VITAMINS

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Channelrhodopsins (ChRs) are a member of microbial rhodopsin and consist of the chromophore retinal and a seven-transmembrane helix (TM7) protein (opsin) with a function of photoreceptor. Retinal forms a protonated Schiff base with a conserved lysine residue located on TM7. Upon light stimulation, ChRs function as cation channels accompanying with the conformational changes of retinal and opsin.
Optogenetics is a powerful new tool, which allows the control of neuronal activity by light. ChRs which are now used in optogenetics are ChR1 and CHR2, and they are the most sensitive to green to blue light. However, short-wavelength light such as blue-green light cannot deeply penetrate into the neural tissues due to scattering or absorption of the light by the tissue. Therefore, the development of red-shifted ChRs, which are sensitive to long-wavelength light such as yellow-red light, are eagerly desired.
To develop a novel red-shifted ChR, the research group including me prepared retinal derivatives which have longer conjugated polyene systems than retinal as the chromophore and evaluated their interactions with opsin proteins.

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Vitamin C (ascorbate) is a potent water-soluble antioxidant and acts as a cofactor for many enzymes. Plants contain ascorbate at very high levels, and, for humans, they are the main dietary source of this vitamin. Despite the tremendous efforts made so far, the following fundamental questions still remain: why and how plants accumulate ascorbate in their body. During the evolution of plants, they have acquired original pathways for ascorbate biosynthesis as well as the use of ascorbate for the antioxidant system and recycling. These allowed plants to synthesize ascorbate ‘safely’ and to use it for the antioxidant system very efficiently. Recently, our research group has studied 1) the impacts of ascorbate levels on plant growth and stress resistance, 2) the physiological significance of plant-specific H₂O₂-scavenging enzymes (ascorbate peroxidases), and 3) the molecular mechanism of ascorbate recycling and its role in ascorbate pool size regulation. In this review, I summarize recent advances in this field and try to answer the above two fundamental questions.

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