Miki U. Ueda

Allocation of nitrogen within the crown during leaf expansion in Quercus serrata saplings

Early season leaf growth requires a large amount of nitrogen, and the amount of N provided for new leaf development has been well tested. Although shoot position within the crown strongly influences leaf properties, little is known about absorbed and remobilized nitrogen allocation in the tree crown. Thus, we investigated differences in the allocation of recently absorbed nitrogen in the tree crown. To quantify nitrogen allocation, we conducted 15N tracer experiments using potted saplings of the temperate deciduous oak (Quercus serrata Thunb. ex. Murray). Allocation of 15N within the crown varied significantly: the top leaves received more remobilized nitrogen than did the lateral leaves, suggesting that remobilized nitrogen is predominantly allocated to the top shoots, which are important for height growth. On the other hand, the proportion of currently-absorbed nitrogen to total nitrogen in the lateral leaves was more than twice that in the top leaves. We also detected the input and the output of nitrogen in the top leaves after the completion of leaf expansion, indicating that significant nitrogen cycling occurs even after full leaf expansion.

Proton spin relaxation induced by quantum tunneling in Fe8 molecular nanomagnet

The spin-lattice relaxation rate T - 1 1 and NMR spectra of 1 H in single crystal of molecular magnets Fe8 have been measured down to 15 mK. The relaxation rate T - 1 1 shows a strong temperature dependence down to 400 mK. The relaxation is well explained in terms of the thermal transition of the iron state between the discreet energy levels of the total spin S = 10. The relaxation time T 1 becomes temperature independent below 300 mK and is longer than 100 s. In this temperature region stepwise recovery of the 1 H-NMR signal after saturation was observed depending on the return field of the sweep field. This phenomenon is attributed to the resonant quantum tunneling at the fields where levels cross and is discussed in terms of the Landau-Zener transition.

Foliage nitrogen turnover: differences among nitrogen absorbed at different times by Quercus serrata saplings.

BACKGROUND AND AIMS Nitrogen turnover within plants has been intensively studied to better understand nitrogen use strategies. However, differences among the nitrogen absorbed at different times are not completely understood and the fate of nitrogen absorbed during winter is largely uncharacterized. In the present study, nitrogen absorbed at different times of the year (growing season, winter and previous growing season) was traced, and the within-leaf nitrogen turnover of a temperate deciduous oak Quercus serrata was investigated. METHODS The contributions of nitrogen absorbed at the three different times to leaf construction, translocation during the growing season, and the leaf-level resorption efficiency during leaf senescence were compared using (15)N. KEY RESULTS Winter- and previous growing season-absorbed nitrogen significantly contributed to leaf construction, although the contribution was smaller than that of growing season-absorbed nitrogen. On the other hand, the leaf-level resorption efficiency of winter- and previous growing season-absorbed nitrogen was higher than that of growing season-absorbed nitrogen, suggesting that older nitrogen is better retained in leaves than recently absorbed nitrogen. CONCLUSIONS The results demonstrate that nitrogen turnover in leaves varies with nitrogen absorption times. These findings are important for understanding plant nitrogen use strategies and nitrogen cycles in forest ecosystems.

Effects of Magnetic Anisotropy on Magnetization in Molecular Mesoscopic Magnet Fe8

We have measured the temperature, magnetic field and angular dependences of the magnetization of a single crystal of a molecular mesoscopic magnet [(C 6 H 15 N 3 ) 6 Fe 8 O 2 (OH) 12 ]Br 7 (H 2 O)Br·8H 2 O, Fe8. The molecule Fe8 consists of eight Fe 3+ ions with spins of s =5/2. The experimental results of the magnetizations at low temperatures show large anisotropy that is dependent on the orientation of the external magnetic field with respect to the crystal axis. These results are well explained by the Hamiltonian for an isolated molecule with total spin S =10 and anisotropies of D =-0.276 K and E =-0.035 K. The easy axis is determined to be oriented with an azimuthal angle of 16° from the a -axis in the a b -plane and an inclinational angle of 0.7° from the a b -plane.

Mutant selection in the self-incompatible plant radish (Raphanus sativus L. var. sativus) using two-step TILLING

Radish (Raphanus sativus L. var. sativus), a widely cultivated root vegetable crop, possesses a large sink organ (the root), implying that photosynthetic activity in radish can be enhanced by altering both the source and sink capacity of the plant. However, since radish is a self-incompatible plant, improved mutation-breeding strategies are needed for this crop. TILLING (Targeting Induced Local Lesions IN Genomes) is a powerful method used for reverse genetics. In this study, we developed a new TILLING strategy involving a two-step mutant selection process for mutagenized radish plants: the first selection is performed to identify a BC1M1 line, that is, progenies of M1 plants crossed with wild-type, and the second step is performed to identify BC1M1 individuals with mutations. We focused on Rubisco as a target, since Rubisco is the most abundant plant protein and a key photosynthetic enzyme. We found that the radish genome contains six RBCS genes and one pseudogene encoding small Rubisco subunits. We screened 955 EMS-induced BC1M1 lines using our newly developed TILLING strategy and obtained six mutant lines for the six RsRBCS genes, encoding proteins with four different types of amino acid substitutions. Finally, we selected a homozygous mutant and subjected it to physiological measurements.

High nitrate reductase activity in sprouts of Phyllostachys pubescens

We investigated the distribution of nitrate reductase activity (NRA) among leaves, roots, culms, twigs, sprouts, culm sheaths, and new leaves of Phyllostachys pubescens Mazel in May, when many sprouts emerge above ground and new leaves of adult culms expand. We found that the NRA differed among parts, and that sprouts showed high NRA. These results indicate that different tissues of P. pubescens vary in nitrate reduction, and sprouts possess high nitrate reduction capacity. We also found that culm sheaths showed high NRA, indicating that they have a high potential for nitrate reduction, even though they are shed in the way of sprout growth.

Quantum tunneling of magnetization in molecular nanomagnet Fe8 studied by NMR

Abstract Magnetization and NMR measurements have been performed for single crystals of molecular magnet Fe8. The field and temperature dependences of magnetization below 25 K are well described in terms of the isolated clusters with the total spin S=10. The stepwise recoveries of 1 H-NMR signals at the level crossing fields caused by the resonant quantum tunneling of magnetization were observed below 400 mK . The recovery of the NMR signals are explained by the fluctuation caused by the transition between the energy states of Fe magnetizations governed by Landau–Zener quantum transitions.

Decades-long effects of high CO2 concentration on soil nitrogen dynamics at a natural CO2 spring

The effects of high atmospheric CO2 concentration ([CO2]) on ecosystem processes have been explored using temporal facilities such as open-top-chambers and free-air CO2 enrichment. However, the effects of high [CO2] on soil properties takes decades and may not be captured by short-term experiments. Natural CO2 springs provide a unique opportunity to study the long-term effects of high [CO2]. In this study, we investigated soil properties at a natural CO2 spring. We found that the amounts of total carbon (C) and nitrogen (N) stored in the soil at the high [CO2] site exceeded those in the reference site by 60 and 30%, respectively. The effects of high [CO2] were large in the upper slope position where the canopy openness was high and plants grew faster, but no effects were detected in the lowest position where the canopy openness was lower (half of that at the upper slope position). In contrast, effects of high [CO2] on soil N dynamics, such as N mineralization and nitrification rates, did not exhibit a slope gradient. This suggests that effects of high [CO2] differed among soil stoichiometric characteristics and N dynamics. These complicated effects of high [CO2] imply that the future effects of high [CO2] on ecosystems could vary widely in conjunction with environmental conditions such as light availability and/or topographic conditions.

Plant–plant interactions mediate the plastic and genotypic response of Plantago asiatica to CO2: an experiment with plant populations from naturally high CO2 areas

BACKGROUND AND AIMS The rising atmospheric CO2 concentration ([CO2]) is a ubiquitous selective force that may strongly impact species distribution and vegetation functioning. Plant-plant interactions could mediate the trajectory of vegetation responses to elevated [CO2], because some plants may benefit more from [CO2] elevation than others. The relative contribution of plastic (within the plants lifetime) and genotypic (over several generations) responses to elevated [CO2] on plant performance was investigated and how these patterns are modified by plant-plant interactions was analysed. METHODS Plantago asiatica seeds originating from natural CO2 springs and from ambient [CO2] sites were grown in mono stands of each one of the two origins as well as mixtures of both origins. In total, 1944 plants were grown in [CO2]-controlled walk-in climate rooms, under a [CO2] of 270, 450 and 750 ppm. A model was used for upscaling from leaf to whole-plant photosynthesis and for quantifying the influence of plastic and genotypic responses. KEY RESULTS It was shown that changes in canopy photosynthesis, specific leaf area (SLA) and stomatal conductance in response to changes in growth [CO2] were mainly determined by plastic and not by genotypic responses. We further found that plants originating from high [CO2] habitats performed better in terms of whole-plant photosynthesis, biomass and leaf area, than those from ambient [CO2] habitats at elevated [CO2] only when both genotypes competed. Similarly, plants from ambient [CO2] habitats performed better at low [CO2], also only when both genotypes competed. No difference in performance was found in mono stands. CONCLUSION The results indicate that natural selection under increasing [CO2] will be mainly driven by competitive interactions. This supports the notion that plant-plant interactions have an important influence on future vegetation functioning and species distribution. Furthermore, plant performance was mainly driven by plastic and not by genotypic responses to changes in atmospheric [CO2].

Magnetic quantum tunneling in Fe8 with excited nuclei

We investigate the effect of dynamic nuclear spin fluctuation on quantum tunneling of the magnetization (QTM) in the molecular magnet Fe8 by increasing the nuclei temperature using radio frequency (RF) pulses before the hysteresis loop measurements. The RF pulses do not change the electrons spin temperature. Independently we show that the nuclear spin-spin relaxation time T2 has strong temperature dependence. Nevertheless, we found no effect of the nuclear spin temperature on the tunneling probability. This suggests that in our experimental conditions only the hyperfine field strength is relevant for QTM. We demonstrate theoretically how this can occur.