Summary: Changes in pyrenoid morphology and the distribution within the chloroplast of ribulose-1, 5-bisphosphate carboxylase/oxygenase(RuBisCO)of Euglena gracilis Z were followed by immunoelectron microscopy during growth and division phase. Most of the immunoreactive protein was found in the pyrenoid during the growth phase with only a small amount of gold particles localized to the stroma. During the division phase, the pyrenoid was not detected and the gold particles were dispersed throughout the stroma. A comparison between rates of photosynthetic CO2-fixation and the amount of total carboxylase activity catalyzed by RuBisCO extracted from Euglena cells in the growth phase suggests that pyrenoid localized RuBisCO is responsible for photosynthetic CO2-fixation. The precursors to the Euglena light-harvesting chlorophyll a/b binding proteins of photosystem II(LHCP II)are large polyproteins containing multiple copies of LHCP II covalently joined by a conserved decapeptide. Light induced LHCP II synthesis is controlled at the translational level in Euglena rather than the transcriptional level as found in higher plants and other algae. Under conditions promoting LHCP II synthesis and accumulation in the thylakoids, a reaction with anti-LHCP II antibody can be observed by immunogold electron microscopy in the Golgi apparatus. The kinetics of LHCP II appearance in the Golgi apparatus as measured by immunogold electron microscopy in synchronous cells and by pulse labeled with H2[35S]O4 in cells undergoing normal light-induced chloroplast development suggests that nascent LHCP II is transported to the Golgi apparatus prior to chloroplast import and thylakoid insertion.

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Summary: The plants of Podostemaceae, an unusual aquatic angiosperm famiy that occur in rapids andwaterfalls, gained a horizontal axis ofdevelopment at the beginning of the famiy, whie lost the verticalbipolar development common in angiosperms. The gain and loss of the axes took place in the seedling stage: the secondary root develops from the hypocotyl or the secondary shoot develops from the axil of the cotyledons. The primule and radicle on either end of the hypocotyl became reduced or disappeared. The crustose rootunique to Podostemoideae evolved with the loss of the root apical meristem and the development of themariginal meristem.

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Summary: In Fagales, the ovary is still immature when pollen is delivered to the stigma and the fertilization occurs more than one month after pollination. Developmental study of the pollen-tube growth in the pistil of three species(Casuarina equisetifolia, Alnus sieboldiana and Myrica rubra)in Fagales showed that the pollen tube grows intermittently in close association with the development of the ovary and ovules. At the stage when the ovary develops an ovule primordium, many pollen tubes germinated on the stigma and reached the style, where they remain for several weeks in Casuarina and Alnus. The pollen-tube growth to the style proceeds irrespective of ovules and embryo sac. Thereafter, the pollen tube resumes growing to the ovary with an immature ovule(s)(megaspore tetrad stage in Casuarina and Alnus and megaspore mother cell stage in Myrica). In these species, the pollen tube reaches the ovule with immature embryo sac. Except in the last step, where the tube grows from the tissue of ovule(the chalaza or the nucellus)to an embryo sac, a mature embryo sac is not necessary for pollen-tube guidance in the pistil. While the intermittent pollen-tube growth appears to play an important role in the selection of a single pollen tube from many and one ovule from two(in Casuarina and Alnus), its detection provides insight into a study of the mechanism of pollen-tube guidance.

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Summary: In Japan, Spiranthes sinensis Ames var. australis(R. Br. )H. Hara et Kitam. ex Kitam. has been known to show variations in the flowering time and plant size. To evaluate the validity of the seasonally differentiated groups and a dwarf form of the species, which is endemic to Yakushima Island, Japan, molecular variations were examined by analyzing nuclear and plastid DNA loci. As a result, above-mentioned variations were to be treated as the rank of forms. Moreover, some unexpected polymorphisms were found. Namely, Japanese and Malaysian S. sinensis var. australis differed significantly in the DNA sequences, suggesting that this variety may not be one biological species. On the other hand, two major groups were recognized among individuals examined, having geological border in Kyushu Island. These data strongly suggested requirement of re-examination of this species, that is widely distributed in eastern Asia and Australia.

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Summary: Glucans are important components of the cell wall and acts to maintain the cell shape. It was confirmed that the secreted glucans of fission yeast stretch into fibrils and then pack into bundles, which are oriented in parallel and connected in a side-by-side manner to develop wide ribbon-like structures. It is suggested that the wide glucan fibrils function to maintain the cell wall integrity by forming the network structures. The analysis of mutants of glucan synthase indicated that theβ-1, 3-andα-1, 3-glucans are essential for the formation of cell-wall layered structures, and each glucan plays a different role. It is also indicated that theα-glucan possibly acts in packing the glucan network. Onlyβ-1, 3-glucan plays a vital role in the primary septum formation. This finding strongly suggested thatβ-1, 3-glucan synthesis, together with the contraction of the contractile ring, is essential in the progress of the septum formation, and shows that one of theβ-1, 3-glucan synthases, Bgslp, functioned in this process. Studies of the glucan synthase localization indicated that the defect inα-1, 3-glucan synthesis affects the secondary septum formation, therefore theα-glucan synthase, Moklp, located in the septum region from the beginning of the septum formation. It is suggested thatα-1, 3-glucan may have a role in the early stage of the septum formation.

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Summary: The Podostemaceae, an unusual aquatic angiosperm family, have unique morphological features. Particularly, in some species the shoot is considered to lack the shoot apical meristem. However, interpretations of whether a shoot apical meristem is present or absent vary from one scientist to another. Here I describe anatomical and developmental studies on the shoot in subfamily Podostemoideae. Some species of Podostemoideae have no shoot apical meristem in the shoot tip where the youngest and second-youngest leaf primordia contact tightly with each other. Some species belonging to the American clades of Podostemoideae form a new leaf primordium at the base of the forgoing one. Furthermore, in some species belonging to the Asian-Australian clade, leaf formation occurs endogenously accompanied with cell separation at the base of the second-youngest leaf primordium, where a new leaf forms, and with tissue splitting in a region between the youngest two leaf primordia, where the shoot apical meristem exists in other angiosperms. In contrast, the shoots of subfamily Tristichoideae and Weddellinoideae are interpreted to have a shoot apical meristem. Taking phylogenetic relationships into account, it may be likely that leaf formation without shoot apical meristem, that is not associated by cell separation appeared in the ancestor of the American clades of Podostemoideae and subsequently was further modified into a more specialized mode involving cell separation in the Asian-Australian clade.

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Summary: Mitochondrial and chloroplast division controls the number and morphology of organelles, but how cells regulate organelle division remains to be clarified. Here, we show that each step of mitochondrial and chloroplast division is closely associated with the cell cycle in Cyanidioschyzon merolae. Electron microscopy revealed direct associations between the spindle pole bodies and mitochondria, suggesting that mitochondrial distribution is physically coupled with mitosis. Mitochondrial final severance was suppressed during S phase and once induced in M phase, when dynamin was specifically recruited. Although microtubule was not directly required for the organelles division, spatial interaction between microtubule and dynamin implied to be working on a possible checkpoint for spindle elongation. Chloroplast division was induced during S phase and suppressed during M phase, which was thought to be as a consequence of synthesis and degradation of dynamin and FtsZ. Molecular networks between cell cycle and the organelles division is discussed.

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Summary: The staining ability of uranyl acetate(UA)solution was examined by dipping100grids with ultrathin sections consecutively in a single drop of this solution using freeze-substituted and epoxy-resin-embedded yeast cells. No decrease in the staining ability was observed. Thus, the repeated use of UA solution is recommended, which should contribute to not only the economical use of UA solution but also the protection of the environment by reducing the amount of undesirable waste.

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