Changes in gene expression patterns by high nitrogen (High-N) and High-N plus cooling at the young microspore stage (High-N-cooling) in rice mature anthers were analyzed by semiquantitative RT-PCR with gene specific primers. Gene expression of alpha-expansin 18 (EXPA18)was repressed under High-N-cooling. Beta-expansin 1 (EXPB1), putative aldehyde dehydrogenase (ALDH) and Fructokinase II (FKII) were upregulated under High-N. EXPB1 and FKII were highly expressed under High-N-cooling. Comprehensive examination of gene expression patterns of 26 alpha-expansins (EXPAs) and 16 beta-expansins (EXPBs) showed that all expansins(EXPs)except EXPA12 were expressed in the anthers. Gene expression of EXPs did not change under High-N except EXPA1, EXPB1 and EXPB5 which were upregulated. In total, 18 EXPAs and 6 EXPBswere repressed under High-N-cooling, and among these, EXPA18, EXPA19 and EXPA20 had high similarities in the amino acid sequences, suggesting that these three genes may constitute a distinct functional gene subfamily related to the decrease in the pollen germination ability.
We found a symptom of abnormally early ripening in a farmer’s field in Natajima, Yamaguchi Prefecture, Japan, in 2004/2005, and examined its physiological mechanisms for two weeks until maturity. In the following two seasons, 2005/2006 and 2006/2007, we examined the mechanisms throughout the grain filling period at another farmer’s field where the symptoms appeared in the preceding four seasons. The grain yield was lower in abnormally early ripening (AER) than in the normal because of lighter grain weight in 2004/2005. The grain weight and water soluble carbohydrate, WSC, in culm were similar at the beginning of symptom, two weeks before maturity, then the grain weight increased and WSC in culm decreased more sharply in the normal than in the AER. So the grain weight was poorer and more WSC in culm remained unutilized at maturity in the AER. Another field showed the symptom of AER in both seasons. The spike dry weight and WSC in culm were the similar between the treatments from anthesis to milk ripe stage in 2005/2006, then they showed almost similar pattern in their change as in 2004/2005 until maturity. It was thought that the slower grain growth in later phase might be due to limited current assimilation and poor remobilization of culm reserves to the grains in AER.
Effects of nitrogen (N) deficiency on photosynthetic gas exchange and photosystem II (PSII) photochemistry of flag leaves during grain-filling stage were investigated in six rice cultivars, Kasalath (a conventional indica), IR36 (an improved indica), Shirobeniya (a conventional japonica), Nipponbare (an improved japonica), Akenohoshi (an improved japonica-indica intermediate type) and BSI429 (an improved tropical japonica, a new plant type line) grown hydroponically in N-sufficient (NS) and N-deficient (ND) solution. From 3 to 24 days after heading (DAH), net photosynthetic rate (PN), maximum quantum yield of photosystem II (PSII) (Fv/Fm), quantum yield of PSII electron transport (ΦPSII), and contents of chlorophyll (Chl) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in the flag leaves decreased, particularly under the ND condition in all six cultivars. A substantial difference was observed among the ND plants for the sustainability index (SI, the ratio of the value at 24 DAH to that at 3 DAH) of PN, Fv/Fm, ΦPSII, Chl content and Rubisco content; SIs of those parameters of Akenohoshi, BSI429, Nipponbare and Shirobeniya were higher than those of IR36 and Kasalath. The SI of PN showed significant positive correlations with those of Fv/Fm, ΦPSII, and the contents of Chl and Rubisco under the ND condition. It was concluded that the sustainability of photosynthesis in the flag leaves was mainly due to those of PSII photochemistry and electron transport, which was associated with the maintenance of Chl and Rubisco under the ND condition.
A two-band digital imaging system —one band for the visible red band (RED, 630−670 nm) and the other for the near infrared band (NIR, 820−900 nm)— was devised and positioned at a height of 12 m above a rice field of 300 m2 in area during the 2007 growing season. The imaging system automatically logged bird’s-eye view images at 10-min intervals from 0800−1600 every day. Radiometric corrections for the pairs of two-band images were done using solar irradiance sensors and preceding calibrations to calculate daily band-reflectance and the normalized difference vegetation index (NDVI) values for 9 plots of rice plants, with 3 levels of planting density and basal fertilization. The daily- averaged reflectance values in the RED and the NIR bands showed different but smooth seasonal changing patterns according to the growth of plants. At the maximum tiller number and the panicle formation stages, the RED and NIR reflectance values had correlation coefficients (r) of 0.79 and 0.81 with above-ground nitrogen absorption per unit land area (NA, g m-2), respectively, whereas the NDVI using the two band reflectance values showed r-value of -0.13. An empirically derived equation for the NA using two band reflectance values showed r-value of 0.96 and a root mean square of error (RMSE) 0.5 g m-2 (10% of the mean observed NA) in the estimation for the original (not validated) data set acquired at the maximum tiller number and the panicle formation stages. The results indicated that reflectance observation in the RED and NIR bands using the digital imaging system was potentially effective for assessing rice growth.
A spectral-image observation technique to measure the reflectance information of rice plant organs (instead of the overall canopy) under either daylight or artificial light at night was developed, and examined for its usefulness as a method for the in-situ assessment of leaf greenness and grain quality during the ripening period. Generally, conditions are less significant for nighttime measurement since cloudiness does not affect the nighttime observations, and the evening calm helps extend the practical observation hours. A digital imaging system corresponding to the wavelength range of 450 nm to 720 nm, at intervals of 10 nm, collected spectral reflectance images of ripening rice-paddy plots on three clear days in daylight and during the night, respectively. The imaging system observed the rice canopies illuminated by the sun during the daytime and with two 100-W xenon lamps at night on each day. The reflectance values observed at several points on the illuminated leaves and panicles were normalized using the mean and the standard deviation for each spectrum. The normalized reflectance (NR) spectra obtained in the day and night agreed well with each other for the same target organs. Exemplary estimation trials for leaf greenness (SPAD value) using the NR spectra, and correlation analyses between 1000-grain weight of harvested rice grains and the NR spectra indicated that nighttime measurement could substitute for daytime measurement.
We investigated the mechanisms of increased sensitivity to Na+ in the apical and basal regions of the rice leaf under salinity. Three-week-old plants were treated with 200 mM NaCl in hydroponic culture for 3 d. Segments 6 cm in length were obtained from the apical and basal regions of the fully expanded uppermost leaves (6th leaf blades) as old and young tissues, respectively. In the plants exposed to 200 mM NaCl, Nitro blue tetrazolium (NBT) reducing activity, and H2O2 and Malondialdehyde (MDA) contents significantly increased, accompanied by the swelling of thylakoids and destruction of thylakoid membranes in the apical regions. However, no indication of oxidative damages was observed in the basal region, even though the Na+ content in the basal region was comparable to that in the apical region. In the apical region, the capacity to scavenge H2O2 was lower than that in the basal region due to decrease in the constitutive levels of ascorbate peroxidase and guaiacol peroxidase. In addition, the activities of antioxidant enzymes except superoxide dismutase and guaiacol peroxidase decreased drastically after 48 hr of exposure to NaCl. By contrast, the activities of catalase and glutathione reductase in the basal region increased compared with those in the control, and other antioxidant enzymes did not decrease under salinity during the experimental period. These results suggest that the capacity to scavenge reactive oxygen species decreased with age, and thus the apical region of the leaf blade suffered severer damage by Na+ than the basal region.
We introduced subsoiling to a field of wheat-soybean rotation where no-tillage practice had been conducted for five years and whose yield tended to decrease or stagnate. By subsoiling a half of each plot just before wheat sowing, treatments of tillage/no-tillage × subsoiling/no-subsoiling were established. Root distribution, shoot growth, water uptake and yield of both crops were examined to elucidate whether the subsoiling improves the productivity such as shoot biomass and yield through the modification of root system development, and how differ the effects of subsoiling between tilled and non-tilled fields. In wheat, roots were less concentrated in surface (0−5 cm) layer in no-tillage, and distributed more in deep (20−25 cm) layer of the soil. Deuterium labeled heavy water analysis revealed that the subsoiling enhanced water uptake from the deep soil layer in the no-tillage field. Both the no-tillage and subsoiling showed positive and significant effect on total biomass and yield. The effect of subsoiling must be related to water supply by deep roots in spring. In soybean no-tillage significantly increased the productivity, but subsoiling did not though distribution of the roots was modified by both practices. Soybean in non-tilled accumulated roots in the surface soil layer, but subsoiling did not significantly modify the root distribution especially in the deep soil layer. Water uptake trend and yield was thus not changed significantly by subsoiling. Subsoiling in the non-tilled field increased rooting depth and showed the possibility of braking yield stagnation in long-term no-tillage cultivation in wheat, but not in soybean.
The mangrove is characterized by the subdaily fluctuations of tidal inundation and, importantly, has many sources of CO2 such as autotrophic and heterotrophic respiration and marine organisms. For these reason, the mangrove ecosystem would be expected to possess different microclimatic profile characteristics from those of terrestrial ecosystems. The objective of this study is to determine the characteristics of vertical profile of CO2, H2O, and air temperature within and above the canopies of mangrove forests at Okukubi River, Okinawa, Japan. The mangrove canopy had low CO2 concentrations, high H2O concentrations in air, and variable temperature. Tidal inundation provides a control on microclimatic variation not experienced by dryland forests.
In order to improve rice dough functionality, we co-transformed the Glu-1Dx5 gene encoding a high molecular weight (HMW) glutenin subunit Dx5 from bread wheat, Triticum aestivum L. and either bar gene conferring resistance to herbicide bialaphos or hpt gene conferring resistance to hygromycin B to rice callus cells of cv. Fatmawati. We molecularly characterized 9 plants regenerated from bialaphos-containing medium and 63 plants from hygromycin-containing medium. The Glu-1Dx5 gene was detected by PCR analysis in 15 transgenic T0 plants. Further analysis of T1 and T2 plants revealed that some transgenic plants carried the Glu-1Dx5 gene. Analysis of the endosperm extracts of T2 plants by SDS-PAGE revealed the existence of a protein similar in size to the wheat Glu-1Dx5 gene product, suggesting successful expression of the transgene. These plants will be incorporated into breeding program for further assessment of their benefits.
The activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is a major limitation of photosynthetic CO2 assimilation in C3 plants. In order to find useful Rubisco for improvement of photosynthesis in rice under elevated CO2, we analyzed the catalytic turnover rate (kcat) of Rubisco in Poaceae including C3 alpine plants, C3 cold-resistant plants and C4 plants. Rubisco in these plants showed 1.1- to 2.8-fold higher kcat than that in rice. However, the most of high kcat Rubisco also showed a higher km for CO2 (Kc) than that of rice, indicating that increase in kcat led to decrease in the affinity for CO2. Rubisco in Festuca ovina,Phleum pratense and Sorghum bicolor showed relatively high kcat to Kc. Although the kcat of Rubisco in F. ovina and P. pratense was not so high (1.5-1.6 fold relative to rice), the Kc was comparable to that in rice and the amino acid sequence of RbcL shared higher identity to that in rice than that in S. bicolor. By contrast, Rubisco of S. bicolor showed considerably high kcat (2.5-fold relative to rice), which is considered to be the most important factor for improvement of photosynthesis. In our estimation, the expression of high kcat Rubisco of F. ovina and S. bicolor in rice could significantly enhance CO2 assimilation at Ci of 50 Pa, the level assumed to be reached by the middle of this century.
We examined the effects of planting time on the dry matter (DM) yield of the forage rice cultivar Tachiaoba in southwestern Japan. DM yield was much higher with early planting than with normal planting. Dry weight (DW) per tiller was much higher with early planting than with normal planting. Thus, early planting is effective to obtain high DM yield. DM yield was closely related to the DW increase from transplanting to the full-heading stage (DW increase before heading) and DW per tiller. These results suggest that early planting leads to an increase in DW at the full-heading stage through an increase in DW per tiller and gives a high DM yield at the yellow-ripe stage. We also examined the effects of nitrogen (N) application rate and method on DM yield at the yellow-ripe stage. DM yield was higher with application of 22.5 g N m-2 than with 15.0 g N m-2. Although DW per tiller was slightly lower with application of 22.5 g N m-2 than with 15.0 g N m-2, the number of tillers per square meter was much higher with application of 22.5 g N m-2 than with 15.0 g N m-2. DM yield was the highest with N application method 1 that was applied more N early, followed by methods 2 that was applied more N evenly over time and 3 that was applied more N later. The number of tillers per square meter was much higher with method 1 than with method 2 or 3. Thus, application of 22.5 g N m-2 by method 1 is effective to obtain high DM yield. With both early and normal plantings, DM yield was closely related to the DW increase before heading and the number of tillers per square meter. These results suggest that application of 22.5 g N m-2 by method 1 lead to an increase in DW at the full-heading stage through an increase in the number of tillers per square meter resulting in a high DM yield at the yellow-ripe stage.
A priming method called sand priming was developed using sand as a priming solid matrix. The effect of sand priming on improving the field emergence performance of five super sweet corn cultivars was investigated. Sand priming significantly improved field emergence performance of all super sweet corn cultivars, and there was marked improvement by priming at 20ºC for 24 hr. After sand priming at 20ºC for 24 hr, field emergence percentage (FEP) of “Green Superman”, “Huatian 1”, “Yangtian 1”, “Mitian 8”, and “Chaotian 43” was increased by 52.1%, 37.5%, 38.0%, 40.9%, and 33.3%, respectively. Their field emergence speed (FES) was 2.3, 1.8, 2.0, 2.0, and 1.8 times of the control, respectively. To further elucidate the effect of sand priming on improving the field emergence performance of super sweet corn, we analyzed the membrane system integrity, α-amylase activity and protein content. Sand priming at 20ºC for 24 hr improved membrane system integrity and α-amylase activity in all super sweet corn cultivars. Furthermore, sand priming at 20ºC for 24 hr accelerated the degradation of embryo protein after 1 d germination in “Green Superman”.
A high nitrogen-uptake capacity and effective use of absorbed nitrogen for dry matter and grain production are required to improve the production cost and environmental pollution. We characterized grain yield, dry matter production and nitrogen accumulation in six rice cultivars: Sekitori (released in 1848) and Aikoku (1882), referred to as SA cultivars hereafter; Koshihikari (1956); Nipponbare (1963) and Asanohikari (1987), referred to as NA cultivars hereafter; and Takanari (in 1990) as a high-yielding modern cultivar. The plants were grown with and without chemical fertilizer in a submerged paddy field. When plants were supplied with manure and chemical fertilizer, Takanari consistently produced the heaviest grain and dry matter, followed by the NA cultivars, and the SA cultivars the lightest. Dry matter production before heading was greater in Takanari and the NA cultivars due to the longer duration of vegetative growth. Dry matter production after heading was greatest in Takanari, with a larger crop growth rate (CGR), and smallest in the SA cultivars with a shorter ripening time. Greater dry matter production during ripening was accompanied by the greater accumulation of nitrogen by Takanari and NA cultivars. These plants developed a larger amount of roots. The smaller light extinction coefficient of the canopy was also attributed to the higher CGR in Takanari. When plants were grown without chemical fertilizer, Takanari also produced heavier grain and dry matter, followed by the NA cultivars. The heavier grain in these cultivars resulted from the greater dry matter production before heading, which was due to the longer period of vegetative growth. The greater dry matter production and nitrogen accumulation by Takanari and NA cultivars were evident when plants were grown with chemical fertilizer. Koshihikari was characterized by a higher CGR and greater nitrogen accumulation during ripening in the absence of chemical fertilizer which should be noted in efforts to decrease rates of nitrogen application.
Scarcity of water and N fertilizer are major constraints to rice production, particularly in developing countries where rainfed upland condition dominates. Improvement of genetic adaptability to inadequate water and N fertilizer is one option to maintain productivity in these regions. NERICAs are expected to yield higher under low input conditions, but growth and yield responses of the cultivars to different ecosystems and N levels remain unknown. The objectives of this study were to characterize the growth and yield performance of NERICAs, in comparison with selected Japanese rice cultivars. The two NERICAs (NERICA 1 and NERICA 5), two Japanese upland cultivars (Toyohatamochi and Yumenohatamochi), and a Japanese lowland cultivar Hitomebore were grown under two ecosystems (irrigated lowland (IL) and rainfed upland (RU)) with two N levels (high (H) and low (L)) for two years. The cultivar difference in the aboveground dry weight and grain yield was the largest in the in RU×L plot, where the values of NERICAs were similar to those in the other plots, but the values of other cultivars were substantially reduced. Regardless of cultivar, N contents of the plants at maturity correlated significantly with the aboveground dry weight at maturity, spikelet number and grain yield per area. These results indicate that NERICAs, compared with the selected Japanese upland cultivars that were bred for drought tolerance, have a higher ability to absorb N under upland conditions, which may contribute to higher biomass production and sink formation, resulting in increased gain yield.
The rice-stylo (Stylosanthes guianensis) relay-intercropping system in paddy fields has previously been shown to increase agricultural productivity in Northeast Thailand, but successive relay-intercropping conducted without irrigation and fertilization during the stylo cropping has resulted in reduced production of stylo. The aim of this study was to determine the effect of nutrient deficiency on the stylo production. The experiment was conducted using pots to control fertilization accurately. The results showed that, after three successive relay-intercroppings, the soil was severely deficient in sulfur, phosphorus, and molybdenum. Sulfate application to the soil after the successive relay-intercroppings was suggested to improve stylo production. We recommend the use of a rain-fed shallow, favorable subecosystem as a field for stylo production in relay-intercropping and the stylo production with a cycle of several years.