Yoshimi Ohmae

Leaf senescence in rice due to magnesium deficiency mediated defect in transpiration rate before sugar accumulation and chlorosis.

Magnesium (Mg) is an essential macronutrient supporting various functions, including photosynthesis. However, the specific physiological responses to Mg deficiency remain elusive. In this study, 2-week-old rice seedlings (Oryza sativa. cv. Nipponbare) with three expanded leaves (L2-L4) were transferred to Mg-free nutrient solution for 8 days. In the absence of Mg, on day 8, L5 and L6 were completely developed, while L7 just emerged. We also studied several mineral deficiencies to identify specific responses to Mg deficiency. Each leaf was analyzed in terms of chlorophyll, starch, anthocyanin and carbohydrate metabolites, and only absence of Mg was found to cause irreversible senescence of L5. Resupply of Mg at various time points confirmed that the borderline of L5 death was between days 6 and 7 of Mg deficiency treatment. Decrease in chlorophyll concentration and starch accumulation occurred simultaneously in L5 and L6 blades on day 8. However, nutrient transport drastically decreased in L5 as early as day 6. These data suggest that the predominant response to Mg deficiency is a defect in transpiration flow. Furthermore, changes in myo-inositol and citrate concentrations were detected only in L5 when transpiration decreased, suggesting that they may constitute new biological markers of Mg deficiency.

Development of a 14 C detectable real-time radioisotope imaging system for plants under intermittent light environment

A new real-time radioisotope imaging system (RRIS) to study the kinetics of nutrient uptake and transfer of photosynthetic products in a living plant was developed and evaluated through a test run. 14C is a common radioisotope of carbon and useful to trace the photosynthetic products as well as a low energy beta emitter. The rationale of this study was to develop a RRIS that has the ability to detect low energy beta emitters, such as 14C, 35S, and 45Ca. To achieve compatibility between the detection of low energy beta emitters and irradiation of the test plant, an intermittent lighting system was added to the RRIS. Furthermore, a commercially available digital camera was added to the RRIS for acquisition of photographic images of the test plants. The capabilities of the new RRIS were evaluated through a test run by using seedlings of rice plants and 35S-labeled sulfate. It was shown that the new RRIS was able to detect 35S absorbed by rice plant seedlings, and it was able to acquire photon-counting images and photographic images of the test plants simultaneously. Despite some limitations, the new RRIS provides a means to study the kinetics of elements in plants by utilizing low energy beta emitters.

Nondestructive real-time radioisotope imaging system for visualizing 14C-labeled chemicals supplied as CO2 in plants using Arabidopsis thaliana

We have developed a real-time radioisotope imaging system (RRIS) that can nondestructively trace 14C-labeled chemicals in plants. In an experiment, after feeding 14CO2 to a plant, the plant was fixed inside a box where lighting was regulated, and beta rays emitted from the 14C in the plant were intermittently imaged using the developed system. As a first step, using a series of standard sources of 14C, the data depth and detection limits of the 14C images captured by the RRIS were evaluated for various integral times. As a result, the linearity between the 14C activity and signal intensity was determined for the range 103. Next, the linearity was validated using plant (Arabidopsis thaliana) organs, resulting that the linearity was shown in the case of young leaf, but was not maintained in the thick organs, such as a flower, mature leaf, siliques, and stem. Considering the good correlation between the intensity by RRIS and the PSL value by an imaging plate (IP) as well as the relative low energy of beta rays emitted from 14C, the thickness of the organs would easily affect the quantitativity of the RRIS as well as an IP. Our findings prove that sequential images of 14C in a living plant sample in a regulated light and air environment can be nondestructively analyzed using the developed system, whose quantitativity is similar to that of an IP.

Carbon-14 labelled sucrose transportation in an Arabidopsis thaliana using an imaging plate and real time imaging system

As an approach to increased production of rape seed oil from Brassica napus L., Arabidopsis thaliana, a species from the same Brassicaceae family, was used to investigate transport behavior and distribution of matter in the plant body. In this study, sucrose, an initial metabolic product of photosynthesis, labeled with carbon-14 was used. The sucrose was applied to A. thaliana via the surface of a rosette leaf. Using the real time radioisotope imaging system we developed and an imaging plate (IP), images of whole or part of the sample were obtained. The sucrose assimilation products were accumulated in maturing tissue such as flowers and fruits, and in a joint part. From the comparison among branches and stems, it was indicated that there were different patterns of demand and distribution of sucrose assimilation products depending on the tissue and its growing stage. This might be caused by either morphological reason such as diameter and location of the sieve tube, or genetic factors such as an activity of a membrane transport protein. Because of self-absorption of carpels, it was difficult to observe the accumulation of carbon-14 in the seeds inside the fruits; however, an IP image of a frozen section of a fruit revealed that carbon-14 transport to seeds was higher than that of carpels. These methods will help us gain insight into matter transport and strategies to improve the production of rape seed oil.

Water adsorption process of bamboo heated at low temperature

Water adsorption capacities were evaluated for moso bamboo samples that were heated at 200°C for various times and conditioned in a closed container at 97% relative humidity at 20°C. Logistic regression analysis was used for curve fitting to the adsorption data and its parameters were analyzed. These parameters were compared with those derived previously from the Dubinin and Radushkevich theory. The properties of the heat-treated samples changed after 5 h of heating. With less than 5 h of heating, hydroxyl groups provided the main adsorption sites but their numbers decreased on heating. After 5 h, gasifi cation of the bamboo increased and capillaries formed.

Mineral composition of frozen taro for determination of geographic origin

The mineral composition of frozen food of taro [Colocasia esculenta (L.) Schott] was analyzed to categorize the geographical production place of taro. The concentrations of Co and H2PO4− were found to be useful to separate the producing place between Japan and China. The analysis was performed by instrumental neutron activation analysis (INAA) and ion chromatography (IC). In the case of INAA, the samples were dried and sealed in a vinyl bag and irradiated with thermal neutrons from JRR3M, installed at Japan Atomic Energy Agency (JAEA). The activated samples were cooled down for a few weeks and the elements (Co, Cr, Fe, Rb, Zn) were determined. Cobalt concentration of frozen taro from China was higher than that from Japan. The tendency was the same in the fresh sample of taro. When concentration of H2PO4− of frozen sample was measured, taro from Japanese product was higher than that of Chinese one, contrary to fresh sample. This result might be caused by the leakage of H2PO4− during freezing process, indicating that we should be careful to apply the discrimination indicators. In addition to Co, there was a significant difference of Rb and Fe concentrations between frozen taro from Japan and China.