Michizo Sugai

A blue-light-activated adenylyl cyclase mediates photoavoidance in Euglena gracilis.

Blue light regulates processes such as the development of plants and fungi and the behaviour of microbes. Two types of blue-light receptor flavoprotein have been identified: cryptochromes, which have partial similarity to photolyases, and phototropins, which are photoregulated protein kinases. The former have also been found in animals with evidence of essential roles in circadian rhythms. Euglena gracilis, a unicellular flagellate, abruptly changes its swimming direction after a sudden increase or decrease in incident blue light intensity, that is, step-up or step-down photophobic responses, resulting in photoavoidance or photoaccumulation, respectively. Although these photobehaviours of Euglena have been studied for a century, the photoreceptor molecules mediating them have remained unknown. Here we report the discovery and biochemical characterization of a new type of blue-light receptor flavoprotein, photoactivated adenylyl cyclase, in the photoreceptor organelle of Euglena gracilis, with molecular genetic evidence that it mediates the step-up photophobic response.

Photobiology of ferns

Fern gametophytes are the haploid phase during the alternation of generations in the life cycle of ferns. They are simple independent organisms, starting from single cells (spores), which develop into heart shaped prothalli after an initial filamentous stage of a few linearly aligned cells. Antheridia and archegonia develop on a three dimensional tissue (called the mat) at the central part of gametophytes and fertilization results in the sporophytic generation. The gametophytic stage, although short and showing simple organization, is indispensable for the ferns’ sexual reproduction.

Discovery of signaling effect of UV-B/C light in the extended UV-A/blue-type action spectra for step-down and step-up photophobic responses in the unicellular flagellate algaEuglena gracilis

SummaryCultures of unicellular algal flagellateEuglena gracilis grown in different conditions were subjected to action spectroscopy for step-down and step-up photophobic responses, respectively. The spectral region was extended into the UV-B/C as well as in the UV-A and visible regions with the Okazaki Large Spectrograph as the monochromatic light source. The photophobic responses of the cells were measured with an individual-cell assay method with the aid of a computerized video motion analyzer. In the UV-A and visible regions, the shapes of the action spectra were the so-called UV-A/blue type. In the newly studied UV-B/C region, new action peaks were found at 270 nm for the step-down response and at 280 nm for the step-up one. The absorption spectrum of flavin adenine dinucleotide (FAD) appeared to fit the action spectrum for the step-up response, whereas the shape of the step-down action spectrum, which has a UV-A peak (at 370 nm) higher than the blue peak (at 450 nm), appeared to be mimicked by the absorption spectrum of a mixed solution of 6-biopterin and FAD. These observations might also account for the fact that the UV-B/C peak wavelength at 270 nm of the action spectrum for the step-down response is shorter by 10 nm than the action spectrum for the step-up response at 280 nm.

Diverse responses of spores in the light-dependent germination of Lygodium japonicum

Abstract The germination of spores of the fern Lygodium japonicum was sometimes induced by a brief irradiation with red light, but was mostly brought about by a prolonged exposure to red light. The former effect was typically reversed by far-red light, and was blocked by a brief exposure to blue light. The latter effect was replaced by intermittent irradiation with red light, the effect of which was reversed by far-red light and was totally canceled by blue light if given immediately after each exposure to red light. The germination of spores in Lygodium is controlled by both phytochrome and a blue light-absorbing pigment irrespective of the diversity of light requirement among samples.

Development of the Casparian strip is delayed by blue light in pea stems

To understand the regulatory mechanisms involved in tissue development by light, the kinetics of regulation of Casparian strip (CS) development in garden pea stems was studied. We found that short-term irradiation with white light delayed the development of the CS and used this delay to assess the quantitative effect of light on CS development. We examined the effect of the duration and fluence rates of white light treatment on CS development and observed a significant relationship between fluence and the delay in CS development indicating that the Bunsen–Roscoe law of reciprocity holds for this response. The effect of white light irradiation was not inhibited in the presence of a photosynthetic inhibitor, DCMU, or a carotenoid biosynthesis inhibitor, Norflurazon, indicating that the delay in CS development by light is a photomorphogenetic response rather than a subsidiary effect mediated by photosynthetic activity. An action spectrum for the response displayed a major peak in the blue-light region, suggesting a dominant role for blue-light receptors. A minor peak in the red-light region also suggested the possible involvement of phytochromes. Although phytochromes are known to contribute to blue-light responses, phytochrome-deficient mutants showed a normal delay of CS development in response to blue light, indicating that the response is not mediated by phytochrome and suggesting a role for one or more specific blue-light receptors.

Chloroplast DNA Variation in the genusSesamum

It is widely approved that comparing restriction profiles and maps of chloroplast DMA provides valuable information concerning inter-and/or intra-specific relationships among plant species. Such chloroplast DNA analysis was applied to species and strains inSesamum which is a genus of approximately 38 species and contains a large number of strains of the cultivated sesame,S. Indlcum. Our chloroplast DNA investigations of 22 species and strains showed that; (i) among four species (S. capense, S. radiatum, S. schinzianum andS. indicum), the chloroplast genome ofS. capense was most distantly related to that of the cultivated species,S. indicum, (ii) chloroplast DNA polymorphism was also recognized among eight cultivated stralns collected from various regions in the tropical zone, but not among eight different varieties grown in the temperate zone, and (iii) the chloroplast DNA alterations observed could be attributed to the site gains or losses with the exception of the alterartion detected within the inverted repeat sequences inS. capense chloroplast DNA. These results demonstrate the presence of chloroplast genome diversity amongSesamum species and strains, suggesting the usefulness of chloroplast DNA analysis for elucidating the species relationships in the genusSesamum and the origin and evolutionary process of the cultivated sesame species.