Effects of Ring D-Modified Gibberellins on Gibberellin Levels and Development in Selected Sorghum bicolor Maturity Genotypes

Plants of early flowering mutant and wild type genotypes of Sorghum bicolor were treated with ring D-modified gibberellins (GAs), and the effects on endogenous GA levels were determined. The growth and timing of floral initiation in 58M plants grown under 18-h days (which significantly delays floral initiation in this short day plant) following treatment with these compounds, relative to GA₃ and GA₅ treatments, were also investigated. Application of the endo-isomer of C16,17-dihydro-GA₅ (endo-DiHGA₅), the exo-isomer of C16,17-dihydro-GA₅ (exo-DiHGA₅), and C16α,17-dichloromethanodihydro-GA₅ (DMDGA₅) altered GA levels in both genotypes. Each ring D-modified GA significantly inhibited shoot growth while significantly decreasing levels of GA₁ and increasing levels of its immediate precursor, GA₂₀. Gibberellin A₈ levels also decreased. Tillering was not affected by any treatment. For the early flowering genotype 58M, grown under noninductive long days, both dihydro-GA₅ isomers promoted floral initiation while shoot growth was strongly inhibited, and floral development was strongly advanced beyond floral stage 4. Gibberellin A₃ and GA₅, applied under the same conditions, promoted shoot growth slightly and gave ``floral-like' apical meristems that did not develop past floral stage 1. These results suggest that the reduced shoot growth of sorghum, which follows application of those ring D-modified GAs, is due to their inhibiting the 3β hydroxylation of GA₂₀ to GA₁, thereby reducing the GA₁ content. That floral initiation was hastened and floral development promoted in genotype 58M by application of both isomers of DiHGA₅ are in contrast to the effects of other GA biosynthesis inhibitors, which act earlier in the GA biosynthesis pathway, but are consistent with results seen for long day grasses. This suggests that endo-DiHGA₅ and exo-DiHGA₅ may be acting directly in promoting floral initiation and subsequent floral apex development of this short day plant under long day conditions. Received October 3, 1996; accepted January 22, 1997     

Interaction of growth retardants,daylength, and gibberellins A19, A20, and A1 on shoot elongation in birch and alder

Gibberellins A₁₉, A₂₀, and A₁ were applied to seedlings of birch (Betula pubescens Ehrh.) and alder (Alnus glutinosa (L.) Gaertn.) in order to test their ability to counteract growth inhibition induced by growth retardants (ancymidol and BX-112) or short day (SD, 12 h) photoperiod. Ancymidol inhibits early and BX-112 inhibits late steps in gibberellin biosynthesis. BX-112 inhibited stem elongation in both species while ancymidol, applied as a soil drench, was effective in alder only. Growth retardants affected stem elongation mainly by inhibiting elongation of internodes. All three gibberellins were equally active when applied to seedlings treated with ancymidol; however, only GA₁ was able to counteract the growth inhibition induced by BX-112. SD-induced cessation of elongation growth in birch was counteracted by GA₁, and to some degree, by GA₂₀, while GA₁₉ was inactive. SD treatment did not induce cessation of apical growth in alder. These results are consistent with the hypothesis that of gibberellins belonging to the early C-13 hydroxylation pathway, GA₁ is the only active gibberellin for stem elongation.     

Photoperiod Control of Gibberellin Levels and Flowering in Sorghum

Regulation of rhythmic peaks in levels of endogenous gibberellins (GAs) by photoperiod was studied in the short-day monocot sorghum (Sorghum bicolor [L.] Moench). Comparisons were made between three maturity (Ma) genotypes: 58M (Ma₁Ma₁, Ma₂Ma₂, phyB-1phyB-1, and Ma₄Ma₄ [a phytochrome B null mutant]); 90M (Ma₁Ma₁, Ma₂Ma₂, phyB-2phyB-2, and Ma₄Ma₄); and 100M (Ma₁Ma₁, Ma₂Ma₂, PHYBPHYB, and Ma₄Ma₄). Plants were grown for 14 d under 10-, 14-, 16-, 18-, and 20-h photoperiods, and GA levels were assayed by gas chromatography-mass spectrometry every 3 h for 24 h. Under inductive 10-h photoperiods, the peak of GA₂₀ and GA₁ levels in 90M and 100M was shifted from midday, observed earlier with 12-h photoperiods, to an early morning peak, and flowering was hastened. In addition, the early morning peaks in levels of GA₂₀ and GA₁ in 58M under conditions allowing early flowering (10-, 12-, and 14-h photoperiods) were shifted to midday by noninductive (18- and 20-h) photoperiods, and flowering was delayed. These results are consistent with the possibility that the diurnal rhythm of GA levels plays a role in floral initiation and may be one way by which the absence of phytochrome B causes early flowering in 58M under most photoperiods.     

Effect of Gibberellin on Growth, Protein Secretion, and Starch Accumulation in Maize Endosperm Suspension Cells

The physiologic effect of gibberellins (GA) in seed development is poorly understood. We examined the effect of gibberellic acid (GA₃) on growth, protein secretion, and starch accumulation in cultured maize (Zea mays L.) endosperm suspension cells. GA₃ (5 and 30 μm) increased the fresh weight, dry weight, and protein content of the cultured cells, but the effect of GA₃ at 50 μm was not significantly different. However, the protein content in the culture medium was increased by these three concentrations of GA₃. The effect of GA₃ on the amount of cellular structural polysaccharides was not significant, but GA₃ had a dramatic effect on the starch content. At 5 μm, GA₃ caused an increase in the starch content, but at 50 μm the starch accumulation was reduced. Chlorocholine chloride (CCC), an inhibitor of GA biosynthesis, significantly increased the starch content and decreased the structural polysaccharide content of the cultured cells. The effects of CCC at 500 μm on the starch and polysaccharide content were partially reversed by 5 μm GA₃ applied exogenously. Based on these results we suggest that GA does not favor starch accumulation in the cell cultures and that the addition of lower concentrations of GA₃ in the medium may provide an improved balance among the endogenous GA in the cultured cells. Received October 31, 1995; accepted March 25, 1997     

Effects of a Plant Growth Regulator, Prohexadione Calcium (BX-112), on the Elongation of Rice Shoots Caused by Exogenously Applied Gibberellins and Helminthosporol, Part II

Prohexadione calcium (BX-112) is a novel plant growth regulatorthat inhibits the late stages of the biosynthesis of gibberellinsin plants. Fourteen kinds of gjbberellin, helminthosporol and'helminthosporic acid were applied simultaneously with BX-112to rice seedlings (Oryza sativa L. ), and their growth-promotingactivities in terms of shoot elongation were examined. The growth-promotingactivities of GA₁, GA₄, GA₁₈, GA₂₂, GA₂₃, GA₃₈, helminthosporoland helminthosporic acid were not inhibited by BX-112, but thoseof GA₅, GA₉, GA₁₅, GA₁₉, GA₂₀, GA₃₁, GA₄₄ and GA₅₃ were inhibited.These results suggest that 3ß-hydroxylation is animportant and necessary step in the biosynthesis of gibberellinsthat promote shoot elongation in rice seedlings. The weak promotionof shoot elongation by GA₂₂ in the presence of BX-112 suggeststhat the effect of a hydroxyl group at C-18 of GA₂₂ might beable to mimic the effect of the 3ß-hydroxyl groupof GA₁. Helminthosporol and helminthosporic acid may promotethe shoot elongation of rice by mimicking physiologically activegibberellins and not by stimulating their biosynthesis. ¹Part I is the previous paper by Nakayama et al. (1990a) ³Present address: Frontier Research Program RIKEN, Wako-shi,Saitama, 351-01 Japan. (Received June 26, 1991; Accepted September 4, 1991)     

Possible Involvement of Altered Gibberellin Metabolism in the Induction of Tomato Irregular Ripening in Dwarf Cherry Tomato by Silverleaf Whitefly

External and internal tomato irregular ripening (TIR) symptoms were associated with the feeding of silverleaf whitefly (SLW), Bemisia argentifolii Bellows and Perring. Four experiments consisting of various soil drench applications of GA₃ (100 ppm) and cycocel (CCC, an inhibitor of GA biosynthesis; 1,000 and 2,000 ppm) were applied to dwarf cherry tomato cv. Florida Petite in the presence and absence of SLW in an attempt to mimic the disorders induced by the SLW. The application of GA₃ induced external and internal TIR symptoms similar to the SLW-induced disorder. Minimal TIR-like symptoms also occurred in the control and CCC treatments. Internal TIR symptoms in GA₃, GA₃ plus SLW, and GA₃ plus CCC treatments ranged from 66% to 97% throughout the experiments. The incidence of external TIR symptoms was highest in the GA₃ plus SLW treatment compared with the other treatments. CCC reduced the incidence of external TIR symptoms induced by GA₃ or GA₃ plus SLW treatments. However, CCC-treated plants also attracted more oviposition and higher populations of SLW and consequently induced a greater incidence of TIR symptoms than SLW treatment alone. Furthermore, although low SLW populations may be associated with low external TIR symptoms, internal TIR symptoms almost always remained high in infested plants. The results suggest that the TIR disorder in dwarf cherry tomato which is induced by the SLW may be a gibberellin-regulated disorder. Received May 27, 1997; accepted September 26, 1997     

Growth-active gibberellins overcome the very slow shoot growth of Hancornia speciosa, an important fruit tree from the Brazilian “Cerrado”

Shoot elongation of Hancornia speciosa, an endangered tree from the Brazilian savannah “Cerrado”, is very slow, thus limiting nursery production of plants. Gibberellins (GAs) A₁, A₃, and A₅, and two inhibitors of GA biosynthesis, trinexapac-ethyl and ancymidol were applied to shoots of Hancornia seedlings. GA₁ and GA₃ significantly stimulated shoot elongation, while GA₅ had no significant effect. Trinexapac-ethyl and ancymidol, both at 100 μg per seedling, inhibited shoot elongation up to 45 days after treatment, though the effect was statistically significant only for ancymidol. Somewhat surprisingly, exogenous GA₃ more effectively stimulated shoot elongation in SD-grown plants, than in LD-grown plants. The results from exogenous application of GAs and inhibitors of GA biosynthesis imply that Hancornia shoot growth is controlled by GAs, and that level of endogenous growth-active GAs is likely to be the limiting factor for shoot elongation in Hancornia. Application of GAs thus offer a practical method for nursery production of Hancornia seedlings for outplanting into the field.     

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     

Effects of a New Plant Growth Regulator Prohexadione Calcium (BX-112) on Shoot Elongation Caused by Exogenously Applied Gibberellins in Rice (Oryza sativa L.) Seedlings

The effects of a novel plant growth regulator (PGR) prohexadionecalcium (BX-112; calcium 3,5-dioxo-4-propionylcyclohexanecarboxylate)on shoot elongation caused by exogenously applied GA₁, GA₃,GA₄₎ GA₁₉ and GA₂₀ were investigated in rice (Oryza sativa L.cv. Nihonbare and cv. Tan-ginbozu) seedling test. Dependingon the dose, BX-112 reduced shoot elongation in both cultivarscaused by GA₁₉ and GA₂₀, but not by GA₁. When a high dose ofBX-112 (e.g. 250 ng/plant and over) was applied with GA₁, orGA₄, shoot elongation was even promoted. This promotive effect,however, was not observed with GA₃. These results suggest thatBX-112 inhibits gibberellin (GA) biosynthesis in the rice plantat the 3ß- and 2ß-hydroxylation of GAs,namely steps of activation and inactivation, respectively. (Received September 6, 1989; Accepted November 27, 1989)     

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     

Gibberellin Regulation of Root Growth with Change in Galactose Content of Cell Walls in Pisum sativum

Root elongation of Alaska pea seedling was suppressed by higherconcentrations of growth retardants, CCC and ancymidol, thanthose required for shoot elongation. Gibberellic acid (GA³)led to recovery of ancymidol-inhibited elongation, with theconcentration (1 nM) required for roots being lower than thatfor shoots (10 µM). Ancymidol caused swelling of corticalcells in the elongating zone of the root, while GA³ completelycanceled this. These results suggest that roots require muchless gibberellin than shoots for normal elongation growth. Growth kinetics recorded by a computer-regulated rhizometerindicated that the lag periods for growth suppression by ancymidoland growth recovery by GA³ were about 10 h and 7 h, respectively. The composition of the cell wall sugars changed remarkably alongthe root axis from the tip to the base. The arabinose contentwas highest in the tip and rapidly decreased toward the base,whereas galactose complementarily increased toward the base.The thickened zone of ancymidol-treated roots had a higher galactosecontent than GA³-treated slender roots. Other neutral sugarswere not significantly influenced by ancymidol and/or GA³. Theseresults suggest that ancymidol makes cells short and thick withgalactose-rich cell walls while GA3 keeps cells extensible andslender with galactose-poor cell walls. (Received March 3, 1987; Accepted December 4, 1987)     

The Response to Gibberellin in Pisum sativum Grown under Alternating Day and Night Temperature

The application of gibberellins (GA) reduces the difference in stem elongation observed under a low day (DT) and high night temperature (NT) combination (negative DIF) compared with the opposite regime, a high DT/low NT (positive DIF). The aim of this work was to investigate possible thermoperiodic effects on GA metabolism and tissue sensitivity to GA by comparing the response to exogenously applied GA (in particular, GA₁ and GA₃) in pea plants (Pisum sativum cv. Torsdag) grown under contrasting DIF. Control plants not treated with growth inhibitors or additional GA were 38% shorter under negative (DT/NT 13/21°C) than positive DIF (DT/NT 21/13°C) because of shorter internodes. Additional GA₁ or GA₃ decreased the difference between positive and negative DIF. In pea plants dwarfed with paclobutrazol, which inhibits GA biosynthesis at an early step, the response to GA₁ was reduced more strongly by negative compared with positive DIF than the response to GA₃. The induced stem elongation by GA₁₉ and GA₂₀ did not deviate significantly from the response to GA₁. Plants treated with prohexadione-calcium, an inhibitor of both the production and the inactivation of GA₁, grew equally tall under the two temperature regimes in response to both GA₁ and GA₃. We hypothesize that the reduced response to GA₁ compared with GA₃ in paclobutrazol-treated plants grown under negative DIF is caused by a higher rate of 2β-hydroxylation of GA₁ into GA₈ under negative than positive DIF. This contributes to lower levels of GA₁ and consequently shorter stems and internodes in pea plants grown under negative than positive DIF. Differences in tissue sensitivity to GA alone cannot account for this specific thermoperiodic effect on stem elongation. Received May 28, 1998; accepted May 29, 1998     

Growth Responses and Allocation of Assimilates of Rice Seedlings by Paclobutrazol and Gibberellin Treatment

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)methyl-4,4-dimethyl-2-(1h-1,2,4-trizol-1-yl)penten-3-ol] effectively decreased vegetative growth of rice (Oryza sativa L.) seedlings and increased the chlorophyll content. The number of veins in a leaf, the calculated number of stomata per leaf, and the length of guard cells were not altered by the paclobutrazol treatment, suggesting an effect on cell elongation. The allocation pattern of carbohydrates was changed by either gibberellin (GA) or paclobutrazol treatment. GA₃ induced more shoot growth and less accumulation of starch than the control and paclobutrazol-treated seedlings. Photosynthetic ability was not affected by either paclobutrazol or GA₃ treatment. Paclobutrazol-treated plants allocated a smaller amount of photosynthates for vegetative shoot growth and stored more as starch in the crowns than the control and GA₃-treated plants. The same starch degrading activity in the crown tissue of paclobutrazol-treated seedlings as in control plants suggests that the accumulated starch is utilized in a normal activity for growth including leaf emergence, tiller formation, and root production, resulting in improved seedling quality. Received May 30, 1996; accepted December 10, 1996     

Gibberellins and Subapical Cell Divisions in Relation to Bud Set and Bud Break in Salix pentandra

In young plants of Salix pentandra, a temperate zone deciduous woody species, elongation growth ceases and a terminal bud is formed at day lengths shorter than a critical length. This is the first step in dormancy development, making survival under harsh winter conditions possible. Early studies strongly indicate that gibberellin is involved in the photoperiodic control of bud set and bud break. GA₁ action was studied by application under short days to plants where cessation of shoot elongation had occurred, followed by subsequent anatomic investigations of shoot tips. Under short days the frequency of cell division decreased rapidly along with the earlier observed decrease in GA₁ levels. Application of GA₁ to short-day–induced terminal buds rapidly stimulated cell division in apices several days before visible shoot elongation in response to this treatment was observed. One day after GA₁ application a fourfold increase in cell division frequency in apices was observed, increasing to a maximum of sevenfold 2 days after application. Long-day treatment leading to induction of bud break after about 4–6 days was followed by slowly increasing frequency of cell divisions. In earlier studies of this species, short days and gibberellins had no effect on cell elongation. These data show that increased GA₁ content, by application or long-day treatment, results in increased frequency of mitosis. This strongly indicates that GA₁ affects stem elongation in connection with bud set and bud break primarily by affecting cell divisions in subapical tissues. Received February 26, 1999; accepted October 8, 1999     

Genetic Regulation of Development in Sorghum bicolor: V. The ma(3) Allele Results in Gibberellin Enrichment

Sorghum bicolor genotypes, near isogenic with different alleles at the third maturity locus, were compared for development, for responsiveness to GA₃ and a GA synthesis inhibitor, and occurrence and concentrations of endogenous GAs, IAA, and ABA. At 14 days the genotype 58M (ma₃^Rma₃^R) exhibited 2.5-fold greater culm height, 1.75-fold greater total height, and 1.38-fold greater dry weight than 90M (ma₃ma₃) or 100M (Ma₃Ma₃). All three genotypes exhibited similar shoot elongation in response to GA₃, and 58M showed GA₃-mediated hastening of floral initiation when harvested at day 18 or 21. Both 90M and 100M had exhibited hastening of floral initiation by GA₃ previously, at later application dates. Tetcyclacis reduced height, promoted tillering, and delayed flowering of 58M resulting in plants which were near phenocopies of 90M and 100M. Based on bioassay activity, HPLC retention times, cochromatography with ²H₂-labeled standards on capillary column GC and matching mass spectrometer fragmentation patterns (ions [m/z] and relative abundances), GA₁, GA₁₉, GA₂₀, GA₅₃, and GA₃ were identified in extracts of all three genotypes. In addition, based on published Kovats retention index values and correspondence in ion masses and relative abundances, GA₄₄ and GA₁₇ were detected. Quantitation was based on recovery of coinjected, ²H₂-labeled standards. In 14 day-old-plants, total GA-like bioactivity and GA₁ concentrations (nanograms GA/gram dry weight) were two- to six-fold higher in 58M than 90M and 100M in leaf blades, apex samples, and whole plants while concentrations in culms were similar. Similar trends occurred if data were expressed on a per plant basis. GA₁ concentrations for whole plants were about two-fold higher in 58M than 90M and 100M from day 7 to day 14. Concentrations of ABA and IAA did not vary between the genotypes. The results indicate the mutant allele ma₃^R causes a two- to six-fold increase in GA₁ concentrations, does not result in a GA-receptor or transduction mutation and is associated with phenotypic characteristics that can be enhanced by GA₃ and reduced by GA synthesis inhibitor. These observations support the hypothesis that the allele ma₃^R causes an overproduction of GAs which results in altered leaf morphology, reduced tillering, earlier flowering, and other phenotypic differences between 58M and 90M or 100M.     

Roles of Soluble Sugars in Protecting Phytochrome- and Gibberellin A3-Mediated Germination Control in Skotodormant Lettuce Seeds

Skotodormant seeds of Lactuca sativa Grand Rapids imbibed in darkness for 10 days (10-day DS) germinated poorly upon terminal treatment with red light (R) or gibberellin A₃ (GA₃). Soluble sugars in the imbibition solutions influenced the depth of skotodormancy. Ten-day DS seeds, imbibed in 50–500 mm sucrose or 100–500 mm glucose and given terminal GA₃ germinated completely and germinated about 80% when imbibed in 100 mm galactose, mannose, lactose, or maltose. In contrast, terminal R applied to 10-day DS seeds caused only 20–50% germination. If given R at day 0 and imbibed for 10 days in darkness in 500 mm sucrose or glucose, seeds washed free of exogenous glucose or sucrose then germinated about 50% in darkness in water. These seeds responded to terminal R or GA₃ with complete germination. When seeds were given FR at day 0, germination responses following terminal R or GA₃ were significantly lower when the duration of DS was increased from 7–10 day DS to 15 days. In 10-day DS seeds given initial FR and imbibed in either solutions of 50 or 100 mm sucrose and KNO₃, either terminal R or GA₃ treatment gave complete or near complete germination. It is concluded that seed exposure to certain soluble sugars and/or nitrate during a 10-day DS protected certain substrates and thereby extended the sensitivity of the seeds to terminal R or GA₃ treatment. The study provides substantial evidence for nonhormonal factors associated with light and GA action in the control of seed skotodormancy. Received October 30, 1996; accepted April 22, 1997     

Thermo- and Photoperiodicity and Involvement of Gibberellins during Day and Night Cycle on Elongation Growth of Begonia x hiemalis Fotsch

The effects of thermo- and photoperiodicity on elongation growth and on endogenous level of gibberellins (GAs) in Begonia x hiemalis during various phases of the day-night cycle have been studied. Plant tissue was harvested during the day and night cycle after temperature and photoperiodic treatments and analyzed for endogenous GAs using combined gas chromatography and mass spectrometry. Elongation growth increased when the difference between day and night temperature (DIF = DT − NT) increased from a negative value (−9.0 and −4.5°C) to zero and with increasing photoperiod from 8 to 16 h. When applied to the youngest apical leaf, gibberellins A₁, A₄, and A₉ increased the elongation of internodes and petioles. GA₄ had a stronger effect on elongation growth than GA₁ and GA₉. In relative values, the effect of these GAs decreased when DIF increased from −9 to 0°C. The time of applying the GAs during a day and night cycle had no effect on the growth responses. In general, endogenous levels of GA₁₉ and GA₂₀ were higher under negative DIF compared with zero DIF. The level of endogenous GA₁ in short day (SD)-grown plants was higher under zero DIF than under negative DIF, but this relationship did not appear in long day (LD)-grown plants. The main effects of photoperiod seem to be a higher level of GA₁₉ and GA₁ at SD compared with LD, whereas GA₂₀ and GA₉ show the opposite response to photoperiod. No significant differences in endogenous level of GA₁, GA₉, GA₁₉, and GA₂₀ were found for various time points during the diurnal day and night cycle. Endogenous GA₂₀ was higher in petiole and leaf compared with stem, whereas there were no differences of GA₁, GA₉, and GA₁₉ between plant parts. No clear relationship was found between elongation of internodes and petioles and levels of endogenous GAs. Received December 26 1996; accepted July 1, 1997     

Gibberellins in Leaves of Alstroemeria hybrida: Identification and Quantification in Relation to Leaf Age

In alstroemeria (Alstroemeria hybrida), leaf senescence is retarded effectively by the application of gibberellins (GAs). To study the role of endogenous GAs in leaf senescence, the GA content was analyzed by combined gas chromatography and mass spectrometry. Five 13-hydroxy GAs (GA₁₉, GA₂₀, GA₁, GA₈, and GA₂₉) and three non-13-hydroxy GAs (GA₉ and GA₄) were identified in leaf extracts by comparing Kováts retention indices (KRIs) and full scan mass sprectra with those of reference GAs. In addition, GA₁₅, GA₄₄, GA₂₄, and GA₃₄ were tentatively identified by comparing selected ion monitoring results and KRIs with those of reference GAs. A number of GAs were detected in conjugated form as well. Concentrations of GAs in alstroemeria changed with the development of leaves. The proportion of biologically active GA₁ and GA₄ decreased with progressive senescence and the fraction of conjugated GAs increased. Received May 26, 1997; accepted August 12, 1997     

Different inhibitors of the gibberellin biosynthesis pathway elicit varied responses during in vitro culture of aspen (<Emphasis Type="Italic">Populus tremula</Emphasis> L.)

Several synthetic plant growth regulators (PGRs), including prohexadione-calcium (ProCa), paclobutrazol (PBZ), and chlormequat chloride (CCC), known for their ability to inhibit gibberellin (GA) biosynthesis, were investigated for their influence on Populus tremula L. (aspen) shoots grown in vitro. Changes in plant growth induced by these inhibitors were compared to the effects of exogenous gibberellins (GA₃ and GA_4/7). All PGRs were added to the nutrient medium at concentrations of either 1 or 5 μM. Stem segments with and without apical buds were excised from in vitro-grown shoot culture, and these explants were incubated either in test tubes or Petri dishes. In the presence of 5 μM ProCa, shoot growth and rooting were inhibited when grown in test tubes, while shoots grown in Petri dishes exhibited strongly enhanced shoot and root growth. PBZ suppressed shoot development both in test tubes and Petri dishes, although 1 μM PBZ promoted adventitious root formation when shoots were grown in test tubes. Five micromolars CCC suppressed shoot and root development in test tubes, but promoted shoot growth in Petri dishes.     

Effects of Auxin Transport Inhibitors on Gibberellins in Pea

The effects of the auxin transport inhibitors 2,3,5-triiodobenzoic acid (TIBA), 9-hydroxyfluorene-9-carboxylic acid (HFCA), and 1-N-naphthylphthalamic acid (NPA) on gibberellins (GAs) in the garden pea (Pisum sativum L.) were studied. Application of these compounds to elongating internodes of intact wild type plants reduced markedly the endogenous level of the bioactive gibberellin A₁ (GA₁) below the application site. Indole-3-acetic acid (IAA) levels were also reduced, as was internode elongation. The auxin transport inhibitors did not affect the level of endogenous GA₁ above the application site markedly, nor that of GA₁ precursors above or below it. When plants were treated with [¹³C,³H]GA₂₀, TIBA reduced dramatically the level of [¹³C,³H]GA₁ recovered below the TIBA application site. The internodes treated with auxin transport inhibitors appeared to be still in the phase where endogenous GA₁ affects elongation, as indicated by the strong response to applied GA₁ by internodes of a GA₁-deficient line at the same stage of expansion. On the basis of the present results it is suggested that caution be exercised when attributing the developmental effects of auxin transport inhibitors to changes in IAA level alone. Received April 13, 1998; accepted April 14, 1998