A comparative study on the structure of vascular cambium of Betulaceous plants has revealed that the typical nonstoried cambium is composed of fusiform and ray initials in all plants examined. The size measurements of fusiform initials in tangential sections have revealed that the average length varies from 347. 6-659. 6μ m in the examined species, the maximum being in Alnus hirsuta and the minimum in Carpinus laxiflora. And then the length of fusiform initials depends on the length of the pseudotransverse end walls which undergo intrusive growth to varying extents in different species. In each species ray initials have their own size, magnitude, frequency of occurrence. The relative proportion of ray initials falls about 13. 4-37. 5%. Shrubby Corylus has lower proportion of ray initials than Alnus which possess wider trunk.

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Changes in the cell structure during and after net formation of zoospores in Hydrodictyon reticulatum were investigated by electron and fluorescence microscopy. Many small vesicles were accumulated around zoospores, and these vesicles later restricted the movement of zoospores. Immediately after cessation of the movement of polyhedral zoospores, the plasma membrane evaginated to form thread-like projections around the closely approaching regions of adacent zoospores. Then the projections seemed to fuse with the adjacent zoospores. Once the connections between the adacent cells were formed by the proections, the contact between two zoospores became progressively tighter. Cell wall materials were deposited on the plasma membrane about 10 minutes after cessation of the cell movement. Cell wall materials appeared firstly as electron-dense discontinuous patches on the plasma membrane. The patches then expanded to connect with one another, finally forming a single electron-dense cell wall layer which covered the cell surface. Netcells were finally linked by their cell walls. Cell wall substances continued to be accumulated in the space between the electron-dense cell wall layer and the plasma membrane.

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GFP was first cloned and sequenced from the jellyfish Aequorea victoria. Wild-type GFP emits green fluorescence when excited with blue or UV light without any additional substrates or cofactors. An engineered sGFP(S 65 T)sequence with codons optimal for high expression of eukaryotic proteins has provided up to100-fold brighter fluorescent signals than the original jellyfish GFP sequence in plant and mammalian cells. The fusion of sGFP(S 65 T)with the nuclear localization signal of SV 40, the plastid transit sequence of RBCS-1A, or the mitochondrial targeting sequence of γ-ATPase, has directed the localization of sGFP(S 65 T)in nuclei, plastids, or mitochondria, respectively, in transient expression assays. I could generate high level GFP expressing and fertile plants as usual frequency. This result indicates that sGFP(S 65 T)is non-toxic in Arabidopsis. The fluorescence intensity of whole plants can be measured under non-disruptive, sterile conditions using a quantitative fluorescent imaging system. Homozygous plants can be distinguished from heterozygous plants, and fully fertile progenies can be obtained from the analyzed plants. This system will be useful in applications such as mutant screening, analysis of whole-body phenomena. I also made transgenic Arabidopsis those stably expressing the nuclear-, plastid-, or mitochondria-targeting sGFP(S 65 T)and could detect the fluorescent signals in each cell including root, leaf and reproductive organs.

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We have employed high pressure freezing techniques to examine cytoskeletal and membrane structures in meristematic cells of plant seedlings. This method results in improved preservation of preprophase bands of microtubules as well as other structures in onion and tobacco roots and in meristematic cells of onion cotyledons. In this paper, we describe the use of high pressure freezing and freeze substitution to obtain thin sections of samples embedded in Spurr's resin and discuss problems with these procedures. We also present new results obtained from high pressure frozen cells and discuss the possible applications of high pressure freezing in plant cell biology.

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Summary: The Cyanidiophyceae species Cyanidium caldarium and Cyanidioschyzon merolae have played important roles in showing the division mechanisms of mitoch ondria and plastids. The apparatus regulating mitochondrial and plastid division was formerly unkonwn. We first identified the division apparatus of plastids, called the plastid-dividing ring(PD ring), in C. caldarium and the division apparatus of mitochondria, called the mitochondrion-dividing ring(MD ring), in C. merolae. Eukaryotic cell division is therefore controlled by at least three dividing apparati---a contractile ring, an MD ring, and a PD ring---while bacterial division is controlled by a single bacterial contractile FtsZ ring.

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Cells of Chlamydomonas reinhardtii Dangeard were synchronized under a 12 hour light: 12hour dark regimen.Behavior of mitochondria in these synchronized cells was examined by fluorescence microscopy using a mitochondrial membrane-binding fluorescent dye, DASMPI, as a specific vital stain as well as by electron microscopy. Three-dimensional models of mitochondria in synchronized cells of C. reinhardtii were constructed from their electron microscopic profiles in serial cell sections using the computer graphics techniques. Based on these observations, the mitochondrial morphologies of C. reinhardtii in the cell cycle were classified into five types. These results were discussed in relation with those reported by previous workers.

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Summary: We have developed an efficient method to isolate the male gametic nuclei(generative nuclei)from pollen grains of Lilium longiflorum and analyzed the chromatin proteins. As a result, it was revealed that the generative nuclei contained three kinds of specific histone variants(p22. 5, p21, p18. 5)in addition to five kinds of somatic histones. Immunofluorescence staining using specific antisera clearly demonstrated that these histone variants were specific to male gametic(generative and sperm)nuclei in L. longiflorum. Because the deduced amino acid sequences of the cDNAs of these specific variants showed some homology to somatic histones H2B, H3and H2A, respectively, they were designated gH2B, gH3and gH2A. They are the first male gamete-specific histones in angiosperms, and are assumed to be related to the condensation of chromatin of the male gametic nuclei.

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We have investigated the plastid DNA replication cycle of Anthoceros Punctatus. In mitotic cycles of this species, plastids divided into two daughter plastids with DNA synthesis. By contrast, in spore mother cells, the DNA content of plastids which had completed their division was halved as well as the DNA content of cell nuclei. The plastid DNA content of unfbrtilized egg cells did not change before and the fertilization because of prefbrential digestion of organelle DNA in sperm cells. In the 2n-generatio, plastids multiplied by binary fission, with DNA duplication. It is thought that plastid DNA content is halved in spore mother cells but recovers before, or immediately after, spore germination. In the n-generation, Plastids multiplied by binary fission, with DNA duplication, and the plastid DNA content was maintained at the same level as that of the 2ngeneration.

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