[show abstract][hide abstract] ABSTRACT: Physiological and biochemical studies on the leaf apoplast have been facilitated by the use of the infiltration-centrifugation technique to collect intercellular washing fluid (IWF). However, this technique has been difficult to implement in rice (Oryza sativa L.) for various reasons. We compared the collection efficiency of leaf IWF between two types of rice varieties (Indica and Japonica), as well as between rice and other species (spinach, snap bean and wheat). Although the extraction of IWF in most species took only 2-3 min, it took up to 35 min in rice. The difficulty in infiltration with rice was ascribed to the small stomatal aperture and hydrophobicity of the leaves. In this study, we have established an improved method for collecting IWF and determining the apoplastic air and water volumes in rice leaves. We have shortened the infiltration time to 8 min via the following improvements: (i) infiltration under outdoor shade in the daytime to prevent stomatal closure and a rise in temperature of the infiltration medium; (ii) soaking of leaves in a surfactant solution to decrease the leaf hydrophobicity; and (iii) continuous pressurization using a sealant injector to facilitate the infiltration. The rapid collection of IWF achieved using this technique will facilitate study of the leaf apoplast in rice.
Plant and Cell Physiology 07/2012; 53(9):1659-68. · 4.13 Impact Factor
[show abstract][hide abstract] ABSTRACT: We studied leaf apoplastic ascorbates in relation to ozone (O(3)) sensitivity in two winter wheat (Triticum aestivum L.) varieties: Yangfumai 2 (Y2) and Yangmai 16 (Y16). The plants were exposed to elevated O(3) concentration 27% higher than the ambient O(3) concentration in a fully open-air field from tillering stage until final maturity. The less sensitive variety Y16 had higher concentration of reduced ascorbate in the apoplast and leaf tissue by 33.5% and 12.0%, respectively, than those in the more sensitive variety Y2, whereas no varietal difference was detected in the decline of reduced ascorbate concentration in response to elevated O(3). No effects of O(3) or variety were detected in either oxidized ascorbate or the redox state of ascorbate in the apoplast and leaf tissue. The lower ascorbate concentrations in both apoplast and leaf tissue should have contributed to the higher O(3) sensitivity in variety Y2.
[show abstract][hide abstract] ABSTRACT: To elucidate the effects of broadcast urea on ammonia (NH3) exchange between the atmosphere and rice, we investigated the NH3 exchange flux between rice leaf blades and the atmosphere, xylem sap ammonium () concentration, leaf apoplastic concentration and pH, and determined the stomatal NH3 compensation point. Paddy rice (Oryza sativa L. cv. Nipponbare) cultivation using experimental pots was conducted in the open air. Three treatments, no nitrogen (NN), standard nitrogen (SN) and high nitrogen (HN), were prepared for two supplemental fertilizations. Urea with 0, 30 and 60 kg N ha−1 for the NN, SN and HN treatments, respectively, was broadcast at panicle initiation, and urea with 0, 20 and 40 kg N ha−1 for the NN, SN and HN treatments, respectively, was broadcast at heading. The NH3 exchange fluxes between the rice leaf blades and the atmosphere (SN treatment) measured using a dynamic chamber technique showed net deposition in general; however, net emission from the old leaves occurred 1 day after the application at heading. In contrast, the xylem sap concentrations increased markedly 1 day after both applications, which suggests direct transportation of from the rice roots to the above-ground parts. The applications resulted in no obvious increase in the leaf apoplastic concentrations. The relationship between the concentration in the xylem sap and that in the leaf apoplast was uncertain, although the in the xylem sap came from the roots and the in the apoplast might be affected by the stomatal deposition of NH3. The stomatal NH3 compensation point of rice was estimated to be 0.1–4.1 nmol mol−1 air (20°C). The direction and intensity of the exchange flux through the stomata, interpreted on the basis of the temperature-corrected NH3 compensation point, agreed with the observed exchange flux between the rice leaf blades and the atmosphere.
[show abstract][hide abstract] ABSTRACT: Predicted increase in ultraviolet-B (UV-B: 280–320 mn) radiation may have adverse impacts on growth and yield of rice (Oryza sativa L.), as has been found in studies hitherto. However, most of the studies were conducted in growth chambers or greenhouses where the plants are generally more sensitive to UV-B than in the field, presumably because of the distorted balance between UV-B and ultraviolet-A as well as PAR. This study was conducted to address the effects of enhanced UV-B on growth and yield of rice under a realistic spectral balance in the field. Three cultivars, “Koshihikari”,‘IR 45’and‘IR 74’were pot-grown and irradiated with enhanced UV-B for most of the growing season in the field at Tsukuba, Japan (36°01′N, 140°07′E). The UV-B enhancement simulated ca 38% depletion of stratospheric ozone at Tsukuba. The results showed no UV-B effects on plant height, numbers of tillers and panicles, dry weight of the plant parts or the grain yield for any of the 3 cultivars. Natural abundance of 13C in the flag leaves was not altered by the UV-B enhancement either. While UV-absorbing compounds showed no response to the UV-B enhancement, chlorophyll contents decreased with enhanced UV-B. However, the decrease of chlorophyll was limited to an early growth stage with no effect later. We thus found no extraordinary impact of the nearly doubled UV-B radiation on rice in the field, and it would appear that a reliable prediction of the effects of UV-B will require experiments carried out over a number of years under various climatic and solar UV-B regimes.
Physiologia Plantarum 04/2006; 96(1):1 - 5. · 3.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: The transport rate of methane from a nutrient solution to the atmosphere via rice plants was controlled both by the methane
concentration in the nutrient solution and by plant physiology. Measurements on 11 rice cultivars indicated that the conductance
of the rice plant for methane increased as the plants developed. The conductance varied from 0.3±0.2 to 1.2±0.7 μmol min-1 mM-1 plant-1 during the tillering stage, and from 0.6±0.3 to 2.5±0. 2 μmol min-1 mM-1 plant-1 during the reproduction stage. Based on measurements of all plants, the conductance positively correlated with parameters
of plant size. Conductance correlated best with stem inter-cellar volume at the tillering stage, and with root volume at the
reproduction stage. For both stages taken together, the correlation between conductance and root volume was the most significant.
The conductance could be approximated by a multiple linear regression using root volume and the length of root bundle. Higher
conductance was found to generally associate with the plants with larger root volume, heavier root fresh weight.
Plant and Soil 01/2000; 222(1):83-93. · 2.64 Impact Factor
[show abstract][hide abstract] ABSTRACT: Ebullition of gas bubbles from the soil surface is, in some cases (e.g., in early growth stage of rice), one of the major pathways for methane transport from rice paddies to the atmosphere. However, the role of the gas phase (entrapped gas) in the paddy soil in plant-mediated methane transport, which is the major pathway for methane emission, has not been clarified. To clarify the effect of the gas phase below ground on the methane emission rate through rice plants, we partly exposed the root and stem base of hydroponically grown rice to a high concentration of methane gas at various gas pressures, and immersed the rest of the roots in a solution with a high methane concentration. The methane emission rate was measured from the top of the rice plant using a flow-through chamber method. The methane emission rate drastically increased with a small increase in gas pressure in the gas phase at the root and stem base zone, with about a 3 times larger emission rate being observed with 10 10-3 atm of extra pressure (corresponding to 10 cm of standing water in rice paddy) compared to no extra pressure. However, when alginate was applied to the stem near the base to prevent contact with the gas phase, the methane emission rate did not increase with increasing gas pressure. On the other hand, from observations in the rice paddy, it was found that the gas is entrapped near the surface (e.g., at a depth of 1 cm) and the gas entrapped in the soil would come into direct contact with a part of the stem near the base of the rice plant. Thus, the gas entrapped in the soil could enter into the rice body directly from the part of the stem near the base which is beneath the soil surface due to gas pressure in the gas phase resulting from the pressure exerted by the standing water. Hence, this mechanism involving the entrapped gas could play an important role in methane emission from rice paddy by affecting the plant-mediated methane transport as well as ebullition of gas bubbles.
Plant and Soil 07/1997; 195(1):65-73. · 2.64 Impact Factor
[show abstract][hide abstract] ABSTRACT: Large diurnal and seasonal variations in methane flux from rice paddies have been found in many studies. Although these variations are considered to result from changes in methane formation rates in the soil and the transport capacity (e.g. biomass, physiological activities, and so on) of rice plants, the real reasons for such variations are as yet unclear. This study was conducted to clarify the effects of temperature on the rate of methane transport from the root zone to the atmosphere using hydroponically grown rice plants. Methane emission rates from the top of the rice plants whose roots were soaked in a solution with a high methane concentration were measured using a flow-through chamber method with the top or root of the rice plants being kept at various temperatures. The methane emission rates and methane concentrations in solution were analyzed using a diffusion model which assumes that the methane emission from a rice paddy is driven by molecular diffusion through rice plants by a concentration gradient. In the experiment where the temperature around the root was changed, the conductance for methane diffusion was typically 2.0-2.2 times larger when the solution temperature was changed from 15 to 30 C. When the air temperature surrounding the top of the rice plant was changed, the change in conductance was much less. In addition, from measurements of methane flux and methane concentration in soil water in a lysimeter rice paddy during the 2 growing seasons of rice, it was found that the conductance for methane transport was correlated with the soil temperature at 5 cm depth. These results suggest that the temperature around the root greatly affects the methane transport process in rice plants, and that the process of passing through the root is important in determining the rate of methane transport through rice plants.
Plant and Soil 03/1997; 191(2):233-240. · 2.64 Impact Factor
[show abstract][hide abstract] ABSTRACT: Rice paddies emit not only methane but also several volatile sulfur compounds such as dimethyl sulfide (DMS: CH3SCH3). However, little is known about DMS emission from rice paddies. Fluxes of methane and DMS, and the concentrations of methane and several volatile sulfur compounds including hydrogen sulfide (H2S), carbonyl disulfide (CS2), methyl mercaptan (CH3SH) and DMS in soil water and flood water were measured in four lysimeter rice paddies (2.5 × 4 m, depth 2.0 m) once per week throughout the entire cultivation period in 1995 in Tsukuba, Japan. The addition of exogenous organic matter (rice straw) was also examined for its influence on methane or DMS emissions. Methane fluxes greatly differed between treatments in which rice straw had been incorporated into the paddy soil (rice straw plot) and plots without rice straw (mineral fertilizer plot). The annual methane emission from the rice straw plots (37.7 g m-2) was approximately 8 times higher than that from the mineral fertilizer plots (4.8 g m-2). Application of rice straw had little influence on DMS fluxes. Significant diurnal and seasonal changes in DMS fluxes were observed. Peak DMS fluxes were found around noon. DMS was emitted from the flood water in the early growth stage of rice and began to be emitted from rice plants during the middle stage. DMS fluxes increased with the growth of rice plants and the highest flux, 15.1 µg m-2 h-1, was recorded before heading. DMS in the soil water was negligible during the entire cultivation period. These facts indicate that the DMS emitted from rice paddies is produced by metabolic processes in rice plants. The total amount of DMS emitted from rice paddies over the cultivated period was estimated to be approximately 5–6 mg m-2. CH3SH was emitted only from flood water during the first month after flooding.
Plant and Soil 01/1997; 195(2):233-245. · 2.64 Impact Factor
[show abstract][hide abstract] ABSTRACT: To investigate the effects of low (0·05 μmol/mol) and relatively low (0·10 μmol/mol) concentrations of ozone on photoassimilate partitioning, rice plants grown in a water culture were fed with 13C-labelled carbon dioxide at the reproductive stage in an assimilation chamber with constant concentration of 12CO2 and 13CO2. Rice plants were exposed to ozone 4 weeks before and 3 weeks after 13CO2 feeding. The dry weight of whole plants decreased with increasing ozone concentration, whereas net photosynthetic rate (apparent CO2 uptake per unit leaf area) was unaffected, compared with the control, at the time of 13CO2 feeding. Dry matter distribution into leaf sheaths and culms was reduced more than that into leaf blades by ozone exposure. Although panicle dry weight per plant was reduced by ozone, the percentage of panicle dry weight to the whole plant tended to increase considerably. Exposure to ozone accelerated translocation of 13C from source leaves to other plant parts. Partitioning of 13C to panicles and roots was higher under ozone treatment than in the control. Respiratory losses of fixed 13C from plants tended to decrease under treatment with ozone. The increase in photoassimilate partitioning in panicles can be considered to be an acclimation response of rice plants to complete reproductive stage under the restricted biomass production caused by ozone.
[show abstract][hide abstract] ABSTRACT: Rice plants were exposed to ozone in field exposure chambers throughout most of the growing seasons of 3 years from 1987 through 1989. Cultivar ‘Koshi-hikari’ was used for the 1987 and 1989 experiments, and cv. ‘Nippon-bare’ was used for the 1988 experiment. Ozone exposure was performed for 7 h from 09:00 to 16:00 h each day, and ozone concentration in each of the five chambers was maintained at either 0.5, 1.0, 1.5, 2.0, or 2.75 times ambient ozone level. Throughout the growing seasons, plant samples were taken for measuring leaf area and dry weight of plant parts. At harvest, samples were taken to determine grain yield and yield components. The results of the ozone exposures indicated no consistent effect of ozone on leaf area growth, whereas total dry matter decreased with increased ozone concentration. The effect of ozone on total dry matter was particularly evident after heading. Ozone also affected dry matter partitioning. There was increased dry matter distribution to the leaf blades compared with the leaf sheaths, culms, or roots. Rice yield was significantly reduced by ozone. Although the yield was significantly different among the 3 years, there was no significant interaction between the ozone treatment and the year of the ozone exposures. The relationship between ozone concentration and yield loss of rice in this study was comparable to the relationship reported for rice cultivars in California, but was different from that reported for soybeans, which showed much greater ozone-induced yield loss than rice. Among the yield components, 1000 grain weight was significantly reduced by ozone. Harvest index was not affected by the ozone treatment. The above results indicated that rice yield is reduced by ozone in a realistic range of 20–100 nl 1−1. The results for yield components were compared with other reports. The increased dry matter distribution to leaf blade was discussed with regard to its implications for leaf area growth and lodging.
[show abstract][hide abstract] ABSTRACT: summaryA field exposure chamber system was constructed in a paddy field. The system consisted of four ozone generators, five exposure chambers equipped with ventilation fans on both ends, and an ozone measurement and control system. Rice plants were exposed to ozone in the exposure chambers for the whole growing season. The ozone concentration in each chamber was maintained in a constant proportion to ambient ozone. The horizontal distribution of ozone concentration within a chamber showed ±10%, of variation with the lowest values at the centre and both ends of the chamber. Wind velocity showed a similar horizontal distribution as ozone but with a greater variation among the locations within a chamber. Diurnal as well as seasonal changes of ozone concentration in the chambers followed the targeted level rather closely except for several occasions of power failure or system malfunctioning. Temperature in the chambers was c. 1 °C higher in the daytime and 0.34 °C higher on daily average than in the field outside. Light flux density in the chambers was reduced to 75% of that outside with little seasonal variation. These results indicated a satisfactory performance of the field exposure chamber system for its intended use.
New Phytologist 01/1994; 126(2):317 - 325. · 6.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: To attempt to develop physicochemical and physiological modelling for methane transport from the rhizosphere to the atmosphere through rice plants, methane flux, methane concentration in the soil water, and the biomass of rice were measured in lysimeter rice paddies (2.5 4 m, depth 2.0 m) once per week throughout the entire growing season in 1992 at Tsukuba, Japan. The addition of exogenous organic matter (rice straw) or soil amendments with the presence or absence of vegetation were also examined for their influence on methane emissions. The total methane emission over the growing season varied from 3.2 g CH4 m-2 y-1 without the addition of rice straw to 49.7 g CH4 m-2 y-1 with rice straw and microbiological amendment. In the unvegetated plot with the addition of rice straw, there was much ebullition of gas bubbles, particularly in the summer. The annual methane emission due to the ebullition of gas bubbles,from the unvegetated plot with the addition of rice straw was estimated to be almost the same as that from the vegetated site with the addition of rice straw. In the early growth stage, the methane flux can be analyzed by the diffusion model (Flux=Methane concentration Conductance of rice body) using parameters for methane concentration in the soil water as a difference in concentration between the atmosphere and the rhizosphere, and for the biomass of rice as a conductance of rice body. On the other hand, although the diffusion model was inapplicable to a large extent from the middle to late growth stage, methane flux could be estimated by air temperature and concentration in the soil water. Thus, methane transport from the rhizosphere to the atmosphere through rice plants consisted of two phases: one was an explainable small part by diffusion in rice body; the other was a large part strongly, governed by air temperature. The existence of gas bubbles in the soil may be related to the transition between the two phases
Plant and Soil 01/1994; 161(2):195-208. · 2.64 Impact Factor
[show abstract][hide abstract] ABSTRACT: The generation of active oxygen in ozone-treated rice protoplasts was measured with a view to examining the initial phases of injury in plants exposed to ozone. The production of superoxide anions was determined in protoplast suspensions on the basis of the rate of formation of adrenochrome from epinephrine following treatment with air including 0 or 8.0 ppm ozone. Hydroxyl radicals were measured by determining the rate of bleaching of p-nitrosodimethylaniline. The rates of both formation of adrenochrome, and bleaching of p-nitrosodimethylaniline, were less in the ozone-treated protoplasts than in those treated with air alone. On the other hand, an increase in the production of malondialdehyde (MDA) and a decrease in sulfhydryl groups (SH) was more noticeable in the ozone-treated protoplasts, while the amount of protein and chlorophyll did not change. The change in the amount of MDA and SH groups is presumed to be due to the influence of direct reactions with the ozone molecule.
[show abstract][hide abstract] ABSTRACT: The effects of antioxidants, ascorbic acid, hydroquinone and mannitol, on ATPase activity in cellular membranes and on the formation of malondialdehyde in rice protoplasts treated with air or ozone in vitro, were examined. All three substances restrained the increase in malondialdehyde (MDA) during the treatment with both air and ozone, and ascorbic acid and hydroquinone were more effective on the protoplasts treated with ozone than those treate With regard to mannitol, however, no difference was noticed in the decrease in MDA between protoplasts treated with ozone and those treated with air. Only ascorbic acid was effective in maintaining ATPase activity in cellular membranes. The addition of ascorbic acid during ozone treatment restrained the decrease the ATPase activity by half compared with treatment without ascorbic acid.
[show abstract][hide abstract] ABSTRACT: Changes in the levels of antioxidants such as ascorbate and glutathione and activities of related enzymes in rice leaves exposed to ozone at high or low concentrations were investigated. In rice plants (Oryza sativa L. cv. Koshihikari) exposed to ozone at a high concentration (0.50 × 10 m m (0.50 ppm)) for 8 h, L-ascorbate was oxidized while the content of oxidized glutathione (GSSG) increased without the concomitant decrease of the content of reduced glutathione (GSH). In addition, the activities of ascorbate peroxidase (AP), dehydroascorbate reductase (DHA reductase), and Superoxide dismutase (SOD) declined, though the glutathione reductase (GR) activity remained unchanged. A high concentration of ozone was considered to destroy the protection system against active oxygen species, resulting in the injury of the cell structure and functions. On the other hand, in the rice leaves exposed for 5 weeks to ozone at low concentrations (0.05 × 10 and 0.10 × 10 m m), the amount of L-ascorbate and total ascorbate increased significantly by exposure to 0.05 × 10 m m O3 while the content of total glutathione (GSH + GSSG) decreased by exposure to 0.10 × 10 m m O3. Activities of AP, GR, and SOD increased by the exposure to ozone at low concentrations. These reactions may be interpreted as protective responses to prevent or alleviate the damage of rice plants induced by ozone.
[show abstract][hide abstract] ABSTRACT: To clarify the response of growth and root functions to low concentrations of ozone (O3), rice plants (Oryza sativa L.) were exposed to O3 at 0·0 (control), 0·05 and 0·10 ppm for 8 weeks from vegetative to early heading stages. Exposure to 0·05 ppm O3 tended to slightly stimulate the dry weight of whole plants up to 5 weeks and then slightly decrease the dry weight of whole plants. However, these effects were statistically significant only at 6 weeks. Exposure to 0·10 ppm O3 reduced the dry weight of whole plants by 50% at 5 and 6 weeks, and thereafter the reduction of the dry weight of whole plants was gradually alleviated. Those changes in dry weight can be accounted for by a decrease or increase in the relative growth rate (RGR). The changes in the RGR caused by 0.05 and 0.10 ppm O3 could be mainly attributed to the effect of O3 on the net assimilation rate.Root/shoot ratio was lowered by both 0.05 and 0.10 ppm O3 throughout the exposure period. The root/shoot ratio which had severely decreased at 0.10 ppm O3 in the first half period of exposure (1–4 weeks) became close to the control in the latter part of exposure (5–8 weeks). Time-course changes in NH4N root uptake rate were similar to those in the root/shoot ratio especially for 0.10 ppm O3. On the other hand, root respiration increased from the middle to later periods. Since it is to be supposed that plants grown under stressed conditions change the ratio of plant organ weight to achieve balance between the proportion of shoots to roots in the plant and their activity for maintaining plant growth, these changes in root/shoot ratio and nitrogen uptake rate under long-term exposure can be considered to be an adaptive response to maintain rice growth under O3 stress.