Suspension culture was established from root segments of rice (Oryza sativa L.) cul-tures in Murashige and Skoog's (1962) medium supplemented with 2.0mg/1 2.4-dichloro-phenoxyacetic acid (2, 4-D) and 2g/l casein hydrolysate. The suspensions were composed of cells rich in cytoplasm with a potential for division and of elongated cells which contained large vacuoles and could not divide. Suspension cultures which were maintained L0r more than 2 months in liquid medium were plated on agar medium containing 0.5 mg/l kinetin and 2g/l casein hydrolysate. Embryogenic calli emerged from the plated suspension cultures. Plantlets were formed from the embryogenic calli by transferring them onto the medium repeatedly. The capacity for plant regeneration decreased in the advanced subculture passages in liquid medium. However, repeated transfer of the embryogenic calli to new regeneration medium promoted plant regeneration efficiently even in long term suspension cultures.

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The diallel analysis was applied to F₁'s derived from crossings in all combinations without reciprocals among five varieties representing Hokkaido rice cultivars with different plant types. Additive gene action (a) predominated over dominance action (b) in the number of panicles per plant, the number of spikelets per panicle, the mean straw weight and culm lemgth. On the other hand, the mean square of the b item was large in panicle weight per plant, 100-kernel weight and grain length. A parent, Shiokari seems to have nearly complete recessive gene(s) which reduce grain length. Panicle weight per plant, which consist of the number of panicles per plant and some other components, did not satisfy the hypothesis of additive gene action. The four F₁ hybrids of Shiokari were superior to the othper F₁ hybrids and the five parents. The percentage of panicle weight to the total plant weight satisfied the hypothesis of additive gene action, though it is a compound character composed of many component characters. This character showed unidirectional positive dominance.

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To define the cytogenetical relationship between Capsicum annuum and C.baccatum, the pattern of chromosome pairing at meiotic metaphase in the F₁ hybrid was analysed. The average frequency was 0.02 for univalents, 8.93 for bivalents, 0.08 for trivalents, 0.72 for quadrivalents, 0.02 for quinquevalents and 0.49 for hexavalents. Occurrence of univalents was very rare. It is, thus, demonstrated that C.annuum and C.baccatum differ from each other by the presence of at least three reciprocal translocations. From the present results, it is concluded that C. annuum and C.baccatum share a basically homologous but structurally differentiated genome. The F₁ hvbrid was sterile because of such a structural differentiation of chromosomes.

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Four rice varieties, Bluebelle, IR8, Panbira and Sensho, were grown on flooded and dry soil in pots in a glasshouse. Photosynthetic rate (P, C02 uptake/time), transpiration rate (Tr, H20 release/time) and temperature (T) of the second expanded leaf (whole single leaf blade) from the top of the main stem were measured under controlled aeration (40 minutes wet, then 40 minutes dry) and illumination in an air sealed leaf chamber in the laboratory, together with leaf area (LA), fresh weight (FW), dry weight (DM) and nitrogen content (LN). CO2 diffusive resistance in the gaseous phase was estimated from Tr. T and air humidity, and actual leaf water content after P and Tr measure-ments was estimated from FW and DM. Photosynthetic efficiencies were evaluated on two bases : per unit leaf area (P/LA) and per unit leaf nitrogen (P/LN). Four varieties tested showed a marked difference in their leaf density-thickness as indicated by leaf areal nitrogen content (LN/LA). Judging Lrom the leaf nitrogen efficiency in photosynthetic energy conversion (P/LN), it was concluded that thinly expanded leaves with a highwer LN/LA were adapted to humid and densely thick leaves with a higher LN/LA were adapted to dry condltlons. With regard to this concluslon relatlonshlps between leaf density-thickness, dehydration avoidance ability, and C02 diffusive resistance were also discussed.

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Regeneration of plantlets from slices of cotyledons in Camellia japonica L. and C.sinensis L. has been accomplished. Differentiation originated from the surface of cotyledon without the mediation of callus formation. It was obvious from histological observations that adventitious embryos were formed directly at the surface of the swelled up part of the cotyledon. Adventitious embryos were formed always in the same way on the cotyledon slices independently of the presence or concentration of growth regulators. In C.japonica, adventitious embryos grew shoots and roots on the medium supplemented with GA3 (Gibberellin), and after several monthly subcultures many plantlets were established. Moreover these somatic embryos formed additional embryos on the hypocotyls with the subcultures and this phenomenon was perpetuated throughout the successive generations of embryos on the GA3 medium. In C.sinensis, adventitious embryos grew shoots and roots on the medium supplemented with 10.0 mg/l BA (N6-Benzylaminopurine) and 0.5 mg/l IBA (Indol-3-butyric acid), but not on the medium supplemented with GA3. It was considered that rapid mass clonal propagation through the culture of cotyledon slices could be obtained from one seed of a selected cross in the Camellia genus.

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A protoplast fusion method in which nuclei of a cytoplasm donor protoplast are inactivated was evaluated as an alternative method for introducing male sterility into tobacco (Nicotiana tabacum). Prior to the fusion, various doses of X-rays were irradiated to the cytoplasm donor of N.debneyi protoplasts, and 10kR was found to be effective to inactivate nuclear function of N.debneyi without damage of the cytoplasmic function. Following the fusion of the X-irradiated N.debneyi protoplasts and nonirradiated N.tabacum cv. Consolation 402 protoplasts, about 300 calli were subjected to regenerate. Almost all the regenerates exhibited N.tabacum characters concerning overall morphologies except flower, and had normal somatic chromosome number of N.tabacum (2n=48). Out of 318 regenerates 30 possessed male sterility. These male sterile regenerates exhibited floral phenotypic variation and could be classified into four types. One of these types (Type C) showed almost identical flower morphology with that of plants which were obtained from N.debneyi repeatedly backcrossed with N.tabacum The other three types showed intermediate morphologies between the normal and the type C. Their distinct flower morphologies were stably transmitted to the progenies, although some minor deviation from those of the parental regenerates was observed. All the progenies of the male sterile regenerates never segregated any fertile plants, indicating that the transmission of the male sterility was stable. Analysis of the large subunit of Fraction I protein (ribulose 1, 5-bisphosphate carboxylase, EC4, 1, 1, 39) encoded by a chloroplast gene revealed that 15 male sterile lines possessed the N.debneyi type chloroplast gene and 11 lines the N.tabacum type gene. These results may indicate that the cytoplasmic factors were transferred through the protoplast fusion, and that the male sterility is independent from chloroplast gene. The protoplast fusion, in which nuclei of a cytoplasmic donor protoplasts are inactivated by X-irradiation, may provide an alternative and efiicient method for obtaining male sterile tobacco, because male sterile tobacco plants could be obtained within 6-7 months from the protoplast fusion and under appreciable frequency.

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Tissue cultures of wheat (Triticum aesticum L., cv. Norin 61, 2n=6x=42) were initiated from the immature haploid embryos which were produced by the intergeneric crosses with Hordeum bulbosum L. Nine immature embryos ca. 0.5mm in diam which were cultured for fifteen weeks on GAMBORG'S B5 medium supplemented with 2ppm of 2, 4-dichlorophenoxyacetic acid, developed to calli ca. 15 mm in diam. The calli were individually divided into ten small pieces and then transferred onto a hormone-free B5 medium for plant regeneration. A total of 63 green plants were regenerated. All the regenerated plants were euhaploids with 21 chromosomes.

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The intragenotypic varlability of a quantitative character can be measured in two ways : (1) variation of mean phenotype to different enviornments and known. as phenotypic plasticity. The latter is generally attributed to developmental instability which is assumed to be due to accidents in the developmental processes of individual plants and unrelated to external environmental conditions. The genetic analysis of the intragenotypic variability for plant height was carried out by mea.ns of complete diallel crosses of six inbred lines in rustica tobacco (Nicotiana rustica L.) under seven conditions. The magnitude of inter-plant variation of plant height was estimated from standard deviation within plot.

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Most of the cultivars of buckwheat (Fagopyrum esculentum MOEINCH) in Japan are classified into two ecotypes ; summer and late-summer types. The summer type cultivars are mainly distributed in regions of high latitude (37-45 whereas the late-summer type cultivars are distributed in regions of low latitude (31-34, the former being assumed to have differentiated from the latter. It has been reported that the summer type cultivars are non-sensitive to day length unlike the late-summer type cultivars. We carried out the present experiment to analyze the process of phylogenetic differentia-tion of the summer type cultivars from the late-summer type cultivars, with emphasis placed on the genetic changes in flowering time and seed yield in the long-day summer and the short-day autumn seasons in Tsukuba, Ibaraki (Lat. 36North) (Table 1 and Fig. 1). The summer type cultivars did not exhibit any variation in the flowering time in either seasons. However, the late-summer type cultivars grown in the summer season showed remarkable variations in the flowering time ranging from early to late (Fig. 2) along with a drastic decrease in seed yield (Table 2).

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By using the protoplast fusion techniqlle we obtained rice-soybean hybrid calli having soybean nuclei and chloroplasts of both parents. In the brown hybrid calli sorting-out of chloroplasts occurred and green calli having soybean chloroplasts and white calli having rice chloroplasts were segregated (NIIZEKI et al. 1985). The heteroplasmic hybrid calli with both parent chloroplasts were extremely sensitive to streptomycin under both light and dark conditions, while the parent calli and the green and white calli produced by the sorting-out of chloroplasts were resistant to streptomycin under light conditions, but very sensitive under dark conditions. From this result it can be assumed that the responses of these calli to streptomycin may be related to the chloroplast for the follow-ing reasons : Firstly, the difference in the response of the parent calli or the calli with sorted-out chloroplasts to streptomycin under light and dark conditions suggests that the sensitivity to streptomycin may be related to the chloroplasts which require light for their functions and secondly, the recovery of streptomycin resistance in the calli with sorted-out chloroplasts indicates that the chloroplasts respond to streptomycin. However, the pcssibility that the sensitivity to streptomycin resides in the other organelles could not be excluded. Also, the reason for the heteroplasmic state of the calli being very sensitive even under light conditions remains unknown. After long term culture streptomycin resistant portions in the heteroplasmic hybrid calli increased in number under light conditions. This means that the sorting-out of chloroplasts progressed in the hybrid calli and the number of callus portions or cells with only one of the parent chloroplasts increased.

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