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Rice (Oryza sativa L.) productivity is greatly affected by soil salinity and melatonin (MLT) has long been recognized as a positive molecule that can alleviate the damage caused by salt. Here, the role of nitric oxide (NO) in the regulation of salt tolerance by MLT was investigated in rice. MLT pretreatment increased the fresh and dry weight of rice seedlings under salt stress. Its beneficial effects include less relative electrolyte leakage (REL) and better K+/Na+ homeostasis. MLT increased the activity of nitric oxide synthase (NOS). The polyamines (PAs) content and the utilization of arginine were also increased, thereby increasing NO content in salt-stressed rice seedlings. Pharmacological approach showed that NO, as a necessary downstream signaling molecule, was involved in the regulation of MLT on the K+/Na+ homeostasis of rice. Under salt stress, MLT improved the H+-pumps activities in plasma membrane (PM) and vacuole membrane (VM) in roots, MLT also increased the ATP content of rice roots by increasing the NO content of rice. Thus, the efflux of Na+ and the influx of K+ were promoted. When endogenous NO was scavenged, the regulation of K+/Na+ homeostasis by MLT was blocked. Therefore, MLT mediated K+/Na+ homeostasis of rice under salt stress by mediating NO. • Melatonin increased NO content in rice under salt stress. • Melatonin increased the efflux of Na+ and the influx of K+ in rice roots. • NO was necessary signaling molecule for melatonin to regulate K+ and Na+ homeostasis of rice. • The function of NO regulated by melatonin was to enhance H+-pump activity. [ABSTRACT FROM AUTHOR]

Nitrogen (N) topdressing often leads to a decline in cooking and eating quality due to alterations in grain chemical composition. Investigation into the response of N compounds in grains, such as protein-bound amino acids (PAA), free amino acids (FAA), and other residue N compounds (N residue), would be beneficial for understanding the impact of N on rice quality. The present study selected five japonica rice cultivars and conducted a two-year field experiment employing two N fertilization treatments: the CK treatment, where all N fertilizer was applied as basal fertilizer, and the topdressing treatment, where 50% of the total N was applied as topdressing at the panicle initiation stage. Averaging across years and cultivars, N topdressing resulted in a 16.3% increase in PAA and an 8.65% decrease in FAA, with no significant impact on N residue. N topdressing resulted in a decrease in the proportion of essential amino acids found in prolamins, as well as a reduction in the proportion of amino acids belonging to the aspartate family and arginine. Significant genotypic variations were observed in the response of nitrogen components to topdressing. Furthermore, elite cultivars with premium quality exhibited greater stability in amylose content compared to protein content. [Display omitted] • We aimed to elucidate the effect of nitrogen (N) topdressing on rice grain quality by field experiments. • N topdressing favored the allocation of N to storage proteins rather than free amino acids. • N topdressing differently affected essential amino acids in glutelin and prolamin. • N Topdressing reduced the proportion of amino acids from the aspartate family as well as arginine. • Genotypic variation in response to N topdressing of grain compositions was detected. [ABSTRACT FROM AUTHOR]

The responses of rice quality including milling, appearance, and eating quality between superior (SG) and inferior grains (IG) to temperature during grain filling stage (T GF) remained poorly understood, especially for eating quality. Therefore, the regulation of T GF (17.6−30.4 °C) on quality of three indica hybrid varieties (IHs) was investigated by setting multiple sowing dates and the mechanism underlying taste difference was explored by monitoring chemical compositions, rapid visco analyser (RVA) profiles, and texture properties. Results suggested that T GF ranging from 23.3 to 25.2 °C could comprehensively improve the milling, appearance and eating quality of IHs, and the optimal T GF of SG was 2.3–4.2 °C lower than that of IG. Compared with chemical compositions and RVA profiles, texture properties were better for evaluating the eating quality of IHs. When T GF was higher than 24.0 °C, the taste value of IG was higher than that of SG mainly due to higher elasticity. The findings indicate that T GF had differential regulatory effects on SG and IG, which could provide a useful reference for cultivation of high-quality rice varieties under global climate change. Besides, the determination of texture properties was a reliable method for taste evaluating of IHs in the breeding process. [Display omitted] • T GF had a significant quadratic function relationship with quality of IHs. • T GF ranging from 23.3 to 25.2 °C could improve the quality of IHs. • The optimal T GF of IG was 2.3–4.2 °C higher than that of SG. • Texture properties can effectively evaluate the eating quality of IHs. • The TV of IG was higher than SG at T GF greater than 24 °C, mainly due to higher elasticity. [ABSTRACT FROM AUTHOR]

Abstract Due to the sensitivity of chalk formation to high temperatures, the global warming will further threaten the improvement of high chalky grain rate in the southern japonica region of China. There have been many studies reported on the role of starch in the formation of chalkiness, but the relationship between nitrogen metabolites and chalkiness has not been given sufficient attention. In this study, we conducted the open field warming experiment and investigated the effects of temperature increase on grain protein metabolism. Results showed under the warming range of predicted global temperature increase (1.9 °C–4.0 °C), field warming apparently accelerated the development of grain endosperm, and the number of protein bodies were increased in both rice varieties, Furthermore, we clarified that the increased temperature regulated the key regulatory factors in protein synthesis and metabolism pathway, and the synthesis, transport, folding, assembly process of grain protein were further affected, and that further lead the component changes of grain storage protein. In conclusion, chalky traits are closely related to the grain storage materials and in this study, increased temperature induced the changes in the accumulation balance of storage proteins, amino acids and starches, which coordinately controls the formation of grain chalkiness. Highlights • We simulated climate warming with the field-warming system in actual rice field. • Endosperm and protein bodies were apparently increased under elevated temperatures. • Elevated temperature regulated regulatory factors in protein anabolism pathway. • Elevated temperatures affect balance of storage material and induce the chalkiness. • Proteins may play a certain role in chalkiness formation under elevated temperature. [ABSTRACT FROM AUTHOR]

To evaluate the actual and comprehensive response of rice grain quality to global warming in lower reaches of Yangtze River delta, a 3-year open-field warming experiment was conducted with two japonica rice cultivars using Free-air temperature enhancement (FATE) facility. Ningjing3 and Wuyunjing24 were planted under two temperature regimes (NT: natural temperature; ET: elevated temperature) during grain-filling. FATE facility increased rice canopy temperature by 2.7 °C (daytime 1.5 °C/nighttime 3.9 °C), 2.0 °C (daytime 1.6 °C/nighttime 2.5 °C) and 3.4 °C (daytime 2.0 °C/nighttime 4.9 °C) in 2012, 2013 and 2014, respectively. Compared with NT, head rice rate, occurrence of perfect grains, amylose content, setback and consistency were decreased by ET, while occurrence of chalky grains, breakdown, cool paste viscosity, pasting temperature were increased under ET. Response of different chalky types to warming were unstable among cultivars and years. Based on Wu-Gilbert model, we found that the relative activity of starch branching enzyme (SBE) to starch synthase (SS) was decreased by ET, which may contribute to longer average amylopectin chain length. ET increased protein content of rice grain but performed no influence on the relative proportion of amino acids. These results revealed that low-amplitude warming during grain-filling could deteriorate rice milling, appearance and cooking quality, but improved its nutritional quality. [ABSTRACT FROM AUTHOR]

This study aimed to prepare germinated brown rice (GBR) with high γ-aminobutyric acid (GABA) content and short root length. Brown rice (BR) was exposed to 10 mT magnetic field at 25 °C for 60 min, followed by incubating in GABA solutions (0–10 mM, 30 °C) for 24 h. After treatment, GABA content in GBR significantly increased from 16.43 to 25.64–50.54 mg/100 g, while root length was shorter than 3.0 mm. Although GABA-aminotransferase activity was reduced by 4.61%–16.14%, the absorption of exogenous GABA caused by higher electrical conductivity, increased cell membrane permeability and more root hairs was the dominant reason for GABA accumulation. The hyperaccumulation of GABA conversely retarded the positive effect of M on α-amylase activity, starch structure, and anti-oxidase activity, thus maintaining the root length at 2.03–2.45 mm. Overall, this study provided an efficient method for preparing GBR with high GABA content and short root. [Display omitted] • Magnetic field (M) greatly increased γ-aminobutyric acid (GABA) content. • M improved endogenous GABA accumulation by reducing GABA-aminotransferase activity. • M enhanced exogenous GABA absorption by increasing cell membrane permeability. • The increased cell membrane permeability dominated in M-enriching GABA. • The root length of germinated brown rice ranged from 2.03 to 2.45 mm. [ABSTRACT FROM AUTHOR]

This study investigated the chain length distribution (CLD) of two japonica rice cultivars under six nitrogen (N) treatments by high performance size exclusion chromatography, with the aims to elucidate the effect of N on rice quality and its biological mechanism. Results showed significant influence of N on CLD. In comparison with low N rate, high N lowered the percentage of short amylopectin branches. Fitting with the CLD model of Wu-Gilbert, it suggested that relative activity of SBE to SS was lower at high N rate, thus producing fewer short amylopectin branches. Comparison of CLD between N rates and between cultivars revealed that decrease in short amylopectin branches or the relative ratio of short to long amylopcetin branches correlated with increase in flour gelatinization temperatures (T o , T p , and T c ) and decrease in pasting values (except PaT) and amylose-lipid gelatinization temperatures. In addition, quality traits of Wuyujing3, a cultivar with premium eating quality, expressed stably across N treatments compared with the high-yielding cultivar Wuyunjing7. [ABSTRACT FROM AUTHOR]

Using white-belly and white-core mutants of a japonica rice cultivar Wuyujing3, this study was conducted to compare the physicochemical properties of grains differing in chalkiness type. Chalky grains were larger in length, width, and thickness than the translucent grains, and consequently had higher weight. The notable differences were observed for chemical compositions, with chalky grains showing lower contents of starch and protein than the translucent. Similar trends were noted in the majority of the 17 amino acids examined and contents of manganese (Mn), potassium (K) and magnesium (Mg), suggesting the important role of storage compounds in chalkiness formation. White-belly grains differed from white-core grains in chemical components, with the former having higher amylose contents and lower Zn content. Additionally, white-core grains exhibited markedly lower contents of amino acids derived from oxaloacetate and phosphoenolpyruvate like phenylalanine, aspartate and threonine. However, no noticeable differences were detected between white-belly and translucent grains. Our results indicate different underlying mechanisms of white-belly and white-core, suggesting the necessity of comparing white-belly and white-core in the studies on chalkiness. In addition, future study should focus on interpreting the active role of protein accumulation in chalkiness formation from perspective of interactions of carbon and nitrogen metabolism. [ABSTRACT FROM AUTHOR]

Heat stress hurts rice, and floral organs are mostly sensitive to heat stress. We aimed to unravel molecular responses to heat stress in rice floral organs using Illumina/Solexa sequencing technology for addressing the increasing concern of globle warming. At meiophase of the pollen mother cell (pulvinus flat), the plants were stressed for 3 d at 38 C, and RNA was extracted from the stressed pistil and stamen for RNA-Seq sequencing to build the heat stress transcriptom library. A total of 7178 defferentially expressed genes (DEGs) between the normal and heat stress libraries were significant, 61% up-regulated and 39% down-regulated. The 7178 DEGs were significantly classified to 34 gene ontology (GO) categories, and 11 of the GO categories were significantly enriched. The GO:0016787 for hydrolase activity of molecular function was mostly enriched with the least probability, and included 11 DEGs named Hy1 – Hy11 . Expression levels of five DEGs, Hy4 – Hy6 and Hy9 – Hy10 for starch and sucrose metablism via pectinase, increased 12 – 14 times in response to the heat stress. Further investigation of the five DEGs for pectin metabolism and association with reported heat responsive genes may help develop a molecular strategy to remedy heat damage in rice. [ABSTRACT FROM AUTHOR]

This paper reports the effect of nitrogen on amino acid composition of leaf and grain for japonica rice during the grain filling stage, using pot experiments with three N rate treatments. Dynamic changes of free amino acids (FAA) and protein amino acids (PAA) in leaves and grains were monitored. Results showed that FAA in leaves decreased with the progress of grain filling. FAA in grains increased at first 14 days after anthesis and then decreased to a nearly constant level. PAA in leaves showed a diminishing trend as leaf senesced after anthesis. Conversely, PAA in grain exhibited an increasing trend with the progress of grain filling. N had significantly positive effect on contents of FAA and PAA in leaves and grains. There was no obvious trend of the variation of FAA in leaves and grains with N rates. PAA in leaves was more sensitive to N fertilization. By contrast, PAA in grains was more stable across N rates, especially at the late stage of grain filling. In addition, composition of leaf PAA was different from that of grain, indicating the reconstruction of amino acids during the process of translocation of N compounds from leaves to grains. [ABSTRACT FROM AUTHOR]

Abstract: A field experiment involving six japonica rice cultivars with contrasting agronomic traits and seven nitrogen (N) fertilizer treatments was performed to determine the effects of N and genotype on distribution of four kinds of grain proteins and amino acids in milled and brown rice. For brown and milled rice, albumin and globulin were controlled more by genotype than N treatments, whereas prolamin and glutelin were largely determined by N. Substantial genotypic differences in response of milled/brown (M/B) ratios of proteins to N treatments were detected. In comparison with large panicle cultivars, small panicle cultivars such as Wuyujing3 had the lower ratio and exhibited more stability under contrasting N treatments. N had significant influence on amino acid composition of brown and milled rice, with contents of the 17 amino acids measured increasing with elevated N rate. However, cysteine and methionine in brown rice and lysine and methionine in milled rice were not significantly affected by N. In addition, N had little effect on ratios of M/B for most of the amino acids. [Copyright &y& Elsevier]

Abstract: Thirty-one japonica cultivars with contrasting agronomic traits were used and 5 nitrogen (N) fertilizer treatments of level and timing were performed to determine the effects of N application on grain phytic acid and proteins including albumin, globulin, prolamin, and glutelin. Variance analysis showed a large effect of N and a smaller effect of cultivar on grain phytic acid and proteins. With increased N level, grain phytic acid concentrations progressively reduced whereas concentrations of the 4 proteins and ratios of glutelin to total protein increased, indicating that N level has a beneficial effect on rice nutritional quality. In addition, substantial genotypic differences in response of grain phytic acid and proteins to N treatments were detected. Some cultivars such as Xiushui09, Zhendao10, and Yanjing5 exhibited more stability of grain proteins under contrasting N treatments, and the significance of this stability is discussed in regard to its use in rice quality improvement. [Copyright &y& Elsevier]