記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

<title>Abstract</title>Watercore is a physiological disorder in apple (<italic>Malus</italic> <italic>×</italic> <italic>domestica</italic> Borkh.) fruits that appears as water-soaked tissues adjacent to the vascular core, although there is little information on what exactly occurs at cell level in the watercored apples, particularly from the viewpoint of cell water relations. By combining picolitre pressure-probe electrospray-ionization mass spectrometry (picoPPESI-MS) with freezing point osmometry and vapor pressure osmometry, changes in cell water status and metabolisms were spatially assayed in the same fruit. In the watercored fruit, total soluble solid was lower in the watercore region than the normal outer parenchyma region, but there was no spatial difference in the osmotic potentials determined with freezing point osmometry. Importantly, a disagreement between the osmotic potentials determined with two methods has been observed in the watercore region, indicating the presence of significant volatile compounds in the cellular fluids collected. In the watercored fruit, cell turgor varied across flesh, and a steeper water potential gradient has been established from the normal outer parenchyma region to the watercore region, retaining the potential to transport water to the watercore region. Site-specific analysis using picoPPESI-MS revealed that together with a reduction in turgor, remarkable metabolic modifications through fermentation have occurred at the border, inducing greater production of watercore-related volatile compounds, such as alcohols and esters, compared with other regions. Because alcohols including ethanol have low reflection coefficients, it is very likely that these molecules would have rapidly penetrated membranes to accumulate in apoplast to fill. In addition to the water potential gradient detected here, this would physically contribute to the appearance with high tissue transparency and changes in colour differences. Therefore, it is concluded that these spatial changes in cell water relations are closely associated with watercore symptoms as well as with metabolic alterations.

DOI： 10.1038/s41438-021-00603-1

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その他リンク： https://www.nature.com/articles/s41438-021-00603-1

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

Abstract

High night temperature (HNT) often reduces yield in field crops. In rice, HNT during the ripening stage diminishes endosperm cell size, resulting in a considerable reduction in final kernel weight; however, little is known about the underlying mechanisms at cell level. In this study, we performed picolitre pressure-probe-electrospray-ionization mass spectrometry to directly determine metabolites in growing inner endosperm cells of intact seeds produced under HNT conditions, combining with ¹³C feeding and water status measurements including in situ turgor assay. Microscopic observation in the inner zone suggested that approximately 24.2% of decrease in cell expansion rate occurred under HNT at early ripening stage, leading to a reduction in cell volume. It has been shown that HNT-treated plants were subjected to mild shoot water deficit at night and endosperm cell turgor was sustained by a decline in osmotic potential. Cell metabolomics also suggests that active solute accumulation was caused by a partial inhibition of wall and starch biosynthesis under HNT conditions. Because metabolites were detected in the single cells, it is concluded that a partial arrest of cell expansion observed in the inner endosperms was caused by osmotic adjustment at mild water deficit during HNT conditions.

DOI： 10.1038/s41598-021-83870-1

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その他リンク： http://www.nature.com/articles/s41598-021-83870-1

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

High night temperature (HNT) at the ripening stage severely affects both rice yield and quality. HNT accelerates embryo growth and chalky formation in the developing grains, accompanying with a diminishment of endosperm cell size. Although these responses may be physiologically interacted each other in the grains, what signals are involved in the accelerated embryo development remains undetermined. In this work, we have used picolitre pressure-probe electrospray-ionization mass spectrometry (picoPPESI-MS) to conduct single-cell metabolomics at several regions in HNT-treated grains, embryonic scutellum and outer endosperms in the basal ('chalky region' at maturation) and middle ('translucent region' at maturation as a reference) positions. Microscopic observations showed that HNT promoted cell expansion rate in the scutellum. When embryonic cell expansion rate reached the maximum, spatial differences in several metabolisms including ascorbate-glutathione (ASC-GSH) pathway and purine were detected, together with considerable sugar and amino acid accumulations in embryonic scutellum cells. There was no treatment difference in GSH content during active cell expansion in HNT-treated embryos, although an increase in GSH/GSSG ratio due to a reduction in oxidized glutathione (GSSG) content has been contrastingly observed. In the endosperms, greater ASC accumulation with a difference in ASC/dehydroascobic acid ratio has been also detected under HNT conditions. Since dormancy is often correlated with GSSG concentration, it is concluded that spatial regulation of GSH redox homeostasis detected at cell-level might be essential for dormancy alleviation and embryo growth accelerated in HNT-treated seeds.

DOI： 10.1016/j.envexpbot.2021.104515

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

Although a loss of healthy pollen grains induced by metabolic heat responses has been indicated to be a major cause of heat-induced spikelet sterility under global climate change, to date detailed information at pollen level has been lacking due to the technical limitations. In this study, we used picolitre pressure-probe-electrospray-ionization mass spectrometry (picoPPESI-MS) to directly determine the metabolites in heat-treated single mature pollen grains in two cultivars, heat-tolerant cultivar, N22 and heat-sensitive cultivar, Koshihikari. Heat-induced spikelet fertility in N22 and Koshihikari was 90.0% and 46.8%, respectively. While no treatment difference in in vitro pollen viability was observed in each cultivar, contrasting varietal differences in phosphatidylinositol (PI)(34:3) have been detected in mature pollen, together with other 106 metabolites. Greater PI content was detected in N22 pollen regardless of the treatment, but not for Koshihikari pollen. In contrast, there was little detection for phosphoinositide in the single mature pollen grains in both cultivars. Our findings indicate that picoPPESI-MS analysis can efficiently identify the metabolites in intact single pollen. Since PI is a precursor of phosphoinositide that induces multiple signaling for pollen germination and tube growth, the active synthesis of PI(34:3) prior to germination may be closely associated with sustaining spikelet fertility even at high temperatures.

DOI： 10.1038/s41598-020-58869-9

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1104/pp.19.00743

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Heat-induced chalkiness of rice grains is a major concern for rice production, particularly with respect to climate change. Although the formation of chalkiness in the endosperm is suppressed by nitrogen, little is known about the cell-specific dynamics of this process. Here, using picolitre pressure-probe electrospray-ionization mass spectrometry together with transmission electron microscopy and turgor measurements, we examine heat-induced chalkiness in single endosperm cells of intact rice seeds produced under controlled environmental conditions. Exposure to heat stress decreased turgor pressure and increased the cytosolic accumulation of sugars, glutathione, and amino acids, particularly cysteine. Heat stress also led to a significant enlargement of the protein storage vacuoles but with little accumulation of storage proteins. Crucially, this heat-induced partial arrest of amyloplast development led to formation of chalkiness. Whilst increased nitrogen availability also resulted in increased accumulation of amino acids, there was no decrease in turgor pressure. The heat-induced accumulation of cysteine and glutathione was much less marked in the presence of nitrogen, and storage proteins were produced without chalkiness. These data provide important information on the cell dynamics of heat acclimation that underpin the formation of chalkiness in the rice endosperm. We conclude that rice seeds employ multiple strategies to mitigate the adverse effects of heat stress in a manner that is dependent on nitrogen availability, and that the regulation of protein synthesis may play a crucial role in optimizing organelle compartmentation during heat adaption.

DOI： 10.1093/jxb/ery427

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/s00425-018-2975-x

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DOI： 10.1080/1343943X.2018.1510292

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER JAPAN KK  

In C-3 plants, part of the CO2 fixed during photosynthesis in chloroplasts is released from mitochondria during photorespiration by decarboxylation of glycine via glycine decarboxylase (GDC), thereby reducing photosynthetic efficiency. The apparent positioning of most mitochondria in the interior (vacuole side of chloroplasts) of mesophyll cells in C-3 grasses would increase the efficiency of refixation of CO2 released from mitochondria by ribulose 1,5-bisphosphate carboxylase/aEuroioxygenase (Rubisco) in chloroplasts. Therefore, in mesophyll cells of C-4 grasses, which lack both GDC and Rubisco, the mitochondria ought not to be positioned the same way as in C-3 mesophyll cells. To test this hypothesis, we investigated the intracellular position of mitochondria in mesophyll cells of 14 C-4 grasses of different C-4 subtypes and subfamilies (Chloridoideae, Micrairoideae, and Panicoideae) and a C-3-C-4 intermediate grass, Steinchisma hians, under an electron microscope. In C-4 mesophyll cells, most mitochondria were positioned adjacent to the cell wall, which clearly differs from the positioning in C-3 mesophyll cells. In S. hians mesophyll cells, the positioning was similar to that in C-3 cells. These results suggest that the mitochondrial positioning in C-4 mesophyll cells reflects the absence of both GDC and Rubisco in the mesophyll cells and the high activity of phosphoenolpyruvate carboxylase. In contrast, the relationship between the mitochondrial positioning and enzyme distribution in S. hians is complex, but the positioning may be related to the capture of respiratory CO2 by Rubisco. Our study provides new possible insight into the physiological role of mitochondrial positioning in photosynthetic cells.

DOI： 10.1007/s10265-017-0947-z

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：TAYLOR & FRANCIS LTD  

In C-3 plants, photosynthetic efficiency is reduced by photorespiration. A part of CO2 fixed during photosynthesis in chloroplasts is lost from mitochondria during photorespiration by decarboxylation of glycine by glycine decarboxylase (GDC). Thus, the intracellular position of mitochondria in photosynthetic cells is critical to the rate of photorespiratory CO2 loss. We investigated the intracellular position of mitochondria in parenchyma sheath (PS) and mesophyll cells of 10 C-3 grasses from 3 subfamilies (Ehrhartoideae, Panicoideae, and Pooideae) by immunostaining for GDC and light and electron microscopic observation. Immunostaining suggested that many mitochondria were located in the inner half of PS cells and on the vacuole side of chloroplasts in mesophyll cells. Organelle quantification showed that 62-75% of PS mitochondria were located in the inner half of cells, and 62-78% of PS chloroplasts were in the outer half. In mesophyll cells, 61-92% of mitochondria were positioned on the vacuole side of chloroplasts and stromules. In PS cells, such location would reduce the loss of photorespiratory CO2 by lengthening the path of CO2 diffusion and allow more efficient fixation of CO2 from intercellular spaces. In mesophyll cells, it would facilitate scavenging by chloroplasts of photorespiratory CO2 released from mitochondria. Our data suggest that the PS cells of C-3 grasses have already acquired an initial structure leading to proto-Kranz and further C-3 - C-4 intermediate anatomy. We also found that in the Pooideae, organelle positioning in PS cells on the phloem side resembles that in mesophyll cells.

DOI： 10.1080/1343943X.2016.1212667

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記述言語：日本語   会議種別：口頭発表（一般）  

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記述言語：日本語   会議種別：口頭発表（一般）  

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記述言語：日本語   会議種別：口頭発表（一般）  

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記述言語：日本語   会議種別：シンポジウム・ワークショップ パネル（指名）  

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記述言語：英語   会議種別：口頭発表（一般）  

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記述言語：英語   会議種別：口頭発表（一般）  

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記述言語：英語   会議種別：ポスター発表  

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記述言語：日本語   会議種別：口頭発表（一般）  

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記述言語：日本語   会議種別：ポスター発表  

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記述言語：日本語   会議種別：ポスター発表  

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記述言語：日本語   会議種別：ポスター発表  

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