We examined α-amylase(EC 188.8.131.52) activity in endosperm in 6 varieties of rice (Oryza sativa L.), which showed different seedling establishment traits in field experiments, using seedlings grown in sterilized agar-bed at 16°C. At the coleoptile elongation stage and the first leaf elongation stage, there were significant differences in α-amylase activity among the varieties investigated. However, the varietal difference in α-amylase activity at the coleoptile elongation stage did not correspond with that in coleoptile growth. Maltose, the immediate product of α-amylase activity, accumulated in the endosperm at the coleoptile elongation stage in a greater amount in Fukuhibiki, which has a poor seedling establishment trait, than in Arroz da Terra, which has a superior seedling establishment trait. The concentration of glucose detected in the exudate from the endosperm adjacent to the scutellum at the coleoptile elongation stage was also higher in Fukuhibiki than in Arroz da Terra. The results obtained in sterile agar-bed conditions clearly demonstrated that neither deficiency in α-amylase activity nor glucose production in the endosperm were responsible for coleoptile growth retardation at 16°C. Therefore, neither α-amylase activity nor sugar supply from the endosperm were responsible for the varietal differences seen in the rate of seedling establishment in paddy fields at around 16°C.
Days from full maturity to combine harvest maturity (DFC) is a major concern in combine harvesting of soybeans (Glycine max(L.)), especially in northern Japan, which has a short harvesting period. The combine harvest maturity, which was defined as the day at which the moisture content of the stem reached 30%, was analyzed using 7 soybean varieties for 3 yr in Hokkaido. There were significant differences in DFC among varieties (12 to 31 d) and among the 3 yr (16 to 25 d). DFC was closely associated with dry matter partitioning to stem (DMPS) at full maturity, that is, high DMPS increased DFC. The relationship between DMPS and DFC was examined by pod removal experiments conducted for 2 yr. In the soybean plants with high DMPS pod removal increased the stem desiccation period and DFC. These results indicated that DMPS at full maturity is an informative indicator for predicting the harvest maturity in the combine harvesting system.
We analyzed the effects of a partial solar eclipse (22 July 2009) on microclimate including vertical gradients of CO2 concentrations ([CO2]), so called [CO2] profile, in a mature sorghum canopy. Together with CO2 measurement, major photosynthetic drivers of microclimate, light intensity, temperature and atmospheric H2O concentration ([H2O]) were also measured simultaneously at the same place and height. [CO2] at 6.0, 3.2, 2.1, 1.4, 0.7, 0 m above the ground (canopy height was 3.2 m) increased by 5.8, 4.8, 9.0, 7.8, 6.4, 7.6 μmol mol-1, respectively, from 1 hour before the eclipse maximum to the eclipse maximum, during which the incident solar radiation above the canopy dropped by 1473 μmol photons m-2 s-1. However, it declined by 3.4, 10.6, 10.8, 6.0, 5.4, and 5.8 μmol mol-1, respectively, from the eclipse to 1 hour later, during which the incident radiation increased by 1350 μmol photons m-2 s-1. The [CO2] profile during the eclipse was uniform except for higher [CO2] near the ground. Comparative analysis of the effect of light intensity on the microclimate during the eclipse-induced light decreasing phase (ELDP) and eclipse-induced light increasing phase (ELIP) revealed that [CO2], [H2O], temperature and relative humidity (RH) are significantly correlated with the light intensity above the canopy in a nearly linear fashion. Furthermore it indicated that detected less light-reacted canopy photosynthesis at a higher layer within the canopy during ELIP might be due to slower response of stomatal opening (than closing) to the light intensity above the canopy.
Our previous study revealed that upland cultivars of New Rice for Africa (NERICAs) exhibited superior biomass production and N uptake compared with selected Japanese cultivars under upland conditions. The objective of this study was to examine whether the N uptake ability of upland NERICAs is attributable to their transpiration and exudation rates. Two NERICA cultivars (NERICA 1 and NERICA 5), two Japanese upland cultivars (Toyohatamochi and Yumenohatamochi), and a Japanese lowland cultivar Hitomebore were grown under rainfed upland conditions at two N levels. The NERICAs exceeded Japanese cultivars in the increment of aboveground dry weight and N content during the ripening stage. The transpiration rate and exudation rate of NERICAs tended to be higher than those of Japanese cultivars during the ripening stage. These results suggest that NERICAs are capable of maintaining higher water uptake ability during the ripening stage, leading to greater N uptake and biomass production at maturity.
Halophytes can be used as a crop on salinized agricultural land. Suaeda japonica Makino is an annual highly salt-tolerant plant, that inhabits salt marshes in the Ariake Sea, Japan. Accompanying growth, leaves of S.japonica change from green to red with accumulation of a red pigment, betacyanin. To elucidate the physiological roles of betacyanin in S. japonica, we tested the antioxidant capacity of purified betacyanin and leaf extracts containing different levels of betacyanin under oxidative-stress conditions. The assay with 1,1-diphenyl-2-picrylhydrazyl (DPPH) showed that the purified betacyanin had antioxidant activity. H2O2-induced protein oxidation of the leaf extracts was prevented by the addition of betacyanin. The antioxidant enzyme activity decreased in the red leaves, but the content of malondialdehyde (MDA), an oxidative stress marker in the red leaves was nearly the same as that in the green leaves. Betacyanin synthesis was induced under photoinhibition-inducible conditions of low temperature and high-intensity light. These results indicate that betacyanin serves as an antioxidant in S. japonica and that the leaf reddening of this species is a key adaptive strategy for coping with the harsh environmental conditions in salt marshes of the Ariake Sea.
We examined biomass dry matter and nutrient uptake of live plant parts, leaf area index, and litter of winged bean (Psophocarpus tetragonolobus) and velvet bean (Mucuna pruriens) 12, 18, 24 and 30 weeks after sowing (WAS). The two plants had similar leaf and stem+petiole biomasses. At 30 WAS winged bean had a significantly lower pod yield than velvet bean. Between 18 and 30 WAS, winged bean produced less litter than velvet bean due to differences in growth stages. The total mulch of live parts and litter of winged bean and velvet bean completely covered the ground by 18 and 12 WAS, respectively. Compared to velvet bean, the leaf and stem+petiole of winged bean had a significantly higher N concentration; significantly higher N uptake at 24 and 30 WAS; significantly lower C/N ratio; and significantly higher P, K and Mg concentrations. In winged bean, P uptake was significantly higher in the leaf at 30 WAS and in the stem+petiole at all harvesting times. The total biomass of the leaf, stem+petiole and litter of winged bean was 317–561 g DM m-2, and their N content was 12.3–17.7 g m-2. The total biomass of live parts and litter of winged bean might be sufficient to suppress weeds and increase soil N. Winged bean is an appropriate legume cover crop and green manure due to its longer growing period and superior ground-covering ability and high N input.
The relay strip intercropping system of wheat-corn-soybean is widely used in southwest China. However, it is hard to obtain a stable production of soybean with this system, since soybean plants grow under shading by corn; the stems are thinner and susceptible to lodging. We examined the effects of seed treatment with uniconazole powder (0, 2, 4 and 8 mg kg-1 seed) on the growth of soybean seedlings under relay strip intercropping, some morphological characteristics and yield. The seedling height, first internode length, cotyledonary node height and leaf area per plant were decreased, while the stem diameter, root dry weight, shoot dry weight, root volume, leaf greenness and root to shoot dry weight ratio were increased by uniconazole treatment. The root vigor and root active absorption area were also increased significantly by uniconazole treatment. Moreover, 2 and 4 mg kg-1 uniconazole powder treatment increased shoot dry weight, number of pods per plant, number of seeds per pod and seed yield significantly. Thus, the results suggested that seed treatment with uniconazole powder at a suitable concentration can improve soybean seedling growth, resist the lodging and also increase the seed yield under shading by corn in relay strip intercropping system.