Oryza glaberrima response strategies to salinity : distinction between osmotic and ionic components

Salinity is an important environmental constraint which strongly reduces crop yield in several areas in the world. Rice (Oryza sativa) is considered as a salt-sensitive species and improvement of salt resistance is a major goal for plant breeders. Some species in the Oryza genus may constitute an interesting source of genes for rice improvement. Comparatively to the classical Asian rice species (Oryza sativa), the African rice Oryza glaberrima is poorly described for its response to salt stress. Our aims were 1-) to identify salt-tolerant varieties of O. glaberrima, 2-) to discriminate between the osmotic and the ionic components of salt stress and 3) to precise the impact of individual ions on salt deleterious impact. Plants were exposed to stress in nutrient solution or in soil culture. Then, a set of parameters related to photosynthesis, mineral nutrition, plant water status, yield, and antioxidative properties were recorded. Our results showed that one accession such as the cultivar TOG5307 was able to maintain a higher net photosynthesis under salt conditions and exhibited a higher level of tolerance to accumulated Na+ ions and a higher capacity for osmotic adjustment comparatively to the salt-sensitive cultivar TOG5949. The salt-resistant cultivar TOG5307 was also less affected by salinity than TOG5949 for yield-related parameters. Na+ ions appeared more toxic than Cl-, although an additive effect was recorded when both ions were simultaneously present in NaCl. The use of non-penetrating osmotic agent PEG demonstrated that osmotic and ionic components of salt stress acted in an additive way in the salt-sensitive cultivar but not in the salt-resistant one where an antagonist action was recorded for several parameters. Data were analyzed in relation to the expression of genes coding for ions transporters.(SC - Sciences) -- UCL, 202

Screening for salinity tolerance of Oryza glaberrima Steud. seedlings

Rice (Oryza sativa) is a salt-sensitive species and improvement of salt resistance is a major goal for plant breeders. Some species of Oryza genus may constitute an interesting source of genes involved in stress resistance for cultivated rice improvement. The African rice Oryza glaberrima is poorly described for its response to salt stress. Twenty-five accessions of O. glaberrima were exposed during 2 weeks to 0 or 60 mM NaCl in nutrient solution. Morphological and physiological parameters were recorded and used to perform principal component analysis allowing us to consider three contrasting groups (salt-resistant, medium, and salt-sensitive). Most of the tested lines appeared more salt-sensitive than the moderately salt-resistant cultivar I Kong Pao from O. sativa. Salt-sensitivity index was higher for roots than for shoots and O. glaberrima was poorly efficient for regulation of Na+ translocation from the root to the shoot. Some accessions such as TOG5307 however were able to maintain a high net photosynthesis under salt conditions and exhibited a high level of tolerance to accumulated Na+ ions and a high capacity for osmotic adjustment. It is concluded that these salt-tolerant accessions constitute a promising material for rice improvement through inter-specific crosses with O. sativa

Unravelling impact of Na+, Cl- and their respective transporter in detrimental effects of salt stress on the African rice species (Oryza glaberrima Steud.)

Salinity resistance of the African rice species (Oryza glaberrima) is poorly documented and the specific responses of the plant to Na+ and Cl- toxic ions remain unknown. Moreover, the roles of Na+/H+ antiport and cation-chloride-cotransporter in salt stresses still remain unclear. In 1st experiment, two distinct cultivars TOG5307 and TOG5949 were maintained for 15 days on iso-osmotic nutrient solutions containing 50 mM NaCl, or a combination of Cl- salts (Cl- - dominant) or Na+ salts (Na+ - dominant). Plant water status, ion accumulation, gas exchange and fluorescence related parameters; carbon (∆13C) and nitrogen (δ15N) isotope discrimination were analyzed. TOG5307 exhibited a higher level of resistance than TOG5949 in terms of growth and photosynthesis maintenance and control of Cl- and Na+ accumulation. NaCl was the most detrimental treatment, followed by Na+ -dominant treatment while Cl- -treatment had the lowest effect. Impact of Na+ and Cl- on considered parameters are additive. In 2nd experiment, the two contrasted cultivars (TOG5307 and TOG5949) were exposed during 3 days in nutrient solutions to 75 mM NaCl containing 100 µM amiloride (inhibitor of Na+-H+ antiporters) or 200 µM bumetanide (inhibitor cation-chloride-cotransporters). Amiloride increased Na+ accumulation in roots and leaves to a higher extent in salt-resistant TOG5307 than in salt-sensitive TOG5949. Bumetanide reduced Cl- accumulation in both cultivars as well as K+ accumulation in TOG5307 and Na+ accumulation in TOG5949. Cultivars exhibiting contrasting levels of salinity resistance are available in Oryza glaberrima and salt-tolerant genotypes may constitute a valuable source of gene for classical rice improvement

Impact of salinity on yield-related parameters in two contrasting cultivars of <i>Oryza glaberrima</i> Steud. in Benin

Salinity is one of the major environmental stresses limiting growth and yield of rice. The objective of the present study was to analyze the impact of NaCl on yield-related parameters of Oryza glaberrima. Two contrasted cultivars of Oryza glaberrima previously tested for salt resistance at the vegetative stage [salt-resistant (TOG5307) and salt-sensitive (TOG5949)] were irrigated with a saline solution containing 30 mM NaCl (EC: 3 dS.m−1 NaCl). After 6 months of treatments, mineral nutrient and yield-related parameters were assessed. Proline was quantified in the panicle leaf at the start of the grain filling stage. NaCl treatment affected most yield-related parameters: panicle length, panicle leaf dry weight, number of branches per panicle, panicle leaf length, days to 50% heading, straw fresh weight per plant, grain yield per plant, number of spikelets per panicle, and number of filled grains per panicle. The weight of 1,000 grains decreased in the salt-sensitive cultivar only, suggesting that grain filling processes were compromised. The salt-resistant cultivar TOG5307 was less affected than the salt-sensitive TOG5949 and accumulated lower amounts of Na+ in the grains. For both cultivars, hulls contained higher concentration of Na+ and K+ than grains. TOG5307 also contained more proline in the panicle leaf than TOG5949, suggesting that TOG5307 can cope with the osmotic component of salt stress. The cultivar exhibiting the highest salt resistance at the vegetative stage also exhibited the highest resistance at the reproductive one

Effects of salinity stress on growth in relation to gas exchanges parameters and water status in amaranth ( Amaranthus cruentus )

Salinity is a major detrimental abiotic factor for plant growth. The main purpose of this study was to analyze the effects of different NaCl concentrations on growth and some physiological parameters related to gas exchanges and water relations in amaranth (Amaranthus cruentus) plants. Three weeks old amaranth plants from the cultivar ‘Locale’ were exposed in nutrient solution to 0, 30 or 90 mM NaCl (electrical conductivities of 1.915; 4.815 and 11.70 dS.m-1 respectively) in phytotron conditions. Shoot elongation as well as fresh and dry masses of shoot and root were determined after two weeks of stress exposure. Net photosynthesis (A), intercellular CO2 concentration (Ci), instantaneous transpiration (E), stomatal conductance (gs), osmotic potential (Ψs) as well as the efficiency of the instantaneous carboxylation (A/Ci), intrinsic (A/gs) and instantaneous (A/E) water use efficiency were estimated. Results reveal that salt stress induced a significant reduction in growth of aerial part as well as net photosynthesis, instantaneous transpiration, stomatal conductance and leaf and root osmotic potentials. In contrast, no significant reductions were recorded for root growth, shoot water content, intercellular CO2 concentration and instantaneous carboxylation efficiency. However, a significant increase was observed for intrinsic (A/gs) and instantaneous (A/E) water use efficiency. The plant growth reduction observed hinges upon a drop in photosynthetic activity due mainly to stomatal closure. These data suggest that photosynthetic activity may be used as a reliable criterion for physiological estimation of salt-tolerance in A. cruentus cultivars

NaCl and Na2SO4 Salinities Have Different Impact on Photosynthesis and Yield-Related Parameters in Rice (Oryza sativa L.)

To elucidate the comparative effect of chloride and sulfate salinities on photosynthesis and yield components in rice, plants of Oryza sativa (cv. I Kong Pao (salt-sensitive)) were exposed in nutrient solutions to 20 mM Na2SO4 or 40 mM NaCl (electrical conductivity of c.a. 4.30 dS m−1 for both solutions) from seedlings to maturity stage. Both types of salt induced a strong decrease in net photosynthesis (AN) at the seedling and tillering stages, while the intercellular CO2 concentrations (Ci) remained unaffected. Instantaneous transpiration (E) and stomatal conductance (gs) decreased at the tillering and seedling stages, respectively, only in plants exposed to NaCl. Chloride salinity also strongly decreased photosynthetic pigments, while no impact was detected in response to Na2SO4. All yield-related parameters were affected by salinities, but NaCl was significantly more deleterious than Na2SO4 for the mean number of tillers produced per plant, spikelets sterility and non-viable pollen percentage. In contrast, both types of salinity similarly impacted the percentage of fertile tillers and 1000-grain weight. At the grain level, more than 90% of toxic ions (Na+, excess of Cl− and S6+) accumulated in the hulls, thus preserving the internal part of the caryopses from toxic ion injurie

Discriminating the impact of Na+ and Cl− in the deleterious effects of salt stress on the African rice species (Oryza glaberrima Steud.)

Salinity resistance of the African rice species (Oryza glaberrima) is poorly documented and the specific responses of the plant to Na+ and Cl− toxic ions remain unknown. Cultivars TOG5307 and TOG5949 were maintained for 15 days on iso-osmotic nutrient solutions containing 50 mM NaCl, or a combination of Cl− salts (Cl−-dominant) or Na+ salts (Na+-dominant). Plant water status, ion accumulation, gas exchange, fluorescence related parameters, carbon (δ13C) and nitrogen (δ15N) isotope ratios were analyzed. TOG5307 accumulated lower amounts of Na+ and Cl− in the shoot (1.63 and 1.49 µmol g−1 DW, respectively) than TOG 5949 (2.5 and 2.2 µmol g−1 DW). At 50 mM NaCl, TOG5307 also exhibited a higher net carbon assimilation rate (2.51 µmol CO2 m−2 s−1) than TOG5949 (1.51 µmol m−2 s−1) and a higher water use efficiency. Most recorded physiological parameters were affected by both Na+ and Cl−. The pattern of modification induced by both types of toxicities was similar in the two studied cultivars which thus mainly differ for the quantitative aspects of the response rather than for the qualitative nature of the response. NaCl was the most detrimental treatment, followed by Na+-dominant treatment while Cl−-treatment had the lowest effect. The two considered cultivars mainly differ for their response to the ionic component of salt stress but not for their osmotic behaviour. The impact of Na+ and Cl− on considered parameters are additive, except for mineral nutrition where synergistic interactions were recorded for Na+ and S accumulation

Differential effects of sulfate and chloride salinities on rice (Oryza sativa L.) gene expression patterns: a comparative transcriptomic and physiological approach

Salinity is a challenge to rice production but most studies are dealing with NaCl and rarely consider Na2SO4 despite its importance in numerous areas of the world. To elucidate genome-level responses to chloride or sulfate salinity stress, seedlings from rice cv. IKP have been exposed for 48 h to two types of Na+-isostrenght nutrient solution (NaCl 200 mM (EC18.84 dS m-1; Ψs = -0.983 MPa); and Na2SO4 100 mM (EC18.05 dS m-1; Ψs = -0.838 MPa)). A combined transcriptomic (microarray analysis) and physiological study was performed. NaCl was more toxic than Na2SO4 to rice seedlings. Contrasting genes were expressed under sulfate and chloride salinity, the difference being the most remarkable in root. Most of the genes involved in response to salt stress were up-regulated in Na2SO4-treated plants while more genes were down-regulated in NaCl-treated plants. Proline accumulated to a higher extent in NaCl-treated plants in relation to up-regulation of genes coding for Δ1-pyrroline-5-carboxylate synthetase and Ornithine-δ-aminotransferase which induced a higher activity of these enzymes in plants exposed to NaCl compared to Na2SO4. In contrast, sucrose accumulated in Na2SO4-treated plants while reducing sugars accumulated in NaCl-exposed ones. These differences could be explained by activities of sucrose-phosphate-synthase, sucrose synthase and acidic invertase but not by upregulation of the corresponding genes. Regulations of the expression of genes coding for signal sensing, perception and transduction and for transcription factors were completely different in response to NaCl and Na2SO4 suggesting that the nature of the counter anion is of primary importance in stress perception and plant response

Comparison between the impact of osmotic and NaCl treatments on the expression of genes coding for ion transporters in Oryza glaberrima Steud.

We analyzed the expression of genes coding for Na+ transporters (OsHKT1.5, OsHKT1.1, OsSOS1, OsSOS2, OsNHX1, OsNHX2), Cl- transporter (OsNRT1, OsCLC, OsCCC1) and gene coding for the transcription factor DREB (OsDREB2) involved in response to desiccation in two cultivars of O. glaberrrima differing in salt-resistance (salt-tolerant cultivar (TOG5307) and salt-sensitive (TOG 5949)) exposed to NaCl, PEG or both agents present simultaneously. Seedlings were grown in iso-osmotic nutrient solution (Ψs = -0.47±0.02 MPa) containing PEG 6,000 12.9% (water stress), NaCl 75 mM (salt stress) and PEG 6.4% + NaCl 37.5 mM (MIX-treatment) during 1 and 7 days. Plants were analyzed for gene expression, mineral nutrients, and photosynthetic-related parameters. Na+ and Cl- accumulations in salt-treated plants were lower in roots and shoots of TOG5307 comparatively to TOG5949 while water content decreased in TOG5307. TOG5307 exhibited tolerance to water stress and maintained higher net photosynthesis and water use efficiency than TOG5949 in response to all treatments, but was less efficient for osmotic adjustment. Dehydration tolerance of TOG5307 involves a higher OsDREB2 expression. TOG5307 also exhibited a higher OsSOS1, OsSOS2, OsNHX1 and OsNHX2 expression than TOG5949 in response to salinity. OsHKT1.5 was slightly induced in the shoot. OsHKT1.1 was recorded in the shoots but remained undetectable in the roots. Chloride and sodium accumulations were strongly reduced in the shoots when PEG was present. Salinity resistance in Oryza glaberrima implies tolerance to dehydration as well as complementary strategies of Na+ exclusion through the SOS system and Na+ tolerance through vacuolar sequestration