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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]