Effect Of High Light Intensity Research Articles

The content of phenols and activity of polyphenol oxidase in the hametophyte of dominant mosses in forest ecosystems of the Ukrainian Roztochia

Bryophytes are indicators of the state of forest ecosystems. Dominant species of forest mosses are sensitive to the influence of abiotic factors and demonstrate adaptive reactions different from vascular plants, which are decisive for the prediction of changes in the natural environment. We have analyzed the changes in the content of water-soluble phenols and the activity of polyphenol oxidase n the hametophyte of dominant epigean forest mosses depending on changes in the intensity of insolation, the water and temperature regime of soils and air in experimental localities of forest ecosystems of the Ukrainian Roztochia. The highest content of water-soluble phenolic compounds was found in the resistant mosses Polytrichum formosum and Atrichum undulatum on the territory of protected beech forest under conditions of low light intensity and sufficient humidity of local vegetation. The maximum indicators of the content of phenolic compounds were found in A. undulatum (199.5±9.8 μg/g of dry matter mass), and the lowest – in Plagiomnium affine (54.7±2.6 μg/g of dry matter mass) that is sensitive to changes in the ecological conditions of local vegetation in all studied areas. A significant decrease in the content of phenolic compounds in areas of disturbed ecosystems may indicate the active participation of phenols in the adaptation of mosses to the effects of high light intensity, elevated temperatures and moisture deficit. The highest indicators of polyphenol oxidase activity were determined in P. affine (120.4±6.1 relative units/g of dry matter mass*s) and P. formosum (41.8±2.1 relative units/g of dry matter mass*s) from local vegetation under unfavorable conditions on the territory of stationary recreation. A direct correlation between the content of phenolic compounds and the activity of polyphenol oxidase was not established. The higher activity of this enzyme under conditions of high light intensity than in shaded local plants may indicate a relationship between polyphenol oxidase and photosynthesis. An increase in the activity of polyphenol oxidase contributes to the significant formation of quinones, which, accumulating in cell walls, reduce the processes of lipid peroxidation, regulate their permeability and ensure better moisture storage in the moss turfs.

Genotype‐dependent Strategies to “Overcome” Excessive Light: Insights into Non‐Photochemical Quenching under High Light Intensity

AbstractHigh light (HL) intensities have a significant impact on energy flux and distribution within photosynthetic apparatus. To understand the effect of high light intensity (HL) on the HL tolerance mechanisms in tomatoes, we examined the response of the photosynthesis apparatus of 12 tomato genotypes to HL. A reduced electron transfer per reaction center (ET0/RC), an increased energy dissipation (DI0/RC) and non‐photochemical quenching (NPQ), along with a reduced maximum quantum yield of photosystem II (FV/FM), and performance index per absorbed photon (PIABS) were common HL‐induced responses among genotypes; however, the magnitude of those responses was highly genotype‐dependent. Tolerant and sensitive genotypes were distinguished based on chlorophyll fluorescence and energy‐quenching responses to HL. Tolerant genotypes alleviated excess light through energy‐dependent quenching (qE), resulting in smaller photoinhibitory quenching (qI) compared to sensitive genotypes. Quantum yield components also shifted under HL, favoring the quantum yield of NPQ (ՓNPQ) and the quantum yield of basal energy loss (ՓN0), while reducing the efficient quantum yield of PSII (ՓPSII). The impact of HL on tolerant genotypes was less pronounced. While the energy partitioning ratio did not differ significantly between sensitive and tolerant genotypes, the ratio of NPQ components, especially qI, affected plant resilience against HL. These findings provide insights into different patterns of HL‐induced NPQ components in tolerant and sensitive genotypes, aiding the development of resilient crops for heterogeneous light conditions.

Light Intensity and Photoperiod Interaction Affects the Survival, Development, Molting and Apoptosis-Related Genes of Swimming Crab Portunus trituberculatus Larvae

A 19-day experiment was conducted to investigate the optimal light intensity and photoperiod combination for larval swimming crabs Portunus trituberculatus in terms of survival, development, and apoptosis-related gene expression. Two photoperiods, i.e., 12 and 18 h photophases, and three light intensities, i.e., 126.08, 173.17, and 191.53 μmol m−2 s−1, were used in the study. The results showed that the cumulative survival rate (CSR) of larvae decreased with the increasing light intensity, and the adverse effect of high light intensity was only observed in long photophase groups. On the contrary, a long photophase and low light intensity elevated the CSR from zoea III to juvenile crabs. A long photophase also accelerated the development of zoea III larvae and upregulated the molting-related (ecr and rxr) and apoptosis-related (jnk, p53, and bcl-2) gene expressions. Taken together, the present study suggested that the light intensity and the photoperiod had a combined effect on P. trituberculatus larvae. The optimal light intensity and photoperiod for P. trituberculatus larvae were 126.08 μmol m−2 s−1 and an 18 h photophase, respectively.

Foliar applied titanium dioxide nanoparticles (TiO2 NPs) modulate growth, physiological and phytochemical traits in Melissa officinalis L. under various light intensities

Lemon balm (Melissa officinalis L.) is a valuable medicinal plant belonging to the mint family Lamiaceae with different uses in the food, cosmetic-hygienic, and pharmaceutical industries. Therefore, it is crucial to identify novel factors affecting growth, yield, and phytochemical compounds of this plant. In the current study, titanium dioxide (TiO2) nanoparticles (NPs) were foliarly applied at different concentrations (0, 50, and 100 mg L−1) following various light intensities (full (control), 75% and 50% sunlight) on lemon balm in a factorial experiment based on randomized complete block design (RCBD) with three replications (n = 3) for two continues years. IAnalytical techniques, SEM and EDX analyses, confirmed the uptake of TiO2 NPs through aerial parts of plant. Output of shoot dry weight, chlorophyll a (Chl-a) content, and total Chl and relative water content (RWC) were at their highest levels on plants grown at 50% light intensity upon foliar application of TiO2 NPs (100 mg L−1) in both years. High shading (50% of light intensity) without TiO2 NPs application markedly reduced EO content (by 60%), when compared to full solar radiation and exposure to TiO2 NPs (at 50 and 100 mg L−1) during two experimental years. Neral and geranial were the two main components of EO, with 30.7% and 45.05% in the first year of experiment, followed by 30.24% and 43.03% in full light intensity under 100 mg L−1 TiO2 NPs applications in the second year, respectively. Thus, a relatively shady environment and 100 mg L−1 TiO2 NPs foliar spray are recommended to attain a higher yield in lemon balm plants. Key findings of this study revealed the beneficial effects of high light intensity with TiO2 NPs foliar spray to improve the quality and quantity output of EO rich in neral and geranial constituents.

Production of astaxanthin, ethanol and methane from Chromochloris zofingiensis microalga in an integrated biorefinery

Astaxanthin-rich carotenoids were produced from Chromochloris zofingiensis green alga through an integrated biorefinery. Simultaneous effects of high light intensity and nitrogen starvation resulted in the production of 10.2 mg total carotenoids per g biomass, including 80 % astaxanthin. A novel extraction method employing ultrasonic-milling pretreatment was then used to reduce the extraction time (33.5 min) and the amount of utilized solvent (30 mL ethanol per 1 g biomass). The extraction method provided the residual biomass with the same anaerobic digestibility as the raw biomass, accumulating 315 mL/g VS methane. Additionally, the residual biomass was hydrolyzed with four commercial enzymes providing a high glucose yield (78.2 %). Overall, the biorefinery consisted of producing ethanol from the algal biomass hydrolysate and biomethane from solids remaining after hydrolysis. Also, fermentation resulted in 8260 kJ energy, in addition to 10.2 g carotenoids from 1 kg biomass.

Warmer water, high light intensity, lithium and microplastics: Dangerous environmental combinations to zooplankton and Global Health?

Nowadays there is a high concern about the combined effects of global warming and emerging environmental contaminants with significant increasing trends of use, such as lithium (Li) and microplastics (MPs), both on wildlife and human health. Therefore, the effects of high light intensity (26,000 lx) or warmer water temperature (25 °C) on the long-term toxicity of Li and mixtures of Li and MPs (Li-MPs mixtures) were investigated using model populations of the freshwater zooplankton species Daphnia magna. Three 21-day bioassays were done in the laboratory at the following water temperatures and light intensities: (i) 20 °C/10830 lx; (ii) 20 °C/26000 lx (high light intensity); (iii) 25 °C/10830 lx (warmer temperature). Based on the 21-day EC50s on reproduction, high light intensity increased the reproductive toxicity of Li and Li-MPs mixtures by ~1.3 fold; warmer temperature increased the toxicity of Li by ~1.2 fold, and the toxicity of Li-MPs mixtures by ~1.4 fold based on the concentration of Li, and by ~2 fold based on the concentrations of MPs. At high light intensity, Li (0.04 mg/L) and Li-MPs mixtures (0.04 Li + 0.09 MPs mg/L) reduced the population fitness by 32 % and 41 %, respectively. Warmer temperature, Li (0.05 mg/L) and Li-MPs mixtures (0.05 Li + 0.09 MPs mg/L) reduced it by 63 % and 71 %, respectively. At warmer temperature or high light intensity, higher concentrations of Li and Li-MPs mixtures lead to population extinction. Based on the population growth rate and using data of bioassays with MPs alone done simultaneously, Li and MPs interactions were antagonistic or synergistic depending on the scenario. High light intensity and chemical stress generally acted synergistically. Warmer temperature and chemical stress always acted synergistically. These findings highlight the threats of long-term exposure to Li and Li-MPs mixtures to freshwater zooplankton and Global Health in a warmer world.

PeVDE, a violaxanthin de-epoxidase gene from moso bamboo, confers photoprotection ability in transgenic Arabidopsis under high light.

Plants employ an array of photoprotection mechanisms to alleviate the harmful effects of high light intensity. The violaxanthin cycle, which is associated with non-photochemical quenching (NPQ), involves violaxanthin de-epoxidase (VDE), and zeaxanthin epoxidase (ZEP) and is one of the most rapid and efficient mechanisms protecting plants under high light intensity. Woody bamboo is a class of economically and ecologically important evergreen grass species widely distributed in tropical and subtropical areas. However, the function of VDE in bamboo has not yet been elucidated. In this study, we found that high light intensity increased NPQ and stimulated the de-epoxidation of violaxanthin cycle components in moso bamboo (Phyllostachys edulis), whereas, samples treated with the VDE inhibitor (dithiothreitol) exhibited lower NPQ capacity, suggesting that violaxanthin cycle plays an important role in the photoprotection of bamboo. Further analysis showed that not only high light intensity but also extreme temperatures (4 and 42°C) and drought stress upregulated the expression of PeVDE in bamboo leaves, indicating that PeVDE is induced by multiple abiotic stresses. Overexpression of PeVDE under the control of the CaMV 35S promoter in Arabidopsis mutant npq1 mutant could rescue its NPQ, indicating that PeVDE functions in dissipating the excess absorbed light energy as thermal energy in bamboo. Moreover, compared with wild-type (Col-0) plants, the transgenic plants overexpressing PeVDE displayed enhanced photoprotection ability, higher NPQ capacity, slower decline in the maximum quantum yield of photosystem II (Fv/Fm) under high light intensity, and faster recovery under optimal conditions. These results suggest that PeVDE positively regulates the response to high light intensity in bamboo plants growing in the natural environment, which could improve their photoprotection ability through the violaxanthin cycle and NPQ.

Heatwave breaks down the linearity between sun-induced fluorescence and gross primary production.

Sun-induced fluorescence in the far-red region (SIF) is increasingly used as a remote and proximal-sensing tool capable of tracking vegetation gross primary production (GPP). However, the use of SIF to probe changes in GPP is challenged during extreme climatic events, such as heatwaves. Here, we examined how the 2018 European heatwave (HW) affected the GPP-SIF relationship in evergreen broadleaved trees with a relatively invariant canopy structure. To do so, we combined canopy-scale SIF measurements, GPP estimated from an eddy covariance tower, and active pulse amplitude modulation fluorescence. The HW caused an inversion of the photosynthesis-fluorescence relationship at both the canopy and leaf scales. The highly nonlinear relationship was strongly shaped by nonphotochemical quenching (NPQ), that is, a dissipation mechanism to protect from the adverse effects of high light intensity. During the extreme heat stress, plants experienced a saturation of NPQ, causing a change in the allocation of energy dissipation pathways towards SIF. Our results show the complex modulation of the NPQ-SIF-GPP relationship at an extreme level of heat stress, which is not completely represented in state-of-the-art coupled radiative transfer and photosynthesis models.

Combined high light and heat stress induced complex response in tomato with better leaf cooling after heat priming

Light and temperature are two primary environmental factors for plant growth and development. The response of plants to multiple stresses of high light intensity and heat stress are complex. The priming effects of high light and heat stress on improving heat tolerance of plants need to be further illuminated. This study aimed to explain the effect of high light intensity, high temperature and their combination on tomato and clarify the response of tomato to heat stress after priming. Tomato plants were treated under control, high light, heat stress and the combination for the first-round treatments, followed by recurring heat stress as the second-round treatments. For the first-round treatments, the net photosynthetic rate (PN) of the plants at individual high light and individual high temperature on day four significantly increased and decreased, respectively, as compared with control. Combined stress caused significant reduction in Fv/Fm (maximum quantum efficiency of photosystem II) and chlorophyll content as well as increase in carotenoids and carbohydrates content. No significant difference in the PN was observed in tomato with and without priming; however, heat priming did improve the heat avoidance ability by increasing evaporation and decreasing leaf temperature. Overall, the high light affected the physiological response of tomatoes at heat stress. The tomato plants developed their defense systems including chlorophyll loss and synthesis of carotenoids to protect themselves from multiple stresses. Our work provided new insights into the understanding of plants response to high light and heat stress.

Effects of high light intensity on egg weight loss, hatchability, embryonic mortality, and supply organ weight at hatch in quail hatching eggs during incubation

The aim of this study is to investigate the effects of high light intensity on egg weight loss, hatchability, embryonic mortality, and supply organ weights at hatch in Japanese quail ( Coturnix coturnix japonica ) eggs. A total of 640 hatching eggs were randomly distributed into 2 groups. The first group of eggs were continuously incubated in the dark (Control; C), the second group of eggs were incubated in continuous light(L), the third group of eggs were incubated in the dark for the first five days of incubation (D5), and the last group were incubated in the light for the first five days in the eggs (L5). The light intensity at the surface of the eggshell varied from 5000 to 6000 lux as measured with a luxmeter. No significant differences were found in egg weight loss, hatchability, and supply organ weight among treatments. Embryonic mortality were higher in the L5 group than in the control group at 10 to 16 days of incubation. These results demonstrate that high light application during incubation affected the embryonic mortality negatively except hatchability and egg weight loss.

Effects of High Light Intensity on Incubation Results in Quail Hatching Eggs during Incubation Period

The purpose of this experiment was to establish the effects of high light intensity application during embryogenesis on incubation results in Japanese quail ( Coturnix coturnix japonica ) eggs. A total of 360 hatching eggs were randomly divided into 2 groups. The quail eggs (n= 360) were incubated 0L+24D (C) and 24L+0D at 2900 lux (L) during the first 14 days of incubation. There were no significant (P>0.05) differences in hatchability and embryonic mortality among treatments groups. The incubation time in the light-treated group was shorter than C group. The higher hatching was observed in L group at 390 to 416 h of incubation than the C group (P<0.01). No significant differences were found between C and L group at other hatching times. These results demonstrate that continuous high light application during incubation affected the hatch time positively without adversely affecting hatchability or embryonic mortality.

Effect of high light intensity on the photosynthetic apparatus of two hybrid lines of Paulownia grown on soils with different salinity

The objective of this investigation was to evaluate the simultaneous action of light stress and salinity. Pulse amplitude modulated chlorophyll fluorescence, P700 redox state, and pigment analysis were used to assess the impact of high light intensity on Paulownia tomentosa × fortunei and Paulownia elongata × elongata grown on soils with different salinity. It was found that light stress reduced the amount of pigments and the efficiency of photochemical energy conversion, inhibited the maximum and the effective quantum yields of PSII photochemistry, decreased photochemical quenching and photosynthetic rate. Data also showed influence on the primary quinone acceptor (QA) reoxidation, which led to the restriction of the electron flow from QA to plastoquinone and stimulation of the cyclic electron flow. The possible reasons for the increased effects of the light stress under conditions of high salt concentration in soil for Paulownia tomentosa × fortunei are discussed.

荒漠短命植物的养分含量与荧光特征初探

短命植物作为荒漠植被类群中的独特类型，植物叶片的荧光生理特征和养分含量之间具有极高的相关性。分别选取5种典型短命植物东方旱麦草(Eremopyrum orientale)、卷果涩芥(Malcolmia scorpioides)、狭果鹤虱(Lappula semiglabra)、四齿芥(Tetracme quadricormis)和硬萼软紫草(Arnebiade cumbens)自然生长比较一致的叶片作为研究材料，对叶片的叶绿素和养分含量以及荧光光响应进行了测定。结果表明，短命植物的叶绿素总量为1.24~2.67 mg∙g−1之间，叶绿素a、b含量之比达到5.80~12.86。叶片含N量在3.1%以上，含P量为0.22%~0.30%，含K量在3.15%~6.24%。短命植物的实际光化学量子产量ΦPSII平均在0.4以上，ETR受光强的抑制不明显，当光合有效辐射值超过1400 mol∙m−2∙s−1时，出现下降。 Ephemerals, including annual ephemerals and ephemeroid plants, are characterized by short- term growth rhythms and specific biological traits adapted to deserts or temperate broad-leaved deciduous forests. Their fluorescence physical characteristics had a significant correlation with their leaf contents. The chlorophyll content, nutrient content and response of the photosynthetic characteristics to the simulated light environmental changes of five desert ephemerals, Eremopyrum orientale, Malcolmia scorpioides, Lappula semiglabra, Tetracme quadricormis and Arnebiade cumbens, which distributed in Northwestern China, were investigated. The results showed that the chlorophyll content of ephemerals was between 1.24 and 2.67 mg∙g−1, with extremely high chla/ chlb values reaching 5.80 - 12.86. Ephemerals growing in barren desert had extremely high nutrient use efficiency, with leaf nitrogen content all above 3.1%, leaf phosphorus content between 0.22% and 0.30%, and leaf potassium content between 3.15% and 6.24%. The ΦPSII of ephemerals on average was above 0.4. The inhibition effect of high light intensity on electron transport rate (ETR) was not obvious, with the latter decreasing only when PAR was above 1400 mol∙m−2∙s−1.

H2 production in Rhodopseudomonas palustris as a way to cope with high light intensities

The ability of coping with the damaging effects of high light intensity represents an essential issue when purple non-sulfur bacteria (PNSB) are grown under direct sunlight for photobiological hydrogen production. This study was aimed at investigating whether H2 photo-evolution could represent, for Rhodopseudomonas palustris 42OL, a safety valve to dissipate an excess of reducing power generated under high light intensities. The physiological status of this strain was assessed under anaerobic (AnG) and aerobic (AG) growing conditions and under H2-producing (HP) conditions at low and high light intensities. The results obtained clearly showed that Fv/Fm ratio was significantly affected by the light intensity under which R. palustris 42OL cells were grown, under either AnG or AG conditions, while, under HP, it constantly remained at its highest value. The increase in light intensity significantly increased the H2 production rate, which showed a positive correlation with the maximum electron transfer rate (rETRmax). These findings are important for optimization of hydrogen production by PNSB under solar light.

Effect of high light intensity on photoinhibition, oxyradicals and artemisinin content in Artemisia annua L.

Artemisia annua L. produces a compound called artemisinin that is a potent anti-malarial compound. However concentration of artemisinin within the plant is typically low (less than 0.8% of dry mass) and currently supply of the drug by the plant does not meet world demand. This investigation was carried out to determine whether high intensity light treatment would increase production of artemisinin in leaves of A. annua. Photoinhibition (14%) was induced in leaves of A. annua when they were subjected to 6 h of high-intensity light [2,000 μmol(photon) m-2 s−1]. Maximum photochemical efficiency of PSII showed a recovery of up to 95% within 24 h of light induced inhibition. During the light treatment, photochemical efficiency of PSII in leaves of the high-intensity light-treated plants was 38% lower than for those from leaves of plants subjected to a low-intensity-light treatment of 100 μmol(photon) m-2 s−1. Nonphotochemical quenching of excess excitation energy was 2.7 times higher for leaves treated with high-intensity light than for those irradiated with low-intensity light. Elevation in oxidative stress in irradiated leaves increased presence of reactive oxygen species (ROS) including singlet oxygen, superoxide anions, and hydrogen peroxide. Importantly, the concentration of artemisinin in leaves was two-fold higher for leaves treated with high-intensity light, as compared to those treated with low-intensity light. These results indicate that A. annua responds to high irradiance through nonphotochemical dissipation of light energy yet is subject to photoinhibitory loss of photosynthetic capacity. It can be concluded that A. annua is capable of rapid recovery from photoinhibition caused by high light intensity. High light intensity also induced oxidative stress characterized by increased concentration of ROS which enhanced the content of artemisinin. Such a light treatment may be useful for the purpose of increasing artemisinin content in A. annua prior to harvest.

Evolution under the sun: optimizing light harvesting in photosynthesis.

The emergence and evolution of life on our planet was possible because the sun provides energy to our biosphere. Indeed, all life forms need energy for existence and proliferation in space and time. Light-energy conversion takes place in photosynthetic organisms that evolve in various environments featuring an impressive range of light intensities that span several orders of magnitude. This property is achieved by the evolution of mechanisms of efficient energy capture that involved development of antenna pigments and pigment-protein complexes as well as the emergence of various strategies on the organismal, cellular, and molecular levels to counteract the detrimental effects of high light intensity on the delicate photosynthetic apparatus. Darwin was one of the first to describe the behaviour of plants towards light. He noticed that some plants try to avoid full daylight and called this reaction paraheliotropism. However, it was only in the second half of the 20th century, when scientists began to discover the structure and molecular mechanisms of the photosynthetic machinery, that the reasons for paraheliotropisms became clear. This review explains the need for the evolution of light adaptations using the example of higher plants. The review focuses on short-term adaptation mechanisms that occur on the minute scale, showing that these processes are fast enough to track rapid fluctuations in light intensity and that they evolved to be effective, allowing for the expansion of plant habitats and promoting diversification and survival. Also introduced are the most recent developments in methods that enable quantification of the light intensities that can be tolerated by plants.

Fatty acid composition of the thermophilic Gloeocapsa gelatinosa under different combinations of temperature, light intensity, and NaNO3 concentration

The combined effect of temperature, light intensity, and NaNO3 concentration on lipid biosynthesis and fatty acid composition was investigated for the thermophilic cyanobacterium Gloeocapsa gelatinosa (Kutzing 1843) isolated from a thermal spring in Tunisia. Under optimal growth conditions, the lipid content was 7.3 % DW. Fatty acid analysis revealed the predominance of 16:0 and 18:0 (23.7 and 18.2 %, respectively) as main straight carbon chains of saturated fatty acids. Unsaturated fatty acids were also identified with 18:1n9c (18.8 %) and 16:1n7 (5 %) being the predominant components. The effect of environmental factors on fatty acid composition was monitored by using principal component analysis and central composite design. Variation of light intensity (20 to 150 μmol photons m−2 s−1), temperature (20 to 60 °C), and nitrogen concentration (0 to 3 g L−1) induced a significant variation in the amount of fatty acid proportions, whereas lipid content was only slightly modified. Results showed that light intensity had the strongest effect on the composition of fatty acids. Temperature had a synergic effect with light intensity while nitrogen concentration had a trivial effect. The combined effect of high light intensity (150 μmol photons m−2 s−1) and high temperature (60 °C) increased the proportion of saturated 16:0 and 18:0 fatty acids along with long-chain fatty acids to 82 % which was twofold higher than that in optimal growth conditions. This induced fatty acid profile makes G. gelatinosa-based biofuels adaptable for higher energetic efficiency and higher oxidative stability.

Loss ofpsbSexpression reduces vegetative growth, reproductive output, and light‐limited, but not light‐saturated, photosynthesis inArabidopsis thaliana(Brassicaceae) grown in temperate light environments

Plants protect themselves against the deleterious effects of high light intensities by inducing a mechanism ubiquitous among plants known as energy dissipation, which safely converts excess light to heat before it can lead to the formation of free radicals. Mutants possessing a deletion of the psbS gene, such as the npq4 mutant, cannot perform energy dissipation and thus offer an opportunity to assess the importance of this process to plant function. In a temperate light environment, greenhouse-grown npq4 mutants of Arabidopsis thaliana had smaller rosette diameters and leaf numbers. The reduction in size observed in npq4 plants was associated with fewer floral stalks, fewer fruits, lower whole-plant and individual seed masses, and lower germination rates. In the field, npq4 mutants developed fewer fruits. After a controlled exposure to high light stress, both PSII efficiency and CO(2) assimilation were more significantly compromised in npq4 mutants at low light intensities, but not at high light intensities. Thus, the protective nature of energy dissipation manifests in light environments that include periods of high light, which predispose plants to PSII photoinactivation, and periods of low light, when PSII photoinactivation decreases the rate of photosynthesis.

Substrate Acidification by Geranium: Light Effects and Phosphorus Uptake

Sudden pH decline (SPD) describes the situation where crops growing at an appropriate pH rapidly (within 1–2 weeks) cause the substrate pH to shift downward one to two units. ‘Designer Dark Red’ geraniums (Pelargonium ×hortorum Bailey) were grown in three experiments to assess possible effects of light on SPD and phosphorous (P) uptake. The first experiment tested the effect of four light intensities (105, 210, 575, and 1020 ± 25 μmol·m−2·s−1) on substrate acidification. At 63 days, substrate pH declined from 6.0 to 4.8 as light intensity increased. Tissue P of plants grown at the highest two light levels was extremely low (0.10%–0.14% of dry weight). P stress has been reported to cause acidification. Because plants in the two lowest light treatments had adequate P, it was not possible to determine if the drop in substrate pH was a direct light effect or a combination of light and P. The second experiment used a factorial combination of the three highest light levels from Expt. 1 and five preplant P rates (0, 0.065, 0.13, 0.26, or 0.52 g·L−1 substrate) to assess this question. When tissue P concentrations were deficient, pH decreased by 0.6 to 1.0 pH units within 2 weeks and deficiency occurred more often with high light intensity. These data indicated that P deficiency caused substrate acidification and indicated the possibility that P uptake was suppressed by high light intensity. The third experiment was conducted in hydroponics to determine the direct effect of high light intensity on P uptake. In this experiment, cumulative P uptake per gram root and the rate of P uptake per gram root per day both decreased 20% when light intensity increased from 500 to 1100 μmol·m−2·s−1. It is clear from this study that P deficiency causes geraniums to acidify the substrate and that high light suppresses P uptake.

Effect of high light intensity on cavity wall adaptation of a resin composite with a self‐etching primer system

This study evaluated the effect of high light intensity using a plasma arc lamp on the cavity wall adaptation of photo-polymerized composite restorations. Bowl-shaped cavities were prepared on the labial surfaces of extracted bovine teeth. Each cavity was restored with a resin composite restorative system (SE Bond & Clearfil AP-X) and then polymerized using a plasma arc lamp (Arc Light II) with a series of light intensities, including 1100, 1200, 1300, 1400, 1500, and 1600 mW/cm(2), and a halogen lamp (Candilux) with 400 mW/cm(2) light intensity (n = 10). The photo-irradiation time was adjusted for each group to receive a total energy output of approximately 16,000 mJ/cm(2). The specimens were subjected to 2500 cycles of thermal fatigue and sectioned bucco-lingually through the center of the restoration. Contraction gaps on the sections were measured using a replica-SEM observation technique. The degree of gap formation was determined as the ratio of the total length of the contraction gaps to the total length of the cavity wall on each sectioned specimen. The value was converted to a percentage. The data were statistically analyzed with Kruskal-Wallis and Mann-Whitney U tests at a 0.05 level of significance. There were no significant differences (p > 0.05) in the cavity adaptation among the composites polymerized by the plasma arc lamp with high light intensities and the composite polymerized with the halogen lamp with 400 mW/cm(2) light intensity. There were no significant differences (p > 0.05) in the degree of cavity adaptation among the specimens polymerized with light intensities higher than 1100 mW/cm(2).