Yoshihiko Sekozawa

Development of a mobile magnetic resonance imaging system for outdoor tree measurements

By combining a 0.3 T permanent magnet with flexible rotation and translation mechanism, a probe with a local electromagnetic shielding, several electrical units, a mobile lift, and an electric wagon, a mobile magnetic resonance imaging (MRI) system was developed for outdoor tree measurements. 2D cross-sectional images of normal and diseased branches of a pear tree were acquired for measurements of T(1), T(2), proton density, and apparent diffusion constant (ADC). The ADC map clearly differentiated diseased from normal branches. A whole-day measurement of the ADC map demonstrated that microscopic water flow in the normal branch changed proportionally with solar radiation. Therefore, we have concluded that our mobile MRI system is a powerful tool for studies of plants in outdoor environments.

Longitudinal NMR parameter measurements of Japanese pear fruit during the growing process using a mobile magnetic resonance imaging system

Longitudinal nuclear magnetic resonance (NMR) parameter measurements of Japanese pear fruit (Pyrus pyrifolia Nakai, Kosui) were performed using an electrically mobile magnetic resonance imaging (MRI) system with a 0.2 T and 16 cm gap permanent magnet. To measure the relaxation times and apparent diffusion coefficients of the pear fruit in relation to their weight, seven pear fruits were harvested almost every week during the cell enlargement period and measured in a research orchard. To evaluate the in situ relaxation times, six pear fruits were longitudinally measured for about two months during the same period. The measurements for the harvested samples showed good agreement with the in situ measurements. From the measurements of the harvested samples, it is clear that the relaxation rates of the pear fruits linearly change with the inverse of the linear dimension of the fruits, demonstrating that the relaxation mechanism is a surface relaxation. We therefore conclude that the mobile MRI system is a useful device for measuring the NMR parameters of outdoor living plants.

Differential adaptation of high- and low-chill dormant peaches in winter through aquaporin gene expression and soluble sugar content

Plants have their own mechanisms for overcoming various stresses. In cold regions, plants are subject to stress and must enter an inherent dormancy, through several complex mechanisms, if they are to continue to exist. In winter, regulation of tonoplast and plasma membrane aquaporin genes differed in the bud cushions of the high-chill peach (Prunus persica L. Batsch) cv. Kansuke Hakuto and the low-chill peach cv. Coral. In December and January, when the temperature was lowest (around 2°C), the increased expression of Pp-γTIP1 and Pp-PIP1 seen in the bud cushions of Kansuke Hakuto may have been related to the concomitant high-soluble sugar content of the cushions of this cultivar. This relationship may have made the cells highly stable and relatively unaffected by low-temperature stress owing to the presence of “glasses” that prevented ice nucleation. However, a simpler form of cold protection regulation seemed to occur in Coral, in which there was no winter increase in Pp-γTIP1 and Pp-PIP1 mRNA and a slow decline in total soluble sugar content in December and January. These results suggested that Pp-γTIP1 and Pp-PIP1, respectively, play important roles in intra- and intercellular membrane transport, enhancing cold resistance in the bud cushions of high-chill cultivars. In addition, Pp-δTIP1 and Pp-PIP2 mRNA increased at the end of endodormancy in both cultivars. This change may be induced by endodormancy-release signals and the resumption of bud activity in both cultivars.

High ice nucleation activity located in blueberry stem bark is linked to primary freeze initiation and adaptive freezing behaviour of the bark

One may have seen wintering rosette leaves totally frozen and wilted in the early morning but recover during the daytime. How can cold hardy plants survive freezing of the tissues, unlike animal tissues? Cold hardy plants seem to have evolved various strategies. One example is extracellular freezing, where icicles primarily form in intercellular spaces whilst the cells are dehydrated, yet the underlying mechanisms remain unclear. In this study, using blueberry stems, we found high ice nucleation activity specifically localized in the cell wall fraction of bark tissues. This activity likely contributes to the primary and spontaneous initiation of freezing in the intercellular spaces of the bark to successfully perform extracellular freezing.

Carbohydrate metabolism in ‘Housui’ Japanese pear floral buds exposed to different temperatures during endodormancy

To elucidate the effects of temperature on carbohydrate metabolism under mild winter conditions, Japanese pear ( Pyrus pyrifolia Nakai) shoots were exposed to temperatures of 0, 6 and 12 °C for 600 hours during endodormancy, and subsequent bud dormancy release and carbohydrate metabolism were examined. Lateral floral buds were collected after 0, 200, 400, and 600 hours under the treatments, and after the accumulation of 2000, 4000, 6000, and 8000 growing degree hours (GDH) under heat accumulation, for carbohydrate and enzyme activities analysis. The bud burst was earliest for the 12 °C treatment, followed by the 6 and 0 °C treatments. Sucrose concentration under heat accumulation decreased early in buds from the 12 °C treatment. The sorbitol and sucrose concentration in the buds increased under 0 °C during the endodormancy. In contrast, glucose and fructose concentrations tended to increase under heat accumulation. Sucrose synthase (SS) activity increased early under heat accumulation in buds from the 6 and 12 °C treatments, but in 0 °C buds it increased more slowly, from 2000 GDH onwards. Similarly, soluble acid invertase (AI) activity increased markedly in all treatments from the middle of the heat accumulation period. We therefore suggest that a temperature of 12 °C during endodormancy may advance bud burst as the result of earlier conversion of sucrose into hexoses.

Metabolomics analysis of 'Housui' Japanese pear flower buds during endodormancy reveals metabolic suppression by thermal fluctuation

Dormancy is a complex phenomenon that allows plants to survive the winter season. Studies of dormancy have recently attracted more attention due to the expansion of temperate fruit production in areas under mild winters and due to climate changes. This study aimed to identify and characterize the metabolic changes induced by chilling temperatures, as well as during thermal fluctuation conditions that simulate mild winter and/or climate change scenarios. To do this, we compared the metabolic profile of Japanese pear flower buds exposed to constant chilling at 6 °C and thermal fluctuations of 6 °C/18 °C (150 h/150 h) during endodormancy. We detected 91 metabolites by gas chromatography paired with time-of-flight mass spectrometry (GC-TOF-MS) that could be classified into eight groups: amino acids, amino acid derivatives, organic acids, sugars and polyols, fatty acids and sterols, phenol lipids, phenylpropanoids, and other compounds. Metabolomics analysis revealed that the level of several amino acids decreased during endodormancy. Sugar and polyol levels increased during endodormancy during constant chilling and might be associated with chilling stress tolerance and providing an energy supply for resuming growth. In contrast, thermal fluctuations produced low levels of metabolites related to the pentose phosphate pathway, energy production, and tricarboxylic acid (TCA) cycle in flower buds, which may be associated with failed endodormancy release. This metabolic profile contributes to our understanding of the biological mechanism of dormancy during chilling accumulation and clarifies the metabolic changes during mild winters and future climate change scenarios.

Effects of Pre-chilling Potassium Nitrate and Post-chilling Hydrogen Cyanamide Application on Carbohydrate and Water Dynamics of ‘Housui’ Japanese Pear Spur Buds During Dormancy Under Mild Winter Conditions

Japanese pear ( Pyrus pyrifolia Nakai) trees were treated with potassium nitrate (KNO 3 ) before the onset of chilling and hydrogen cyanamide (CH 2 N 2 ) after the trees had accumulated 600 chilling hours (CH) to determine the effects on bud dormancy release, carbohydrate dynamics, and water content. For the carbohydrate and water content analyses, Japanese pear spur buds were collected after 0, 300, and 600 CH, and after the accumulation of 2000, 4000, 6000, and 8000 growing degree hours (GDH) during the dormancy period. Bud burst and flowering were hastened by both KNO 3 and CH 2 N 2 application, and both chemicals affected carbohydrate and water dynamics during dormancy. Sucrose concentration tended to increase during the chilling period, and to decrease under forcing conditions. Hexose concentrations increased in buds treated with KNO 3 , CH 2 N 2 , or both, and were associated with advances in bud burst. Sorbitol concentration decreased early in buds treated with CH 2 N 2 , suggesting rapid sorbitol catabolism. Water content gradually increased under forcing conditions in all buds, although those treated with both KNO 3 and CH 2 N 2 exhibited the highest values. Accordingly, we recommend the use of KNO 3 and CH 2 N 2 , before and after chilling, respectively, to promote the release of bud dormancy and increase bud burst rate in ‘Housui’ Japanese pear grown in regions with mild winter conditions.