NATIONAL INSITUTE FOR BASIC BIOLOGY

National Institute for Basic Biology

OFFICE OF DIRECTOR

Director-General:
Hideo Mohri
Associate Professors:
Shigeru Itoh
Ryuji Kodama
Research Associate:
Katsunori Aizawa (on leave)


Evolution of photoysnthesis and the mechanism of electron transfer

Shigeru Itoh

We study the evolution of molecular mechanism of plant and bacterial photosynthesis. Anoxygenic photosynthesis of bacteria seems to have evolved in the Precambrian Earth just after the evolution of life. Oxygen-evolving photosynthesis was then established by cyanobacteria 3.5-2.7 billion years ago and increased atomospheric oxygen. Symbiosis of cyanobacteria inside the larger cells produced the first plant about 2 billion years ago.

Wat can we study to explore the past? We take three approaches (1) Survey of electron transfer mechanism in photosyntheic reaction center (RC) pigment-protein complexes. We replaced cofactors in the complex to see what happens. We studied light reactions by the ps-ns laser and the spin-echo ESR spectroscopy between 4 and 280 K in the cofactor-replaced RCs and found that the molecular architecture of plant and bacterial RCs are highly optimized in different directions. The result that was the first evidence of the energy-gap dependence of the ultra-fast electron tunnnelling in plant, also suggeted us the design of prototype RC. (2) Site-directed mutagenesis of electron transfer proteins in attempts to construct prototype electron transfer protein. (3) Survey of ever-unknown photosynthesis as well as the comparative studies of photosynthesis in purple, green sulfur, hellio-, cyanobacteria and plant. A recent topic was the discovery of a new bacterium, Acidiphilium rubrum that undergoes photosynthesis with Zn-bacteriochlorophyll, instead of Mg-chlorophylls used in all the ever-known plant and bacterial photosynthesis. This finding was a supprise by itself, and led to the study of another, completely new oxygen-evolving photosynthesis now.

Fig. 1
Space-filling (lower) and wire-frame (upper) models of Rhodopseudomonas capsulata ferredoxin (FdxN). Pink-coloured moiety in native (left) protein was altered (right) by site-directed mutagenesis. The mutation exposed the Fe-S cluster (yellow and red) and decreased its reducing power detectable by EPR.


Mechanisms determining the outline shape of the adult lepidopteran wings

Ryuji Kodama

Wings of the lepidopteran insects (butterflies and moths) develop from the wing imaginal disc, which is a hollow sac made of simple epithelium. When the pupariation is completed, the wing, which was hidden inside the body wall of the larvae, is exposed on the surface of the pupa, which gradually turns into the adult wing. The outline shape of the adult wing is often different from that of the pupal wing. This difference is brought about by the programmed cell death of the marginal area of the pupal wing, while the internal area develops as adult wing blade. The marginal dying area is called the degeneration region and the internal area is called the differentiation region, hereafter.

The cell deaths in the degeneration region proceeds very rapidly and completes in a half to one day period in Pieris rapae or several other species examined. It was shown that the dying cells in the regeneration region have two characteristics common with the apoptotic cell death in mammalian cells. These are i) the presence of apoptotic bodies, which are heavily condensed cells or their fragments engulfed by other cells or macrophages, shown by transmission electron microscopy and ii) the presence of conspicuous accumulation of fragmented DNA evidenced by the TUNEL histological staining (Kodama, R. et al., Roux's Arch. Dev. Biol. 204, 418-426, 1995).

The cells in the degeneration region are actively engulfed by the macrophages in the cavity beneath the wing epithelium. Moreover, the macrophages seem to be concentrated beneath the degeneration region by the strong adhesion between basal surfaces of the dorsal and ventral epithelium in the differentiation region. By injecting the india ink or ferritin solution to the body cavity of the pupa, we have confirmed that this adhesion is tight enough to exclude the macrophages from the differentiation region, because the injected probes was found mostly concentrated in the degeneration region when observed several minutes later (Yoshida, A. (Biohistory Research Hall) and Kodama, R., unpublished).

These studies were done using the small cabbage butterfly, Pieris rapae, and the silk moth, Bombyx mori. We have recently begun studies using another lepidopteren species, Orgyia recens approximans, provided by Drs. Y. Arita and K. Yamada (Meijo University). In this species, the wing is normally formed until the beginning of the pupal period, but becomes conspicuously degenerated only in the female adult (Fig. 2). In our preliminary study, it was shown that the pupal wing is normally formed both in male and female pupa, but after about two days, female pupal wing starts degeneration on its margin, as if the degeneration region is continuously formed deep into the center of the wing (Kodama, R. et al., unpublished). It is thus suggested that the control mechanism which demarcates the region to be degenerated is defective in the female in this species. Further investigation using this species might give important insight into such mechanisms.

Fig. 2
The adult wing of the male (upper) and female (lower) moth, Orgyia recens approximans, are shown at the same magnification. Only a part of the left forewing is shown for the male wing. In the female, wings are degenerated to small protrusions (arrows) covered with scales similar to those covering the body.


Publication List:
Dzuba, S. A., Hara,H., Kawamori, A., Iwaki, M., Itoh, S. and Tsvetkov, Yu. D. (1997) Electron spin echo of spin-polarized radical pairs in the intact and quinone-reconstituted plant photosystem I reaction centers. Chem. Phys. Lett. 264, 238-244.
Hara, H., Dzuba, S.A., Kawamori, A., Akabori, K., Tomo, T., Satoh, K., Iwaki, M. and Itoh, S. (1997) The distance between P680 and QA in Photosystem II determined by ESEEM spectrocscopy. Biochim. Biophys. Acta 1322, 77-85.
Ogawa, K. and Mohri, H. (1997) Establishment of a dynein motor superfamily. In ÒRecent Advances in Marine Biotechnology. Vol. 1. Endocrinology and ReproductionÓ (M. Fingerman, R. Nagabhushanam and M.-F. Thompson, eds.), pp. 249-281. Oxford & IBH Publishing Co., New Delhi, Calcutta.
Ohoka, H., Iwaki, M. and Itoh, S. (1997) Viscosity dependence of the electron transfer rate from bound cytochrome c to P840 in the photosynthetic reaction center of a green sulfur bacterium Chlorobium tepidum. Biochemistry 36, 9267-9272.
Tomo, T., Mimuro, M., Iwaki, M., Kobayashi, M., Itoh, S. and Satoh, K. (1997) Topology of pigments in the isolated photosystem II reaction center studied by selective extraction. Biochim. Biophys. Acta 1321, 21-30.

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Last Modified: 12:00, May 28, 1998