How does the meristem of sunflower capitulum cope with tissue expansion and floret initiation? A quantitative analysis

Authors

  • Guillermo A. A. Dosio,

    1. UMR 759 Ecophysiologie des Plantes sous Stress Environnementaux, INRA-Agro.M, 2 place Viala, 34060 Montpellier Cedex 01, France;
    2. Unidad Integrada UNMdP – INTA Balcarce, CC 276, 7620 Balcarce, Argentina
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  • François Tardieu,

    1. UMR 759 Ecophysiologie des Plantes sous Stress Environnementaux, INRA-Agro.M, 2 place Viala, 34060 Montpellier Cedex 01, France;
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  • Olivier Turc

    1. UMR 759 Ecophysiologie des Plantes sous Stress Environnementaux, INRA-Agro.M, 2 place Viala, 34060 Montpellier Cedex 01, France;
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Author for correspondence: Olivier Turc Tel: +33 499612 633 Fax: +33 467522 116 Email: turc@ensam.inra.fr

Summary

  • • The coordination between floret initiation and tissue expansion has been studied and quantified in the apical meristem of sunflower (Helianthus annuus) plants grown under different light availability.
  • • A method was developed to quantify tissue expansion in the meristem during floret initiation from measurements of meristem area, number of florets and primordium size.
  • • Initially, floret initiation and tissue expansion occurred simultaneously at the meristem surface. The duration of this phase remained unchanged across environments, whereas the rate of tissue expansion varied greatly. Floret initiation rate depended on meristem initial size and tissue-expansion rate. Thereafter, floret initiation continued without tissue expansion in the meristem, resulting in a rapid decrease of meristem area.
  • • A set of equations was proposed to predict floret initiation rate and floret number as a function of the rates of tissue expansion in the meristem before and during floret initiation. This formalism demonstrated the role of tissue expansion in determining the final number of florets, and provided a framework to analyse the response of floret initiation to genotype and environment.

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