Yoshihiro Hirooka

Response of the leaf photosynthetic rate to available nitrogen in erect panicle-type rice (Oryza sativa L.) cultivar, Shennong265

Abstract Increasing the yield of rice per unit area is important because of the demand from the growing human population in Asia. A group of varieties called erect panicle-type rice (EP) achieves very high yields under conditions of high nitrogen availability. Little is known, however, regarding the leaf photosynthetic capacity of EP, which may be one of the physiological causes of high yield. We analyzed the factors contributing to leaf photosynthetic rate (Pn) and leaf mesophyll anatomy of Nipponbare, Takanari, and Shennong265 (a EP type rice cultivar) varieties subjected to different nitrogen treatments. In the field experiment, Pn of Shennong265 was 33.8 μmol m−2 s−1 in the high-N treatment, and was higher than that of the other two cultivars because of its high leaf nitrogen content (LNC) and a large number of mesophyll cells between the small vascular bundles per unit length. In Takanari, the relatively high value of Pn (31.5 μmol m−2 s−1) was caused by the high stomatal conductance (gs; .72 mol m−2 s−1) in the high-N treatment. In the pot experiment, the ratio of Pn/Ci to LNC, which may reflect mesophyll conductance (gm), was 20–30% higher in Nipponbare than in Takanari or Shennong265 in the high N availability treatment. The photosynthetic performance of Shennong265 might be improved by introducing the greater ratio of Pn/Ci to LNC found in Nipponbare and greater stomatal conductance found in Takanari.

Short-term evaluation of oxygen transfer from rice (Oryza sativa) to mixed planted drought-adapted upland crops under hydroponic culture

Abstract Mixed cropping is a cultivation method widely practiced in tropical regions. The newly developed close mixed planting technique mitigates the flood stress of drought-adapted upland cereal species by co-growing rice (Oryza sativa) plants under field flood conditions. We tested the hypothesis that O2 was transferred from rice to upland crops using the model system of hydroponic culture. To confirm the hypothesis, the phenomena of O2 absorption and release by plants were evaluated in a water culture condition without soil. Experiments were conducted in a climate chamber to estimate the amount of O2 released from the roots of rice and pearl millet (Pennisetum glaucum) under both O2-rich (20.0 ± .0% conc. in phase I) and O2-free dark (.8 ± .0% conc. in phase II) conditions. The total O2 change (between the two phases) in a single planting of rice and pearl millet was significantly higher than that of the mixed planting of rice and pearl millet, which indicated that O2 was transferred from rice to pearl millet under a water culture condition. The result indicated that approximately 7 μM O2 g fresh root weight−1 h−1 was transferred between the two plant species. O2 transfer was confirmed between the two plant species in a mix cultured in water, implying its contribution to the phenomenon that improved the physiological status of drought-adapted upland crops under field flood conditions.

Yield and growth characteristics of erect panicle type rice (Oryza sativa L.) cultivar, Shennong265 under various crop management practices in Western Japan

Abstract Erect panicle rice cultivars utilize solar energy effectively and have improved ecological growing conditions. Among such cultivars, Shennong265 has been grown successfully throughout Northern China. Nevertheless, no studies have yet examined the relationships between crop dry matter productivity, weather conditions, and nitrogen uptake of the erect panicle type rice cultivar in Japan. The objective of our study was to evaluate the productivity of erect panicle rice Shennong265 in Western Japan under varied conditions. Three rice cultivars, Shennong265, Nipponbare, and Takanari were grown in the field under different fertilizer and plant density conditions in Western Japan; using this information, we compared yield and growth characteristics of Shennong265 with those of Nipponbare and Takanari. Although Shennong265 had radiation use efficiency similar to that of the high yielding cultivar (Takanari) and much higher leaf nitrogen content than Takanari and Nipponbare, the average grain yield of Shennong265 grown under normal fertilizer and plant density conditions was approximately 6.9 t ha−1 as against 6.2 t ha−1 for Nipponbare and 9.6 t ha−1 for Takanari. These results suggest that, while Shennong265 has a high yield potential, the environmental conditions including climate, fertilizer, and planting period provided in this study were not suitable for achieving its maximum yield. The reduced performance of Shennong265 may be caused by insufficient fertilizer after heading and by shorter growth periods, as well as by the climate of Western Japan. Additional fertilizer application during the heading stage and earlier transplanting may be needed to obtain higher Shennong265 yields in Western Japan.

Parameterization of the vertical distribution of leaf area index (LAI) in rice ( Oryza sativa L.) using a plant canopy analyzer

Monitoring the vertical distribution of leaf area index (LAI) is an effective method for evaluating canopy photosynthesis and biomass productivity. In this study, we proposed a novel method to characterize LAI vertical distribution non-destructively by utilizing LAI-2200 plant canopy analyzer, followed by the application of statistical moment equations. Field experiments were conducted with 5 rice cultivars under 2 fertilizer treatments in 2013 and with 3 rice cultivars under 3 plant density treatments in 2014. LAI readings obtained by a plant canopy analyzer for non-destructive stratified measurements were relatively consistent with LAI estimations using the stratified clipping method for every cultivar and treatment. The parameters calculated using the statistical moment equations numerically showed the changes in LAI vertical distribution with plant growth up to the heading stage. The differences in the parameters also quantified the effect of cultivar, fertilizer, and plant density treatments. These results suggest that the non-destructive stratified measurements and the statistical moments evaluated in this study provide quantitative, reliable information on the dynamics of LAI vertical distribution. The method is expected to be utilized by researchers in various research fields sharing common interests.

Absence of correlation between ACh-induced Ca influx and phosphatidic acid labeling in rat uterus

Rat uterine smooth muscle was preincubated in Ca-depleted modified Locke-Ringer solution to investigate the correlation between the 32Pi incorporation into phosphatidic acid induced by acetylcholine and the contractile response to acetylcholine induced by the addition of CaCl2 (Ca influx). The results showed that in rat uterine smooth muscle under these conditions phosphatidic acid does not act as a Ca ionophore or as a trigger for opening the Ca channel.