Three temperature-sensitive mutants of Arabidopsis thaliana that were defective in the redifferentiation of shoots were isolated as tools for the study of organogenesis. Plasticity is a key feature of cytodifferentiation in higher plants. In response to phytohormones and/or wounding, various types of mature, differentiated plant cells are reactivated so that they acquire organogenic competence and then proliferate to form shoots, roots, or somatic embryos. Physiological, biochemical, and molecular biological studies of this process have provided information important for an understanding of the differentiation of plant cells. However, in spite of many efforts, the key to organogenic competence and the molecular mechanisms of organogenesis is still unknown. Genetic analysis, which has not been exploited extensively in this field, can be expected to improve the present situation.With respect to organogenesis, dependence on genotype has bgen practically the only focus of genetics to date. Organogenic responses in tissue culture often vary, depending on genotype. The genetic basis of such variations has been studied in severa1 crop species (Ohki et al

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Some cell lines retain intrinsic phototransduction pathways to control the expression of light-regulated genes such as the circadian clock gene. Here we investigated the photosensitivity of a Fugu eye, a cell line established from the eye of Takifugu rubripes, to examine whether such a photosensitive nature is present. Microarray analysis identified 15 genes that showed blue light-dependent change at the transcript level. We investigated temporal profiles of the light-induced genes, as well as Cry and Per, under light-dark, constant light (LL), and constant dark (DD) conditions by quantitative RT-PCR. Transcript levels of Per1a and Per3 genes showed circadian rhythmic changes under both LL and DD conditions, while those of Cry genes were controlled by light. All genes examined, including DNA-damage response genes and photolyase genes, were upregulated not only by blue light but also green and red light, implying the contribution of multiple photopigments. The present study is the first to identify a photosensitive clock cell line originating from a marine fish. These findings may help to characterize the molecular mechanisms underlying photic synchronization of the physiological states of fishes to not only daily light-dark cycles but also to various marine environmental cycles such as the lunar or semi-lunar cycle.

In Arabidopsis thaliana, shoot redifferentiation and root redifferentiation can be induced at high frequency from hypocotyl and root explants by a two-step culture method. Tissues are precultured on callus-inducing medium and then transferred onto shoot-inducing medium for shoot redifferentiation or onto root-inducing medium for root redifferentiation. In an attempt to dissect these organogenic processes genetically, we characterized the responses in tissue culture of srd1, srd2 and srd3 mutants that were originally isolated as temperature-sensitive strains with defects in shoot redifferentiation (Yasutani, I., Ozawa, S., Nishida, T., Sugiyama, M. and Komamine, A. (1994) Plant Physiol. 105, 815–822). These mutants exhibited temperature sensitivity at different steps of organogenesis, which allowed the identification of three states associated with organogenic competence: IC (incompetent); CR (competent with respect to root redifferentiation); and CSR (competent with respect to shoot and root redifferentiation). Hypocotyl explants were shown to be in the IC state at the initiation of culture and to enter the CSR state, via the CR state, during preculture on callus-inducing medium, whereas root explants seemed to be in the CR state at the initiation of culture. The transition from IC to CR and that from CR to CSR appeared to require the functions of SRD2 and SRD3, respectively. It appears that explants in the CSR state redifferentiate shoots with the aid of the products of SRD1 and SRD2 when transplanted onto shoot-inducing medium. Histological examination of the srd mutants revealed that the function of SRD2 is required not only for organogenesis but also for the reinitiation of cell proliferation in hypocotyl explants during culture on callus-inducing medium. Linkage analysis using RFLP markers indicated that SRD1, SRD2, and SRD3 are located at the lower region, the central region, and the upper region of chromosome 1, respectively.

Relaxation processes of the energy-rich protonated water dimer H+(H2O)2 were investigated by the ab initio molecular dynamics (AIMD) method. At first, the energy-rich H+(H2O)2 was reproduced by simulating a collision reaction between the protonated water monomer H3O+ and H2O. Next it was collided with N2 in order to observe the effects of intramolecular vibration redistribution and intermolecular energy transfer. Forty-eight AIMD simulations of the collision of H+(H2O)2 with N2 were performed by changing the initial orientation and the time interval between two collisions. It was revealed that the amount of energy transferred from H+(H2O)2 to N2 decreased the longer the time interval. The relationship between the intermolecular energy transfer and the vibrational states was examined with the use of an energy-transfer spectrogram (ETS), which is an analysis technique combining energy density analysis and short-time Fourier transform. The ETS demonstrates a characteristic vibrational mode for the energy transfer, which corresponds to the stretching of the hydrogen bond between H+(H2O)2 and N2 in an active complex.