Promotion of Flowering in the Pinaceae by Gibberellins

Gibberellins (GAs) were effective in promoting flowering in sexually mature (45-year-old scions) grafts of loblolly pine (Pinus taeda L.). Seed-cone production was increased 12-fold in field-grown, grafted ramets by bi-weekly, May-September applications of 500 μg per branch of GA_4/7. Gibberellin A₃ was equally effective at 500 μg but not at 100 μg per branch, while GA₅ was ineffective at either concentration. A second study using potted, less-sexually mature (8-to 10-year-old scions) grafts gave a reduced level of seed cones in response to GAs. However, even on these younger grafts GA_4/7 was a significant promotive treatment, GA₃ being considerably less effective. Branch girdling, tested as an adjunct treatment, was ineffective. It is now apparent that exogenous applications of GA_4/7 are effective on a number of Pinaceae species, and their use to promote earlier and more abundant flowering in breeding orchards of grafted ramets for at least two species, loblolly pine and Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] is practical.     

Promotion of flowering in the Pinaceae by gibberellins

Significant female flowering of 6- to 11-year-old seedlings and grafted ramets of sexually mature scions of lodgepole pine (Pinus contorta Dougl.) was promoted by both topical and spray applications of a gibberellin (GA) A_4/7 mixture (1.6 to c. 5 mg per plant in total) during that period (June to September) when sexual differentiation of lateral primordia would be expected to take place. Girdling was used in most experiments to enhance the GA_4/7 effect, as was the auxin, naphthaleneacetic acid (NAA). Average frequency of flowering branches on treated plants over all experiments ranged from 27 to 59% (control ranged from 0 to 36%) and average number of female strobili was increased from 2- to 6-fold by growth regulator treatment, relative to controls. Within an experiment, clonal or family frequency of flowering for treated plants ranged from 11 to 67% (controls were 0 to 28%), and number of female strobili was increased from 2- to 14-fold by growth regulator treatment, relative to controls. Movement of the flowering stimulus from the point of application was apparent in several experiments, the response in adjacent branches being correlated positively with increasing dosage of GA_4/7. Significant male flowering occurred only in one experiment, girdling and GA_4/7 treatment being promotive factors. The use of spray applications of GA_4/7+ NAA is warranted to induce early and enhanced flowering in lodgepole pine seedlings and vegetative propagules for genetic improvement programs.     

Promotion of flowering in the Pinaceae by gibberellins

Significant male and female flowering (cone bud production) by girdled branches of 6-year-old Douglas fir (Pseudotsuga menziesii (Mirb. Franco) seedlings was promoted by applications (mid-April to June) of 1.6 or 3.2 mg per branch (in total) of certain non-polar gibberellins (GA's). Girdling alone was ineffective. When tested alone, a mixture of GA_4/7 was most effective. GA₉ less so, while GA₅ and the more polar GA₃ were essentially ineffective. For female cone buds GA_4/7+ GA₉ were synergistically effective, but for male cone buds GA_4/7 alone was best. The auxin naphthaleneacetic acid (NAA) was not tested alone, but at low dosage (0.175 mg/branch in total) NAA enhanced the flowering efficacy of GA's for both sexes; at a high dosage (0.875 mg/branch in total) male cone bud production was further enhanced, but only at the expense of females. For female flowering the best treatment (90% frequency of flowering 6.8 cone buds/branch), was GA_4/7+ GA₉+ low NAA; for male flowering, it was GA_4/7+ high NAA (30% frequency and 4.2 cone buds/branch. Frequency of flowering for controls was 18% and 0%, average number of cone buds/branch was 0.9 and 0, for females and males, respectively. The successful treatments did not affect promordia initiation, rather they caused the differentiation of previously initiated, but undetermined, lateral primordia into cone and latent buds at the expense of vegetative bud differentiation. The lack of success reported by earlier workers in promoting flowering in Pinaceae species by GA's appears to be the unfortunate result of selecting GA₃ for initial testing. The practical implications of this early and enhanced flowering by non-polar GA's seedlings of a commercially important conifer are discussed in relation to accelerating the processes of tree improvement.     

The Effect of Gibberellins on Flowering in Roses

The gibberellins A₁, A₃, A₅, A₈, A₁₉, A₂₀, and A₂₉ were identified in vegetative shoot tips of Rosa canina by comparing their mass spectra and Kovats retention indices with those of standards. Most wild roses have a short flowering season of 2–4 weeks in spring, whereas most modern cultivars flower recurrently. `Félicité et Perpétue' is a short-season hybrid from a cross between a wild rose and a recurrent-flowering rose, whereas its sport, `Little White Pet,' flowers recurrently. The concentrations of gibberellins (GAs) were measured in shoot apices of both cultivars. In March (before floral initiation in spring) the concentrations of GA₁ and GA₃ were respectively threefold and twofold higher in `Félicité et Perpétue' than in `Little White Pet.' In April (after floral initiation) the concentrations of both gibberellins were substantially greater than in March, and concentrations of GA₁ and GA₃ were, respectively, 17-fold and 12-fold greater in `Félicité et Perpétue' than in `Little White Pet.' It is postulated that, in `Félicité et Perpétue,' floral initiation occurs when concentrations of GAs are low and is inhibited when concentrations of GAs are high, whereas in `Little White Pet' concentrations of GAs remain at permissive levels throughout the growing season. Applications of GA₁ and GA₃ to axillary shoots in March inhibited floral development in `Félicité et Perpétue' but not in `Little White Pet.' This suggests that the combined concentration of exogenous and endogenous gibberellins might have been raised to inhibitory levels in the former but not in the latter cultivar. Received January 10, 1999; accepted June 16, 1999     

Promotion of Growth and Flowering and Increase in Content of Endogenous Gibberellins in Gladiolus Plants Treated with the Growth Retardant CCC

Application of the growth retardant CCC to gladiolus plants resulted in stimulation of stem lenth, increased number of flowers per spike and a slight advancement of anthesis date. Leaves of treated plants were heavier than control and contained a higher amount of water and chlorophyll. The anthocyanin content in petals was also greatly increased. CCC had little or no effect on the content of the endogenous gibberellins in the acidic ethyl acetate fraction, but markedly increased the content of the native gibberellins in the aqueous fraction. The mode of action of CCC in plants is discussed on the basis of these results and a review of the literature.     

Gibberellins in Relation to Growth and Flowering in Pharbitis nil Chois

Flowering can be modified by gibberellins (GAs) in Pharbitis nil Chois. in a complex fashion depending on GA type, dosage, and the timing of treatment relative to a single inductive dark period. Promotion of flowering occurs when GAs are applied 11 to 17 hours before a single inductive dark period. When applied 24 hours later the same GA dosage is inhibitory. Thus, depending on their activity and the timing of application there is an optimum dose for promotion of flowering by any GA, with an excessive dose resulting in inhibition. Those GAs highly promotory for flowering at low doses are also most effective for stem elongation (2,2-dimethyl GA₄ GA₃₂ > GA₃ > GA₅ > GA₇ > GA₄). However, the effect of GAs on stem elongation contrasts markedly with that on flowering. A 10- to 50-fold greater dose is required for maximum promotion of stem elongation, and the response is not influenced by time of application relative to the inductive dark period. These differing responses of flowering and stem elongation raise questions about the use of relatively stable, highly bioactive GAs such as GA₃ to probe the flowering response. It is proposed that the `ideal' GAs for promoting flowering may be highly bioactive but with only a short lifetime in the plant and, hence, will have little or no effect on stem elongation.     

Induction and Promotion of Flowering by Heat-Treated Catecholamines in Lemna paucicostata

Alkali- and heat-treated norepinephrine, a catecholamine, induced flowering of short-day (SD) plant Lemna paucicostata 151 even under long-day (LD) conditions. Flowering induced with a lower concentration of heat-treated norepinephrine was promoted under SD conditions but inhibited by a night break. The related compounds L-dopa and dopamine also promoted flowering under SD conditions when they were heat-treated.     

The Effect of Gibberellins on Growth and Flowering of Fragaria and Duchesnea

In a series of experiments petiole lengths were increased, steminternode elongation induced, runner formation promoted, andflower initiation inhibited both in the perpetual-fruiting andthe seasonal-fruiting varieties of strawberry by applicationsof gibberellic acid. Runners were induced to form in Fragariavesca semper-florcns var. Baron Solemacher, which does not normallyrunner. Thus the physiological processes which lead to the morphologicaldifferences between perpetual and seasonal fruiting types wereoverruled by treatment with gibberellic acid. Gibberellins A₁, A₄, A₇, and A₉, like gibberellic acid (A₃),induced elongation of petioles (a normal photoperiodic response),elongation of internodes on the main stem, and inhibition offlower formation in Baron Solemacher (responses not inducedby photoperiod). When applied to the cut stump of a debladed petiole, gibberellicacid inhibited flower formation at the growing apex of the stem,thus substituting for the leaf blade, which in long photoperiodsinhibited flower formation. A morphological study suggested that in Duchesnea indica, arelated genus, flower initiation is not regulated by environmentalcircumstances, but is the inevitable consequence of growth.Although promoting increase in petiole length and in elongationof lateral growths as in strawberry, gibberellic acid did notinhibit flower initiation in this species, except in so faras it caused a retardation in the growth of certain axillarybuds, so that a lower proportion of them reached the stage offlower initiation within the duration of the experiment. These results are discussed in relation to the hypothesis thatflower formation is regulated by an inhibitory hormone in seasonal-fruitingstrawberries.     

Promotion of Flowering in Sagittaria pygmaea Miq. by 2,6-Diisopropylphenoxyacetic Acid

The flowering of Sagittaria pygmaea Miq. was promoted by 2,6-diisopropylphenoxyacetic acid, as well as by gibberellic acid (GA₃). Uniconazole canceled the promotive effect of the phenoxy-acetic acid, while prohexadione shortened the period required for flowering. Endogenous GAs seem to play an important role in the flowering of S. pygmaea, and 2,6-diisopropylphenoxyacetic acid might affect GA biosynthesis or metabolism.     

Gibberellins in Relation to Flowering and Stem Elongation in the Long Day Plant Silene armeria

Two long days induced some flowering and 4 or more long days caused 100% flowering in Silene armeria. On long days microscopically detectable flower primordia were first seen after 6 days, which is at least 1 day before the start of stem elongation. Both gibberellin A₃ and A₇ caused flowering on short days, but the results were variable and flowering was never 100%. Three different gibberellins were detected in Silene extracts. The pattern of gibberellins extracted from plants on short and long days was qualitatively the same, but on long days gibberellin content was up to 100% higher than on short days. Only small amounts of diffusible gibberellins were obtained from Silene shoot tips (including very young leaves) on short days. However, on long days the diffusible gibberellins increased by as much as 10-fold after 4 to 6 long days but then declined somewhat after 10 long days. The gibberellins extracted from the shoot tips at the completion of the diffusion period also increased under long days, although the increase was not as large as for the diffusible gibberellins. An A₅-like gibberellin present in extracts was not detected in diffusates.     

Promotion of Flowering in Brassica campestris L. cv Ceres by Sucrose

Flower initiation of the quantitative long-day plant Brassica campestris cv Ceres was earlier and at a lower final leaf number when sucrose was added to the medium in which plants were grown in sterile culture. The optimal concentration of sucrose was 40 to 80 millimolar. This flower-promoting effect of sucrose was not osmotic, as mannitol, sodium chloride, and polyethylene glycol were not effective at equal osmotic potentials.

Seedlings grown heterotrophically after treatment with 4-chloro-5-(dimethylamino)-2-phenyl-3-(2H)-pyridazinone to prevent chlorophyll accumulation were also induced to form flower primordia earlier as the sucrose concentration in the medium was increased up to 80 millimolar. Inclusion of 4 millimolar sodium nitrate in the culture medium of green plants did not reduce the flower-promoting effects of sucrose but delayed initiation in plants grown without added sucrose.

Removal of CO₂ during a single main or supplementary light period, or both, greatly reduced flower initiation. It is concluded that sucrose may be an important controlling factor determining floral initiation in Brassica.

     

The Control of Flowering in the Strawberry Fragaria ananassa Duch: II. The Role of Gibberellins

Activity of gibberellin-like substances was lacking in leavesof strawberry plants at time of flower initiation, but peduncleelongation was accompanied by significant activity of two substancesprobably related to GA₃ and GA₇. Exogenous gibberellin (GAS),applied to strawberry plants at the flower-differentiation stage,strongly promoted peduncle elongation, while similar applicationof the growth-retardant (2 chloro-ethyl) trimethylammonium chloride(CCC), an inhibitor of gibberellin biosynthesis, inhibited peduncleelongation. These treatments also affected subsequent runnering,GA increasing the number of runners, as well as their mean individuallength, while CCC caused the opposite effect. Application of gibberellin immediately after flower-bud initiation,but before peduncle emergence, affected the distribution offruit yield. GA-treated plants produced more than untreatedones in the first half of the fruiting season, but the situationwas reversed in the second half of the season—so thattotal yields were unaffected. It was suggested that the exogenousgibberellin hastened yield by anticipating the endogenous gibberellinwhich is normally formed at a somewhat later stage in the plant'sdevelopment. The parallel responses with regard to elongationof vegetative runners and flower peduncles together with thedata of the other experiments seem to indicate that peduncleelongation is a typical vegetative growth response enhancedby gibberellin and checked by substances which inhibit biosynthesisof endogenous gibberellin.     

Flowering in Tobacco Needs Gibberellins but is not Promoted by the Levels of Active GA1 and GA4 in the Apical Shoot

The above article was     

Gibberellins and Inhibitors in Relation to Flowering of White Clovers (Trifolium repens L.)

Flower primordia appeared sooner and flowering intensity increasedas day length was extended beyond 8 h (short day) in two whiteclovers: cv. Tamar and cv. Tammisto, originating from Israeland Finland, respectively. Application of GA₃ under short dayscaused Tamar to flower more intensively as much as the doseof GA₃ was increased, but it did not affect the flowering ofTammisto. The level of gibberellin-like substances in stolon apices washigher under long (16 h) than under short days in both cultivars.The level of inhibitors extracted from leaves was not affectedby day length in Tamar. However, in Tammisto this level wasalmost twice as high under short than under long days. It issuggested that the presence of a relatively high level of inhibitorsin Tammisto when grown under short days interfered with theactivity of gibberellins in its effect on flowering. ABA wasamong the inhibitors: its application under long days had noeffect on flowering, but it increased the number of stolons.Possibly inhibitors other than ABA are involved in the preventionof flowering. Leaf expansion responded to day length and GA₃ and ABA applicationin a similar way as the response of flowering, i.e. towardsflowering the size of the leaves increased.     

Promotion of Flowering in Lemna paucicostata 6746 (a Short-Day Duckweed) by Cytokinins

Lemna paucicostata 6746 is a short-day plant and flowers inresponse to a single photoinductive cycle. Flowering in thisduckweed could be promoted, under short days, in the presenceof a cytokinin in the nutrient medium. 6-Benzyladenine (BA)was the most effective for promotion of flowering, followedby zeatin and kinetin. Since EDTA itself is promotive for floweringin this plant, the cytokinin effect is best observed in mediumdevoid of EDTA. Nevertheless, in their combined presence floweringwas more as compared to when either of these was individuallypresent. This additive effect on flowering was especially prominentwhen the plants were kept in near-critical photoperiods. Besidesthe increase in percentage of the flowering fronds, floweringis also sustained a little longer in the cytokinin-treated plants.BA, however, did not alter the critical dark period requirement,either in the presence or absence of EDTA. (Received March 26, 1983; Accepted May 6, 1983)     

Comparative mapping in the Pinaceae

A comparative genetic map was constructed between two important genera of the family Pinaceae. Ten homologous linkage groups in loblolly pine (Pinus taeda L.) and Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) were identified using orthologous expressed sequence tag polymorphism (ESTP) and restriction fragment length polymorphism (RFLP) markers. The comparative mapping revealed extensive synteny and colinearity between genomes of the Pinaceae, consistent with the hypothesis of conservative chromosomal evolution in this important plant family. This study reports the first comparative map in forest trees at the family taxonomic level and establishes a framework for comparative genomics in Pinaceae.     

Gibberellins in Gramineae

Data on the occurrence of free and conjugated gibberellins in different tribes of Gramineae are compiled and discussed with regard to their biosynthetic pathways. From the gibberellins detected so far the functioning of both the early 13-hydroxylation and the non-3,13-hydroxylation pathway of GA biosynthesis in gramineous plants can be deduced and the discovery of further gibberellin conjugates may be expected.     

Early evolution in the Pinaceae

Nineteen species of structurally preserved ovulate cones of the Pinaceae are known from the Cretaceous. One of these belongs to Pinus, while the others contain anatomical features necessitating their classification in the organ genera Pityostrobus and Pseudoaraucaria. The six species of the latter group are very similar to one another and probably represent a natural, thought extinct, genus. By contrast, there is so much variety in the twelve Cretaceous species of Pityostrobus that when they are considered with respect to the uniformity of cone structure within each of the modern genera, each of the species of this organ genus may well reperesent an natural genus by itself. All expect one of these fossil forms contain features that are today characteristic of Pinus. This, combined with the Early Cretaceous occurrence of a structurally preserved Pinus cone, suggests that Pinus or something very close to it represents the phylogenetic centrum of the ancestral complex. Lack of cones showing distinct affinity with other modern genera supports this idea and further suggests that, while Pinus was in existence in the Early Cretaceous, other Recent genera of the Pinaceae may not have diverged from the complex until the Late Cretaceous or Early Tertiary.