Shingo Ueda

The chloroplast avoidance response decreases internal conductance to CO2 diffusion in Arabidopsis thaliana leaves

The relationship between chloroplast arrangement and diffusion of CO(2) from substomatal cavities to the chloroplast stroma was investigated in Arabidopsis thaliana. Chloroplast position was manipulated by varying the amount of blue light and by cytochalasin D (CytD) treatment. We also investigated two chloroplast positioning mutants. Chloroplast arrangement was assessed by the surface area of chloroplasts adjacent to intercellular airspaces (S(c)). Although it has been previously shown that long-term acclimation to high light is linked with a large S(c), we found that the short-term chloroplast avoidance response reduces S(c). This effect was not apparent in the blue-light-insensitive phot2 mutant, which did not show the avoidance response. As expected, the smaller S(c) induced by the avoidance response was coupled to a similar decrease in internal conductance. This reduction in internal conductance resulted in an increased limitation of the rate of photosynthesis. The limiting effect of S(c) on internal conductance and photosynthesis was also shown in chup1, a mutant with a constant small S(c) as the result of an unusual chloroplast arrangement. We conclude that chloroplast movements in A. thaliana can rapidly alter leaf morphological parameters, and this has significant consequences for the diffusion of CO(2) through the mesophyll.

Activities of the cyanide-resistant respiratory pathway in leaves of sun and shade species

Higher plant mitochondria have a cyanide-resistant alternative respiratory pathway of electron transport (AP) that is not coupled to proton translocation. To characterise the ecophysiology of this apparently ‘wasteful’ pathway, we constructed a system consisting of a gas-phase oxygen electrode and an air sampling line for measurement of stable oxygen isotope ratios. With this system, we were able to measure respiratory rates of a small amount of leaf segments of ca 0.6 g fresh weight, and collect about 100 L of the air from the oxygen electrode chamber several times. The 18 O/16 O ratio in the air samples was measured by mass spectrometry. The activity of AP was estimated based on the isotopic discrimination of 18 O. We used the leaves of Alocasia odora (Lodd.) Spach., a shade species, and Spinacia oleracea L. and Phaseolus vulgaris L., sun species. These plants were grown at two levels of photosynthetically active photon flux density (PPFD). Three main findings were: (1) in the leaves of A. odora, the contribution of AP was less than 10% of the total respiratory rate, irrespective of growth PPFD; (2) for the sun species grown at high PPFD, the contribution of AP in the leaves was about 40% early in the night, but decreased dramatically late in the night; and (3) when S. oleracea was grown at low PPFD, the contribution of AP in the leaves declined. The low activity of AP in the leaves of A. odora suggests that the efficiency of adenosine triphosphate (ATP) production (ATP/O 2 ) of this species is high. This may be especially important in shaded environments where input of light energy is low. We also suggest that, in the leaves of sun species, ATP/O 2 changes depending on the conditions.

Distribution of dissolved organic carbon in Lake Baikal and its watershed

Abstract Concentrations of dissolved organic carbon (DOC) in Lake Baikal ranged from 90 to 110 μM C, considerably higher than those in oceanic environments. The DOC concentrations in the epilimnion were higher than those in the hypolimnion. Since particulate organic carbon (POC) concentrations in the pelagic waters of Lake Baikal were <10–40 μM C in the epilimnion and 2–5 μM C in the hypolimnion, DOC constitutes a major component of the organic carbon pool in Lake Baikal, especially in the deep layers. The DOC concentrations downstream of the Barguzin and Selenga Rivers were quite high (400–500 μM C). Probably because of the high concentrations of DOC in these rivers, the DOC levels in Barguzin Bay and offshore at the mouth of the Selenga River were higher than those in the pelagic regions of the central and south basins of Lake Baikal. The relationship between DOC and electric conductivity revealed the transport of DOC from rivers to the pelagic area in Lake Baikal. The spatial distribution of DOC suggested that a major part of DOC in the lake was allochthonous (land-derived).

Simultaneous removal of phenol and ammonia by an activated sludge process with cross-flow filtration

Attempts were made for removing ammonia from synthetic wastewater under the presence of phenol, which is inhibitory to nitrification, by using a single-stage activated sludge process with cross-flow filtration. Activated sludge biomass which had been acclimated with phenol for over 15 years was used for the inoculum, and synthetic wastewater was continuously supplied to the process retaining biomass at 8000 mg VSS l(-1). Phenol was completely removed, and ammonia was simultaneously nitrified to nitrate; nitrification rate reached 200 mg N l(-1) d(-1) when phenol was removed at a rate up to 300 mg l(-1) d(-1). It was observed that 0-13% of the ammonia was removed via denitrification. Intermittent aeration enhanced the denitrification rate to 160 mg N l(-1) d(-1) by utilizing phenol. and approximately 24% of the denitrified nitrogen was recovered as nitrous oxide. Methanol, which is the most commonly used electron donor in conventional nitrogen removal processes, did not enhance the denitrification rate of the phenol-acclimated activated sludge used in this study, however phenol did. The results suggest that this process potentially works as a space- and energy-saving nitrogen removal process by utilizing substances inhibitory to nitrifiers as electron donors for denitrification.

Nitrogen stable isotope ratio of groundwater N2O

δ15N of N2O and NO3− were measured to determine the mechanisms producing N2O in nitrate contaminated groundwaters. These groundwaters contained N2O at concentrations between thirty to one hundred times higher than the atmospheric equilibrium. The N2O/NO3− molar ratios in groundwaters were from 0.2 × 10−3 to 4.4 × 10−3. The δ15N values of N2O, −5.8 to −21.3 permil, were much lower than those of coexistent NO3−, +3.6 to +7.3 permil. In the light of evidence that 15N in N2O from nitrification is highly depleted, the present findings suggest nitrification as a dominant mechanism for the production of N2O in the groundwaters. However, unlike other aquatic systems where nitrification is a major route of N2O production, no clear correlation was observed between ΔN2O and −ΔO2 in the groundwater. This poor correlation strongly suggests that N2O in the groundwater was predominantly produced in the soil column and/or unsaturated zone. Based on two-year observation of N2O flux from a spring, a possible charging rate of N2O to the aquifer was estimated as 1.2–2.3 mg N2O-N·m−2·y−1. The rate is much smaller than the reported soil emission rates, suggesting the groundwater N2O to be an insignificant source for atmospheric N2O. Large discrepancies in δ15N of N2O between the groundwaters and the surface airs support this view.

Accumulation of nitrous oxide in aerobic groundwaters

Abstract N 2 O concentrations in the groundwaters collected in the Kanto District and Nagano Prefecture in Japan and five counties in New York State were determined. These N 2 O data were obtained from the water samples from wells, springs and seepages from soils in forests and cropping fields. The N 2 O concentrations in all samples greatly exceeded those of atmospheric equilibration. The average concentration of 690 nM N 2 O is one order of magnitude larger than that in deep ocean. All groundwaters of the present study were aerobic with a high level of NO 3 − , but with the absence of NO 2 − and NH 4 + , and with a very low level of dissolved organic carbon. These characteristics suggest that the nitrate respiration in the aquifers is of little significance for the production of N 2 O. ΔN 2 O/NO 3 − molar ratios in the groundwaters were between 10 −4 and 10 −2 (Δ indicates the excess gas over that which would be in equilibrium). This supports the above view since the observed N 2 O yield agrees with that reported for the production during an ammonia oxidation. If nitrification was indeed a major mechanism for the production of groundwater N 2 O, subsequent release of N 2 O from the aquifers that are polluted with nitrogen may deserve more close attention as a potential source of atmospheric N 2 O via diffusion and discharge.

Costs of protein turnover and carbohydrate export in leaves of sun and shade species

In mature leaves, adenosine triphosphate (ATP) provided by respiration is used for maintenance of leaves and carbohydrate export (starch mobilisation and phloem loading). The main maintenance processes of mature leaves include turnover of existing structures (e.g. proteins and membranes) and the trans-membrane transport of solutes. In order to mechanistically estimate these costs in mature leaves and compare them between sun and shade species, we measured the costs of protein turnover and carbohydrate export in mature leaves of Alocasia odora (Lodd.) Spach., a shade-tolerant species, and Phaseolus vulgaris L., a sun species, in the night. We estimated the rate of ATP production from the rate of O 2 uptake, taking account of the contribution of the alternative respiratory pathway, assessed by the O 2 isotope fractionation technique. The energy consumption of protein turnover was estimated from the decrease in the rate of ATP production in the presence of an inhibitor of cytosolic protein synthesis. Examination of the anatomy of the minor veins in the leaves revealed that A. odora employs symplastic phloem loading, while P. vulgaris was reported to employ apoplastic loading. Based on these phloem loading types and the difference between the rate of carbohydrate decrease and the CO 2 efflux rate in the leaves, we calculated the ATP cost for carbohydrate export. The costs estimated for two processes amounted to about 40% of the ATP production rate in A. odora and 80% in P. vulgaris. The absolute costs for the two processes in the leaves of A. odora were much lower than those of P. vulgaris. Both the cost of protein turnover per unit leaf nitrogen and that of carbohydrate export per exported carbon were lower in the leaves of A. odora. Low ATP consumption rates by these cellular processes would explain the low respiratory rate in A. odora.

Dynamics of dissolved O2, CO2, CH4, and N2O in a tropical coastal swamp in southern Thailand

We studied the distribution of dissolved O2, CO2, CH4, and N2O in a coastal swamp system in Thailand with the goal to characterize the dynamics of these gases within the system. The gas concentrations varied spatially and seasonally in both surface and ground waters. The entire system was a strong sourcefor CO2 and CH4, and a possible sink for atmospheric N2O. Seasonal variation in precipitation primarily regulated the redox conditions in the system. However, distributions of CO2, CH4, and N2O in the river that received swamp waters were not always in agreement with redox conditions indicated by dissolvedO2 concentrations. Sulfate production through pyriteoxidation occurred in the swamp with thin peat layerunder aerobic conditions and was reflected by elevatedSO42−/Cl− in the river water. When SO42−/Cl− was high, CO2 and CH4 concentrations decreased, whereas the N2O concentration increased. The excess SO42− in the river water was thus identified as a potential indicator for gas dynamics in this coastal swamp system.

Stable isotope and radiocarbon compositions of methane emitted from tropical rice paddies and swamps in Southern Thailand

Stable isotopes (δ13C, δD) and radiocarbon weremeasured in methane bubbles emitted from rice paddies and swamps in southernThailand. Methane emitted from the Thai rice paddies was enriched in13C (mean δ13C; −51.5 ±7.1‰ and−56.5 ± 4.6‰ for mineral soil and peat soil paddies,respectively)relative to the reported mean value of methane from temperate rice paddies(− 63 ± 5‰). Large seasonal variation was observed inδ13C(∼32‰) in the rice paddies, whereas variationinδD was much more smaller (∼20‰), indicating that variation inδ13C is due mainly to changes in methane production pathways.Values of δ13C were lower in swamps (−66.1 ±5.1‰)than in rice paddies. The calculated contribution of acetate fermentation fromδ13C value was greater in rice paddies (mineral soils:62–81%, peat soils: 57–73%) than in swamps (27–42%). δDin methane from Thai rice paddies (−324± 7‰ (n=46)) isrelativelyhigher than those from 14 stations in Japanese rice paddies ranging from−362 ± 5‰ (Mito: n=2) to −322 ± 8‰(Okinawa: n=3), due tohigher δD in floodwaters. 14C content in methane produced fromThai rice paddies (127±1 pMC) show higher 14Cactivity compared with previous work in paddy fields and those from Thai swamps(110±2 pMC).

Distribution and characteristics of molecular size fractions of freshwater-dissolved organic matter in watershed environments: its implication to degradation

Distributions of molecular size and fluorescence properties of dissolved organic matter (DOM) in the Lake Biwa and Lake Baikal watersheds were investigated using the cross-flow ultrafiltration technique and three-dimensional fluorescence measurements. From the fluorescence properties, protein-like substances were usually found in the 0.1 μm-GF/F fraction (the Durapore membrane retentate of the GF/F filtrate) of the lake DOM. The results indicated autochthonous production of protein-like organic-matters in the lake environment. Fulvic acid (FA)-like components were composed of two fractions with respect to fluorescence properties and molecular size. Two FA-like fluorescence peaks, which showed different fluorescence peak positions in the excitation-emission matrix (EEM), were partly fractionated by the molecular size of 5000 daltons (5 kDa). The FA-like fluorescence peak position of the <5-kDa fraction was observed at the shorter wavelength region compared with that of the fraction between 5 kDa and 0.1 μm (5 kDa20.1 μm fraction). A blue shift of the FA-like fluorescence peak position as well as a decrease in the molecular size of the DOM was observed in lake samples. The relative contribution of the <5 kDa fraction to the DOC concentration was high in lake waters (68%–79%) compared with river waters (44%–68%), suggesting characteristic changes in molecular size between riverine and lacustrine DOM. DOM of the 5 kDa–0.1 μm fraction was relatively higher in river waters than in lake waters. These findings coincided with in situ distributions of the fluorescence properties and molecular size of DOM found in both stream and lake environments. These results indicate that FA-like substances from forested watersheds are decomposed qualitatively and quantitatively in the river-lake environment by photochemical and biological processes.