Elsevier

Phytochemistry

Volume 62, Issue 2, January 2003, Pages 165-174
Phytochemistry

3β,13-Dihydroxylated C20 gibberellins from inflorescences of Rumex acetosa L.

https://doi.org/10.1016/S0031-9422(02)00442-9Get rights and content

Abstract

Using full scan GC–MS a wide range of gibberellins (GAs) was identified in the young inflorescences of the dioecious species Rumex acetosa L., consistent with the ubiquitous early 13-hydroxylation pathway in both male and female plants. In addition, R. acetosa is the first species in which all three 3β,13-dihydroxylated C20-GAs—GA18, GA38 and GA23—have been identified in the same organism, suggesting an early 3β,13-dihydroxylation biosynthesis pathway in this species. Authentic GA18, GA38 and GA23 were synthesized and their effects and that of GA1, a GA common to both pathways, on the time to inflorescence emergence was investigated. GA1 accelerated the emergence of inflorescences in both male and female plants. In addition some evidence for biological activity per se of the C20-GA38 was obtained.

Introduction

Rumex acetosa L. (common sorrel) is a dioecious perennial (Korpelainen, 1992). Inflorescences are initiated in spring and early summer and it is during the reproductive phase of development that the phenological differences between the sexes become most evident (Ainsworth et al., 1999). Gibberellins (GAs) in R. acetosa shoots have been analysed previously by full-scan GC–MS (Rijnders et al., 1997). GA53, GA29, GA19, GA4 and GA1 were identified, which suggested the operation of two biosynthesis pathways in these tissues: the early 13-hydroxylation pathway and the non 13-hydroxylation pathway. In the current paper we report the results from a study using full-scan GC–MS to identify the suite of endogenous GAs in young inflorescences of R. acetosa. Unlike the previous study, where the sex of the plants was not specified, the samples from male and female plants were analysed separately to reveal any qualitative differences in their content of GAs.

Since the seminal work of Lang, many studies have demonstrated the involvement of GAs in the floral induction of photoperiod-sensitive species under non-inductive conditions and/or in accelerating flowering under inductive conditions (Michniewicz & Lang, 1962, Wilson et al., 1992, Hisamatsu et al., 1998, Lee et al., 1998). Rosette plants do not show any obvious stem development in the vegetative state, but produce a flowering stem during the reproductive phase of development. The use of GA biosynthesis inhibitors on some rosette plants, such as Beta vulgaris (Van Roggen et al., 1998) and Silene armeria (Talon and Zeevaart, 1990), has revealed that, although GAs are not involved in floral induction in these species, they are required for stem elongation. In Rumex acetosa, the involvement of GAs during the reproductive phase of development has not been previously investigated. However, in a related species, R. acetosella, exogenous treatment of plants with GA3 under long-day (LD) conditions advanced the production of ‘floral buds’ by 70 days from the time of treatment, compared to control plants (Bavrina et al., 1991).

From early biochemical studies to the more recent molecular studies there is persuasive evidence for the role of GAs in floral induction of the facultative LD rosette plant Arabidopsis thaliana. Non-vernalizable ‘races’ of this species flower under both LD and SD conditions, but flowering is considerably accelerated under LD conditions. An early study by Langridge (1957) demonstrated that inflorescence induction was promoted by GA3 under SD conditions. There is now evidence of at least three flowering pathways in A. thaliana: a GA-dependent, a LD and an autonomous pathway (Reeves and Coupland, 2001).

The ga1-3 mutants in A. thaliana are impaired in their synthesis of CPP synthase which catalyses the conversion of GGPP to CPP in early GA biosynthesis. Consequently the GA levels in these mutants is greatly reduced (Sun and Kamiya, 1994). Wilson et al. (1992) found that under continuous light the ga1–3 mutants initiated flowers, but flowering was delayed compared to wild-type plants, possibly indicating a partial requirement for GAs for flowering under such conditions. However, under non-inductive SD conditions, ga1-3 mutants did not flower unless treated with exogenous GA3, therefore showing an absolute requirement for GAs under such conditions.

In A. thaliana the transition to flowering is partly dependent on the inflorescence meristem identity gene LEAFY (LFY). As the plant develops, levels of LFY expression in the primordia on the shoot apex increase until a threshold is reached and subsequently floral rather than leaf primordia are developed (Blázquez et al., 1998). Blázquez et al. (1998) found that the failure of the severely GA-deficient mutant ga1-3 to flower in SD corresponded to the lack of significant upregulation in expression of LFY during the three months of the experiment. Constitutive expression of LFY in such mutants restored their ability to flower under SD conditions.

Biochemical studies using exogenous applications of a wide range of authentic GAs have revealed that the extent of biological activity of GAs in advancing flowering and/or promoting bolting may depend on the structural features of the GA molecules, as well as the species under investigation (Evans et al., 1990, Mandel et al., 1992). For example, GAs without a hydroxyl group on C-13 but carrying one at C-3, such as GA4, promote both inflorescence initiation and stem elongation in Matthiola incana (Hisamatsu et al., 2000), but in Lolium temulentum GAs with a hydroxyl group at C-3 have reduced levels of activity in promoting inflorescence initiation, while the presence of a hydroxyl group on C-13 increased activity (Evans et al., 1990).

Relatively few GAs are considered to be biologically active (Lange, 1998). Treatment of mutants defective in GA biosynthesis with authentic labelled or unlabelled GAs has demonstrated that certain C19-GAs such as GA1, GA3, GA4 and GA5 have biological activity per se (Zeevaart & Talon, 1992, Spray et al., 1996). However, as suggested by Lange (1998), GAs with relatively low or negligible activity in common bioassays may be physiologically active in some plant species, at specific development stages and/or in certain tissues. Early bioassays have indicated that some 3β,13-hydroxylated C20-GAs may have intrinsic biological activity, that is their activity is not entirely dependent on metabolic conversion to C19-GAs (Reeve and Crozier, 1974). Following the identification of GA18, GA38 and GA23 in R. acetosa tissues by full-scan GC–MS, authentic samples of these GAs were prepared and their biological activity was examined in flowering time studies.

Section snippets

Results and discussion

Nine GAs—GA8, GA29, GA17, GA97, GA17, 16, 17-dihydro-17-hydroxy GA53, GA18, GA38 and GA23—were identified for the first time in this species and were detected in inflorescence tissues (Table 1). GA17 and GA97, the inactive metabolites of GA19 and GA53 respectively, were only identified in the sample of inflorescences from female plants. The presence of GA18, GA38 and GA23 is consistent with the operation of the putative early 3β, 13-dihydroxylation pathway (MacMillan, 1997) in floral tissues,

General experimental procedures

Inorganic chemicals were from Sigma Chemical Co., Poole, UK, unless stated otherwise. The solvents used were of the highest purity: HPLC grade from BDH Chemicals Ltd., Poole, UK. Water used in all solutions was ‘polished water’ from an Elga system. Infrared spectra were recorded on a Perkin-Elmer 1800 Fourier Transform Infrared spectrometer. 1H and 13C NMR spectra were recorded on a Varian Gemini 300 instrument. Chemical shifts are reported as values in parts per million. For proton spectra

Acknowledgements

T.S.S. is grateful to the BBSRC and Advanced Technologies, Cambridge for sponsorship of part of this work. Dr. Anthony Lowe is gratefully acknowledged for providing the plants for sampling and propagation.

References (43)

  • G Davis et al.

    Gibberellin biosynthesis in maize. Metabolic studies with GA15, GA24, GA25, GA7 and 2, 3-dehydro GA9

    Plant Physiology

    (1999)
  • L.T Evans et al.

    Gibberellin structure and florigenic activity in Lolium temulenteum, a long-day plant

    Planta

    (1990)
  • H Fukui et al.

    The structure of gibberellin A23 and the biological properties of 3, 13-dihydroxy C20-gibberellins

    Agricultural and Biological Chemistry

    (1972)
  • S.J Gilmour et al.

    Gibberellin metabolism in cell-free extracts from spinach leaves in relation to photoperiod

    Plant Physiology

    (1986)
  • P Hedden

    The use of combined gas chromatography-mass spectrometry in the analysis of plant growth substances

  • K Hiraga et al.

    Isolation and characterization of plant growth substances in immature seeds and etiolated seedlings of Phaseolus vulgaris

    Agricultural and Biological Chemistry

    (1974)
  • T Hisamatsu et al.

    Effect of gibberellin A4 and GA biosynthesis inhibitors on growth and flowering of stock [Matthiola incana]

    Journal of the Japanese Society of Horticultural Science

    (1998)
  • T Hisamatsu et al.

    The role of gibberellin biosynthesis in the control of growth and flowering in Matthiola incana

    Physiologia Plantarum

    (2000)
  • G.V Hoad

    Gibberellin bioassays and structure-activity relationships

  • B Jiang et al.

    Studies on the synthesis of gibberellins—stereoselective synthesis of GA23 methyl ester

    Chin. Sci. Bull

    (1989)
  • Y Kamiya et al.

    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

    Plant and Cell Physiology

    (1991)
  • Cited by (3)

    View full text