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Hydroponic studies were conducted to investigate the role of iron plaque on transport and distribution of chromium (Cr) by rice seedlings. Microscopical observations indicate that iron plaque developed quickly at the root surface of rice seedlings, but the distribution of iron plaque was more intense near root base and less towards root tip. Results showed that rice seedlings exposed to Cr(III) depicted significantly higher capacity for Cr accumulation in plant tissues than Cr(VI) in the presence of iron plaque. However, transport of Cr within plant cells was more evident in Cr(VI) treatment with iron plaque than Cr(III) treatment. Results also showed that there are significant impact on transport of K, Mn and Zn in rice seedlings treated with Cr(VI) in the presence of iron plaque, while significant effect on transport of Mn and Zn were observed in Cr(III)-treated rice seedlings. Results from detached root test provide additional evidence to confirm the presence of iron plaque, that had different impact on Cr uptake when Cr(VI) or Cr(III) was supplied.

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In order to breed rice cultivars for resistance to the brown planthopper, Nilaparvata lugens Stål (BPH) in Bangladesh, were evaluated for resistance in greenhouse screening tests. Over a period of six years (2005–2010), 1,767 entries/cultivars were screened using the plant hopper screening (PHS) system. The results showed 87 donors possessing different levels of resistance to the BPH. One exotic cultivar was highly resistant to the BPH and 86 materials showed medium resistance (tolerance) to the BPH. The rest of the materials including germplasm, F2, exotic, IRBPHN (International Rice Brown Planthopper Nursery) and advanced lines were susceptible. Most of entries coming from the International Rice Research Institute (IRRI) via the IRBPHN were moderately resistant.

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Gibberellins (GAs) are a class of plant hormones that play important roles in diverse aspects during plant growth and development. A series of GA synthesis and metabolism genes have been reported or proved to have essential functions in different plant species, while a small number of GA 2-oxidase genes have been cloned or reported in wheat. Previous studies have provided some important findings on the process of GA biosynthesis and the enzymes involved in its related pathways. These may facilitate understanding of the complicated process underlying GA synthesis and metabolism in wheat. In this study, GA 2-oxidase genes TaGA2ox1-1, TaGA2ox1-2, TaGA2ox1-3, TaGA2ox1-4, TaGA2ox1-5, and TaGA2ox1-6 were identified and further overexpressed in rice plants to investigate their functions in GA biosynthesis and signaling pathway. Results showed overexpression of GA 2-oxidase genes in rice disrupted the GA metabolic pathways and induced catalytic responses and regulated other GA biosynthesis and signaling pathway genes, which further leading to GA signaling disorders and diversity in phenotypic changes in rice plants.

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High ozone (O3) can cause great damage to plants. However, the effect of high O3 on nitrogen (N) absorption, distribution, and utilization in rice at different growth stages under different planting densities is poorly understood. In the present study, a conventional cultivar (Yangdao 6) and a hybrid cultivar (II You 084) with different planting densities were exposed to an elevated amount of O3 (E-O3; 50% higher than that of the control, C-O3) under a freeair gas concentration enrichment (FACE) system. N absorption, distribution, and utilization of the green leaves, stems, and shoots at tillering, jointing heading, and maturity were investigated. Results showed that E-O3 significantly increased the N content in the shoots of Yangdao 6 by 7.5%, 12.7%, and 19.6%, respectively, at jointing, heading, and maturity. Also, the N content in the shoots of II You 084 increased by 5.4%, 6.5%, and 8.4% at the corresponding growth stage upon E-O3 application. E-O3 significantly decreased N accumulation of II You 084 by 8.3%, 4.9%, 4.7%, and 19.2%, respectively, at tillering, jointing, heading, and maturity. Further, E-O3 had a decreasing effect on the N distribution in green leaves (p ≤ 0.05) of both cultivars, but exerted an increasing effect on that in the stems of both cultivars (p ≤ 0.05). In addition, E-O3 significantly decreased the N use efficiency (NUE) for biomass of the two cultivars in all growth stages. These results revealed that E-O3 could increase the N content in rice plants but decrease the N accumulation and utilization in both cultivars. The effects of E-O3 on N absorption, distribution, and utilization were not affected by planting density.

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Aerobic rice offers an attractive alternative approach over transplanting system as it consumes less water with low labour expenses. Flag leaf of six rice cultivars, viz. PR 120, PR 115, PR 116, Feng Ai Zan, PAU 201 and Punjab Mehak 1 was analysed for antioxidant defence mechanism and polyamine catabolism under the aerobic and the transplanting conditions. Ascorbate peroxidase (APX), guaiacol peroxidase (GPX), catalase (CAT), superoxide dismutase (SOD), diamine oxidase (DAO) and polyamine oxidase (PAO) activities increased gradually from tillering to anthesis stage and then declined towards maturity stage under both planting conditions. Apparently, contents of ascorbic acid, α-tocopherol, proline and polyamines (PAs) also revealed similar trend. The aerobic condition elevated activities of PAO, SOD as well as contents of PAs, lipid peroxide and H2O2 whereas the transplanting condition had higher levels of APX, GPX, CAT and total antioxidant activities and contents of ascorbate, α-tocopherol and proline. Cultivars Feng Ai Zan, PR 115 and PR 120 exhibited superior tolerance over other cultivars by accumulating higher contents of PAs with increasing levels of PAO and SOD activities under the aerobic condition. However, under the transplanting condition PR 116 and PAU 201 showed higher activities of antioxidative enzymes with decreasing contents of lipid peroxide and H2O2. We infer that under the aerobic condition, enhancement of PAs and PAO activity enabled rice cultivars to tolerate oxidative stress, while under the transplanting condition, antioxidative defence system with decreasing of lipid peroxide content was closely associated with the protection of flag leaf by maintaining membrane integrity. In crux, results indicated that H2O2 metabolic machinery was strongly up-regulated especially at the anthesis stage.

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This study was to determine the gene expression pattern and phenotypic change of Cheongcheong, Nagdong, TN1, and 8 different pedigrees of the CNDH population when WBPH infestation initiated at the reproductive stage of the crop. WBPH infested plants generally showed higher expression level of defense genes compared with the uninfected plants. LOX transcriptional levels in Nagdong and CNDH42-1 did not increase after WBPH feeding at all-time course. Chlorophyll content declined in infested plants compared to their controls, but still CNDH3, CNDH14-2, and CNDH65 were healthier. Heavy and extensive WBPH feeding affected rice yield and grain quality although the infestation started at the reproductive stage.

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Nitrogen (N) is an important nutrient for plant growth and yield production, and rice grown in paddy soil mainly uses ammonium (NH4 +) as its N source. Previous studies have shown that N status is tightly connected to plant defense; however, the roles of NH4 + uptake and assimilation in rice sheath blight disease response have not been studied previously. Here, we analyzed the effects of different N sources on plant defense against Rhizoctonia solani. The results indicated that rice plants grown in N-free conditions had higher resistance to sheath blight than those grown under N conditions. In greater detail, rice plants cultured with glutamine as the sole N source were more susceptible to sheath blight disease compared to the groups using NH4 + and nitrate (NO3 ) as sole N sources. N deficiency severely inhibited plant growth; therefore, ammonium transporter 1;2 overexpressors (AMT1;2 OXs) were generated to test their growth and defense ability under low N conditions. AMT1;2 OXs increased N use efficiency and exhibited less susceptible symptoms to R. solani and highly induced the expression of PBZ1 compared to the wild-type controls upon infection of R. solani. Furthermore, the glutamine synthetase 1;1 (GS1;1) mutant (gs1;1) was more susceptible to R. solani infection than the wild-type control, and the genetic combination of AMT1;2 OX and gs1;1 revealed that AMT1;2 OX was less susceptible to R. solani and required GS1;1 activity. In addition, cellular NH4 + content was higher in AMT1;2 OX and gs1;1 plants, indicating that NH4 + was not directly controlling plant defense. In conclusion, the present study showed that the activation of NH4 + uptake and assimilation were required for rice resistance against sheath blight disease.

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Cereal Research Communications
Authors: H. Sonah, R. Deshmukh, S. Chand, M. Srinivasprasad, G. Rao, H. Upreti, A. Singh, N. Singh, and T. Sharma

Flag leaf architecture is a very important trait which ensures the yield bearing capacity of plants by providing excellent source for photosynthesis. In this study, quantitative trait loci (QTLs) for flag leaf length and other traits were identified using rice recombinant inbred lines (RILs) derived from HP2216 × Tetep. A total of 12 QTLs were identified for the four traits located on seven different chromosomes of rice and analysis of interaction among the QTLs revealed additive effect for the leaf length and epistatic main effect for panicle length. More interestingly a QTL qLL12.1 responsible for the flag leaf length was identified on chromosome 12 within the marker interval RM247-RM6296 consistently at three climatic zones in India. Furthermore to saturate the qLL12.1 interval, additional 58 simple sequence repeat (SSR) markers were used for polymorphism survey which showed that qLL12.1 region was more conserved among parental lines. Finally, two polymorphic SSR markers were used for saturation of qLL12.1 region. Consequently, candidate gene approach was used to compliment QTL mapping. Co-localization of linkage map with physical map revealed 75 genes with evidence for expression. Functional annotation of these genes using in silico approaches and detailed literature search revealed nine candidate genes for flag leaf length. The stable QTL qLL12.1 identified in this study will provide starting point for map based cloning of leaf length related genes and tightly linked flanking markers can be used in marker assisted breeding programmes.

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The use of poor quality water for agriculture is now receiving major attention especially in arid and semi-arid regions. This experiment was carried out to evaluate the effects of different irrigation water qualities on the grain yield and nutrient uptake of rice and on the heavy metal concentration in the grains. Six water treatments were applied at intervals of three days, involving either fresh water (FW), drainage water (DW), mixed water (MW), fresh water followed by drainage water (1FW + 1DW), two applications of fresh water followed by one of drainage water (2FW + 1DW) or one application of fresh water followed by two of drainage water (1FW + 2DW). The rice grain yield and the uptake of nitrogen (N), phosphorus (P) and potassium (K) were determined. The grains were also analysed for the concentration of nickel (Ni), cadmium (Cd) and lead (Pb). The results showed that the grain yield, the uptake of N, P and K in the plant biomass and the concentration of heavy metals in the grains were significantly affected by the water quality. The rice grain yield exhibited a close correlation with the water quality. The highest grain yield was obtained in the FW treatment and the lowest yield in the DW treatment. The uptake of N, P and K was detrimentally affected by poor quality water. However, the uptake trend for these elements was similar across all the irrigation treatments. The concentrations of heavy metal in the grains were significantly higher in plots irrigated with poor quality water. Among the treatments the cumulative concentrations of heavy metal were in the order of: DW ≯1FW + 2DW ≯ MW ≯ 1FW + 1DW ≯ 2FW + 1DW ≯ FW. This study showed that there is a potential risk of heavy metal contamination in rice crops treated with poor quality water. The lower grain yield after irrigation with poor quality water could be due to the disturbed mineral nutrition or to relatively higher salt toxicity.

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Effects of salinity on correlation, path and stress indices, yield and its components were studied in a set of 34 promising rice genotypes collected from various national and international organizations. These genotypes were evaluated in a randomized complete block design with three replications during the wet seasons (kharif) of 2009 and 2010 in normal (ECiw ∼ 1.2 dS/m) and salinity stress (ECiw ∼ 10 dS/m) environments in micro plots at Central Soil Salinity Research Institute (CSSRI), Karnal, India. Grain yield per plant showed positive significant association with plant height, total tillers, productive tillers, panicle length, and biological yield per plant and harvest index under normal environment, whereas grain yield showed positive significant association with biological yield and harvest index under salinity stress. These results clearly indicate that selection of high yielding genotypes would be entirely different under normal and saline environments. The stress susceptibility index (SSI) values for grain yield ranged from 0.35 (HKR 127) to 1.55 (TR-2000-008), whereas the stress tolerance index (STI) values for grain yield ranged from 0.07 (PR 118) to 1.09 (HKR 120). The genotypes HKR 120, HKR 47 and CSR-RIL-197 exhibited higher values of stress tolerance index (STI) in salinity. Under salinity, negative and significant association was shown by SSI and grain yield in contrast to positive and significant association shown by STI and grain yield. These associations could be useful in identifying salt tolerant and sensitive high yielding genotypes. The stress susceptible and stress tolerance indices suggest that the genotypes developed for salinity tolerance could exhibit higher tolerance, adaptability and suitability. Harvest index and biological yield traits emerged as the ideal traits for improvement through selection and could be used to increase the rice productivity under saline stress environments.

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