Metamitron, a photosynthetic electron transport chain inhibitor, modulates the photoprotective mechanism of apple trees

Yuval Tadmor, Amir Raz, Shira Reikin-Barak, Vivek Ambastha, Eli Shemesh, Yehoram Leshem, Omer Crane, Raphael A. Stern, Martin Goldway, Dan Tchernov, Oded Liran

Research output: Contribution to journalArticlepeer-review


Chemical thinning of apple fruitlets is an important practice as it reduces the natural fruit load and, therefore, increases the size of the final fruit for commercial markets. In apples, one chemical thinner used is Metamitron, which is sold as the commercial product Brevis® (Adama, Israel). This thinner inhibits the electron transfer between Photosystem II and Quinone-a within light reactions of photosynthesis. In this study, we investigated the responses of two apple cultivars—Golden Delicious and Top Red—and photosynthetic light reactions after administration of Brevis®. The analysis revealed that the presence of the inhibitor affects both cultivars’ energetic status. The kinetics of the photoprotective mechanism’s sub-processes are attenuated in both cultivars, but this seems more severe in the Top Red cultivar. State transitions of the antenna and Photosystem II repair cycle are decreased substantially when the Metamitron concentration is above 0.6% in the Top Red cultivar but not in the Golden Delicious cultivar. These attenuations result from a biased ab-sorbed energy distribution between photochemistry and photoprotection pathways in the two cultivars. We suggest that Metamitron inadvertently interacts with photoprotective mechanism-related enzymes in chloroplasts of apple tree leaves. Specifically, we hypothesize that it may interact with the kinases responsible for the induction of state transitions and the Photosystem II repair cycle.

Original languageEnglish
Article number2803
Issue number12
StatePublished - 17 Dec 2021

Bibliographical note

Publisher Copyright:
© 2021 by the authors. Licensee MDPI, Basel, Switzerland.


  • Apple
  • Electron transport rate
  • Fruitlet thinners
  • Golden Delicious
  • Light reactions
  • PSII repair cycle
  • Photoprotective mechanism
  • Photosynthesis
  • State transitions
  • Top Red

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Plant Science
  • Ecology


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