Salinity improves chilling resistance in Suaeda salsa

Suaeda salsa L., a C3 euhalophytic herb, is native to saline soils, demonstrates high resistance to salinity stress. The effect of chilling stress on S. salsa under high salinity, particularly the change in unsaturated fatty acid content within membrane lipids, has not been investigated. After a 12 h chilling treatment (4 °C) performed under low irradiance (100 μmol m^?2 s^?1), the chlorophyll contents, maximal photochemical efficiency of photosystem II (F _v/F _m) and actual PSII efficiency (ΦPSII) were determined. These measurements were significantly decreased in S. salsa leaves in the absence of salt treatment yet there were no significant changes with a 200 mM NaCl treatment. Chlorophyll contents, F _v/F _m and ΦPSII in S. salsa under 200 mM NaCl were higher than those without salt treatment. The unsaturated fatty acid content and the double bond index (DBI) of major membrane lipids of monogalactosyldiacylglycerols, digalactosyldiacylglycerols (DGDG), sulphoquinovosyldiacylglycerols and phosphatidylglycerols (PG) significantly increased following the chilling treatment (4 °C) (with 12 h of low irradiance and 200 mM of NaCl). The DBI of DGDG and PG was decreased in the absence of the salt treatment. These results suggest that in the euhalophyte S. salsa, a 200 mM NaCl treatment increases chilling tolerance under conditions of low irradiance (100 μmol m^?2 s^?1).     

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.     

Lanthanum improves salt tolerance of maize seedlings

In this study, the effects of lanthanum were investigated on contents of pigments, chlorophyll (Chl) fluorescence, antioxidative enzymes, and biomass of maize seedlings under salt stress. The results showed that salt stress significantly decreased the contents of Chl and carotenoids, maximum photochemical efficiency of PSII (F_v/F_m), photochemical quenching (q_P), and quantum efficiency of PSII photochemistry (Φ_PSII), net photosynthetic rate (P_N), and biomass. Salt stress increased nonphotochemical quenching (q_N), the activities of ascorbate peroxidase, catalase, superoxide dismutase, glutathione peroxidase, and the contents of malondialdehyde and hydrogen peroxide compared with control. Pretreatment with lanthanum prior to salt stress significantly enhanced the contents of Chl and carotenoids, F_v/F_m, q_P, q_N, Φ_PSII, P_N, biomass, and activities of the above antioxidant enzymes compared with the salt-stressed plants. Pretreatment with lanthanum also significantly reduced the contents of malondialdehyde and hydrogen peroxide induced by salt stress. Our results suggested that lanthanum can improve salt tolerance of maize seedlings by enhancing the function of photosynthetic apparatus and antioxidant capacity.     

The unsaturation of phosphatidylglycerol in thylakoid membrane alleviates PSII photoinhibition under chilling stress

Over-expression of chloroplast glycerol-3-phosphate acyltransferase gene (LeGPAT) in tomato increased cis-unsaturated fatty acid content in phosphatidylglycerol (PG) of the thylakoid membrane. Under chilling stress, the oxygen evolving activity, the maximal photochemical efficiency of PSII (F _v/F _m), and superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities decreased less in sense lines than in antisense lines compared to wild-type (WT) plants. Consistently, the relative electric conductivity, \textO₂ ^{. -} {\text{O}}_{2} ^{{. - }} and H₂O₂ contents in sense lines were lower than those of WT and antisense lines. The antisense lines with low level of unsaturated fatty acids in PG were extremely susceptible to photoinhibition of PSII and had a significant reduction in the D1 protein content of PSII reaction center under chilling stress. However, in the presence of streptomycin (SM), the degradation of D1 protein was faster in sense lines than in WT and antisense plants. These results suggested that, under chilling stress conditions, increasing cis-unsaturated fatty acids in PG through over-expression of LeGPAT can alleviate PSII photoinhibition by accelerating the repair of D1 protein and improving the activities of antioxidant enzymes in chloroplasts.     

Antioxidants and unsaturated fatty acids are involved in salt tolerance in peanut

To explore the possible physiological mechanism of salt tolerance in peanut, we investigated the effect of salinity on antioxidant enzyme activity, fatty acid composition, and chlorophyll fluorescence parameters. Seedlings at the initial growth stage had been treated with 0, 100, 150, 200, 250, and 300 mM NaCl for 7 days. Results showed that fresh mass and dry mass decreased with the rise of the NaCl concentration. They decreased significantly when the NaCl concentration was more than 200 mM. The PSII’s highest photochemical efficiency (F _v/F _m) was not affected before treating 250 mM NaCl. However, the PSII (ΦPSII)’s actual photochemical efficiency of decreased after treating 200 mM NaCl. Both the initial fluorescence (F _o) and non-photochemical quenching (NPQ) increased after 200 mM NaCl treatment. PSI oxidoreductive activity (ΔI/I _o) was not affected before 200 mM NaCl. The malondialdehyde (MDA) content increased with the rise of the NaCl concentration. The activities of ascorbate peroxidase (APX) and superoxide dismutase (SOD) activities increased first and then decreased, while the content of H₂O₂ and O ₂ ^?· decreased first and then increased. Treated with 150 mM NaCl, the linolenic acid (18:3) and linoleic acid (18:2) of monogalactosyldiacylglycerols (MGDG), digalactosyldiacylglycerols (DGDG), sulphoquinovosyldiacylglycerols (SQDG) as well as phosphatidylglycerols (PG), the ratio of DGDG/MGDG increased, and the opposite results were obtained with 300 mM NaCl. The double bond index (DBI) of MGDG, DGDG, SQDG, and PG also increased after treating 150 mM NaCl. These conclusions verified that increased unsaturated fatty acid content in membrane lipid of peanut leaves could improve salt tolerance by alleviating photoinhibition of PSII and PSI.     

The increase in unsaturation of fatty acids of phosphatidylglycerol in thylakoid membrane enhanced salt tolerance in tomato

Overexpression of chloroplastic glycerol-3-phosphate acyltransferase gene (LeGPAT) in tomato increased cis-unsaturated fatty acid content in phosphatidylglycerol (PG) of thylakoid membrane. By contrast, suppressing the expression of LeGPAT decreased the content of cis-unsaturated fatty acid in PG. Under salt stress, sense transgenic plants exhibited higher activities of chloroplastic antioxidant enzymes, lower content of reactive oxygen species (ROS) and less ion leakage compared with the wild type (WT) plants. The net photosynthetic rate (P _N) and the maximal photochemical efficiency (F_v/F_m) of photosystem II (PSII) decreased more slightly in sense lines but more markedly in the antisense ones, compared to WT. D1 protein, located in the reactive center of the PSII, is the primary target of photodamage and has the highest turnover rate in the chloroplast. Under salt stress, compared with WT, the content of D1 protein decreased slightly in sense lines and significantly in the antisense ones. In the presence of streptomycin (SM), the net degradation of the damaged D1 protein was faster in sense lines than in other plants. These results suggested that, under salt-stress conditions, increasing cis-unsaturated fatty acids in PG by overexpression of LeGPAT can alleviate PSII photoinhibition by accelerating the repair of D1 protein and improving the activity of antioxidant enzymes in chloroplasts.     

Assessment of the preventive effect of vermicompost on salinity resistance in tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis> cv. Ailsa Craig)

To determine the effects of vermicompost leachate (VCL) on resistance to salt stress in plants, young tomato seedlings (Solanum lycopersicum, cv. Ailsa Craig) were exposed to salinity (150 mM NaCl addition to nutrient solution) for 7 days after or during 6 mL L^??1 VCL application. Salt stress significantly decreased leaf fresh and dry weights, reduced leaf water content, significantly increased root and leaf Na⁺ concentrations, and decreased K⁺ concentrations. Salt stress decreased stomatal conductance (g_s), net photosynthesis (A), instantaneous transpiration (E), maximal efficiency of PSII photochemistry in the dark-adapted state (F_v/F_m), photochemical quenching (qP), and actual PSII photochemical efficiency (ΦPSII). VCL applied during salt stress increased leaf fresh weight and g_s, but did not reduce leaf osmotic potential, despite increased proline content in salt-treated plants. VCL reduced Na⁺ concentrations in leaves (by 21.4%), but increased them in roots (by 16.9%). VCL pre-treatment followed by salt stress was more efficient than VCL concomitant to salt stress, since VCL pre-treatment provided the greatest osmotic adjustment recorded, with maintenance of net photosynthesis and K⁺/Na⁺ ratios following salt stress. VCL pre-treatment also led to the highest proline content in leaves (50 µmol g^??1 FW) and the highest sugar content in roots (9.2 µmol g^??1 FW). Fluorescence-related parameters confirmed that VCL pre-treatment of salt-stressed plants showed higher PSII stability and efficiency compared to plants under concomitant VCL and salt stress. Therefore, VCL represents an efficient protective agent for improvement of salt-stress resistance in tomato.     

Photosynthetic characteristics and effects of exogenous glycine of Chorispora bungeana under drought stress

We investigated the photosynthetic characteristics of Chorispora bungeana under conditions of drought stress caused by different concentrations of polyethylene glycol-6000 (PEG; 0, 5, 20, and 40%) and various concentrations of exogenous glycine (0, 5, 10, and 20 mM) with 20% PEG. We showed that moderate and severe drought stress of PEG reduced the chlorophyll (Chl) content (both Chl a and b), maximal quantum yield of PSII photochemistry (F_v/F_m), actual photochemical efficiency of PSII in light (Y_II), and quantum yield of regulated energy dissipation (Y_NPQ), while Chl a/b and quantum yield of nonregulated energy dissipation (Y_NO) increased. The low and moderate drought stress increased Mg²⁺ and Fe³⁺ contents, while a decrease in Mg²⁺ and Fe³⁺ was found under severe drought stress. Compared to sole PEG stress, the addition of exogenous 10 mM glycine increased Chl, Mg²⁺ and Fe³⁺ contents, F_v/F_m, Y_II, and Y_NPQ, and reduced Y_NO. On the contrary, 20 mM glycine showed an opposite effect, except for Y_NO. Our results proved that Chl contents and fluorescence parameters are reliable indicators for drought tolerance of C. bungeana. We suggest that a proper glycine content can relieve the effect of drought stress on C. bungeana.     

Ecophysiological responses of Caragana korshinskii Kom. under extreme drought stress: Leaf abscission and stem survives

Caragana korshinskii Kom. is a perennial xerophytic shrub, well known for its ability to resist drought. In order to study ecophysiological responses of C. korshinskii under extreme drought stress and subsequent rehydration, diurnal patterns of gas exchange and chlorophyll (Chl) fluorescence parameters of photosystem II as well as Chl content were analyzed. Plant responses to extreme drought included (1) leaf abscission and using stem for photosynthesis, (2) improved instantaneous water-use efficiency, (3) decreased photosynthetic rate and partly closed stomata owing to leaf abscission and low water status, (4) decreased maximum photochemical efficiency of photosystem II (PSII) (variable to maximum fluorescence ratio, F_v/F_m), quantum efficiency of noncyclic electron transport of PSII, and Chl a and Chl b. Four days after rehydration, new leaves budded from stems. In the rewatered plants, the chloroplast function was restored, the gas exchange and Chl fluorescence returned to a similar level as control plant. The above result indicated that maintaining an active stem system after leaf abscission during extreme drought stress may be the foundation which engenders these mechanisms rapid regrowth for C. korshinskii in arid environment.     

Growth and leaf gas exchange in Populus euphratica across soil water and salinity gradients

Soil water and salinity conditions of the riparian zones along the Tarim River, northwest China, have been undergoing alterations due to water use by human or climate change, which is expected to influence the riparian forest dominated by an old poplar, Populus euphratica. To evaluate the effects of such habitat alterations, we examined photosynthetic and growth performances of P. euphratica seedlings across experimental soil water and salinity gradients. Results indicated that seedlings were limited in their physiological performance, as evidenced by decreases in their height and biomass, and the maximal quantum yield of photosystem II (PSII) photochemistry (F_v/F_m), the effective quantum-use efficiency of PSII (F_v′/F_m′), and photochemical quenching (q_P) under mild (18% soil water content, SWC; 18.3 g kg^?1 soil salt content, SSC) and moderate (13% SWC, 22.5 g kg^?1 SSC) water or salinity stress. However, seedlings had higher root/shoot ratio (R/S), increased nonphotochemical quenching (NPQ), and water-use efficiency (WUE) relative to control under such conditions. Under severe (8% SWC, 27.9 g kg^?1 SSC) water or salinity stress, P. euphratica seedlings had only a fifth of biomass of those under control conditions. It was also associated with damaged PSII and decreases in WUE, the maximal net photosynthetic rate (P _Nmax), light-saturation point (LSP), and apparent quantum yield (_α). Our results suggested that the soil conditions, where P.euphratica seedlings could grow normally, were higher than ～ 13% for SWC, and lower than ～22.5 g kg^?1 for SSC, the values, within the seedlings could acclimate to water or salinity stress by adjusting their R/S ratio, improving WUE to limit water loss, and rising NPQ to dissipate excessive excitation energy. Once SWC was lower than 8% or SCC higher than ～28 g kg^?1, the seedlings suffered from the severe stress.     

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.     

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.     

The interplay of anthocyanin biosynthesis and chlorophyll catabolism in senescing leaves and the question of photosystem II photoprotection

Fully exposed, senescing leaves of Cornus sanguinea and Parthenocissus quinquefolia display during autumn considerable variation in both anthocyanin and chlorophyll (Chl) concentrations. They were used in this study to test the hypothesis that anthocyanins may have a photoprotective function against photosystem II (PSII) photoinhibitory damage. The hypothesis could not be confirmed with field sampled leaves since maximum photochemical efficiency (F_v/F_m) of PSII was negatively correlated to anthocyanin concentration and the possible effects of anthocyanins were also confounded by a decrease in F_v/F_m with Chl loss. However, after short-term laboratory photoinhibitory trials, the percent decrease of F_v/F_m was independent of Chl concentration. In this case, a slight alleviation of PSII damage with increasing anthocyanins was observed in P. quinquefolia, while a similar trend in C. sanguinea was not statistically significant. It is inferred that the assumed photoprotection, if addressed to PSII, may be of limited advantage and only under adverse environmental conditions.     

Traits of fatty acid accumulation in dimorphic seeds of the euhalophyte Suaeda salsa in saline conditions

The mechanism on of how salinity affects seed fatty acids accumulation remains unclear in halophytes. The present results revealed that the content of total unsaturated fatty acids in black seeds was higher than in brown seeds in the euhalophyte Suaeda salsa under controlled saline conditions. Salinity (200?mM NaCl) significantly increased the total oil content, unsaturated acid/saturated acid ratio, and content of α-linolenic acid (C18:3) (ALA), especially in brown seeds. The most abundant fatty acid in dimorphic seeds is linoleic acid (C18:2) (>70%). It appears that more ALA accumulated in brown seeds compared to black seeds. The enzyme activity of omega-3 fatty acid desaturase (ω-3 FAD) in brown seeds was much higher than that in black seeds, but salinity had no significant effect on the activity of ω-3 FAD in both brown and black seeds. The relative expression of SsFAD7 was increased by salinity, and the value in brown seeds was much higher than that in black seeds. This means salinity can, salinity can improve the quantity of fatty acids in dimorphic seeds of S. salsa, and the enzyme of ω-3 FAD and SsFAD7 may involve in the accumulation of ALA in dimorphic seeds under salinity.     

Overexpression of <Emphasis Type="Italic">CCCH</Emphasis> zinc finger protein gene delays flowering time and enhances salt tolerance in Arabidopsis by increasing fatty acid unsaturation

CCCH-type zinc-finger proteins constitute a large family playing key roles during plant development and growth. In the present study, we investigated the involvement of the CCCH-type zinc finger protein of AtZFP1 (At2g25900) in flowering and salt stress response in Arabidopsis. Compared with the wild type (WT), bolting and flowering were delayed in AtZFP1-overexpressing plants. Real-time PCR analysis of floral regulating genes in overexpressing Arabidopsis revealed that enhanced expression of FLC decreased the expressions of FT and SOC1. The Fv/Fm of overexpressing Arabidopsis lines was unchanged under salt stress. In contrast, ΦPSII activity and PSI oxidoreduction decreased in WT, overexpressing and mutant strains under salt stress conditions, with the smallest reduction in these parameters observed in the overexpressing strains. These results suggest that the CCCH zinc-finger protein AtZFP1 primarily controls flowering time by changing the expression of flowering genes under long-day conditions. The overexpression of this protein delayed flowering and increased the content and double-bond index of unsaturated fatty acids. Elevation of unsaturated fatty acid content might play important role in protecting the photosynthetic apparatus and maintaining the membrane function at salt stress by alleviating PSII and PSI photoinhibition.     

Photosynthesis,chlorophyll fluorescence,inorganic ion and organic acid accumulations of sunflower in responses to salt and salt-alkaline mixed stress

Sunflowers were treated with mixing proportions of NaCl, Na₂SO₄, NaHCO₃, and Na₂CO₃. Effects of salt and saltalkaline mixed stress on growth, photosynthesis, chlorophyll fluorescence, and contents of inorganic ions and organic acids of sunflower were compared. The growth of sunflower decreased with increasing salinity. The contents of photosynthetic pigments did not decrease under salt stress, but their contents decreased sharply under salt-alkaline mixed stress. Net photosynthetic rates, stomatal conductance and intercellular CO₂ concentration decreased obviously, with greater reductions under salt-alkaline mixed stress than under salt one. Fluorescence parameters showed no significant differences under salt stress. However, maximal efficiency of PSII photochemistry, photochemical quenching coefficient, electron transport rate, and actual PSII efficiency significantly decreased but non-photochemical quenching increased substantially under salt-alkaline mixed stress. Under salt-alkaline mixed stress, sunflower leaves maintained a low Na⁺- and high K⁺ status; this may be an important feature of sunflower tolerance to salinity. Analysis of the mechanism of ion balance showed that K⁺ but not Na⁺ was the main inorganic cation in sunflower leaves. Our results indicated that the change in organic acid content was opposite to the change of Cl⁻, and the contribution of organic acid to total charge in sunflower leaves under both stresses decreased with increasing salinity. This may be a special adaptive response to stresses for sunflower. Sunflower under stress conditions mainly accumulated inorganic ions instead of synthesizing organic compounds to decrease cell water potential in order to save energy consumption.     

Epidermal UV-shielding and photosystem II adjustment in wild type and chlorina f2 mutant of barley during exposure to increased PAR and UV radiation

The wild-type barley (WT; Hordeum vulgare L.) and its chlorophyll (Chl) b-less mutant chlorina f2 (clo f2) grown under shaded conditions in a greenhouse were transferred to outdoor conditions in early June with predominantly bright sunny days. During 6 days following transfer of plants we monitored the content of photosynthetic pigments, functional state of photosystem II (PSII) by means of Chl fluorescence induction kinetics and epidermal UV-shielding efficiency using Chl fluorescence imaging technique. Clo f2 mutant was more sensitive to exposure to an enhanced natural solar irradiance than WT barley. Nevertheless, clo f2 as well as WT were able to cope with stressful outdoor conditions, as was documented by the recovery of Chl a content and the maximal photochemical efficiency of PSII (F_V/F_M) after an initial decline. This was due to the immediate carotenoid-mediated photoprotection, reflected by strongly increased total carotenoids content and thermal energy dissipation localized within light-harvesting complexes of PSII (assessed by non-photochemical quenching of minimal fluorescence level). The positive acclimation response was further documented by an enhanced light-saturated electron transport rate through PSII (ETR). Based on the ratios of blue- to UV-excited Chl fluorescence we found that for both WT and clo f2 epidermal UV-shielding increased clearly after transfer to outdoor conditions and reached a saturation level after 3 days. In comparison with WT, clo f2 exhibited lower ability to induce UV-shielding. The kinetics of UV-shielding development during the outdoor treatment was different for the particular leaf regions. We suggest that this is related to the different age and developmental stage of the tissue along the leaf blade. The complementarity of carotenoid-mediated photoprotection and UV-shielding in acclimation of the assimilatory apparatus to increased visible and UV radiation is discussed.     

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.     

Epidermal UV-shielding and photosystem II adjustment in wild type and chlorina f2 mutant of barley during exposure to increased PAR and UV radiation

The wild-type barley (WT; Hordeum vulgare L.) and its chlorophyll (Chl) b-less mutant chlorina f2 (clo f2) grown under shaded conditions in a greenhouse were transferred to outdoor conditions in early June with predominantly bright sunny days. During 6 days following transfer of plants we monitored the content of photosynthetic pigments, functional state of photosystem II (PSII) by means of Chl fluorescence induction kinetics and epidermal UV-shielding efficiency using Chl fluorescence imaging technique. Clo f2 mutant was more sensitive to exposure to an enhanced natural solar irradiance than WT barley. Nevertheless, clo f2 as well as WT were able to cope with stressful outdoor conditions, as was documented by the recovery of Chl a content and the maximal photochemical efficiency of PSII (F_V/F_M) after an initial decline. This was due to the immediate carotenoid-mediated photoprotection, reflected by strongly increased total carotenoids content and thermal energy dissipation localized within light-harvesting complexes of PSII (assessed by non-photochemical quenching of minimal fluorescence level). The positive acclimation response was further documented by an enhanced light-saturated electron transport rate through PSII (ETR). Based on the ratios of blue- to UV-excited Chl fluorescence we found that for both WT and clo f2 epidermal UV-shielding increased clearly after transfer to outdoor conditions and reached a saturation level after 3 days. In comparison with WT, clo f2 exhibited lower ability to induce UV-shielding. The kinetics of UV-shielding development during the outdoor treatment was different for the particular leaf regions. We suggest that this is related to the different age and developmental stage of the tissue along the leaf blade. The complementarity of carotenoid-mediated photoprotection and UV-shielding in acclimation of the assimilatory apparatus to increased visible and UV radiation is discussed.     

Exogenous Diethyl Aminoethyl Hexanoate,a Plant Growth Regulator,Highly Improved the Salinity Tolerance of Important Medicinal Plant <Emphasis Type="Italic">Cassia obtusifolia</Emphasis> L.

The purpose of the present study was to investigate the mechanism of DA-6 in alleviating the salinity inhibition of Cassia obtusifolia L. seeds and seedlings. NaCl (100 mM) was used to mimic salinity stress in a series of experiments. Varying combinations of DA-6 were added to seeds and seedlings under salinity stress. Seed germination indices and seedling parameters were investigated. Seed germination and seedling growth were significantly inhibited under salinity stress. NaCl-induced inhibitory effects on seed germination and seedling growth were ameliorated by DA-6 with different concentrations. Addition of DA-6 to seeds (50 µM) and seedlings (100 µM) significantly alleviated damage to the plant cells under salinity stress. DA-6 (regardless of the presence or absence of NaCl) enhanced chlorophyll concentration, total soluble sugars, free proline, and soluble protein, and improved photosystem II (PSII) photochemical efficiency levels (F _v/F _m), PSII actual photochemical efficiency (ΦPSII), and the photochemical quench coefficient. In contrast, the initial fluorescence (F _o) and the non-photochemical quenching coefficient decreased. Application of DA-6 also enhanced the activities of superoxide dismutase (SOD; EC 1.15.1.1), peroxidase (POD; EC 1.11.1.7), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11), and glutathione reductase (GR; EC 1.6.4.2), thus alleviating oxidative damage, as indicated by decreases in thiobarbituric acid-reactive substances, hydrogen peroxide concentration (H₂O₂), relative conductivity, and lipoxygenase activity (LOX; EC 1.13.11.12). Based on the experimental results, we conclude that DA-6 induces advantageous effects on the attenuation of salt-stress inhibition of C. obtusifolia seeds and seedlings and alleviates oxidative damage by conferring beneficial cytoprotection and activating antioxidant enzymes. DA-6 can be used as an effective plant growth regulator to alleviate salinity stress.