To evaluate the effect of sink restriction on dry-matter partitioning to rice plant organs during ripening, we observed the dry-weight partitioning and accumulation of carbon and nitrogen in a female-sterile line, FS1, which has intact panicles with only a few fertile grains, in comparison with those in a normal counterpart, Fujisaka 5. In spite of the loss of sink function in the panicles, FS1 produced a larger amount of dry-matter than Fujisaka 5. Without a change of panicle dry weight throughout the ripening period, FS1 increased dry weights of culms and leaf sheaths at the early stage and of late tillers at the late stage. The amounts of dry-matter partitioned to panicles, culms plus leaf sheaths and late tillers in FS1 were comparable to those amounts in Fujisaka 5 at maturity, indicating that the latter two organs function as a sink of dry matter to substitute for panicles. Carbon partitioning to plant organs was basically similar to the dry-matter partitioning. Since the amount of nitrogen in a plant hardly increased during the ripening period in FS1 and Fujisaka 5, nitrogen partitioning to plant organs was different from the partitioning of dry matter and that of carbon. Culms, leaf sheaths and late tillers function as a sink of nitrogen partly to substitute for panicles, but the sum of nitrogen partitioned to these organs and panicles in FS1 was markedly smaller than in Fujisaka 5 at maturity, suggesting that other organs do not substitute for panicles in the sink function for nitrogen partitioning. FS1 developed late tillers rapidly at the late stage and had a carbon-nitrogen ratio in the stems different from that in Fujisaka 5.
Previous studies have suggested that the deep roots of sesbania (Sesbania sesban) function less efficiently in water acquisition than those of pigeon pea (Cajanus cajan) despite similar rooting depths. To investigate this phenomenon, both species were grown in a vertically split-root system. The top soil was watered at two-day intervals and the bottom soil was kept wet. Fifty-seven days after sowing, the watering to the top soil was withheld and the water uptake was monitored in both the layers. At any given rate of transpiration, the water influx rate per unit root surface (WIR/RS) was higher in the top soil than in the bottom soil in sesbania, despite the greater availability of water in the latter. By contrast, in pigeon pea, the WIR/RS was higher in the bottom soil than in the top soil. In sesbania, aerenchyma tissue was observed only in the cortex of the roots in the bottom soil. On the other hand, aerenchyma tissue was scarcely observed in pigeon pea roots, suggesting that the presence of aerenchyma tissue led to the reduced WIR/RS of sesbania roots in the bottom soil. Thermal image analysis showed that the stomata of sesbania leaves did not respond to water shortage. Instead, the sesbania leaves were shed in order to avoid desiccation, further reducing the potential to extract water. We therefore conclude that the water-extraction ability of deep roots was lower in sesbania than in pigeon pea as a result of aerenchyma formation and leaf shedding.
High temperature in summer is a major limiting factor for the growth of snap bean in the subtropical islands of Okinawa, Japan. The effect of temperature on biomass production, yield components, and morphological characters were studied in five snap-bean cultivars and strains in the phytotron. Plants were initially grown at 24/20°C (day/night temperature, 12/12hr) and transferred to 24/20°C, 27/23°C (control) or 30/26°C at the onset of flowering (34 days after sowing). High temperature (30/26°C) increased single pod weight and the number of flowers and branches, but reduced the number of pods/plant, pod set ratio, and plant weight. ‘Haibushi’ a heat-tolerant cultivar, had higher pod weight/plant, number of pods/plant, pod weight/pod, pod set ratio, number of branches, and rate of biomass allocation to pods, but lower rates of biomass allocation to leaves, stems, and roots than ‘Kentucky Wonder’ a heat-sensitive cultivar, in all temperature regimes. The number of flowers, biomass, and accumulative temperature affected both the yield components (number of pods/plant, single pod weight) antithetically. The yield components were estimated by a stepwise multiple regression analysis. The number of pods/plant was estimated from the number of flowers, leaf weight, pod set ratio per branch, and plant weight with a reasonable precision (R2=0.78). Single pod weight was determined (R2=0.69) from pod set ratio, number of branches, root weight, and accumulative temperature. The results indicated that higher biomass allocation to pods and higher pod set in branches, which were observed in heat-tolerant cultivars at all temperature regimes, were most effective for the estimation of heat tolerance in snap bean.
Intergeneric crosses between Japanese wheat cultivars (Triticum aestivum L. cv. Nishikazekomugi and Zenkojikomugi) and a tetraploid wild barley, Hordeum bulbosum L. were used to examine the effect of 2,4-dichlorophenoxyacetic acid (2,4-D) on the formation of wheat haploid embryo and its development into plantlets. The detached wheat spikes with florets pollinated with H. bulbosum were cultured for 14 days in a sucrose and sulfurous acid solution to which 2,4-D was added at the concentrations of 0, 25, 50, 75, 100, 125, 150, and 175 mg L-1. The percentages of florets with seeds set and with embryos formed were increased by increasing the concentration of 2,4-D up to 100 mg L-1. Fourteen days after pollination, embryos (haploid) were isolated from the seed and cultured on agarose-solidified B5 medium. Embryo size tended to decrease as the concentration of 2,4-D increased, but the larger embryos tended to have higher ability to develop into haploid plants. The percentage of florets from which haploid plantlets were developed by embryo culture was slightly increased by the treatment of the spikes with 25-100 mg L-1 2,4-D, but significantly reduced by 125-175 mg L-1 2,4-D. It is suggested that treatment with 2,4-D at 25 100 mg L-1 would be effective for haploid wheat production by of H. bulbosum method.
In vitro pollen germination experiment using agar plates showed that the growth under high nitrogen conditions enhanced the damage to pollen germination ability caused by the cooling at the young microspore stage. To clarify the physiological factors related to this damage to pollen germination, we performed the comparative proteome analysis of mature anthers and identified proteins that were changed by high nitrogen conditions or high nitrogen plus cooling conditions. Proteins were extracted from mature anther samples and separated by two-dimensional polyacrylamide gel electrophoresis. By comparing anther protein maps of the samples collected from the plants grown under standard nitrogen conditions, high nitrogen conditions and high nitrogen plus cooling conditions, we found 11 protein spots, which varied with the treatment. These protein spots were identified based on the rice proteome database and/or peptide mass fingerprinting (PMF) analysis after digestion with trypsin. Digested samples were analyzed by matrix-assisted laser desorption/ionization-time flight mass spectrometry to produce PMF data. Database searches using these PMF data revealed the identities of 9 proteins. Seven of these proteins were polypeptides involved in cell elongation, stress responses and sugar metabolism. The relation between the fluctuations of these proteins and the decrease in pollen germination are discussed.
The intra-plant distribution of 15N in common bean, cowpea and soybean having different levels of responses to shading and N2-fixing ability were analyzed under shaded and non-shaded conditions. Maize was used as a reference (non N2-fixing) plant. Seedlings were grown in pot soils for 3 weeks then transferred to shaded (55% of control) and non-shaded (control) conditions in a greenhouse, and sampled at 13 days and 24 days after shading. The proportion of plant N derived from N2-fixation (%Ndfa) estimated by the natural 15N abundance method was higher in cowpea and soybean (74−91%) than in common bean (37−38%). Shade treatment reduced %Ndfa significantly in cowpea and soybean. The difference in δ15N between shoot and root (Δδ15Ns-r) was the highest in maize followed by common bean, cowpea and soybean. Shading increased Δδ15Ns-r in each legume species, particularly in cowpea and soybean. A significant negative correlation was found between Δδ15Ns-r and %Ndfa in all legumes at both sampling dates (R2 = 0.67−0.96, P<0.1). The slope and Y-intercept of the regression line was similar at the sampling dates, but varied with the species. The slope was −0.05 in cowpea, −0.06 in common bean, and −0.11 in soybean. The Δδ15Ns-r value estimated by extrapolation of the regression line was 2.9, 2.5 and 8.6‰ at 0 %Ndfa, and −3.2, −2.8 and −2.6‰ at 100 %Ndfa, in common bean, cowpea and soybean, respectively. The consistent relationships between Δδ15Ns-r and %Ndfa found among legume species suggest that Δδ15Ns-r could be used as a parameter for estimating %Ndfa without using a reference plant, although the component of regression line was characteristically different among legume species.
The expression of photosynthesis-related genes, rbcS (small subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase) and cab (light-harvesting chlorophyll a/b-binding protein), in emerging rice leaves was examined. We performed in situ hybridization to visualize the spatial expression pattern of the photosynthesis-related genes. In the basal region of the leaf blade, which is the youngest region in a leaf blade of monocotyledonous plants, the expression of the genes was observed in both bundle sheath and mesophyll cells, while in the older middle and the oldest tip regions, the expression was only observed in mesophyll cells and not in bundle sheath cells. These results indicate that the expression of these photosynthesis-related genes is developmentally regulated and becomes mesophyll-specific in mature leaves. The expression of the photosynthesis-related genes in the lamina joint was also examined. These genes were not expressed in the lamina joint of immature leaves nor in the mature leaves. Therefore, the lamina joint was considered to be a photosynthetically inactive region.
The nitrogen content of leaves in rice plants at various planting densities in the field and under high and low levels of nitrogen in pots were comparatively examined, and thereby the effect of the nitrogen content of leaves on the nodal positions of the last visible primary tiller on the main stem was clarified. The nodal positions of the last visible primary tiller, which determine the potential number of cumulative tillers, were negatively correlated with the planting density. However, critical nitrogen contents of leaves for tillering on a leaf-area basis (NA), and those on a dry-weight basis (Nw) were estimated as 1.4−1.6 g m-2, and 3.8−4.5%, respectively, at the time when the last visible primary tiller emerged, even when the planting densities varied from 24 to197 plants m-2. The critical NA for tillering of rice plants grown under high and low levels of nitrogen fertilization was also nearly the same at the time when the primary tiller ceased to emerge. Therefore, the higher nodal position of the last visible primary tiller caused by lower plant density was attributable to the delayed canopy development and delayed competition for soil nitrogen resources. Suppression of the emergence of the primary tiller when the NA was less than 1.6 g m-2 by an insufficient supply of nitrogen was explained satisfactorily by assuming an insufficient supply of assimilates from leaves to a primary tiller bud.
To effectively utilize symbiotic nitrogen fixation, we examined the formation of root nodules along with root system development in two leading peanut cultivars in Japan, Chibahandachi and Nakateyutaka. Differences in the number, size and distribution pattern of root nodules between the two cultivars are discussed in relation to their root architecture. Many root nodules are formed on the 1st-order lateral roots in the peanut. The difference between the two cultivars in the number of nodules on the 1st-order lateral roots and the diameter of the 1st-order lateral roots at the basal part of the taproot increased during secondary thickening period. Those changes were significantly greater in Chibahandachi than in Nakateyutaka at later growth stages. Chibahandachi had fewer, but larger nodules than those in Nakateyutaka. In Nakateyutaka, a larger number of new nodules were formed on the lateral roots at the middle part of the taproot than in Chibahandachi. This suggests that in Chibahandachi nodules grow for a longer period during plant growth, and in Nakateyutaka new nodules are formed even at late stages of plant growth. In addition, there appears to be an optimal diameter of the 1st-order lateral roots for nodulation at each growth stage.
Zea mays is an NADP-malic enzyme (ME)-type C4 plant. The C4 plants of this type are attractive species for ultrastructural and physiological studies because they possess reduced grana in bundle sheath cell (BSC) chloroplasts. The present study evaluated the effect of salinity on granal development in BSC chloroplasts of maize. The plants were grown in soil media and after the second leaf was fully developed they were irrigated with four different concentrations (0, 1, 2 and 3%) of NaCl for 5 d. Ultrastructure, quantitative properties of chloroplasts and chlorophyll fluorescence parameters were evaluated. Granal stacking in BSC chloroplasts was induced by treatment with 2 or 3% NaCl. In contrast, granal stacking in mesophyll cell (MC) chloroplasts was reduced and disorganized by the NaCl treatment due to swelling of thylakoid. In control plants, only 2% of grana in BSC chloroplasts contained more than three thylakiods. In the plants treated with 3% NaCl, however, 66% of grana contained more than three thylakoids in BSC chloroplasts. The maximum number of thylakoids in grana of BSC chloroplasts in the control and 3% NaCl-treated plants, was 4 and 16 respectively. The granal index in BSC chloroplasts of 3% NaCl-treated plants was more than three times higher than that in the control plants. Chlorophyll fluorescence parameter analysis showed that the maximal quantum yield (Fv/Fm), the effective quantum yield of PSII (ΦPSII) and PSII-driven electron transport rate (ETR) decreased with the increase of salinity stress. These results suggest that the suppression mechanism of granal development in BSC chloroplasts of maize is influenced by salinity.
The number and thickness of crown root primordia (CRP) were examined with special reference to the size of the peripheral cylinder of longitudinal vascular bundles (PV), in which CRP are formed. Unelongated parts of main stems were sampled from the plant at 3.2, 5.2 and 7.2 plant age in leaf number; this index was adopted because of the morphological similarity to rice plants. Serial cross sections were made to investigate the position and the basal diameter of CRP in the unelongated stem. No relationship was observed between the CRP number and the PV side area in each growth stage. In contrast, the basal diameter of CRP increased with the increment of the circumference length of PV at each stage. Taken together, the number of CRP is not related to the PV size, whereas the CRP thickness shown by the basal diameter depend largely upon the PV size. Investigation using physiological approaches is necessary for further understanding of factors that determine CRP frequencies.
Carbon isotope discrimination (Δ) occuring in the process of photosynthesis, shows variation among rice (Oryza sativa L.) cultivars. Elucidation of specific traits associated with the extent of this discrimination under irrigated conditions may be useful to improve photosynthetic ability in rice plants. We measured leaf photosynthesis and Δ in Milyang 23 and Akihikari, and conducted quantitative trait loci (QTL) analysis on Δ at heading stage using a population of 126 recombinant inbred lines (RILs), derived from a cross between the two cultivars. While the two parental cultivars showed a similar Δ, the RILs showed a wide variation in Δ including transgressive segregation. Seven QTLs were detected for Δ; four on chromosomes 2 (two regions), 7, and 11 were those for Δ that is increased by the Milyang 23 allele, whereas the other three on chromosomes 1, 2, and 6 were those for Δ that is increased by the Akihikari allele. These results suggest that 13C in Milyang 23 may be discriminated through a photosynthetic process different from that in Akihikari. Milyang 23 showed a higher stomatal conductance and a higher ratio of intercellular to ambient CO2 concentration (Ci/Ca), while Akihikari showed a higher carboxylation efficiency but a lower Ci/Ca. According to the theory that a higher Ci/Ca leads to a higher Δ, the QTLs for Δ that is increased by the Milyang 23 allele might be related to a higher stomatal conductance. However, the theory provided no persuasive factors to explain the QTLs for Δ that is increased by the Akihikari allele. Plausible factors associated with these QTLs are discussed.
Germination characteristics at different temperatures were examined in Formosan lily (Lilium formosanum Wall.) seeds collected at different latitudes (22° 46’-24° 47’ N) and elevations (50-3000 m) in Taiwan. Germination was sensitive to temperature and varied among the populations, especially at 5°C and 25°C. All tested populations germinated fastest at 18°C. At this temperature, it took 8-14 days for initiation of germination (Gin) and 10-19 days to reach 50% of final germination percentage (G50). Days to Gin and G50, were 10-21 and 14-41, respectively, at 10°C, 42-82 and 51-136, respectively, at 5°C and 10-39 and 15-100, respectively, at 25°C. In the low elevation (50-880 m) populations, seeds from higher latitude populations germinated more rapidly at 5°C but more slowly at 25°C than those from a lower latitude. Furthermore, seeds from the lower latitude populations had significantly higher final germination percentages than those from the higher latitude populations at 25°C. Some germination characteristics of seeds from higher elevation habitats at the middle latitude were very similar to those from lower elevation habitats at the lower latitude despite of the difference in air temperature between the habitats. The eco-physiological germination characteristics of Formosan lily in response to temperatures were discussed in relation to the climatic conditions of each habitat.
The protein contents of the grain of 50 interspecific progenies developed from the cross between WAB56-104, an Oryza sativa variety, and CG 14, an Oryza glaberrima line, were investigated. In contrast to the higher protein content of O. glaberrima than O. sativa on the average, the protein content of CG 14 was always lower than that of WAB56-104. However, judging from the average of three seasons, 72% of the interspecific progenies had a higher protein content than the mid-parent and 50% of them had a higher protein content than WAB56-104. Although the actual values of protein content of the interspecific progenies were significantly different among the seasons, a highly significant correlation was always observed in protein content between any two of the three seasons. Protein content therefore was considered character of each interspecific progeny though it was also affected by environment. A significant correlation was not observed between paddy yield and protein content in any season; several interspecific progenies showed higher protein content and paddy yield than the mid-parents. A low paddy yield is likely to be associated with high protein content through physiological regulation without a genetic linkage between the two traits. However, the results suggest that the transgressive segregation of protein content observed in the interspecific progenies is attributed not to this physiological regulation but to a certain mechanism to concentrate protein in grains with a genetic background.
The effect of planting density on grain yield and water productivity was evaluated in rice (Oryza sativa L.) grown in non-flooded lowland fields in Japan in comparison with flooded fields. One rice cultivar, IR24 was grown both in flooded and non-flooded lowland fields in 2001 and 2002, and only in flooded field in 2003, with different planting densities ranging from 5.6 to 44 hills m-2. Another rice cultivar, Dontokoi was also grown in 2001. Straw mulching treatment was added in non-flooded field in 2002. In non-flooded fields, standing water disappeared from 36 and 8 days after transplanting until maturity in 2001 and 2002, respectively, the mean water content of surface soil during non-flooded period was 72 % g g-1 on a dry basis and 63 % v v-1. Grain yield in flooded fields (637 g m-2; average of 2001 and 2002) was higher than that in non-flooded fields (467 g m-2; average of 2001 and 2002), due to larger spikelet number per panicle in both years, larger 1000 grain weight in 2001, and higher percentage of ripened grains in 2002. Straw mulching tended to increase sink size but reduced percentage of ripened grains, resulting in no yield advantage in 2002. Water productivity in non-flooded fields (0.34 kg m-3; average of 2001 and 2002) was significantly higher than that in flooded fields (0.14 kg m-3). Grain yield increased with higher planting density in flooded fields in 2001 and 2003. In non-flooded fields, however, the effects of planting density on grain yield were little or marginal in both cultivars, due to the trade-off relationship between panicle number and spikelet number per panicle. This study showed that higher planting density would result in higher grain yield in favourable flooded fields, but is not advantageous for higher grain yield under non-flooded lowland fields in Japan in improved cultivars with relatively high tillering and yielding abilities.
The polarization of light reflected from crop canopies gives information on the canopy structure, such as the distribution of leaf inclinations. In order to verify those findings and to put the technique to practical use, we conducted two experiments in wheat fields. In the first experiment, the reflectance and polarized reflectance at 660 nm in the canopies of wheat plants, sown in both narrow and wide rows, and at two levels of topdressing, were measured periodically with a spectropolarimeter. We also probed the leaf orientation geometry of the plants using a 3-D digitizer and a plant canopy analyzer (LAI-2000). In the second experiment, we observed the polarization of light reflected from wheat planted in plots fertilized with basal dressing, and topdressing at the jointing and booting stages. Polarization showed a seasonal change with an upward convex clearly indicating the heading time. This pattern was not found by conventional band reflectance. Using polarization, it was possible to detect the differences in row width and fertilization conditions during the booting stage. The mean leaf inclination angle (MLI) detected with the 3-D digitizer and the mean tip angle (MTA) detected with the LAI-2000 were relatively closely correlated with the polarization than the reflectance at 660 nm and normalized difference vegetation index (NDVI) that was derived from the reflectance at 660 nm and 830 nm. Topdressing at the jointing stage was well detected by polarization obtained at the heading stage. Polarization measurements are useful in practical terms for remote detection of changes in stand geometry induced by cultivation management such as topdressing.
Meteorological conditions including temperature, sunshine and precipitation during grain growth are the primary factors determining the variation of the protein content of grain (PC) in wheat. On the basis of field experiments, a simplified regression model was developed for predicting the PC in winter wheat. From stepwise regression analysis, it was found that the PC of high-protein cultivars was correlated with the difference between daily maximum and minimum temperatures (Δ T) when Δ T variation under the environment was significant, but with the interaction of mean temperature (Tmean) × total sunshine hours from anthesis to maturity (TSUN) under the environment with Δ T variation less than 5%. In medium-protein cultivars, the PC was correlated with TSUN, and in low-protein cultivars, with the combination of Tmean, total rainfall from anthesis to maturity (TR) and TSUN. The climatic factors influencing PC were further quantified incorporating five genetic parameters. The Δ T and TSUN were linearly correlated with PC, and Tmean was quadratically correlated with PC. The precipitation was linearly correlated with PC if it was less than 50mm, otherwise quadratically. The average root mean square error (RMSE) values of the estimated PC relative to the observed value were less than 7 percent, indicating a good fit between the estimated and observed PC. Thus, it is concluded that the present model can predict the PC of different winter wheat cultivars under various climate environments.
In order to investigate effects of planting pattern on the interception of solar radiation by the canopy and the light extinction coefficient of the canopy in rice, the rice plants direct-sown in a submerged paddy field were grown in six planting patterns (A through F). In plots A, B and C, the planting density was 20.7 hills m-2 (22 cm×22 cm spacing) with five, three and one plant per hill, respectively, and in plots D, E and F, the planting density was 82.6 hills m-2 (11 cm×11 cm spacing), 44.4 hills m-2 (15 cm×15 cm spacing), and 44.4 hills m-2 (7.5 cm×30 cm spacing), respectively, with one plant per hill. At the tillering stage, the greater the tiller number and leaf area index, the larger the interception of solar radiation by the canopy. The tiller number was larger in the plots with one plant per hill, higher plant density and square arrangement of hills. At the early ripening stage, the light extinction coefficient of the canopy was smaller in such plots. The larger the average inclination of leaf blades, the smaller the light extinction coefficient of the canopy. The difference in stem inclination in the canopy might be responsible for the difference in the inclination of leaf blades. In the plots with one plant per hill, higher plant density and square arrangement of hills, stems were more erect. Within the range of planting patterns in our study, both the rate of interception of solar radiation by the canopy and the light-intercepting characteristics were significantly more favorable in the plots with one plant per hill, higher density and a square arrangement of hills.