The extreme dwarf phenotype of the GA-sensitive mutant of sunflower, dwarf2, is generated by a deletion in the ent-kaurenoic acid oxidase1 (HaKAO1) gene sequence

A dwarf mutant, dw arf 2 (dw2), was isolated from sunflower (Helianthus annuus). The most obvious alterations of dw2 plants were the lack of stem growth, reduced size of leaves, petioles and flower organs, retarded flower development. Pollen and ovules were produced but the filaments failed to extrude the anthers from the corolla. The dw2 phenotype was mainly because of reduced cell size. In dw2 leaves, the dark-green color was not so much due to higher pigment content, but was correlated with a changed leaf morphology. The mutant responded to the application of bioactive gibberellins (GAs). The levels of ent-7α-hydroxykaurenoic acid, GA(19), GA(20) and GA(1) in dw2?seedlings were severely decreased relative to those in its wild type (WT). ent-Kaurenoic acid was actively converted to ent-7α-hydroxykaurenoic acid in WT plants but quite poorly in dw2 plants. All together these data suggested that the dw2 mutation severely reduced the flux through the biosynthetic pathway leading to active GAs by hampering the conversion of ent-kaurenoic acid to GA(12). Two ent-kaurenoic acid oxidase (KAO) genes were identified. HaKAO1 was expressed everywhere in sunflower organs, while HaKAO2 was mainly expressed in roots. We demonstrated that a DNA deletion in HaKAO1 of dw2 generated aberrant mRNA-splicing, causing a premature stop codon in the amino acid sequence. In dw2 calli, Agrobacterium-mediated transfer of WT HaKAO1 cDNA restored the WT endogenous levels of GAs. In segregating BC(1) progeny, the deletion co-segregated with the dwarf phenotype. The deletion was generated near to a breakpoint of a more complex chromosome rearrangement.     

Uncoupling brassinosteroid levels and de-etiolation in pea

The suggestion that brassinosteroids (BRs) have a negative regulatory role in de-etiolation is based largely on correlative evidence, which includes the de-etiolated phenotypes of, and increased expression of light-regulated genes in, dark-grown mutants defective in BR biosynthesis or response. However, we have obtained the first direct evidence which shows that endogenous BR levels in light-grown pea seedlings are increased, not decreased, in comparison with those grown in the dark. Similarly, we found no evidence of a decrease in castasterone (CS) levels in seedlings that were transferred from the dark to the light for 24 h. Furthermore, CS levels in the constitutively de-etiolated lip1 mutant are similar to those in wild-type plants, and are not reduced as is the case in the BR-deficient lkb plants. Unlike lip1 , the pea BR-deficient mutants lk and lkb are not de-etiolated at the morphological or molecular level, as they exhibit neither a de-etiolated phenotype or altered expression of light-regulated genes when grown in the dark. Similarly, dark-grown WT plants treated with the BR biosynthesis inhibitor, Brz, do not exhibit a de-etiolated phenotype. In addition, analysis of the lip1lkb double mutant revealed an additive phenotype indicative of the two genes acting in independent pathways. Together these results strongly suggest that BR levels do not play a negative-regulatory role in de-etiolation in pea.     

Overexpression of 20-Oxidase Confers a Gibberellin-Overproduction Phenotype in Arabidopsis

In the gibberellin (GA) biosynthesis pathway, 20-oxidase catalyzes the oxidation and elimination of carbon-20 to give rise to C₁₉-GAs. All bioactive GAs are C₁₉-GAs. We have overexpressed a cDNA encoding 20-oxidase isolated from Arabidopsis seedlings in transgenic Arabidopsis plants. These transgenic plants display a phenotype that may be attributed to the overproduction of GA. The phenotype includes a longer hypocotyl, lighter-green leaves, increased stem elongation, earlier flowering, and decreased seed dormancy. However, the fertility of the transgenic plants is not affected. Increased levels of endogenous GA₁, GA₉, and GA₂₀ were detected in seedlings of the transgenic line examined. GA₄, which is thought to be the predominantly active GA in Arabidopsis, was not present at increased levels in this line. These results suggest that the overexpression of this 20-oxidase increases the levels of some endogenous GAs in transgenic seedlings, which causes the GA-overproduction phenotype.     

Narrow-band light regulation of ethylene and gibberellin levels in hydroponically-grown <Emphasis Type="Italic">Helianthus annuus</Emphasis> hypocotyls and roots

Both hypocotyl and root growth of sunflower (Helianthus annuus) were examined in response to a range of narrow-band width light treatments. Changes in two growth-regulating hormones, ethylene and gibberellins (GAs) were followed in an attempt to better understand the interaction of light and hormonal signaling in the growth of these two important plant organs. Hydroponically-grown 6-day-old sunflower seedlings had significantly elongated hypocotyls and primary roots when grown under far-red (FR) light produced by light emitting diodes (LEDs), compared to narrow-band red (R) and blue (B) light. However, hypocotyl and primary root lengths of seedlings given FR light were still shorter than was seen for dark-grown seedlings. Light treatment in general (compared to dark) increased lateral root formation and FR light induced massive lateral root formation, relative to treatment with R or B light. Levels of ethylene evolution (roots and hypocotyls) and concentrations of endogenous GAs (hypocotyls) were assessed from both 6-day-old sunflower plants either grown in the dark, or treated with FR, R or B light. Both R and B light had similar effects on hypocotyl and root growth as well as on ethylene and on hypocotyl GA levels. Dark treatment resulted in the highest ethylene levels, whereas FR treatment significantly reduced ethylene evolution for both hypocotyls and roots. R- and B-light treatments elevated ethylene evolution relative to FR light. Endogenous GA₅₃ and GA₁₉ levels in hypocotyls were significantly higher and GA₄₄, GA₂₀ and GA₁ levels significantly lower, for dark and FR light treatments compared to R and B light-treatments. The patterns seen for changes in GA concentrations indicate FR-, R- and B-light-mediated effects [differences] in the metabolism of the early C₂₀ GAs, GA₅₃ → GA₄₄ → GA_19. Surprisingly, GA₂₀, GA₁ and GA₈ levels in hypocotyls were very much reduced by treatment of the plants with FR light, relative to B and R-light treatments, e.g. the increased hypocotyl elongation induced by FR light was correlated with reduced levels of all three of the downstream C₁₉ GAs. The best explanation, albeit speculative, is that a more rapid metabolism, i.e. GA₂₀ → GA₁ → GA₈ → GA₈ conjugates occurs under FR light. Although this study provided no evidence that elevated ethylene evolution by roots or hypocotyls of sunflower is controlling growth via endogenous GA biosynthesis, there are differences between soil-grown and hydroponically-grown sunflower seedlings with regard to trends seen for hypocotyl GA concentrations and both root and hypocotyl ethylene evolution in response to narrow band width R and FR light signaling.     

Gibberellin biosynthesis: metabolic evidence for three steps in the early 13-hydroxylation pathway of rice

[14C4]GA53, [14C4]GA44, and [2H2/14C4]GA19 were injected separately into seedlings of rice (Oryza sativa) using a dwarf mutant (d35) that has low levels of endogenous gibberellins (GAs). After 8 h incubation, the shoots were extracted and the labeled metabolites were identified by full-scan gas chromatography mass spectrometry (GC-MS) and Kovats retention indices (KRIs). Our results document the metabolic sequence, GA53-->GA44-->GA19-->GA20 and the presence of endogenous GA53, GA44, GA19, GA20 and GA1. Previous metabolic studies have shown the presence of the step, GA20-->GA1 in rice. Taken together, the data establish in vegetative shoots of rice the presence of the early 13-hydroxylation pathway, a pathway that originates from GA12 and leads to bioactive GA1.     

Phytochrome B affects responsiveness to gibberellins in Arabidopsis.

Plant responses to red and far-red light are mediated by a family of photoreceptors called phytochromes. Arabidopsis thaliana seedlings lacking one of the phytochromes, phyB, have elongated hypocotyls and other tissues, suggesting that they may have an alteration in hormone physiology. We have studied the possibility that phyB mutations affect seedling gibberellin (GA) perception and metabolism by testing the responsiveness of wild-type and phyB seedlings to exogenous GAs. The phyB mutant elongates more than the wild type in response to the same exogenous concentrations of GA3 or GA4, showing that the mutation causes an increase in responsiveness to GAs. Among GAs that we were able to detect, we found no significant difference in endogenous levels between wild-type and phyB mutant seedlings. However, GA4 levels were below our limit of detectability, and the concentration of that active GA could have varied between wild-type and phyB mutant seedlings. These results suggest that, although GAs are required for hypocotyl cell elongation, phyB does not act primarily by changing total seedling GA levels but rather by decreasing seedling responsiveness to GAs.     

Ectopic expression of pumpkin gibberellin oxidases alters gibberellin biosynthesis and development of transgenic Arabidopsis plants

Immature pumpkin (Cucurbita maxima) seeds contain gibberellin (GA) oxidases with unique catalytic properties resulting in GAs of unknown function for plant growth and development. Overexpression of pumpkin GA 7-oxidase (CmGA7ox) in Arabidopsis (Arabidopsis thaliana) resulted in seedlings with elongated roots, taller plants that flower earlier with only a little increase in bioactive GA4 levels compared to control plants. In the same way, overexpression of the pumpkin GA 3-oxidase1 (CmGA3ox1) resulted in a GA overdose phenotype with increased levels of endogenous GA4. This indicates that, in Arabidopsis, 7-oxidation and 3-oxidation are rate-limiting steps in GA plant hormone biosynthesis that control plant development. With an opposite effect, overexpression of pumpkin seed-specific GA 20-oxidase1 (CmGA20ox1) in Arabidopsis resulted in dwarfed plants that flower late with reduced levels of GA4 and increased levels of physiological inactive GA17 and GA25 and unexpected GA34 levels. Severe dwarfed plants were obtained by overexpression of the pumpkin GA 2-oxidase1 (CmGA2ox1) in Arabidopsis. This dramatic change in phenotype was accompanied by a considerable decrease in the levels of bioactive GA4 and an increase in the corresponding inactivation product GA34 in comparison to control plants. In this study, we demonstrate the potential of four pumpkin GA oxidase-encoding genes to modulate the GA plant hormone pool and alter plant stature and development.     

Control by Light of Hypocotyl Elongation and Levels of Endogenous Gibberellins in Seedlings of Lactuca sativa L.

Four 13-hydroxygibberellins, gibberellin A₁ (GA₁), 3-epi-GA₁,GA₁₉ and GA₂₀ were identified by full-scan GC/MS in extractsof lettuce seedlings (Lactuca sativa L. cv. Grand Rapids). Theresults suggest that the early-13-hydroxylation biosyntheticpathway to GA₁ functions in the lettuce seedlings. It was alsofound that GA₁ is active per se in the control of hypocotylelongation in lettuce seedlings. To investigate the relationshipbetween control by light of hypocotyl elongation and levelsof endogenous GAs in lettuce, endogenous levels of GAs werequantified by radioimmunoassay in seedlings that had been grownfor 5 days in the dark (5D) and in those that had been grownfor 4 days in the dark and then under white light for 1 day(4D1L). The endogenous level of GA₁ in the upper and lower partsof hypocotyls in 5D seedlings was about four times higher thanthat in 4D1L seedlings. The response of explants (hypocotylsegments with cotyledons) from dark-grown seedlings to GA₁ isknown to be similar in the dark and under white light when theexplants are treated with inhibitors of the biosynthesis ofGA. Therefore, the above information suggests that the highlevel of GA₁ in hypocotyls of dark-grown seedlings is responsiblefor the rapid elongation of hypocotyl, while irradiation bywhite light decreases the endogenous level of GA₁ in the hypocotylswith a resultant decrease in the rate of hypocotyl elongation. (Received March 13, 1992; Accepted May 21, 1992)     

Gibberellins in seedlings and flowering trees of Prunus avium L

Extracts of acids from mature seeds, germinating seeds, first, second and third year seedlings as well as mature, flowering trees of sweet cherry (Prunus avium L. cv. Stella) were analysed by gas chromatography-mass spectrometry. The presence of the known gibberellins (GAs) GA1 (1), GA3 (4), GA5 (7), GA8 (11), GA19 (14), GA20 (12), GA29 (13), GA32 (5), GA85 (2), GA86 (3) and GA87 (6) was confirmed by comparison of their mass spectra and Kovats retention indices with those of standards or literature values. In addition, 16alpha,17-dihydrodihydroxy GA25 (16) was identified and its stereochemistry confirmed by rational synthesis. The 12alpha,13-dihydroxy GAs, GA32 (5), GA86 (2), GA86 (3) and GA87 (6), were detected in mature seeds, germinating seeds and young seedlings, but not in flowering plants. The 13-hydroxy GAs, GA1 (1) and GA3 (4), were present in germinating seeds and, in addition to these, GA5 (7), GA8 (11), GA19 (14), GA20 (12) and GA29 (13) were detected in seedlings and mature flowering plants. In germinating seeds and seedlings (while the plants were growing actively), concentrations of the 12alpha,13-dihydroxy GAs, measured by bioassay, declined and those of the 13-hydroxy GAs increased. The results are discussed with reference to the known and predicted effects of the GAs on the vegetative growth and flowering of P. avium plants.     

Involvement of endogenous gibberellins in potato tuber dormancy and early sprout growth: a critical assessment

The role of endogenous gibberellins (GAs) in the regulation of potato (Solanum tuberosum) tuber dormancy was examined by determining: 1. changes in endogenous GA levels during natural dormancy progression, 2. the effects of GA biosynthesis inhibitors on tuber dormancy duration and 3. the dormancy status and tuber GA levels in a dwarf mutant of potato. The tubers (cv. Russet Burbank) used in these studies were still completely dormant after 98 days of storage. Between 98 and 134 days of storage, dormancy began to end and tubers exhibited limited (< 2 mm) sprout growth. Tuber dormancy weakened with further storage and tubers exhibited greater rates of sprout growth after 187 days of storage. Tubers stored for 212 days or longer were completely non-dormant and exhibited vigorous sprout growth. Immediately after harvest, the endogenous contents of GA19, GA20, and GA1 were relatively high (0.48-0.62 ng g fresh weight(-1)). The content of these GAs declined between 33 and 93 days of storage. Internal levels of GA19, GA20, and GA, rose slightly between 93 and 135 days of storage reaching levels comparable to those found in highly dormant tubers immediately after harvest. Levels of GA19, GA20, and GA1 continued to increase as sprout growth became more vigorous. Neither GA4 nor GA8 was detected in any tuber sample regardless of dormancy status. Dormant tubers exhibited a time-dependent increase in apparent GA sensitivity. Freshly harvested tubers were completely insensitive to exogenous GAs. As postharvest storage continued, exogenous GAs promoted premature dormancy release with GA1 and GA20 eliciting the greatest response. Injection of up to 5 microg tuber(-1) of kaurene, GA12, GA19 or GA8 had no effect on dormancy release. Sprout growth from non-dormant tubers was also promoted by exogenous GA in the following sequence of activity: GA1 = GA20 > GA19. Kaurene, GA12, and GA8 were inactive. Continuous exposure of developing tubers to inhibitors of GA biosynthesis (AMO-1618, ancymidol, or tetcyclasis) did not extend tuber dormancy but rather hastened dormancy release. Comparison of tuber dormancy and GA1 content in tubers of a wild-type and dwarf mutant of S. tuberosum ssp. andigena revealed a near-identical pattern of dormancy progression in spite of the absence of detectable levels of GA1 in tubers of the dwarf sibling at any time during dormancy progression. Collectively, these results do not support a role for endogenous GA in potato tuber dormancy release but are consistent with a role for GAs in the regulation of subsequent sprout growth.     

Gibberellin-responding and non-responding dwarf mutants in foxtail millet

The sensitivity of foxtail millet (Setaria italica Beauv.) dwarf mutants to GA was studied. Seedlings of dwarf mutants, Aininghuang (ANH) and CH84113 were treated with GAs (GA1, GA4, GA9, GA19 and GA20) using the micro-drop method, or by soaking in GA3 solution. Plants were also sprayed with GA3 solution at the jointing stage. It was found that ANH was a GA-responding dwarf mutant, whose leaf blade, leaf sheath and internode length increased significantly after GA application, whereas CH84113 was a non-GA-responding dwarf mutant. However, the mesocotyl in etiolated seedlings of both ANH and CH84113 responded to exogenous GA3 in a similar way. With the help of an enzyme-linked immunosorbent assay, it was found that the endogenous GA1+3 level in leaves was lower in the GA-responding dwarf mutant ANH, but higher in the non-GA-responding dwarf mutant CH84113, compared with levels in normal cultivars.     

A study of gibberellin homeostasis and cryptochrome-mediated blue light inhibition of hypocotyl elongation

Cryptochromes mediate blue light-dependent photomorphogenic responses, such as inhibition of hypocotyl elongation. To investigate the underlying mechanism, we analyzed a genetic suppressor, scc7-D (suppressors of cry1cry2), which suppressed the long-hypocotyl phenotype of the cry1cry2 (cryptochrome1/cryptochrome2) mutant in a light-dependent but wavelength-independent manner. scc7-D is a gain-of-expression allele of the GA2ox8 gene encoding a gibberellin (GA)-inactivating enzyme, GA 2-oxidase. Although scc7-D is hypersensitive to light, transgenic seedlings expressing GA2ox at a level higher than scc7-D showed a constitutive photomorphogenic phenotype, confirming a general role of GA2ox and GA in the suppression of hypocotyl elongation. Prompted by this result, we investigated blue light regulation of mRNA expression of the GA metabolic and catabolic genes. We demonstrated that cryptochromes are required for the blue light regulation of GA2ox1, GA20ox1, and GA3ox1 expression in transient induction, continuous illumination, and photoperiodic conditions. The kinetics of cryptochrome induction of GA2ox1 expression and cryptochrome suppression of GA20ox1 or GA3ox1 expression correlate with the cryptochrome-dependent transient reduction of GA(4) in etiolated wild-type seedlings exposed to blue light. Therefore we propose that in deetiolating seedlings, cryptochromes mediate blue light regulation of GA catabolic/metabolic genes, which affect GA levels and hypocotyl elongation. Surprisingly, no significant change in the GA(4) content was detected in the whole shoot samples of the wild-type or cry1cry2 seedlings grown in the dark or continuous blue light, suggesting that cryptochromes may also regulate GA responsiveness and/or trigger cell- or tissue-specific changes of the level of bioactive GAs.     

Gibberellins promote vegetative phase change and reproductive maturity in maize.

Postembryonic shoot development in maize (Zea mays L.) is divided into a juvenile vegetative phase, an adult vegetative phase, and a reproductive phase that differ in the expression of many morphological traits. A reduction in the endogenous levels of bioactive gibberellins (GAs) conditioned by any one of the dwarf1, dwarf3, dwarf5, or another ear1 mutations in maize delays the transition from juvenile vegetative to adult vegetative development and from adult vegetative to reproductive development. Mutant plants cease producing juvenile traits (e.g. epicuticular wax) and begin producing adult traits (e.g. epidermal hairs) later than wild-type plants. They also cease producing leaves and begin producing reproductive structures later than wild-type plants. These mutations greatly enhance most aspects of the phenotype of Teopod1 and Teopod2, suggesting that GAs suppress part but not all of the Teopod phenotype. Application of GA3 to Teopod2 mutants and Teopod1, dwarf3 double mutants confirms this result. We conclude that GAs act in conjunction with several other factors to promote both vegetative and reproductive maturation but affect different developmental phases unequally. Furthermore, the GAs that regulate vegetative and reproductive maturation, like those responsible for stem elongation, are downstream of GA20 in the GA biosynthetic pathway.     

Vernalization and Gibberellin Physiology of Winter Canola (Endogenous Gibberellin (GA) Content and Metabolism of [3H]GA1 and [3H]GA20

Winter canola (Brassica napus cv Crystal) is an oilseed crop that requires vernalization (chilling treatment) for the induction of stem elongation and flowering. To investigate the role of gibberellins (GAs) in vernalization-induced events, endogenous GA content and the metabolism of [3H]GAs were examined in 10-week vernalized and nonvernalized plants. Shoot tips were harvested 0, 8, and 18 d postvernalization (DPV), and GAs were purified and quantified using 2H2-internal standards and gas chromatography-selected ion monitoring. Concentrations of GA1, GA3, GA8, GA19, and GA20 were 3.1-, 2.3-, 7.8-, 12.0-, and 24.5-fold higher, respectively, in the vernalized plants at the end of the vernalization treatment (0 DPV) relative to the nonvernalized plants. Thermoregulation apparently occurs prior to GA19 biosynthesis, since vernalization elevated the concentration of all of the monitored GAs. [3H]GA20 or [3H]GA1 was applied to the shoot tips of vernalized and nonvernalized plants, and after 24 h, plants were harvested at 6, 12, and 15 DPV. Following high-performance liquid chromatography analyses, vernalized plants showed increased conversion of [3H]GA20 to a [3H]GA1-like metabolite and reduced conversion of [3H]GA1 or [3H]GA20 to polar 3H-metabolites, putative glucosyl conjugates. These results demonstrate that vernalization influences GA content and GA metabolism, with GAs serving as probable regulatory intermediaries between chilling treatment and subsequent stem growth.     

Involvement of gibberellins in the stem elongation of sun and shade ecotypes of Stellaria longipes that is induced by low light irradiance

Plants from two ecotypes of Stellaria longipes, alpine (an open, sunny habitat) and prairie (where adjacent plants provide a shaded habitat), were grown under normal and reduced levels of photosynthetically active radiation (PAR). Growth under low PAR is significantly promoted in both ecotypes. When quantified by the stable isotope dilution method, endogenous gibberellins (GAs) (GA1, GA8, GA20, GA19) were significantly elevated under low PAR in both 'sun' and 'shade' ecotypes, as was GA53 in the shade ecotype. Changes in endogenous GA1 levels were significantly correlated with stem growth during a 28 d growth cycle and with relative growth rate (RGR) for height under low PAR for both ecotypes. Interestingly, under low irradiance PAR, changes (both increases and decreases) in GA8, the 2beta-hydroxylated 'inactive' catabolite of GA1, closely parallel bidaily stem growth changes for both ecotypes. Because the significantly greater stem elongation of both ecotypes in response to low irradiance PAR is associated with significant increases in the endogenous levels of five GAs (GA53, GA19, GA1, GA8) in the early 13-hydroxylation GA biosynthesis pathway (measured at days 7,14 and 21), we conclude that the low irradiance PAR has very likely induced an overall increase in GA biosynthesis.     

Overexpression of a novel class of gibberellin 2-oxidases decreases gibberellin levels and creates dwarf plants

Degradation of active C(19)-gibberellins (GAs) by dioxygenases through 2beta-hydroxylation yields inactive GA products. We identified two genes in Arabidopsis (AtGA2ox7 and AtGA2ox8), using an activation-tagging mutant screen, that encode 2beta-hydroxylases. GA levels in both activation-tagged lines were reduced significantly, and the lines displayed dwarf phenotypes typical of mutants with a GA deficiency. Increased expression of either AtGA2ox7 or AtGA2ox8 also caused a dwarf phenotype in tobacco, indicating that the substrates for these enzymes are conserved. AtGA2ox7 and AtGA2ox8 are more similar to each other than to other proteins encoded in the Arabidopsis genome, indicating that they may constitute a separate class of GA-modifying enzymes. Indeed, enzymatic assays demonstrated that AtGA2ox7 and AtGA2ox8 both perform the same GA modification: 2beta-hydroxylation of C(20)-GAs but not of C(19)-GAs. Lines containing increased expression of AtGA2ox8 exhibited a GA dose-response curve for stem elongation similar to that of the biosynthetic mutant ga1-11. Double loss-of-function Atga2ox7 Atga2ox8 mutants had twofold to fourfold higher levels of active GAs and displayed phenotypes associated with excess GAs, such as early bolting in short days, resistance to the GA biosynthesis inhibitor ancymidol, and decreased mRNA levels of AtGA20ox1, a gene in the GA biosynthetic pathway.     

Gibberellins and stem growth in Arabidopsis thaliana. Effects of photoperiod on expression of the GA4 and GA5 loci.

Arabidopsis thaliana (L.) Heynh. is a quantitative long-day (LD) rosette plant in which stem growth is mediated by gibberellins (CAs). Application of GAs to plants in short-day (SD) conditions resulted in rapid stem elongation and flower formation, with GA4 and GA9 being equally effective, and GA1 showing lower activity. The effects of photoperiod on the levels of endogenous GAs were measured by combined gas chromatography-mass spectrometry with selected ion monitoring. When plants were transferred from SD to LD conditions there was a slight decrease in the level of GA53 and an increase in the levels of C19-GAs, GA9, GA20, GA1, and GA8, indicating that GA 20-oxidase activity is stimulated in LD conditions. Expression of GA5, which encodes GA 20-oxidase, was highest in elongating stems and was correlated with the rate of stem elongation. By contrast, GA4, which encodes 3 beta-hydroxylase, showed low expression in stems and its expression was not correlated with the rate of stem elongation. We conclude that stem elongation in LD conditions is at least in part due to increased expression of GA5, whereas expression of GA4 is not under photoperiodic control.