Endosperm cell size reduction caused by osmotic adjustment during nighttime warming in rice

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.

Physiological and molecular attributes contribute to high night temperature tolerance in cereals

“…Changes in metabolite levels under HNT were mainly measured by gas‐chromatography–mass‐spectrometry (GC–MS) under controlled environmental conditions for rice (Dhatt et al, 2019; Glaubitz et al, 2015; Glaubitz et al, 2017) and winter wheat (Impa et al, 2019), and under field conditions for rice (Schaarschmidt, Lawas, et al, 2020). Metabolites were also determined in inner endosperm cells of intact seeds of the rice cultivar Koshihikari by picolitre pressure‐probe‐electrospray‐ionization mass spectrometry combined with 13 C feeding (Wada et al, 2021).…”

“…An accumulation of aspartic acid under HNT was also discovered in developing grains of six rice cultivars without genotype‐specific alterations regarding their HNT tolerance on metabolite or yield parameter levels, but no changes of the other amino acids were reported (Dhatt et al, 2019). Furthermore, a greater content of aspartic acid together with ascorbic acid, fumaric acid, glycerol and 3‐cyano‐l‐alanine was discovered in HNT‐treated rice endosperm cells during the day (Wada et al, 2021). During the night instead, cell wall related metabolites, redox‐related metabolites and stress response plant hormones were increased compared to control conditions (Wada et al, 2021).…”

“…Furthermore, a greater content of aspartic acid together with ascorbic acid, fumaric acid, glycerol and 3‐cyano‐l‐alanine was discovered in HNT‐treated rice endosperm cells during the day (Wada et al, 2021). During the night instead, cell wall related metabolites, redox‐related metabolites and stress response plant hormones were increased compared to control conditions (Wada et al, 2021). Increased accumulation of aspartic acid could be related to higher activity of AAT under HNT (Glaubitz et al, 2017) catalysing a reversible transamination to generate aspartic acid and 2‐oxoglutarate.…”

Advances in Plant Metabolomics and Its Applications in Stress and Single-Cell Biology

“…Ultra-high performance 21T-FTICR-MS enabled simultaneous capture of delicate isotopic structures for 47 known and 11 unknown metabolites, thereby elucidating their elemental compositions from single cells and providing information on metabolic heterogeneity in the cell population. Wada et al [203] performed picolitre pressure-probe-ESI MS 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 an in situ turgor assay. Their studies revealed the accumulation of active solute, including UDP-glucose, UDP-D-xylose (arabinose), and UDP, was caused by inhibition of wall and starch biosynthesis, leading to the partial arrest of cell expansion in the inner endosperms under the HNT conditions.…”

Direct evidence for dynamics of cell heterogeneity in watercored apples: turgor-associated metabolic modifications and within-fruit water potential gradient unveiled by single-cell analyses

“…A cell pressure probe has been used to measure cell water status and hydraulic properties of intact plant cells 21 , 22 . Combining the cell pressure probe and an Orbitrap mass spectrometer, picolitre Pressure-Probe Electrospray-Ionization Mass Spectrometry (picoPPESI-MS) 23 technique has been successfully applied to several in situ cell-specific metabolic analyses 23 – 27 . In this work, the novel technique has been utilised to directly assay both the cell water status and metabolites in the following three regions: watercore region, outer region (i.e., normal cortical parenchyma) and the border (i.e., the outermost layer of watercore region) in the flesh, in both watercored and non-watercored (normal) fruit.…”