Biochemical foundation of the aroma and antioxidant activity of Indian traditional rice landrace Maharaji and the effect of radiation-induced mutagenesis on its metabolome.

Maharaji rice, an aromatic variety with medium slender grains, is traditionally cultivated in the central regions of India. This study aimed to identify the biochemical compounds responsible for Maharaji rice's distinctive fragrance and enhance its agro-morphological traits through mutation breeding. Using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) analysis, forty major metabolites were identified which may be responsible for its characteristic aroma. The bioactive compounds included terpenes, flavonoids, and amino acids. Maharaji brown rice extract exhibited potent radical scavenging activity. Radiation-induced mutation breeding improved the agro-morphological traits and also triggered biochemical diversification in different mutants. Maharaji Mutant-2 exhibited improved aroma due to higher abundance of aromatic compounds, improved yield and morphological characters as compared to the parent. This study, for the first time identifies the compounds associated with the characteristic aroma of Maharaji rice. Global metabolomics may, therefore, expedite the selection of mutants with suitable aroma and desirable biological properties.

Effects of UV-B Radiation Exposure on Transgenerational Plasticity in Grain Morphology and Proanthocyanidin Content in Yuanyang Red Rice.

The effect of UV-B radiation exposure on transgenerational plasticity, the phenomenon whereby the parental environment influences both the parent's and the offspring's phenotype, is poorly understood. To investigate the impact of exposing successive generations of rice plants to UV-B radiation on seed morphology and proanthocyanidin content, the local traditional rice variety 'Baijiaolaojing' was planted on terraces in Yuanyang county and subjected to enhanced UV-B radiation treatments. The radiation intensity that caused the maximum phenotypic plasticity (7.5 kJ·m-2) was selected for further study, and the rice crops were cultivated for four successive generations. The results show that in the same generation, enhanced UV-B radiation resulted in significant decreases in grain length, grain width, spike weight, and thousand-grain weight, as well as significant increases in empty grain percentage and proanthocyanidin content, compared with crops grown under natural light conditions. Proanthocyanidin content increased as the number of generations of rice exposed to radiation increased, but in generation G3, it decreased, along with the empty grain ratio. At the same time, biomass, tiller number, and thousand-grain weight increased, and rice growth returned to control levels. When the offspring's radiation memory and growth environment did not match, rice growth was negatively affected, and seed proanthocyanidin content was increased to maintain seed activity. The correlation analysis results show that phenylalanine ammonialyase (PAL), cinnamate-4-hydroxylase (C4H), dihydroflavonol 4-reductase (DFR), and 4-coumarate:CoA ligase (4CL) enzyme activity positively influenced proanthocyanidin content. Overall, UV-B radiation affected transgenerational plasticity in seed morphology and proanthocyanidin content, showing that rice was able to adapt to this stressor if previous generations had been continuously exposed to treatment.

Synergistic effects of salt and ultraviolet radiation on the rice-field cyanobacterium Nostochopsis lobatus HKAR-21.

Environmental variation has a significant impact on how organisms, including cyanobacteria, respond physiologically and biochemically. Salinity and ultraviolet radiation (UVR)-induced variations in the photopigments of the rice-field cyanobacterium Nostochopsis lobatus HKAR-21 and its photosynthetic performance was studied. We observed that excessive energy dissipation after UVR is mostly caused by Non-Photochemical Quenching (NPQ), whereas photochemical quenching is important for preventing photoinhibition. These findings suggest that ROS production may play an important role in the UVR-induced injury. To reduce ROS-induced oxidative stress, Nostochopsis lobatus HKAR-21 induces the effective antioxidant systems, which includes different antioxidant compounds like carotenoids and enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). The study indicates that Nostochopsis lobatus HKAR-21 exposed to photosynthetically active radiation + UV-A + UV-B (PAB) and PAB + NaCl (PABN) had significantly reduced photosynthetic efficiency. Furthermore, maximum ROS was detected in PAB exposed cyanobacterial cells. The induction of lipid peroxidation (LPO) has been investigated to evaluate the impact of UVR on the cyanobacterial membrane in addition to enzymatic defensive systems. The maximal LPO level was found in PABN treated cells. Based on the findings of this research, it was concluded that salinity and UVR had collegial effects on the major macromolecular components of the rice-field cyanobacterium Nostochopsis lobatus HKAR-21.

The rice germin-like protein OsGLP1 participates in acclimation to UV-B radiation.

Exposure to ultraviolet B radiation (UV-B) stress can have serious effects on the growth and development of plants. Germin-like proteins (GLPs) may be involved in different abiotic and biotic stress responses in different plants, but little is known about the role of GLPs in UV-B stress response and acclimation in plants. In the present study, knockout of GLP 8-14 (OsGLP1) using the CRISPR/Cas9 system resulted in mutant rice (Oryza sativa L.) plants (herein called glp1) that exhibited UV-B-dependent formation of lesion mimic in leaves. Moreover, glp1 grown under solar radiation (including UV-B) showed decreased plant height and increased leaf angle, but we observed no significant differences in phenotypes between wild-type (WT) plants and glp1 grown under artificial light lacking UV-B. Fv/Fm, Y (II) and the expression of many genes, based on RNA-seq analysis, related to photosynthesis were also only reduced in glp1, but not in WT, after transfer from a growth cabinet illuminated with artificial white light lacking UV-B to growth under natural sunlight. The genes-associated with flavonoid metabolism as well as UV resistance locus 8 (OsUVR8), phytochrome interacting factor-like 15-like (OsPIF3), pyridoxal 5'-phosphate synthase subunit PDX1.2 (OsPDX1.2), deoxyribodipyrimidine photolyase (OsPHR), and deoxyribodipyrimidine photolyase family protein-like (OsPHRL) exhibited lower expression levels, while higher expression levels of mitogen-activated protein kinase 5-like (OsMPK3), mitogen-activated protein kinase 13-like (OsMPK13), and transcription factor MYB4-like (OsMYB4) were observed in glp1 than in WT after transfer from a growth cabinet illuminated with artificial white light to growth under natural sunlight. Therefore, mutations in OsGLP1 resulted in rice plants more sensitive to UV-B and reduced expression of some genes for UV-B protection, suggesting that OsGLP1 is involved in acclimation to UV-B radiation.

Genome-Wide Association Study Unravels LRK1 as a Dark Respiration Regulator in Rice (Oryza sativa L.).

Respiration is a major plant physiological process that generates adenosine triphosphate (ATP) to support the various pathways involved in the plant growth and development. After decades of focused research on basic mechanisms of respiration, the processes and major proteins involved in respiration are well elucidated. However, much less is known about the natural variation of respiration. Here we conducted a survey on the natural variation of leaf dark respiration (Rd) in a global rice minicore diversity panel and applied a genome-wide association study (GWAS) in rice (Oryza sativa L.) to determine candidate loci associated with Rd. This rice minicore diversity panel consists of 206 accessions, which were grown under both growth room (GR) and field conditions. We found that Rd shows high single-nucleotide polymorphism (SNP) heritability under GR and it is significantly affected by genotype-environment interactions. Rd also exhibits strong positive correlation to the leaf thickness and chlorophyll content. GWAS results of Rd collected under GR and field show an overlapped genomic region in the chromosome 3 (Chr.3), which contains a lead SNP (3m29440628). There are 12 candidate genes within this region; among them, three genes show significantly higher expression levels in accessions with high Rd. Particularly, we observed that the LRK1 gene, annotated as leucine rich repeat receptor kinase, was up-regulated four times. We further found that a single significantly associated SNPs at the promoter region of LRK1, was strongly correlated with the mean annual temperature of the regions from where minicore accessions were collected. A rice lrk1 mutant shows only ~37% Rd of that of WT and retarded growth following exposure to 35 °C for 30 days, but only 24% reduction in growth was recorded under normal temperature (25 °C). This study demonstrates a substantial natural variation of Rd in rice and that the LRK1 gene can regulate leaf dark respiratory fluxes, especially under high temperature.

Very high sensitivity of African rice to artificial ultraviolet-B radiation caused by genotype and quantity of cyclobutane pyrimidine dimer photolyase.

Ultraviolet-B (UVB) radiation damages plants and decreases their growth and productivity. We previously demonstrated that UVB sensitivity varies widely among Asian rice (Oryza sativa L.) cultivars and that the activity of cyclobutane pyrimidine dimer (CPD) photolyase, which repairs UVB-induced CPDs, determines UVB sensitivity. Unlike Asian rice, African rice (Oryza glaberrima Steud. and Oryza barthii A. Chev.) has mechanisms to adapt to African climates and to protect itself against biotic and abiotic stresses. However, information about the UVB sensitivity of African rice species is largely absent. We showed that most of the African rice cultivars examined in this study were UVB-hypersensitive or even UVB-super-hypersensitive in comparison with the UVB sensitivity of Asian O. sativa cultivars. The difference in UVB resistance correlated with the total CPD photolyase activity, which was determined by its activity and its cellular content. The UVB-super-hypersensitive cultivars had low enzyme activity caused by newly identified polymorphisms and low cellular CPD photolyase contents. The new polymorphisms were only found in cultivars from West Africa, particularly in those from countries believed to be centres of O. glaberrima domestication. This study provides new tools for improving both Asian and African rice productivity.

Global Transcriptome and Co-Expression Network Analysis Reveal Contrasting Response of Japonica and Indica Rice Cultivar to γ Radiation.

Japonica and indica are two important subspecies in cultivated Asian rice. Irradiation is a classical approach to induce mutations and create novel germplasm. However, little is known about the differential response between japonica and indica rice after γ radiation. Here, we utilized the RNA sequencing and Weighted Gene Co-expression Network Analysis (WGCNA) to compare the transcriptome differences between japonica Nipponbare (NPB) and indica Yangdao6 (YD6) in response to irradiation. Japonica subspecies are more sensitive to irradiation than the indica subspecies. Indica showed a higher seedling survival rate than japonica. Irradiation caused more extensive DNA damage in shoots than in roots, and the severity was higher in NPB than in YD6. GO and KEGG pathway analyses indicate that the core genes related to DNA repair and replication and cell proliferation are similarly regulated between the varieties, however the universal stress responsive genes show contrasting differential response patterns in japonica and indica. WGCNA identifies 37 co-expressing gene modules and ten candidate hub genes for each module. This provides novel evidence indicating that certain peripheral pathways may dominate the molecular networks in irradiation survival and suggests more potential target genes in breeding for universal stress tolerance in rice.

Lsi1 modulates the antioxidant capacity of rice and protects against ultraviolet-B radiation.

Silicon (Si) enhances the resistance of rice to biotic and abiotic stress. In rice, the accumulation of Si is controlled by the low silicon rice 1 (Lsi1) gene; overexpression of Lsi1 (Lsi1-OX) increases Si uptake and accumulation, while the reverse is observed in Lsi1-RNA interference (Lsi1-RNAi) transgenic rice. When the two transgenic rice lines and wild-type (WT) rice were exposed to ultraviolet (UV)-B radiation, the Lsi1-OX or Lsi1-RNAi rice showed differential microRNA (miRNA) expression, compared to WT rice. These miRNAs were predicted to target genes involved in light signal transduction and cell detoxification. The greatest capacities of ascorbate peroxidase, superoxide dismutase, peroxidase, and phenylalanine ammonia lyase (PAL) and highest contents of phenolics, flavonoids, and proline were found in Lsi1-OX rice, followed by WT rice and Lsi1-RNAi transgenic rice. A further comparison of the transcript levels of individual PAL genes revealed that the expression of PAL2-2 (Os02g0626400) was positively regulated by Lsi1. Our results demonstrate that Lsi1 overexpression or interference causes changes in both miRNA expression and antioxidant capacity in rice, and therefore modulates rice tolerance to UV-B radiation. Furthermore, we demonstrated that PAL2-2 was positively regulated by Lsi1 during this process.

Influence of enhanced ultraviolet-B radiation during rice plant growth on rice straw decomposition with nitrogen deposition.

Although straw decomposition is important for ecosystem fertility and carbon balance, influence of ultraviolet-B (UV-B) radiation and nitrogen (N) deposition on this process is unclear. In this study, UV-B-exposed rice straw was decomposed under different N addition treatments for 15 months to investigate the indirect effects of UV-B radiation on straw chemistry and direct effects of N deposition on decomposition. UV-B exposure during rice plant growth changed the rice straw chemical composition, increasing the concentrations of acid-insoluble fraction (AIF), acid-soluble fraction, and UV-B-absorbing compounds. High N content had a negative effect on decomposition of rice straw exposed to enhanced and ambient UV-B radiation. Both AIF concentration and FTIR peak intensities indicated that lignin in rice straw was selectively preserved following N addition and UV-B radiation, reducing straw decomposition rate, which corresponded to lower activities of lignin-degrading enzymes in the later stage of decomposition. Thus, enhanced UV-B radiation during rice plant growth produced more recalcitrant substrates (lignin) and N reacted with lignin to produce more resistant compounds, further decreasing straw decomposition rate. UV-B radiation during plant growth and N deposition inhibit litter decomposition in agroecosystem, and their effects should be considered when establishing biogeochemical models in response to global changes.

Analysis of DNA methylation alterations in rice seeds induced by different doses of carbon-ion radiation.

To investigate the mechanism underlying differences in biological effects induced by low- versus high-dose heavy-ion radiation (HIR) in rice plants, two-dimensional gel electrophoresis (2-DE) coupled with methylation-sensitive amplification polymorphism (MSAP) analysis were used to check the expression changes in rice leaf proteome profiles and the changes in DNA methylation after exposure of seeds to ground-based carbon-ion radiation at various cumulative doses (0, 0.01, 0.02, 0.1, 0.2, 1, 2, 5 or 20 Gy; 12C6+; energy, 165 MeV/u; mean linear energy transfer, 30 KeV/µm). In this study, principal component analysis (PCA) and gene ontology (GO) functional analysis of differentially expressed proteins of rice at tillering stage showed that proteins expressed in rice samples exposed to 0.01, 0.02, 0.1, 0.2 or 1 Gy differed from those exposed to 2, 5 or 20 Gy. Correspondingly, the proportion of hypermethylation was higher than that of hypomethylation at CG sites following low-dose HIR (LDR; 0.01, 0.2 or 1 Gy), whereas this was reversed at high-dose HIR (HDR; 2, 5 or 20 Gy). The hypomethylation changes tended to occur at CHG sites with both low- and high-dose HIR. Furthermore, sequencing of MSAP variant bands indicated that the plants might activate more metabolic processes and biosynthetic pathways on exposure to LDR, but activate stress resistance on exposure to HDR. This study showed that radiation induced different biological effects with low- and high-dose HIR, and that this may have been caused by different patterns of hyper- and hypomethylation at the CG sites.

Diurnal changes in CN metabolism and response of rice seedlings to UV-B radiation.

Plants regulate a number of primary metabolites, including carbohydrates, organic acids, and amino acids, in response to UV-B radiation. Therefore, it is essential to understand the time-dependent response of rice plants to UV-B stress. This study focused on the response of plants to UV-B at different leaf developmental phases (emerging, growing, and maturing) in an attempt to fully comprehend the metabolic shift. We analyzed the expression levels of genes related to starch/sucrose metabolism in the leaf blades of rice seedlings (Oryza sativa L. "Saechuchenog") exposed to UV-B irradiation for short (1 day) and long terms (5 days) using quantitative real-time polymerase chain reaction. We also examined the diurnal variations in the contents of primary metabolites using an established GCTOF-MS (gas chromatography time of flight-mass spectrometry) method. The results showed that the levels of primary metabolites were largely dependent upon the diurnal rhythm and leaf developmental phase. The young leaves (sink) produced and accumulated starch rather than sucrose. The short-term (4 h, 1 day) UV-B exposure inhibited sucrose synthesis, which could be the first target of UV-B radiation. Following short- and long-term (5 days) exposure to UV-B radiation, the dynamic response of primary metabolites was evaluated. It was found that the content of carbohydrates decreased throughout the period of exposure to UV-B stress, especially in terms of sucrose concentration. However, the content of the majority of amino acids increased after an early decrease. Our data revealed that the metabolic response, as well as the gene expression, differed with the period (intensity) of exposure to UV-B radiation and with the phase of leaf development. These findings provide new insights for a better understanding of the metabolic response of a variety of plant species exposed to a wide range of UV-B radiation.

Stabilization of immature rice grain using infrared radiation.

Immature rice grain is one of the underutilized by-products of paddy milling process. Despite its high potential of use as a food ingredient, it is mainly utilized as feed due to the rancidity problem. In the present study, the composition of immature rice grain, the potential of using infrared (IR) radiation for stabilization, and the effects of IR stabilization on color, fatty acid composition, tocopherol and γ-oryzanol contents of the grain were investigated. The free fatty acid (FFA) value of the unprocessed immature rice grain was 5.49% and increased to 35.71% at the end of 3 months of storage at room temperature. However, FFA content of the grains stabilized with IR radiation at specific conditions remained unchanged throughout the storage period. Moreover, IR stabilization did not caused a negative effect on the noted components of the immature rice grain.

Ultraviolet-B enhances the resistance of multiple plant species to lepidopteran insect herbivory through the jasmonic acid pathway.

Land plants protect themselves from ultraviolet-B (UV-B) by accumulating UV-absorbing metabolites, which may also function as anti-insect toxins. Previous studies have shown that UV-B enhances the resistance of different plant species to pierce-sucking pests; however, whether and how UV-B influences plant defense against chewing caterpillars are not well understood. Here we show that UV-B treatment increased Spodoptera litura herbivory-induced jasmonic acid (JA) production in Arabidopsis and thereby Arabidopsis exhibited elevated resistance to S. litura. Using mutants impaired in the biosynthesis of JA and the defensive metabolites glucosinolates (GSs), we show that the UV-B-induced resistance to S. litura is dependent on the JA-regulated GSs and an unidentified anti-insect metabolite(s). Similarly, UV-B treatment also enhanced the levels of JA-isoleucine conjugate and defense-related secondary metabolites in tobacco, rice, and maize after these plants were treated with simulated herbivory of lepidopteran insects; consistently, these plants showed elevated resistance to insect larvae. Using transgenic plants impaired in JA biosynthesis or signaling, we further demonstrate that the UV-B-enhanced defense responses also require the JA pathway in tobacco and rice. Our findings reveal a likely conserved JA-dependent mechanism by which UV-B enhances plant defense against lepidopteran insects.

Flavodiiron Protein Substitutes for Cyclic Electron Flow without Competing CO2 Assimilation in Rice.

Flavodiiron protein (FLV) mediates photoreduction of O2 to H2O. It is conserved from cyanobacteria to gymnosperms but not in angiosperms. The introduction of a moss (Physcomitrella patens) FLV (PpFLV) gene into Arabidopsis (Arabidopsis thaliana) made photosystem I (PSI) resistant to fluctuating light. Here, we used the same strategy with three rice (Oryza sativa) genotypes. PpFLV in the wild-type rice background functioned as an efficient PSI electron sink and increased resistance to PSI photodamage under fluctuating light. The introduction of PpFLV into the PGR5-RNAi mutant [defective in PROTON GRADIENT REGULATION5 (PGR5)-dependent cyclic electron transport around PSI, CET-PSI], the crr6 mutant [defective in chloroplast NAD(P)H-dehydrogenase-like complex (NDH)-dependent CET-PSI], and the PGR5-RNAi crr6 double mutant (double defective in CET-PSI activity) alleviated PSI photodamage under fluctuating light. Furthermore, PpFLV substituted for the function of PGR5- and NDH-dependent CET-PSI without competing for CO2 assimilation under constant light, as there was no difference in CO2 assimilation per Rubisco content and biomass production was recovered to the wild-type level. Thus, the exogenous FLV system could act not only as a safety valve under fluctuating light, but also generate a proton motive force for balancing the ATP/NADPH production ratio during steady-state photosynthesis.

Progress Toward Rice Seed OMICS in Low-Level Gamma Radiation Environment in Iitate Village, Fukushima.

Here, we present an update on the next level of experiments studying the impact of the gamma radiation environment, created post-March, 2011 nuclear accident at Fukushima Daiichi nuclear power plant, on rice plant and its next generation-the seed. Japonica-type rice (Oryza sativa L. cv. Koshihikari) plant was exposed to low-level gamma radiation (~4 µSv/h) in the contaminated Iitate Farm field in Iitate village (Fukushima). Seeds were harvested from these plants at maturity, and serve as the treated group. For control group, seeds (cv. Koshihikari) were harvested from rice grown in clean soil in Soma city, adjacent to Iitate village, in Fukushima. Focusing on the multi-omics approach, we have investigated the dry mature rice seed transcriptome, proteome, and metabolome following cultivation of rice in the radionuclide contaminated soil and compared it with the control group seed (non-radioactive field-soil environment). This update article presents an overview of both the multi-omics approach/technologies and the first findings on how rice seed has changed or adapted its biology to the low-level radioactive environment.

Effects of UV-B radiation on the infectivity of Magnaporthe oryzae and rice disease-resistant physiology in Yuanyang terraces.

The traditional rice variety "Baijiaolaojing" was planted in Yuanyang terraces (1600 m altitude) under field conditions. The effects of enhanced UV-B radiation (0 kJ m-2, 2.5 kJ m-2, 5.0 kJ m-2 and 7.5 kJ m-2) on the rice-Magnaporthe oryzae system were studied with respect to the Magnaporthe oryzae infection, the disease-resistance physiology of the rice and the rice blast disease condition. The results showed that under enhanced UV-B radiation, the infectivity of Magnaporthe oryzae was decreased, which could significantly inhibit its growth and sporulation. The activities of rice leaf disease-resistance-related enzymes (phenylalanine ammonia-lyase, lipoxygenase, chitinase and ß-1,3-glucanase) were significantly increased under enhanced UV-B radiation. Following inoculation with Magnaporthe oryzae, levels of disease-resistance-related substances in the rice leaves were significantly increased. Among the results, it was found that leaves after UV-B radiation had a more significant resistance response. The level of UV-B irradiation showed a parabolic relationship with the rice blast index (r2 = 0.85, P < 0.01; in the control group, r2 = 0.88, P < 0.01). The disease index decreased with increase in irradiation. The DI was at a minimum with enhanced UV-B irradiance of 4 kJ m-2; thereafter, it increased with increasing irradiation. The enhanced UV-B radiation had a direct impact on the growth of rice and Magnaporthe oryzae, and it indirectly changed the rice-Magnaporthe oryzae system. UV-B radiation could reduce the harmful impact of rice blast.

Chromatin states responsible for the regulation of differentially expressed genes under 60Co~γ ray radiation in rice.

BACKGROUND: The role of histone modifications in the DNA damage response has been extensively studied in non-plant systems, including mammals and yeast. However, there is a lack of detailed evidence showing how chromatin dynamics, either an individual mark or combined chromatin states, participate in regulating differentially expressed genes in the plant DNA damage response. RESULTS: In this study, we used RNA-seq and ChIP-seq to show that differentially expressed genes (DEGs), in response to ionizing radiation (IR), might be involved in different pathways responsible for the DNA damage response. Moreover, chromatin structures associated with promoters, exons and intergenic regions are significantly affected by IR. Most importantly, either an individual mark or a certain chromatin state was found to be highly correlated with the expression of up-regulated genes. In contrast, only the chromatin states, as opposed to any individual marks tested, are related to the expression of the down-regulated genes. CONCLUSIONS: Our findings demonstrate that IR-related DEGs are modulated by distinct epigenetic mechanisms. Either chromatin states or distinct histone dynamics may act sequentially or in combination in regulating up-regulated genes, but the complex chromatin structure is mainly responsible for the expression of down-regulated genes. Thus, this study provides new insights into how up- and down-regulated genes are epigenetically regulated at the chromatin levels, thereby helping us to understand distinct epigenetic mechanisms that function in the plant DNA damage response.

Molecular dissection of the response of the rice Systemic Acquired Resistance Deficient 1 (SARD1) gene to different types of ionizing radiation.

PURPOSE: Exposure to ionizing radiation induces plant defenses by regulating the expression of response genes. The systemic acquired resistance deficient 1 (SARD1) is a key gene in plant defense response. In this study, the function of Oryza sativa SARD1 (OsSARD1) was investigated after exposure of seeds/plants to ionizing radiation, jasmonic acid (JA) or salicylic acid (SA). MATERIALS AND METHODS: Rice seeds exposed to two types of ionizing radiations (gamma ray [GR] and ion beam [IB]) were analyzed by quantitative reverse transcription PCR (qRT-PCR) to identify the genes that are altered in response to ionizing radiation. Then, OsSARD1-overexpressing homozygous Arabidopsis plants were generated to assess the effects of OsSARD1 in the response to irradiation. The phenotypes of these transgenic plants, as well as control plants, were monitored after GR irradiation at doses of 200 and 300 Gray (Gy). RESULTS: The OsSARD1 transcript was strongly downregulated after exposure to GR and IB irradiation. Previous phylogenetic analysis showed that the Arabidopsis SARD1 (AtSARD1) protein is closely related to Arabidopsis calmodulin-binding protein 60g (AtCBP60g), which is known to be required for activation of SA biosynthesis. In this study, phylogenetic analysis showed that OsSARD1 was grouped with AtSARD1. The OsSARD1 gene was induced after exposure to SA and JA. The biological phenotype of OsSARD1-overexpressing Arabidopsis plants was examined. OsSARD1-overexpressing plants displayed resistance to GR; in comparison with wild-type plants, the height and weight of OsSARD1-overexpressing plants were significantly greater after GR irradiation. In addition, OsSARD1 protein was abundantly accumulated in the nucleus. CONCLUSIONS: The results indicate that OsSARD1 plays an important role in the regulation of the defense responses to GR and IB irradiation and exhibits phytohormone induced expression.

Influence of gamma radiation on the physical and sensory properties of two Brazilian rice cultivars.

BACKGROUND: Little has been reported about the effects of gamma radiation on the physical and sensory characteristics of rice. Samples were irradiated with 60 Co in doses 0, 1, 2 and 5 kGy, on a rate of 0.4 kGy h-1 . RESULTS: The evaluation of instrumental color showed that increasing doses promoted the yellowing (higher b* value) of the rice grains. Hardness was decreased and stickiness was increased in cooked rice with increasing doses. Sensory evaluation using quantitative descriptive analysis showed that increasing doses promoted higher occurrence of yellowish appearance, emergence of burnt aroma, and an increase of bitter and burnt taste. The sensory acceptance test by 9-point hedonic scale showed alteration of the samples irradiated with 5 kGy in all evaluated attributes (appearance, color, aroma, taste and texture). The lowest dose (1 kGy), however, had good acceptability by the panelists. CONCLUSION: Rice may be subjected to 1 kGy dose of gamma radiation without changes or with small changes in physical properties and with good overall acceptability. © 2016 Society of Chemical Industry.

Effect of enhanced UV-B radiation on methane emission in a paddy field and rice root exudation of low-molecular-weight organic acids.

A local rice variety, "Baijiaolaojing", was grown in a paddy field in the Yuanyang rice terraces under ambient and supplemental levels of ultraviolet-B (UV-B, 280-315 nm) radiation. The effects of enhanced UV-B radiation (5 and 10 kJ m(-2) d(-1)) on methane emissions in the paddy field were evaluated using a closed-chamber gas chromatography-based system, and the contents of low-molecular-weight organic acids (LMWOAs) in root exudates were determined by high-performance liquid chromatography (HPLC). Peaks in methane emissions in the paddy field were detected at 60, 80 and 100 days after rice transplantation. The highest level of cumulative methane emissions occurred at the tillering stage, followed by the jointing-booting and maturity stages. The lowest level was found at the flowering stage. The enhanced UV-B radiation did not change the seasonal variation in methane emissions in the paddy field; however, it induced a significant increase in the flux of methane emissions at the jointing-booting and maturity stages, as well as a significant increase in the cumulative flux of methane emissions throughout the growth period. In addition, the enhanced UV-B radiation caused an increase in the contents of oxalic acid and succinic acid and a decrease in the contents of tartaric acid and malic acid in rice root exudates. Furthermore, a significant positive correlation (r = 0.725, p < 0.01) was found between the content of oxalic acid and the methane emissions in the paddy field. The results indicated that enhanced UV-B radiation promoted methane emissions in the paddy field, which was closely associated with its impact on the exudation of LMWOAs by rice roots.