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
Affiliations
Yuval Tadmor
Group of Agrophysics Studies, MIGAL—Galilee Research Institute, Kiryat Shemona, Upper Galilee 11016, Israel
Amir Raz
Group of Molecular Genetics in Agriculture, MIGAL—Galilee Research Institute, Kiryat Shemona, Upper Galilee 11016, Israel
Shira Reikin-Barak
Northern R&D, Kiryat Shemona, Upper Galilee 11016, Israel
Vivek Ambastha
Group of Plant Development and Adaptation, MIGAL—Galilee Research Institute, Kiryat Shemona, Upper Galilee 11016, Israel
Eli Shemesh
Morris Kahn Marine Research Station, Department of Marine Biology, Leon H. Charney School of Marine Sciences, University of Haifa, Mt. Carmel, Haifa 3498838, Israel
Yehoram Leshem
Faculty of Sciences and Technology, Tel-Hai Academic College, Kiryat-Shemona, Upper Galilee 12208, Israel
Omer Crane
Northern R&D, Kiryat Shemona, Upper Galilee 11016, Israel
Raphael A. Stern
Faculty of Sciences and Technology, Tel-Hai Academic College, Kiryat-Shemona, Upper Galilee 12208, Israel
Martin Goldway
Group of Molecular Genetics in Agriculture, MIGAL—Galilee Research Institute, Kiryat Shemona, Upper Galilee 11016, Israel
Dan Tchernov
Morris Kahn Marine Research Station, Department of Marine Biology, Leon H. Charney School of Marine Sciences, University of Haifa, Mt. Carmel, Haifa 3498838, Israel
Oded Liran
Group of Agrophysics Studies, MIGAL—Galilee Research Institute, Kiryat Shemona, Upper Galilee 11016, Israel
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, Ashdod, Israel). This thinner inhibits the electron transfer between Photosystem II and Quinone-b 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 absorbed 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.
