The desert green algae Chlorella ohadii thrives at excessively high light intensities by exceptionally enhancing the mechanisms that protect photosynthesis from photoinhibition |
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Authors: | Guy Levin Sharon Kulikovsky Varda Liveanu Benjamin Eichenbaum Ayala Meir Tal Isaacson Yaakov Tadmor Noam Adir Gadi Schuster |
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Affiliation: | 1. Faculty of Biology, Technion, Haifa, 32000 Israel;2. Department of Vegetable Research, Agricultural Research Organization, Newe Ya'ar Research Center, Ramat Yishay, Israel;3. Grand Technion Energy Program, Technion, Haifa, 32000 Israel |
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Abstract: | Although light is the driving force of photosynthesis, excessive light can be harmful. One of the main processes that limits photosynthesis is photoinhibition, the process of light-induced photodamage. When the absorbed light exceeds the amount that is dissipated by photosynthetic electron flow and other processes, damaging radicals are formed that mostly inactivate photosystem II (PSII). Damaged PSII must be replaced by a newly repaired complex in order to preserve full photosynthetic activity. Chlorella ohadii is a green microalga, isolated from biological desert soil crusts, that thrives under extreme high light and is highly resistant to photoinhibition. Therefore, C. ohadii is an ideal model for studying the molecular mechanisms underlying protection against photoinhibition. Comparison of the thylakoids of C. ohadii cells that were grown under low light versus extreme high light intensities found that the alga employs all three known photoinhibition protection mechanisms: (i) massive reduction of the PSII antenna size; (ii) accumulation of protective carotenoids; and (iii) very rapid repair of photodamaged reaction center proteins. This work elucidated the molecular mechanisms of photoinhibition resistance in one of the most light-tolerant photosynthetic organisms, and shows how photoinhibition protection mechanisms evolved to marginal conditions, enabling photosynthesis-dependent life in severe habitats. |
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Keywords: | photoinhibition photoprotection chlorella green algae photosynthetic antenna size xanthophyll cycle D1 turnover |
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