Actual PSII Efficiency Research Articles

Photosynthetic adaptation mechanisms of waterlogged wheat (Triticum aestivum) at flowering under exogenous nitric oxide donor application

AbstractThe effects of nitric oxide (NO) on the photosynthetic adaptation mechanisms of wheat plants in waterlogging during the flowering stage are poorly understood. Field and pot experiments using two cultivars were conducted with three treatments: waterlogging (WL), waterlogging plus NO donor sodium nitroprusside (WLsnp), and adequate water (CK). The results indicated that the WLsnp and CK treatments exhibited significantly higher 1000‐kernel weight and yield than the WL treatment because of high photosynthetic potential(P<0.05). We found that the photosynthetic performance, including photosynthetic rate (Pn), stomatal conductance (gs), mesophyll conductance (gm), carbon dioxide concentration at the carboxylation site (Cc), maximum carboxylation rate (Vcmax), maximum electron transfer rate (Jmax), actual electron transfer rate (J), actual PSII efficiency (ΦPSII) and potential maximum efficiency in PSII (Fv/Fm), was significantly improved in the WLsnp treatment compared to the WL treatment, both during waterlogging and after de‐waterlogging. Little difference was observed in the photosynthetic performance between the WLsnp and CK treatments during waterlogging for cultivar YM15 and after de‐waterlogging for cultivar YM24. Further analysis indicated that gs, gm and J were identified as key physiological indicators that synergistically regulate Pn of waterlogged wheat plants. Overall, the improvement of wheat's waterlogging resistance capacity after spraying NO is mainly related to high gs, great gm, and high J.

Photo-protection and photo-inhibition during light induction in Barbula indica and Conocephalum conicum under different light gradients.

The objectives of this study were to measure the chlorophyll fluorescence (ChlF) parameters of Barbula indica (Hook.) Spreng and Conocephalum conicum (L.) Dumort subjected to various light intensities (LI) as a reflection of their adaptability to their habitats. The electron transport rate (ETR) of all plants under 500μmolm-2s-1 photosynthetic photon flux density (PPFD) was significantly higher than other LI treatments, implying that these plants could be grown under a specific and optimal light intensity adapted to 500 PPFD conditions. As LI increased from 50 to 2,000 PPFD, we observed in all plants increased non-photochemical quenching (NPQ) and photo-inhibitory quenching (qI) and decreased photosystem II efficiency (ΦPSII), potential quantum efficiency of PSII (Fv/Fm), actual PSII efficiency (ΔF/Fm'%), and Fv/Fm%. In addition, energy-dependent quenching (qE), the light protection system (qE + qZ + qT), and qI increased as ΦPSII decreased and photo-inhibition% increased under 1000, 1500, and 2000 PPFD conditions, suggesting that these plants had higher photo-protective ability under high LI treatments to maintain higher photosynthetic system performance. B. indica plants remained photochemically active and maintained higher qE under 300, 500, and 1000 PPFD, whereas C. conicum qZ + qT exhibited higher photo-protection under 500, 1000, and 1500 PPFD conditions. These ChlF indices can be used for predicting photosynthetic responses to light induction in different bryophytes and provide a theoretical basis for ecological monitoring.

Association of photosynthesis of flag leaves with grain yield in pearl millet (Pennisetumglaucum (L.) R. Br.)

The grain yield of pearl millet has increased continuously in past decades through development of hybrids and improved production practices. Elite inbred lines are crucial for innovating new germplasm/traits to break the yield plateau. Hence, 64 inbred lines of pearl millet were evaluated to assess the extent of genetic variability and association among agronomic, physiological and grain yield contributing traits. Analysis of variance showed significant differences among the lines for all the traits indicating sufficient variability for genetic exploitation. The preferred arid adaptation traits, early flowering and high tillering were associated with each other making them amenable for simultaneous selection and these two traits were not associated with grain yield. Hence, for deriving ideotypes suitable for arid adaptation, intensive selection for grain yield in early flowering background was suggested. In productive regions, the plants having greater plant height, larger size of leaves including flag leaf, larger panicle size to accommodate the photosynthates are desirable and these traits were found to be associated among themselves and with grain yield in the current study. Though the maximal photosynthetic efficiency, Fv/Fm was significantly associated with leaf length, flag leaf length, flag leaf width and actual PSII efficiency (Y(II)), these physiological parameters did not significantly associate with grain yield directly and their effects are confounded within the leaf morphological variation.

Responses of photosynthesis and chlorophyll fluorescence during light induction in different seedling ages of Mahonia oiwakensis

BackgroundThe aim of this study was to determine the actual state of the photosynthetic apparatus and exhibit distinguishable differences in the chlorophyll fluorescence (ChlF) components in different seedling ages of M. oiwakensis plants subjected to different light intensity (LI). Potted 6-month-old greenhouse seedlings and field collected 2.4-year-old seedlings with 5 cm heights were selected and randomly separated into seven groups for photosynthesis measurements illuminated with 50, 100 (assigned as low LI), 300, 500, 1,000 (as moderate LI), 1,500 and 2,000 (as high LI) μmol m–2 s–1 photosynthetic photon flux density (PPFD) treatments.Resultsn 6-month-old seedlings, as LI increased from 50 to 2,000 PPFD, the values of non-photochemical quenching and photo-inhibitory quenching (qI) increased but potential quantum efficiency of PSII (Fv/Fm) and photochemical efficiency of photosystem II (ΦPSII) values decreased. High electron transport rate and percentage of actual PSII efficiency by Fv/Fm values were observed in 2.4-year-old seedlings at high LI conditions. Furthermore, higher ΦPSII was detected under low LI conditions, with lower energy-dependent quenching (qE) and qI values and photo-inhibition % decreased as well. However, qE and qI increased as ΦPSII decreased and photo-inhibition% increased under high LI treatments.ConclusionsThese results could be useful for predicting the changes in growth and distribution of Mahonia species grown in controlled environments and open fields with various combinations of varying light illuminations, and ecological monitoring of their restoration and habitat creation is important for provenance conservation and helps to formulate better conservation strategies for the seedlings.

Clonal variation in growth, PSII photochemical activity and polar metabolites in Pinus elliottii × P. caribaea

Pinus elliottii × P. caribaea is a widely planted commercial tree hybrid in South China. To investigate the potential of physiological parameters for clonal selection, cuttings of three clones (EH3, EH4 and EH5) and a control were grown in phosphorus treated pots. Significant variations to phosphorous, photosystem II activity and polar metabolite abundance in needles were noted among clones. Clone EH5 was the most P-responsive and had maximum height growth. The highest maximum quantum yield of PSII in the dark (Fv/Fm), maximum quantum yield of PSII in the light (Fvʹ/Fmʹ) and the actual PSII efficiency (ΦPSII) values were also found in EH5. A total of 64 polar metabolites were identified, 21 were regulated by phosphorous, while 28 accumulated differentially among the three clones. There were few overlapping responsive metabolites to phosphorous fertilization. In EH5, the abundance of maltotriitol, neohesperidin and raffinose were highest, whereas galactinol and shikimic acid were lower compared with EH3 and EH4. The results reveal that physiological traits were genetically controlled and might be useful for selecting clones with high phosphorous utilization efficiency.

Arbuscular mycorrhizal fungi can ameliorate salt stress in Elaeagnus angustifolia by improving leaf photosynthetic function and ultrastructure

Arbuscular mycorrhizal fungi (AMF) can form symbiosis with Elaeagnus angustifolia, allowing this species to tolerate salt stress. However, the physiological mechanism through which AMF improve E. angustifolia tolerance is still unclear. In this study, we examined E. angustifolia inoculated with AMF Rhizophagus irregularis (M) or inactivated inoculum (NM) under 0 and 300mM NaCl stress for the determination of photosynthetic gas exchange, pigment content, chlorophyll fluorescence, antioxidant capacity and chloroplast ultrastructural in leaves. Photosynthetic gas exchange parameters in the leaves of M and NM decreased significantly under salt stress, while the M treatment significantly reduced the effect of salt stress compared with NM. Various chlorophyll components in the M treatment were two- to three-fold higher than in NM, together with a much more complex chloroplast structure and higher number of plastoglobules. The total flavonoid and proline content in leaves of M increased significantly, while the concentration of malondialdehyde (MDA) decreased significantly under salt stress. Chlorophyll fluorescence data also showed good PSII function in the M treatment, together with salt stress reduction of photochemical reactions and sharp enhancements in non-photosynthetic quenching (NPQ). AMF inoculation ameliorated the inhibition on the actual PSII efficiency (ФPSII) and the photochemical quenching coefficient (qP ) by 10-15%. Our results clearly demonstrate that R. irregularis can improve the salt tolerance of plants by improving leaf photosynthetic performance, PSII function, antioxidant capacity and leaf chloroplast ultrastructure, and that E. angustifolia inoculated with AMF could enhance saline soil rehabilitation.

Comparative effect of 28-homobrassinolide and 24-epibrassinolide on the performance of different components influencing the photosynthetic machinery in Brassica juncea L.

BRs are polyhydroxylated sterol derivatives, classified as phytohormones. Plants of Brassica juncea var. Varuna were grown in pots and an aqueous solution (10−8 M) of two brassinosteroid isomers 28-homobrassinolide (HBL) and 24-epibrassinolide (EBL) of same concentration (10−8 M) was applied to their leaves. The treatment up-regulated the photosynthetic machinery directly by enhancing water splitting activity, photochemical quenching, non-photochemical quenching, maximum PSII efficiency, actual PSII efficiency, electron transport rate, stomatal movement, stomatal conductance, internal CO2 concentration, transpiration rate, net photosynthetic rate and carbohydrate synthesis. Moreover, the level of biochemical enzymes (carbonic anhydrase and nitrate reductase), reactive oxygen species (superoxide and hydrogen peroxide) generation, antioxidant enzyme activity and mineral status (C, N, Mg, P, S, K), which indirectly influence the rate of photosynthesis, also improved in the treated plants. Out of the two BR analogues tested, EBL excelled in its effects over HBL.

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).

Pretreatment with alternation of light/dark periods improves the tolerance of tobacco (Nicotiana tabacum) to clomazone herbicide

This work analyses the effects of alternation of light/dark periods pretreatment (AL) in tobacco plantlets (Nicotiana tabacum L. cv.Virginie vk51) growing in solution with low concentration of the clomazone herbicide. The experimentation has been carried out by exposing the plantlets to successive and regulated periods of light (16min light/8min dark cycles, PAR 50μmolm−2s−1) for three days. The photosynthesis efficiency was determined by mean of the chlorophyll fluorescence and JIP-test. The AL pretreatment improved the clomazone tolerance; this has been observed by the increase in the leaf area of the plant, the maximal photochemical quantum efficiency of PSII (Fv/Fm), the actual PSII efficiency (ФPSII), the performance index (PIabs), the electron flux beyond Quinone A (1−VJ), and also by the diminution of the energy dissipating into heat (DI0/RC). Furthermore, AL pretreatment led to low accumulation of hydrogen peroxide (H2O2) which proves that the scavenging enzymatic system have been activated before clomazone treatment. In the plantlets pretreated with AL, with regard to the ascorbate content, some of antioxidant enzyme whose function is associated with it have continued to scavenge reactive oxygen species (ROS) induced by clomazone, such as ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR). So, the observed photooxidative damages induced by clomazone herbicide were noticeably reduced.

Salt-induced photoinhibition of PSII is alleviated in halophyte Thellungiella halophila by increases of unsaturated fatty acids in membrane lipids

The effect of salinity on plant growth, chlorophyll content, photosynthetic parameters, photochemical efficiency of PSII, membrane lipid content and fatty-acid composition of halophyte Thellungiella halophila and glycophyte Arabidopsis thaliana was investigated to examine the possible role of unsaturated fatty acids in photosynthesis under saline conditions. The growth of Arabidopsis was significantly decreased by the 100 and 200 mM NaCl treatments; however, there was no significant difference in the fresh and dry weight of Thellungiella at different concentrations of NaCl. Exposure of Arabidopsis to salt resulted in a progressive decline in chlorophyll content, while there was no significant change in that of Thellungiella. The net photosynthetic rate, maximal photochemical efficiency of PSII (Fv/Fm) and actual PSII efficiency were significantly reduced in Arabidopsis but remained unaffected in Thellungiella. Arabidopsis under NaCl treatment showed decreased PG levels and decreased values for the unsaturated fatty acid content and the double bond index (DBI) of monogalactosyldiacylglycerols and phosphatidylglycerols; these values significantly increased in Thellungiella under NaCl treatment, as did the DBI values of digalactosyldiacylglycerols and sulphoquinovosyldiacylglycerols. These results suggest that Thellungiella under salt stress displays high resistance to photoinhibition and that increased concentrations of unsaturated fatty acids in membrane lipids enhances the tolerance of photosystem II to salt stress.

Diurnal variations of chlorophyll fluorescence and CO2 exchange of biological soil crusts in different successional stages in the Gurbantunggut Desert of northwestern China

AbstractBiological soil crusts (BSCs) formed by different combinations of photosynthetic algae, cyanobacteria, lichens and mosses are well‐developed in the Gurbantunggut Desert of northwestern China. To investigate the different responses of BSCs to environmental factors, the diurnal variations of chlorophyll fluorescence and CO2 exchange of BSCs in different successional stages were measured following artificial rehydration in the field. Results showed that the maximum potential quantum efficiency of PSII (Fv/Fm), the actual PSII efficiency (ΦPSII) and the relative rate of electron transport as well as net photosynthesis of the different successional BSCs varied similarly and changed markedly with diurnal fluctuations in light and temperature. Further analyses indicated that CO2 exchange and photosynthetic pigment content of chlorophyll (Chl) a, Chl b and carotenoids increased with the developmental level of BSCs, from cyanobacterial crust to lichen crust to moss crust. The differences in responses of BSCs to environmental factors and photosynthetic pigment content may be partially attributed to differences in species composition and morphological characteristics of the various BSCs. Overall, moss crust is better adapted to a wide range of irradiance and higher temperatures than lichen and cyanobacterial crusts. Therefore, BSCs in a later successional stage are expected to play a more important role in desertification control than those of the earlier stages.

Protection effect of nitric oxide on photosynthesis in rice under heat stress

The effect of exogenous applied nitric oxide on photosynthesis under heat stress was investigated in rice seedlings. High temperature resulted in significant reductions of the net photosynthetic rate (P N) due to non-stomatal components. Application of nitric oxide donors, sodium nitroprusside (SNP) or S-nitrosoglutathione (GSNO), dramatically alleviated the decrease of P N induced by high temperature. Chlorophyll fluorescence measurement revealed that high temperature caused significant increase of the initial fluorescence (F o) and non-photochemical quenching (NPQ) whereas remarkable decrease of the maximal fluorescence (F m), the maximal efficiency of PSII photochemistry (F v/F m), the actual PSII efficiency (ΦPSII), and photochemical quenching (q p). In the presence of SNP or GSNO pretreatment, the increase of F o and decrease of F m, F v/F m, ΦPSII and q p were markedly mitigated, but NPQ was further elevated. Moreover, with SNP or GSNO pretreatment, H2O2 accumulation and electrolyte leakage induced by heat treatment were significantly reduced, whereas zeaxanthin content and carotenoid content relative to chlorophyll were elevated. The potassium salt of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a specific NO scavenger, arrested NO donors mediated effects. These results suggest that NO can effectively protect photosynthesis from damage induced by heat stress. The activation effect of NO on photosynthesis may be mediated by acting as ROS scavenging, or/and alleviating oxidative stress via maintaining higher carotenoid content relative to chlorophyll or/and enhancing thermal dissipation of excess energy through keeping higher level of zeaxanthin content under heat stress.

Effects of Salinity and Nitrate Nitrogen on Growth, Ion Accumulation, and Photosynthesis of Sugar Beet

Effects of salinity and nitrate nitrogen (NO3--N) on growth, ion accumulation, chlorophyll content, chlorophyll fluorescence, and photosynthetic characteristics of sugar beet cultivar KWS3418 were investigated in a greenhouse experiment. Seedlings were exposed to 0 and 1% NaCl in 0.5, 5 or 10 mM NO3--N treatments for 25 days. The results showed that increasing NO3- supply improved shoot and root dry weights, decreased the Cl- concentration in leaves and roots regardless of NaCl concentration. Higher NO3--N supply also increased concentration of chlorophyll, net photosynthetic rate (Pn), actual PSII efficiency (ΦPSII) in leaves and soluble sugar concentration in roots. The results indicate that increasing NO3- supply can help sugar beet to mediate ion homeostasis, to increase the ability of photosynthesis, and subsequently to increase the growth under high salinity. The interactive effects of salinity and nitrate availability can significantly increase soluble sugar in roots of sugar beet.

Does Prescribed Burning Affect Leaf Secondary Metabolites in Pine Stands?

Prescribed burning (PB) is gaining popularity as a low-cost forest protection measure that efficiently reduces fuel build-up, but its effects on tree health and growth are poorly understood. Here, we evaluated the impact of PB on plant defenses in Mediterranean pine forests (Pinus halepensis and P. nigra ssp. laricio). These chemical defenses were estimated based on needle secondary metabolites (terpenes and phenolics including flavonoids) and discussed in terms of chlorophyll fluorescence and soil nutrients. Three treatments were applied: absence of burning (control plots); single burns (plots burned once); and repeated burns (plots burned twice). For single burns, we also explored changes over time. In P. laricio, PB tended to trigger only minor modifications consisting exclusively of short-lived increases (observed within 3 months after PB) in flavonoid index, possibly due to the leaf temperature increase during PB. In P. halepensis, PB had detrimental effects on physiological performance, consisting of (i) significant decreases in actual PSII efficiency (ΦPSII) in light-adapted conditions after repeated PB, and (ii) short-lived decreases in variable-to-maximum fluorescence ratio (Fv/Fm) after single PB, indicating that PB actually stressed P. halepensis trees. Repeated PB also promoted terpene-like metabolite production, which increased 2 to 3-fold compared to control trees. Correlations between terpene metabolites and soil chemistry were found. These results suggest that PB impacts needle secondary metabolism both directly (via a temperature impact) and indirectly (via soil nutrients), and that these impacts vary according to species/site location, frequency and time elapsed since last fire. Our findings are discussed with regard to the use of PB as a forest management technique and its consequences on plant investment in chemical defenses.

Photosystem II photochemistry and phycobiliprotein of the red algae Kappaphycus alvarezii and their implications for light adaptation.

Photosystem II photochemistry and phycobiliprotein (PBP) genes of red algae Kappaphycus alvarezii, raw material of κ-carrageenan used in food and pharmaceutical industries, were analyzed in this study. Minimum saturating irradiance (I k) of this algal species was less than 115 μmol m−2 s−1. Its actual PSII efficiency (yield II) increased when light intensity enhanced and decreased when light intensity reached 200 μmol m−2 s−1. Under dim light, yield II declined at first and then increased on the fourth day. Under high light, yield II retained a stable value. These results indicate that K. alvarezii is a low-light-adapted species but possesses regulative mechanisms in response to both excessive and deficient light. Based on the PBP gene sequences, K. alvarezii, together with other red algae, assembled faster and showed a closer relationship with LL-Prochlorococcus compared to HL-Prochlorococcus. Many amino acid loci in PBP sequences of K. alvarezii were conserved with those of LL-Prochlorococcus. However, loci conserved with HL-Prochlorococcus but divergent with LL-Prochlorococcus were also found. The diversities of PE and PC are proposed to have played some roles during the algal evolution and divergence of light adaption.

Increase in unsaturated fatty acids in membrane lipids of Suaeda salsa L. enhances protection of photosystem II under high salinity

In order to examine the possible role of unsaturated fatty acids in photosynthesis of halophytes under high salinity, the effect of salinity on plant growth, chlorophyll (Chl) content, photochemical efficiency of PSII, membrane lipid content and fatty acids composition of a C3 euhalophyte Suaeda salsa L. was investigated. Salt stress induced a slight increase of the maximal photochemical efficiency of PSII (Fv/Fm), actual PSII efficiency (ΦPSII), Chl a content and Chl a/b ratio. The unsaturated fatty acid content also increased under salt stress. The proportion of MGDG, DGDG, SQDG, and PC decreased, while the proportion of PG increased from 10.9% to 26.9% under salt stress. These results suggest that S. salsa displays high resistance to photoinhibition under salt stress and that increased concentration of unsaturated fatty acids in membrane lipids of S. salsa enhances the tolerance of photosystem II to salt stress.

Are symplast tolerance to intense drought conditions and xylem vulnerability to cavitation coordinated? An integrated analysis of photosynthetic, hydraulic and leaf level processes in two Mediterranean drought-resistant species

In the last decades, plant resistance to drought conditions has been studied intensively both at whole-tree level and at tissue level. These studies have highlighted the role of xylem cavitation in the global resistance of plants to drought. In this paper, we investigate the coordination among several symplastic variables during intense drought conditions and its relationship to resistance to xylem cavitation. We selected 2-year-old seedlings of Pistacia lentiscus L. and Quercus coccifera L., two Mediterranean drought-resistant species with differences in both xylem vulnerability to cavitation and survival rates under field conditions. Drought provoked large decreases in photosynthetic rates and predawn F v/ F m ratios, as well as less marked decreases in actual PSII efficiency (due to decreases in both intrinsic PSII efficiency and photochemical quenching). Photosynthetic pigment composition remained fairly unchanged down to water potentials of −8 MPa, despite inter-conversions within the xanthophyll cycle in both species. Cell membrane injury and proline accumulation followed similar patterns, and were much more intense in P. lentiscus than in Q. coccifera. Comparisons between variables revealed that both species: (i) followed a drought avoidance strategy, (ii) were very resistant to drought conditions at symplastic level, and (iii) showed an overall good relationship between apoplast (xylem cavitation) and symplast resistance (membrane stability, PSII functionality, proline accumulation and pigment composition). Differences between species in functional symplastic and apoplastic characteristics are discussed.

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.

Effects of salt stress on photosynthesis, PSII photochemistry and thermal energy dissipation in leaves of two corn (Zea mays L.) varieties

The effect of four different NaCl concentrations (from 0 to 102 mM NaCl) on seedlings leaves of two corn (Zea mays L.) varieties (Aristo and Arper) was investigated through chlorophyll (Chl) a fluorescence parameters, photosynthesis, stomatal conductance, photosynthetic pigments concentration, tissue hydration and ionic accumulation. Salinity treatments showed a decrease in maximal efficiency of PSII photochemistry (Fv/Fm) in dark-adapted leaves. Moreover, the actual PSII efficiency (ϕPSII), photochemical quenching coefficient (qp), proportion of PSII centers effectively reoxidized, and the fraction of light used in PSII photochemistry (%P) were also dropped with increasing salinity in light-adapted leaves. Reductions in these parameters were greater in Aristo than in Arper. The tissue hydration decreased in salt-treated leaves as did the photosynthesis, stomatal conductance (g s) and photosynthetic pigments concentration essentially at 68 and 102 mM NaCl. In both varieties the reduction of photosynthesis was mainly due to stomatal closure and partially to PSII photoinhibition. The differences between the two varieties indicate that Aristo was more susceptible to salt-stress damage than Arper which revealed a moderate regulation of the leaf ionic accumulation.

Ecophysiological responses of the euhalophyte Suaeda salsa to the interactive effects of salinity and nitrate availability

Effects of salinity and nitrate nitrogen (NO 3 −-N) on ion accumulation and chlorophyll fluorescence were monitored for two populations of Suaeda salsa grown from seeds in a greenhouse experiment. One population inhabits the intertidal zone and the other occurs on inland saline soils. Ion contents in soils and in leaves of the two populations were also investigated in field. In the greenhouse, seedlings were exposed to a NaCl concentration of 0.6 and 35.1 ppt, with 0.1 or 5 mM NO 3 −-N treatments for 20 days. The contents of Na + and Cl − were higher, but NO 3 − was lower in soils of the intertidal zone than at the inland site. In the field, ion concentrations and the estimated contribution of these ions to osmotic potential in leaves showed no difference between the two populations, except that the estimated contribution of Na + to osmotic potential in leaves of the intertidal population was lower than that in the inland population. In the greenhouse, in contrast, the concentration of Cl − was lower, but NO 3 − concentration and the estimated contribution of NO 3 − to osmotic potential were higher, in the leaves of plants from the intertidal zone. Salinity had no effect on the maximal efficiency of PSII photochemistry ( Fv/ Fm) and the actual PSII efficiency (ΦPSII). The results indicated that S. salsa from the intertidal zone was better able to regulate Cl − to a lower level, and accumulate NO 3 − even with low soil NO 3 − concentrations. Tolerance of the PSII machinery to high salinity stress may be an important characteristic for the studied species supporting growth in highly saline environments.