A mutant gene that increases gibberellin production in brassica

Moving on up - controlling internode growth

Plant reproductive success depends on making fertile flowers but also upon developing appropriate shoot internodes that optimally arrange and support the flowering shoot. Compared to floral morphogenesis, we understand little about the networks directing internode growth during flowering. However, new studies reveal that long-range signals, local factors, and age-dependent micoRNA-networks are all important to harmonize internode morphogenesis with shoot development. Some of the same players modulate symplastic transport to seasonally regulate internode growth in perennial species. Exploring possible hierarchical control amongst symplastic continuity, age, systemic signals and local regulators during internode morphogenesis will help elucidate the mechanisms coordinating axial growth with the wider plant body.

Agrobacterium-mediated vacuum infiltration and floral dip transformation of rapid-cycling Brassica rapa

BACKGROUND

Rapid-cycling Brassica rapa (RCBr), also known as Wisconsin Fast Plants, are small robust plants with a short lifecycle that are widely used in biology teaching. RCBr have been used for decades but there are no published reports of RCBr genetic transformation. Agrobacterium-mediated vacuum infiltration has been used to transform pakchoi (Brassica rapa ssp. chinensis) and may be suitable for RCBr transformation. The floral dip transformation method, an improved version of vacuum infiltration, could make the procedure easier.

RESULTS

Based on previous findings from Arabidopsis and pakchoi, plants of three different ages were inoculated with Agrobacterium. Kanamycin selection was suboptimal with RCBr; a GFP screen was used to identify candidate transformants. RCBr floral bud dissection showed that only buds with a diameter less than 1 mm carried unsealed carpels, a key point of successful floral dip transformation. Plants across a wide range of inflorescence maturities but containing these immature buds were successfully transformed, at an overall rate of 0.1% (one per 1000 T₁ seeds). Transformation was successful using either vacuum infiltration or the floral dip method, as confirmed by PCR and Southern blot.

CONCLUSION

A genetic transformation system for RCBr was established in this study. This will promote development of new biology teaching tools as well as basic biology research on Brassica rapa.

Transcriptome Profiling of Tiller Buds Provides New Insights into PhyB Regulation of Tillering and Indeterminate Growth in Sorghum

Phytochrome B (phyB) enables plants to modify shoot branching or tillering in response to varying light intensities and ratios of red and far-red light caused by shading and neighbor proximity. Tillering is inhibited in sorghum genotypes that lack phytochrome B (58M, phyB-1) until after floral initiation. The growth of tiller buds in the first leaf axil of wild-type (100M, PHYB) and phyB-1 sorghum genotypes is similar until 6 d after planting when buds of phyB-1 arrest growth, while wild-type buds continue growing and develop into tillers. Transcriptome analysis at this early stage of bud development identified numerous genes that were up to 50-fold differentially expressed in wild-type/phyB-1 buds. Up-regulation of terminal flower1, GA2oxidase, and TPPI could protect axillary meristems in phyB-1 from precocious floral induction and decrease bud sensitivity to sugar signals. After bud growth arrest in phyB-1, expression of dormancy-associated genes such as DRM1, GT1, AF1, and CKX1 increased and ENOD93, ACCoxidase, ARR3/6/9, CGA1, and SHY2 decreased. Continued bud outgrowth in wild-type was correlated with increased expression of genes encoding a SWEET transporter and cell wall invertases. The SWEET transporter may facilitate Suc unloading from the phloem to the apoplast where cell wall invertases generate monosaccharides for uptake and utilization to sustain bud outgrowth. Elevated expression of these genes was correlated with higher levels of cytokinin/sugar signaling in growing buds of wild-type plants.

Phytochrome-hormonal signalling networks

Through time, plants have evolved an extraordinary ability to interpret environmental cues. One of the most reliable of these cues is light, and plants are particularly adept at sensing and translating environmental light signals. The phytochrome family of photoreceptors monitor cues such as daylength or vegetative shade and adjust development to reflect change in these parameters. Indeed, it is their ability to coordinate these complex developmental changes that underpins the remarkable success of plants. Evidence is mounting that hormones control many of these light-mediated changes. Therefore, if we are to understand how light manipulates development we need to explore the interplay between light and hormonal signalling. Toward this goal, this review highlights the known convergence points of the phytochrome and the hormonal networks and explores their interactions. Contents Summary 449 I. Introduction 449 II. The phytochrome protein 450 III. Bacteriophytochromes 450 IV. IBacteriophytochrome signalling 450 V. Plant phytochrome signalling 451 VI. Ethylene perception and signalling 451 VII. Cytokinin perception and signalling 452 VIII. Brassinosteroid perception and signalling 453 IX. Gibberellin signalling 455 X. Auxin signalling 456 XI. Proteolysis in light and hormonal signalling 458 XII. Conclusion 459 Acknowledgements 459 References 459.

Reduced de-etiolation of hypocotyl growth in a tomato mutant is associated with hypersensitivity to, and high endogenous levels of, abscisic acid

A recessive single gene mutant, 7B-1, in tomato was originally selected for its photoperiod-dependent male sterility. The 7B-1 mutant also has some pleiotropic effects including reduced light-induced inhibition, i.e. de-etiolation, of the hypocotyl in long days (LD), increased seed size and weight, and reduced transpiration rate. These traits led us to investigate the sensitivity of 7B-1 to exogenous hormones and the interaction of these responses with daylength. In LD, but not in short days (SD), 7B-1 was more sensitive than wild-type (WT) to exogenous abscisic acid (ABA) for inhibition of seed germination, root elongation and transpiration rate. 7B-1 mutant also exhibited reduced responses to exogenous gibberellin (GA(3)) for hypocotyl elongation, and to inhibitors of GA biosynthesis for seed germination and root and hypocotyl elongation. 7B-1 hypocotyls contained a higher level of endogenous ABA than WT in both photoperiods, although ABA levels were higher in LD than in SD. In contrast, growth-active GAs, i.e. GA(1), GA(3) and GA(4), and IAA were low in the mutant hypocotyls. The 7B-1 mutant appears to be an ABA-overproducer, and the photoperiod-regulated ABA levels may be responsible for the hypersensitivity of the mutant to exogenous ABA.

Regulation of transcript levels of a potato gibberellin 20-oxidase gene by light and phytochrome B

Up to three gibberellin (GA) 20-oxidase genes have now been cloned from several species including Arabidopsis, bean (Phaseolus vulgaris), and potato (Solanum tuberosum). In each case the GA 20-oxidase genes exhibit different patterns of tissue expression. We have performed extensive northern analysis on one of the potato GA 20-oxidase genes (StGA20ox1), which is the only one that shows significant transcript levels in leaves. We show that levels of StGA20ox1 transcript are elevated in transgenic antisense plants that have reduced levels of phytochrome B (PHYB) compared with wild-type plants, implicating PHYB in the control of GA biosynthesis. We show that StGA20ox1 transcript levels vary in leaves of different age throughout the plant and cycle throughout the day, furthermore they are up-regulated by light and down-regulated in the dark. The degree of the response to the light-on signal is similar in potato plants deficient in phytochrome A or PHYB and wild-type plants. The induction of StGA20ox1 by blue light raises the possibility that a blue light receptor may be involved in the control of this gene by light.

Independent regulation of flowering by phytochrome B and gibberellins in Arabidopsis

Phytochromes and gibberellins (GAs) coordinately regulate multiple aspects of Arabidopsis development. Phytochrome B (PHYB) promotes seed germination by increasing GA biosynthesis, but inhibits hypocotyl elongation by decreasing the responsiveness to GAs. Later in the life cycle of the plant, PHYB and GAs have opposite effects on flowering. PHYB delays flowering, while GAs promote flowering, particularly under noninductive photoperiods. To learn how PHYB and GAs interact in the control of flowering, we have analyzed the effect of a phyB mutation on flowering time and on the expression of the floral meristem-identity gene LFY (LEAFY). We show that the early flowering caused by phyB correlated with an increase in LFY expression, which complements our previous finding that GAs are required for activation of LFY under noninductive photoperiods (M.A. Blázquez, R. Green, O. Nilsson, M.R. Sussman, D. Weigel [1998] Plant Cell 10: 791-800). Since phyB did not change the GA responsiveness of the LFY promoter and suppressed the lack of flowering of severe GA-deficient mutants under short days, we propose that PHYB modulates flowering time at least partially through a GA-independent pathway. Interestingly, the effects of PHYB on flowering do not seem to be mediated by transcriptional up-regulation of genes such as CO (CONSTANS) and FT (Flowering locus T), which are known to mediate the effects of the photoperiod-dependent floral-induction pathway.

Phytochrome regulates gibberellin biosynthesis during germination of photoblastic lettuce seeds

Germination of lettuce (Lactuca sativa L.) seed is regulated by phytochrome. The requirement for red light is circumvented by the application of gibberellin (GA). We have previously shown that the endogenous content of GA1, the main bioactive GA in lettuce seeds, increases after red-light treatment. To clarify which step of GA1 synthesis is regulated by phytochrome, cDNAs encoding GA 20-oxidases (Ls20ox1 and Ls20ox2, for L. sativa GA 20-oxidase) and 3beta-hydroxylases (Ls3h1 and Ls3h2 for L. sativa GA 3beta-hydroxylase) were isolated from lettuce seeds by reverse-transcription polymerase chain reaction. Functional analysis of recombinant proteins expressed in Escherichia coli confirmed that the Ls20ox and Ls3h encode GA 20-oxidases and 3beta-hydroxylases, respectively. Northern-blot analysis showed that Ls3h1 expression was dramatically induced by red-light treatment within 2 h, and that this effect was canceled by a subsequent far-red-light treatment. Ls3h2 mRNA was not detected in seeds that had been allowed to imbibe under any light conditions. Expression of the two Ls20ox genes was induced by initial imbibition alone in the dark. The level of Ls20ox2 mRNA decreased after the red-light treatment, whereas that of Ls20ox1 was unaffected by light. These results suggest that red light promotes GA1 synthesis in lettuce seeds by inducing Ls3h1 expression via phytochrome action.

GIBBERELLIN BIOSYNTHESIS: Enzymes, Genes and Their Regulation

The recent impressive progress in research on gibberellin (GA) biosynthesis has resulted primarily from cloning of genes encoding biosynthetic enzymes and studies with GA-deficient and GA-insensitive mutants. Highlights include the cloning of ent-copalyl diphosphate synthase and ent-kaurene synthase (formally ent-kaurene synthases A and B) and the demonstration that the former is targeted to the plastid; the finding that the Dwarf-3 gene of maize encodes a cytochrome P450, although of unknown function; and the cloning of GA 20-oxidase and 3beta-hydroxylase genes. The availability of cDNA and genomic clones for these enzymes is enabling the mechanisms by which GA concentrations are regulated by environmental and endogenous factors to be studied at the molecular level. For example, it has been shown that transcript levels for GA 20-oxidase and 3beta-hydroxylase are subject to feedback regulation by GA action and, in the case of the GA 20-oxidase, are regulated by light. Also discussed is other new information, particularly from mutants, that has added to our understanding of the biosynthetic pathway, the enzymes, and their regulation and tissue localization.

Gibberellin deficiency and response mutations suppress the stem elongation phenotype of phytochrome-deficient mutants of Arabidopsis

Plant growth and development are regulated by numerous internal and external factors. Among these, gibberellin (GA) (an endogenous plant growth regulator) and phytochrome (a photoreceptor) often influence the same processes. For example, in plants grown in the light Arabidopsis thaliana hypocotyl elongation is reduced by GA deficiency and increased by phytochrome deficiency. Here we describe experiments in which the phenotypes of Arabidopsis plants doubly homozygous for GA-related and phytochrome-related mutations were examined. The double mutants were studied at various stages in the plant life cycle, including the seed germination, young seedling, adult, and reproductive phases of development. The results of these experiments are complex, but indicate that a fully functional GA system is necessary for full expression of the elongated phenotypes conferred by phytochrome deficiency.

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.

Far-red light stimulates internode elongation, cell division, cell elongation, and gibberellin levels in bean

The contributions of cell division and cell elongation and the potential role of gibberellins in the far-red light stimulation of bean internode elongation were investigated. When bean plants, Phaseolus vulgaris cv. Kentucky Wonder, were grown in white light supplemented with far-red light a significant increase, up to threefold, in internode elongation was observed. Microscopic examination revealed that cell lengths were also increased but by a lower magnitude than internode length. Cell-labeling studies with [3H]thymidine showed that nuclei labeling was increased in internodes receiving supplemental far-red light. Thus far-red light induced increased internode elongation is a result of both increased cell elongation and increased cell division. Gibberellins A1, A20, A19, A44, and A4 and kaurenoic acid were identified in extracts of internode tissue by gas chromatography – mass spectroscopy using [2H2]-labeled internal standards for quantification. It thus appears that the early C-13 hydroxylation pathway is operative in the elongating internode. Endogenous GA1 and GA20 were approximately twofold higher in the first internodes of plants receiving supplemental far-red light. A comparison of the metabolism of exogenously supplied [2H2]GA19 suggested that GA turnover was greater in tissues exposed to supplemental far-red light. These results indicate that both cell division and elongation contribute to the enhanced elongation response of bean internodes to far-red light and that these processes are correlated with an increase in GA levels and (or) metabolism. Keywords: Phaseolus, gibberellins, phytochrome, far-red light.

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.

Phytochrome A overexpression in transgenic tobacco. Correlation of dwarf phenotype with high concentrations of phytochrome in vascular tissue and attenuated gibberellin levels

Phytochromes are a family of related chromoproteins that regulate photomorphogenesis in plants. Ectopic overexpression of the phytochrome A in several plant species has pleiotropic effects, including substantial dwarfing, increased pigmentation, and delayed leaf senescence. We show here that the dwarf response is related to a reduction in active gibberellins (GAs) in tobacco (Nicotiana tabacum) overexpressing oat phytochrome A under the control of the cauliflower mosaic virus (CaMV) 35S promoter and can be suppressed by foliar applications of gibberellic acid. In transgenic seedlings, high concentrations of oat phytochrome A were detected in stem and petiole vascular tissue (consistent with the activity of the CaMV 35S promoter), implicating vascular tissue as a potential site of phytochrome A action. To examine the efficacy of this cellular site, oat phytochrome A was also expressed using Arabidopsis chlorophyll a/b-binding protein (CAB) and the Arabidopsis ubiquitin (UBQ1) promoters. Neither promoter was as effective as CaMV 35S in expressing phytochrome in vascular tissue or in inducing the dwarf phenotype. Collectively, these data indicate that the spatial distribution of ectopic phytochrome is important in eliciting the dwarf response and suggest that the phenotype is invoked by elevated levels of the far-red-absorbing form of phytochrome within vascular tissue repressing GA biosynthesis.

Phytochrome, Gibberellins, and Hypocotyl Growth (A Study Using the Cucumber (Cucumis sativus L.) long hypocotyl Mutant)

The possible involvement of gibberellins (GAs) in the regulation of hypocotyl elongation by phytochrome was examined. Under white light the tall long hypocotyl (lh) cucumber (Cucumis sativus L.) mutant, deficient in a type B-like phytochrome, shows an increased "responsiveness" (defined as response capability) to applied GA4 (the main endogenous active GA) compared to the wild type. Supplementing far-red irradiation results in a similar increase in responsiveness in the wild type. Experiments involving application of the precursor GA9 and of an inhibitor of GA4 inactivation suggest that both the GA4 activation and inactivation steps are phytochrome independent. Endogenous GA levels of whole seedlings were analyzed by combined gas chromatography-mass spectrometry using deuterated internal standards. The levels of GA4 (and those of GA34, the inactivated GA4) were lower in the lh mutant under low-irradiance fluorescent light compared with the wild type, similar to wild type under higher irradiance light during the initial hypocotyl extension phase, and higher during the phase of sustained growth, in which extension involved an increase in the number of cells in the upper region. In all cases, growth of the lh mutant was more rapid than that of the wild type. It is proposed that GA4 and phytochrome control cell elongation primarily through separate mechanisms that interact at a step close to the terminal response.

The DIMINUTO gene of Arabidopsis is involved in regulating cell elongation

We have isolated a recessive mutation named diminuto (dim) from T-DNA transformed lines of Arabidopsis thaliana. Under normal growth conditions, the dim mutant has very short hypocotyls, petioles, stems, and roots because of the reduced size of cells along the longitudinal axes of these organs. In addition, dim results in the development of open cotyledons and primary leaves in dark-grown seedlings. The gene for DIM was cloned by T-DNA tagging. DIM encodes a novel protein of 561 amino acids that possesses bipartite sequence domains characteristic of nuclear localization signals. Molecular and physiological studies indicate that the loss-of-function mutant allele does not abolish the response of seedlings to light or phytohormones, although the inhibitory effect of light on hypocotyl elongation is greater in the mutant than in wild type. Moreover, the dim mutation affects the expression of a beta-tubulin gene, TUB1, which is thought to be important for plant cell growth. Our results suggest that the DIM gene product plays a critical role in the general process of plant cell elongation.

Genetic Regulation of Development in Sorghum bicolor (VIII. Shoot Growth, Tillering, Flowering, Gibberellin Biosynthesis, and Phytochrome Levels Are Differentially Affected by Dosage of the ma3R Allele

Sorghum [Sorghum bicolor (L.) Moench] homozygous for ma3R lacks a type II, light-stable phytochrome of 123 kD and has a number of phenotypic characteristics consistent with the absence of functional phytochrome B. We have used plants heterozygous at Ma3 (Ma3/ma3R and ma3/ma3R) to determine the effect of dosage of ma3R on plant growth, flowering, gibberellin (GA) levels, and content of the 123-kD phytochrome. Both Ma3/ma3R and ma3/ma3R produced the same number of tillers per plant as their respective homozygous non-ma3R parents. Height of the heterozygotes was intermediate between the homozygous parents, although it was more similar to the non-ma3R genotypes. In both field and growth-chamber environments, the timing of floral initiation and anthesis in the heterozygotes also was intermediate, again more similar to non-ma3R plants. In Ma3/ma3R, levels of GA53, GA19, GA20, and GA1 were almost exactly intermediate between levels detected in Ma3/Ma3 and ma3R/ma3R plants. Immunoblot analysis indicated that there was less of the 123-kD phytochrome in Ma3/ma3R than in homozygous Ma3, whereas none was detected in ma3R/ma3R. The degree of dominance of Ma3 and ma3 over ma3R varies with phenotypic trait, indicating that mechanisms of activity of the 123-kD phytochrome vary among the biochemical processes involved in each phenotypic character. Although the heterozygotes were similar to homozygous Ma3 and ma3 plants in growth and flowering behavior, Ma3/ma3R contained 50% less of the bioactive GA (GA1) than non-ma3R genotypes. Thus, sensitivity to endogenous GAs also may be regulated by the 123-kD phytochrome. To fully regulate plant growth and development, two copies of Ma3 or ma3 are required to produce sufficient quantities of the light-stable, 123-kD phytochrome.

Mutations in the gene for the red/far-red light receptor phytochrome B alter cell elongation and physiological responses throughout Arabidopsis development

Phytochromes are a family of plant photoreceptors that mediate physiological and developmental responses to changes in red and far-red light conditions. In Arabidopsis, there are genes for at least five phytochrome proteins. These photoreceptors control such responses as germination, stem elongation, flowering, gene expression, and chloroplast and leaf development. However, it is not known which red light responses are controlled by which phytochrome species, or whether the different phytochromes have overlapping functions. We report here that previously described hy3 mutants have mutations in the gene coding for phytochrome B (PhyB). These are the first mutations shown to lie in a plant photoreceptor gene. A number of tissues are abnormally elongated in the hy3(phyB) mutants, including hypocotyls, stems, petioles, and root hairs. In addition, the mutants flower earlier than the wild type, and they accumulate less chlorophyll. PhyB thus controls Arabidopsis development at numerous stages and in multiple tissues.

Photophysiology of the Elongated Internode (ein) Mutant of Brassica rapa: ein Mutant Lacks a Detectable Phytochrome B-Like Polypeptide

Several phytochrome-controlled processes have been examined in etiolated and light-grown seedlings of a normal genotype and the elongated internode (ein/ein) mutant of rapid-cycling Brassica rapa. Although etiolated ein seedlings displayed normal sensitivity to prolonged far-red light with respect to inhibition of hypocotyl elongation, expansion of cotyledons, and synthesis of anthocyanin, they displayed reduced sensitivity to prolonged red light for all three of these deetiolation responses. In contrast to normal seedlings, light-grown ein seedlings did not show a growth promotion in response to end-of-day far-red irradiation. Additionally, whereas the first internode of light-grown normal seedlings showed a marked increase in elongation in response to reduced ratio of red to far-red light, ein seedlings showed only a small elongation response. When blots of protein extracts from etiolated and light-treated ein and normal seedlings were probed with monoclonal antibody to phytochrome A, an immunostaining band at about 120 kD was observed for both extracts. The immunostaining intensity of this band was substantially reduced for extracts of light-treated normal and ein seedlings. A mixture of three monoclonal antibodies directed against phytochrome B from Arabidopsis thaliana immunostained a band at about 120 kD for extracts of etiolated and light-treated normal seedlings. This band was undetectable in extracts of ein seedlings. We propose that ein is a photoreceptor mutant that is deficient in a light-stable phytochrome B-like species.

Internode length in Pisum : A new, slender mutant with elevated levels of C19 gibberellins

A new, elongated mutant of garden pea (Pisum sativum L.) is described, and shown to be conferred by a recessive allele of a new gene, sln. At the seedling stage, the mutant resembles the previously described slender type (genotype la cry (s) ), possessing markedly longer basal internodes than the wild-type. Furthermore, as for la cry (s) plants, application of gibberellin (GA)-biosynthesis inhibitors to the dry seeds (before sowing) did not markedly affect internode length in the mutant. However, the inheritance of the new slender phenotype is unusual, since in crosses between sln and Sln plants the mutant phenotype is absent in the F2 generation, reappearing in the F3. Young shoots possessing the new slender phenotype (sln) contained much higher levels of GA1, GA8, GA20 and GA29 than did wild-type shoots. Mature, near-dry seeds from slender plants contained very high levels of GA20, marginally more GA29, and very little (if any) GA29-catabolite, compared with seeds harvested from wild-type (Sln-) plants. It is suggested that sln may impair the catabolism of GA20 in maturing seeds. As a result, GA20 accumulates and on germination may move into the seedling where it is converted to GA1, promoting elongation growth. A model is proposed to explain the inheritance of the sln phenotype and its physiological implications are discussed. The new sln slender mutation has a different mode of action from the established la cry (s) slender gene combination.

Immunochromatographic purification of gibberellins from vegetative tissues of Cucumis sativus L: Separation and identification of 13-hydroxy and 13-deoxy gibberellins

Immunological methods are described for the separation and purification of 13-hydroxy and 13-deoxy-gibberellins of Cucumis sativus. Qualitative and quantitative data show that 13-deoxygibberellins predominate over 13-hydroxygibberellins in stems and leaves of this species.

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 GA(3) and a GA synthesis inhibitor, and occurrence and concentrations of endogenous GAs, IAA, and ABA. At 14 days the genotype 58M (ma(3) (R)ma(3) (R)) exhibited 2.5-fold greater culm height, 1.75-fold greater total height, and 1.38-fold greater dry weight than 90M (ma(3)ma(3)) or 100M (Ma(3)Ma(3)). All three genotypes exhibited similar shoot elongation in response to GA(3), and 58M showed GA(3)-mediated hastening of floral initiation when harvested at day 18 or 21. Both 90M and 100M had exhibited hastening of floral initiation by GA(3) 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 (2)H(2)-labeled standards on capillary column GC and matching mass spectrometer fragmentation patterns (ions [m/z] and relative abundances), GA(1), GA(19), GA(20), GA(53), and GA(3) 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, GA(44) and GA(17) were detected. Quantitation was based on recovery of coinjected, (2)H(2)-labeled standards. In 14 day-old-plants, total GA-like bioactivity and GA(1) 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. GA(1) 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 ma(3) (R) causes a two- to six-fold increase in GA(1) concentrations, does not result in a GA-receptor or transduction mutation and is associated with phenotypic characteristics that can be enhanced by GA(3) and reduced by GA synthesis inhibitor. These observations support the hypothesis that the allele ma(3) (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.

Growth and development of Brassica genotypes differing in endogenous gibberellin content. I. Leaf and reproductive development

Leaf and reproductive development were compared in 3 rapid cycling Brassica rapa genotypes grown for 4 weeks under greenhouse conditions. The dwarf mutant, rosette (ros), is gibberellin (GA)-deficient, while the tall mutant, elongated internode (ein), has enhanced endogenous GA levels. Germination was delayed in ros and a selection of a more severe form of ros, named dormant (do), has even more retarded germination and some seeds entirely fail to germinate. Seeds of do and ros respond to exogenous GA, by rapid germination. The 3 genotypes, ros, normal and ein, displayed similar developmental sequences, although floral bud formation and subsequent floral development and anthesis were delayed in ros. Conversely, anthesis was slightly accelerated in ein. Individual leaf areas were reduced in both ros and ein relative to the normal genotype, but leaf numbers were similar in all 3 genotypes. Differences in leaf morphology (heterophylly) were also observed; the normal genotype and ein plants possessed uniform leaf shapes and relatively smooth leaf margins, although petiole length was increased in ein. The mutant ros had scalloped leaf margins and convoluted leaf blades in addition to shortened petioles. These phenotypes suggest a role for GA in the regulation of germination and reproductive and leaf development in Brassica.

Growth and development of Brassica genotypes differing in endogenous gibberellin content. II. Gibberellin content, growth analyses and cell size

Three rapid cycling Brassica rapa genotypes were grown in greenhouse conditions to investigate the possible relationships between endogenous gibberellin (GA) content and shoot growth. Endogenous GA(1) GA(3) and GA(20) were extracted from stem samples harvested at 3 weekly intervals and analyzed by gas chromatography-mass spectrometry with selected ion monitoring, using [(2) H(2) ]-GA(1) and [(2) H(2) ]-GA(20) as quantitative internal standards. During the first 2 weeks, GA levels of the dwarf, rosette (ros), averaged 36% of levels in normal plants (on a per stem basis). Levels in the tall mutant, elongated internode (ein), were consistently higher, averaging 305% of levels in normal plants. Differences in shoot height across the genotypes resulted from varying internode length which resulted from epidermal cell length and number being increased in ein and decreased in ros relative to the normal genotype. The exogenous application of GA(3) to normal plants increased cell length while the application of paclobutrazol (PP333), a triazole plant growth retardant, reduced cell size. Thus, exogenous GA manipulations mimicked the influence of the mutant genes ros and ein. The dwarf, ros, had reduced shoot dry weights and relative growth rates compared to the other genotypes. Total dry weights were similar in ein and the normal genotype but stem weights were increased in ein, compensating for decreased leaf weights. Thus, the gibberellin-deficiency of ros resulted in generally reduced shoot growth. The overproduction of endogenous GA by ein did not result in enhanced shoot growth but rather a specific enhancement of internode elongation and stem growth at the expense of leaf size.