Biodiversity and physiology of Begonia iridoplasts

  • O-Phart Phrathep

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Iridoplasts and minichloroplasts are forms of modified plastid found in epidermal pavement cells of Begonia leaves. The repeated membrane system inside the iridoplasts has been shown to function as a multilayered photonic crystal generating iridescence while the special role of minichloroplasts remains unknown. The purposes of this study aimed to investigate the occurrence of iridoplasts, minichloroplasts and iridescence in phylogenetically diverse taxa of Begonia and the plastid locations in the leaf tissue as well as the plasticity of iridoplast and minichloroplast ultrastructure and iridescence under varying light intensities. Due to the new finding of the cryptic hypodermal iridoplasts, computational optical modelling method was introduced to determine their photonic properties.

The results presented here confirm that both iridoplasts and minichloroplast exist in only dermal tissue of Begonia leaves, and they are both species- and dorsoventrally tissue- specific. Multilayered thylakoid stacked membranes within Iridoplasts function as photonic structure generating iridescence, resulting in reflected light in blue to green wavelengths in both real spectral measurement and predicted spectra by optical modelling. The changes of iridoplast and minichloroplast ultrastructure and iridescence under altered light conditions indicate their plasticity; however, they are not interconvertible. The finding of the existence of these modified epidermal plastids and their alterations responding to high and low light levels suggests the mechanisms underpinning adaptive strategies of plants to the changes of light environments.
Date of Award26 Nov 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SponsorsRoyal Thai Government & Mahidol Wittayanusorn School (Public Organization)
SupervisorJill Harrison (Supervisor) & Heather M Whitney (Supervisor)


  • Begonia, iridoplast, light, TEM

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