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.

Watercore is a so-called physiological disorder of apple (Malus domestica L.) that commonly occurs in several well-known cultivars. It is associated with a rapid softening of the flesh that causes a marked changed in flavor and texture. In Asia, apples with watercore are preferred and considered a delicacy because of their enhanced sweet flavor. The ‘Fuji’ cultivar, the first cultivar with rich watercore that is free from texture deterioration, has played a key role in the development of the market for desirable watercored apples. This review aimed to summarize and highlight recent studies related to the physiology of watercore in apples with special focus on ‘Fuji’ and related cultivars.

Watercore is a physiological disorder in apple (Malus × domesticaBorkh.) 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.

1-Deoxynojirimycin (DNJ) is a potent α-glucosidase inhibitor and thus beneficial for prevention of diabetes. While we have succeeded in obtaining the culture supernatant extract (CSE) rich in DNJ from microorganism source, information regarding its anti-hyperglycemic effect and safety were still limited. Therefore, this study was aimed to evaluate the anti-hyperglycemic effect and safety of microorganism DNJ. Oral sucrose tolerance test was performed, and the result showed that CSE was able to significantly suppress the blood glucose elevation and suggested DNJ as the main active compound. To determine its safety, the absorption and excretion of microorganism DNJ were evaluated using ¹⁵N labeling method. Our findings investigated the recovery rate of ¹⁵N from DNJ reached 80% up to 48 hours after oral administration, suggesting its rapid excretion, suggesting the safety of DNJ. This study verified the functional properties and safety of DNJ from microorganisms, suggesting its potential use for functional purpose.