Fucoxanthin excitation energy transfer

This chapter presents a personal historical perspective of the role of carotenoids in photosynthesis. It leads the reader into the early literature on the carotenoids and photosynthesis that are related to the discoveries on the excitation energy transfer and, to a lesser extent, on photoprotection. Excitation energy transfer from the carotenoid fucoxanthin to chlorophyll (Chi) a was shown first in the diatoms by H. Dutton, W. M. Manning and... 

The difference in the fluorescence spectra between intact and dissociated FCPA is rather dramatic, as can be seen in Fig. 7. The main emission band at 677 nm shown in Fig. 7 (A) was excited at 440,460 and 515 nm, wavelengths absorbed predominantly by Chi a, Chi c and fucoxanthin, respectively. The emission spectra indicate that both Chi c and fucoxanthin transfer excitation energy to Chi a with high efficiency. The emission spectrum excited by 460 nm shows a weak emission at 640 nm, originating from Chi c. However, the 640-nm emission is not seen when the sample was excited at 515 nm, which suggests that fucoxanthin transfers energy directly to Chi a without the mediation of Chi c. 

Fig. 10. Fluorescence emission and excitation (or absorption) spectra in CSj of p-carotene (A) and fucoxanthin (B). See text for details. Figure source (A) Glllbro and Cogdell (1989) Carotenoid fluorescence. Chem Phys Lett. 158 313. (B) Katoh, Nagashima, and Mimuro (1991) Fluorescence properties of the allenic carotenoid fucoxanthin impiication for energy transfer in photosynthetic pigment systems. Photosynthesis Res 27 223.

In the dissociated FCPA, excitation at 440, 460 and 515 nm evokes quite different emission patterns [Fig. 7 (B)]. The 460-nm light, preferentially absorbed by Chi c, produces an increase in the emission at 640 nm and much less emission at 670 nm. Similarly, excitation by 515-nm light absorbed primarily by fucoxanthin also produced very little 677-nm emission but no emission at all at 640 nm. These results suggest that the coupling between Chi c and Chi a and that between fucoxanthin and Chi a are both disrupted and they also confirm that transfer of energy from fucoxanthin to Chi a does not go through Chi c. 

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