A pot experiment was conducted to analyze the relationship between the size of each apical dome (AD) and the numbers of differentiated primary rachis-branches (PBs) and spikelets. Two rice cultivars were used one was a heavy-panicle type ‘Akenohoshi' and the other was a many-tillering type ‘Nipponbare'. Rice plants were applied nitrogen (N) at various rates (75-600mg N pot^>-1< week^>-1<) during the vegetative stage. The base diameter and the height of ADs were measured at the panicle initiation (PI) stage. At heading, the numbers of differentiated PBs, secondary rachis-branches (SBs), and spikelets were counted. The N treatment increased shoot N concentration in both cultivars. The N treatment increased the base diameter of AD in Akenohoshi at the PI stage, but not in Nipponbare. The ADs in Akenohoshi had a base diameter about 6.2% larger on average than that in Nipponbare. The N treatment did not affect AD height. In Akenohoshi, the plants with a larger AD base diameter differentiated more PBs per panicle and then differentiated more SBs and spikelets than did those plants with a smaller AD diameter. However, in Nipponbare, the N treatments did not affect the number of differentiated PBs per panicle. These results suggest that the AD size at the PI stage, which is enlarged by higher N nutrition in the vegetative stage, is a determinant of the number of differentiated PBs and spikelets and that a larger AD size is responsible for a higher number of PBs and spikelets in Akenohoshi.

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In order to evaluate the allelopathic potential of the early developmental stage of rice plants (Oryza sativa L.), a search for allelopathic substances was undertaken in acetone extract of 10-d-old rice seedlings. Two growthinhibiting substances were found in the neutral fraction of the extract after silica gel column chromatography, and one substance was further purified by thin layer chromatography, C₁8 Sep Pack cartridge and HPLC. The purified substance inhibited the growth of lettuce (Lactuca sativa L.) at concentrations greater than 0.3 μg mL^>-1<. These two substances may be released into the environment, either as exudates from living tissues or leachates from residues of the plant, and act as allelochemicals to other plants, which should be investigated further in the laboratory and the field.

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The differences in the rates of ethylene production and growth between the calluses derived from the seeds of rice (16 cultivars of Oryza sativa L., Japonica and Indica types) and soybean (10 cultivars of Glycine max (L.) Merr.) were investigated. On the medium containing 2, 4-dichlorophenoxyacetic acid (2, 4-D) and benzylaminopurine (BAP), soybean calluses produced a larger amount of ethylene (208-1541 nLg^>-1< FW 24 h^>-1<) than rice calluses (8-37 nLg^>-1< FW 24 h^>-1<), and the rate of ethylene production from the calluses of both species greatly varied with the cultivar. The combined application of 2, 4-D and BAP greatly increased the ethylene production rate and the growth of calluses in soybean, but not in rice. Moreover, the addition of BAP to the medium strikingly promoted ethylene production in soybean calluses cultured on the medium containing 2, 4-D, but not in those cultured on the medium containing indolebutyric acid (IBA). The rate of ethylene production in both soybean and rice negatively correlated with the growth of calluses. The ethylene production and growth of calluses cultured under various conditions greatly differed between soybean and rice, and also varied with the cultivar of each species. The different aspects of the growth and ethylene production between soybean and rice calluses may represent the difference between dicots and monocots.

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The nature of gene action may be revealed and desirable parents may be found by analyzing the combining ability and estimating the degree of heterosis in an early generation. Currently, varieties with a good eating quality are preferred. This study was carried out to obtain information on the action of genes using the analysis of variance components estimated by minimum norm quadratic unbiased estimation (MINQUE (1)) and to estimate the genetic effects on amylose and protein contents, as criteria for selection of good eating quality by adjusted unbiased prediction (AUP). The mean values of amylose content, protein content and grain yield in the parents were 18.4%, 7.78% and 19.8 g plant^>-1<, respectively, and those in crossed F₁ seeds were 17.4%, 10.8% and 23.6 g plant^>-1<, respectively. The effects of additive were significant for both amylose and grain yield, but not for protein content, indicating the importance of the additive gene action on amylose content and grain yield. The effects of dominance were highly significant for amylose content, protein content and grain yield. Especially, the effect of dominance was greater than that of additive on protein content. The effect of maternal was detected in only amylose content, and L 42 and L 53 showed significant and negative maternal effect on amylose content. Ansanbyeo, Hinohikari, L 42 and L 53 exhibited negative additive effects on amylose content, which suggested the possibility of a decreased amylose content in their crossed progenies. Mid-parent heterosis for amylose content ranged from -44.7% (L 42 × Hinohikari) to 32.9% (L 53 × Lemont) with an average value of -7.2% for all crossed F₁ hybrids. However, all of the crossed seed showed positive mid-parent heterosis for protein content in this study and the differences were not significant among the hybrids.

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Hydraulic properties of leaf blade were studied to provide basic knowledge to examine relationships between leaf vulnerability to hydraulic dysfunction due to low water potential (Ψ) and plant adaptation to water stress in rice. The objectives were to find the appropriate portion along a leaf blade for measurements of hydraulic dysfunction due to low Ψ and to examine whether leaf vulnerability to hydraulic dysfunction changed with the growing season. The early cultivar Bouzu (to supply materials earlier) and Koshihikari (a leading cultivar of Japan) were grown in pots. Hydraulic profile along a leaf blade was determined under well-watered and drought conditions in the two cultivars. The vulnerability to leaf hydraulic dysfunction was compared between plants sown at different dates only in Koshihikari. In both cultivars, leaf hydraulic conductivity (K) was constant in the basal half of a leaf blade, whereas it became smaller toward the tip and this pattern was maintained under drought conditions, indicating that the basal half was an appropriate portion for estimation of leaf hydraulic dysfunction. In Koshihikari, K decreased as relative water content (RWC) decreased and RWC at which K was reduced to 50% of the maximum (RWC_>K50<) was determined for each sowing date. Then leaf Ψ corresponding to RWC_>K50< (Ψ_>K50<) was estimated from the relationship between Ψ and RWC. As a sowing date was delayed from May to August, Ψ_>K50< increased from -1.44 MPa to -1.13 MPa. It was concluded that rice leaves became vulnerable to hydraulic dysfunction due to low Ψ as the growing season was delayed.

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The effects of exogenously applied glycinebetaine on the salt-stress-induced inhibition of growth and ultrastructural damages in rice seedlings were investigated. Glycinebetaine was not effective in alleviating the NaCl-induced inhibition of root growth and rather enhanced the NaCl-induced inhibition. However, it was found to alleviate the inhibition of shoot growth induced by NaCl stress. Concentrations of Na were higher in salt-stressed plants than in unstressed plants. Stressed plants receiving glycinebetaine had a significantly lower Na and higher K concentrations in the shoots than the plants grown without application of glycinebetaine. Salinity induced ultrastructural damages in leaf such as swelling of thylakoids, disintegration of grana stacking and intergranal lamellae and destruction of mitochondria (deficiency of cristae, swelling and vacuolation). Such damages were largely prevented by pretreatment with glycinebetaine resulting in greening of the plants. In roots, the epidermis, cortex and root cap were more sensitive to salt stress than the meristem and stele. The most frequently observed ultrastructural alteration due to NaCl salinity was the formation of many large vacuoles in the root tip and root cap cells. The number of mitochondria was increased and they were aggregated in the cytoplasm of the root tip and root cap cells by treatment with NaCl or NaCl plus glycinebetaine. Glycinebetaine could not prevent the NaCl-induced ultrastructural damages in root cells. The effects of glycinebetaine to mitigate the ultrastructural damages in the chloroplast and mitochondria induced by NaCl might be due to the production of many vacuoles in root cells which may act to store Na and decrease its accumulation in the shoot.

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We studied the varietal differences in the rice cake hardening rate, which is one of the important characters in waxy rice processing. Waxy upland rice cv. Kanto-mochi172 had fewer short chains (dp 7 to 10) of amylopectin and more intermediate-length chains (dp 12 to 21) than cv. Tsukuba-hatamochi and cv. Mangetsu-mochi, which harden much more slowly when made into rice cakes, mochi, than does Kanto-mochi172. Based on zymogram analysis of the soluble fraction from the developing endosperm, the activity of starch synthase 2 (SS2), a candidate enzyme responsible for the difference in the amylopectin chain length was detected with Kanto-mochi172. SS2 activity was absent, however, in Tsukuba-hatamochi and Mangetsu-mochi. Using the progeny derived from a cross between Kanto-mochi172 and Mangetsu-mochi, we showed that differences in amylopectin chain length corresponded to the gelatinisation temperatures of the rice flours and rice cake hardening rates. The progeny of those rich in short amylopectin chains showed lower gelatinisation temperature and slower rice cake hardening rate than the progeny of those having amylopectin with fewer short chains. These results indicate that the differences in chain length distribution of amylopectin, polymorphisms in starch synthase activity, differences in rice flour gelatinisation temperature, and differences in rice cake hardening rate are not merely correlated with each other but are intimately linked since they are related to amylopectin properties.

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Kunitz-type soybean trypsin inhibitor (KSTI) is a major factor lowering the nutritional quality of soybean proteins. KSTI might be degraded during protein processing. In the present work, we determined the effect of removal of C-terminal amino acid residues on the inhibitory activity of KSTI in the cotyledons during germination in Japanese soybean cultivars, Toyokomachi and Wasekogane. The type of KSTI in both cultivars was determined by analysis of the complete nucleotide sequences of PCR products amplified from genomic DNA and partial amino acid sequences of both cultivars. These KSTI were identical to Ti^b in Toyokomachi and Ti^a in Wasekogane. KSTI from cotyledons at 4 days after germination in both cultivars was separated clearly into two bands T1 and T2 in Toyokomachi and W1 and W2 in Wasekogane upon native-PAGE. Based on the C-terminal amino acid sequences, KSTIs with higher mobility (T1, W1) were found to lack 13 amino acid residues at the C-terminus. The KSTI with lower mobility (T2, W2) lacked 14 or 15 amino acid residues at the C-terminus. Further, KSTI with lower mobility showed high inhibitory activity compared with that of KSTI with higher mobility. Thus, the changes in the form of KSTI from T1 or W1 to T2 or W2 by removal of C-terminal amino acid residues during seed germination may change the structure at the active site and consequently increase the inhibitory activity of KSTI.

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Experiments were conducted in 1997 and 1999 to determine how long-term soil fertilization influences the performance of maize crop under water deficit on alluvial soil (sandy loam) at the Kyoto University Farm, Japan. The field had been applied large amounts of chemical fertilizer and/or farmyard manure since 1988 as four treatments, i.e., no fertilizer (NF), chemical fertilizer (CF), farmyard manure (MF) and chemical fertilizer + manure (CM) each with two replications. Water stress was imposed naturally in 1997 from 54 to 81 days after sowing (DAS). In 1999, water stress was imposed in one of the two replicate blocks artificially during 22-65 DAS by controlling irrigation under a rain shelter and another replicate block was well watered. Leaf area index and biomass in CM and MF were maintained higher than in CF and NF in both years under both water-stressed and well-watered conditions. With the progress of water stress, the major water depletion zone in the soil tended to shift deeper to a greater extent in MF and CM than in NF and CF. The total amount of water depleted from 100cm-depth soil during the stress periods was larger in MF and CM than in NF and CF by 20 to 80 percent. Water-use efficiency (biomass production per total water depletion) was similar in OF, MF and CM with an average of 3.9 g kg^>-1< and it was lower in NF (1.8 g kg^>-1<) Leaf conductance and photosynthetic rate during the stress period were higher in MF than in CF. The results indicated that water extraction during the stress period was greater in the plots manured for a tong time, which resulted in well-maintained physiological activity and growth.

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The ^>15<N - labeled technique was used to study the stock, transformation, fate and utilization efficiency of N in the farming-pig husbandry-biogas ecosystem in rice areas. It was shown that the crude protein digestibility of the ensilaged milk vetch by pig was 53.76%, the recovery rates of ensilaged milk vetch N from the pig feces and urine were 39.36% and 24.71%, respectively. The recovery rate of biogas fermentation N of pig feces and urine was 97.9%. The quantity of alkali-hydrolysable N was 2.6 times as great as before the fermentation. The mixed application of milk vetch, biogas-tank sludge and chemical fertilizer could promote N partitioning to rice grain, therefore it was advantageous to yield improvement. The residual quantity in soil of the fertilizer N was equivalent to 2.0 - 2.5 times that of only chemical fertilizer and yet gaseous loss N of the latter was 2.6-8.2 times that of the former. The comprehensive economic effect of the whole ecosystem increased by times, compared with the only milk vetch-early rice-late rice pattern, and ecological effect and social effect were also very prominent.

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Inconsistent seedling establishment is a major constraint in rice direct-sown into puddled and leveled soil. We clarified the effect of water management on seedling emergence and establishment at different sowing depth for seeds with or without calcium peroxide coating. Drainage during 10 to 15 days after sowing scarcely affected the early-stage emergence compared with the wet and flooded conditions. Drainage and wetness promoted the late-stage emergence compared with the flooded conditions regardless of sowing depth and seed coating. The numbers of floating and turned down seedlings, and seedlings with delayed emergence were lower in the drained and wet plots than in the flooded plot. Thus, seedling establishment in such plots was markedly higher than that in the flooded plot, especially when seeds were sown at the soil surface. The dry weight of plants at seedling establishment was greater in the drained and wet plots than in the flooded plot, when seeds coated with calcium peroxide were sown below the soil surface. Drainage during seedling establishment thus improved seedling emergence and establishment regardless of sowing depth and seed coating treatment, and the drainage treatment enhanced the growth and dry weight increase of plants during seedling establishment compared to flooding treatment.

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Four cultivars of rice (Oryza sativa L.) different in plant stature were grown on a paddy field, fairly fertile without nitrogen application, with or without barnyard grass, Echinochloa oryzicola Vasing, in the middle of the rice rows. The reduction of the growth variables of the four cultivars by competition with E. oryzicola was examined. The effect of a veneer board inserted in the soil between the rice and barnyardgrass rows was also examined to evaluate the growth reduction by shoot competition (WC_s) and root competition (WC_r) separately. On the average, the reduction of top dry weight (DW_>top<) by competition with weed (full competition, WC_f) and by WC_r increased with the time during the early growth period. Thereafter, the reduction of DW_>top< by WO_r decreased steeply and instead the reduction by WC_s increased and became a primary factor of the reduction by WC_f in the late growth period. Nitrogen accumulation in the top (N_>top<) tended to be reduced at a higher rate than DW_>top< by WC_r. The cultivar difference in the rate of DW_>top< reduction by WC_f was largest at maturity ranging from 0.22 in Ch86 (very tall indica) to 0.45 in Taichung65d47 (short japonica), and was intermediate in Taichung65 (moderately tall japonica) and Takanari (moderately short indica). The reduction of DW_>top< and N_>top< by WC_s in all cultivars almost fully accounted for that by WC_f at maturity and closely correlated with the height of rice plant. Although the rate of DW_>top< reduction by WC_r before heading significantly differed among cultivars (0.13 - 0.28), it did not contribute to the rate of DW_>top< reduction by WC_f at maturity (0.01 - 0.06). These results indicated that shoot competition was a more important factor to cause cultivar difference in the reduction of final biomass by competition with E. oryzicola. Considering its great contribution to WC_f during the early growth period especially for N_>top< WC_r might be an important factor in the competition with weed of rice cultivars under crucially nitrogen-limited conditions.

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Rice grain production in a long-term unfertilized paddy field was compared with that in an adjacent paddy field which had been supplied with the standard level of fertilizers in 1980-1998 to elucidate the mechanism of maintained grain production in the unfertilized field. Average grain yield (brown rice) in the unfertilized paddy field was 382.7 g m^-2 that in the fertilized field in the adjacent field was 480.0 g m^-2 indicating that 80% of grain production was constantly maintained without supplying any nitrogen fertilizer. The amount of nitrogen absorbed by rice plants for producing 1 g grain was estimated to be 14.1 mg, 55% higher than that in the fertilized field in terms of grain production efficiency. The amount of nitrogen absorbed by rice plants per year in the unfertilized field was calculated to be 5.4 g m^-2 This amount of nitrogen should have been supplied annually to maintain the stable grain production for the period of 18 years. Quantitative analysis of nitrogen in the unfertilized field demonstrated that 1.4 g m^-2 nitrogen was supplied from irrigation water containing suspended solids, 0.68 g m^-2 biological fixation, and 9.0 g m^-2 from soil, respectively, to maintain the stable grain production. Total nitrogen of soil in the unfertilized paddy field had been maintained at a constant level during these 18 years, suggesting that grain production of around 380 g m^-2 (brown rice) could be supported without fertilization for an extended period of time.

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