Doubled haploid lines (DHLs) of rice (Oryza sativa L.) were used to examine responses to drought and rewatering in controlled rainfed lowland conditions, in order to determine whether confounding by unrelated traits would be less than has been reported previously for contrasting cultivars that differ in genetic background. IR62266 and four DHLs derived from the cross between IR62266 and CT9993 (DHL-32, -51, -54 and -79) were grown in pot experiments in the greenhouse during the 2000 dry and wet seasons at IRRI, Los Baños, Philippines. There were two water regimes (well-watered and drought). Estimated water extraction obtained by time domain reflectometry (TDR) was similar to cumulative transpiration estimated from pot weighing for each genotype. Genotypic variation was observed in root traits and water extraction, with extraction slower in DHL-32 and faster in DHL-79, especially in deeper soil layers. An upper bound relationship between water extraction from a soil layer and root length density (RLD) in that layer was readily apparent over DHLs and soil depths, suggesting a critical value of RLD for water extraction of 0.30 cm cm^-3 in these conditions. Because soils in the field would not be as homogenous as the puddled soils used in these greenhouse experiments, this critical RLD for water extraction from a soil layer is a reference for ideal conditions, and requires careful validation in the field. Use of DHLs permitted comparisons with reduced confounding by genetic background, with consequent improvements in precision.

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High germinability of seeds and establishment of young seedlings in rice (Oryza sativa L.) are necessary for direct seeding in paddy fields. We investigated whether germinability and seedling growth were promoted by treatment of rice seeds (cv. Hitomebore) with hydrogen peroxide solution (H₂O₂) during the imbibition for 24 h. H₂O₂ treatment with 50 mM H₂O₂ promoted seed germination, and seedling growth (shoot length, root length and shoot fresh weight) in agar culture under a low temperature condition (18°C day/14°C night). Seedling growth was promoted by H₂O₂ treatment not only under the low-temperature condition but also under a normal (23°C day/18°C night) temperature condition. Furthermore, H₂O₂ treatment promoted seedling growth under a flooding condition in a greenhouse. These results suggest that H₂O₂ treatment of rice seeds during the imbibition is advantageous for direct seeding. We discussed the relation between the promotion of the seed germinability and the seedling growth under a low-temperature condition, and the expression of some genes encoding ROS scavenger enzymes induced by H₂O₂ treatment.

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We examined the differential elongation of gravitropically bending roots of Pisum sativum L. in terms of cell enlargement and water uptake by cells in the growing tissue. Hydraulic conductivity between the elongating and mature tissues (Lp) was estimated from the equation G = A × Lp × ΔΨ, where G is the water-uptake rate, A is the surface area of a single cell and ΔΨ is the driving force. The rate of entry of water into a cell was estimated from the rate of increase in the volumes of cells in the outer cortex, which were calculated from longitudinal sections at given times. Gravitropic bending occurred 1 h after the application of gravi-stimulation and the curvature increased rapidly for the next 3 h. The biggest difference in the partial elongation rate between opposite sides of a root was found in the region 3 to 4 mm from the root tip at the start of stimulation. Cell enlargement rate was 2.8 to 3.8 times greater on the upper side of the root than on the lower side. The water potential and the osmotic potential, in both the elongating and mature tissues, were the same on both sides of the root. Therefore, there was no difference in the driving force for water flow. Hydraulic conductivity was 2.3 to 4.2 times greater on the upper side of the root than on the lower side. There was no difference between the upper and lower sides of the root in the amounts of 19-kD and 24-kD proteins in membrane fractions, which we assumed to be aquaporins (putative aquaporins), as estimated with two preparations of polyclonal antibodies. The differential elongation that occurred during root gravitropism was caused by a difference in Lp. However, the difference in Lp did not appear to be regulated by the concentration in cell membranes of the putative aquaporins.

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Common buckwheat (Fagopyrum esculentum Moench cv. Shinano No.1) and Tartary buckwheat (F. tataricum (L.) Gaertn. cv. Nepal) were grown in pots to examine their responses to soil flooding. Flooding treatment was carried out during the early growth stage by completely submerging the pots in a nutrient solution from 12 to 36 days after sowing. The plant growth rate, relative growth rate and mean leaf area under the flooding treatment were reduced to 72, 90 and 83% of the control, respectively, in Shinano No.1, and to 29, 71 and 45% of the control, respectively, in Nepal. The excess moisture stress had no effect on the net assimilation rate (NAR) in Shinano No.1, but lowered the NAR to 68% of that in the control in Nepal. Excess moisture stress decreased the total leaf area to 76 and 34% of the control in Shinano No.1 and Nepal, respectively. Leaf growth rate, number of leaves and leaf area per leaf, which influenced the total leaf area, were reduced by the excess soil moisture. The relative water content of leaves was unchanged in Shinano No.1, but was decreased in Nepal. Reduction in bleeding from the cut end of stem due to flooding was greater in Nepal than in Shinano No.1. Excess moisture stress reduced the K⁺ concentration of the stem and increased the Na⁺ concentration of leaves, stem and roots more strongly in Nepal than in Shinano No.1. Development of adventitious roots in the surface layer of the nutrient solution was better in Shinano No.1 than in Nepal. In conclusion, Shinano No.1 (common buckwheat) had a stronger tolerance to excess soil moisture than Nepal (Tartary buckwheat). In Shinano No. 1, leaf growth and photosynthetic rate were not markedly affected and the capacity of absorbing water and nutrients was retained by developing adventitious roots in the solution above the surface of the soil keeping proper physiological activity under excess moisture conditions.

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Common buckwheat (Fagopyrum esculentum Moench cv. Tsushima) and Tartary buckwheat (F. tataricum (L.) Gaertn. cv. Pontivy) were grown in a nutrient solution with or without added NaCl to investigate interspecific differences in their responses to salinity, based on their dry-matter production. The mechanism of salt tolerance was also studied. Addition of 100 mM NaCl to the culture solution (salt treatment) lowered the plant growth rate to 48% and 16% of the control in Tsushima and Pontivy, respectively, and decreased the net assimilation rate and mean leaf area of Pontivy more severely than in Tsushima. The salt treatment decreased the leaf growth rate and leaf area per leaf to 30% and 72% of the control, respectively, in Tsushima, and to 12% and 52%, respectively, in Pontivy. It decreased the photosynthetic rate to 67% and 35% of the control, and stomatal conductance to 25% and 15% of the control in Tsushima and Pontivy, respectively. It also decreased the transpiration rate to 41% and 30% of the control in Tsushima and Pontivy, respectively, and increased the wateruse efficiency 1.6 times in Tsushima, but did not influence the wateruse efficiency in Pontivy. In the saline solution, the accumulation of Na⁺ in leaves and stem was greater in Pontivy than in Tsushima, but that in the roots, was greater in Tsushima than in Pontivy. In both species, Na⁺ accumulated rapidly in the leaves after removal of the roots in the saline solution. We conclude that the difference in salt tolerance between common and Tartary buckwheat may result from the difference in accumulation of Na⁺ in leaves and absorption of Na⁺ by the roots.

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We found that several BC₂F₄ lines had high leaf photosynthetic rates under light-saturated and ambient CO₂ conditions. These lines are progenies of BC₂F₁ plants with high photosynthetic capacities which were generated by backcrossing between Oryza rufipogon (W630) and O. sativa cv. Nipponbare, as a recurrent parent. Some photosynthetic characteristics of the BC₂F₄ lines were investigated to identify the factors increasing photosynthetic rates. Photosynthetic rates of these lines under light-saturated conditions at 50 to 700 ppm CO₂ concentrations were higher than those in Nipponbare. The estimated-maximum photosynthetic rates under light-saturated and CO₂-saturated conditions in BC₂F₄ lines were also higher than that in Nipponbare. The photosynthetic rate under light-saturated and ambient CO₂ conditions was positively correlated with the carboxylation efficiency as an indicator of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity in vivo rather than stomatal conductance. Initial and total Rubisco activities in vitro tended to be higher in the BC₂F₄ lines than in Nipponbare. The content of active Rubisco calculated from the activation state of Rubisco was also higher in the BC₂F₄ lines than in Nipponbare. These results suggest that high photosynthetic capacities of BC₂F₁ plants can be maintained high in their progenies and high photosynthetic rates under light-saturated and ambient CO₂ conditions in the BC₂F₄ lines are achieved mainly by the high activity of Rubisco due to the high active Rubisco content.

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In rice plant, carbohydrates accumulated in leaf sheaths before heading are translocated to grain and affect yield formation greatly. To clarify the intrinsic mechanism of carbohydrate metabolism in the leaf sheath, we investigated the temporal and spatial variations of carbohydrate metabolism in the third leaf sheath counted from the top and their varietal differences. The results revealed that the amount of carbohydrate decreased from the base to the tip of the leaf sheath, irrespective of variety and developmental stage. However, the proportion of starch content in the basal one-fifth of the leaf sheath to that in the whole sheath varied from 35% to 60% with the variety. Comparing the activities of enzymes related to starch metabolism at the base, middle and tip of the leaf sheath in IR65598-112-2 (New plant type) with those in Nipponbare, the activities of ADP-glucose pyrophosphorylase, branching enzyme and granule-bound starch synthase (GBSS) showed varietal differences. Particularly, the activity of GBSS may play an important role in the varietal difference in spatial variation of starch content in the leaf sheath. In IR65598-112-2, the sucrose content in the leaf sheath was extremely high, suggesting that sucrose may be one of the carbohydrate reserves in this line.

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The difference in rooting pattern between two grain sorghum cultivars differing in drought tolerance was investigated under drought stress. The cultivars, Gadambalia (drought-tolerant) and Tabat (drought-susceptible), were grown in bottomless wooden or acrylic root boxes to examine root parameters. Gadambalia consistently exhibited higher dry matter production and leaf water potential than Tabat under drought stress in both root boxes. In the experiment with wooden root boxes, under a drought condition, Gadambalia extracted more water from deep soil layers (1.1-1.5 m), which was estimated from the reduction in soil water content, than Tabat. This was because Gadambalia had a significantly higher root length density in these soil layers. The high root length density was due to enhanced lateral root development in Gadambalia. In the other experiment with acrylic root boxes, though total root length in the upper soil layer (0-0.5 m) was declined by limited irrigation in both cultivars, the reduction in Gadambalia was moderate compared with that in Tabat owing to the maintenance of fine root growth. Unlike Tabat, Gadambalia had an ability to produce the nodal roots from higher internodes even under drought, which resulted in the high nodal root length of Gadambalia. The growth angle of nodal roots was significantly correlated with root diameter, and the nodal roots from the higher internodes had large diameters and penetrated into the soil more vertically. These results indicate that the responses of roots (i.e. branching and/or growth of lateral root, and nodal root emergence from higher internodes) to soil dryness could be associated with the drought tolerance of Gadambalia.

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The changes in chloroplast ultrastructure and the contents of chlorophyll, Na and K in response to salinity stress were investigated in leaves of maize, an NADP-malic enzyme-type C₄ plant species possessing dimorphic chloroplasts. The seedlings were treated with 0, 1, 2 or 3% NaCl for three or five days under a light or dark condition. In both light and dark conditions, the dry weight of salt-treated plants decreased as NaCl concentration increased. Chlorophyll and K contents of the second leaf blade decreased as NaCl concentration increased under the light condition but not under the dark condition. Na content of the second leaf blade was significantly higher at high NaCl concentrations under both light and dark conditions. However, Na content was much lower under the dark condition than light condition. Higher concentrations (2 and 3%) of NaCl significantly increased the size of plastoglobules, decreased the number and size of starch granules and altered the chloroplast ultrastructure. Under the light condition, mesophyll cell (MC) chloroplasts appeared more sensitive to the damaging effect of salinity than the bundle sheath cell (BSC) chloroplasts. MC chloroplasts became more globular in shape and showed swollen and disorganized thylakoids and reduced thickness of grana by salinity. BSC chloroplasts were less affected by salinity than MC chloroplasts. Although chloroplast size and number and size of starch granules were reduced, there was no structural distortion in the thylakoids of BSC chloroplasts. However, the thickness of grana was increased by salinity. Under the dark condition, the chloroplast structure was less affected by salinity. Though the envelope of BSC chloroplasts was occasionally damaged, the thylakoids in both MC and BSC chloroplasts were preserved under salinity stress. The present study suggests that the chloroplast damage caused by salinity is light-dependent and MC chloroplasts are more sensitive to salinity than BSC chloroplasts.

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Wheat cultivar Jing 411 which is susceptible to powdery mildew, and wheat cultivar Brock and NILs of Jing 411, which are resistant to powdery mildew were analysized for polymophisms using 213 random amplified polymorphic DNA primers. Only one primer (S2092) stably produced a polymorphic band between the resistant and susceptible plants. Linkage analysis of this marker (S2092₉₇₂) revealed that the polymorphism existed in a 131 F₂ segregating population. S2092₉₇₂ was closely linked to a powdery mildew resistance gene in wheat cultivar Brock, at a linkage distance was 4.9 cM. S2092₉₇₂ was converted to sequence characterized amplified region (SCAR) markers SCAR₈₆₀ and SCAR₂₀₀. The two SCAR markers were used for detecting F₂ segregating population. SCAR₈₆₀ and SCAR₂₀₀ existed in resistant plants but were absent in the susceptible plants. We concluded that S2092₉₇₂ was located on the chromosome 3BL. These markers will be useful for marker-assisted selection and gene pyramiding in wheat resistance breeding.

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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. In this study, the difference in the properties of starch and protein among the Hattan-type varieties was examined. Six Hattan-type varieties, Hattanso, Hattan No.10, Hattan No.35, Hattan No.40, Hattan-nishiki No.1 and Hattan-nishiki No.2, were used. As the properties of starch, amylose content, pasting properties and gelatinization properties were examined. The pasting and gelatinization properties were examined using a rapid viscoanalyzer (RVA) and a differential scanning calorimetry (DSC), respectively. As the properties of protein, the compositional ratio of two types of protein bodies (PB-II/PB-I) was analyzed. However, no significant differences in the above properties were observed among these Hattan-type varieties. The above properties of starch and protein in Hattanso seem to be retained in all of these varieties. In these varieties, breeding might not have been aimed at improvement of the properties of starch and protein.

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This research was conducted to determine the yield and water-use efficiency of maize under fixed and variable alternate furrow irrigation (fixed AFI, variable AFI) and every furrow irrigation (EFI) at different irrigation intervals in areas with shallow and deep groundwater. In variable AFI, water was applied to the furrow, which was dry in the previous irrigation cycle. The results indicated that even at 4-day irrigation intervals the water needs of maize on a fine textured soil in both areas (with deep and shallow water table) are not met by AFI. The decrease in grain yield due to water stress was mainly due to the decrease in the number of grains per cob and to a lesser extent to the decrease in 1000-grain weight. At the Kooshkak site with shallow groundwater (between 1.31 and 1.67 m), grain yields in AFI at 4- and 7-day intervals were comparable to those obtained in EFI at 7- and 10-day intervals, respectively. This might be due to the contribution of groundwater to the water use of the plant (about 5-10%). In the Badjgah area, with deep water depth, grain yield in AFI at 7-day intervals was statistically lower than that obtained in EFI at 10-day interval. In AFI, a shorter irrigation interval (4-day) may alleviate the water stress and result in no yield reduction compared with that in EFI at 7-day intervals even though water application was reduced. Furthermore, in the area with a shallow water table, AFI at 7-day intervals may be superior to EFI at 10-day irrigation intervals. When seasonal irrigation water is less than 700 mm, it may be preferable to use AFI at 10-day intervals to increase water-use efficiency, especially in areas with shallow groundwater. In general, when water was insufficient for full irrigation, the relative grain yield (yield per unit water applied) of maize under AFI was higher than those under EFI.

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We have studied establishment of cultivation technique of sweet sorghum for monosodium glutamate (MSG) production on dry land in Indonesia, where the supply of raw materials has become restrictive recently. Previously, we confirmed the feasibility of cultivation in this area during the rainy season. Meanwhile, cultivation during the dry season is also important because vast expanses of heretofore unirrigated fields have remained unused. The stem, which comprises internodes, is the main product of sweet sorghum used as a raw material by fermentation industries. This study analyzes differences in growth and yielding ability between dry and rainy seasons by comparing internode characteristics. A sweet sorghum cultivar – Wray – was cultivated in the rainy season from 1995 and in the dry season of 1996 in Madura Island of East Java, Indonesia. Stems of sweet sorghum cultivated during the dry season were shorter and lighter, with two fewer elongated internodes than those of plants raised during the rainy season. They accumulated sugar slower and to a lower peak, but they were inferred to be harvestable for a relatively long period during 30–60 days after anthesis. Through research of internode characteristics, the difference in stem length was inferred to result from differences in internode numbers (25%) and in individual internode length (75%). The difference in weight seemed to result mainly from the fewer elongated internodes. Further experiments must explore the cultivation period (sowing and ratoon crop), varieties, and planting density to establish a sweet-sorghum cultivation technique that is suitable for the dry season.

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To develop a new fertilizing system with a reduced amount of phosphatic fertilizer in sweet corn production, we applied potassium phosphate to the plug seedlings before transplanting to the field, and examined its effects on growth, yield, photosynthetic activity and absorption of minerals. The amount of phosphatic and potash fertilizers necessary to grow sweet corn could be reduced by the pre-transplanting KP application (PTKPA) to the plug seedlings. We considered the mechanisms involved in the reduction of P and K application rate by PTKPA as follows; 1) PTKPA increased the P content of plant, which accelerated the root establishment. 2) The advanced root establishment not only reduced the duration of water stress, but also increased absorption of the essential nutrients such as N and Mg. 3) Higher content of N and Mg led to higher chlorophyll content and possibly protein content, which activated photosynthesis during the early growth stage. 4) Improved photosynthetic activities increased NAR during the early growth stage. 5) This increase in NAR accelerated leaf expansion, increasing LAI. 6) Larger LAI during the early growth stage led to larger LAI throughout the growing stage, resulting in a higher CGR and ear yield.

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