Cold treatments enhance responsiveness to gibberellin in stock (Matthiola incana (L.) R. Br.)

Summary

Endogenous GAs have been suggested as regulators of stem elongation and flowering of cold-requiring plants. Here, the relationship between temperature conditions and responsiveness to GA₄ on stem elongation and flowering of stock (Matthiola incana) was investigated. The optimum temperature for induction of flower bud initiation was 10°C, and the minimum duration was 20 d in the late flowering cv. Banrei; the type of cold treatment effect on flowering was classified as a “direct effect”. Stem elongation was markedly promoted by cold treatment regardless of flower bud initiation. The cold treatment amplified the stem elongation response to GA₄. The GA₄ level necessary for flower bud initiation was lower in the 10°C treatment than in the 15°C treatment, and it became lower at longer durations of cold treatment. These results indicate that the cold treatments enhance responsiveness to GA₄ not only in the stem elongation process but also in the flower bud initiation process and that the development of responsiveness to GA₄ may correlate with the temperature and duration of cold treatment.     

Effect of exogenous growth regulators on flowering and cytokinin levels in azaleas

‘Alaska’ and ‘Redwing’ azaleas having dormant flower buds were sprayed with gibberellins (GA₃ or GA_{4 + 7}) alone and in combination with thiourea, N⁶ benzyl adenine (BA) or kinetin weekly for 3 or 4 weeks to test the efficacy of these materials in breaking bud dormancy. Additional plants received 6 weeks of cold storage at 4.5°C or glasshouse day temperatures of 21°C and above. The 2000 and 3000 mg l^?1 GA₃ and Ga_{4 + 7} sprays were better than 1000 mg l^?1 in promoting flowering, with ‘Redwing’ responding better than ‘Alaska’. GA-treated plants flowered in fewer days than those receiving cold storage. Flower diameter and pedicel length increased with higher levels of GA, and flower uniformity was comparable to cold-stored plants on most GA-treated ‘Redwing’-plants. Thiourea, BA and kinetin applied alone had no effect and considerable cytokinin activity was highest in GA-treated buds 14–21 days after treatment application. No increase in activity occurred on plants not receiving GA.     

The Influence of Foliar Applications of GA3 GA4,7 and PBA on Breaking Flower Bud Dormancy on Azalea CVS Redwing and Dogwood

Foliar applications of gibberellins (GA₃, GA₄,₇) and 6-benzylamino-9-(2-tetra- hydropyranyl)-9H-purine (PBA) were compared with untreated controls and the conventional low temperature treatment for breaking flower bud dormancy. GA₃ and GA₄, ₇ were compared for their role in promoting flower development. Treatments were initiated when microscopic examination showed the flower buds had reached Stage 6 (style elongated and closed). Plants that did not receive a dormancy-breaking treatment failed to reach anthesis. Application of GA₃ or GA₄, ₇ hastened flowering and increased flower size and pedicel length.     

The response of partly cooled tulips to vacuum infiltration with gibberellins

Partly cooled (5°C) tulip ‘Apeldoorn’ were treated with gibberellins GA₃ and GA_{4 + 7} by vacuùm infiltration, with a view to defining conditions suitable for exploiting the effects of GA on forced tulips (faster flowering, control of stem extension, reduction of floral bud blasting).The first experiment showed that GA₃ and GA_{4 + 7} were equally effective in reducing the glasshouse period following 6 or more weeks cold storage; with less than 6 weeks cold storage, effects were less marked. Stem length at flowering was reduced by GA treatments, particularly by GA₃ and following more than 6 weeks cold storage. However, the vacuum infiltration method used (30 min at 10 torr) resulted in serious flower losses.Next, the effect of GA₃ concentration (up to 1500 mg 1^?1) was studied using vacuum infiltration treatments for 1–15 min at 20–510 torr, which resulted in fewer flower losses. Following 4 weeks cold storage, reducing pressure or increasing GA₃ concentration reduced both glasshouse period and stem length, with no effect of duration of treatment; GA₃ concentration was the only factor affecting flower length, which was increased. Following 8 weeks cold storage, increasing GA₃ concentration, vacuum or duration reduced glasshouse period. With all 3 factors at their maximum levels, 16 days earliness was obtained compared with controls. With maximum earliness, stem length was reduced to about 23 cm, compared to about 26 cm for treatments giving about 1 week's earliness, and 32 cm for untreated controls. Increasing vacuum appeared the most economical way of obtaining earliness, 20 torr giving 7 days earliness even at only 250 mg GA₃ 1^?1. Treatments giving earlier flowering also gave larger flowers. For comparison, there was little effect of soaking bulbs at atmospheric pressure even at 500 mg GA₃ 1^?1 for up to 20 h.Further experiments, conducted with vacuum infiltration at 260 torr for 15 min, confirmed these GA effects using formulated GA₃ (as “Berelex”) and GA_{4 + 7} (as “Regulex”). Effects of GA on stem length at flowering had disappeared by the time stems reached their final length. Comparisons with bulb injection of GA showed that this method required less GA than vacuum infiltration for similar effects, and that the greater effectiveness of GA_{4 + 7} compared with GA₃ was less marked using vacuum infiltration.     

Factors affecting the response of tulips to gibberellin

Gibberellic acid (GA₃) treatment of forced tulip crops has potential for producing faster growth to anthesis in the glasshouse, for reducing losses due to floral bud blasting, and for reducing the duration of cold storage needed to obtain satisfactory flowers. Using partly and fully cooled direct-forced tulips, cultivar ‘Apeldoorn’, several factors (relevant to the definition of GA₃ treatments) were studied. Experiments confirmed the previously recorded effects of gibberellins in tulips: GA₃ injections reduced the duration of the glasshouse period, enhanced flower survival and flower length, and reduced stem length at flowering.Following bulb storage at temperatures from ?2 to 20°C, GA₃ reduced the glasshouse period by 15–25% and increased flower length, compared to controls, irrespective of storage temperature. Stem length was also reduced by GA₃, this effect being greater following a storage temperature of 5°C or lower. When GA₃ was applied during the period of 17°C-storage which precedes cool storage, or during or after storage at 5°C, it was found that treatments during or at the end of cool storage were more effective in producing the characteristic effects of GA₃ than were pre-cooling applications. In partly cooled bulbs (but not fully cooled ones), the GA₃-induced earliness of flowering was about doubled when GA₃ injections were given repeatedly at 2-week intervals throughout storage. The responses to GA₃ injections were found to be unmodified by early-lifting and heat-treatment (for earlier forcing), by delaying the start of 5°C storage (for later forcing), by glasshouse temperature (16 and 18°C), and by shading treatments; there was little effect of bulb size.     

Effect of fruit load on 9,10-ketol-octadecadienoic acid (KODA), GA and jasmonic acid concentrations in apple buds

The relationship between 9,10-ketol-octadecadienoic acid (KODA), GAs and jasmonic acid (JA) and flower bud formation influenced by fruit load in apples (Malus domestica Borkh.) was investigated. The endogenous KODA and JA concentrations in apical buds in plants subjected to flower thinning treatment (FTT), under which all flowers were removed were higher than those in plants subjected to heavy crop treatment (HCT), under which the number of leaves per fruit was adjusted to 20 from 60 to 120 days after full bloom (DAFB). In contrast, the gibberellic acid concentrations [total of gibberellin A₁ (GA₁) and gibberellin A₄ (GA₄)] in FTT plants were low compared with those in HCT plants. The result suggests that KODA and JA in contrast to GAs may have opposite effects on flower bud formation which is significantly influenced by fruit load in apples and that KODA and JA may also be associated with flower bud formation in apples.     

Flowering in pyrethrum (Tanacetum cinerariaefolium L.). II. Changes in plant growth regulator concentrations

Radioimmunoassays were used to quantify the endogenous concentrations of plant growth regulators (PGRs) in pyrethrum during flower initiation and development. The concentrations of gibberellins, abscisic acid, indole acetic acid, zeatin and zeatin riboside, dihydrozeatin and dihydrozeatin riboside, and isopentenyladenine and isopentyladenosine were assayed. Fluctuations in PGR concentrations were correlated with flower bud initiation, flower stem elongation and floral differentiation. The gibberellin concentration increased during vernalization (6°C night temperature), a treatment known to promote floral initiation. A marked increase in gibberellin concentration was correlated with the onset of flower stem elongation. The concentration of the auxin indole acetic acid declined significantly at this time and remained low during flower bud development. Low photon flux density conditions, which retard floral initiation in otherwise inductive vernalizing conditions, failed to induce a decrease in indole acetic acid concentration.     

Regulation of gibberellin biosynthesis and stem elongation by low temperature in Eustoma grandiflorum

Summary

Heat-induced rosetted Eustoma grandiflorum requires low temperature for induction of stem elongation and flowering. Although heat-induced rosetting is associated with a reduction of gibberellin A₁ (GA₁) content, how thermo-induction affects GA biosynthesis is unclear. Thus, we examined levels of GA, precursors including that of ent-kaurene which is the first committed step in GA biosynthesis. We used uniconazole, an ent-kaurene oxidase inhibitor to estimate the ent-kaurene biosynthesis activity. The accumulation level of ent-kaurene in stems of the cold-treated seedlings was approximately 1.8 times that of the non-cold-treated seedlings, whereas no difference was observed in the leaves. No change was observed in endogenous levels of GA₁ and GA₂₀ in stems of the heat-induced rosetted plants during the cold treatment, whereas their levels increased with stem elongation after transfer to warm conditions. In contrast to the levels of GA₁ and GA₂₀, endogenous levels of ent-kaurene, ent-kaurenoic acid, GA₅₃, GA₄₄ and GA₁₉ in the stems markedly increased at the end of cold treatment. These results indicate that ent-kaurene biosynthesis and its metabolism early in the GA biosynthetic pathway are stimulated by low temperature and, later, the stimulation leads to an increment of endogenous levels of GA₁ which is essential for stem elongation of the heat-induced rosetted E. grandiflorum.     

The interaction of a dormancy-breaking cold treatment,ancymidol, and ethephon in relation to stem elongation and flower production of Lilium cultivars

Stem elongation of Lilium cultivars ‘Black Beauty’, ‘Jamboree’ and ‘Nutmegger’ was lessened by treating the bulbs with ancymidol (10 p.p.m.) or ethephon (500 p.p.m.). Ancymidol was the more effective inhibitor of stem elongation, although applied at a much lower concentration. Application of the growth regulators prior to a dormancy-breaking cold treatment provided more effective control of stem elongation than post cold-treatment application. The total number of flowers and the number of secondary flowers per stem of ‘Black Beauty’ and ‘Nutmegger’ were increased by treating the bulbs with ancymidol. However, unlike the optimal time for lessening stem elongation, enhancement of flower production was greatest when ancymidol was applied after completion of the cold treatment. Ethephon was unsatisfactory, since it inhibited flower production by ‘Black Beauty’ and ‘Nutmegger’, while ‘Jamboree’ was relatively insensitive to it, as indicated by a lack of inhibition of flower production and a small degree of inhibition of stem elongation.     

Asymmetric growth of citrus fruit peel induced by localized application of gibberellins in lanolin pastes

Lanolin pastes containing 0.02–1.0% gibberellin A₄₊₇(GA₄₊₇) were applied to one side of developing citrus fruitlets and caused thickening of the peel in the proximity of the treated zone. Enlargement of albedo (= the white portion of citrus peel) cells was involved, as revealed by scanning electron microscopy. The flavedo (= the coloured portion of the peel) and the pulp were not affected by the hormone. Gibberellin A₃ was slightly less active than GA₄₊₇. Cultivars with a naturally thick peel, such as ‘Marsh’ grapefruit (Citrus paradisi Macf.) and ‘Shamouti’ orange (Citrus sinensis (L.) Osbeck) responded more strongly than thin-peel cultivars. The role of gibberellins in the differential growth of citrus fruit tissues is discussed.     

A role for carbohydrate levels in the control of flowering in citrus

Girdling in October of small or large fruitless branches increased 2–3-fold both starch content of leaves and flower numbers as compared with ungirdled ‘Murcott’ mandarin trees. Autumn girdling and GA₃ treatments were both effective and additive in increasing starch contents of leaves and twigs of ‘Shamouti’ orange trees. GA₃, however, had the expected effect of depressing the reproductive inflorescences in both girdled and ungirdled branches, while girdling had the opposite effect. Girdling and fruit removal in October also additively and dramatically increased flower production in ‘Murcott’. Lowtemperature regimes in a phytotron caused young ‘Minneola’ budlings to flower earlier in the season and more profusely, while having no effect on starch content of leaves and twigs. The interactions of increased carbohydrate content and gibberellin in the control of flower formation in citrus are discussed.     

GA3对杨梅叶片木质素水平及其相关酶活性和成花的影响

 ‘荸荠种’杨梅小年树花芽孕育初期, 苯丙氨酸解氨酶(PAL) 活性首先达到高峰; 之后多酚氧化酶(PPO) 活性出现高峰。花芽孕育盛期过氧化物酶(POD) 活性达到高峰, 且与木质素积累到最大值相一致。花芽发端期间, POD活性和木质素水平均降低。GA₃处理降低了花芽孕育期间PAL、PPO 和POD 的活性, 导致木质素合成滞缓, 抑制花芽发端和降低成花率。     

Gibberellin producing Neosartorya sp. CC8 reprograms Chinese cabbage to higher growth

Gibberellins production by soil fungi received little attention, although substantial work has been carried out on other growth promoting aspects of soil borne fungi. We investigated gibberellins production and growth promoting capacity of a novel fungal strain of Neosartorya, which was isolated from the roots of Chinese cabbage (Bassica rapa L. ssp. pekinensis). Fungal culture filtrates (CF) obtained from pure cultures of 16 endophytic fungi were bioassayed on Waito-C, in order to investigate plant growth promoting capacity of these fungi. The fungal isolate CC-8 induced maximum shoot length of Waito-C (13.0 cm) as compared to control treatments. In a separate experiment, the CF of fungus CC-8 significantly promoted plant length and biomass of Chinese cabbage. The fungal CF also increased endogenous bioactive GA₁ and GA₄ contents of Chinese cabbage. Gibberellin analysis of CF of CC-8 showed presence of both physiologically active and non active gibberellins in higher concentrations (GA₁, 1.42 ng/ml; GA₃, 5.93 ng/ml; GA₄, 11.36 ng/ml; GA₇, 3.25 ng/ml; GA₉, 0.79 ng/ml; GA₁₅, 1.18 ng/ml). The culture filtrate of CC-8 produced higher amounts of GA₃, GA₄, GA₇ and GA₉ than wild type Fusarium fujikuroi, a well known gibberellins producing fungus. The fungal isolate CC-8 was later identified as a new strain of Neosartorya species on the basis of traditional and advance molecular techniques.     

Gibberellin-mediated suppression of floral initiation in the long-day plant Rhododendron cv. Hatsugiri

In a number of woody perennial species a decrease in gibberellins concentrations in the apical meristems is required for floral initiation to occur. In Rhododendron, applied gibberellins inhibit flowering and gibberellin biosynthesis inhibitors promote flowering. However, unlike previous reports on other Rhododendron cultivars, Rhododendron cv. Hatsugiri is a faculatitive LDP. It was therefore unknown how gibberellins regulate flowering in this cultivar and if non-inductive short daylengths stimulate the productions of endogenous gibberellins to suppress flowering. By inhibiting floral initiation while not stimulating vegetative growth we found applications of GA₅ to best match the natural response of Rhododendron cv. Hatsugiri under short-day regimes. GA₅-mediated effects on flowering have previously been reported to be due to conversion to GA₆, however, GA₅ was found to be present in tissue samples at up to 0.57 ng g⁻¹ FW, while GA₆ was never found. In addition, foliar applications of [¹⁴C] GA₅ were not found to have metabolised to GA₆. In line with the hypothesis that gibberellins inhibit floral initiation in short days in Rhododendron cv. Hatsugiri, the concentration of GA₂₀, a precursor to many bioactive gibberellins, was higher in leaf tissues from plants in short days, compared to those in permissive long days when analysed using GC–MS.     

Fruit set and June drop in Cox's Orange Pippin apple as affected by pollination and treatment with a mixture of gibberellins A4 and A7

Single spray applications of 100 ppm of a mixture of the gibberellins A₄ and A₇ (GA_{4 + 7}) were made on fruiting spurs of the apple cultivar Cox's Orange Pippin to investigate the effect on set, June drop and growth of fruits, as well as on shoot development and flower-bud formation on the bourses. Applications were made from 1 to 50 days after full bloom following partial hand-pollination of flowers, i.e. two stigmas per flower pollinated. In another experiment applications were made from 1 to 20 days after full bloom following complete (five stigmas per flower) or partial (two stigmas per flower) hand-pollination, after open pollination, or on emasculated flowers.GA_{4 + 7} only temporarily increased fruit set after open pollination or after effemination of flowers, and then only after application 1 day after full bloom. GA_{4 + 7} did not affect the very high fruit set after complete or partial hand-pollination. Both latter pollination treatments induced an equally high fruit set.GA_{4 + 7} reduced June drop significantly whenever fruits were left after first drop, except after early applications following open pollination. GA_{4 + 7} was effective in June-drop reduction up to 40 days after full bloom, i.e. until the onset of the June drop.Fruit size was not clearly affected by GA_{4 + 7}. The smaller fruits obtained in some cases after GA treatment could be explained by assuming that maturity was reached by fruits that would have abscised without an exogenous GA_{4 + 7} supply. GA_{4 + 7} also increased seed abortion. Fruit length was increased by GA_{4 + 7} only for applications made up to 20 days after full bloom.GA_{4 + 7} stimulated bourse-shoot development to some extent. Flower-bud formation on the bourses was not clearly affected by GA_{4 + 7}, but was markedly influenced by the presence of fruits.That GA_{4 + 7} reduced June drop so much in spite of a slight promotive effect on bourse-shoot growth and a slight abortive action on seeds suggests that these gibberellins may be specific stimuli for apple-fruit growth after actual fruit set is achieved.     

The influence of timing of application and gibberellic acid on the effects of ancymidol on growth and flowering of Mid-Century Hybrid lily cv. Enchantment

The response of Mid-Century Hybrid lily ‘Enchantment’ to ancymidol has been investigated in two experiments. In the first, three dates of application were employed, the earliest at inflorescence initiation, the second and third 10 and 20 days later, respectively. Application (750 μg/plant as a 15 ppm soil drench) on the second date produced the shortest plants, a result attributed to more extensive uptake by a better-developed root system. Plants subjected to treatment on the third date were, by then, too tall for the maximum dwarfing effect to occur. Flower number was unaffected by treatment, but ancymidol delayed anthesis by between 4 and 6 days and promoted earlier senescence of basal leaves.In the second experiment, interactions between gibberellic acid (GA₃) and ancymidol were demonstrated. Increasing amounts of GA₃ (20, 200 and 2 000 μg/plant as aqueous applications to the shoot tip) progressively counteracted the dwarfing effect of ancymidol (500 μg/plant as a 10 ppm soil drench) and, in the absence of ancymidol, 2 000 μg GA₃/plant significantly promoted stem extension. Flower number was slightly decreased by GA₃ in the absence of ancymidol. An ancymidol-induced delay in anthesis of almost 5 days was progressively reduced by increasing levels of GA₃, which, in the absence of ancymidol, did not significantly influence the time of anthesis. Applied separately, neither ancymidol nor GA₃ significantly affected pedicel length of the first flower, but increasing levels of GA₃ progressively promoted pedicel elongation in the presence of ancymidol.     

GA3 和PP333调控苹果花芽孕育机理的研究

 连续3 年用多效唑(PP₃₃₃) 1 000 mg/L 和赤霉素(GA₃) 1 000 mg/L 处理‘首红’苹果, 结果表明, PP₃₃₃处理降低了芽内吲哚乙酸( IAA) 和赤霉素( GAS) 含量, 增加了玉米素核苷(ZR) 和脱落酸(ABA) 含量, 提高了ZR/ IAA、ZR/ GAS、ABA/ IAA 和ABA/ GAS 比值,从而促进了花芽形成。GA₃ 处理则增加了IAA、GAS 含量, 降低了ZR、ABA 含量, 降低了ZR/IAA、ZR/ GAS、ABA/ IAA 和ABA/ GAS 比值, 从而抑制了花芽形成。PP₃₃₃和GA₃ 在花芽孕育临期内应用效果显著, 在其它时期无效。     

Hormonal control of shoot elongation in tulips

Shoot elongation of both cooled and uncooled ‘Apeldoorn’ and ‘Oxford’ tulips, as regulated by the leaves and the flower-bud, was studied. Leaves and/or flower-buds were excised and IAA, BA, or GA₃ in lanolin paste, was applied at various sites.Excision of the leaves and flower-buds of cooled tulips inhibited the elongation of the stem internodes. Administration of auxin after leaf and flower excision restored the elongation, mainly basipetally from the site of application. The findings may indicate that both the leaves and the floral organs provide auxin-like substances which control the elongation growth of the stem.Stems of uncooled tulips also elongated after IAA administration to the stem, but the response was slower and weaker. One part of the effect of cooling might be the stimulation of an auxin-releasing activity in the leaves and the flowers, another part an effect on the auxin-response system.     

Modification of episodic growth in Skimmia japonica ‘Rubella’ by gibberellic acid treatment

Applications of GA₃ in May/June, when the first flush of growth was maturing, induced an extra flush of vegetative growth and initiated lateral bud break. Flower initiation was delayed and flower size reduced by the GA₃. These responses were only slightly modified by additional sprays with BAP and TIBA. GA₄₊₇ was ineffective in promoting either extra extension growth or lateral bud break, but it did reduce flower size.