Effect of salinity on root-nodule conductance to the oxygen diffusion in the Medicago truncatula–Sinorhizobium meliloti symbiosis

In order to determine the effect of salinity on the nodule conductance, oxygen uptake by the nodulated roots was measured by registering the concentration of O₂ as a function of time in a tight incubator of known volume containing the nodulated roots of Medicago truncatula. Four lines, namely TN8.20 and TN6.18, originated from local populations, F83005.5 originated from Var (France) and Jemalong 6, a cultivar from Australia, were hydroponically grown in 250 ml glass bottles under semi-controlled conditions in a glasshouse, after germination and inoculation with the strain Sinorhizobium meliloti 2011. The saline treatment was applied gradually to reach 75 mM after 2 weeks. Results show that oxygen uptake increased significantly with salinity in TN6.18 and F83005.5, but not in Jemalong nor in TN8.20. Without salt, Jemalong showed a significantly higher O₂ uptake of 240 μmol O₂ per h per plant than the mean of 130 μmol O₂ per h per plant for other lines. Salinity increased significantly the nodule conductance in all genotypes. This salt effect was significantly higher for TN6.18 than for TN8.20, and for Jemalong than for F83005.5. Without salt there was less genotypic variation in nodule conductance in the range of 5–8 μm s^–1 for F83005.5 and TN8.20, respectively. Thus the sensitivity to salinity appears to be associated with an increase in nodule conductance that supports the increased respiration of N₂-fixing nodules under salinity.     

Growth, nitrogen fixation and ion distribution in Medicago truncatula subjected to salt stress

This study compared the growth, nodulation, N₂ fixation, and ion distribution in three Medicago truncatula lines, in response to salt in nutrient solution. Two local lines (TN8.20 and TN6.18) and a reference line (Jemalong 6) were inoculated with a reference strain Sinorhizobium meliloti 2011, a very tolerant strain to salinity (700 mM NaCl) and grown in a controlled glasshouse with or without 75 mM NaCl. A genotypic variation in tolerance to salt was found: TN6.18 was the most sensitive line whereas TN8.20 was the most tolerant. The relative tolerance of TN8.20 was concomitant with the lowest leaf Na⁺ concentration and the highest nodule biomass production. However, nodule efficiency (amount of nitrogen fixed per g dry weight nodule) decreased in all lines. Results suggest that the tolerance to salt seems to depend on the host plant ability to protect its leaves against an excessive Na⁺ (and Cl^?) accumulation, and its ability to maintain the development of an abundant nodular system, which in turn determines an important rate of nitrogen fixation and allows the plants to conserve their growth potentialities. The loss of the nodular efficiency under salt stress seems to be compensated by a large nodule biomass.     

Biodiversity within Medicago truncatula genotypes toward response to iron deficiency: Investigation of main tolerance mechanisms

Iron (Fe) deficiency is one of the major environmental stresses affecting plant production in the world. The selection of tolerant genotypes is considered an effective remediation strategy for this stress. The present study was carried out in order to investigate the biodiversity within Medicago truncatula plants in response to Fe deficiency, to identify tolerant genotypes and to assess the main tolerance mechanisms. To do this, a screening test was performed on 20 M. truncatula genotypes cultivated in minimal medium. Biometric and physiological markers were analyzed, including plant biomass, chlorophyll and root architecture. Results showed a biodiversity among the 20 genotypes. Interestingly, Fe deficiency tolerance was highest in TN8.20 and A17 genotypes. However, the lowest tolerance behavior was observed in TN1.11 and TN6.18. In order to investigate the main tolerance mechanisms, an experiment was conducted in the hydroponic system on already selected genotypes. Assessment of Fe deficiency tolerance was performed mainly on plant growth parameters, Fe (III)-chelate-reductase activity, rhizosphere acidification and antioxidant system defense. The relative better tolerance of A17 and TN8.20 to Fe deficiency was positively correlated with their capacity to maintain higher Fe-acquisition efficiency in roots via rhizosphere acidification and the stimulation of Fe (III)-chelate-reductase activity. Moreover, tolerant genotypes showed the lowest decreases in chlorophyll content and photosynthetic activity (CO₂ assimilation) compared to the sensitive ones. The efficiency of antioxidant capacity of the tolerant genotypes was revealed in stimulation of catalase (CAT) and peroxidase (POX) activities as well as accumulation of polyphenols, leading to the maintenance of cell integrity under Fe deficiency.     

Salinity tolerance is related to cyanide‐resistant alternative respiration in Medicago truncatula under sudden severe stress

Salt respiration is defined as the increase of respiration under early salt stress. However, the response of respiration varies depending on the degree of salt tolerance and salt stress. It has been hypothesized that the activity of the alternative pathway may increase preventing over‐reduction of the ubiquinone pool in response to salinity, which in turn can increase respiration. Three genotypes of Medicago truncatula are reputed as differently responsive to salinity: TN1.11, A17 and TN6.18. We used the oxygen‐isotope fractionation technique to study the in vivo respiratory activities of the cytochrome oxidase pathway (COP) and the alternative oxidase pathway (AOP) in leaves and roots of these genotypes treated with severe salt stress (300 mM) during 1 and 3 days. In parallel, AOX capacity, gas exchange measurements, relative water content and metabolomics were determined in control and treated plants. Our study shows for first time that salt respiration is induced by the triggered AOP in response to salinity. Moreover, this phenomenon coincides with increased levels of metabolites such as amino and organic acids, and is shown to be related with higher photosynthetic rate and water content in TN6.18.     

氮调控对盐环境下甜菜功能叶光系统Ⅱ荧光特性的影响

采用盆栽试验方法,以NaCl为盐分模拟不同盐度环境,研究了施氮(N)对盐环境下生长的甜菜(Beta vulgaris)功能叶光系统Ⅱ (PSⅡ)荧光特性的影响及光合色素含量的变化.结果表明:在轻度、中度及重度盐环境下,施N均能增大PSⅡ最大光化学效率(Fv/Fm)、PSⅡ潜在活性(Fv/Fo)、PSⅡ实际光量子产量(Y(Ⅱ))、非调节性能量耗散的量子产量(Y(NO))、相对电子传递速率(ETR)及光化学猝灭系数(qp),且在适宜的施N范围内(0-1.2 g·kg-1)上述参数随施N量的增加而增大.各叶绿素荧光参数光响应的结果表明,随着光强的增加,各处理下调节性能量耗散的量子产量(KNPQ))、ETR及非光化学猝灭系数(NPQ)旱上升趋势,相反,Y(Ⅱ)、Y(NO)及qp则呈下降趋势,在有效的光强范围内(0-1 000 μmol·m-2·s-1)施N提高了甜菜功能叶PSⅡ反应中心的开放程度,并且在高光强下调节PSⅡ耗散掉过剩的光能以避免对其反应中心造成伤害.各盐度环境下施N也显著增加了甜菜功能叶叶绿素与类胡萝卜素含量,增大了叶绿素a/叶绿素b值,且叶绿素与类胡萝卜素含量随施N水平的增加而增加.说明盐环境下施N能够增强甜菜功能叶PSⅡ的活性,提高PSⅡ光能利用率,从而增强其对盐渍环境的适应性.     

Multiple effects of salinity on photosynthesis of the protist Euglena gracilis

The effect of NaCl in the culture medium on growth, photosynthesis and cell content of chlorophyll, K⁺, Na⁺, Ca²⁺ and Mg²⁺ in Euglena gracilis was studied. O₂ production, quantum yield of photosystem II (PSII), the non-photochemical quenching of chlorophyll fluorescence (q_N) and the chlorophyll alb ratio all diminished by 0.2 M NaCl. Respiration and chlorophyll a and b increased, whereas the photochemical quenching (q_p) of chlorophyll fluorescence was not affected by 0.2 M NaCl. Salt stress also induced an increase in cell volume and in K⁺ and Na⁺ concentrations, but decreased the concentrations of Ca²⁺ and Mg²⁺. Except for a protective effect on O₂ production, additional Ca²⁺ in the culture medium did not attenuate the salt effect on the parameters measured. The addition of HCO₃^? restored the PSII quantum yield of O₂ production in cells grown in high salt. Salt stress promoted a decrease in the apparent rate of quinone A (Q_A) reduction and an apparent obstruction of Q_B reduction, which were not prevented by excess HCO₃^?; the addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) did not increase chlorophyll fluorescence in salt-grown cells. These results indicate that photosynthesis in Euglena grown under salt stress exhibits: (1) diminution of the HCO₃^? dependent water-splitting activity of PSII; (2) inhibition of the electron transfer at the quinone pool level; (3) probable increase in thylakoid stacking (as indicated by the effect on the chlorophyll alb ratio); and (4) dissipation of the H⁺ gradient across the thylakoid membranes (as indicated by the decrease of q_N).     

Application of chlorophyll fluorescence to screen eggplant (Solanum melongena L.) cultivars for salt tolerance

The objective of this study was to investigate the relative salt tolerance of four eggplant cultivars (Solanum melongena L.) by studying chlorophyll (Chl) fluorescence parameters during the vegetative growth stage under increasing salinity levels. The plants were grown in pots filled with peat under controlled conditions and were subjected to the salt stress ranging from 0 (control), 20, 40, 80, and 160 mM NaCl for 25 days. The results showed that the increasing NaCl concentration affected hardly the maximum quantum yield of photosystem (PS) II. The quantum yield of PSII (Φ_PSII) decreased significantly in ‘Adriatica’ and ‘Black Beauty’ under the salt stress. The photochemical quenching decreased in ‘Black Beauty’ and nonphotochemical quenching increased in ‘Adriatica’ under the salt stress. The Chl fluorescence parameters did not change significantly under the salt stress in ‘Bonica’ and ‘Galine’, revealing their tolerance to salinity. After 25 days of the salt stress, the plant growth was reduced in all cultivars, however, this decline was more pronounced in ‘Adriatica’ and ‘Black Beauty’. Additionally, a significant correlation between the biomass and Φ_PSII was observed in ‘Adriatica’ and ‘Black Beauty’. Our results suggest that Φ_PSII can be used as a diagnostic tool to identify salt-tolerant egg-plant cultivars.     

Influence of salt stress on C4 photosynthesis in Miscanthus sinensis Anderss.

• Miscanthus sinensis Anderss. is a good candidate for C₄ bioenergy crop development for marginal lands. As one of the characteristics of marginal lands, salinization is a major limitation to agricultural production. The present work aimed to investigate the possible factors involved in the tolerance of M. sinensis C₄ photosynthesis to salinity stress.
• Seedlings of two accessions (salt‐tolerant ‘JM0119’ and salt‐sensitive ‘JM0099’) were subjected to 0 mm NaCl (control) or 250 mm NaCl (salt stress treatment) for 2 weeks. The chlorophyll content, parameters of photosynthesis and chlorophyll a fluorescence, activity of C₄ enzymes and expression of C₄ genes were measured.
• The results showed that photosynthesis rate, transpiration rate, chlorophyll content, PSII operating efficiency, coefficient of photochemical quenching, activity of phosphoenolpyruvate carboxylase (PEPC) and pyruvate, orthophosphate dikinase (PPDK) and gene expression of PEPC and PPDK under salinity were higher after long‐term salinity exposure in ‘JM0119’ than in ‘JM0099’, while activity of NADP‐malate dehydrogenase (NADP‐MDH) and NADP‐malic enzyme (NADP‐ME), together with expression of NADP‐MDH and NADP‐ME, were much higher in ‘JM0099’ than in ‘JM0119’.
• In conclusion, the increased photosynthetic capacity under long‐term salt stress in the salt‐tolerant relative to the salt‐sensitive M. sinensis accession was mainly associated with non‐stomatal factors, such as reduced chlorophyll loss, higher PSII operating efficiency, enhanced activity of PEPC and PPDK and relatively lower activity of NADP‐ME.

     

Natural variation of photosynthetic efficiency in Arabidopsis thaliana accessions under low temperature conditions

Low, but non-freezing, temperatures have negative effects on plant growth and development. Despite some molecular signalling pathways being known, the mechanisms causing different responses among genotypes are still poorly understood. Photosynthesis is one of the processes that are affected by low temperatures. Using an automated phenotyping platform for chlorophyll fluorescence imaging the steady state quantum yield of photosystem II (PSII) electron transport (Φ_PSII) was measured and used to quantify the effect of moderately low temperature on a population of Arabidopsis thaliana natural accessions. Observations were made over the course of several weeks in standard and low temperature conditions and a strong decrease in Φ_PSII upon the cold treatment was found. A genome wide association study identified several quantitative trait loci (QTLs) that are associated with changes in Φ_PSII in low temperature. One candidate for a cold specific QTL was validated with a mutant analysis to be one of the genes that is likely involved in the PSII response to the cold treatment. The gene encodes the PSII associated protein PSB27 which has already been implicated in the adaptation to fluctuating light.     

Detecting <Emphasis Type="Italic">Suaeda salsa</Emphasis> L<Emphasis Type="Italic">.</Emphasis> chlorophyll fluorescence response to salinity stress by using hyperspectral reflectance

Measurements of chlorophyll fluorescence and hyperspectral reflectance were used to detect salinity stress in Suaeda salsa L., beach of Dongtai, Jiangsu Province, China. Three experimental sites were used in our study, which belong to low salinity, middle salinity and high salinity. The results showed that leaf chlorophyll fluorescence changed along salinity gradient. To select the sensitive hyperspectral ranges of leaf chlorophyll fluorescence, the correlationship between leaf chlorophyll fluorescence and hyperspectral reflectance was regressed and analyzed. Statistical results indicated that the 680 and 935 nm were the most sensitive hyperspectral bands for estimating leaf chlorophyll fluorescence. Then, 11 relative hyperspectral indices were selected based on the sensitive bands and previous literature. (R ₆₈₀ − R ₉₃₅)/(R ₆₈₀ + R ₉₃₅) and R ₆₈₀/R ₉₃₅ have higher correlationship coefficient (R) and lower root mean square error, may be used for detecting chlorophyll fluorescence, such as F _o, F _m, F _v/F _m, qP, and ΦPSII, while NPQ may be detected by (R ₇₈₀ − R ₇₁₀)/(R ₇₈₀ − R ₆₈₀). These results suggest that chlorophyll fluorescence of halophyte response to salinity stress could be identified by remote sensing.     

Sugar accumulation,photosynthesis and growth of two indica rice varieties in response to salt stress

Sugar, a final product of photosynthesis, is reported to be involved in the defense mechanisms of plants against abiotic stresses such as salinity, water deficiency, extreme temperature and mineral toxicity. Elements involved in photosynthesis, sugar content, water oxidation, net photosynthetic rate, activity of enzyme and gene expression have therefore been studied in Homjan (HJ), salt-tolerant, and Pathumthani 1 (PT1), salt-sensitive, varieties of rice. Fructose-1,6-biphosphatase (FBP) and fructokinase (FK) genes were rapidly expressed in HJ rice when exposed to salt stress for 1–6 h and to a greater degree than in PT1 rice. An increase in FBP enzyme activity was found in both roots and leaves of the salt-tolerant variety after exposure to salt stress. A high level of sugar and a delay in chlorophyll degradation were found in salt-tolerant rice. The total sugar content in leaf and root tissues of salt-tolerant rice was 2.47 and 2.85 times higher, respectively, than in the salt-sensitive variety. Meanwhile, less chlorophyll degradation was detected. Salt stress may promote sugar accumulation, thus preventing the degradation of chlorophyll. Water oxidation by the light reaction of photosynthesis in the salt-tolerant variety was greater than that in the salt-sensitive variety, indicated by a high maximum quantum yield of PSII (F _v/F _m) and quantum efficiency of PSII (Φ_PSII) with low nonphotochemical quenching (NPQ), leading to a high net photosynthetic rate. In addition, the overall growth performances in the salt-tolerant variety were higher than those in the salt-sensitive variety. The FBP gene expression and enzyme activity, sugar accumulation, pigment stabilization, water oxidation and net photosynthetic rate parameters in HJ rice should be further investigated as multivariate salt-tolerant indices for the classification of salt tolerance in rice breeding programs.     

Photosynthetic Gas Exchange and Chlorophyll a Fluorescence in Salicornia brachiata (Roxb.) Under Osmotic Stress

Osmotic stress negatively affects the photosynthetic efficiency and cause a significant loss of crop productivity. Salicornia brachiata (Roxb.) is a eu-halophyte. We hereby report on photosynthetic gas exchange and chlorophyll fluorescence in S. brachiata under sodium chloride (NaCl), seawater and polyethylene glycol (PEG) induced osmotic stress. It grows luxuriantly and exhibited a higher tolerance index and better accumulation of organic solutes under 100% strength of seawater (32.5 ppt) and 0.5 M NaCl salinity. It exhibited comparatively better gas exchange, stomatal conductance, PSII photochemistry and electron transfer under 100% strength of seawater salinity. Higher chlorophyll a/b ratio under stress conditions indicated a lower ratio of PSII to PSI and balanced excitation of PSI and PSII in S. brachiata resulting in efficient photosynthetic processes. The lower total chlorophyll/carotenoids ratio and higher non-photochemical quenching indicated the photo-protection and safer dissipation of heat energy in S. brachiata under stress. The 100% strength of seawater and 0.5 M NaCl salinity in S. brachiata did not cause significant changes in antenna size, connectivity between PSII reaction centres (RCs) and reduction of electrons on PSII donor side. The 20% PEG induced the inactivation of RCs and cause damage to PSII RCs in S. brachiata thus reduced the electron transfer from QA^– to QB pool-sized and activity of water-splitting complex. Higher φ(P₀) and F_V/F_M in S. brachiata under seawater salinity indicated a comparatively better quantum yield of primary photochemistry. The higher PI_Total in S. brachiata under 100% strength of seawater and 0.5 M NaCl stress indicated a better energy flux reaching to PSII RCs, electron transport and performance of RCs. The higher strengths of osmotic stress cause reduction in the quantum yield of PSII electron transport and capturing efficiency of excitation energy by open PSII RCs in S. brachiata.

Graphic Abstract

     

Responses of photosynthetic apparatus of the halotolerant microalga <Emphasis Type="Italic">Dunalliella maritima</Emphasis> to hyperosmotic salt shock

Chlorophyll fluorescence induction curves were used as a means to assess the functional condition of the photosynthetic apparatus in cells of the halotolerant green microalga Dunaliella maritima (Massjuk) (division Chlorophyta) exposed to hyperosmotic salt shock of various intensities. The shock was caused by the transfer of algal cells grown in the medium with 0.5 M NaCl to the media with elevated NaCl concentrations (1.0, 1.5, and 2.0 M). Parameters of chlorophyll fluorescence (F ₀, F _m, F ₀′, F _t′) were measured by means of a specialized pulse-amplitude-modulation fluorometer PAM 2100. In addition, the rate of photosynthetic oxygen evolution as well as the intracellular Na⁺ and glycerol content (the main osmolyte in this microalga) were determined. The hyperosmotic salt shock was found to elevate the intracellular Na+ content and reduce the functional activity of PSII in D. maritima. The suppression of PSII activity was evident from the decrease in the maximal quantum yield of photochemical energy conversion in PSII, the decreased rate of linear electron transport, the increased reduction of the primary acceptor Q_A, and the suppression of photosynthetic O₂ evolution. The functional activity of PSII recovered gradually along with restoration of osmotic and ionic balance in algal cells. It is proposed that PSI ensures energy supply during cell responses of D. maritima to hyperosmotic salt shock.     

Effect of Glomus mosseae on chlorophyll content, chlorophyll fluorescence parameters, and chloroplast ultrastructure of beach plum (Prunus maritima) under NaCl stress

The present study was undertaken to investigate the effect of Glomus mosseae on chlorophyll (Chl) content, Chl fluorescence parameters and chloroplast ultrastructure of beach plum seedlings under 2% NaCl stress. The results showed that compared to control, both Chl a and Chl b contents of NaCl + G. mosseae treatment were significantly lower during the salt stress, while Chl a/b ratio increased significantly. The increase of minimal fluorescence of darkadapted state (F₀), and the decrease of maximal fluorescence of dark-adapted state (F_m) and variable fluorescence (F_v) values were inhibited. The maximum quantum yield of PSII photochemistry (F_v/F_m), the maximum energy transformation potential of PSII photochemistry (F_v/F₀) and the effective quantum yield of PSII photochemistry (??_PSII) increased significantly, especially the latter two variables. The values of the photochemical quenching coefficient (q_P) and the nonphotochemical quenching (NPQ) were similar between G. mosseae inoculation and noninoculation. It could be concluded that G. mosseae inoculation could protect the photosystem II (PSII) of beach plum, enhance the efficiency of primary light energy conversion and improve the primitive response of photosynthesis under salinity stress. Meanwhile, G. mosseae inoculation was beneficial to maintain the integrity of thylakoid membrane and to protect the structure and function of chloroplast, which suggested that G. mosseae can alleviate the damage of NaCl stress to chloroplast.     

Low salinities adversely affect photosynthetic performance of the mangrove,Avicennia marina

Photosynthetic performance of the highly salt tolerant mangrove, Avicennia marina, was compared at two sites differing insubstrate soil salinities. Carbon dioxide exchange and chlorophyll fluorescence weremonitored at a high salinity site in Durban Bay (35) and at a low salinitysite in Beachwood (< 12). Mean CO₂ exchange, conductanceand transpiration were consistently higher at the high salinity site. Carbondioxide response curves indicated that carboxylation efficiency was higherand stomatal limitation lower at the Durban Bay site. PSII quantum yield,electron transport rates (ETR) and intrinsic PSII efficiency(F_v/F_m) were significantly higher at the high salinity site.Quenching analysis indicated a higher degree ofphotoinhibition/photoprotection in leaves at the low salinity site. Predawnand midday leaf water potentials were –1.6 and –3.1 MPa at Beachwood,compared to –2.6 and –3.8 MPa, respectively, at Durban Bay. Leafconcentrations of Na⁺, K⁺, Ca²⁺, Mg²⁺,Cl^- and N were significantly higher at Durban Bay. Photosyntheticperformance is apparently impaired at the low salinity site in Beachwood asa result of K⁺ and N deficiencies in the leaves.     

Nodule carbohydrate metabolism and polyols involvement in the response of Medicago sativa to salt stress

Alterations of plant growth, chlorophyll fluorescence parameters, nodule carbon metabolism and polyols concentration as result of salt stress were examined in alfalfa (Medicago sativa). Plants, in symbiosis with Sinorhizobium meliloti GR4 strain, were grown under controlled conditions for 35 days (DAS) and subjected to 150 mM of NaCl stress. Plant biomass (PDW) and nitrogen fixation rate (NFR) were markedly affected by salt stress conditions; the highest reductions of PDW (50%) and NFR (40%) were registered at 84 DAS and 56 DAS, respectively. In addition, salinity affected the chlorophyll fluorescence parameters, decreased initial chlorophyll fluorescence (F₀) and increased the optimum quantum yield of PSII (F_v/F_m ratio). The enzyme activities sucrose synthase activity and phosphoenolpyruvate carboxylase, responsible for the carbon supply to the bacteroids by the formation of dicarboxylates, were drastically inhibited by salinity, mainly at 56 DAS with the beginning of flowering. The content of total soluble sugars and proline increased under salt stress, and these concentrations were higher in nodule than in leaf. This last result suggests that the nodule is an organ specially protected in order to maintain its functioning, even under stress conditions. Besides, the content of myoinositol and pinitol in leaves and nodules changed with the plant growth stage and the saline treatment. Under salinity stress, the concentrations of pinitol in nodule were higher than in leaf, which supports the central function of this molecule in the adaptive response of nodules to salt stress. The increase of pinitol synthesis in nodule of M. sativa under salt stress could be one of the adaptive features used by the plant.     

Inhibition of cyanobacterial photosynthetic activity by natural ketones

Microbial volatiles have a significant impact on the physiological functions of prokaryotic and eukaryotic organisms. Various ketones are present in volatile mixtures produced by plants, bacteria, and fungi. Our earlier results demonstrated the inhibitory effects of soil bacteria volatiles, including ketones, on cyanobacteria. In this work, we thoroughly examined the natural ketones, 2‐nonanone and 2‐undecanone to determine their influence on the photosynthetic activity in Synechococcus sp. PCC 7942. We observed for the first time that the ketones strongly inhibit electron transport through PSII in cyanobacteria cells in vivo. The addition of ketones decreases the quantum yield of primary PSII photoreactions and changes the PSII chlorophyll fluorescence induction curves. There are clear indications that the ketones inhibit electron transfer from Q_A to Q_B, electron transport at the donor side of PSII. The ketones can also modify the process of energy transfer from the antenna complex to the PSII reaction center and, by this means, increase both chlorophyll fluorescence quantum yield and the chlorophyll excited state lifetime. At the highest tested concentration (5 mM) 2‐nonanone also induced chlorophyll release from Synechococcus cells that strongly indicates the possible role of the ketones as detergents.     

Chlorophyll fluorescence and lipid peroxidation changes in rice somaclonal lines subjected to salt stress

The aim of the present work was to explore physiological changes provoked by somaclonal variation in response to salinity. Two parental cultivars (La Candelaria and Yerua) and their derived somaclones were used as a source for breeding new rice lines with improved salt tolerance. We studied the effect of NaCl salt stress on chlorophyll fluorescence-related parameters, such as the maximum quantum yield of primary PSII photochemistry (F _v/F _m) and the performance index for energy conservation from photon absorbed by PSII antenna (PI_ABS). In addition malondialdehyde (MDA) content and leaf temperature (LT) responses were also measured. In somaclonal lines, F _v/F _m, PI_ABS, MDA and LT showed coefficients of variation of 13.7, 39.3, 25.5, and 3 %, respectively, for La Candelaria and 1.4, 17.6, 34.4 and 3 % for Yerua. However, the fragrant character did not differ in the aromatic somaclonal lines with respect to their parentals. Our results suggest that the F _v/F _m ratio would not be as good marker of PSII vitality as PI_ABS for salinized rice somaclones, unless they are highly susceptible to salinity. On other hand, the MDA content showed a strong negative correlation with the PI_ABS content in somaclones of both rice cultivars, suggesting that MDA levels could also be used as an oxidative damage index in rice somaclones.     

Vegetative growth,compatible solute accumulation,ion partitioning and chlorophyll fluorescence of ‘Malas-e-Saveh’ and ‘Shishe-Kab’ pomegranates in response to salinity stress

The present research was conducted to assess physiological responses of ‘Malas-e-Saveh’ (Malas) and ‘Shishe-Kab’ (Shishe) pomegranates to water of different salt content and electrical conductivity (1.05, 4.61, and 7.46 dS m^?1). Both cultivars showed a reduced trunk length due to salinity. Relative water content and stomatal conductivity of both cultivars were significantly reduced under salt stress, but ion leakage increased. In both cultivars, total chlorophyll (Chl) and carbohydrates decreased with rise in salinity, while proline accumulation increased. With salinity increment, the Chl fluorescence parameters (maximum photochemical efficiency of PSII and effective quantum yield of PSII) declined significantly in both cultivars, with higher reduction observed in Shishe. Generally, more Na⁺ accumulated in shoots and more Cl^? was observed in leaves. Cl^? accumulation increased by salinity in leaves of Malas, but it was reduced in Shishe. The K⁺/Na⁺ ratio in leaves decreased in both cultivars by salinity increment. Malas was less affected by osmotic effects of NaCl, but it accumulated more Cl^? in its leaves. Thus, Malas might be more affected by negative effects of salinity.     

Influence of High Salt on Protein Contents and Lipid Peroxidation and their Interaction with High Photon Flux Density on Isolated Chloroplasts of Mustard

The salinity and its interaction with high photon flux density (PFD) on in vivo chlorophyll fluorescence were investigated in isolated chloroplasts of mustard (Brassica juncea L. cv. Pusa Bold). Increase in salt stress decreases the protein contents of leaves and causes increase in lipid peroxidation. F_v/F_mratios suggesting that the efficiency of the photochemistry of PSII was not affected alone with the salt stressed plants. With high PFD, F_v/F_m ratio decreased with increased salt concentration. Our results indicate that salt stress enhances the photoinhibition of isolated chloroplasts.