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.     

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.     

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.     

Changes in photosynthesis, chlorophyll fluorescence, and antioxidant enzymes of mulberry (Morus ssp.) in response to salinity and high-temperature stress

Photosynthesis, chlorophyll (Chl) fluorescence, and antioxidant enzymes were measured in the mulberry (Morus spp.) cultivars Da 10, Hongguo 2, Anza 1, and Taiwan 72C002, which were subjected to salinity and high-temperature stress (STS; 0.1%, 0.3%, and 0.5% NaCl concentrations, 34.5°C–40.5°C/27.8°C–29.2°C day/night temperatures). Control plants were watered with 1 L of full-strength Hoagland’s nutrient solution with no added NaCl. Net photosynthetic rate (P _N), stomatal conductance (g _s), and effective quantum yield of photosystem II photochemistry (Φ_PSII) increased in Anza 1 and Taiwan 72C002 under 0.1% STS but decreased in Da 10 and Hongguo 2 compared with the control. However, all the above parameters, including Chl content, maximum quantum yield of photosystem II photochemistry (F_v/F_m), nonphotochemical quenching (NPQ), and maximum carboxylation velocity of Rubisco (V _cmax, decreased in Taiwan 72C002, Honggua 2, and Da 10 under 0.3% and 0.5% STS, suggesting that photoinhibition occurred under severe STS. Under STS, there were no significant changes in P _N, F_v/F_m, Φ_PSII, ascorbate peroxidase (APX) activity, superoxide dismutase (SOD) activity, catalase activity, superoxide anion radical (O ₂ ^? ) content, malondialdehyde (MDA) content, soluble sugar content (SSC), and leaf biomass in Anza 1 even at 0.5% STS, showing that Anza 1 displays high resistance to STS. In addition, peroxidase activity was significantly higher in Anza 1 than in the other mulberry cultivars. Significant adverse effects of severe salinity on photosynthesis and Chl fluorescence parameters were observed in Da 10. Additionally, SOD, peroxidase, and APX activities were lower in Da 10, whereas O ₂ ^? and MDA contents were higher in comparison with the other mulberry cultivars under 0.3% and 0.5% STS, suggesting that Da 10 had low resistance to STS. These results show that 0.1% STS had a positive effect on photosynthesis and Chl fluorescence parameters in Anza 1 and Taiwan 72C002, and higher peroxidase activity can to a certain extent explain the higher STS tolerance in Anza 1. Damages to DSM photosystems might be related to lower SOD, POD, and APX activities, which resulted in the accumulation of reactive oxygen species.     

不同基因型茶菊对盐胁迫的响应

为探讨不同基因型茶菊(tea Chrysanthemum)在盐胁迫下的生理响应并对其进行耐盐性评价, 以4个不同基因型茶菊为材料, 采用营养液浇灌法, 研究了不同浓度NaCl (0、40、80、120、160、200 mmol·L^-1)胁迫下茶菊生理生化和光合生理响应特性。结果表明: 随着NaCl胁迫程度加大, 不同基因型茶菊叶片细胞膜透性(Cond)、丙二醛(MDA)含量、叶片脯氨酸(Pro)含量和可溶性糖(SS)含量增加; 超氧化物歧化酶(SOD)含量呈先升后降趋势; ‘乳荷’、‘黄滁龙’叶绿素(Chl)含量持续下降, ‘繁白露’和‘玉人面’叶绿素含量呈先升后降的趋势; 净光合速率(P_n)、蒸腾速率(T_r)和气孔导度(G_s)随NaCl胁迫浓度提高而极显著降低, 气孔限制值呈先升后降的趋势。采用隶属函数法对茶菊进行耐盐性评价, 不同基因型茶菊耐盐性由强到弱依次为‘乳荷’ > ‘玉人面’ > ‘繁白露’ > ‘黄滁龙’。其中, 耐盐性品种‘玉人面’、‘乳荷’在NaCl胁迫下, Chl含量、P_n、T_r和G_s下降幅度小, MDA含量和气孔限制值增幅较小。     

Influence of foliar-applied triacontanol on growth, gas exchange characteristics, and chlorophyll fluorescence at different growth stages in wheat under saline conditions

A greenhouse experiment was conducted to examine the effect of foliar application of triacontanol (TRIA) on two cultivars (cv. S-24 and MH-97) of wheat (Triticum aestivum L.) at different growth stages. Plants were grown in full strength Hoagland’s nutrient solution under salt stress (150 mM NaCl) or control (0 mM NaCl) conditions. Three TRIA concentrations (0, 10, and 20 μM) were sprayed over leaves at three different growth stages, i.e. vegetative (V), boot (B), and vegetative + boot (VB) stages (two sprays on same plants, i.e., the first at 30-d-old plants and the second 78-d-old plants). Salt stress decreased significantly growth, net photosynthetic rate (P _N), transpiration rate (E), chlorophyll contents (Chl a and b), and electron transport rate (ETR), while membrane permeability increased in both wheat cultivars. Stomatal conductance (g _s) decreased only in salt-sensitive cv. MH-97 under saline conditions. Foliar application of TRIA at different growth stages enhanced significantly the growth, P _N, g _s, Chl a and b contents, and ETR, while membrane permeability was reduced in both cultivars under salt stress. Of various growth stages, foliar-applied TRIA was comparatively more effective when it was applied at V and VB stages. Overall, 10 μM TRIA concentration was the most efficient in reducing negative effects of salinity stress in both wheat cultivars. The cv. S-24 showed the better growth and ETR, while cv. MH-97 exhibited higher nonphotochemical quenching.     

Investigation of the salt tolerance of new Polish bread and durum wheat cultivars

In some regions of the world, low annual precipitation necessitates irrigation of crop plants which usually leads to soil salinity. Due to climatic changes this effect is also expected in the countries of Central Europe, and so in Poland. The aim of the study was (1) to compare tolerance to salt stress of Polish Triticum aestivum cvs. ‘Bogatka’ and ‘Banderola’ with T. durum cv. ‘Komnata’ and breeding line 121, and (2) to indicate the physiological parameter/parameters most suitable for such comparison. The investigation was performed in two experiments. In the first one, the germination ability of caryopses and coleoptiles’ growth were estimated at 0–250 mM of NaCl. The second experiment was conducted on plants grown in a glasshouse in saline soil at 0–150 mM of NaCl for 6 weeks. Salt tolerance was evaluated on the basis of following parameters: chlorophyll fluorescence, net photosynthesis rate (P _N), transpiration rate (E), stomatal conductance (g _s), cell membrane permeability (EL), proline content, fresh weight (FW), dry weight (DW), and relative water content (RWC). Highest germination of caryopses of durum cultivars was recorded at all the salinity levels; however, their coleoptiles were shorter than coleoptiles of bread wheat cultivars. Analysis of chlorophyll fluorescence showed that applied salt doses did not disturb the light phase of photosynthesis in all cultivars under study. Plants of durum wheat showed the higher dissipation of energy excess at the level of the antenna chlorophyll (DIo/CSm) under salinity as compared to plants of bread wheat. Both ‘Komnata’ and line 121 showed stronger P _N reduction as an effect of salinity. A decline of P _N was closely connected with a decrease in g _s. The P _N correlated with a decrease in DW in all studied cultivars except ‘Bogatka’. Control plants of ‘Komnata’ and line 121 were characterized by higher EL and proline level than bread wheat cultivars. An increasing cell membrane permeability correlated with a decrease of RWC in ‘Banderola’ and ‘Komnata’. The content of proline under the increasing salinity correlated with changes of RWC in ‘Banderola’, ‘Komnata’ and line 121, which indicate protectoral role of proline against dehydration of tissue. Dry weight and RWC seem to be the parameters most useful in the salt-tolerance estimation of wheat plants. Taking into account the studied parameters ‘Banderola’ could be recognized as more salt tolerant, the degree of salinity tolerance of ‘Bogatka’ is the same as line 121, while ‘Komnata’ seems to be the most salt sensitive. The salt tolerance of T. aestivum and T. durum depends on the cultivar rather than the wheat species.     

Effect of salt stress on photosynthesis and chlorophyll fluorescence in Medicago truncatula

In the present study, photosynthetic parameters including gas exchanges, pigment contents, and chlorophyll fluorescence, were compared in two contrasting local Medicago truncatula lines TN6.18 and TN8.20, in response to salt added to the nutrient solution. Plants were cultivated under symbiotic nitrogen fixation (SNF) after inoculation with a reference strain Sinorhizobium meliloti 2011, a very tolerant strain to salinity (700 mM NaCl), and grown in a controlled glasshouse. On one month old plants (with active SNF), salt treatment (75 mM NaCl) was gradually applied. Photosynthesis, assimilating pigments and chlorophyll fluorescence were monitored throughout the experiment during both short and long terms, compared to control (non-saline) conditions. A genotypic variation in salt tolerance was found; TN6.18 was the more sensitive to salinity. The relative tolerance of TN8.20 was concomitant with the highest photochemical quenching coefficient (q_P) affecting the maximum quantum yield of PSII (Y); the real quantum yield (?_exc) was the most affected in the sensitive line. Moreover, stomatal and PSII reaction centers activities differed clearly between the studied lines. We found that the effect of salinity on photosynthesis of M. truncatula was related to PSII activity reduction rather than to stomatal conductance limitation. Photosynthesis was reduced by the inhibition of CO₂ assimilation caused by PSII damage. This was clearly estimated by the Y, ?_exc and especially by the quantum yield of electron transport of PSII (Φ_PSII). Thus, on the basis of our results on the two local M. truncatula lines, we recommend the use of chlorophyll fluorescence as non-destructive screening method to discriminate susceptible and resistant legumes to salt stress.     

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 (F_v/F_m), actual PSII efficiency (Φ_PSII), 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.     

Drought tolerance of photosynthetic electron transport under CO2‐enriched and normal air in cereal species

The quantum yield of photosynthetic electron transport (ΦPSII), evaluated by means of chlorophyll (Chl) fluorescence analysis, has proven to be a useful screening test for drought tolerance in durum wheat (Triticum durum Desf.). To explore the potential of this parameter further in detecting drought-tolerant genotypes, three cereal species were studied; ΦPSII measurements were carried out under two different gas mixtures, at three points of the induction curve (to obtain the maximal ΦPSII and both the transient and steady-state actual ΦPSII), and at three different water stress levels (moderate, severe and drastic). The species investigated were durum and bread wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.); two cultivars per species, characterized by different levels of drought tolerance, were tested. The two gas mixtures used were normal air (21% O₂, 0.035% CO₂ in N₂) to monitor the whole photosynthetic process under physiological conditions, and CO₂ enriched-low O₂ air (1% O₂, 5% CO₂ in N₂) to monitor ΦPSII reduction under stress mainly related to Calvin cycle activity. When ΦPSII related to both assimilatory and non-assimilatory metabolism was evaluated, the cultivar differences observed under normal Air were more representative of the agronomic performance upon drought stress than under high CO₂-low O₂ air. Maximal ΦPSII showed no difference among either cultivars, gas mixtures or stress levels, the efficiency of excitation capture being highly resistant to drought. The ΦPSII evaluated during the transient yielded predictable values in respect of drought tolerance for durum wheat and barley cultivars, highlighting the key role of regulatory processes such as the Mehler peroxidase reaction and possibly also cyclic electron transport, in preventing overreduction under stress. The results clearly show that when Chl fluorescence analysis is used as a parameter in plant breeding, different experimental conditions should be used depending on the physiological mechanism that is bred or selected for.     

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.

     

The ectomycorrhizal fungus (Paxillus involutus) modulates leaf physiology of poplar towards improved salt tolerance

Ectomycorrhizas (EMs) are mutualistic associations between soil fungi and plant roots. Although the physical interaction occurs only in roots, mycorrhizas may alter the physiology of the whole plant, resulting in changes in host responses to abiotic stress. To elucidate the influence of an ectomycorrhizal fungus on leaf physiology and performance under salt stress, we analysed the levels of nutrient elements, phytohormones, carbohydrates, amino compounds and fatty acids in leaves of Populus × canescens. The poplars were cultivated either in the presence or absence of Paxillus involutus and either with or without salt stress imposed by 150 mM NaCl. Leaves of ectomycorrhizal plants displayed higher quantum yield of photochemistry (Φ_PSII), increased concentrations of phosphorus and potassium, decreased concentrations of galactose, increased concentrations of the stress metabolite γ-amino butyric acid and a lower unsaturated-to-saturated fatty acid ratios than those of non-ectomycorrhizal plants. Salt exposure of P. × canescens led to leaf chlorosis and shedding, decreases in Φ_PSII, K⁺-to-Na⁺ ratio, 9Z-hexadecenoic acid, 9Z-octadecenoic acid and unsaturated-to-saturated fatty acid ratio, and increases in ABA, glucose, fructose and some amino compounds. Under salinity leaves of ectomycorrhizal plants showed an alleviation of leaf chlorosis, improved water status, higher Φ_PSII and K⁺-to-Na⁺ ratio, less accumulation of major amino compounds and lower unsaturated-to-saturated fatty acid ratios than those of non-mycorrhizal plants. These results indicate that ectomycorrhizas attenuate salinity induced injury in leaves of P. × canescens, which may be ascribed to the improved nutrient status, osmo-regulation and changes in fatty acid composition in leaves of ectomycorrhizal plants.     

Intra- and inter-cultivar impacts of salinity stress on leaf photosynthetic performance,carbohydrates and nutrient content of nine indigenous Greek olive cultivars

Nine indigenous Greek olive cultivars (‘Aetonicholia Kynourias’, ‘Arvanitolia Serron’, ‘Ntopia Atsicholou’, ‘Koroneiki’, ‘Lefkolia Serron’, ‘Ntopia Pierias’, ‘Petrolia Serron’, ‘Smertolia’ and ‘Chryssophylli’) were evaluated for their tolerance to salinity stress (four levels of sodium chloride salt, i.e., 0, 50, 100 and 200 mM) under hydroponic conditions. Their photosynthetic performance, leaf carbohydrates (mannitol, glucose, fructose and sucrose) and nutrients (nitrogen, potassium, calcium, sodium and chloride) were assessed. Photosynthetic performance was reduced under salt stress and this was mostly evident in ‘Koroneiki’ and ‘Ntopia Atsicholou’ (approximately 20% of the corresponding controls), while ‘Ntopia Pierias’, ‘Smertolia’ and ‘Petrolia Serron’ did not exhibit significant changes with salinity level. Photosynthesis (A) was reduced mainly due to severe stomatal limitations. A weak correlation was detected between A and intercellular CO₂ (Ci) indicating a minor role of non-stomatal limitations. Carbohydrates in the leaves did not seem to undergo significant changes. Mannitol accumulated in ‘Chryssophylli’ leaves and glucose in ‘Arvanitolia Serron’ leaves under the highest salinity level. Potassium concentration per leaf water volume was significantly reduced (especially under the highest salinity level ?45 to 60% of control). Calcium was not significantly affected although Ca/Na ratio was reduced, due to the great increase of sodium concentration. ‘Lefkolia Serron’ and ‘Arvanitolia Serron’ accumulated the least sodium in their leaves, exhibiting high K/Na ratio under the highest salinity level, indicating a better regulation of potassium influx under high sodium concentration. Based on the present data and on previous research ‘Lefkolia Serron’ and ‘Arvanitolia Serron’ are the two cultivars with the highest tolerance against salinity stress.     

Comparison of thermostability of PSII between the chromatic and green leaf cultivars of <Emphasis Type="Italic">Amaranthus tricolor</Emphasis> L.

In the present study, we investigated the antioxidative potential in leaves of the chromatic (CC) versus green (GC) Amaranthus tricolor L. under moderate high-temperature stress at 45°C. Before heat stress, CC had significantly higher levels of betacyanins [about 3.2 mg g⁻¹(FM)] than the green [1.8 mg g⁻¹(FM) (p<0.01), while similar chlorophyll (Chl) content [about 2 mg g⁻¹(FM)] was observed between both cultivars. After exposure to high temperature (45°C) for 6 days, betacyanins in leaves of CC were remarkably increased (about 2 times of that in control samples grown at 30°C). In contrast, betacyanins in GC significantly decreased by 56% in comparison with that of the control. Chl level in CC was higher than that in GC after heat stress for 6 days. Flavonoids and total phenolics in both cultivars were increased, but much more in CC. Significantly less H₂O₂ accumulation was observed in the leaves and stems of CC than in those of GC under heat stress. Interestingly, much stronger circadian oscillation in fluorescence was observed in both cultivars after treatment at 45°C, which suggested that heat stress stimulates endogenous rhythms of photosystem II (PSII). Under moderate high-temperature stress, Chl fluorescence parameters F_v/F_m (maximum quantum yield of PSII), q_P (coefficient of photochemical quenching), Φ_PSII (effective PSII quantum yield), and ETR (electron transport rate) exhibited a gradual decrease, NPQ (nonphotochemical quenching) showed a slight increase followed by a gradual decline, whereas F_o (minimum fluorescence of a dark-adapted leaf) increased continuously. In contrast to GC, after 120 h of high-temperature treatment, CC exhibited significantly lower Fo level, and higher levels of F_v/F_m and NPQ. It is clear that PSII in CC was more stable than that in GC. The results indicate that betacyanins are an effective antioxidant, and probably contribute greatly to the higher thermal stability of PSII and higher tolerance to heat stress.     

Chlorophyll fluorescence imaging reveals genetic variation and loci for a photosynthetic trait in diploid potato

Physiology and genetics are tightly interrelated. Understanding the genetic basis of a physiological trait such as the quantum yield of the photosystem II, or photosynthetic responses to environmental changes will benefit the understanding of these processes. By means of chlorophyll fluorescence (CF) imaging, the quantum yield of photosystem II can be determined rapidly, precisely and non‐invasively. In this article, the genetic control and variation in the steady‐state quantum yield of PSII (Φ_PSII) is analyzed for diploid potato plants. Current progress in potato research and breeding is slow due to high levels of heterozygosity and complexity of tetraploid genetics. Diploid potatoes offer the possibility of overcoming this problem and advance research for one of the globally most important staple foods. With the help of a diploid genetic mapping population two genetic loci that were strongly associated with differences in Φ_PSII were identified. This is a proof of principle that genetic analysis for Φ_PSII can be done on potato. The effects of three different stress conditions that are important in potato cultivation were also tested: salt stress, low temperature and deficiency in the macronutrient phosphate. For the last two stresses, significant decreases in photosynthetic activity could be shown, revealing potential for stress detection with CF based tools. In general, our findings show the potential of high‐throughput phenotyping for physiological research and breeding in potato.     

Effects of Exogenous Putrescine on Chlorophyll Fluorescence Imaging and Heat Dissipation Capacity in Cucumber (Cucumis sativus L.) Under Salt Stress

The objective of this study was to identify the effects of exogenous putrescine on photosynthetic performance and heat dissipation capacity in cucumber seedlings under salt stress. The stress of 75 mM NaCl for 7 days caused a significant decrease in net photosynthetic rate (P _N ). The experiment employed a chlorophyll fluorescence imaging technique and demonstrated that the maximal quantum yield of photosystem II photochemistry (Fv/Fm) and the actual photochemical efficiency of photosystem II (ΦPSII) were reduced by salt stress. Moreover, salt stress markedly reduced the photochemical quenching coefficient (qP) and non-photochemical quenching coefficient (qN), and significantly increased non-regulated heat dissipation (ΦNO). However, stressed plants supplied with exogenous putrescine exhibited higher P _N and ΦPSII, which indicated that putrescine can alleviate the detrimental effects on photosynthesis induced by salt stress. Putrescine sprayed on stressed plants significantly enhanced the regulated energy dissipation (ΦNPQ) and decreased ΦNO. Application of exogenous putrescine also changed the levels of xanthophyll cycle components and further enhanced the de-epoxidation state of xanthophyll cycle pigments under salt stress. Under control conditions, putrescine exerted little influence on the photosynthetic parameters in cucumber leaves. In conclusion, the application of exogenous putrescine may improve the heat dissipation capacity by promoting the xanthophyll cycle to reduce the damage caused by excess excitation energy, thus enhancing the salt tolerance of cucumber seedlings.     

Salt stress induced sex-related spatial heterogeneity of gas exchange rates over the leaf surface in Populus cathayana Rehd.

The sex-related spatial heterogeneity of gas exchange rates over the leaf surface under salt stress was investigated in the dioecious species, Populus cathayana Rehd. Cuttings were subjected to two salt regimes: 0 and 75 mM NaCl added to the Hoagland solution, the control and the treatment group, respectively. Measurements of gas exchange parameters were taken from over 40 sites on the surfaces of representative ‘non-stressed’ and ‘salt-treated’ leaves which had the same insertion point for two sexual cuttings. Compared to the control group, the treatment group showed a significant decrease in the mean values of the following: water use efficiency (WUE), Chlorophyll a (Chl a) concentration, chlorophyll b (Chl b) concentration, concentration of carotenoids (Caro), total chlorophyll concentration (TC) in two sexes, and net photosynthesis rate (P _n), stomatal conductance (g _s), and stomatal length/width ratio (SR) in females. Also, in the treatment group, females exhibited lower WUE, P _n, g _s, E, Chl a, Chl b, TC, and SR than males. Comparison of contour maps showed that the net photosynthesis rate decreased gradually from apical to basal zones over the leaf surface occurred in the two sexes under natural conditions, but under salt stress, the opposite trend was found in females only. The results suggest that the heterogeneity pattern of the gas exchange parameters in response to salt stress between the two sexes is quite different due to different strategies employed by males and females to maintain the photosynthesis rate under salt stress. This heterogeneity phenomenon under salt stress may mainly be attributed to the chlorophyll pigments in males and the stomatal apertures in females.     

Photosynthetic activity and leaf antioxidative responses of Atriplex portulacoides subjected to extreme salinity

Responses of Atriplex portulacoides upon 40-day-long exposure to salinity (0?C1,000?mM NaCl) were investigated. Mother plants originated from a sabkha located in a semi-arid region of Tunisia. The plant relative growth rate and leaf expansion increased significantly at 200?mM NaCl but decreased at higher salinities. Interestingly, the plants survived salinity as high as 1,000?mM NaCl without displaying salt-induced toxicity symptoms. Despite significant increase in leaf Na⁺ and Cl^? concentrations upon salt treatment, no significant effect on leaf relative water content was registered. Chlorophyll contents and the gas exchange parameters showed a significant stimulation at the optimal salinity (200?mM NaCl) followed by a decline at higher salinities. Extreme salinity hardly impacted the maximal efficiency of photosystem II photochemistry (F _v/F _m), but a marked decrease in the relative quantum yield of photosystem II (??_PSII) was observed, along with a significant increase in non-photochemical quenching (NPQ). Leaf malondialdehyde and carotenoid contents were generally unaffected following salt exposure, whereas those of anthocyanins, polyphenols, and proline increased significantly, being maximal at 1,000?mM NaCl. Leaf superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11), and glutathione reductase (EC 1.6.4.2) activities were significantly stimulated by salinity, whereas catalase (EC 1.11.1.6) activity was maximal in the 0?C400?mM NaCl range. As a whole, protecting the photosynthetic machinery from salt-induced photodamage together with the sustained antioxidant activity may account for the performance of A. portulacoides under high salinity.     

Spectral effects of LEDs on chlorophyll fluorescence and pigmentation in Phalaenopsis ‘Vivien’ and ‘Purple Star’

We examined the effect of light emitting diode (LED) lighting in greenhouse facilities on growth, chlorophyll fluorescence and pigmentation in Phalaenopsis ‘Vivien’ and ‘Purple Star’ under purpose‐built LED arrays yielding c. 200 µmol m^?2 s^?1 at plant height for 14 h per day and 24/18°C day/night temperature, respectively, from January to April 2013. The light treatments were (1) 40% blue in 60% red (40% B/R), (2) 0% blue in 100% red (0% B/R) and (3) white LEDs with 32% blue in white (32% B/W, control), with background daylight under shade screens. The plants were harvested twice for leaf growth and pigmentation. There was no clear pattern in the spectral effect on growth since the order of leaf size differed between harvests in March and April. F_v/F_m was in the range of 0.52–0.72, but overall slightly higher in the control, which indicated a permanent downregulation of PSII in the colored treatments. The fluorescence quenching showed no acclimation to color in ‘Purple Star’, while ‘Vivien’ had lower ETR and higher NPQ in the 40% B/R, resembling low light acclimation. The pigmentation showed corresponding spectral response with increasing concentration of lutein while increasing the fraction of blue light, which increased the light absorption in the green/yellow part of the spectrum. The permanent downregulation of PSII moved a substantial part of the thermal dissipation from the light regulated NPQ to non‐regulated energy losses estimated by Φ_NPQ and Φ_NO and the difference found in the balance between Φ_PSII and Φ_NPQ in ‘Vivien’ disappeared when Φ_NO was included in the thermal dissipation.     

Effect of day/night temperature difference on chlorophyll content,photosynthesis and fluorescence parameters of tomato at fruit stage

In order to investigate the effect of day/night temperature difference (DIF) on photosynthetic characteristics of tomato plants (Solanum lycopersicum, cv. Jinguan 5) at fruit stage, an experiment was carried out in climate chambers. Five day/night temperature regimes (16/34, 19/31, 25/25, 31/19, and 34/16°C) with respective DIFs of -18, -12, 0, +12, and +18 were used and measured at mean daily temperature of 25°C. The results showed that chlorophyll (Chl) a, Chl b, net photosynthetic rate (P_N), stomatal conductance (g_s), maximum quantum yield of PSII photochemistry (F_v/F_m), effective quantum yield of PSII photochemistry (?_PSII), and photochemical quenching (qp) significantly increased under positive DIF, while they decreased with negative DIF. In contrast, the Chl a/b ratio and nonphotochemical quenching (NPQ) decreased under positive DIF, while increased with negative DIF. Chl a, Chl b, P_N, g_s, F_v/F_m, ?_PSII, and qp were larger under +12 DIF than those at +18 DIF, while Chl a/b and NPQ showed an opposite trend.