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Background: This study investigated effects of rapid high-intensity light-curing (3 s) on increasing transdentinal temperature and cell viability. Methods: A total of 40 dentin discs (0.5 mm) obtained from human molars were prepared, included in artificial pulp chambers (4.5 × 5 mm), and subjected to four light-curing protocols (n = 5), with a Valo Grand light curing unit: (i) 10 s protocol with a moderate intensity of 1000 mW/cm2 (Valo-10 s); (ii) 3 s protocol with a high intensity of 3200 mW/cm2 (Valo-3 s); (iii) adhesive system + Filtek Bulk-Fill Flow bulk-fill composite resin in 10 s (FBF-10 s); (iv) adhesive system + Tetric PowerFlow bulk-fill composite resin in 3 s (TPF-3 s). Transdentinal temperature changes were recorded with a type K thermocouple. Cell viability was assessed using the MTT assay. Data were analyzed using one-way ANOVA and Tukey tests for comparison between experimental groups (p < 0.05). Results: The 3 s high-intensity light-curing protocol generated a higher temperature than the 10 s moderate-intensity standard (p < 0.001). The Valo-10 s and Valo-3 s groups demonstrated greater cell viability than the FBF-10s and TPF-3 s groups and statistical differences were observed between the Valo-3 s and FBF-10 s groups (p = 0.023) and Valo-3 s and TPF-3 s (p = 0.025), with a potential cytotoxic effect for the FBF-10 s and TPF-3 s groups. Conclusions: The 3 s rapid high-intensity light-curing protocol of bulk-fill composite resins caused a temperature increase greater than 10 s and showed cell viability similar to and comparable to the standard protocol. [ABSTRACT FROM AUTHOR]

The effects of high-intensity blue light (HIBL, 500/1000 µmol m−2s−1, 450 nm) on Solanum lycopersicum mutants with high pigment (hp) and low pigment (lp) levels and cryptochrome 1 (cry1) deficiency on photosynthesis, chlorophylls, phenols, anthocyanins, nonenzymatic antioxidant activity, carotenoid composition, and the expression of light-dependent genes were investigated. The plants, grown under white light for 42 days, were exposed to HIBL for 72 h. The hp mutant quickly adapted to 500 µmol m−2s−1 HIBL, exhibiting enhanced photosynthesis, increased anthocyanin and carotenoids (beta-carotene, zeaxanthin), and increased expression of key genes involved in pigment biosynthesis (PSY1, PAL1, CHS, ANS) and PSII proteins along with an increase in nonenzymatic antioxidant activity. At 1000 µmol m−2s−1 HIBL, the lp mutant showed the highest photosynthetic activity, enhanced expression of genes associated with PSII external proteins (psbO, psbP, psbQ), and increased in neoxanthin content. This mutant demonstrated greater resistance at the higher HIBL, demonstrating increased stomatal conductance and photosynthesis rate. The cry1 mutant exhibited the highest non-photochemical quenching (NPQ) but had the lowest pigment contents and decreased photosynthetic rate and PSII activity, highlighting the critical role of CRY1 in adaptation to HIBL. The hp and lp mutants use distinct adaptation strategies, which are significantly hindered by the cry1 mutation. The pigment content appears to be crucial for adaptation at moderate HIBL doses, while CRY1 content and stomatal activity become more critical at higher doses. [ABSTRACT FROM AUTHOR]

Background: This study investigated effects of rapid high-intensity light-curing (3 s) on increasing transdentinal temperature and cell viability. Methods: A total of 40 dentin discs (0.5 mm) obtained from human molars were prepared, included in artificial pulp chambers (4.5 × 5 mm), and subjected to four light-curing protocols (n = 5), with a Valo Grand light curing unit: (i) 10 s protocol with a moderate intensity of 1000 mW/cm2 (Valo-10 s); (ii) 3 s protocol with a high intensity of 3200 mW/cm2 (Valo-3 s); (iii) adhesive system + Filtek Bulk-Fill Flow bulk-fill composite resin in 10 s (FBF-10 s); (iv) adhesive system + Tetric PowerFlow bulk-fill composite resin in 3 s (TPF-3 s). Transdentinal temperature changes were recorded with a type K thermocouple. Cell viability was assessed using the MTT assay. Data were analyzed using one-way ANOVA and Tukey tests for comparison between experimental groups (p < 0.05). Results: The 3 s high-intensity light-curing protocol generated a higher temperature than the 10 s moderate-intensity standard (p < 0.001). The Valo-10 s and Valo-3 s groups demonstrated greater cell viability than the FBF-10s and TPF-3 s groups and statistical differences were observed between the Valo-3 s and FBF-10 s groups (p = 0.023) and Valo-3 s and TPF-3 s (p = 0.025), with a potential cytotoxic effect for the FBF-10 s and TPF-3 s groups. Conclusions: The 3 s rapid high-intensity light-curing protocol of bulk-fill composite resins caused a temperature increase greater than 10 s and showed cell viability similar to and comparable to the standard protocol.

The effects of high-intensity blue light (HIBL, 500/1000 µmol m−2s−1, 450 nm) on Solanum lycopersicum mutants with high pigment (hp) and low pigment (lp) levels and cryptochrome 1 (cry1) deficiency on photosynthesis, chlorophylls, phenols, anthocyanins, nonenzymatic antioxidant activity, carotenoid composition, and the expression of light-dependent genes were investigated. The plants, grown under white light for 42 days, were exposed to HIBL for 72 h. The hp mutant quickly adapted to 500 µmol m−2s−1 HIBL, exhibiting enhanced photosynthesis, increased anthocyanin and carotenoids (beta-carotene, zeaxanthin), and increased expression of key genes involved in pigment biosynthesis (PSY1, PAL1, CHS, ANS) and PSII proteins along with an increase in nonenzymatic antioxidant activity. At 1000 µmol m−2s−1 HIBL, the lp mutant showed the highest photosynthetic activity, enhanced expression of genes associated with PSII external proteins (psbO, psbP, psbQ), and increased in neoxanthin content. This mutant demonstrated greater resistance at the higher HIBL, demonstrating increased stomatal conductance and photosynthesis rate. The cry1 mutant exhibited the highest non-photochemical quenching (NPQ) but had the lowest pigment contents and decreased photosynthetic rate and PSII activity, highlighting the critical role of CRY1 in adaptation to HIBL. The hp and lp mutants use distinct adaptation strategies, which are significantly hindered by the cry1 mutation. The pigment content appears to be crucial for adaptation at moderate HIBL doses, while CRY1 content and stomatal activity become more critical at higher doses.

Salicylic acid (SA) plays a pivotal role in plant response to biotic and abiotic stress. Several core SA signaling regulators and key proteins in SA biosynthesis have been well characterized. However, much remains unknown about the origin, evolution, and early diversification of core elements in plant SA signaling and biosynthesis. In this study, we identified 10 core protein families in SA signaling and biosynthesis across green plant lineages. We found that the key SA signaling receptors, the nonexpresser of pathogenesis-related (NPR) proteins, originated in the most recent common ancestor (MRCA) of land plants and formed divergent groups in the ancestor of seed plants. However, key transcription factors for SA signaling, TGACG motif-binding proteins (TGAs), originated in the MRCA of streptophytes, arguing for the stepwise evolution of core SA signaling in plants. Different from the assembly of the core SA signaling pathway in the ancestor of seed plants, SA exists extensively in green plants, including chlorophytes and streptophyte algae. However, the full isochorismate synthase (ICS)-based SA synthesis pathway was first assembled in the MRCA of land plants. We further revealed that the ancient abnormal inflorescence meristem 1 (AIM1)-based β-oxidation pathway is crucial for the biosynthesis of SA in chlorophyte algae, and this biosynthesis pathway may have facilitated the adaptation of early-diverging green algae to the high-light-intensity environment on land. Taken together, our findings provide significant insights into the early evolution and diversification of plant SA signaling and biosynthesis pathways, highlighting a crucial role of SA in stress tolerance during plant terrestrialization. Salicylic acid (SA) plays a pivotal role in plant response to biotic and abiotic stress. This study traces the origin and evolutionary trajectory of core SA signaling regulators and key proteins in SA biosynthesis. The study also reveals that the extensive presence of SA in green plant lineages is crucial for plant adaptation to high-irradiance environments. [ABSTRACT FROM AUTHOR]

Fructans are important polysaccharides synthesized from sucrose which are present in about 12–15% of angiosperms. Sunflower (Helianthus annuus L.) is considered a non-fructan bearing plant even though its close relative, Helianthus tuberosus , accumulates the inulin type of the polymer in large amounts. Previous work suggested that putative fructan-synthesizing enzymes may be expressed in sunflower, but only very limited amounts of the trisaccharide isokestose were found in stems of plants storing high levels of sucrose due to capitulum removal. The present work is aimed at investigating whether intact sunflower plants may indeed synthesize fructans in any of its parts when grown in conditions that favor sucrose availability. Plants were grown in the field at a low density, resulting in a high light availability and low competition for resources, in comparison with controls (usual crop planting density). Plants were harvested at anthesis. Thinned treatment led to an increase in carbohydrates level especially in the capitulum. Carbohydrates analysis of this tissue in thinned plants revealed, for the first time in this species, the presence of inulin-type fructans. The amount of each member of the series appeared to decline starting from isokestose, being DP = 15 the longest fructan detected. Results suggest that, in sunflower, fructans could be synthesized only when sucrose availability exceeds a high threshold, which may not be attained under usual growing conditions. Given the relationship between fructans and tolerance to abiotic stresses including drought, the present finding opens a new perspective for breeding and management of this crop. • Sunflower capitulum was the main site of carbohydrate accumulation at anthesis. • Inulin-type fructan were found in sunflower capitulum under high irradiance conditions. • A certain amount of carbohydrates should be attained to trigger the induction of fructan synthesis. • Fructan synthesis in sunflower opens a new perspective for breeding and management of this crop. [ABSTRACT FROM AUTHOR]

This study compared the growth, proximate composition, and photosynthesis of Chlorella vulgaris cultures between a compound parabolic concentrator (CPC) coupled to a glass tube and a plain tube without the concentrator. The system with a concentrator increased the irradiance level on the culture by 351% and the average light intensity on cells by 462% compared to the plain tube system. During the exponential growth phase, the growth rate of C. vulgaris was higher in the tube system (1.14 div by day−1) versus the system with a concentrator (0.98 div by day−1), but the cell size was higher in the system with the concentrator (11.23 μm) compared with the tube system (6.28 μm). From day 2 to 4 of culture, biomass production (as organic dry weight: 3.43 to 9.85 pg cell−1) and proximate composition (proteins: 12.13 to 31.36 pg cell−1, lipids: 10.44 to 17.55 pg cell−1, and carbohydrates: 13.04 to 38.38 pg cell−1) were higher in the system with concentrator versus tube system. The biomass productivity (0.07 to 0.37 g L−1) and lipid productivity (1.23 to 5.94 g L−1 day−1) were significantly higher in the tube system in the same period. From a practical perspective, these results emphasize the importance of controlling irradiance in C. vulgaris cultures and suggest that a CPC can be used for microalgae cultures to increase the irradiance and induce stress by light. The CPC system can be used to shift the biochemical composition of microalgae cells toward the production of fine chemicals (e.g., pigments and lipids). [ABSTRACT FROM AUTHOR]

Microbial food spoilage is an important cause of health and economic issues and can occur via resilient contamination of food surfaces. Novel technologies, such as the use of visible light, have seen the light of day to overcome the drawbacks associated with surface disinfection treatments. However, most studies report that photo-inactivation of microorganisms with visible light requires long time treatments. In the present study, a novel light electroluminescent diode (LED)-based device was designed to generate irradiation at an ultra-high power density (901.1 mW/cm2). The efficacy of this technology was investigated with the inactivation of the yeast S. cerevisiae. Short-time treatments (below 10 min) at 405 nm induced a ~4.5 log reduction rate of the cultivable yeast population. The rate of inactivation was positively correlated to the overall energy received by the sample and, at a similar energy, to the power density dispatched by the lamp. A successful disinfection of several food contact surfaces (stainless steel, glass, polypropylene, polyethylene) was achieved as S. cerevisiae was completely inactivated within 5 min of treatments. The disinfection of stainless steel was particularly effective with a complete inactivation of the yeast after 2 min of treatment. This ultra-high irradiance technology could represent a novel cost- and time-effective candidate for microbial inactivation of food surfaces. These treatments could see applications beyond the food industry, in segments such as healthcare or public transport. Key points: • A novel LED-based device was designed to emit ultra-high irradiance blue light • Short time treatments induced high rate of inhibition of S. cerevisiae • Multiple food contact surfaces were entirely disinfected with 5-min treatments [ABSTRACT FROM AUTHOR]

Tetraselmis sp. strain MD-01, a microalga isolated from the Tunisian marine coast, has been studied for autotrophic lipids production with two stage process. This strategy was conducted for maximum cells production under moderated conditions (2.12 g L−1), followed by cultivation under stressed conditions to induce lipid synthesis. High irradiance (300 μmol m−2 s−1) and nitrogen depletion (S mode) showed better carotenoids accumulation and lower chlorophylls content in microalgae compared to those obtained in biomass cultivated under high irradiance (Sg mode). This two-stage strategy allowed to increase of lipid content in cells cultivated in Sg and S modes from 18% DW (stage I) to 50 and 61.5% DW (stage II), respectively, with an increase of saturated and long chain fatty acids levels. Based on fluorometry analyses, an increase of lipids in Nile-Red stained cells and a decrease of chlorophylls auto-fluorescence under stressed conditions were shown. From spectral data, the lipids: amide I ratio obtained from S mode was 2.17 and 4.45 times higher than that from Sg mode and control conditions, respectively. These results revealed the potential of Tetraselmis strain MD-01 for biodiesel production. [Display omitted] [ABSTRACT FROM AUTHOR]

Excess radiation is one of frequent natural environmental stresses that plants have to cope with on a daily basis. Therefore, plants have evolved many short- and long-term mechanisms to acclimate to high irradiance and tolerate it. Ureides, generated from purine degradation, have been proposed as compounds involved in environmental stress responses, including altered irradiance. In the present study, high irradiance was used to investigate ureide content and gene expression in Arabidopsis thaliana. Arabidopsis plants shifted to high irradiance showed high content of a specific ureide compound, allantoin. The accumulation of allantoin was associated with increased expression of uricase, an enzyme involved in its production. When an Arabidopsis mutant (aln-3), which constitutively accumulates elevated amounts of allantoin, was exposed to high irradiance, mutant plants demonstrated enhanced tolerance to the stress conditions compared to the wild-type plants. Our results provide evidence that accumulation of the allantoin might contribute in plants response to increased growth irradiance.

Proanthocyanidins (PAs) are the main products of the flavonoid biosynthetic pathway in many plants. However, their biological function during environmental stresses in plants is rarely reported. In the present study, the effects of pretreatment with PAs on the response of cucumber (Cucumis sativus L.) seedlings to high irradiance (HI), polyethylene glycol (PEG), and cold stress were investigated. The PAs pretreament alleviated stress-induced oxidative damage in plant cells and increased the activity of alternative oxidase (AOX) and content of abscisic acid (ABA). Furthermore, PAs-pretreated seedlings suffered less damage by the stress conditions, maintained higher content of chlorophyll a+b and AOX proteins in comparison with the control. Therefore, our findings suggest that PAs might contribute to plant tolerance to environmental stresses.

• Stuckenia pectinata failed to colonise a turbid and saline shallow lake. • Salinity reduced maximum photosynthesis of S. pectinata at high irradiance. • Salinity reduced chlorophyll-a at cellular level in high-light acclimated leaves. • Salinity increased carotenoid content and heat dissipation in high-light leaves. Thick beds of Stuckenia pectinata , a submerged macrophyte, were lost from Te Waihora (Lake Ellesmere) in 1968, following an extreme storm event. Subsequently, it has failed to re-establish what is now a turbid coastal lagoon with a rapid light attenuation and fluctuating salinities. We investigated the interacting effects of irradiance and salinity on photosynthesis of S. pectinata in a laboratory experiment. S. pectinata plants were first acclimated to three irradiances: 340 ± 20 μmol photons m−2 s−1, 110 ± 10 μmol photons m−2 s−1, and 45 ± 5 μmol photons m−2 s−1. At each irradiance, half of the plants experienced increasing salinity stress in a stepwise manner (0, 6, 12 and 18 ppt), whereas the other half remained in freshwater. The intrinsic and effective quantum yield of photosystem II, photosynthesis-irradiance relationships, chlorophyll-a and total carotenoids content, and PSII quantum efficiency of regulated heat dissipation were determined. On a chlorophyll-a basis, light-saturated gross photosynthesis was reduced at high irradiance by 12 and 18 ppt salinity, and at medium irradiance by 18 ppt salinity. Coincidently, plants displayed lowered chlorophyll-a to carotenoids ratios and enhanced heat dissipation in the same treatments. The photosynthetic apparatus in leaves of S. pectinata responded to salinity stress as if in acclimation to high light stress. The response of photosynthesis to an interaction of high salinity and high-light reduces the light conversion efficiency of surface reaching leaves, undermining the default shade-avoidance strategy of S. pectinata of etiolation, and thus contributes to the reduced overall photosynthetic capacity and its ability to colonise the lake. [ABSTRACT FROM AUTHOR]

Highlights • Phosphorylation of p38-like and JNK-like is crucial in D. viridis to environmental stress. • Phosphorylation of ERK-like protein was significantly lower at 4 M of NaCl. • There was a key dependence between stress and phosphorylation of JNK-like protein. • With p38 phosphorylation inhibitor, no response to high irradiance stress was detected. • After the use of specific inhibitor the phosphorylation of MAPKs decreased significantly. Abstract The green unicellular microalga Dunaliella viridis has the ability to cope with a wide variety of environmental stressful conditions, such as thermal and osmotic shocks, high PAR, UV radiation and nitrogen deficiency. The lack of a rigid cell wall makes D. viridis an excellent model organism to study stress signaling in eukaryotic unicellular organisms. Mitogen-activated protein kinases (MAPKs) are highly conserved serine/threonine kinases that convert extracellular stimuli into a wide range of responses at both cellular and nuclear levels. In eukaryotic cells, MAPKs are involved in both cell proliferation and differentiation (ERK pathway) and stress responses (JNK and p38 pathways), through protein kinase cascades. Significantly lesser phosphorylation levels of ERK-like protein were observed in D. viridis cultures acclimated to high salinity (3–4 M NaCl). In contrast, JNK-like and p38-like proteins phosphorylation levels increased in stressed cells. Likewise, the efficacy of specific commercial inhibitors of the phosphorylation of ERK (PD98059), JNK (SP600125) and p38 (SB203580) revealed the importance of JNK-like proteins in the maintenance of cell viability, the highlighted participation of p38-like proteins and the non-direct implication of the ERK-like proteins in the acclimatization process. In summary, specific blockade of JNK- and p38-like cascades in stressed cells led to rapid cell death. The behavior of MAPK-like proteins in algae is not known in depth, so the analysis of their mechanism of action, as well as their function in this model microalga, will allow to estimate the fate of unicellular eukaryotic organisms in aquatic ecosystems subjected to environmental stress derived from the conditions prevailing within a framework of global climate change. [ABSTRACT FROM AUTHOR]

Vanilla orchid, which is well-known for its flavor and fragrance, is cultivated in tropical and subtropical regions. This shade-loving plant is very sensitive to high irradiance. In this study, we show that vanilla chloroplasts started to have avoidance movement when blue light (BL) was higher than 20 μmol m−2s−1 and significant avoidance movement was observed under BL irradiation at 100 μmol m−2s−1 (BL100). The light response curve indicated that when vanilla was exposed to 1000 μmol m−2s−1, the electron transport rate (ETR) and photochemical quenching of fluorescence (qP) were significantly reduced to a negligible amount. We found that if a vanilla orchid was irradiated with BL100 for 12 days, it acquired BL-acclimation. Chloroplasts moved to the side of cells in order to reduce light-harvesting antenna size, and chloroplast photodamage was eliminated. Therefore, BL-acclimation enhanced vanilla orchid growth and tolerance to moderate (500 μmol m−2s−1) and high light (1000 μmol m−2s−1) stress conditions. It was found that under high irradiation, BL-acclimatized vanilla maintained higher ETR and qP capacity than the control without BL-acclimation. BL-acclimation induced antioxidant enzyme activities, reduced ROS accumulation, and accumulated more carbohydrates. Moreover, BL-acclimatized orchids upregulated photosystem-II-associated marker genes (D1 and PetC), Rubisco and PEPC transcripts and sustained expression levels thereof, and also maximized the photosynthesis rate. Consequently, BL-acclimatized orchids had higher biomass. In short, this study found that acclimating vanilla orchid with BL before transplantation to the field might eliminate photoinhibition and enhance vanilla growth and production.

The susceptibility of photosynthesis to photoinhibition and its recovery were studied on cultures of the heterocystous filamentous cyanobacterium Nostoc muscorum grown under different light intensities and varying concentrations of cadmium (Cd). Various physiological parameters viz. growth, pigments content, photosynthetic oxygen evolution, photoinactivation and reactivation of photosynthesis were carried out. A general decline was observed in all these parameters with increasing concentration of Cd under normal and photoinhibitory light intensity. After the exposure of photoinhibitory light N. muscorum showed a rapid decrease in oxygen evolution followed by a quasi steady state rate of photosynthesis. It showed different manner, which became severe and prominent in the presence of Cd. Reactivation of photosynthesis in dim light after the photoinhibitory light treatment was rapid: 85 to 95 % necessary occurred within 2 h, which slowed down and stoped in the presence of cadmium. In the presence of the translation inhibitor, streptomycin (250 mg ml-1), no reactivation occurred. We also found that the damage increased dramatically when the culture was irradiated with high light exposed to streptomycin. A transcription inhibitor, rifampicin did not inhibit the reactivation process. Based on these observations, we conclude that the photoinhibitory damage observations is the net result of a balance between the photoinhibitory process and operation of the repairing mechanisms. Cadmium not only increased the photoinhibitory rate but also arrest recovery process. [ABSTRACT FROM AUTHOR]

Excess radiation is one of frequent natural environmental stresses that plants have to cope with on a daily basis. Therefore, plants have evolved many short- and long-term mechanisms to acclimate to high irradiance and tolerate it. Ureides, generated from purine degradation, have been proposed as compounds involved in environmental stress responses, including altered irradiance. In the present study, high irradiance was used to investigate ureide content and gene expression in Arabidopsis thaliana. Arabidopsis plants shifted to high irradiance showed high content of a specific ureide compound, allantoin. The accumulation of allantoin was associated with increased expression of uricase, an enzyme involved in its production. When an Arabidopsis mutant (aln-3), which constitutively accumulates elevated amounts of allantoin, was exposed to high irradiance, mutant plants demonstrated enhanced tolerance to the stress conditions compared to the wild-type plants. Our results provide evidence that accumulation of the allantoin might contribute in plants response to increased growth irradiance. [ABSTRACT FROM AUTHOR]

In response to stresses, Haematococcus pluvialis accumulates triacylglycerols (TAGs) and astaxanthin, which are highly positively correlated in cells. Coatomer protein I (COPI) complexes play important roles in protein and lipid transportation between endoplasmic reticulum (ER) and Golgi apparatus. The proposed functions of COPI alpha-subunit (COPA1) were to maintain the integrity of endomembrane system and to regulate cellular physiological activities (such as autophagy, protein sorting, secretory trafficking and lipid metabolism). However, only scarce information has been reported on this subunit. In this study, the full-length cDNA encoding H. pluvialis COPA1 ( HpCOPA1 ) and its promoter were cloned and further analyzed by bioinformatics tools. The predicted length of HpCOPA1 was 1234 amino acids (AAs), including WDR, Coatomer-WDAD and COPI-C motifs. The AA sequence of HpCOPA1 was highly identical (78%–99%) to other algal COPA1 and had a highly conserved WDR domain at the N terminus. The promoter of HpCOPA1 contained cis -elements in relation to light and salt stresses, such as AE-box, MNF1, CCAAT-box and TCA-element. Moreover, real-time qPCR analyses showed that the mRNA level of HpCOPA1 was strongly induced by treatments with either high irradiance, or high salinity (45 mM sodium acetate) or in combination. HpCOPA1 revealed a delayed but higher peak expression level in treatments with high salinity (12.5-fold at 4 h) compared with high irradiance (4.7-fold at 2 h). To investigate its subcellular localization, HpCOPA1 was expressed in tobacco lower epidermal leaf cells in fusion with GFP. The results showed that HpCOPA1 was localized to plasma membrane and endomembrane system, partly similar to the localization of COPA1 in higher plants and animals. Taken together, the present results would contribute to the further elucidation of the regulatory mechanisms underlying the biosynthesis and transportation of lipids and astaxanthin in H. pluvialis . [ABSTRACT FROM AUTHOR]

Proanthocyanidins (PAs) are the main products of the flavonoid biosynthetic pathway in many plants. However, their biological function during environmental stresses in plants is rarely reported. In the present study, the effects of pretreatment with PAs on the response of cucumber ( Cucumis sativus L.) seedlings to high irradiance (HI), polyethylene glycol (PEG), and cold stress were investigated. The PAs pretreament alleviated stress-induced oxidative damage in plant cells and increased the activity of alternative oxidase (AOX) and content of abscisic acid (ABA). Furthermore, PAs-pretreated seedlings suffered less damage by the stress conditions, maintained higher content of chlorophyll a+ b and AOX proteins in comparison with the control. Therefore, our findings suggest that PAs might contribute to plant tolerance to environmental stresses. [ABSTRACT FROM AUTHOR]

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Chlorella pyrenoidosa was cultivated in secondary wastewater effluent to assess its nutrient removal capabilities. Wastewaters were obtained from a wastewater treatment plant located in Ouargla, Algeria. The experiments were conducted in winter under natural sunlight in an outdoor open raceway pond situated in the desert area. The highest biomass of the microalgae was found to be 1.71 ± 0.04 g/L. Temperatures ranged between 18 and 31 °C. The average annual insolation was no less than 3500 h with an annual solar irradiance of more than 2000 kWh/m 2 . Analyses of different parameters including COD, NH 4 + -N and TP were conducted throughout the cultivation period. Their average removal efficiencies were 78%, 95% and 81% respectively. The results demonstrated the potential of nutrient removal by microalgae grown on secondary wastewater in arid areas. [ABSTRACT FROM AUTHOR]

Seedlings of bean plants (Phaseolus vulgaris L. Sel 9) were grown for 2 weeks with half strength Hoagland solution containing 0 ppm (deficient), 5 ppm (sufficient) and 50 ppm (excess) ZnSO4*7H2O. Changes in photosynthetic pigments, soluble proteins, soluble starch, photosystem (PSII) activities and thylakoid membrane proteins were investigated. The degree of photoinhibition was determined by the ratio of variable to maximum chlorophyll (Chl) fluorescence (Fv/Fm). Photosynthetic pigments, soluble proteins and soluble starch decreased significantly in Zn-deficient and Zn-excess leaves. Though the maximum quantum yield of primary photochemistry (Fv/Fm), maximum variable fluorescence (Fv) were significantly decreased to a greater extent in Zn-excess leaves the restoration was excellent. The exogenous electron donors, diphenylcarbazide (DPC) and NH2OH restored the loss of PSII activity in Zn-deficient and Zn-excess leaves. A slight degradation 33, 28-25, 23 and 17 kDa polypeptides were observed in the Zn-deficient and Zn-excess leaves. Upon recovery from HI stress, the Zn-excess leaves restored the 47, 33, and 28-25 kDa polypeptides.

The effects of inhibition of mitochondrial alternative oxidase (AOX) respiratory pathway on photosynthetic apparatus in Rumex K-1 leaves were studied. Under high irradiance, the inhibition of AOX pathway caused over-reduction of photosystem (PS) 2 acceptor side, a decrease in the energy transfer in the PS 2 units, damage of donor side of PS 2 and decrease in pool size of electron acceptors. The inhibition of AOX pathway also decreased photosynthetic performance index (PIABS), actual photochemical efficiency (ΦPS2), photochemical quenching (qP) and photosynthetic O2 evolution rate. The results demonstrate that mitochondrial AOX pathway plays a vital role in photoprotection of photosynthetic apparatus.

Effect of high irradiance (HI) on the activity of antioxidant enzymes, rate of lipid peroxidation and hydrogen peroxide accumulation were investigated in non Bt and Bt cotton. The accumulation of malondialdehyde (MDA) and H2O2 was higher in Bt cotton. Sustained cultivation of Bt cotton requires stable transgene expression under HI stress. In the present study, Bt toxin proteins (Cry1Ac and Cry2Ab), which are essential for the control of lepidopteron pests, were found to be reduced in Bt cotton under HI stress.

* Background The spatial arrangement and expression of foliar syndromes within tree crowns can reflect the coupling between crown form and function in a given environment. Isolated trees subjected to high irradiance and concomitant stress may adjust leaf phenotypes to cope with environmental gradients that are heterogeneous in space and time within the tree crown. The distinct expression of leaf phenotypes among crown positions could lead to complementary patterns in light interception at the crown scale. * Methods We quantified eight light-related leaf traits across 12 crown positions of ten isolated Olea europaea trees in the field. Specifically, we investigated whether the phenotypic expression of foliar traits differed among crown sectors and layers and five periods of the day from sunrise to sunset. We investigated the consequences in terms of the exposed area of the leaves at the tree scale during a single day. * Key Results All traits differed among crown positions except the length-to-width ratio of the leaves. We found a strong complementarity in the patterns of the potential exposed area of the leaves among day periods as a result of a non-random distribution of leaf angles across the crown. Leaf exposure at the outer layer was below 60 % of the displayed surface, reaching maximum interception during morning periods. Daily interception increased towards the inner layer, achieving consecutive maximization from east to west positions within the crown, matching the sun's trajectory. * Conclusions The expression of leaf traits within isolated trees of O. europaea varies continuously through the crown in a gradient of leaf morphotypes and leaf angles depending on the exposure and location of individual leaves. The distribution of light-related traits within the crown and the complementarity in the potential exposure patterns of the leaves during the day challenges the assumption of low trait variability within individuals. [ABSTRACT FROM AUTHOR]

The effects of irradiance and temperature on growth and flowering in seed propagated Sinningia cardinalis especially to increase the number of flowers were investigated. To understand the effect of irradiance on flowering and the number of flowers, seedlings were grown under 30% shade (30% SH), natural irradiance (ND), and ND supplemented with 14 h of high irradiance at 14 W/m 2 (ND + 14HID) at 3 stages (ST) lasted for 40 days (d) at each ST (Expt. 1). Flowering was the earliest (205 d) when 20-d old plants were grown under 30% SH during the entire three stages (July 1 through October 31). Longer than 215 d to flower was required when plants received ND + 14HID during stage 3 (ST 3) (September 21–October 31). The number of flowers was highest (22) when grown under 30% SH during ST 1 (July 1–August 10) followed by ND or ND + 14HID during the ST 2 (August 12–September 20) or ST 3. To investigate the effect of temperature on flowering and the number of flowers, 42 d of 15/13 °C (15 °C), 19/17 °C (19 °C), 23/21 °C (23 °C), and 27/25 °C (27 °C) and under ND + 10HDI were given to 45-d old plants (Expt. 2). The number of days to flower was only significantly accelerated at 23° and 27 °C as compared to 15 °C and 19 °C, but not by irradiance treatments. The highest number of flowers (24) was produced when plants were grown at 15 °C under ND + 10HID given prior to formation of three pairs of leaves (<3L). To further refine the level of reduced of light irradiance on the number of flowers, plants were grown under 45% shade (45% SH), 30% shade (30% SH) from 08:00 to 20:00 h, and ND were given to 128-d old plants between days 0 and 20 (0 and 20), 21 and 40, and 0 and 40 (Expt. 3). The number of flowers (17.6) was significantly increased when grown under 45% SH, especially during the 21–40 d period. To investigate the effect of temperature on plants at visible buds stages, plants were transferred to growth chambers maintained at 18, 21, 24, 27, and 30 °C during the day (0800–1600 h; 35 W/m 2 ) and at 16 °C at night for 42 d (Expt. 4). Flowering was delayed from 100 to 115 d as day temperatures were increased from 18° to 30 °C, and the number of flowers was the highest number (26.5 flowers) at 24 °C. Therefore, to promote flowering and to increase the flower numbers, S. cardinalis should be grown under 30% SH or under ND photoperiod during May–October. At a later stage of flower bud development, temperature rather than irradiance controls the speed of flowering. The differences in flowering time for only 16 d from sowing to flowering may suggest that S. cardinalis can be considered as a day-neutral plant for flower bud initiation. [ABSTRACT FROM AUTHOR]

The current study compares responses to open field and shade enclosure condition (plastic shading nets were used to imitate a natural shading rate) to test the possible benefit of shading in terms of physiological and growth characteristics in Ginkgo biloba L. during the reproductive stage in summer. Compared with the net shade treated plants (NS-plants), the open-field plants (O-plants) contained lower chlorophyll (Chl) a + b content and Chl a/b ratio, and exhibited a decreased ratio of Chl/Car. Results showed that the chlorophyll fluorescence characteristics including maximum PSII photochemical efficiency ( F /F), potential electron transport per excited leaf cross-section (ET/CS), potential electron transport per PSII reaction center (ET/RC), dissipation per excited leaf cross-section (DI/CS), dissipation per PSII reaction center (DI/RC), and overall performance index of PSII photochemistry on absorbtion basis (PI) were altered by the net shade treatment. It was observed that the grana were illegible and difficult to distinguish by transmission electron microscopy, especially, in the cells of O-plants in which phenols were observed in the vacuole. The phenomenon of photoinhibition induced by excessive irradiance was confirmed by the abnormally high levels of the reactive oxygen species. Moreover, antioxidant enzymes activities were induced by high irradiance in the ginkgo leaves. In addition, significant differences were observed in the fresh weight and dry weight of leaves and seeds. Comparison of the variation of underlying physiological and biochemical mechanisms suggested that there was a better efficiency of ginkgo plants under artificial net shade conditions. Therefore, ginkgo plant would be best grown at 30-35 % of natural irradiance in summer months to be more profitably harvested and then meet the increasing demand of leaves and seeds. [ABSTRACT FROM AUTHOR]

Abstract: The presence and activation of MAPK-like proteins in intertidal macroalgae is described in the current study. Two MAPK-like proteins of 40 and 42kDa in size similar to p38 and JNK, of mammalian cells have been identified in six representative species of intertidal macroalgae from the Strait of Gibraltar (Southern Spain), namely in the chlorophytes Ulva rigida and Chaetomorpha aerea, the rhodophytes Corallina elongata and Jania rubens, and the phaeophytes Dictyota dichotoma and Dilophus spiralis. Phosphorylation of MAPK-like proteins was studied during semi-tidal cycles. Analysis of p38-like and JNK-like MAPKs in macroalgae protein extracts was carried out by using specific antibodies against the phosphorylated forms of both MAPKs. Protein blot analysis of samples collected from 2009 to 2011 in natural growing sites on days when either low or high tide occurred at midday, indicated that MAPK-like proteins in all species were highly phosphorylated in response to desiccation imposed by low tide or high irradiance. Phosphorylation of p38-like MAPK always preceded that of JNK-like MAPK. In addition, phosphorylation of MAPKs was fastest in rhodophytes, followed by chlorophytes and then finally phaeophytes. In the first group, phosphorylation was mostly dependent on desiccation, whereas both high irradiance and desiccation were responsible for p38-like and JNK-like phosphorylation in chlorophytes. In phaeophytes, high irradiance was mostly responsible for MAPK-like activation. [Copyright &y& Elsevier]

The effects of boron (B) and high irradiance (HI) on the growth and activities of antioxidant enzymes have been investigated in cowpea plants (Vigna unguiculata L. Walp. ‘P152’). A significant decrease in root and shoot lengths were observed in B-deficient (0 ppm) and B-excess (50 ppm) plants compared to B-sufficient (0.5 ppm) plants. Under B and B + HI stress, significant increase in membrane permeability (EC), lipid peroxidation (MDA) and hydrogen peroxide (H2O2) were observed in B-deficient and B-excess leaves. Under B and B + HI stress, the superoxide dismutase (SOD) activity was found to be significantly high whereas the peroxidase (POX), polyphenol oxidase (PPO) activities and the non-enzymatic antioxidants, ascorbic acid and proline accumulation were found to be significantly decreased in B-deficient and B-excess leaves which showed the B inefficiency and susceptible nature of the cowpea plants to B and B + HI stress. [ABSTRACT FROM AUTHOR]

ABSTRACT Although leaf size is one of the most responsive plant traits to environmental change, the functional benefits of large versus small leaves remain unclear. We hypothesized that modification of leaf size within species resulting from differences in irradiance can allow leaves to acclimate to different photosynthetic or evaporative conditions while maintaining an efficient balance between hydraulic supply (vein density) and evaporative demand. To test this, we compared the function and anatomy of leaf hydraulic systems in the leaves of a woody angiosperm ( Toona ciliata M. Roem.) grown under high and low irradiance in controlled conditions. Our results confirm that in this species, differential leaf expansion regulates the density of veins and stomata such that leaf hydraulic conductance and stomatal conductance remain proportional. A broader sample of field-grown tree species suggested that differences in leaf venation and stomatal traits induced by sun and shade were not regulated by leaf size in all cases. Our results, however, suggest that leaf size plasticity can provide an efficient way for plants to acclimate hydraulic and stomatal conductances to the contrasting evaporative conditions of sun and shade. [ABSTRACT FROM AUTHOR]

The effects of increased photon flux (100 μmol m s), ventilation, and standard in vitro culture (40 μmol m s) with no ventilation were investigated on the physiological and histological characteristics of microshoots of Gevuina avellana. The increase in photon flux (light treatment) produced significant improvement in the fluorescence parameters of photochemical quenching, non-photochemical quenching, electron transport rate and photochemical efficiency of PSII, compared to the ventilation and control treatments. Nursery plants showed similar values compared to the microshoots in the light treatment, indicating that the plants in the light treatment developed a management for dissipating excess light. Moreover, chlorophyll a and b concentrations increased significantly in both light and ventilation treatments. The chl a/chl b ratio decreased in the ventilation treatment compared to the control treatment. Similar results were found for soluble carbohydrates. Finally, both the photon flux increase and ventilation had a positive effect on foliar anatomy, showing a more organized mesophyll and a better development of the palisade mesophyll compared to the control treatment. The changes observed in the microshoots with regards to foliar anatomy and photochemical behavior were very similar to nursery plants. [ABSTRACT FROM AUTHOR]

The effects of inhibition of mitochondrial alternative oxidase (AOX) respiratory pathway on photosynthetic apparatus in Rumex K-1 leaves were studied. Under high irradiance, the inhibition of AOX pathway caused over-reduction of photosystem (PS) 2 acceptor side, a decrease in the energy transfer in the PS 2 units, damage of donor side of PS 2 and decrease in pool size of electron acceptors. The inhibition of AOX pathway also decreased photosynthetic performance index (PI), actual photochemical efficiency (Φ), photochemical quenching (qP) and photosynthetic O evolution rate. The results demonstrate that mitochondrial AOX pathway plays a vital role in photoprotection of photosynthetic apparatus. [ABSTRACT FROM AUTHOR]

Abstract: Zinc (Zn) is a necessary element for plants, but excess Zn can be detrimental. The effect of Zn and high irradiance (HI) stress on the growth, lipid peroxidation (MDA), membrane permeability (EC), hydrogen peroxide (H2O2) accumulation, non-enzymatic antioxidants like proline accumulation and ascorbic acid (AsA) and the activities of major antioxidant enzymes (superoxide dismutase, SOD; peroxidase, POX; polyphenol oxidase, PPO) of bean leaves were investigated under controlled growth conditions. The root length was not reduced at excess Zn level. Application of Zn significantly increased Zn concentration in the leaves of bean plants. Under Zn and HI stress, the Zn-deficient and Zn-excess conditions significantly increased the EC, MDA and H2O2 content of excised leaves of bean. The SOD activity was found to be increased significantly in both Zn-deficiency and Zn-excess leaves under Zn and HI stress. Under both Zn and HI stress conditions, the antioxidant enzyme activities; POX, PPO and the non-enzymatic antioxidants, AsA and proline accumulation were found to be significantly increased in the Zn-excess leaves which showed that the bean plant had the ability to tolerate the excess level of Zn and HI stress. A significant increase in MDA, H2O2, and EC with a simultaneous decrease in the antioxidant enzyme activities under Zn-deficiency compared to Zn-sufficient condition shows the inefficiency of the bean plant in response to Zn deficiency. To the best of our knowledge, this is the first report on the effect of Zn stress combined with HI stress in bean plant. [Copyright &y& Elsevier]

In this study, a cDNA microarray was developed from over 60,000 mRNA readings to analyze the expression profiles of transcriptomes of Haematococcus lacustris under astaxanthin-inducing culture conditions, high irradiance and nitrate starvation. Among 20,033 genes on the cDNA microarray, 2,675 genes exhibited a twofold or greater difference in expression. Of these, 1,333 genes were up-regulated and 1,342 genes were down-regulated. A significant decrease in the expression of chlorophyll biosynthesis and light harvesting complex (LHC) related genes were observed under astaxanthin inducing conditions (forming red cyst cells). On the other hand, respirationrelated genes, lipid metabolism-related genes and stress response-related genes were activated in the red cyst cells under stress conditions. These results enabled a better understanding of the cell responses during stress induction of H. lacustris such as photosynthesis, respiration, and some biopathways. [ABSTRACT FROM AUTHOR]

Abstract: The widespread use of NO3 − fertilization has had a major ecological impact. NH4 + nutrition may help to reduce this impact, although high NH4 + concentrations are toxic for most plants. The underlying tolerance mechanisms are not yet fully understood, although they are thought to include the limitation of C, the disruption of ion homeostasis, and a wasteful NH4 + influx/efflux cycle that carries an extra energetic cost for root cells. In this study, high irradiance (HI) was found to induce a notable tolerance to NH4 + in the range 2.5–10mM in pea plants by inducing higher C availability, as shown by carbohydrate content. This capacity was accompanied by a general lower relative N content, indicating that tolerance is not achieved through higher net N assimilation on C-skeletons, and it was also not attributable to increased GS content or activity in roots or leaves. Moreover, HI plants showed higher ATP content and respiration rates. This extra energy availability is related to the internal NH4 + content regulation (probably NH4 + influx/efflux) and to an improvement of the cell ionic balance. The limited C availability at lower irradiance (LI) and high NH4 + resulted in a series of metabolic imbalances, as reflected in a much higher organic acid content, thereby suggesting that the origin of the toxicity in plants cultured at high NH4 + and LI is related to their inability to avoid large-scale accumulation of the NH4 + ion. [Copyright &y& Elsevier]

Large-scale RNA profiling revealed that high irradiance differentially regulated 577 out of 1,439 non-redundant genes of the Antarctic marine diatom Chaetoceros neogracile, represented on a custom cDNA chip, during 6 h of treatment. Among genes that were up- or down-regulated more than twofold within 30 min of treatment (310/1,439), about half displayed an acclimatory response during 6 h under high light. Expression of the remaining non-acclimatory genes also rapidly returned to initial levels within 30 min following a shift to low irradiance. High light altered expression of most of the photosynthesis genes (48/70), in contrast to genes in other functional categories. In addition, opposite response patterns were provoked in genes encoding fucoxanthin chlorophyll a/ c binding protein (FCP), the main component of the diatom light-harvesting complex; high irradiance caused a decrease in expression of most FCP genes, but drove the rapid and specific up-regulation of ten others. C. neogracile responded very promptly to a change in light intensity by rapidly adjusting the transcript levels of FCP genes up-regulated by high light, and these dynamic adjustments coincided well with diatoxanthin (Dtx) levels formed by the xanthophyll cycle under the same conditions. The observation that the non-photochemical quenching (NPQ) capacity of this polar diatom was highly dependent on Dtx, which could bind to FCP and trigger NPQ, suggests that the up-regulated FCP gene products may participate in a photoprotective process as Dtx-binding proteins. [ABSTRACT FROM AUTHOR]

[Display omitted] • Realization of high flux transmission via plastic optical fiber. • Combination of infrared filter and liquid water to filter infrared light in the range of 780–2500 nm. • Plastic optical fiber avoiding overheating under 2000 suns. Due to low cost and flexibility, Polymethylmethacrylate (PMMA) plastic optical fibers were widely used in the daylighting system. However, the overheating damage caused by infrared thermal effects has seriously affected the safety of PMMA optical fibers. To solve this problem, this work experimented three configurations in Tibet, which include homogenizer, infrared light filter, and liquid water. The analysis showed that the infrared light filter and liquid water are complementary in filtering infrared light, which filter infrared light in the range of 780–1100 nm and 1100–2500 nm respectively. The experimental results demonstrated that the PMMA optical fibers can transmit high solar flux safely under the combined protection of homogenizer, infrared light filter, and liquid water. [ABSTRACT FROM AUTHOR]

Fucus vesiculosus from the northern Baltic Sea (5 psu) and from the Irish Sea (35 psu) were cultivated at different temperatures, salinities and dissolved inorganic carbon (DIC) concentrations with the addition of different nutrient concentrations. The influence of these abiotic factors was assessed by measuring photosynthesis as electron transport rate (ETR) and growth as relative growth rate (RGR). The maximal ETR and the RGR of the Irish Sea plants in their natural seawater (50.8 µmol electrons m-2 s-1; 0.024 g g-1 day-1) were significantly higher than those of the Baltic plants in their natural seawater (21.9 µmol electrons m-2 s-1; 0.007 g g-1 day-1). When Baltic F. vesiculosus was cultivated at a DIC concentration similar to that of the Irish Sea, the ETR as well as RGR increased, but never equalled the rates of the marine F. vesiculosus from the Irish Sea. Cultivation at different salinities showed that F. vesiculosus from the Baltic has a higher ETRmax and RGR at low salinities (5-10 psu) than F. vesiculosus from the Irish Sea, whose ETR and RGR decreased sharply in salinities below 20 psu. Plants from both sites grown at high nutrient concentrations, however, performed better at low salinities than those grown under low nutrient conditions. Salinity had the greatest impact on differences in ETR and RGR between the two populations, followed by differences in DIC and nutrient concentrations. There was a highly significant correlation between ETRmax and RGR in plants from both sites and across the full range of culture conditions, indicating that the same amount of energy from photosynthesis is used for growth in both varieties of the species at different salinities. The photosynthesis of F. vesiculosus in the northern Baltic is close to the minimum demand for growth, which may account for their small size. The temperature optimum for F. vesiculosus from the Baltic was 4-10°C, while that for F. vesiculosus from the Irish Sea was 15-20°C. The photosynthesis of Irish Sea plants was less strongly affected by exposure to high irradiances than that of plants from the Baltic. [ABSTRACT FROM AUTHOR]

Under 30-min high irradiance (1500 μmol m−2 s−1), the roles of the xanthophyll cycle and D1 protein turnover were investigated through chlorophyll fluorescence parameters in morning glory ( Ipomoea setosa) leaves, which were dipped into water, dithiothreitol (DTT) and lincomycin (LM), respectively. During the stress, both the xanthophyll cycle and D1 protein turnover could protect PSI from photoinhibition. In DTT leaves, non-photochemical quenching (NPQ) was inhibited greatly and the oxidation level of P700 (P700+) was the lowest one. However, the maximal photochemical efficiency of PSII (Fv/Fm) in DTT leaves was higher than that of LM leaves and was lower than that of control leaves. These results suggested that PSI was more sensitive to the loss of the xanthophyll cycle than PSII under high irradiance. In LM leaves, NPQ was partly inhibited, Fv/Fm was the lowest one among three treatments under high irradiance and P700+ was at a similar level as that of control leaves. These results implied that inactivation of PSII reaction centers could protect PSI from further photoinhibition. Additionally, the lowest of the number of active reaction centers to one inactive reaction center for a PSII cross-section (RC/CSo), maximal trapping rate in a PSII cross-section (TRo/CSo), electron transport in a PSII cross-section (ETo/CSo) and the highest of 1-qP in LM leaves further indicated that severe photoinhibition of PSII in LM leaves was mainly induced by inactivation of PSII reaction centers, which limited electrons transporting to PSI. However, relative to the LM leaves the higher level of RC/CSo, TRo/CSo, Fv/Fm and the lower level of 1-qP in DTT leaves indicated that PSI photoinhibition was mainly induced by the electron accumulation at the PSI acceptor side, which induced the decrease of P700+ under high irradiance. [ABSTRACT FROM AUTHOR]

Net photosynthetic rate ( PN), transpiration rate ( E), water use efficiency (WUE), stomatal conductance ( gs), and stomatal limitation (Ls) were investigated in two Syringa species. The saturation irradiance (SI) was 400 µmol m-2s-1 for S. pinnatifolia and 1 700 µmol m-2s-1 for S. oblata. Compared with S. oblata, S. pinnatifolia had extremely low g s. Unlike S. oblata, the maximal photosynthetic rate ( Pmax) in S. pinnatifoliaoccurred around 08:00 and then fell down, indicating this species was sensitive to higher temperature and high photosynthetic photon flux density. However, such phenomenon was interrupted by the leaf development rhythms before summer. A relatively lower PN together with a lower leaf area and shoot growth showed the capacity for carbon assimilation was poorer in S. pinnatifolia. [ABSTRACT FROM AUTHOR]

The effect of a short cold stress in combination with photoinhibition stress, similar to a low temperature and a high irradiance situation during early morning in the spring time, was examined on four maize cultivars common for Belgium, that differ in early vigour. After 1 h of 2 °C and 500 μmol(photon) m−2 s−1, quantum efficiency and maximum photosynthesis rate at saturating irradiance decreased on average by 11 and 8 %, respectively. For one cultivar, Magister, the decrease was the largest: by 23 and 10 %, respectively. For this cultivar it was combined with a decrease of the water vapour conductance after the stress. The decrease of Fv/F0 due to the cold/light stress was dependent on the cold tolerance (early vigour) of the cultivars. Fv/F0 changed with −45.5 and −40.2 % for the cultivars Ardiles and Banguy, respectively (cultivars with a less good early vigour) in comparison to −36.3 and −35.9 % for Fjord and Magister, which have a good early vigour. Also the ratio of total chlorophylls/total carotenoids changed in dependence on cold tolerance of the cultivars. For more cold tolerant cultivars, the relative amount of total carotenoids (x+c) was higher, indicating a higher protective state. Both the parameter Fv/F0 and the ratio of total chlorophylls to total carotenoids can be used to differentiate the cold tolerant cultivars from the cold non-tolerant ones. Fv/F0 has the advantage because its resolving power is larger and the measurement is less expensive than determination of the pigment ratio. [ABSTRACT FROM AUTHOR]

An account is given of the setting up and use of a novel type of closed tubular photobioreactor at the Academic and University Centre in Nove Hrady, Czech Republic. This "penthouse-roof" photobioreactor was based on solar concentrators (linear Fresnel lenses) mounted in a climate-controlled greenhouse on top of the laboratory complex combining features of indoor and outdoor cultivation units. The dual-purpose system was designed for algal biomass production in temperate climate zone under well-controlled cultivation conditions and with surplus solar energy being used for heating service water. The system was used to study the strategy of microalgal acclimation to supra-high solar irradiance, with values as much as 3.5 times the ambient value, making the approach unique. The cultivation system proved to be fully functional with sufficient mixing and cooling, efficient oxygen stripping and light tracking. Experimental results (measurement of the maximum photochemical yield of PSII and non-photochemical quenching) showed that the cyanobacterium Spirulina (= Arthrospira) platensis cultivated under sufficient turbulence and biomass density was able to acclimate to irradiance values as high as 7 mmol photon m−2 s−1. The optimal biomass concentration of Spirulina cultures in September ranged between 1.2 to 2.2 g L−1, which resulted in a net productivity of about 0.5 g L−1 d−1 corresponding to a biomass yield of 32.5 g m−2 d−1 (based on the minimum illuminated surface area of the photobioreactor). [ABSTRACT FROM AUTHOR]

Exposure of plants to irradiation, in excess to saturate photosynthesis, leads to reduction in photosynthetic capacity without any change in bulk pigment content. This effect is known as photoinhibition. Photoinhibition is followed by destruction of carotenoids (Cars), bleaching of chlorophylls (Chls), and increased lipid peroxidation due to formation of reactive oxygen species if the excess irradiance exposure continues. Photoinhibition of photosystem 2 (PS2) in vivo is often a photoprotective strategy rather than a damaging process. For sustainable maintenance of chloroplast function under high irradiance, the plants develop various photoprotective strategies. Cars perform essential photoprotective roles in chloroplasts by quenching the triplet Chl and scavenging singlet oxygen and other reactive oxygen species. Recently photoprotective role of xanthophylls (zeaxanthin) for dissipation of excess excitation energy under irradiance stress has been emphasised. The inter-conversion of violaxanthin (Vx) into zeaxanthin (Zx) in the light-harvesting complexes (LHC) serves to regulate photon harvesting and subsequent energy dissipation. De-epoxidation of Vx to Zx leads to changes in structure and properties of these xanthophylls which brings about significant structural changes in the LHC complex. This ultimately results in ( 1) direct quenching of Chl fluorescence by singlet-singlet energy transfer from Chl to Zx, ( 2) trans-thylakoid membrane mediated, ΔpH-dependent indirect quenching of Chl fluorescence. Apart from these, other processes such as early light-inducible proteins, D1 turnover, and several enzymatic defence mechanisms, operate in the chloroplasts, either for tolerance or to neutralise the harmful effect of high irradiance. [ABSTRACT FROM AUTHOR]

Field studies of gas exchange and chlorophyll fluorescence of three desert shrub species, Hedysarum fruticosum var. mongolicum, Artemisia ordosia, and Salix pasmmophylla, showed different patterns under different leaf temperature (T1) and incident photosynthetic photon flux density (PPFD). H. fruticosum var. mongolicum and A. ordosia exhibited higher PN and gs than S. pasmmophylla, especially under very high T1 (>46 °C) and high PPFD (>2 100 µmol m−2 s−1) in hot summer. The decreases of PN with the diurnal course were due mainly to stomata closure. However, PN of S. pasmmophylla was seriously depressed by very high temperature from midday to evening as shown by the negative PN in hot summer, whereas none of such depression was found in spring. Maximal spring photochemical efficiency of photosystem 2 (PS2), i.e, Fv/Fm, was the lowest at 16:00, indicating the injury of PS2 by heat at this stage. In hot summer again, all the three shrubs underwent pronounced midday depression of PN and gs, while in spring they showed a one-peak response. And the first peak appeared 2 h earlier in hot summer than in spring for all the three shrubs. It was the high temperature that led to the different patterns of gas exchange and the serious depression of PN in S. pasmmophylla. H. fruticosum var. mongolicum and A. ordosia were much more tolerant to heat and high irradiance than S. pasmmophylla, which fixed most of CO2 at the fast growing stage in spring. Nevertheless, in hot summer it had to survive the severe hot environment through strong respiration and storage of CO2 only in the early morning. [ABSTRACT FROM AUTHOR]

Spatial heterogeneity of chlorophyll (Chl) fluorescence over thalli of three foliose lichen species was studied using Chl fluorescence imaging (CFI) and slow Chl fluorescence kinetics supplemented with quenching analysis. CFI values indicated species-specific differences in location of the most physiologically active zones within fully hydrated thalli: marginal thallus parts ( Hypogymnia physodes), central part and close-to-umbilicus spots ( Lasallia pustulata), and irregulary-distributed zones within thallus ( Umbilicaria hirsuta). During gradual desiccation of lichen thalli, decrease in Chl fluorescence parameters (FO - minimum Chl fluorescence at point O, FP - maximum Chl fluorescence at P point, Φ2 - effective quantum yield of photochemical energy conversion in photosystem 2) was observed. Under severe desiccation (>85 % of water saturation deficit), substantial thalli parts lost their apparent physiological activity and the resting parts exhibited only a small Chl fluorescence. Distribution of these active patches was identical with the most active areas found under full hydration. Thus spatial heterogeneity of Chl fluorescence in foliose lichens may reflect location of growth zones (pseudomeristems) within thalli and adjacent newly produced biomass. When exposed to high irradiance, fully-hydrated thalli of L. pustulata and U. hirsuta showed either an increase or no change in FO, and a decrease in FP. Distribution of Chl fluorescence after the high irradiance treatment, however, remained the same as before the treatment. After 60 min of recovery in the dark, FO and FP did not recover to initial values, which may indicate that the lichen used underwent a photoinhibition. The CFI method is an effective tool in assessing spatial heterogeneity of physiological activity over lichen thalli exposed to a variety of environmental factors. It may be also used to select a representative area at a lichen thallus before application of single-spot fluorometric techniques in lichens. [ABSTRACT FROM AUTHOR]

The mechanistic basis for protection of exogenous ascorbate against photoinhibition at low temperature was examined in leaves of rice ( Oryza sativa L.). Exposure of intact leaves to chilling temperature resulted in a drastic decrease in the speed of development of non-photochemical fluorescence quenching (NPQ). This was related to the low temperature-imposed restriction on the formation of the fast relaxing component of NPQ (qf). Feeding with 20 mM ascorbate markedly increased the rate of qf development at chilling temperature due primarily to the enhanced rate of zeaxanthin (Z) formation. On the other hand, ascorbate feeding had no influence on photosystem 2 (PS2)-driven electron flow. The reduced state of the PS2 primary electron acceptor QA decreased in ascorbate-fed leaves exposed to high irradiance at chilling temperature owing to the increased Z-associated thermal energy dissipation in the light-harvesting antenna system of PS2. Furthermore, ascorbate feeding increased the photosynthetic apparatus of rice leaves to resist photoinhibition at low temperature. The protective effect of exogenous ascorbate was fully accounted for by the enhanced xanthophyll cycle activity. [ABSTRACT FROM AUTHOR]

Long-term drought stress on photosystem II (PSII) was studied in pea ( Pisum sativum L.) seedlings. Drought stress (reduction of water content by 35-80%) led to a considerable depletion of the PSII core, and the remaining PSII complex appeared to be functional and reorganized, with a unit size (LHCP/PSII core) twofold greater than that of well-irrigated plants. By immunoblotting analysis of the PSII proteins from grana and stroma lamellae, the enhanced degradation of CP43 and D1 proteins was observed in water-stressed plants. Also, water stress caused increased phosphorylation of the PSII core and increased D1 protein synthesis. Water-stress-mediated increase in D1 synthesis did not occur when plants were exposed to photoinhibitory light. The depletion of the PSII core was essentially reversed when water-stressed plants grown at low visible irradiance were watered. We suggest that the syndrome caused by the effect of long-term water stress on photosynthesis is a combination of at least two events: a reduction in the number of active PSII centres caused by a physical destabilization of the PSII core and a PSII reorganization with enhanced D1 turnover to counteract the core depletion. [ABSTRACT FROM AUTHOR]

Vanilla orchid, which is well-known for its flavor and fragrance, is cultivated in tropical and subtropical regions. This shade-loving plant is very sensitive to high irradiance. In this study, we show that vanilla chloroplasts started to have avoidance movement when blue light (BL) was higher than 20 μmol m−2s−1 and significant avoidance movement was observed under BL irradiation at 100 μmol m−2s−1 (BL100). The light response curve indicated that when vanilla was exposed to 1000 μmol m−2s−1, the electron transport rate (ETR) and photochemical quenching of fluorescence (qP) were significantly reduced to a negligible amount. We found that if a vanilla orchid was irradiated with BL100 for 12 days, it acquired BL-acclimation. Chloroplasts moved to the side of cells in order to reduce light-harvesting antenna size, and chloroplast photodamage was eliminated. Therefore, BL-acclimation enhanced vanilla orchid growth and tolerance to moderate (500 μmol m−2s−1) and high light (1000 μmol m−2s−1) stress conditions. It was found that under high irradiation, BL-acclimatized vanilla maintained higher ETR and qP capacity than the control without BL-acclimation. BL-acclimation induced antioxidant enzyme activities, reduced ROS accumulation, and accumulated more carbohydrates. Moreover, BL-acclimatized orchids upregulated photosystem-II-associated marker genes (D1 and PetC), Rubisco and PEPC transcripts and sustained expression levels thereof, and also maximized the photosynthesis rate. Consequently, BL-acclimatized orchids had higher biomass. In short, this study found that acclimating vanilla orchid with BL before transplantation to the field might eliminate photoinhibition and enhance vanilla growth and production. [ABSTRACT FROM AUTHOR]