The temperature dependence of the duration of a biological process can be analyzed using the Arrhenius equation. However, germination time does not precisely follow the Arrhenius equation, which is based on the assumption that temperature dependence can be explained by the behavior of one step. In the present study, to analyze germination time precisely, I assumed that temperature dependence could be explained by the behavior of multiple independent steps. According to this assumption, the germination time corresponds to the summed durations of multiple steps, and the duration of each step follows the Arrhenius equation. From these relations, I derived the s-equation, which relates germination time to changes in temperature. This s-equation method was then applied to the germination times of rice seeds at various temperatures. The results were compared to those of the classic breakpoint method, in which different Arrhenius equations are fitted to each temperature range, divided at the breakpoint temperatures. Germination time was correlated more precisely to changes in temperature, and obtained values of activation energies were more stable, with the two-step s-equation method than with the breakpoint method. These results suggest that the two-step s-equation method should be used to relate germination time to changes in temperature and that the temperature dependence of germination time involves two steps.

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In Japan, wheat-rice crop rotation with the practice of rice transplanting has been quite popular in the past. Mechanized direct-planted wheat-rice sequential cropping was developed at the Aichi Prefecture Agricultural Research Center by intercropping them for two months in spring. An objective of this study was to evaluate the introduction of continuous no-tillage to the cropping system with emphasis on water stress. The water source of intercropped wheat was also elucidated using deuterated heavy water to analyze water competition between crops. Continuous no-tillage of wheat-rice direct planting was performed for six seasons (three years) in an experimental small paddy field. No-tillage resulted in a doubled soil penetration resistance in the surface layer of soil, indicating the risk of suppressing root development. The higher yield of wheat in the dry plot suggested that excess-moisture stress occurs in the field. In the no-tillage plot, light transmission to intercropped rice seedlings increased significantly due to the reduced wheat biomass production. Wheat and rice yields were not statistically lowered by the no-tillage practice. This indicated that it is possible to introduce continuous no-tillage to the cropping system. The no-tillage significantly increased the deuterium concentrations in the xylem sap in wheat after the application of simulated rainfall with deuterated water. This indicated that the water uptake dependency of wheat shifted from stored soil water to recently applied water, which suggested the higher competition between the crops may occur under no-tillage conditions.

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A snap bean (Phaseolus vulgaris L.) cultivar Haibushi shows high productivity under high-temperature conditions. Together with intensive radiation, high temperature enhances transpiration and causes water deficit in plants even when they are irrigated enough. To characterize daily change in water balance of the heat-tolerant cultivar, we compared parameters of water balance, dry matter production and pod yield among cultivars. Four snap bean cultivars, Haibushi, Kurodane-Kinugasa, Oregon and Kentucky Wonder, were grown under optimal temperature (spring cropping) and high temperature (summer cropping) condition in the field. The daily water balance and gas exchange rate in the heat-tolerant cultivar Haibushi were compared with those in the heat-sensitive cultivar Kentucky Wonder, grown in 0.02 m² Wagner pots. In the summer cropping in the field, dry matter production, pod yield, stomatal conductance, photosynthetic rate and transpiration rate were higher in Haibushi and Kurodane-Kinugasa than in the other cultivars. In a glasshouse, the sap flow rate was lower than the transpiration rate in the morning when the transpiration rate rapidly increased in both Haibushi and Kentucky Wonder. In spite of the higher transpiration rate, Haibushi showed a higher sap flow rate and smaller cumulative water loss in the morning than Kentucky Wonder. We conclude that better growth of the heat-tolerant snap bean cultivar Haibushi under high temperature was due to higher photosynthetic rate resulting from higher stomatal conductance during the daytime, which had a higher water uptake rate.

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Effects of potassium cyanide (KCN), salicylhydroxamic acid (SHAM), and oxygen concentrations on mitochondrial respiration were investigated in purified mitochondria of a typical phosphoenolpyruvate carboxykinase (PCK) crassulacean acid metabolism (CAM) plant Ananas comosus (pineapple) and a typical malic enzyme (ME)-CAM plant Kalanchoë daigremontiana. Mitochondria of A. comosus oxidized succinate and NADH faster than that of K. daigremontiana. Succinate and NADH oxidations in mitochondria of both species were partially inhibited by KCN and SHAM, indicating that these oxidations were connected to cytochrome and alternative pathways in their electron transport chain (ETC). NADH oxidation was more sensitive to KCN than succinate oxidation, suggesting that the ETC from NADH oxidation was less connected to the alternative pathway than that from succinate in mitochondria of both species. Concurrent oxidation of succinate and NADH resulted in much higher rates of cytochrome and alternative respirations than each individual oxidation alone in both species. NADH oxidation in A. comosus mitochondria was more connected to the cytochrome pathway, so A. comosus could produce much more ATP than K. daigremontiana. This capacity might be one of the fitting mechanisms of A. comosus to produce a sufficient amount of ATP for cytosolic PCK in the daytime. In addition, the reduction of oxygen concentrations decreased not only the cytochrome respiration, but also the alternative respiration on succinate oxidation in mitochondria of both species, and the decrease was greater in K. daigremontiana than in A. comosus.

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The growth characters and productivity of the soybean plants that developed from seeds stored for various periods at 5C and 40% relative humidity, but having 80% or higher germinability were examined in comparison with those of newly harvested seeds (new seeds). The seedlings at one month after sowing from the very old seeds (stored for 10 years and 7 months) showed morphological characters significantly different from those from the new seeds, but not those from the moderately old seeds (stored for 2 years and 7 months) or the old seeds (stored for 7 years and 7 months). In the plants from the old seeds, the mean emergence date, flowering date, maturing date, length of the main stem, yield components, seed yield, and inspection-grade or protein content of seed were not significantly different from those in the plants from the new seeds. On the other hand, in the plants from the very old seeds, the mean emergence date, length of main stem, yield components and seed yield were significantly different from those in the plants from the new seeds. We concluded that the seeds of soybean stored for 2 years and 7 months, or 7 years and 7 months having a germinability of higher than 80% are practically useful, and show normal growth characters and productivity. However, it should be noted that the seed storage for over 10 years had inferior grain yield.

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Metabolic processes related to ammonium release and assimilation were investigated in a salt-sensitive rice (Oryza sativa L.) cultivar Anapurna. Ammonium content of the 3^rd leaves increased 3-4 times when seedlings were treated with 100 mM NaCl for 6 days under both growth chamber light condition and in darkness (non-photorespiration). An in vitro experiment revealed strong inhibition of protein synthesis as an effect of NaCl on the incorporation of ¹⁴C-leucine into protein. Exposure to salt stress slightly increased leaf proteolytic activity. The increase of proteolytic activity and decrease of protein synthesis, which directly causes accumulation of free amino acids, might lower the need for ammonium incorporation to form amino acids and indirectly cause the excessive accumulation of ammonium. No significant changes in the assimilatory activities of glutamine synthetase (GS; EC 6.3.1.2) and ferredoxin-dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) were found under salt stress. Salt treatment changed the balance of the direction of glutamate dehydrogenase (NAD(H); EC 1.4.1.2); the aminating (NADH-GDH) activity increased while deaminating (NAD-GDH) activity decreased. We conclude that the accumulation of ammonium under salt stress was not due to inhibition of assimilatory activity of GS/GOGAT cycle or aminating GDH. Since these enzymes require supply of C-skeleton in the form of 2-oxoglutarate, reductant and energy to function, the reduction of photosynthetic capacity and the decrease of 2-oxoglutarate might be responsible for the excess accumulation of ammonium in salt-stressed seedlings.

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Supernodulating soybean lines have more than several times as many nodules as normal cultivars. They are expected to have high nitrogen-fixing ability and enhanced productivity, but their yields have been inferior to those of normal genotypes. We have recently developed a new supernodulating cultivar, ‘Sakukei 4’ (formerly ‘En-b0-1-2’, presently ‘Kanto 100’), with improved growth and yield. The objective of the present study was to identify the characteristics of the nodulation and nitrogen-fixing ability of Sakukei 4. In pot trials, the nodule number of Sakukei 4 was 8.3 times that of a normal cultivar, ‘Enrei’, and the nodule weight per plant was 2.3 to 2.8 times the value for Enrei. The acetylene reduction activity per plant in Sakukei 4 was higher than that in Enrei and conventional supernodulating genotypes, especially during the late growth stage. Compared with conventional supernodulating lines, the improved vegetative growth in shoots and roots of Sakukei 4, especially after flowering, probably enhanced its nitrogen-fixing ability per plant. We consider that its high nitrogen-fixing ability at the seed-filling stage, would help increase its yield in fields with low nitrogen fertility.

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Supernodulating soybeans, having several times more nodules than normal genotypes, are expected to produce higher dry matter and grain yields through a higher nitrogen fixation potential. However, their growth and yield have been inferior to those of normal genotypes. We have recently developed the supernodulating genotype ‘Sakukei 4’ (formerly ‘En-b0-1-2’, presently ‘Kanto 100’), with improved growth and yield and a high nitrogen fixation potential. The objective of the present study was to examine the time course of changes in plant nitrogen content, leaf chlorophyll content (SPAD value), and photosynthetic rate of Sakukei 4 to reveal the source of its advantages in growth. The leaf nitrogen content after the flowering stage and the stem nitrogen content after the seed-filling stage were higher in Sakukei 4 than in the normal cultivar ‘Enrei’. The SPAD values in Enrei and another normal cultivar, ‘Tamahomare’, decreased rapidly after the seed-filling stage, whereas that in Sakukei 4 stayed high until the late seed-filling stage. Differences in photosynthetic rate and leaf SPAD value between Sakukei 4 and Enrei were negligible at the beginning of podding but became very clear at the seed-filling stage because of the drop in the values for Enrei. In Sakukei 4, a large amount of nitrogen might not be translocated from leaf to seed during the seed-filling stage because of the higher capability of the nodules to send fixed nitrogen to the growing seeds. Sakukei 4 could thus maintain a high photosynthetic rate and grain growth during the seed-filling stage.

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Soybean requires more nitrogen (N) than gramineous crops because it accumulates a large amount of N in seeds, and its photosynthetic rate per leaf N is low. The supernodulating genotype Sakukei 4 has a superior symbiotic N₂ fixation capability, and thereby is potentially high-yielding. In our previous study, Sakukei 4 was characterized by having a superior ability to maintain high leaf N content and high photosynthetic rate. The objectives of this study were to know photosynthetic characteristics of Sakukei 4 in detail, especially, the responses to CO₂ concentration and light intensity, and to elucidate how the photosynthetic characteristics of Sakukei 4 are associated with the amounts of photosynthesis-related N compounds (chlorophyll and Rubisco). The three genotypes (Sakukei 4 - supernodulating cultivar derived from Enrei, Enrei - normally nodulating cultivar, En1282- non-nodulating line derived from Enrei) were grown at various N levels in this study. The CO₂ exchange rate (CER) in Sakukei 4 was higher than, or equal to that in Enrei at wide ranges of CO₂ concentrations (150-700 mmol mol^-1) and light intensities (200-1,500 mmol m^-2 s^-1 PPFD). Sakukei 4 had higher leaf N (N_L), chlorophyll (Chl_L) and Rubisco (Rub_L) contents per leaf area, but lower chlorophyll and Rubisco contents per leaf N content (Chl_L/N_L, Rub_L/N_L) than Enrei. The specific leaf weight (SLW) and leaf area trended to be lower in Sakukei 4 than in Enrei. These results indicate that the superior photosynthetic rate in Sakukei 4 is attributed to higher total N, chlorophyll and Rubisco contents per leaf area, but not to high rate of allocation of total N to these N compounds.

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The morphological plasticity of roots in nutrient-enriched patches of soil is regarded as an adaptive response in plants, but its functional efficiency is still debatable. We examined whether the efficiency is dependent upon the patch size, or the amount of phosphate (P) supplied in maize (Zea mays L.). Two levels of P-input (high and low) and three patch sizes (large, medium and small) were used in various combinations in containers filled with soil. Irrespective of the P-inputs, P uptake and biomass were greatest in large patches together with root proliferation restricted to the soil inside patches, indicating that the effect of P-patch size was stronger than the amount of P supplied. Due to the fine root proliferation (about 0.5mm-width) of higher specific root length, the root length promoted was not accompanied by more biomass investment inside the patches. For the medium and small patches, such a localized root proliferation disappeared, resulting in impaired plant growth with limited P acquisition. It was concluded that the efficiency of the root plasticity on P acquisition depends on the size of P patches more strongly than the inputs.

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In semi-arid areas, pearl millet is an important staple food crop that is traditionally intercropped with cowpea. This study evaluated the water competition between pearl millet and cowpea using deuterated water. At vegetative stage, pearl millet biomass production was lower in the pearl millet-cowpea (PM-CP) combination than in the pearl millet-pigeon pea (PM-PP) and pearl millet-bambara nut (PM-BN) combinations. PM-CP used more water than PM-PP and PM-BN under well-watered conditions; however, all combinations used similar amounts of water under dry conditions. The biomass production, photosynthetic rates, transpiration rates, and midday leaf water potential of pearl millet at early flowering stage were not significantly reduced by mixed planting with cowpea sown two weeks later as compared with single planted pearl millet. When pearl millet and cowpea were sown at the same time, mix planting significantly increased the recovery rates of recently irrigated heavy water in pearl millet, but not in cowpea in both vegetative and early flowering stages. Midday leaf water potential and transpiration rates in pearl millet were lowered by mixed planting but those in cowpea were not. These indicate that the water source of pearl millet is shifted to the recently irrigated and easily accessible water. By contrast, when cowpea was sown two weeks later than pearl millet, this trend was not observed. These results provide new evidence on water competition in the PM-CP intercropping system; cowpea has higher ability to acquire existing soil water than pearl millet when both crops are sown at the same time.

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Submergence induces rapid elongation of internodes in floating rice (Oryza sativa L.). We examined the distributions of p-coumaric, ferulic and 5-5-coupled diferulic acids ester-linked to cell walls along the axis of highest internodes of submerged and air-grown floating rice stem segments. The amounts of ferulic and 5-5-diferulic acids per cell wall weight were lowest around the intercalary meristem, and increased as the distance from the meristematic zone increased toward the upper part of the internode in both air-grown and submerged stem segments. The ratio of 5-5-diferulic acid to ferulic acid also increased toward the upper, old parts of internodes in both air-grown and submerged stem segments. These observations suggest that the feruloylation of cell wall polysaccharides and the formation of diferulic acids contribute to the cessation of internodal cell elongation and that the formation of diferulic acids in cell walls is controlled by the coupling reaction in addition to the feruloylation. The amounts of p-coumaric acid per unit length and per cell-wall weight were markedly low in the newly elongated region of submerged internodes, and closely correlated with cell-wall dry mass in both air-grown and submerged internodes, suggesting that the deposition of p-coumaric acid in cell walls is related to the formation of secondary cell walls in floating rice internodes.

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We examined the involvement of p-coumaric, ferulic and 5-5-coupled diferulic acids ester-linked to cell walls in determining the elongation rate of internodes of floating rice (Oryza sativa L.). When floating rice stem segments were exposed to air after 2 days of submergence, the elongation rate of internodes was reduced and the degree of reduction was greater in the light than in the dark, while the internodes of stem segments submerged further for a comparable period continued rapid elongation. The amounts of ferulic and 5-5-coupled diferulic acids in the cell walls in the elongation zone of internodes significantly increased during the first day after exposure to air either in light or darkness. The increase of these phenolics in the cell walls after exposure to air was also observed on the second day in light, but not in darkness. On the other hand, the amount of p-coumaric acid increased only slightly on the first day after exposure to air, but rapidly on the second day in light. This pattern of change in the amounts of p-coumaric acid resembled that in the cell-wall mass (dry weight). The application of sucrose to the segments in darkness increased the amounts of phenolics in the cell walls of internodes to almost the same amount as those in light. These results indicate that the accumulation of ferulic and 5-5-coupled diferulic acids in cell walls may be related to the cessation of internodal elongation in floating rice and that the synthesis of phenolics in the cell wall is caused partially by the provision of sugar in light.

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Pearl millet is better adapted to hot and semi-arid conditions than most other major cereals. The objective of this study was to compare the deep water uptake ability and water use efficiency (WUE) of pearl millet among millet species. First, the WUE of six millet species was evaluated in pots under waterlogging, well-watered (control), and drought conditions. Secondly, the water uptake from deep soil layers by pearl millet and barnyard millet, which showed the highest drought and waterlogging tolerance, respectively, was compared in long tubes which consisted of three parts (two loose soil layers separated by a hardpan and a Vaseline layer). Soil moisture was adjusted to well-watered and drought conditions in the upper (topsoil) layer, while the lower (deep) layer was always kept wet. WUE was significantly reduced in all millet species by waterlogging but not by drought. The ratio of WUE to the control condition indicated that pearl millet had the highest and lowest resistances to drought and waterlogging conditions, respectively, while barnyard millet was the most stable under both conditions. The deuterium concentration in xylem sap water, relative water uptake from deep soil layers, and water uptake efficiency of deep roots were significantly increased in barnyard millet but not in pearl millet by drought in topsoil layers. In conclusion, the drought resistance of pearl millet is explained by higher WUE but not by increased water uptake efficiency in deep soil layers as compared to barnyard millet, another drought-resistant millet species.

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By successive crossing using Hattan-type varieties originating from "Hattanso" as a parent, "Hattan-type varieties" of rice suitable for brewing the original Hiroshima sake have been bred. The varieties were improved inheriting the flavor of Hattan-type sake, and Hattan-nishiki No.1 and No.2 were bred in 1984. However, neither variety was suitable for brewing high-grade sake such as Ginjoshu and Daiginjoshu, which require high-degree polishing of rice grains. Therefore, their parent cultivar, Hattan No. 35, is attracting attention for the production of high-grade sake. We have been trying to breed a new variety, which retains the sake-brewing suitability of Hattan-type varieties but can endure high-degree polishing. In this study, to establish a guideline for further breeding, we examined the polishing characteristics and suitability for sake brewing of six Hattan-type varieties derived from Hattanso. In the process of breeding of "Hattan-type varieties" of rice, grain size, white-core size and % of white-core grains increased resulting in an increased suitability for sake brewing, such as water absorptivity and digestibility, in Hattan No.35, Hattan-nishiki No.1 and Hattan-nishiki No.2. However, Hattan-nishiki No.1 and No.2 had many ellipsoidal-white-cores with large white tissue, which cause the grains to be easily broken during high-degree polishing. On the other hand, Hattan No.35, having grains with relatively many lined-white-cores with small white tissue, was superior for high-degree polishing. In the future, breeding of a new variety, which has the superior cultivation characteristics of Hattan-nishiki No.1 and No.2, but with improved white-core characteristics, is expected.

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The effect of soil moisture and temperature on decomposition of waste materials, bagasse, coir dust, rice chaff and rice straw, in soil were examined by measuring the decrease in weight of and CO₂ generation from each waste material. The rate of the decrease in weight increased as temperature rose, and was highest in rice straw followed by bagasse, rice chaff and coir dust in this order, irrespective of soil moisture and temperature level. In all waste materials, the rate of decrease in weight was highest in the soil holding the water equivalent to field capacity (saturated soil) followed by submerged soil and dry soil in this order. CO₂ generation rate was also highest in rice straw followed by bagasse, rice chaff and coir dust. It was highest in saturated soil followed by half-saturated or submerged soil and dry soil in this order. The rate of CO₂ generation from rice straw in saturated soil was highest at the initial period of incubation and it decreased thereafter, but the rate in submerged soil was highest at 40 and 20 days after the start of incubation at 20 and 35°C, respectively. The rate of CO₂ generation from coir dust and rice chaff was very low at all soil moisture levels at either 20 or 35°C. The content of total N in the waste materials was positively and significantly correlated with the rate of decrease in weight in saturated and submerged soils at a moderate temperature (Oct.—Dec.), and in submerged soil at a high temperature (Aug.—Oct.). It was also significantly correlated with CO₂ generation rate in submerged soil at 20°C. Holocellulose and hemicellulose contents were negatively and significantly correlated with CO₂ generation rate in dry soil at 20°C. Lignin content was also significantly and negatively correlated with CO₂ generation in dry soil at 35°C.

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We evaluated growth, yield and quality of turmeric (Curcuma longa L.) cultivated in pots with dark-red soil (pH 5.2), gray soil (pH 7.4) and red soil (pH 4.4) in Okinawa, Japan. The soils were collected from the 50-cm deep layer of the fields. We did not use any chemicals or organic fertilizers. Turmeric cultivated on dark-red soil had the highest plant height, root biomass and shoot biomass as compared with that cultivated on other soil types. Turmeric on dark-red soil had the highest yield with favorable color of the deep yellow and high curcumin content (0.20%). Protein content of turmeric in dark-red soil was 5.2%, which was around 40% higher than that in other soil types. Turmeric cultivated on dark-red and gray soils had a fat content 71% higher than that in red soil. The content of Ca, K and Mg was the highest when turmeric was cultivated on gray soil, and Fe was the highest when cultivated on dark-red soil. To gain a high yield and high contents of curcumin, fat, protein and Fe, we should cultivate turmeric in dark-red soil in Okinawa. We could not recognize the specific soil factor(s) required for high yielding and high quality of turmeric; however, it seems that a proper combination of soil factors, nutrients and/or pH level may be necessary to gain a high yield and high quality.

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To reduce water requirement and improve water productivity (the grain yield per unit volume of water irrigated) by water-saving irrigation techniques, we examined the effects of very shallow intermittent irrigation (VSII, 2cm), shallow intermittent irrigation (SII, 4cm) and traditional deep water irrigation (DWI, 10cm) on rice growth and yield in the field for two years. The amount of water irrigation during the rice-growing period (average of two years) was 318, 391 and 469 mm in VSII, SII and DWI, respectively. Rice growth and grain yield were not significantly influenced by the treatments. As the irrigation water input decreased, the water productivity increased. The water productivity increased by 46 % in VSII and 20 % in SII on the average as compared with DWI. The shallower the irrigation depth, the lower the breaking weight and the higher the lodging resistance, and the deeper the roots in the paddy soil. In DWI, the percentage of head rice was lower and the protein content was higher, suggesting deterioration in the palatability of cooked rice due to the increase of chalky rice. The water-saving rate was 32.9 % in VSII and 17.2 % in SII as compared with typical deep water irrigation in Korea.

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