Response of chalkiness in high-quality rice (Oryza sativa L.) to temperature across different ecological regions

Field experiments were conducted to determine the relationship between chalkiness of high-quality rice and temperature during grain filling period in 2016–2017. Significant differences in chalkiness and response to temperature during grain filling period were observed among the cultivars and years of production. A positive correlation between chalkiness and temperature that includes daily minimum temperature (T-min), daily mean temperature (T-mean) and daily maximum temperature (T-max) during grain filling period was observed. The correlation between chalkiness and T-min during 7 days after heading was lower than that of other stages, while the correlation between chalkiness and T-mean during the ripening stage was the highest than other stages. The chalkiness values of some varieties such as Jiuxiangzhan, Zhendao18 and Yongyou1538 were sensitive to temperature, however, it might be reached optimum level through suitable ecological regions. Other varieties such as Huanghuazhan, Wangxiangyouhuazhan and Ganchangjing1 could maintain lower level of chalkiness regardless of different ecological regions in southern China. These high-quality rice varieties with low and relatively stable chalkiness could be moderately planted in Chinese double-rice cropping systems, and could be used as breeding materials to cope with the adverse effects of future global temperature increase (mainly night temperature) on the appearance quality of rice

Reduced Iron-Containing Clay Minerals as Antibacterial Agents

Previous work documented the general antibacterial mechanism of iron containing clays that involved hydroxyl radical (•OH) production from soluble Fe²⁺, and attack of cell membrane and intracellular proteins. Here we explore the role of clay structural Fe­(II) in •OH production at near neutral pH and identify a lipid involved in the antibacterial process. Structural Fe­(III) in nontronite NAu-2 was reduced (rNAu-2) and <i>E. coli</i>, a model bacterium, was exposed to rNAu-2 in oxic suspension. The antibacterial activity of rNAu-2 was dependent on pH and Fe­(II) concentration, where <i>E. coli</i> were completely killed at pH 6, but survived at pH 7 and 8. In the presence of a •OH scavenger or in anaerobic atmosphere, <i>E. coli</i> survived better, suggesting that cell death may be caused by •OH generated from oxidation of structural Fe­(II) in rNAu-2. In-situ imaging revealed damage of a membrane lipid, cardiolipin, in the polar region of <i>E. coli</i> cells, where reactive oxygen species and redox-active labile Fe were enriched. Our results advance the previous antibacterial model by demonstrating that the structural Fe­(II) is the primary source of •OH, which damages cardiolipin, triggers the influx of soluble Fe²⁺ into the cell, and ultimately leads to cell death

Role of UDP-Glucuronic Acid Decarboxylase in Xylan Biosynthesis in Arabidopsis

UDP-xylose (UDP-Xyl) is the Xyl donor used in the synthesis of major plant cell-wall polysaccharides such as xylan (as a backbone-chain monosaccharide) and xyloglucan (as a branching monosaccharide). The biosynthesis of UDP-Xyl from UDP-glucuronic acid (UDP-GlcA) is irreversibly catalyzed by UDPglucuronic acid decarboxylase (UXS). Until now, little has been known about the physiological roles of UXS in plants. Here, we report that AtUXS1, AtUXS2, and AtUXS4 are located in the Golgi apparatus whereas AtUXS3, AtUXS5, and AtUXS6 are located in the cytosol. Although all six single AtUXS T-DNA mutants and the uxs1 usx2 uxs4 triple mutant show no obvious phenotype, the uxs3 uxs5 uxs6 triple mutant has an irregular xylem phenotype. Monosaccharide analysis showed that Xyl levels decreased in uxs3 uxs5 uxs6 and linkage analysis confirmed that the xylan content in uxs3 xus5 uxs6 declined, indicating that UDP-Xyl from cytosol AtUXS participates in xylan synthesis. Gel-permeation chromatography showed that the molecular weight of non-cellulosic polysaccharides in the triple mutants, mainly composed of xylans, is lower than that in the wild type, suggesting an effect on the elongation of the xylan backbone. Upon saccharification treatment stems of the uxs3 uxs5 uxs6 triple mutants released monosaccharides with a higher efficiency than those of the wild type. Taken together, our results indicate that the cytosol UXS plays a more important role than the Golgi-localized UXS in xylan biosynthesis