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 .     

Metabolism of C19- and C20-gibberellins by cell-free preparations from immature Phaseolus coccineus seed

Gibberellin biosynthesis pathways were investigated using isotopically-labelled C₁₉- and C₂₀-gibberellins and cell-free preparations from immature seed of Phaseous coccineus cv. Prizewinner. The initial steps in an early 13-hydroxylation pathway involved the conversion gibberellin A₁₂-aldehyde (GA₁₂-aldehyde) to GA₁₂ which was 13-hydroxylated to yield GA₅₃, Metabolism of GA₅₃ yielded GA₄₄. In contrast to other cell-free systems, GA₄₄ was not further converted, either as a δ-lactone or an open-lactone structure, to the C-20 aldehyde GA₁₉. GA₁₉ was, however, metabolised to GA₂₀, GA₅ and GA₁. GA₂₀ represented a branch point in the pathway as it was converted both to GA₁, which was an end product, and GA₅ which was further converted to GA₆. Like GA₁, GA₆ was also an end-product of the early 13-hydroxylation pathway.
A non-13-hydroxylation pathway involving GA₄, GA₁₅, GA₂₄ GA₃₇ and GA₃₆ also originated from GA₁₂. The terminal product of this pathway was the 3β-hydroxy C₁₉-gibberellin, GA₄.     

Growth-promoting activity of gibberellins on shoot elongation in Salix pentandra is reduced by 16,17-dihydro derivatisation

The metabolism of GA₁₀ is thought to be under photoperiodic control in the woody plant Salix pentandra . However, in a recent study using 16,17-[³H₂]GA₁₉ as a mimic of Ga₁₀, no effect of photoperiod was found on its metabolism to 16,17-dihydro-GA₂₀ and 16,17-dihydro-GA₁. To investigate if this was due to differential action of exogenous 16,17-dihydro-GAs and GAs, the effects of the 16,17-dihydro-derivatives of the gibberellins GA₁₉, GA₁, and GA₁ as compared with their parent GAs, on shoot elongation in seedlings of S. pentandra were studied. 16,17-Dihydro-GA₁₉, and -GA₂₀ were both almost inactive, while 16,17-dihydro-GA₁ induced some shoot elongation in seedlings treated with ancymidol as well as under short days. GA₁₉, GA₂₀ and GA₁ were all able to counteract the inhibitory effect of ancymidol under continuous light, while inhibition induced by a 12-h photoperiod was antagonised only by GA₂₀ and GA₁. Thus, the growth-stimulating activity of the tested GAs is significantly reduced by 16,17-dihydro derivatisation, but the derivatives do not inhibit stem elongation in S, pentandra , as has been found in monocotyledons.     

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.     

Comparison of endogenous gibberellins in roots and shoots of elongating Salix pentandra seedlings

Gibberellins GA₁, GA₈. GA₁₉. GA₂₉. GA₂₀ and GA₅₆ (2-epi-GA₈). were identified by combined gas chromatography-mass spectrometry in root extracts of elongating Salix pentandra L. seedlings. The presence of GA₈ was also demonstrated for the first time in S. pentandra shoots. The levels of GA₁, GA₈, GA₁₉, GA₂₀ in shoot tissue and in roots were estimated by selected ion monitoring. While the amounts of GA₈ and GA₁₉ were similar in both plant parts. the levels of the biologically active GA₁ and its immediate precursor GA₂₀. were found to be much lower in roots than in shoots.     

Metabolism of tritiated and deuterated gibberellins A1, A4 and A9 in Sitka spruce (Picea sitchensis) shoots during the period of cone-bud differentiation

A mixture of tritiated and deuterated gibberellins (GAs) was injected into elongating shoots of Sitka spruce [ Picea sitchensis (Bong.) Carr.] grafts grown under environmental conditions that were either inductive (heat and drought, HD) or non-inductive (cool and wet, CW) for flowering. The metabolites were purified by high performance liquid chromatography (HPLC), detected by liquid scintillation counting of aliquots of collected fractions and identified by gas chromatography–mass spectrometry (GC-MS). Deuterated GA₉ was converted to deuterated GA₄, deuterated GA₃₄, and deuterated GA₁ in both treatments. Deuterated GA₄ was metabolized to deuterated GA₃₄ and deuterated GA₁ in the CW material, but only deuterated GA₁ was detected in the HD material. The amount of detected metabolites was higher in the HD material, caused by a higher rate of metabolism and/or smaller losses of the metabolites during sample purification. GA₁ was converted to a polar unidentified metabolite in both treatments, but to a higher degree in the CW treatment.     

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 .     

Photoperiodic control of endogenous gibberellins in seedlings of Salix pentandra

In the temperate-zone woody species Salix pentandra elongation growth is regulated by the photoperiod. Long days sustain active growth, whereas short days induce cessation of apical growth, which is a prerequisite for winter hardening. It is shown that this is correlated to quantitative changes in levels of endogenous GA₁₉ GA₂₀, and GA₁. Within two short days the amount of the active GA₁ and its immediate precursor GA₂₀, decreased markedly in young leaves us well as in stem tissue. Also, the amount of GA¹⁹, declined, but the decrease was delayed relative to that of GA₁ and GA₂₀. The ability of S. pentandra seedlings to respond to exogenous GA₁₉, decreased with increasing numbers of short days. Observations that support the hypothesis that the level of GA₁ in S. pentandra is regulated by the photoperiod in a quantitative mode with conversion of GA₁₉, to GA₂₀, being one target for control.
Different distribution of GAs in various plant parts was observed. The level of GA was higher in young leaves than in other plant parts, and the amount of GA₁₉ was 5–10 times higher in stem tissue than in leaves and roots. The ratios of GA₈ to GA¹ and GA₂₀, were higher in roots as compared with other parts, as rods contained very low levels of GA₁ and GA₂₀, but amounts of GA₂₀ comparable with other parts.     

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.     

Metabolism of tritiated and deuterated gibberellin A9 in Norway spruce (Picea abies) shoots during the period of cone-bud differentiation

A mixture of tritiated and deuterated gibberellin A₉ (GA₉) was injected into elongating shoots of Norway spruce [ Picea abies (L.) Karst.] grafts grown under environmental conditions that were either inductive (heat and drought, HD) or noninductive (cool and wet, CW) for flowering. The shoots were divided into needles and shoot stems. The metabolites were purified by high performance liquid chromatography (HPLC), detected by liquid scintillation counting of aliquots of collected fractions and identified by gas chromatography-mass spectrometry (GC-MS). Deuterated GA₉ was converted to deuterated GA₄ in both treatments. The major metabolite in the CW-treated material was GA₅₁. The HD-treated material did not convert GA₉ to GA₅₁, but a cellulase-hydrolysable GA₉-conjugate was formed. The same metabolites were found in the shoot stems, though in smaller amounts. The amounts of detected metabolites were higher in the HD material, caused by a higher rate of metabolism and/or smaller losses of the metabolites during sample purification. The estimated amounts of endogenous GAs show that the HD-treated material contained higher amounts of GA₉ but no differences in the amounts of GA₄ were found.     

Gibberellic acid decreases anthocyanin accumulation in wild carrot cell suspension cultures but does not alter 3'-nucleotidase activity

Gibberellic acid (GA₃) applied at different times during the growth of wild carrot ( Daucus carota ssp. Carota ) cell suspension cultures inhibited anthocyanin accumulation. Application of 3 × 10^–6 M GA₃ to cultures on day 0 or day 4 gave, respectively, 10 or 35% of anthocyanin accumulation relative to levels occurring when GA₃ was applied at the end of the growth period. Endogenous GAs were separated by high pressure liquid chromatography, and identified and quantified by gas chromatography-selected ion monitoring. Gibberellins GA₁, GA₃ and traces of GA₈. GA₁₉ and GA₂₀ were identified in carrot cell suspension cultures of both high and low anthocyanin-accumulating clones. The concentrations of GA₁. GA₃ and GA₈ in the two clones were similar and were not significantly different after the application of uniconazole which promoted anthocyanin accumulation. This suggests that these endogenous GAs are not the sole factors controlling the accumulation of anthocyanin in these different clones. Exogenous GA₃ and uniconazole had no effect on 3'-nucleotidase and 5'-nucleotidase activity in the carrot cell suspension cultures. Thus 3'-nucleotidase does not appear to play a role in the inhibition of anthocyanin accumulation by exogenous GA₃.     

Identification and quantitation of gibberellins in fruits of Lycopersicon esculentum, and their relationship to fruit size in L. esculentum and L. pimpinellfolium

GA₁, GA₈, GA₁₇, GA₁₉, GA₂₀ and GA₂₉ were identified by combined gas chromatography-mass spectrometgry (GC-MS) in immature seeds and pericarp of Lycopersicon esculentum Mill. (tomato). Higher levels of these GAs were present in the seeds than in the pericarp; seeds in addition contained GA₁₅, GA₂₄, GA₂₅, and GA₄₄. Fruits of the Lycopersicon pimpinellifolium Mill. mutant I were smaller and contained lower GA₁ concentrations, but higher GA₂₀ concentrations, than those of mutants III and IV. In contrast, differences in fruit size in L. esculentum due to position on the truss did not correlate with GA₁ concentration in either the pericarp or seeds.     

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.     

Detection and identification of gibberellins in Sitka spruce (Picea sitchensis) of different ages and coning ability by bioassay, radioimmunoassay and gas chromatography – mass spectrometry

Gibberellins Al (GA₁), GA₃, GA₄, GA₉, and after enzymatic hydrolysis of GA-conjugate-like fractions, GA₉ and GA₁₅, were identified in shoots of Sitka spruce [ Picea sitchensis (Bong.) Carr.] of different ages by combined gas chromatography-mass spectrometry (GC-MS). The purification and separation of the GAs involved the use of reverse phase and normal phase high performance liquid chromatography (HPLC). The Tan-ginbozu dwarf rice bioassay and binding to antibodies raised against GA₁, GA₄ and GA₉ were used for detection of GA-like substances. The qualitative differences between the three ages of plant material were the presence of GA₃ and GA₁ in the 48-year-old material and the absence of detectable amounts of GA₄ in the same material. This indicates a difference in GA metabolism which may reflect the difference in ability to form reproductive buds.     

Detection and identification of gibberellins in extracts of Begonia leaves by bioassay, radioimmunoassay and gas chromatography – mass spectrometry

Gibberellins A₁ (GA₁), GA₄, GA₉, GA₁₉, and GA₂₀ were identified in extracts of leaves of Begonia x cheimantha Everett cv. Nova (Christmas or Lorraine Begonia). GA-like substances were purified by reverse phase and normal phase high performance liquid chromatography (HPLC) and detected by Tan-ginbozu dwarf rice bioassay and binding to antibodies raised against GA₁, GA₄ and GA₉. The final identifications were made by gas chromatography—mass spectrometry (GC-MS).     

The plant-growth-promoting rhizobacteria Bacillus pumilus and Bacillus licheniformis produce high amounts of physiologically active gibberellins

The plant-growth-promoting rhizobacteria (PGPR), Bacillus pumilus and Bacillus licheniformis, isolated from the rhizosphere of alder ( Alnus glutinosa [L.] Gaertn.) have a strong growth-promoting activity. Bioassay data showed that the dwarf phenotype induced in alder seedlings by paclobutrazol (an inhibitor of gibberellin [GA] biosynthesis) was effectively reversed by applications of extracts from media incubated with both bacteria and also by exogenous GA₃. Full-scan gas chromatography-mass spectrometry analyses on extracts of these media showed the presence of GA₁, GA₃, GA₄and GA₂₀, in addition to the isomers 3- epi -GA₁ and iso -GA₃. Isotope dilution analysis indicated that epi -GA₁ was an artefact. Likewise, iso -GA₃ is also probably an artifact spontaneously formed during extraction and/or analysis. In both culture media, GA₁ was present in higher concentrations (130–150 ng ml⁻¹) than GA₃ (50–60 ng ml⁻¹), GA₄ (8–12 ng ml⁻¹) and GA₂₀ (2–3 ng ml⁻¹). The data indicated that culture of both bacteria accumulate bioactive C19-gibberellins in relative high amounts and that these GAs appear to be physiologically active in the host plant. The evidence suggests that the promotion of stem elongation induced by the PGPR could be mediated by bacterial GAs.     

A localised decrease of GA1 in shoot tips of Salix pentandra seedings precedes cessation of shoot elongation under short photoperiod

By application of a recently developed method allowing analysis of gibberellins (GAs) in mg amounts of tissue, the effect of photoperiod on levels of GAs in shoot tips of individual seedlings of the woody species Salix pentandra was studied. In elongating long day-grown seedlings, maximum levels of GA₁ were found 5–20 mm below the apex, approximately twice the levels in other segments. After exposure of plants to 5 or 15 short days, the levels of GA₁ were about 50% lower within this specific region of the stem, as compared with seedlings grown under long days. Short day-induced cessation of shoot elongation also correlated with overall declines in the levels of GA₅₃, GA₁₉, GA₂₀ and GA₈, Within each photoperiodic treatment the levels of these GAs were generally relatively similar throughout the upper 35 mm of stems. No differences in internode lengths or in lengths of pith or epidermal cells were found in plants grown under long days compared with those exposed to 5 short days. In both cases, cells in mitosis were observed in the subapical stem tissues of shoot tips. After 15 short days, stem elongation was completed, and dividing cells were generally not found in the subapical part of the stem. However, short day exposure did not prevent elongation of internodes and cells differentiated before the treatment was started. Thus, the localised decrease in level of GA₁ in shoot tips under short days precedes the morphological and anatomical changes connected with the short day-induced cessation of elongation growth. This supports the hypothesised role for GA₁ in photoperiodic control of shoot elongation in S. pentandra .     

Internode length in Pisum. The lrs mutation reduces gibberellin response and levels

We describe a new mutation, lrs , which reduces internode length in Pisum sativum L. The mutation appears to act by reducing both GA synthesis and the response to GA₁. The levels of the 13‐hydroxylated GAs, GA₅₃, GA₄₄, GA₁₉, GA₂₀, GA₁, and GA₈ in the lrs mutant were greatly reduced compared with the wild‐type. The extent of the reduction in GA₁ content in the apical tissues would, at least in part, account for the dwarf phenotype of the mutant. The reduced GA responsiveness of the new mutant was indicated by the inability of applied GA₁ to remove the difference in elongation between lrs and LRS plants. The lrs mutant appears to be unique amongst internode length genotypes, possessing characteristics of both GA synthesis and GA response mutants.     

Growth and gibberellin relations of the extreme dwarf dx tomato mutant

The extreme dwarf d ^x tomato ( Lycopersicon esculentum Mill.) mutant has very short internodes which were found to contain shorter and fewer epidermal cells. The leaves are highly abnormal. The mutant showed a substantial stem growth response to GA₃, without approaching normal stature or morphology. The active gibberellin GA₁ and its precursors GA₁₉ and GA₂₀ were identified by coupled gas chromatography-mass spectrometry (GC/MS) in d ^x shoots. Quantitative GC/MS revealed that GA₂₀ accumulated to far higher levels than normal in stems and leaves of the mutant.