Sensitive Rice Cultivars Research Articles

Screening of Arsenic toxicity in Oryza sativa L. (rice) and assessment of variation in growth, ROS, and antioxidant responses in tolerant and sensitive rice cultivars

ABSTRACT Arsenic (As) in rice plants has toxic effects on their quality and human health. In the present study, 100 rice cultivars have been screened in hydroponics to analyze As toxicity and select As-tolerant and sensitive rice cultivars. The findings showed that rice cultivars responded differently to As stress at varying levels of effect. As treatments significantly changed morphological traits, the arsenic tolerance index (ATI %), pigments, and H2O2 concentrations. The rice cultivars Luit and Swarna demonstrated remarkable results (tolerant and sensitive) in terms of growth, as well as in terms of ATI, chlorophyll content, H2O2 content, and enzymatic and non-enzymatic antioxidants. Arsenic-induced pigment degradation and antioxidant content reduction were greater in Swarna than in Luit. Moreover, the results of biochemical analysis correlated with the morphological parameters. The selected As-tolerant and sensitive cultivars may be used to explore the tolerance mechanism in greater depth, which will require further molecular investigations.

Both Short-term and Long-term Ozone Pollution Alters the Chemical Composition of rice Grain.

The increasing ground-level ozone (O3) is threatening food security, especially in Asian areas, where rice is one of the most important staple crops. O3 impacts on rice could be exacerbated by its spatiotemporal heterogeneity. To improve evaluation accuracy and develop effective adaptations, direct data is urgently needed. Studies on the short-term effects of O3 on rice grain, however, are lacking. Which may lead to an underestimation of the O3 impacts. Through a field experiment, we studied the responses of grain nitrogen, grain carbon, and grain protein in rice cultivars to elevated concentrations of O3 (40 ppb plus that in background air, eO3), especially examining the effects of short-term eO3 during different plant growth stages. We found that long-term eO3 increased grain nitrogen by 29.29% in a sensitive rice cultivar, and short-term eO3 at the tillering and jointing stages increased grain nitrogen by 19.31%, and the grain carbon to nitrogen ratio was decreased by 14.70%, and 21.14% by short-term and long-term eO3. Here we demonstrate that short-term eO3 may significantly affect the chemical composition of rice grains. Previous evaluations of the effects of eO3 may be underestimated. Moreover, changes in the grain nitrogen and grain protein were greater when the short-term eO3 was added to rice plants during the tillering and jointing stage, compared to heading and ripening stage. These results suggest that to improve the tolerance of rice to eO3 to achieve food security, studies on cultivar screening, as well as developing growth-stage-specific adaptations are needed in future.

Is the time of anthesis in rice (Oryza sativa) influenced by photoperiod?

Photoperiod sensitivity in rice cultivars is defined when the cultivar begins anthesis on a relatively invariant date, varying by < 7days, regardless of the date of sowing or germination. While the date of flowering in photoperiod sensitive (PPS) rice cultivars is characteristically determined by the day length, especially during the short-day season (September-December), the response of the flower opening time (FOT) to photoperiod remains hitherto unexplored. This paper examines whether day length restrains year-to-year variation in FOT in PPS cultivars. We examined 105 PPS and 173 photoperiod insensitive (PPI) cultivars grown in different years and estimated their year-to-year FOT difference (or FOTD) and the year-to-year difference of sunrise to anthesis duration (or SADD). Wilcoxon signed rank test and bootstrap test were then performed to test whether these descriptors significantly differed between PPS and PPI groups of cultivars. The means of FOTD and SADD were detected to be significantly less in the PPS group than in the PPI group of cultivars, indicating significantly lesser variability of FOT in PPS than in PPI cultivars. This is the first report of a strong restraining influence of photoperiod on FOT variability in PPS cultivars.

Effect of Cd(II) adsorption onto rice roots on its uptake by different indica and japonica rice varieties and toxicity effect of Cd(II) under acidic conditions.

The rapid increase in soil acidity coupled with the deleterious effects of cadmium (Cd) toxicity had led to a decline in worldwide agricultural production. Rice absorbs and accumulates Cd(II) from polluted paddy soils, increasing human health risks throughout the food chain. A 35-day hydroponic experiment with four japonica and four indica (two each of them tolerant and sensitive cultivars) was conducted in this study to investigate the adsorption and absorption of Cd(II) by rice roots as related with surface chemical properties of the roots. The results showed that the three chemical forms of exchangeable, complexed, and precipitated Cd(II) increased with the increase in Cd(II) concentration for all rice cultivars. The roots of indica rice cultivars carried more negative charges and had greater functional groups and thus adsorbed more exchangeable and complexed Cd(II) than those of japonica rice cultivars. This led to more absorption of Cd(II) by the roots and greater toxicity of Cd(II) to the roots of indica rice cultivars and more inhibition of Cd(II) stress on the growth of the roots and whole plants of indica rice cultivars compared with japonica rice cultivars, which was one of the main reasons for more declines in the biomass and length of indica rice roots and shoots than japonica rice cultivars. Cd(II) stress showed more toxicity to the sensitive rice cultivars and thus greater inhibition on the growth of the cultivars due to more exchangeable and complexed Cd(II) adsorbed by their roots induced by more negative charges and functional groups on the roots compared with tolerant rice cultivar for both indica and japonica, which resulted in greater decreases in the biomass and length of roots and shoots as well as chlorophyll contents of the sensitive cultivars than the tolerant cultivars. The roots of sensitive rice cultivars also absorbed more Cd(II) than tolerant rice cultivars due to the same reasons as above. These findings will provide useful references for the safe utilization and health risk prevention of Cd-contaminated paddy fields.

Analysis of Morphological, Physiological, and Biochemical Traits of Salt Stress Tolerance in Asian Rice Cultivars at Seedling and Early Vegetative Stages

Rice (Oryza sativa L.) is a primary energy food for the Asian population. One of the greatest constraints in rice production is soil salinity because rice is very susceptible to salt. Meanwhile, many agricultural lands in Asia are in saline areas. It is important to identify and develop salt-tolerant rice varieties that highly adapt to Asian climates. By combining morphological, physiological, and biochemical assessments for screening the salt tolerance of 116 Asian rice cultivars, we were able to classify them into tolerant, moderate, and sensitive rice cultivars under salinity stress conditions and also understand salt tolerance mechanisms. The rice cultivars that are salt-tolerant include Pokkali from India, TCCP 266 and IR 45427 from the Philippines, and Namyang 7 from Republic of Korea. However, salt-sensitive rice varieties like IR29 and IR58 are from the Philippines, and Daegudo and Guweoldo are from Korea. The salt-tolerant varieties showed signs of tolerance, including a lower percent reduction in germination percentage, root length, root fresh weight, shoot length, plant biomass, and chlorophyll content. In order to maintain the cellular osmotic balance under saline conditions, the salt-tolerant varieties exhibited less membrane damage, a lower Na/K ratio, high proline and sugar accumulation, and lower levels of malondialdehyde (MDA) and hydrogen peroxide (H2O2). Pokkali from India, TCCP 266 and IR 45427 from the Philippines, and Namyang 7 from Republic of Korea are recommended as valuable germplasm resources for Asian rice breeding programs in saline agricultural areas.

The Efficiency of Humic Acid for Improving Salinity Tolerance in Salt Sensitive Rice (Oryza sativa): Growth Responses and Physiological Mechanisms

High-yielding rice cultivars exhibit a great performance in non-saline fields; however, their growth and productivity are greatly reduced in salt-affected lands. Humic acid has a promising stress-mitigating potential and can be effective in improving salt tolerance in salinity sensitive rice cultivars. Herein, seeds of Giza 177 (high-yielding but salt-sensitive rice cultivar) were primed in 40 mg/l humic acid, sown, and maintained. Then growth and physiological responses of the humic acid-primed plants to increased levels of salinity (EC: 0.55, 3.40, 6.77, and 8.00 mS/cm) were evaluated at the reproductive stage. Increasing salinity induced a progressive retardation in plant height, leaf area, fresh and dry weights. Such retardation was associated with Na+ buildup in shoot and root, high electrolyte leakage and accumulation of malondialdehyde, total soluble sugars, sucrose, glucose, proline, total soluble proteins, flavonoids, and phenolics. In contrast, salinity reduced K+, K+/Na+ ratio, total carbohydrates, and the activity of catalase, peroxidase, and polyphenol oxidase. Humic acid enhanced growth under non-saline and saline conditions. The humic acid-induced improvement in salt tolerance was associated with the reduction of Na+ toxicity, increasing K+/Na+ ratio, regulating osmolytes concentration, and enhancing the activities of antioxidant enzymes and thus reduce the oxidative stress. These results indicate that humic acid successfully reduced the salinity-induced plant damage, improved metabolism, and maintained active growth of Giza 177 under saline irrigation.

Morpho-physiological and biochemical attributes as tools to screen tolerance and susceptible rice cultivars for drought stress

Present research work was aimed to observe possible changes in the metabolism of rice plants (Oryza sativa L.) through drought stress. Rice belongs to the family Poaceae. It is considered as a vital food crop across all the major countries worldwide. Rice is prone to be affected by drought stress. Therefore, developing the drought tolerant cultivars of cereal crops assumed considerable importance. This work was carried out with an objective to study the Screening of rice cultivars against water stress and compare biochemical characteristic among different drought tolerant and sensitive rice cultivars. A set of 25 cultivars of rice were screened against drought stress at vegetative stage through various morpho-physiological characters such as moisture, relative water content (RWC), membrane stability index(MSI), membrane injury(MI), seedling length and seedling weight. The RWC is a best criterion for plant water status. The osmotic adjustment is a influential mechanism of conserving cellular hydration under water stress and RWC expression also affects osmotic adjustment in this respect. Thus, it can be considered that the higher RWC having cv. GAR-13 and NWGR-16026 were tolerant and lower RWC having cv. NWGR-16009 and NWGR-16019 were susceptible. Hence, cv. GAR-13 &amp; NWGR-16026 was used as tolerant and NWGR-16009 &amp; NWGR-16019 were used as susceptible. On the basis of first experiment total four cultivars (Two tolerant NWGR-16026 &amp; GAR-13, two susceptible NWGR-16009 &amp; NWGR-16019) were selected for various biochemical analysis. The results indicated that total soluble sugars (TSS), glycine betaine and ascorbic acid content were found significantly higher in cultivar NWGR-16026. The proline content was found significantly higher in cultivar GAR-13. So, RWC and some biochemical parameters are best indicators for selection regarded as potentially useful for drought tolerant rice cultivars and targets for development through transgenic approaches.

Concurrent effect of aluminum toxicity and phosphorus deficiency in the root growth of aluminum tolerant and sensitive rice cultivars

Concurrent effect of aluminum toxicity and phosphorus deficiency in the root growth of aluminum tolerant and sensitive rice cultivars

Efficiency of protectants in alleviating ozone stress on rice cultivars (Oryza sativa L.)

Tropical countries like India, as a result of increased greenhouse gases like tropospheric ozone (O3), are concerned about a loss of agricultural output and food security. As a result, adopting a new method to protect crops against ozone is a must. The most efficient protectant is ethylene diurea (EDU), which is often used by researchers, however, the effectiveness of other protectants remains still unexplored. Hence, this study aims in screening the potential protectants in alleviating the ozone stress (100 ppb) in O3 sensitive rice cultivar in open top chambers. The protectants used includes neem coated urea (NCU), ascorbic acid (AsA), calcium acetate (CaAc), panchagavya, neem oil, pink pigmented facultative methylotrophs (PPFM) and ethylene diurea (EDU). Results indicate that besides EDU, NCU and AsA were highly effective in mitigating O3 stress and were on par with each other. The application of protectants significantly improved the physiological, growth, and yield attributes; while, the malondialdehyde and proline content declined. The effect of protectants was relatively higher in O3 – sensitive cultivar. . The growth and yield traits were observed to be higher in EDU > NCU, AsA > CaAc > Panchagavya > Neem oil > PPFM. In O3 – sensitive cultivar, application of 300 ppm EDU, 1% NCU, and 1% AsA decreased the malondialdehyde content by 26.82, 26.92 and 27.47%, and proline by 18.64, 17.88 and 14.33%, respectively. Similarly, the application of 300 ppm EDU, 1% NCU and 1% AsA improved the number of spikelets per panicle by 69.09, 63.64 and 58.15% and the number of filled spikelets per panicle by 95.97, 95.35 and 93.02%, respectively. The present study concludes that NCU and AsA are the best alternatives to EDU for protecting plants against ozone stress.

Effects of Salt-Alkaline Stress on Carbohydrate Metabolism in Rice Seedlings

The aim of this study was to investigate carbohydrate metabolism in rice seedlings subjected to salt-alkaline stress. Two relatively salt-alkaline tolerant (Changbai 9) and sensitive (Jinongda 138) rice cultivars, grown hydroponically, were subjected to salt-alkaline stress via 50 mM of salt-alkaline solution. The carbohydrate content and the activities of metabolism-related enzymes in the leaves and roots were investigated. The results showed that the contents of sucrose, fructose, and glucose in the leaves and roots increased under salt-alkaline stress. Starch content increased in the leaves but decreased in the roots under salt-alkaline stress. The activities of sucrose-phosphate synthase, sucrose synthase, amylase, and ADP-glucose pyrophosphorylase increased whereas the activities of neutral invertase and acid invertase decreased in the leaves under salt-alkaline stress. The activities of sucrose-phosphate synthase, sucrose synthase, amylase, neutral invertase, and acid invertase increased in the roots under salt-alkaline stress. In conclusion, salt-alkaline stress caused the accumulation of photosynthetic assimilates in the leaves and decreased assimilation export to the roots.

Maghemite nano-fertilization promotes fluoride tolerance in rice by restoring grain yield and modulating the ionome and physiome

The present manuscript elucidated the ameliorative potential of nano-maghemite (FeNPs) against the hazardous effects of fluoride toxicity in the sensitive rice cultivar, IR-64. Fluoride pollution triggered bioaccumulation in root, shoot and spikelets which inhibited reproduction, agronomic development and mineral uptake. Suppressed activity of enzymatic antioxidants and excessive cobalt translocation manifested severe ROS-induced oxidative injuries. Seedling priming with FeNPs reduced fluoride bioaccumulation and promoted efficient uptake of macroelements and micronutrients like potassium, calcium, iron, zinc, copper, nickel, manganese, selenium and vanadium and reduced the translocation of cobalt in mature seedlings during stress. This altogether triggered growth and activated the enzymes like SOD, CAT, APX and GPOX. High accumulation of non-enzymatic antioxidants like proline, anthocyanins, flavonoids, phenolics along with stimulated GSH synthesis (determined from high GR, GST and GPX activity) and glyoxalase activity enabled FeNP-pulsed plants to efficiently scavenge ROS, O2-, H2O2 and methylglyoxal, and mitigate oxidative injuries. The ROS production was also lowered due to suppressed NADPH oxidase activity. This ensured subsequent revitalization of Hill activity and the level of photosynthetic pigments. Due to reduced fluoride partitioning and improved nutritional sink, the grain and panicle development in FeNP-primed, stressed seedlings were more stimulated than even control sets. Overall, our findings supported by statistical modelling established the potential of iron-nanotechnology in promoting safe rice cultivation even in fluoride-polluted environments.

Carbon and nitrogen metabolism in rice cultivars affected by salt-alkaline stress

Salt-alkaline stress generally leads to soil compaction and fertility decline. It also restricts rice growth and nutrient acquisition, so reduces rice yield. However, little is known about the effect of salt-alkaline stress on the carbon and nitrogen metabolism of rice. In this study, two relatively salt-alkaline tolerant (Changbai 9 and Dongdao 12) and sensitive (Jinongda 138 and Tongyu 315) rice cultivars were grown in a field experiment conducted with two soil types including black soil and salt-alkaline soil to evaluate the characteristics of yield, carbon and nitrogen metabolism in rice. Results showed that yield and nitrogen use efficiency (NUE) in rice greatly decreased under salt-alkaline stress. Changbai 9 (CB9) and Dongdao 12 (DD12) showed higher NUE than Jinongda 138 (JND138) and Tongyu 315 (TY315) under the salt-alkaline stress. Additionally, carbon and nitrogen metabolism enzyme activity and compound content were significantly affected by salt-alkali stress; different performances were observed between cultivars under salt-alkaline stress. In conclusion, our results indicate that salt-alkaline tolerant rice cultivars may have more stable carbon and nitrogen metabolism than sensitive genotypes under salt-alkaline conditions.

De novo RNA-Seq analysis in sensitive rice cultivar and comparative transcript profiling in contrasting genotypes reveal genetic biomarkers for fluoride-stress response

The fluoride-sensitive indica rice cultivar, IR-64 was subjected to NaF-treatment for 25 days, following which RNA-Seq analysis identified significant up and down regulation of 1,303 and 93 transcripts respectively. Gene ontology (GO) enrichment analysis classified transcripts into groups related to ‘cellular part’, ‘membrane’, ‘catalytic activity’, ‘transporter activity’, ‘binding’, ‘metabolic processes’ and ‘cellular processes’. Analysis of differentially expressed genes (DEGs) revealed fluoride-mediated suppression of abscisic acid (ABA) biosynthesis and signaling. Instead, the gibberellin-dependent pathway and signaling via ABA-independent transcription factors (TFs) was activated. Comparative profiling of selected DEGs in IR-64 and fluoride-tolerant variety, Khitish revealed significant cytoskeletal and nucleosomal remodelling, accompanied with escalated levels of autophagy in stressed IR-64 (unlike that in stressed Khitish). Genes associated with ion, solute and xenobiotic transport were strongly up regulated in stressed IR-64, indicating potential fluoride entry through these channels. On the contrary, genes associated with xenobiotic mobility were suppressed in the tolerant cultivar, which restricted bioaccumulation and translocation of fluoride. Pairwise expression profile analysis between stressed IR-64 and Khitish, supported by extensive statistical modelling predicted that fluoride susceptibility was associated with high expression of genes like amino acid transporter, ABC transporter2, CLCd, MFS monosaccharide transporter, SulfT2.1 and PotT2 while fluoride tolerance with high expression of Sweet11.

Differential responses of photosynthetic parameters and its influence on carbohydrate metabolism in some contrasting rice (Oryza sativa L.) genotypes under arsenate stress.

Influence of arsenic (As) in As tolerant and sensitive rice genotypes based chloroplastic pigments, leaf gas exchange attributes and their influence on carbohydrate metabolism were investigated in the present study. As retards growth of crop plants and increase several health ailments by contaminating food chain. Photosynthetic inhibition is known to be the prime target of As toxicity due to over-production of ROS. Hydroponically grown rice seedlings of twelve cultivars were exposed to 25, 50, and 75 μM arsenate (AsV) that exerted negative impact on plastidial pigments content and resulted into inhibition of Hill activity. Internal CO2 concentration lowered gradually due to interference of As with stomatal conductance and transpiration rate that subsequently led to drop in net photosynthesis. Twelve contrasting rice genotypes responded differentially to As(V) stress. Present study evaluated As tolerant and sensitive rice cultivars with respect to As(V) imposed alterations in pigments content, photosynthetic attributes along with sugar metabolism. Starch contents, the principle carbohydrate storage declined differentially among As(V) stressed test cultivars, being more pronounced in cvs. Swarnadhan, Tulaipanji, Pusa basmati, Badshabhog, Tulsibhog and IR-20 compared to cvs. Bhutmuri, Kumargore, Binni, Vijaya, TN-1 and IR-64. Therefore, the six former cultivars tried to adapt defensive mechanisms by accumulating higher levels of reducing and non-reducing sugars to carry out basal metabolism to withstand As(V) induced alterations in photosynthesis. This study could help to screen As tolerant and sensitive rice genotypes based on their photosynthetic efficiency in As polluted agricultural fields to reduce As contamination assisted ecotoxicological risk.

Low nitrogen stress regulates chlorophyll fluorescence in coordination with photosynthesis and Rubisco efficiency of rice.

Nitrogen (N) is the basis of plant growth and development and, is considered as one of the priming agents to elevate a range of stresses. Plants use solar radiations through photosynthesis, which amasses the assimilatory components of crop yield to meet the global demand for food. Nitrogen is the main regulator in the allocation of photosynthetic apparatus which changes of the photosynthesis (Pn) and quantum yield (Fv/Fm) of the plant. In the present study, dynamics of the photosynthetic establishment, N-dependent relation with chlorophyll fluorescence attributes and Rubisco efficacy was evaluated in low-N tolerant (cv. CR Dhan 311) and low-N sensitive (cv. Rasi) rice cultivars under low-N and optimum-N conditions. There was a decrease in the stored leaf N under low-N condition, resulting in the decreased Pn and Fv/Fm efficiency of the plants through depletion in the activity and content of Rubisco. The Pn and Fv/Fm followed the parallel trend of leaf N content during low-N condition along with depletion of intercellular CO2 concentration and overall conductance under low-N condition. Photosynthetic saturation curve cleared abrupt decrease of effective quantum yield in the low-N sensitive rice cultivar than the low-N tolerant rice. Also, the rapid light curve highlighted the unacclimated regulation of photochemical and non-photochemical quenching in the low-N condition. The low-N sensitive rice cultivar triumphed non-photochemical quenching, whereas the low-N tolerant rice cultivar rose gradually during the light curve. Our study suggested that the quantum yield is the key limitation for photosynthesis in low-N condition. Regulation of Rubisco, photochemical and non-photochemical quenching may help plants to grow under low-N level.

Early cold stress responses in post-meiotic anthers from tolerant and sensitive rice cultivars

BackgroundRice grain production is susceptible to a changing environment that imposes both biotic and abiotic stress conditions. Cold episodes are becoming more frequent in the last years and directly affect rice yield in areas with a temperate climate. Rice is particularly susceptible to cold stress during the reproductive phase, especially in anthers during post-meiotic stages which, in turn, affect pollen production. However, a number of rice cultivars with a certain degree of tolerance to cold have been described, which may represent a good breeding resource for improvement of susceptible commercial varieties. Plants experiencing cold stress activate a molecular response in order to reprogram many metabolic pathways to face these hostile conditions.ResultsHere we performed RNA-seq analysis using cold-stressed post-meiotic anther samples from a cold-tolerant, Erythroceros Hokkaido (ERY), and a cold-susceptible commercial cultivar Sant’Andrea (S.AND). Both cultivars displayed an early common molecular response to cold, although the changes in expression levels are much more drastic in the tolerant one. Comparing our datasets, obtained after one-night cold stress, with other similar genome-wide studies showed very few common deregulated genes, suggesting that molecular responses in cold-stressed anthers strongly depend on conditions and the duration of the cold treatments. Cold-tolerant ERY exhibits specific molecular responses related to ethylene metabolism, which appears to be activated after cold stress. On the other hand, S.AND cold-treated plants showed a general downregulation of photosystem I and II genes, supporting a role of photosynthesis and chloroplasts in cold responses in anthers, which has remained elusive.ConclusionsOur study revealed that a number of ethylene-related transcription factors, as putative master regulators of cold responses, were upregulated in ERY providing promising candidates to confer tolerance to susceptible cultivars. Our results also suggest that the photosynthesis machinery might be a good target to improve cold tolerance in anthers. In summary, our study provides valuable candidates for further analysis and molecular breeding for cold-tolerant rice cultivars.

Cold plasma treatment to improve germination and enhance the bioactive phytochemical content of germinated brown rice

The changes in the bioactive phytochemicals of six cultivars of Thai germinated brown rice (GBR) were monitored in parallel to those of cold plasma-treated GBR (PGBR). After treatment with the optimal plasma conditions, the germination percentage, root length, and seedling height measurements of the most sensitive rice cultivar increased by 84%, 57%, and 69%, respectively. For all of the rice cultivars, there were no significant differences in the antioxidant activities of the GBRs and PGBRs. Conversely, higher contents of γ-oryzanols were observed in the PGBR group than in the GBR group during the 2-day germination period. Certain cultivars in the PGBR group reached their maximum values for total phenolic compounds, total vitamin E, certain simple phenolics, phytosterols, triterpenoids, and anthocyanins one day earlier than the same values for GBR. In contrast, the concentrations of 2-acetyl-1-pyrroline in both the GBR and PGBR samples were reduced significantly with increased germination time.

Ancient rice cultivar extensively replaces phospholipids with non-phosphorus glycolipid under phosphorus deficiency.

Recycling of phosphorus (P) from P-containing metabolites is an adaptive strategy of plants to overcome soil P deficiency. This study was aimed at demonstrating differences in lipid remodelling between low-P-tolerant and -sensitive rice cultivars using lipidome profiling. The rice cultivars Akamai (low-P-tolerant) and Koshihikari (low-P-sensitive) were grown in a culture solution with [2 mg l-1 (+P)] or without (-P) phosphate for 21 and 28 days after transplantation. Upper and lower leaves were collected. Lipids were extracted from the leaves and their composition was analysed by liquid chromatography/mass spectrometry (LC-MS). Phospholipids, namely phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and phosphatidylinositol (PI), lysophosphatidylcholine (lysoPC), diacylglycerol (DAG), triacylglycerol (TAG) and glycolipids, namely sulfoquinovosyl diacylglycerol (SQDG), digalactosyldiacylglycerol (DGDG), monogalactosyldiacylglycerol (MGDG) and 1,2-diacyl-3-O-alpha-glucuronosyl glycerol (GlcADG), were detected. GlcADG level was higher in both cultivars grown in -P than in +P and the increase was larger in Akamai than in Koshihikari. DGDG, MGDG and SQDG levels were higher in Akamai grown in -P than in +P and the increase was larger in the upper leaves than in the lower leaves. PC, PE, PG and PI levels were lower in both cultivars grown in -P than in +P and the decrease was larger in the lower leaves than in the upper leaves and in Akamai than in Koshihikari. Akamai catabolised more phospholipids in older leaves and synthesised glycolipids in younger leaves. These results suggested that extensive phospholipid replacement with non-phosphorus glycolipids is a mechanism underlying low-P-tolerance in rice cultivars.

Identification of miRNA-mediated drought responsive multi-tiered regulatory network in drought tolerant rice, Nagina 22

Comparative characterization of microRNA-mediated stress regulatory networks in contrasting rice cultivars is critical to decipher plant stress response. Consequently, a multi-level comparative analysis, using sRNA sequencing, degradome analysis, enzymatic and metabolite assays and metal ion analysis, in drought tolerant and sensitive rice cultivars was conducted. The study identified a group of miRNAs “Cultivar-specific drought responsive” (CSDR)-miRNAs (osa-miR159f, osa-miR1871, osa-miR398b, osa-miR408-3p, osa-miR2878-5p, osa-miR528-5p and osa-miR397a) that were up-regulated in the flag-leaves of tolerant cultivar, Nagina 22 (N22) and Vandana, but down-regulated in the sensitive cultivar, Pusa Basmati 1 (PB1) and IR64, during drought. Interestingly, CSDR-miRNAs target several copper-protein coding transcripts like plantacyanins, laccases and Copper/Zinc superoxide dismutases (Cu/Zn SODs) and are themselves found to be similarly induced under simulated copper-starvation in both N22 and PB1. Transcription factor OsSPL9, implicated in Cu-homeostasis also interacted with osa-miR408-3p and osa-miR528-5p promoters. Further, N22 flag leaves showed lower SOD activity, accumulated ROS and had a higher stomata closure. Interestingly, compared to PB1, internal Cu levels significantly decreased in the N22 flag-leaves, during drought. Thus, the study identifies the unique drought mediated dynamism and interplay of Cu and ROS homeostasis, in the flag leaves of drought tolerant rice, wherein CSDR-miRNAs play a pivotal role.

Evaluating the effect of zinc oxide nanoparticles on the physiological responses of nine non-photoperiod sensitive rice cultivars

The effects of nanopaticles on plant growth and metabolites have been reported in previous studies, but knowledge of the potential impacts of physiological responses is still unclear. Therefore, this study focused on the effect of exposure of zinc oxide (ZnO) nanoparticles on photosynthetic pigment contents (chlorophyll A, chlorophyll B and carotenoids) and the antioxidant enzyme activities (catalase and peroxidase) in nine non-photoperiod sensitive rice cultivars consisting of RD41, RD49, Chai Nat 1, Suphan Buri 1, Suphan Buri 2, Suphan Buri 3, Pathum Thani 1, Pathum Thani 80 and Phitsanulok 2. Rice plants were treated with 200 mg L-1 ZnO nanoparticles for every 15 days-interval. Rice plants were collected at 37, 44 and 51 days after planting for the evaluation of ZnO nanoparticles toxicity. The results showed that nine non-photoperiod sensitive rice cultivars treated with ZnO nanoparticle, as determined by the reduction of photosynthetic pigment contents. The activities of antioxidant enzymes protected plant cell when exposed to the toxicity of ZnO nanoparticles. This study showed that the supplementation of ZnO nanoparticles was no significant difference in photosynthetic pigment contents of rice cultivars. The results indicated that the accumulation of antioxidant enzyme activities could be protecting damage of the photosynthetic pigments in plant cells.