃ application on some growth components suggests the involvement of other regulatory factors in addition to GA.     

Gibberellins and the floral transition in Sinapis alba

The putative role of gibberellins in the transition to flowering was investigated in Sinapis alba , a caulescent long-day (LD) plant. It was observed that: (1) physiological doses of exogenous gibberellins (GA₁, GA₃, GA₉) do not cause the floral shift of the meristem when applied to plants grown in short days but have some positive effect on the flowering response to a suboptimal LD; no inhibition was observed in any case; (2) GA-biosynthesis inhibitors (prohexadione-Ca and paclobutrazol) considerably inhibit stem growth but have some negative effect on flowering only when a suboptimal LD is given; and (3) the floral transition induced by one 22-h LD does not correlate with any detectable change in GA content of the apical bud, of the leaves, and of the phloem exudate reaching the apex. Taken together, these results suggest that GAs do not act as a major signal for photoperiodic flower induction in Sinapis .     

Gibberellin substitution for long day secondary induction of flowering in Poa pratensis

Plants of Poa pratensis cv. Holt initiate inflorescence primordia when exposed to short days (SD) and low temperature, but require a secondary induction by at least 4 long days (LD) for further inflorescence development and stem elongation. Single or double applications of 10 µg per plant of gibberellins A₁, A₃, A₅ and 16,17‐dihydro A₅ (DHGA₅) induced inflorescence development in a high proportion of plants in SD, but only if the plants were detillered to a single stem. Exposure to 2 LD cycles did not cause heading and flowering alone but enhanced the effect of exogenous gibberellins (GAs), bringing flowering to 100%. GA₅ and DHGA₅ were less effective than GA₁ and GA₃ in SD, especially with double applications, but were more effective than GA₁ and GA₃ when given together with 2 LD. The GAs had differential effects on vegetative growth and flowering, GA₅ and DHGA₅ causing much less leaf and stem growth than the other two GAs. Marginal induction, whether by LD or GA application, resulted in a high proportion of spikelets with viviparous proliferation. Thus, whereas GAs are inhibitory to the primary induction by SD, they can replace secondary induction by LD when vegetative growth is limited.     

Effects of prohexadione (BX-112) and gibberellins on shoot growth in seedlings of Salix pentandra

Effects of gibberellins A₁, A_4/7, A₉, A₁₉ and A₂₀ and growth retardants were studied on shoot elongation in seedlings of Salix pentandra L. The growth-retarding effects of CCC and ancymidol were antagonized by all the gibberellins tested. The novel plant growth regulator prohexadione (free acid of BX-112), which is suggested to block 3β-hydroxylation of gibberellins, effectively prevented shoot elongation in seedlings grown under long photoperiod. Initiation of new leaves was only slightly reduced. GA₁, but not GA₁₉ and GA₂₀, was active in overcoming the inhibition of stem elongation of seedlings, treated with prohexadione, GA₁₉, GA₂₀ and GA₁ are native in S. pentandra , and the results are compatible with the hypothesis that GA₁ is active per se in shoot elongation, and that the effect of GA₁₉ and GA₂₀ is dependent on their conversion to GA₁.
A mixture of GA₄ and GA₇ was as active as GA₁ in promoting shoot elongation in seedlings treated with prohexadione, while GA₉ showed slight activity only when applied at high doses.     

Identification and quantification of endogenous gibberellins in apical buds and the cambial region of Eucalyptus

Endogenous gibberellins (GAs) were extracted and purified from apical buds of Eucalyptus nitens (Deane and Maid.) Maid. and the cambial region of E. globulus (Labill.). then analysed by capillary gas chromatography-mass spectrometry. GA₁ GA₁₉ GA₂₀ and GA₂₉ were identified by full scan mass spectra. Kovats retention indices and high resolution selected ion monitoring. Using deuterated internal standards. GA₁. GA₁₉. GA₂₀ and putative GA₂₉ and GA₅₃ were quantified in the apical buds, while GA₄. GA₈. GA₉ and GA₄₄ were shown to be either absent or present at very low levels. From the cambial region. GA₁ and GA₂₀ were quantified at levels of 0.30 ng (g fresh weight)-¹ and 8.8 ng (g fresh weight)-¹ respectively. These data suggest that the early 13-hydroxylation pathway is the dominant pathway for GA biosynthesis in Eucalyptus .     

Biological activity, identification and quantification of gibberellins in seedlings of Norway spruce (Picea abies) grown under different photoperiods

Short photoperiod induces growth cessation in seedlings of Norway spruce ( Picea abies (L.] Karst.). Application of different gibberellins (GAS) to seedlings growing under a short photoperiod show that GA₉ and GA₂₀ can not induce growth. In contrast application of GA, and GA₄ induced shoot elongation. The results indicate that 3β-hydroxylation of GA₉ to GA₄ and of GA₂₀ to GA₁ is under photoperiodic control. To confirm that conclusion, both qualitative and quantitative analyses of endogenous GAs were performed. GA₁, GA₃, GA₄, GA₇, GA₉, GA₁₂, GA₁₅, GA₁₅, GA₂₀, GA₂₉, GA₃₄ and GA₅₁ were identified by combined gas chromatography-mass spectrometry in shoots of Norway spruce seedlings. The effect of photoperiod on GA levels was determined by using deuterated and ¹⁴C-labelled GAs as intermal standards. In short days, the amounts of GA₉, GA₄ and GA₁ are less than in plants grown in continuous light. There is no significant difference in the amounts of GA₃, GA₁₂, and GA₂₀ between the different photoperiods. The lack of accumulation of GA₉ and GA₂₀ under short days is discussed.     

The end-of-day far-red irradiation increases gibberellin A1 content in cowpea (Vigna sinensis) epicotyls by reducing its inactivation

It has been shown previously that gibberellins (GAs) mediate the phytochrome (Phy) control of cowpea ( Vigna sinensis L.) epicotyl elongation induced by end-of-day (EOD)-far-red light (FR). In the present work, the EOD-FR effect on GA metabolism and GA levels in cowpea has been investigated. GA₁, GA₈, GA₁₉ and GA₂₀ were identified in epicotyls, and GA₁, GA₁₉, GA₂₀ and GA₂₉-catabolite in leaves of 6-day-old cowpea seedlings. The content of GA₁ in the epicotyl paralleled the decrease of its growth rate, supporting the hypothesis that this is the GA bioactive in controlling cowpea epicotyl elongation. FR enhanced both the amount of [3H]GA₁ in the epicotyl produced from applied [3H]GA₂₀, and that of applied [3H]GA₁ that remained unmetabolized in epicotyl explants, suggesting that Phy may regulate the inactivation of GA₁. In agreement with this effect of light on GA₁ metabolism, the contents of GA₁ in the epicotyl remained higher in FR-treated than in R-treated explants. Moreover, in intact seedlings EOD-FR treatment increased both epicotyl elongation and GA₁ content in the responsive epicotyl, whereas it was not altered in the leaves. These results show, for the first time, that photostable Phys modulate the stem elongation in light-grown plants by locally controlling the GA₁ levels through regulation of its inactivation.     

Effects of different gibberellins on elongation growth under short day conditions in seedlings of Salix pentandra

Fifteen different gibberellins (GA's) were tested for their ability to induce elongation growth under short day conditions in seedlings of Salix pentandra L. GA's were applied either to the apex or they were injected into a mature leaf. GA₃ was highly active and also GA₄₊₇ and GA₄ showed high activity. GA₁, GA₂, GA₅, GA₉, GA₁₃, GA₂₀, GA₃₆ and GA₄₇ showed moderate activity. GA₁₆, GA₁₇, GA₂₇ and GA₄₁ exhibited low or no activity in doses up to 10 μg per plant. In general, a better growth response was obtained with an application to the apex than with an injection into the leaf.     

Role of gibberellins in parthenocarpic fruit development induced by the genetic system pat-3/pat-4 in tomato

The role of gibberellins (GAs) in the induction of parthenocarpic fruit-set and growth by the pat-3/pat-4 genetic system in tomato ( Lycopersicon esculentum Mill.) was investigated using wild type (WT; Cuarenteno) and a near-isogenic line derived from the German line RP75/59 (the source of pat-3/pat-4 parthenocarpy). Unpollinated WT ovaries degenerated but GA₃ application induced parthenocarpic fruit growth. On the contrary, parthenocarpic growth of pat-3/pat-4 fruits, which occurs in the absence of pollination and hormone treatment, was not affected by applied GA₃. Unpollinated pat-3/pat-4 fruit growth was negated by paclobutrazol, an inhibitor of ent -kaurene oxidase, and this inhibitory effect was negated by GA₃. The quantification of the main GAs of the early 13-hydroxylation pathway (GA₁, GA₈, GA₁₉, GA₂₀, GA₂₉ and GA₄₄) in unpollinated ovaries at 3 developmental stages (flower bud, FB; pre-anthesis, PR; and anthesis, AN), by gas chromatography-selected ion monitoring, showed that the concentration of most of them was higher in pat-3/pat-4 than in WT ovaries at PR and AN stages. The concentration of GA₁, suggested previously to be the active GA in tomate, was 2–4 times higher. Unpollinated pat-3/pat-4 ovaries at FB, PR and AN stages also contained relatively high amounts (5–12 ng g⁻¹) of GA₃, a GA found at less than 0.5 ng g⁻¹ in WT ovaries. It is concluded that the mutations pat-3/pat-4 may induce natural facultative parthenocarpy capacity in tomato by increasing the concentration of GA₁ and GA₃ in the ovaries before pollination.     

An acylcyclohexadione retardant inhibits gibberellin A1 metabolism, thereby nullifying phytochrome-modulation of cowpea epicotyl explants

The regulation by phytochrome of stem elongation in light-grown plants depends on gibberellins (GAs). To investigate whether this is mediated by a change in GA metabolism, the effect of the GA biosynthesis inhibitor LAB 198 999 (an acylcyclohexadione derivative) on the end-of-day far-red (FR) response in cowpea ( Vigna sinensis L.) epicotyl explants has been investigated. Growth of epicotyl explants of light-grown seedlings was enhanced when treated with far-red light before incubation in the dark (end-of-day FR effect). Low doses of LAB 198 999 (0.05 and 0.5 μg explant⁻¹) reduced the effect of FR, whereas 5 to 50 μg explant⁻¹ stimulated elongation of both red light (R)- and FR-treated epicotyl explants while nullifying the differences between R and FR treatments. In paclobutrazol-treated epicotyl explants, FR enhanced the response to applied GA₁ and GA₂₀, whereas LAB 198 999 increased the activity of GA₁ and decreased that of GA₂₀, [³H]Gibberellin A₁, injected into the basal part of the epicotyl, was transported and metabolized mainly to [³H]GA₈ in the apical 20 mm of the epicotyl. The conversion of [³H]GA₁ to [³H]GA₈ was dramatically reduced by both end-of-day FR treatments and LAB 198 999 applications. In addition, both treatments enhanced epicotyl elongation. It is proposed that the regulation of cowpea epicotyl growth by phytocrome is mediated, at least partially, by modifying GA₁ degradation.     

Gibberellins and photoperiodic control of shoot elongation in Salix

Effects of exogenous gibberellins GA₅₃, GA₄₄, GA₁₉, GA₂₀ and GA₁ on photoperiodically controlled shoot elongation in seedlings of Salix pentandra L. were studied. Gibberellins GA₂₀ and GA₁ induced shoot elongation under short days (SD) and could substitute for a transfer to long day (LD), while gibberellins A₅₃, A₄₄ and A₁₉ were inactive. In seedlings exposed to a prolonged SD-treatment (30 days) there was a significant positive interaction between a transfer to LD and a treatment with GA₂₀ and GA₁ on shoot elongation. In addition, GA₁₉ enhanced the growth promotive effect of LD in these seedlings. The results are compatible with the suggestion that conversion of GA₁₉ to GA₂₀ is blocked under SD. This effect is supposed to be an early process leading to the cessation of shoot elongation under SD. Responsiveness of the seedlings to LD and to a GA-treatment gradually decreased with an increasing length of exposure to SD.     

BIOASSAY OF ANTHERIDIOGEN IN LYGODIUM JAPONICUM

Antheridia were induced by exogenously applied GA₃ at concentrations between 10⁻⁶ and 3 × 10⁻⁴ M in very young filamentous protonemata of Lygodium japonicum grown in darkness; the longer the dark preculture of protonemata, the lower was the sensitivity of the protonemata to GA₃. Antheridial initials were discernible after 36 hr of GA₃ treatment in the most sensitive protonemata, and the timing of antheridial initiation was delayed with increasing protonemal age.
This quantitative response of the protonemata provided the basis for a new method of assaying gibberellins in terms of the degree of antheridial formation. According to this method, all the gibberellins tested and one of their precursors were active in inducing antheridia in the protonemata, and the activity spectrum of the gibberellins was as follows: GA₇>GA₄>GA₉>GA₃>GA₅>GA₁>GA₈.
The amounts of antheridiogen contained in conditioned media were measured by the present bioassay. A semi-logarithmic relation was shown between the percentage of antheridial formation and the concentration of conditioned medium within a certain dilution range. The amounts of antheridiogen secreted by the prothallia were quantitatively compared by transferring samples onto fresh media for a short period of time.     

Interaction of gibberellic acid and photoperiod on leaf sheath elongation in normal and gibberellin-insensitive genotype of wheat

Effect of gibberellic acid (GA₃) on leaf sheath elongation in a normal (cv. Møystad) and a gibberellin(GA)-insensitive (cv. Siete Cerros) genotype of wheat ( Triticum aestivum L.) were studied at 18 and 12°C under short (SD, 12 h) or long (LD, 24 h) photoperiod. Leaf sheath length in cv. Møystad was signficantly increased by exogenous GA₃ both under SD and LD. LD alone stimulated leaf sheath elongation and the combined effect of LD and GA₃ was additive, and there was no statistically signficant interaction between photoperiod and GA₃ concentrations. Leaf sheath length in cv. Siete Cerros was not significantly affected by GA₃ under any conditions. However, there was a highly significant stimulation of leaf sheath elongation by LD in cv. Siete Cerros as well. These results indicate that stimulation of elongation growth in wheat leaves by LD is not mediated by gibberellin.     

Inhibitory and promotive effects of gibberellic acid on floral initiation and development in Poa pratensis and Bromus inermis

Flowering in Poa pratensis L. cv. Holt and Bromus inermis Leyss. cv. Manchar requires exposure to short days (SD) for primary induction to occur, followed by long days (LD) to allow the inflorescence to develop. Weekly sprays with gibberellic acid (GA₃) during primary induction inhibited flower initiation in both P. pratensis and B. inermis . With 10⁻⁴ M GA₃ flowering of P. pratensis was suppressed even after an induction period of 10 weeks. Since both GA₃ and non-inductive LD conditions greatly stimulate leaf elongation, the degree of primary induction was closely negatively correlated with plant height (leaf sheath and blade length) at the end of the induction period. GA₃ application or the interpolation of LD during SD induction were most inhibitory during the later middle part of the SD period, whereas they were stimulatory near the beginning or immediately before the SD period. We suggest that changes in the portfolio or levels of endogenous gibberellins mediate photoperiodic control of growth and floral initiation in these plants. However, GA₃ sprays could not substitute for LD in causing heading and culm elongation in SD induced plants of the two species. The results are discussed in the light of results with other plants with dual floral induction requirements.     

Hormone directed sucrose transport during fruit set induced by gibberellins in Pisum sativum

A new system has been developed to study hormone-directed transport in intact plants during parthenocarpic fruit set induced by gibberellins. Gibberellic acid (GA₃) and gibberellin A₁ (GA₁) applied to unpollinated ovaries of pea ( Pisum sativum L. cv. Alaska) promoted sucrose transport from the leaf to the site of hormone application. In vivo experiments showed an early (30 min) accumulation of [¹⁴C]-sucrose in ovaries of pea stimulated by gibberellins. This activation of sucrose transport appears to be mediated by gibberellins (GA₁, GA₃), increasing both loading of phloem with sucrose in the leaf (source) and sucrose unloading in the ovary (sink). The ability of pea tissue segments to take up sucrose in vitro was not affected by the hormonal treatment.