title: UV-B light contributes directly to the synthesis of chiloglottone floral volatiles.
abstract: OBJECTIVE
  Australian sexually deceptive Chiloglottis orchids attract their specific male wasp pollinators by means of 2,5-dialkylcyclohexane-1,3-diones or 'chiloglottones', representing a newly discovered class of volatiles with unique structures. This study investigated the hypothesis that UV-B light at low intensities is directly required for chiloglottone biosynthesis in Chiloglottis trapeziformis.
  
  
  METHODS
  Chiloglottone production occurs only in specific tissue (the callus) of the labellum. Cut buds and flowers, and whole plants with buds and flowers, sourced from the field, were kept in a growth chamber and interactions between growth stage of the flowers and duration and intensity of UV-B exposure on chiloglottone production were studied. The effects of the protein synthesis inhibitor cycloheximide were also examined.
  
  
  RESULTS
  Chiloglottone was not present in buds, but was detected in buds that were manually opened and then exposed to sunlight, or artificial UV-B light for ≥5 min. Spectrophotometry revealed that the sepals and petals blocked UV-B light from reaching the labellum inside the bud. Rates of chiloglottone production increased with developmental stage, increasing exposure time and increasing UV-B irradiance intensity. Cycloheximide did not inhibit the initial production of chiloglottone within 5 min of UV-B exposure. However, inhibition of chiloglottone production by cycloheximide occurred over 2 h of UV-B exposure, indicating a requirement for de novo protein synthesis to sustain chiloglottone production under UV-B.
  
  
  CONCLUSIONS
  The sepals and petals of Chiloglottis orchids strongly block UV-B wavelengths of light, preventing chiloglottone production inside the bud. While initiation of chiloglottone biosynthesis requires only UV-B light, sustained chiloglottone biosynthesis requires both UV-B and de novo protein biosynthesis. The internal amounts of chiloglottone in a flower reflect the interplay between developmental stage, duration and intensity of UV-B exposure, de novo protein synthesis, and feedback loops linked to the starting amount of chiloglottone. It is concluded that UV-B light contributes directly to chiloglottone biosynthesis. These findings suggest an entirely new and unexpected biochemical reaction that might also occur in taxa other than these orchids.
authors: Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia, Research School of Chemistry, The Australian National University, Canberra, ACT 0200, Australia, Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA and School of Animal Biology & Oceans Institute, University of Western Australia, Perth, WA 6009, Australia.
authors: Ranamalie
authors: R
authors: Amarasinghe
authors: Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia, Research School of Chemistry, The Australian National University, Canberra, ACT 0200, Australia, Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA and School of Animal Biology & Oceans Institute, University of Western Australia, Perth, WA 6009, Australia.
authors: Jacqueline
authors: J
authors: Poldy
authors: Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia, Research School of Chemistry, The Australian National University, Canberra, ACT 0200, Australia, Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA and School of Animal Biology & Oceans Institute, University of Western Australia, Perth, WA 6009, Australia.
authors: Yuki
authors: Y
authors: Matsuba
authors: Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia, Research School of Chemistry, The Australian National University, Canberra, ACT 0200, Australia, Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA and School of Animal Biology & Oceans Institute, University of Western Australia, Perth, WA 6009, Australia.
authors: Russell A
authors: RA
authors: Barrow
authors: Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia, Research School of Chemistry, The Australian National University, Canberra, ACT 0200, Australia, Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA and School of Animal Biology & Oceans Institute, University of Western Australia, Perth, WA 6009, Australia.
authors: Jan M
authors: JM
authors: Hemmi
authors: Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia, Research School of Chemistry, The Australian National University, Canberra, ACT 0200, Australia, Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA and School of Animal Biology & Oceans Institute, University of Western Australia, Perth, WA 6009, Australia.
authors: Eran
authors: E
authors: Pichersky
authors: Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia, Research School of Chemistry, The Australian National University, Canberra, ACT 0200, Australia, Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA and School of Animal Biology & Oceans Institute, University of Western Australia, Perth, WA 6009, Australia rod.peakall@anu.edu.au.
authors: Rod
authors: R
authors: Peakall
mesh_terms: D003512:Cyclohexanones / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D035264:Flowers / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects*; D029595:Orchidaceae / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects*; D010940:Plant Proteins / Q000037:antagonists & inhibitors; D054817:Pollination; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D014466:Ultraviolet Rays
chemical_list: C478538:2-ethyl-5-propylcyclohexan-1,3-dione; D003512:Cyclohexanones; D010940:Plant Proteins; D011500:Protein Synthesis Inhibitors; D003513:Cycloheximide
keywords: 2; 3-diones; 5-dialkylcyclohexane-1; Chiloglottis trapeziformis; Orchidaceae; UV-B; biochemistry; chiloglottone; floral semiochemical; floral volatiles; orchids; pollination; sexual deception
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