Babak Nakhoda

Physiology and proteome responses of two contrasting rice mutants and their wild type parent under salt stress conditions at the vegetative stage.

Salinity is one of the major environmental limiting factors that affects growth and productivity of rice (Oryza sativa L.) worldwide. Rice is among the most sensitive crops to salinity, especially at early vegetative stages. In order to get a better understanding of molecular pathways affected in rice mutants showing contrasting responses to salinity, we exploited the power of 2-DE based proteomics to explore the proteome changes associated with salt stress response. Our physiological observations showed that standard evaluation system (SES) scores, Na+ and K+ concentrations in shoots and Na+/K+ ratio were significantly different in contrasting mutants under salt stress condition. Proteomics analysis showed that, out of 854 protein spots which were reproducibly detected, 67 protein spots showed significant responses to salt stress. The tandem mass spectrometry analysis of these significantly differentially accumulated proteins resulted in identification of 34 unique proteins. These proteins are involved in various molecular processes including defense to oxidative stresses, metabolisms, photosynthesis, protein synthesis and processing, signal transduction. Several of the identified proteins were emerged as key participants in salt stress tolerance. The possible implication of salt responsive proteins in plant adaptation to salt stress is discussed.

Comparative proteomic and physiological characterisation of two closely related rice genotypes with contrasting responses to salt stress

Salinity is a limiting factor affecting crop growth. We evaluated the responses of a salt-tolerant recombinant inbred rice (Oryza sativa L.) line, FL478, and the salt-sensitive IR29. Seedlings were exposed to salt stress and the growth rate was monitored to decipher the effect of long-term stress. At Day 16, IR29 produced lower shoot biomass than FL478. Significant differences for Na+ and K+ concentrations and Na+ : K+ ratios in roots and shoots were observed between genotypes. Changes in the proteomes of control and salt-stressed plants were analysed, identifying 59 and 39 salt-responsive proteins in roots and leaves, respectively. Proteomic analysis showed greater downregulation of proteins in IR29. In IR29, proteins related to pathways involved in salt tolerance (e.g. oxidative stress response, amino acid biosynthesis, polyamine biosynthesis, the actin cytoskeleton and ion compartmentalisation) changed to combat salinity. We found significant downregulation of proteins related to photosynthetic electron transport in IR29, indicating that photosynthesis was influenced, probably increasing the risk of reactive oxygen species formation. The sensitivity of IR29 might be related to its inability to exclude salt from its transpiration stream, to compartmentalise excess ions and to maintain a healthy photosynthetic apparatus during salt stress, or might be because of the leakiness of its roots, allowing excess salt to enter apoplastically. In FL478, superoxide dismutase, ferredoxin thioredoxin reductase, fibre protein and inorganic pyrophosphatase, which may participate in salt tolerance, increased in abundance. Our analyses provide novel insights into the mechanisms behind salt tolerance and sensitivity in genotypes with close genetic backgrounds.

QTL Mapping of Salt Tolerance Traits with Different Effects at the Seedling Stage of Bread Wheat

We evaluated salt tolerance in 319 recombinant inbred lines derived from a cross between Roshan and Falat (seri82) in bread wheat (Triticum aestivum L.). This study identified quantitative trait lci (QTLs) with additive (a) and additive × additive (aa) epistatic effects, and characterized their salt treatment interactions (at and aat) at the seedling stage. Using a genetic map of 730 DArT and SSR markers, we identified 65 additive QTLs governing 13 traits using the QTL Cartographer program to assess single-treatment phenotypic values. We further identified 13 additive and 14 epistatic QTLs for 10 traits with the QTLNetwork program using multitreatment phenotypic values. Our results show that four of the additive and seven of the epistatic QTLs exhibited an effect on the response to salt treatment. Morphological traits had less effect on treatment than physiological traits did. Of the three additive QTLs found to affect shoot Na+ concentration, two colocalized with loci governing shoot fresh or dry weight (1B-2 and 3B-1). Thirteen pairs of QTLs across five chromosomal groups were detected at homologous positions in the A, B, and D genomes, indicative of synteny.

Field screening for drought tolerance in Setaria italica and Panicum miliaceum millet germplasm from Iran

The present study aims at field screening of Proso and Foxtail millet ecotypes for drought tolerance. Accordingly, 96 promising millet ecotypes along with four checks were evaluated under field conditions in Yazd province of Iran. Field experiment was conducted using an incomplete block design (LATTICE) with two replications under drought stress and control conditions in a period of two years. Multivariate analyses showed variance significant genetic variation (P < 0.01) among millet ecotypes of Iranian origin. Drought stress tremendously affected grain yield of all genotypes. The interaction between genotype and drought was significant for panicle weight, panicle length and days to flowering. Based on the results of multivariate analyses we identified the effective traits which are the foremost factor responsible for grain yield and dry weight of fodder under drought stress. Therefore, the selection based on these traits would be preferable to identify genotypes with high yield. Eventually, eight ecotypes with the higher grain yield and 8 with the higher dry weight fodder were found highly adoptive under moisture stress conditions. Such ecotypes can be recommended as promising genotypes which may eventually be released as new cultivars for drought-affected areas.