S umnlary: Shoot development of higher plants is largely dependent on the shoot apical meristem, a small group of undifferentiated cells at the tip. Establishment of the meristem during embryogenesis is animportant step for postembryonic shoot organ formation. Recent molecular genetic studies have led to the identification of numerous genes which are important for this step. These analyses have demonstrated that the molecular program responsible for shoot meristem formation starts long before morphological fbatures of the meristem become evident, and progresses through several steps.

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Summary: filamentous flower(fil)mutant of Arabidopsis thaliana generates clusters of filamentous structures and of flowers with floral organs of altered number and shape. The FIL gene is involved in the fate determination of the floral meristem, because a homeotic conversion from a flower to an inflorescence was observed in fil ap1double mutants. In double mutants with leafy(lfy), filamentous structures are formed, but very few or no flowers with floral organs are formed, showing that FIL gene is required for the formation and development of the floral meristem. The enhanced phenotype in the fil ap1and the fil lfy double mutants suggests that FIL protein may work coordinately with AP1and LFY proteins. We cloned a gene, FIL, that regulates the maintenance and growth of inflorescence and floral meristems, and of floral organs of Arabidopsis thaliana. FIL encodes a protein that carries a HMG-related domain and is localized in the nucleus. Expression of FIL was detected in the abaxial side of young primordia of leaves and floral organs. The spatially-controlled expression indicates that cells at the abaxial side of the lateral organs may be responsible for the normal development of the organs as well as for maintaining the activity of the meristems.

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Summary: An old collection of mutants of Pharbitis nil is proposed to be used as a new experimental material for the study of flower morphogenesis. Most of the mutants were isolated over100years ago, and recorded in colored woodblock printings. The mutants were later analyzed from the view point of modern plant genetics. The author recently observed some of them. With the knowledge of the reported genetical analysis and the present anatomical observation, the mutants appeared in the old woodblock paintings were classified into seven groups. These mutations seem difficult to be explained through the ABC model. Many of the genes involved in the P. nil flower morphology has a characteristics of pleiotropism, that is, some mutations accompany with dwarfism, reduced apical dominance, narrow- or curled-leaved phenotype. The fact that the flower morphogenesis cannot be explained through the ABC model suggests that some new genes with an unreported function regarding flower morphogenesis could be isolated. If the morphology of flower, leaf and stem is analyzed simultaneously, taking the p leiotropism advantage, the common mechanism of morphogenesis may be clarified.

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Summary: Because of their simple structure, fern gametophytes have been used as experimental materials for a wide variety of studies in plant morphogenesis. These include cytological, physiological and biochemical studies of spore germination, elongation and division of protonemata, pattern formation of prothallia, differentiation of sexual organs, and movements and fertilization of sperms at the cellular level. Japanese researchers have published many papers in this area over the past100years. In this review, I would like to introduce and evaluate some of contributions of Japanese researches in this field.

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ummary: In dormant spores of the cellular slime mold, Dietyostelium discoideum, half of actin molecules were tyrosine-phosphorylated and actin rods appeared. The high levels of the actin phosphorylation may cause a static state of vesicle transport and concern in maintaining spore dormancy. The dephosphorylation is required for spore germination, indicating that the pathway locates on upstream of the signal transduction for the germination. Since the dephosphorylation depends on uptake of D-glucose and energy production through its consumption, vesicle transport necessary to the germination may rely upon the transport and metabolism of glucose, similarly to the secretion of insulin from pancreatic β-cells. Actin rods were composed of tubules twice thicker than F-actin. It is first found that actin molecules construct tubules. The rods, that may maintain capsule-like shape of spores, seem to be a reservoir for actin-meshwork reconstructed in swollen spores. Thus actin cytoskeleton has crucial roles on regulating spore dormancy in Dictyostelium.

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Summary: The centrosome, composed of a pair of centrioles and pericentriolar materials, can be observed through the cell cycle of brown algal cells. Almost all microtubules radiate from the centrosome during interphase. he centrosome duplicates, migrates to both mitotic poles and participates in the formation of the mitotic spindle. We have studied the behavior of centrioles in both the processes of sexual reproduction(fertilization)and asexual reproduction(zoosporogenesis)in the life cycle of brown algae. Through these studies, it has become clear that centrioles of a female gamete selectively disappear and those of a male gamete remain in the zygote of brown algae, although various types of sexual reproduction(isogamy, anisogamy and oogamy)exist. In zoosporogenesis, coordinative nuclear and chloroplast divisions occur after meiosis to result the close association between the nucleus and the chloroplast that has been mediated by the centrosome.

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Summary: Although100years have passed since the discovery of double fertilization, details of the fertilization processes of flowering plants still remain unclear. This is mostly because thick layers of ovular sporophytic tissues hide the embryo sac(haploid female gametophyte)of most angiosperms. We established an in vitro fertilization system using Torenia fournieri, in which the embryo sac protrudes from the ovule. It was revealed that pollen tubes are directly guided to the embryo sac in vitro. Moreover, we succeeded in directly observing the discharge of the pollen tube contents into the embryo sac for the first time. Pollen tubes discharged their contents into the embryo sac explosively resulting in almost instantaneous breakdown of the synergid cell adjacent to the egg cell. The T. fournieri in vitro system revealed the covert sexual intercourse of flowering plants.

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Summary: We isolated the genes that are specifically or predominantly expressed in the cap of maize primary root by cDNA subtraction and differential screening, and characterized them in detail. One of such genes is a novel glycine-rich protein, zmGRP4(Zea mays glycine-rich protein4).In situ hybridization analysis has shown zmGRP4to be strongly expressed in the lateral root cap and weakly in the root epidermis. Immunoblot and immunohistochemical analysis using a polyclonal antibody raised against zmGRP4 protein revealed that the protein, which is posttranslationally modified, is secreted into and accumulated in the mucilage that covers the root apex. Two novel homologous genes, zmRCP1 a nd zmRCP2(Zea mays root cap-periphery gene), are specifically expressed in a few cell layers of the peripheral root cap. The peripheral root cap cells are namely the sloughing-off cap cells, which may undergo programmed cell death.

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