Photosynthesis-related Parameters Research Articles

Importance of the alternative oxidase (AOX) pathway in regulating cellular redox and ROS homeostasis to optimize photosynthesis during restriction of the cytochrome oxidase pathway in Arabidopsis thaliana.

The importance of the alternative oxidase (AOX) pathway, particularly AOX1A, in optimizing photosynthesis during de-etiolation, under elevated CO2, low temperature, high light or combined light and drought stress is well documented. In the present study, the role of AOX1A in optimizing photosynthesis was investigated when electron transport through the cytochrome c oxidase (COX) pathway was restricted at complex III. Leaf discs of wild-type (WT) and aox1a knock-out mutants of Arabidopsis thaliana were treated with antimycin A (AA) under growth-light conditions. To identify the impact of AOX1A deficiency in optimizing photosynthesis, respiratory O2 uptake and photosynthesis-related parameters were measured along with changes in redox couples, reactive oxygen species (ROS), lipid peroxidation and expression levels of genes related to respiration, the malate valve and the antioxidative system. In the absence of AA, aox1a knock-out mutants did not show any difference in physiological, biochemical or molecular parameters compared with WT. However, after AA treatment, aox1a plants showed a significant reduction in both respiratory O2 uptake and NaHCO3-dependent O2 evolution. Chlorophyll fluorescence and P700 studies revealed that in contrast to WT, aox1a knock-out plants were incapable of maintaining electron flow in the chloroplastic electron transport chain, and thereby inefficient heat dissipation (low non-photochemical quenching) was observed. Furthermore, aox1a mutants exhibited significant disturbances in cellular redox couples of NAD(P)H and ascorbate (Asc) and consequently accumulation of ROS and malondialdehyde (MDA) content. By contrast, WT plants showed a significant increase in transcript levels of CSD1, CAT1, sAPX, COX15 and AOX1A in contrast to aox1a mutants. These results suggest that AOX1A plays a significant role in sustaining the chloroplastic redox state and energization to optimize photosynthesis by regulating cellular redox homeostasis and ROS generation when electron transport through the COX pathway is disturbed at complex III.

Changes of Photosynthesis-Related Parameters and Productivity of Spring Oilseed Rape under Different Nitrogen and Sulphur Fertilizers Supply

Fertilization with essential mineral elements is important to get high quality yield results. The lack of necessary mineral elements in soil can affect oilseed rape plant physiological functions, photosynthesis and plant productivity. Oilseed rape plants have high requirements for nitrogen and as oil crop – for sulphur. The aim of the investigation was to explain changes of chlorophyll a fluorescence parameters in spring oilseed rape leaves and yield changes under nitrogen and sulphur supply. During laboratory experiments changes of chlorophyll a fluorescence parameters and during field experiments changes of yield parameters under different nitrogen and sulphur supply were observed. Laboratory and field experiments showed that sulphur fertilizer rate 18 kg ha-1 is the most effective sulphur dose for spring oilseed rape, when nitrogen 55 kg ha-1 is added, because its presence has positive effect on photosynthetic reactions. There was found out in laboratory experiments that chlorophyll a fluorescence parameters Fv/Fm and PI can be used to describe sulphur and nitrogen mineral element supply efficacy on spring oilseed rape. There was observed in the field experiment that oilseed rape yield increases significantly (from +0.34 t ha-1 to +0.64 t ha-1) under optimal (S18N55) nutrient supply, but lack of sulphur leads to significant yield losses. To avoid excessive fertilizer usage, its negative impact on plant physiology and yield losses, we consider that sulphur: nitrogen = 1:3 as additional fertilizer is optimal for spring oilseed rape plants.

Exploring natural variation of photosynthetic, primary metabolism and growth parameters in a large panel of Capsicum chinense accessions

Collectively, the results presented improve upon the utility of an important genetic resource and attest to a complex genetic basis for differences in both leaf metabolism and fruit morphology between natural populations. Diversity of accessions within the same species provides an alternative method to identify physiological and metabolic traits that have large effects on growth regulation, biomass and fruit production. Here, we investigated physiological and metabolic traits as well as parameters related to plant growth and fruit production of 49 phenotypically diverse pepper accessions of Capsicum chinense grown ex situ under controlled conditions. Although single-trait analysis identified up to seven distinct groups of accessions, working with the whole data set by multivariate analyses allowed the separation of the 49 accessions in three clusters. Using all 23 measured parameters and data from the geographic origin for these accessions, positive correlations between the combined phenotypes and geographic origin were observed, supporting a robust pattern of isolation-by-distance. In addition, we found that fruit set was positively correlated with photosynthesis-related parameters, which, however, do not explain alone the differences in accession susceptibility to fruit abortion. Our results demonstrated that, although the accessions belong to the same species, they exhibit considerable natural intraspecific variation with respect to physiological and metabolic parameters, presenting diverse adaptation mechanisms and being a highly interesting source of information for plant breeders. This study also represents the first study combining photosynthetic, primary metabolism and growth parameters for Capsicum to date.

The effects of constraining variables on parameter optimization in carbon and water flux modeling over different forest ecosystems

The ability of terrestrial biogeochemical models in predicting land-atmospheric carbon and water exchanges is largely hampered by the insufficient characterization of model parameters. The direct observations of carbon/water fluxes and the associated environmental variables from eddy covariance (EC) flux towers provide a notable opportunity to examine the underlying processes controlling carbon and water exchanges between terrestrial ecosystems and the atmosphere. In this study, we applied the Metropolis simulated annealing technique to conduct parameter optimization analyses of a process-based biogeochemical model, simplified PnET (SIPNET), using a variety of constraining variables from EC observations and leaf area index (LAI) from MODIS at three ChinaFLUX forest sites: a temperate mixed forest (CBS), a subtropical evergreen coniferous plantation (QYZ) and a subtropical evergreen broad-leaved forest (DHS). Our analyses focused on (1) identifying the key model parameters influencing the simulation of carbon and water fluxes with SIPNET; (2) evaluating how different combinations of constraining variables influence parameter estimations and associated uncertainties; and (3) assessing the model performance with the optimized parameterization in predicting carbon and water fluxes in the three forest ecosystems. Our sensitivity analysis indicated that, among three different forest ecosystems, the prediction of carbon and water fluxes was mostly affected by photosynthesis-related parameters. The performances of the model simulations depended on different parameterization schemes, especially the combinations of constraining variables. The parameterization scheme using both net ecosystem exchange (NEE) and evapotranspiration (ET) as constraining variables performed best with most well-constrained parameters. When LAI was added to the optimization, the number of well-constrained model parameters was increased. In addition, we found that the model cannot be well-parameterized with only growing-season observations, especially for those forest ecosystems with distinct seasonal variation. With the optimized parameterization scheme using both NEE and ET observations all year round, the SIPNET were able to simulate the seasonal and inter-annual variations of carbon and water exchanges in three forest ecosystems.

Managing the pools of cellular redox buffers and the control of oxidative stress during the ontogeny of drought-exposed mungbean (Vigna radiata L.)—role of sulfur nutrition

Impacts of increasing environmental stresses (such as drought) on crop productivity can be sustainably minimized by optimizing mineral nutrients (such as sulfur, S). This study, based on a pot-culture experiment conducted in greenhouse condition, investigates S-mediated influence of drought stress (imposed at pre-flowering, flowering and pod-filling stages) on growth, photosynthesis and tolerance of mungbean (Vigna radiata L.) plants. Drought stress alone hampered photosynthesis functions, enhanced oxidative stress [measured in terms of H2O2; lipid peroxidation (LPO); electrolyte leakage (EL)] and decreased the pools of cellular redox buffers (namely ascorbate (AsA); glutathione (GSH)], and the overall plant growth (measured as leaf area and plant dry mass), maximally at flowering stage, followed by pre-flowering and pod-filling stages. Contrarily, S-supplementation to drought-affected plants (particularly at flowering stage) improved the growth- and photosynthesis-related parameters considerably. This may be ascribed to S-induced enhancements in the pools of reduced AsA and GSH, which jointly manage the balance between the production and scavenging of H2O2 and stabilize cell membrane by decreasing LPO and EL. It is inferred that alleviation of drought-caused oxidative stress depends largely on the status of AsA and GSH via S-application to drought-stressed V. radiata at an appropriate stage of plant growth, when this nutrient is maximally or efficiently utilized.

Salicylic acid alleviates cold-induced photosynthesis inhibition andoxidative stress in Jasminum sambac

Salicylic acid (SA) is a signal molecule that mediates many biotic and abiotic stress-induced physiological responses in plants. In the current study the protective effects of SA on cold stress-caused oxidative damage and photosynthesis inhibition in jasmine plants (Jasminum sambac) were examined. Jasmine seedlings were pretreated with 100 µM SA for 3 days and then subjected to cold stress (4 °C) for 15 days. The amounts of superoxide radicals (O_2^{-}) and hydrogen peroxide (H_{2}O_{2}) significantly increased in leaves of plants exposed to cold stress and resulted in oxidative damage, indicated by an increase in malondialdehyde accumulation and membrane leakage. The total chlorophyll content, stomatal conductance (g_s), photochemical efficiency (F_v/F_m), and net photosynthesis rate (P_n) were significantly reduced in response to the cold treatment. However, plants pretreated with exogenous SA (100 µM) exhibited significantly higher photosynthesis-related parameters and antioxidant enzyme activities (peroxidase and catalase) and lower reactive oxygen species levels compared with the cold control. It was therefore concluded that SA could alleviate the cold treatment-caused oxidative stress and photosynthesis decline by enhancing the activities of antioxidant enzymes in leaves of jasmine.

Relation between O3-Inhibition of Photosynthesis and Ethylene in Paddy Rice Grown under Different CO2 Concentrations

This study was conducted to evaluate the role of ethylene in acute ozone (O3: 0, 0.1, and 0.3 cm3 m–3; O0, O0.1 and O0.3, respectively)-induced photosynthetic inhibition of paddy rice leaves grown under different atmospheric carbon dioxide concentrations (CO2: 400 and 800 cm3 m–3; C400 and C800, respectively). Ethephon and silver thiosulfate complex (STS) were applied one day before exposure to O3. Gas exchange, chlorophyll fluorescence, and ascorbic acid were measured immediately before (BE), immediately after (AE-0), and 1 d and 3 d after (AE-1, AE-3) the start of the exposure to O3. In the plants exposed to O3, visible leaf symptoms on the adaxial leaf surface appeared at AE-3. O3 decreased photosynthesis-related parameters, total ascorbic acid content, and redox state of ascorbic acid (RDS), and C800 ameliorated O3-induced damage. STS ameliorated the O3-induced visible leaf symptoms and O3-inhibition of photosynthesis but ethephon worsened slightly or did not affect them. Additionally, we evaluated the effects of O3 and CO2 on ethylene production in rice leaves. Although elevated CO2 did not affect ethylene production, exposure to O3 greatly increased ethylene production at AE-0 and rapidly reduced it at AE-1. These results indicate that ethylene is an important component of signal transduction for the extension of O3 injury in paddy rice.

Breeding for enhanced drought resistance in barley and wheat - drought-associated traits, genetic resources and their potential utilization in breeding programmes

Drought represents the most devastating abiotic stress factor worldwide. It severely limits plant growth and development as well as agricultural characteristics including the final yield. The aim of this review is to summarise recent results of the breeding of barley (Hordeum vulgare) and wheat (Triticum aestivum; T. durum) for improved resistance to drought stress. First, drought-associated terms and definitions are outlined and plant strategies to cope with drought are presented. A brief overview of plant physiological mechanisms involved in water uptake and release is provided. Photosynthesis-related parameters (CO<sub>2</sub> availability and associated features such as ribulose-1,5-bisphosphate carboxylase/oxygenase activity, <sup>13</sup>C discrimination activity, water use efficiency) are discussed due to the crucial role of plant leaf stomata in both photosynthesis and water management. The second part describes the present state of research on drought resistance-associated traits in barley and wheat. Different strategies of plant water management aimed at maximising the final yield under various types of drought stress are discussed. Possibilities of the detection, identification and characterization of quantitative trait loci (QTLs) in barley and wheat germplasm are discussed and the future approaches to breeding for enhanced drought resistance as a complex physiological and agronomical trait are outlined.

Effects of Arbuscular Mycorrhizal Fungal Inoculation and Phosphorus (P) Addition on Maize P Utilization and Growth in Reclaimed Soil of a Mining Area

Crop phosphorus (P) and water utilization and growth in mining-disturbed land can be improved through inoculation of arbuscular mycorrhizal fungi (AMF). Researchers evaluated the effects of AMF and fertilizer P on maize P and water utilization and maize growth in a mining-disturbed loess soil. Compared with non-AMF (NAMF), AMF increased shoot and root P contents by 16.7 and 72.9%, respectively, net photosynthetic rate (Pn) by 12.2%, and P-use efficiency by 44.3%. Regardless of AMF inoculation, maize P content increased linearly with the increases of P rate, whereas root colonization, Pn, and shoot biomass responded quadratically to P rate. Measurements of photosynthesis-related parameters decreased with the increases of P rate, but the extents of decline reduced with AMF relative to NAMF. Water-use efficiency increased linearly with increases of P rate, but the effect was reduced with AMF. Inoculation of AMF promoted maize growth and reduced the dependency on P addition.

Ectomycorrhizal fungi affect Scots pine photosynthesis through nitrogen and water economy, not only through increased carbon demand

Symbiotic ectomycorrhizal fungi have been shown to enhance host plant photosynthesis because the fungal symbiont are claimed to increase belowground carbon (C) demand. We aimed to study the effect of eight common symbiotic ectomycorrhizal (ECM) fungi on Scots pine photosynthesis and carbon (C) allocation because very few studies have investigated this phenomenon under controlled axenic conditions. The CO2 assimilation, stomatal conductance, chlorophyll fluorescence parameters, biomass allocation, moisture content, mycorrhization rate, nitrogen (N) uptake and N content of Scots pine seedlings, with or without symbiotic fungi, were measured after a four month growth period under axenic laboratory conditions. We hypothesized that ECM fungi are capable of increasing plant CO2 assimilation compared to non-mycorrhizal control fungi by increasing belowground C demand. This hypothesis was not supported since mycorrhizal and non-mycorrhizal plants did not differ significantly in any of the photosynthesis-related parameters. In addition, the common assumption that ECM fungi impose a C cost on the host plant was not supported by our study because mycorrhizal plants had the same or larger biomass compared to non-mycorrhizal plants. However, the mycorrhizal seedlings had a lower N percentage and allocated relatively more N to roots than shoots compared to control sterile seedlings, and the mycorrhizal seedlings had lower water content. In general, Needle N and water content correlated positively with CO2 assimilation. Based on our results, the N distribution within plant and plants water economy are the main effects of mycorrhizal symbiosis that affect plant C allocation and photosynthesis. These factors need to be considered when mycorrhizal effect on plant net primary production (NPP) also under natural conditions is estimated.

Toxicity induced by three antibiotics commonly used in aquaculture on the marine microalga Tetraselmis suecica (Kylin) Butch

Aquaculture facilities are a potential source of antibiotics to the aquatic ecosystems. The presence of these compounds in the environment may have deleterious effects on non-target aquatic organisms such as microalgae, which are often used as biological indicators of pollution. Therefore, the toxicity induced by chloramphenicol (CHL), florphenicol (FLO) and oxytetracycline (OTC), three antibiotics widely used in aquaculture, on the marine microalga Tetraselmis suecica was evaluated. Growth inhibition and physiological and biochemical parameters were analysed. All three antibiotics inhibited growth of T. suecica with 96 h IC50 values of 11.16, 9.03 and 17.25 mg L−1 for CHL, FLO and OTC, respectively. After 24 h of exposure no effects on growth were observed and cell viability was also unaffected, whereas a decrease in esterase activity, related with cell vitality, was observed at the higher concentrations assayed. Photosynthesis related parameters such as chlorophyll a cellular content and autofluorescence were also altered after 24 h of antibiotics addition. It can be concluded that T. suecica was sensitive to the three antibiotics tested.

다환방향족탄화수소가 콩과 벼의 생육에 미치는 영향

화석연료의 연소나 유류 오염 등으로 인해 발생하는 PAHs는 우리 주변 어디에서나 존재하는 위험한 오염물질 중 하나로, 생태계에 영향을 끼치며 작물 생육에도 영향을 준다. PAHs는 작물에서도 흡수가 가능하기 때문에, 작물생육에 대한 저해 효과를 알아보기 위해 콩과 벼에 대한 영향을 유묘기부터 검정하였다. PAHs가 처리된 토양에서 자란 벼와 콩의 초장과 건물중은 다소 감소하였고, 벼보다 콩에서 생장 저해가 강하게 발생되었다. 토양에 100 ppm 농도에서 처리된 경우 콩의 초장은 58.9 cm로 처리되지 않은 콩의 87.2% 값을 보였다. 벼의 경우, 처리 후 80일 100 ppm에서 자란 벼가 처리되지 않은 벼의 96.0% 값을 보여, 초장에 있어서 저해 효과가 낮게 나타났다. 광합성과 관련된 엽록소 함량과 엽록소 형광은 PAHs 처리 후 20일부터 70일까지 저해가 약간 되었지만, 출수기 이후는 저해 정도가 약하게 나타났다. 어린 유묘의 한천 배지 실험은 100 ppm phenanthrene 농도일 때, 성숙한 작물의 폿트 실험과 비교시 유묘 길이와 생체중의 저해가 높게 나타났다. 벼에서는 유묘 길이와 생체중이 각 각 54.2%, 33.3% 감소하였고, 콩에서는 각 각 27.9%, 13.2% 감소되었다. 이러한 결과를 통하여 PAHs은 성숙기보다 영양 생장 초기에 저해가 높게 발생하며, 영양생장기의 피해는 콩보다 벼에서 저해가 높게 발생하였다. Polycyclic aromatic hydrocarbons (PAHs) are a group of ubiquitous hazardous pollutants derived from fossil fuel, various combustion sources and pyrolysis of a wide range of plastics. Because PAHs can be uptake into crop plants, the inhibitory effects on rice and soybean plants were examined in greenhouse and growth chamber experiment. Soil-applied PAHs (phenanthrene of 0, 10, 30, 100 ppm) slightly reduced the plant height and dry weight both in transplanted rice and soybean plant. The inhibitory effect on growth was greater in soybean than rice. Plant height of soybean plants treated by 100 ppm was 58.9 cm and this value was 87.2% of untreated plant. In rice plant, the plant height was less inhibited (96.0% of untreated plant) by 100 ppm at 80 days after treatment (DAT). However, leaf chlorophyll content and chlorophyll fluorescence were less inhibited by PAHs at late growth stage (after heading) although the photosynthesis-related parameters were slightly inhibited from 20 DAT to 70 DAT. In agar medium experiment with infant seedlings, inhibition of seedling length and fresh weight by phenanthrene at 100 ppm were greater as compared to the experiment with adult plant in pot. Seedling length and fresh weight were reduced by 54.2% and 33.3% for rice and 27.9% and 13.2% for soybean, respectively. The results reflected that PAHs were more inhibitory during juvenile stage than adult stage and more inhibitory to rice plant than soybean for juvenile stage.

Alleviation of cadmium toxicity by cerium in rice seedlings is related to improved photosynthesis, elevated antioxidant enzymes and decreased oxidative stress

Cadmium contamination is a critical constraint to plant production in agricultural soils in some regions. Cerium is one of the rare earth elements, it plays a positive role in plant growth with a appropriate content. The present study was conducted to examine the role of cerium nutrition in the amelioration of effects on cadmium toxicity in rice (Oryza sativa L.) seedlings by a hydroponic experiment. Measurements included growth condition, photosynthesis related parameters, chloroplast ultra-structure and antioxidant enzymes content. Our results showed that the growth of rice seedlings was markedly inhibited by cadmium (100 μM), and the inhibition was significantly alleviated by cerium (10 μM). Fresh weight, single seedling height and chlorophyll content of rice plants in cerium treated groups were increased by 24.4, 18.2 and 32.05 % compared to those of plants cultivated in only cadmium-present condition. Additionally, in cadmium treated plants, the addition of cerium significantly increased the value of the maximum quantum yield of primary photochemistry (Fv/Fm), indicator of PSII ‘structure and functioning’ (SFIABS) and the performance index on absorption basis (PIABS), elevated the activity of whole chain electron transport activity, enhanced photophosphorylation and its coupling factor Ca2+-ATPase activities. The result showed that the chloroplasts and thylakoid membrane of the rice seedlings leaves grown in cerium treatment developed better than that in cerium-absent group under cadmium toxicity. Moreover, addition with 10 μM cerium mitigated cadmium stress by inducing leaf enzyme activities for antioxidation like superoxide dismutase, peroxidase and catalase, dramatically depressed superoxide (O2·−), hydrogen peroxide and malondialdehyde accumulation. Results indicated that alleviation of cadmium toxicity by cerium application is partly related to improved light-use-efficiency, increased antioxidant enzymes, decreased oxidative stress in rice seedlings.

High temperatures limit plant growth but hasten flowering in root chicory (Cichorium intybus) independently of vernalisation

An increase in mean and extreme summer temperatures is expected as a consequence of climate changes and this might have an impact on plant development in numerous species. Root chicory (Cichorium intybus L.) is a major crop in northern Europe, and it is cultivated as a source of inulin. This polysaccharide is stored in the tap root during the first growing season when the plant grows as a leafy rosette, whereas bolting and flowering occur in the second year after winter vernalisation. The impact of heat stress on plant phenology, water status, photosynthesis-related parameters, and inulin content was studied in the field and under controlled phytotron conditions. In the field, plants of the Crescendo cultivar were cultivated under a closed plastic-panelled greenhouse to investigate heat-stress conditions, while the control plants were shielded with a similar, but open, structure. In the phytotrons, the Crescendo and Fredonia cultivars were exposed to high temperatures (35°C day/28°C night) and compared to control conditions (17°C) over 10 weeks. In the field, heat reduced the root weight, the inulin content of the root and its degree of polymerisation in non-bolting plants. Flowering was observed in 12% of the heat stressed plants during the first growing season in the field. In the phytotron, the heat stress increased the total number of leaves per plant, but reduced the mean leaf area. Photosynthesis efficiency was increased in these plants, whereas osmotic potential was decreased. High temperature was also found to induced flowering of up to 50% of these plants, especially for the Fredonia cultivar. In conclusion, high temperatures induced a reduction in the growth of root chicory, although photosynthesis is not affected. Flowering was also induced, which indicates that high temperatures can partly substitute for the vernalisation requirement for the flowering of root chicory.

Significant relationships among frost tolerance and net photosynthetic rate, water use efficiency and dehydrin accumulation in cold-treated winter oilseed rapes

Five winter oilseed rape cultivars (Benefit, Californium, Cortes, Ladoga, Navajo) were subjected to 30 days of cold treatment (4°C) to examine the effect of cold on acquired frost tolerance (FT), dehydrin (DHN) content, and photosynthesis-related parameters. The main aim of this study was to determine whether there are relationships between FT (expressed as LT50 values) and the other parameters measured in the cultivars. While the cultivar Benefit accumulated two types of DHNs (D45 and D35), the other cultivars accumulated three additional DHNs (D97, D47, and D37). The similar-sized DHNs (D45 and D47) were the most abundant; the others exhibited significantly lower accumulations. The highest correlations were detected between LT50 and DHN accumulation (r=−0.815), intrinsic water use efficiency (WUEi; r=−0.643), net photosynthetic rate (r=−0.628), stomatal conductance (r=0.511), and intracellular/intercellular CO2 concentration (r=0.505). Those cultivars that exhibited higher Pn rate in cold (and further a significant increase in WUEi) had higher levels of DHNs and also higher FT. No significant correlation was observed between LT50 and E, PRI, or NDVI. Overall, we have shown the selected physiological parameters to be able to distinguish different FT cultivars of winter oilseed rape.

Physiological and proteomics analyses of Holm oak (Quercus ilex subsp. ballota [Desf.] Samp.) responses to Phytophthora cinnamomi

Phytophthora cinnamomi is one of the agents that trigger the decline syndrome in Quercus spp., this being a serious threat to Mediterranean Holm oak forest sustainability and reforestation programs. Quercus ilex responses to Phytophthora cinnamomi have been studied in one-year olds seedlings from two Andalucía provenances, assessing the physiological water status and photosynthesis-related parameters. Upon inoculation with mycelium a reduction in water content, chlorophyll fluorescence, stomatal conductance and gas exchange was observed along a 90 days post inoculation period in both provenances. The reduction was higher in the most susceptible (SSA) provenance, than in the most tolerant (PCO), being these typical plant responses to drought stress. Leaf protein profiles were analyzed in non-inoculated and inoculated seedlings from the two provenances by using a 2-DE coupled to MS proteomics strategy. Ninety seven proteins changing in abundance in response to the inoculation were successfully identified after MALDI-TOF-TOF analyses. The largest group of variable identified proteins were chloroplasts ones, and they were involved in the photosynthesis, Calvin cycle and carbohydrate metabolism. It was noted that a general tendency was a decrease in the protein abundance as a consequence of the inoculation, being it less accused in the least susceptible, the Northern provenance (PCO), than in the most susceptible, the Southern provenance (SSA). This trend is clearly manifested in photosynthesis, amino acid metabolism and stress/defence proteins. On the contrary, some proteins related to starch biosynthesis, glycolysis and stress related peroxiredoxin showed an increase upon inoculation. These changes in protein abundance were correlated to the estimated physiological parameters and have been frequently observed in plants subjected to drought stress.

Leaf Gas Exchange Responses to Irrigation Timing and Nigari (Effluent of Salt Industries) of Sweet Pepper (Capsicum annuum L.) in Soilless Culture

There is increasing interest in reducing fertilizer cost and establishing proper irrigation management for sustainable vegetable production. Nigari, an effluent of salt industries, is cheaper than commercial fertilizers. Another important vegetable production factor is nutrient application timing to improve soilless cultivation in crops like sweet pepper. Therefore, this study evaluated the effects of nigari and nutrient solution application timing on leaf gas exchanges of sweet pepper cultivated under a soilless system. Treatments included three nigari rates [no nigari plus a standard nutrient solution as control, 2 mL·L−1 nigari + additional nitrogen–phosphorus–potassium (N–P–K) to equal the standard, and 4 mL·L−1 nigari + additional N–P–K to equal the standard]. Three daily application timings (T1 = 0700 hr + 1500 hr, T2 = 0900 hr + 1500 hr, and T3 = 0700 hr + 0900 hr + 1500 hr) were used for each nutrient solution. Leaf gas exchange parameters were studied during the vegetative and reproductive growth stages of sweet pepper cv. Papri new-E-red. Photosynthetic responses and its related parameters, namely transpiration (E), stomatal conductance (gS), and maximum photosynthesis (Amax), were significantly affected by nigari rates and nutrient solution application timing. Photosynthesis-related parameters, E, gS, Amax, and initial slope of photosynthesis in response to light curve were the highest and light compensation point (LCP) and leaf vapor pressure deficit (LVPD) were the lowest at 2 mL·L−1 nigari compared with the control at both plant vegetative and reproductive growth stages. For nutrient solution application timing, the highest E, gS, and Amax were observed at T3 treatment at both plant growth stages. Furthermore, marketable yield of sweet pepper was the highest when 2 mL·L−1 nigari was applied at 0700, 0900, and 1500 hr a day. Leaf gas exchange parameters showed that nutrient solution application timing of 0700, 0900, and 1500 hr a day was better for obtaining high yield of sweet pepper under nigari treatment in soilless culture.

Aluminium long-term stress differently affects photosynthesis in rye genotypes

The ability of crops to overcome Al toxicity varies among crop species and cultivars. Among the Triticeae genus, rye (Secale cereale) is considered the most Al-tolerant species. In the present work, two rye genotypes differing in Al tolerance ('Riodeva': Al-sensitive and 'Donkowsky Zlote': Al-tolerant) were exposed to 1.11 and 1.85mM Al during three weeks. Growth, water status and photosynthesis related parameters were assessed. After three weeks of Al exposure, both genotypes presented similar decrease in leaf growth. Al-induced RWC decreased in both genotypes, but was more remarkable in 'Riodeva'. Al toxicity induced a decrease in net photosynthetic rate only after three weeks of exposure. In 'D. Zlote', A decrease was accompanied by stomatal closure, Chl a content and q(p) reduction, but no alterations in RuBisCo or sFBPase activity were observed. In 'Riodeva' plants exposed to 1.11mM Al, A decrease was accompanied by C(i)/C(a) increase whereas in plants exposed to 1.85mM Al C(i)/C(a) was not affected. Nevertheless, for both conditions RuBisCo activity decreased. A decrease did not limited glucose accumulation in neither of the rye genotypes. This study revealed that Al-induced earlier damages in the 'Riodeva' genotype, but both genotypes showed long-term high susceptibility to Al. Furthermore, the photosynthetic parameters proved to be a good tool to monitor Al-sensitivity and long-term exposure showed to be crucial to evaluate Al-sensitivity.

Can photosynthesis-related parameters be used to establish the activity of acetolactate synthase–inhibiting herbicides on weeds?

The application of the acetolactate synthase (ALS)–inhibiting herbicide metsulfuron on greenhouse- and field-grown black nightshade and greenhouse-grown ladysthumb resulted in progressive inhibition of the level of carbon dioxide (CO2) fixation, the relative quantum efficiency of electron transport through photosystem I (ΦPSI) and II (ΦPSII), and the leaf chlorophyll content. Photosynthetic-related measurements, measured 2 to 4 d after treatment (DAT) at photon flux densities of 400 to 500 μmol m−2 s−1, provided valuable information before the visual symptoms that first appeared at 7 to 10 DAT with the herbicide. Measurements of the quantum efficiency for electron transport by photosystem II and the loss in leaf chlorophyll content appeared to be two of the most practical parameters to use when designing an early detection method to assess the toxicity of metsulfuron. The use of chlorophyll fluorescence would require a comparison of steady-state ΦPSII measurements for control and treated plants, which could be realized by either measuring in time (before/after application) or space (treated/untreated patch).

Long-term acclimation to UV radiation: effects on growth, photosynthesis and carbonic anhydrase activity in marine diatoms

Oyster-ponds are characterized by cyclical changes in the composition of the microalgal population, and are mainly colonized by diatoms. Species living in oyster-ponds experience higher levels of UV-R than those living in the ocean because of the low turbidity and shallow depth in ponds (where no stratification occurs). In artificial laboratory conditions, five marine Bacillariophyceae species commonly found in the oyster-ponds were acclimated to three artificial UV radiation (UV-R) treatments with differing durations (2.25 h, 5 h and 8 h) and intensities of exposure, but with the same daily UV-R dose (110 kJ m-2 d-1, unweighted) and UVB-R/UVA-R ratio (4.5%), equivalent to that observed in the natural medium. Benthic species were able to sustain active growth, in contrast to the pelagic Skeletonema costatum that failed to acclimate. Amphora coffeaeformis was the only acclimated species that did not display any significant decrease, or even change in photosynthesis-related pigments and chlorophyll a (Chl a) content when acclimated to UV-R. The other acclimated species showed different patterns of pigment content change, depending on their ability to sustain an active growth rate under UV-R exposure: Haslea ostrearia accumulated photoprotective pigments and exhibited increased diatoxanthin-diadinoxanthin content. The pigment content of Entomoneis paludosa was only slightly modified by the longest UV-R exposure, and Phaeodactylum tricornutum exhibited a marked increase in Chl a turnover, coupled with accumulation of Chl c. In all acclimated species, photosynthesis-related parameters were differently, but in general moderately, affected by UV-R treatments, with a decrease of less than 50% in the maximum photosynthetic capacity. Some species exposed to UV-R exhibited similar or higher photosynthetic capacities than the controls. Carbonic anhydrase activity was strongly enhanced in UV-R tolerant species. Correlation between carbonic anhydrase activity and UV-R tolerance (i.e., ability to sustain active growth rate) in UV-R acclimated algae was established for all the acclimated species. This original finding is concordant with other results that suggest UV-R might play a role in the shift in species composition, since in oyster ponds, Skeletonema costatum, which is usually the dominant species, was the most sensitive diatom under the UV-R conditions tested here.