Non-photochemical Energy Dissipation Research Articles

Effect of knockout of α-carbonic anhydrase 4 gene on photosynthetic characteristics and starch accumulation in leaves of Arabidopsis thaliana

Effects of knockout of the gene encoding α-carbonic anhydrase 4 (α-CA4) on growth and photosynthesis of Thale cress (Arabidopsis thaliana (L.) Heynh., var. Columbia) were investigated. The shoot weight of mutant plants was found to be higher than in wild-type plants, and the leaves of mutants were enriched in starch content. The electron microscopy study revealed a considerable increase in the number and size of starch grains in chloroplasts of mutant plants. Comparison of wild-type and mutant plant leaves in terms of chlorophyll a fluorescence, coefficient of photochemical fluorescence quenching, effective quantum yield of photosystem II reaction, and nonphotochemical fluorescence quenching under steady-state illumination and saturating CO2 content in the air led to the proposal that α-CA4 participates in the development of nonphotochemical energy dissipation by accelerating the supply of protons for activation of violaxanthin deepoxidase and for structural changes in the light-harvesting complexes.

Time-dependent changes in antioxidative enzyme expression and photosynthetic activity of Chlamydomonas reinhardtii cells under acute exposure to cadmium and anthracene

Heavy metals (HM) and polycyclic aromatic hydrocarbons (PAHs) are present in the freshwater environment at concentrations that can be hazardous to the biota. Among HMs and PAHs, cadmium (Cd) and anthracene (ANT) are the most prevalent and toxic ones. The response of Chlamydomonas cells to Cd and ANT at concentrations that markedly reduced the growth of algal population was investigated in this study. At such concentrations, both cadmium and anthracene were recognized as oxidative stress inducers, since high concentration of H2O2 in treated cultures was observed. Therefore, as a part of the “molecular phase” of the cell response to this stress, we examined the time-dependent expression of genes encoding the main antioxidative enzymes: superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), as well as the activity of these enzymes in cells, with special attention paid to chloroplastic and mitochondrial isoforms of SOD. To characterize the cell response at the “physiological level”, we examined the photosynthetic activity of stressed cells via analysis of chlorophyll a fluorescence in vivo. In contrast to standard ecotoxicity studies in which the growth end-points are usually determined, herein we present time-dependent changes in algal cell response to Cd- and ANT-induced stress. The most significant effect(s) of the toxicants on photosynthetic activity was observed in the 6th hour, when strong depression of PI parameter value, an over 50 percent reduction of the active reaction center fraction (RC0) and a 3-fold increase in non-photochemical energy dissipation (DI0/RC) were noted. At the same time, the increase (up to 2.5-fold) in mRNA transcript of SOD and CAT genes, followed by the enhancement in the enzyme activity was observed. The high expression of the Msd 3 gene in treated Chlamydomonas cells probably complements the partial loss of chloroplast Fe-SOD and APX activity, while catalase and Mn-SOD 5 seem to be the major enzymes responsible for mitochondrion protection. The progressive increase in SOD and CAT activities seems to be involved in the recovery of photosynthesis within 12–24h after the application of the toxicants.

Photosynthetic physiological response of Radix Isatidis (Isatis indigotica Fort.) seedlings to nicosulfuron.

Radix Isatidis (Isatis indigotica Fort.) is one of the most important traditional Chinese medicine plants. However, there is no suitable herbicide used for weed control in Radix Isatidis field during postemergence stage. To explore the safety of sulfonylurea herbicide nicosulfuron on Radix Isatidis (Isatis indigotica Fort.) seedlings and the photosynthetic physiological response of the plant to the herbicide, biological mass, leaf area, photosynthetic pigment content, photosynthetic rate, chlorophyll fluorescence characteristics, and P700 parameters of Radix Isatidis seedlings were analyzed 10 d after nicosulfuron treatment at 5th leaf stage in this greenhouse research. The results showed that biological mass, total chlorophyll, chlorophyll a, and carotenoids content, photosynthetic rate, stomatal conductance, PS II maximum quantum yield, PS II effective quantum yield, PS II electron transport rate, photochemical quenching, maximal P700 change, photochemical quantum yield of PS I, and PS I electron transport rate decreased with increasing herbicide concentrations, whereas initial fluorescence, quantum yield of non-regulated energy dissipation in PS II and quantum yield of non-photochemical energy dissipation due to acceptor side limitation in PS I increased. It suggests that nicosulfuron ≥1 mg L−1 causes the damage of chloroplast, PS II and PS I structure. Electron transport limitations in PS I receptor side, and blocked dark reaction process may be the main cause of the significantly inhibited growth and decreased photosynthetic rate of Radix Isatidis seedlings.

The relationship between maximum tolerated light intensity and photoprotective energy dissipation in the photosynthetic antenna: chloroplast gains and losses

The principle of quantifying the efficiency of protection of photosystem II (PSII) reaction centres against photoinhibition by non-photochemical energy dissipation (NPQ) has been recently introduced by Ruban & Murchie (2012 Biochim. Biophys. Acta 1817, 977-982 (doi:10.1016/j.bbabio.2012.03.026)). This is based upon the assessment of two key parameters: (i) the relationship between the PSII yield and NPQ, and (ii) the fraction of intact PSII reaction centres in the dark after illumination. In this paper, we have quantified the relationship between the amplitude of NPQ and the light intensity at which all PSII reaction centres remain intact for plants with different levels of PsbS protein, known to play a key role in the process. It was found that the same, nearly linear, relationship exists between the levels of the protective NPQ component (pNPQ) and the tolerated light intensity in all types of studied plants. This approach allowed for the quantification of the maximum tolerated light intensity, the light intensity at which all plant leaves become photoinhibited, the fraction of (most likely) unnecessary or 'wasteful' NPQ, and the fraction of photoinhibited PSII reaction centres under conditions of prolonged illumination by full sunlight. It was concluded that the governing factors in the photoprotection of PSII are the level and rate of protective pNPQ formation, which are often in discord with the amplitude of the conventional measure of photoprotection, the quickly reversible NPQ component, qE. Hence, we recommend pNPQ as a more informative and less ambiguous parameter than qE, as it reflects the effectiveness and limitations of the major photoprotective process of the photosynthetic membrane.

Photosystem I shows a higher tolerance to sorbitol‐induced osmotic stress than photosystem II in the intertidal macro‐algae Ulva prolifera (Chlorophyta)

The photosynthetic performance of the desiccation-tolerant, intertidal macro-algae Ulva prolifera was significantly affected by sorbitol-induced osmotic stress. Our results showed that photosynthetic activity decreased significantly with increases in sorbitol concentration. Although the partial activity of both photosystem I (PS I) and photosystem II (PS II) was able to recover after 30 min of rehydration, the activity of PS II decreased more rapidly than PS I. At 4 M sorbitol concentration, the activity of PS II was almost 0 while that of PS I was still at about one third of normal levels. Following prolonged treatment with 1 and 2 M sorbitol, the activity of PS I and PS II decreased slowly, suggesting that the effects of moderate concentrations of sorbitol on PS I and PS II were gradual. Interestingly, an increase in non-photochemical quenching occurred under these conditions in response to moderate osmotic stress, whereas it declined significantly under severe osmotic stress. These results suggest that photoprotection in U. prolifera could also be induced by moderate osmotic stress. In addition, the oxidation of PS I was significantly affected by osmotic stress. P700(+) in the thalli treated with high concentrations of sorbitol could still be reduced, as PS II was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), but it could not be fully oxidized. This observation may be caused by the higher quantum yield of non-photochemical energy dissipation in PS I due to acceptor-side limitation (Y(NA)) during rehydration in seawater containing DCMU.

Characterizing photoinhibition and photosynthesis in juvenile-red versus mature-green leaves of Jatropha curcas L

The new leaves of Jatropha curcas (L.) appear dark red in colour due to the presence of anthocyanin pigments, these leaves subsequently turn green on maturity. The aim of the study was to characterize the photosynthetic efficiency of the juvenile red and mature green leaves and to understand the possible role of anthocyanin pigment in the juvenile leaves of J. curcas. We studied the localization of anthocyanin pigment, reflectance properties, diurnal gas-exchange performance, carboxylation efficiency and photosynthetic efficiency under different light intensities by investigation of the photochemical and non-photochemical energy dissipation processes related to Photosystem II (PSII) and Photosystem I (PSI), of the juvenile and the mature leaves of J. curcas. The JIP test analysis of chlorophyll a fluorescence transients and the gas-exchange studies revels the low photosynthetic efficiency of red leaves is due to the immaturity of the leaf. The low value of quantum yield of non-photochemical energy dissipation due to acceptor side limitation, Y (NA) under high light in the red leaf, suggests that over-reduction of PSI acceptor side was prevented and it results in the accumulation of oxidized P700, which dissipates excess light energy harmlessly as heat and thereby alleviate photoinhibition of PSI in case of the juvenile red leaves. Further our results of photoinhibition and relaxation on exposure of red and green leaves to monochromatic blue light showed that effective quantum yield of PSII recovers faster and completely under darkness in juvenile red leaves as compared to mature green leaves, supporting the role of anthocyanin pigments in protecting both PSII and PSI in the red leaves.

Moderate warming increases PSII performance, antioxidant scavenging systems and biomass production in Stylosanthes capitata Vogel

Stylosanthes capitata Vogel is an important forage legume in tropical and subtropical regions. To study the response of S. capitata to the moderate warming expected as a result of climate change, plants were subjected to elevated temperature (2°C increase over the ambient temperature) in a temperature free-air controlled enhancement (T-FACE) facility. Photosystem II (PSII) performance, the activity of antioxidant enzymes, the chlorophyll index, the leaf area index (LAI) and the aboveground biomass production were evaluated. The maximum PSII quantum yield (FV/FM) and the quantum yield of regulated energy dissipation Y (NPQ) were not affected by the warming. However, we observed a significant increase in the electron transport rate (ETR), the non-photochemical energy dissipation (NPQ), the effective PSII quantum yield Y(II) and the coefficient of photochemical quenching (qP) in the warmed leaves compared with the control leaves. In contrast, a significant reduction in the quantum yield of the relative reduction state of QA (1-qP) and non-regulated power dissipation Y(NO) was observed in the warmed leaves. The increase in ETR under moderate warming was associated with the increase (31%) in chlorophyll content. The activities of antioxidant enzymes increased in the leaves of the warmed plants, but the malondialdehyde (MDA) content of the leaves was not affected by warming, suggesting that higher levels of the antioxidant defense system induced by warming may improve the protection of photosynthesis against oxidative damage and attenuate the destructive effects of reactive oxygen species. As a result of warming, leaf area index (LAI) and biomass production increased by 32% and 16%, respectively. The improved PSII functioning of the warmed leaves of S. capitata may reflect their capacity to acclimate better to warming growth conditions. We conclude that the warming induced by increasing the temperature by 2°C, under non stressing conditions, was beneficial for the physiology and for the biophysical and physiological processes involved in plant growth of S. capitata, suggesting that slight increases in the leaf temperature may benefit some plants, especially those in tropical environments.

Photosynthetic response of poikilochlorophyllous desiccation-tolerant Pleurostima purpurea (Velloziaceae) to dehydration and rehydration

The poikilochorophyllous, desiccation-tolerant (PDT) angiosperm, Pleurostima purpurea, normally occurs in less exposed rock faces and slightly shady sites. Our aim was to evaluate the light susceptibility of the photosynthetic apparatus during dehydration-rehydration cycle in P. purpurea. In a controlled environment, the potted plants were subjected to water deficit under two different photosynthetic photon flux densities [PPFD, 100 and 400 µmol(photon) m –2 s –1 ]. In the higher PPFD, net photosynthetic rate (PN) become undetectable after stomata closure but photochemical efficiency of photosystem II, electron transport rate, and photochemical quenching coefficient were maintained relatively high, despite a partial decrease. The photochemical activity was inhibited only after the complete loss of chlorophylls, when leaf relative water content dropped below 72% and total carotenoids reached maximal accumulation. Nonphotochemical energy dissipation increased earlier in response to dehydration under higher PPFD. PN and photochemical activity were fully recovered after rehydration under both light treatments. Our results suggested that the natural occurrence of P. purpurea should not be restricted by the light intensity during the complete desiccation-rehydration cycles.

Enhancement of photosynthetic performance, water use efficiency and grain yield during long-term growth under elevated CO2 in wheat and rye is growth temperature and cultivar dependent

The effects of long-term elevated CO2 on photosynthetic performance of winter (cv Musketeer) and spring (cv SR4A) rye (Secale cereale) and winter (cv Norstar) and spring (cv Katepwa) wheat (Triticum aestivum) grown at either 20/16°C (non-acclimated (NA)) or 5/5°C (cold acclimated (CA) and at either ambient (380μmolCmol−1) or elevated (700μmolCmol−1) CO2 were studied. Compared to NA counterparts, CA winter cereals exhibited a 30–40% increase in light and CO2-saturated rates of photosynthesis at both ambient and elevated CO2. This was accompanied by a 35–50% decrease in excitation pressure and non-photochemical energy dissipation. Concomitantly, biomass increased by 28–46% and grain yield per plant by 60%. In contrast, both CA spring cultivars exhibited a 45–60% inhibition of light- and CO2-saturated rates of photosynthesis at ambient CO2 as well as growth at elevated CO2 relative to NA controls. This inhibition was specific for photosynthesis since cold acclimation stimulated rates of respiration by 22–47% in all cultivars tested. This was accompanied by a 58% increase in excitation pressure and a 17% increase in non-photochemical energy dissipation in the cold acclimated spring rye and spring wheat. Consequently, biomass accumulation was reduced by about 25% in CA versus NA spring cultivars at elevated CO2. We conclude that the potential for enhancement of photosynthetic performance, water use efficiency and grain yield of cereals grown at elevated CO2 is both growth temperature and cultivar dependent.

Induction time of Fe-SOD synthesis and activity determine different tolerance of two Desmodesmus (green algae) strains to chloridazon: A study with synchronized cultures

Cells of two Desmodesmus armatus strains (276-4a and 276-4d) grown asynchronously in batch cultures after 24-h treatment revealed different tolerance to chloridazon (photosynthetic herbicide) applied at a concentration of 3.45mgL−1. To find time- and cell cycle-dependent biochemical reasons leading to such a difference, a population of young autospores of both strains synchronized by a light/dark (14/10) regime were exposed to chloridazon at the initiation of the light period. Chloridazon reduced the growth and number of divisions of cell strain 276-4d. In consequence, at the end of the dark phase the number of released autospores was reduced by 50% compared with the control. In contrast, the growth and reproductive processes of cell strains 276-4a was unaffected. Moreover, chloridazon treatment speeded up cell development, as a result of which the release of autospores took this process observed in the control cells over. There is a relationship between photosynthetic activity response to chloridazon and time-dependent changes in Fe-SOD content and activity. The energy trapped in the reaction centre (RC) was similar in both strains, but the amount of energy absorbed by RCs was twice as high in strain 276-4d as in 276-4a. In consequence, non-photochemical energy dissipation occurring in the cells of 276-4d strain far exceed the value obtained for 276-4a strain. The control cells of both strains differed significantly in the content of FSD 1 and FSD 2 proteins, whereas the differences in Fe-SOD isoforms activities were slight. The 8-fold increase in SOD content in CHD treated cells of strain 276-4a was associated with the transience of photosynthetic efficiency impairment. In CHD treated cells of strain 276-4d, neither activity of Fe-SOD nor FSDs protein content was instantly affected. Different response of developing cells of two Desmodesmus strains to CHD is influenced by the inherent features of cells; the short time required to induce stress adaptive mechanism involving chloroplastic Fe-SOD activity and biosynthesis in the cells of CHD tolerant strain 276-4a seems to play the key role, being an overriding on the high, but not induced in response to stress, FSD protein level and activity in cells of strain 276-4d.

Photosynthetic adaptation of Euphorbia fractiflexa (Euphorbiaceae) and survival in arid regions of the Arabian Peninsula

Arid regions of the Arabian Peninsula are characterized by a short wet season with erratic rainfall, high temperature, and high evaporation. In these arid regions, the leafless stem succulent Euphorbia fractiflexa S. Carter & J.R.I.Wood (Euphorbiaceae) is an abundant perennial. Work presented in this paper aimed at investigating crassulacean acid metabolism (CAM) as a physiological adaptation crucial for survival of E. fractiflexa in arid regions of the Arabian Peninsula. Work involved investigations of stomatal diffusive conductance, chlorophyll fluorescence, and cell sap titratable acidity. Results represent the first report of obligate CAM in E. fractiflexa. Low values of stomatal conductance and dampening of CAM acidification–deacidification cycles during the long dry season also denoted tendency of this species to shift from obligate CAM to CAM-idling. Results also showed water stress-induced reduction in Photosystem II (PSII) activity occurring in concomitance with increased non-photochemical quenching of chlorophyll fluorescence denoting operation of non-photochemical energy dissipation mechanisms that are important for photoprotection of the photosynthetic machinery under stress conditions.

Cold acclimation and BnCBF17-over-expression enhance photosynthetic performance and energy conversion efficiency during long-term growth of Brassica napus under elevated CO2 conditions

The effects of cold acclimation and long-term elevated CO(2) on photosynthetic performance of wild-type (WT) and BnCBF17-over-expressing line of Brassica napus cv. Westar (BnCBF17-OE) grown at either 20/16°C (non-acclimated) or 5/5°C (cold acclimated) and at either ambient (380μmolCmol(-1)) or elevated (700μmolCmol(-1)) CO(2) were studied. Compared with non-acclimated WT, the BnCBF17-OE grown at 20°C mimicked the effects of cold acclimation on WT B. napus with respect to compact dwarf phenotype and increased rates of light-saturated CO(2) assimilation and photosynthetic electron transport. This was associated with enhanced energy conversion efficiency into biomass as assessed by decreased excitation pressure coupled to decreased dependence on non-photochemical energy dissipation for a given irradiance. Growth at elevated CO(2) decreased the light and CO(2)-saturated rates of photosynthesis by 30% for non-acclimated WT relative to growth at ambient CO(2). This was associated with inhibition in electron transport rates (20%), decrease in amount of rbcL (35%) and cytosolic FBPase (70%) and increased excitation pressure and non-photochemical quenching in elevated versus ambient CO(2)-grown non-acclimated WT. In contrast, light and CO(2)-saturated rates of photosynthesis, electron transport, excitation pressure, non-photochemical quenching and levels of rbcL, cytosolic FBPase and Lhcb1 were insensitive to growth under elevated CO(2) in BnCBF17-OE and cold-acclimated WT. Thus, BnCBF17-over-expression and cold acclimation maintain enhanced energy conversion efficiency and reduced sensitivity to feedback-limited photosynthesis during long-term growth of B. napus under elevated CO(2). Our results indicated that CBFs transcription factors regulate not only freezing tolerance but also has major whole plant effects.

Herbivory of wild Manduca sexta causes fast down-regulation of photosynthetic efficiency in Datura wrightii: an early signaling cascade visualized by chlorophyll fluorescence

Plants experiencing herbivory suffer indirect costs beyond direct loss of leaf area, but differentially so based on the herbivore involved. We used a combination of chlorophyll fluorescence imaging and gas exchange techniques to quantify photosynthetic performance, the efficiency of photochemistry, and heat dissipation to examine immediate and longer-term physiological responses in the desert perennial Datura wrightii to herbivory by tobacco hornworm, Manduca sexta. Herbivory by colony-reared larvae yielded no significant reduction in carbon assimilation, whereas herbivory by wild larvae induced a fast and spreading down-regulation of photosynthetic efficiency, resulting in significant losses in carbon assimilation in eaten and uneaten leaves. We found both an 89% reduction in net photosynthetic rates in herbivore-damaged leaves and a whole-plant response (79% decrease in undamaged leaves from adjacent branches). Consequently, herbivory costs are higher than previously estimated in this well-studied plant-insect interaction. We used chlorophyll fluorescence imaging to elucidate the mechanisms of this down-regulation. Quantum yield decreased up to 70% in a small concentric band surrounding the feeding area within minutes of the onset of herbivory. Non-photochemical energy dissipation by the plant to avoid permanent damage was elevated near the wound, and increased systematically in distant areas of the leaf away from the wound over subsequent hours. Together, the results underscore not only potential differences between colony-reared and wild-caught herbivores in experimental studies of herbivory but also the benefits of quantifying physiological responses of plants in unattacked leaves.

Photobiology of corals from Brazil’s near-shore marginal reefs of Abrolhos

Coral communities were examined from highly turbid near-shore marginal reefs of Abrolhos (Brazil) to test a paradigm previously developed from observations in clear water reefs; specifically, that coral photobiological properties follow a highly conserved linear relationship with optical depth (ζ) via preferential ‘non-photochemical’ over ‘photochemical’ dissipation of absorbed light energy. PAM flourometry in situ was used to examine the photobiology of the most dominant coral species throughout the platform surfaces and bases of Abrolhos’ characteristic ‘chapeirões’ reef framework; however, none of the species consistently adhered to the ‘clear water paradigm’. PAM measurements further demonstrated that species conformed to two different strategies of non-photochemical energy dissipation: transient but relatively rapid for the two closely related endemic species (Mussismilia braziliensis and Mussismilia harttii) as opposed to more persistent for Montastrea cavernosa, Porites astreoides and Siderastrea stellata. Further experiments demonstrated that tolerance to anomalous stress amongst species did not correspond with the non-photochemical energy dissipation strategy present but was consistent with the relative dominance of species within the chapeirões coral communities.

Effects of Mediterranean summer conditions on chlorophyll a fluorescence emission in the epiphytic lichen Flavoparmelia soredians: a field study

Recent hypotheses suppose that dry lichens emit a faint chlorophyll a fluorescence because of a “long-wavelength quencher” embedded in the antenna complex that protects photosystem II (PSII) from photodamage. To verify in the field the PSII re-activation promptness induced by water availability, chlorophyll a fluorescence was measured on the epiphytic lichen Flavoparmelia soredians after two months without rainfall events in a Mediterranean cork oak wood (Bosco Santo Pietro, Sicily, Italy). Measurements were carried out at dawn and sunset on north- and south-exposed populations under different regimes of hydration and dark-adaptation. The results show that prolonged hydration increases the photochemical conveying of energy to PSII and decreases the non-photochemical energy dissipation that otherwise might occur in the antenna complex of the lichen photobionts. A slight decrease in PSII efficiency caused by photoinhibition was observed in thalli exposed to ambient light (up to 600 μmol photons m−2 s–1) only when kept fully hydrated. The results are discussed on the basis of our knowledge on the ecology of the species, that is a representative component of Mediterranean epiphytic lichen communities.

5-Aminolevulinic Acid Synthase를 과발현하는 형질전환 벼에서 광역학적 스트레스가 유도하는 비효소적 항산화반응

색소체 transit 서열이 결여된 Bradyrhizobium japonicum ALA-S 유전자를 과발현하는 형질전환 벼의 광역학적 스트레스에 의해 유도되는 항산화반응을 조사하였다. <TEX>$350{\mu}mol\;m^{-2}\;s^{-1}$</TEX> 의 높은 광 수준은 야생형 벼에 비교하였을 때 형질전환 계통인 C4와 C5의 quantum yield를 감소시켰다. 대조적으로, 높은 광수준 하에서 형질전환 계통 C4와 C5의 nonphotochemical quenching (NPQ) 수준은 야생형 계통과 낮은 광 수준 하의 형질전환 계통에 비해 높은 증가를 보여주었다. 형질전환 계통에서 높은 NPQ 수준은 xanthophyll인 zeaxanthin 수준의 증가와 밀접한 관련이 있었다. <TEX>$150{\mu}mol\;m^{-2}\;s^{-1}$</TEX> 의 낮은 광 수준과 비교하였을 때 높은 광 수준에서 violaxanthin 수준이 야생형 벼에서 증가하였으나, 형질전환 C4와 C5 계통에서는 현저하게 감소하였다. 형질전환 벼에서 nonphotochemical energy dissipation과 광보호기작을 가진 xanthophyll 색소가 광역학적 피해를 조절하는데 결정적인 역할을 하는 것으로 생각되나, 이러한 기작이 광역학 스트레스를 극복하지는 못하였고 결과적으로 photobleaching 증상에 이르게 하였다. We investigated photodynamic stress-induced antioxidant responses in transgenic rice overexpressing Bradyrhizobium japonicum 5-aminolevulinic acid synthase (ALA-S) coding sequence lacking plastidal transit sequence. High light of <TEX>$350{\mu}mol\;m^{-2}\;s^{-1}$</TEX> decreased the quantum yield in the transgenic lines, C4 and C5, compared to that of wild-type line. By contrast, non-photochemical quenching (NPQ) levels of C4 and C5 under high light were higher than those of the transgenic lines under low light of <TEX>$150{\mu}mol\;m^{-2}\;s^{-1}$</TEX> as well as wild-type line under low and high light. Greater levels of NPQ in the transgenic lines exposed to high light were in a close correlation with increases in the xanthophyll pigment, zeaxanthin. Under high light, levels of neoxanthin, violaxanthin, lutein, and <TEX>${\beta}$</TEX>-carotene in the transgenic lines were lower than those in wild-type line. Taken together, nonphotochemical energy dissipation and photoprotectant xanthophyll pigments play a critical role to deal with the severe photodynamic damage in the transgenic rice plants, although they could not overcome the photodynamic stress, leading to severe photobleaching symptoms.

Xanthophyll cycle pigment and antioxidant profiles of winter-red (anthocyanic) and winter-green (acyanic) angiosperm evergreen species

Leaves of many angiosperm evergreen species change colour from green to red during winter, corresponding with the synthesis of anthocyanin pigments. The ecophysiological function of winter colour change (if any), and why it occurs in some species and not others, are not yet understood. It was hypothesized that anthocyanins play a compensatory photoprotective role in species with limited capacity for energy dissipation. Seasonal xanthophyll pigment content, chlorophyll fluorescence, leaf nitrogen, and low molecular weight antioxidants (LMWA) of five winter-red and five winter-green angiosperm evergreen species were compared. Our results showed no difference in seasonal xanthophyll pigment content (V+A+Z g(-1) leaf dry mass) or LMWA between winter-red and winter-green species, indicating red-leafed species are not deficient in their capacity for non-photochemical energy dissipation via these mechanisms. Winter-red and winter-green species also did not differ in percentage leaf nitrogen, corroborating previous studies showing no difference in seasonal photosynthesis under saturating irradiance. Consistent with a photoprotective function of anthocyanin, winter-red species had significantly lower xanthophyll content per unit chlorophyll and less sustained photoinhibition than winter-green species (i.e. higher pre-dawn F(v)/F(m) and a lower proportion of de-epoxidized xanthophylls retained overnight). Red-leafed species also maintained a higher maximum quantum yield efficiency of PSII at midday (F'(v)/F'(m)) during winter, and showed characteristics of shade acclimation (positive correlation between anthocyanin and chlorophyll content, and negative correlation with chlorophyll a/b). These results suggest that the capacity for photon energy dissipation (photochemical and non-photochemical) is not limited in red-leafed species, and that anthocyanins more likely function as an alternative photoprotective strategy to increased VAZ/Chl during winter.

Analysis of the photosynthetic response induced by variation potential in geranium

Electrical signals (action and variation potentials) caused by environmental stimuli induce a number of physiological responses in plants including changes in photosynthesis; however, mechanisms of these changes remain unclear. We investigated the influence of the variation potential on photosynthesis in geranium (Pelargonium zonale) under different conditions (control, low external CO₂ concentration, and actinic light absence). The variation potential caused by lamina burning induced a reduction in photosynthesis (decreases in effective quantum yields of photosystem I and II, CO₂ assimilation rate, and stomatal conductance) in unstimulated leaves under control conditions. Changes in the majority of light-stage parameters (photosystem I and II quantum yields, coefficients of photochemical and non-photochemical quenching, quantum yield of non-photochemical energy dissipation in photosystem I due to donor-side limitation) were correlated with a decrease in CO₂ assimilation rate. The changes were similar to those caused by lowering [CO₂]; their magnitudes decreased both under low external CO₂ concentration and without actinic light. These results support the hypothesis that Calvin cycle inactivation plays a key role in photosynthetic response induced by electrical signals. However, a decrease in electron transport through the PSI acceptor side also induced by variation potential was not correlated with a decrease in the CO₂ assimilation rate and did not depend on the external CO₂ concentration or actinic light intensity. Thus, we suggest that there are two different mechanisms of light-stage inactivation induced by the variation potential in geranium: one strongly dependent on dark-stage inactivation and one weakly dependent on dark-stage inactivation.

Tree size and light availability increase photochemical instead of non-photochemical capacities of Nothofagus nitida trees growing in an evergreen temperate rain forest

Nothofagus nitida (Phil.) Krasser (Nothofagaceae) regenerates under the canopy in microsites protected from high light. Nonetheless, it is common to find older saplings in clear areas and adults as emergent trees of the Chilean evergreen forest. We hypothesized that this shade to sun transition in N. nitida is supported by an increase in photochemical and non-photochemical energy dissipation capacities of both photosystems in parallel with the increase in plant size and light availability. To dissect the relative contribution of light environment and plant developmental stage to these physiological responses, the photosynthetic performance of both photosystems was studied from the morpho-anatomical to the biochemical level in current-year leaves of N. nitida plants of different heights (ranging from 0.1 to 7&emsp14;m) growing under contrasting light environments (integrated quantum flux (IQF) 5-40 mol m(-2). Tree height (TH) and light environment (IQF) independently increased the saturated electron transport rates of both photosystems, as well as leaf and palisade thickness, but non-photochemical energy flux, photoinhibition susceptibility, state transition capacity, and the contents of D1 and PsbS proteins were not affected by IQF and TH. Spongy mesophyll thickness and palisade cell diameter decreased with IQF and TH. A(max), light compensation and saturation points, Rubisco and nitrogen content (area basis) only increased with light environment (IQF), whereas dark respiration (R(d)) decreased slightly and relative chlorophyll content was higher in taller trees. Overall, the independent effects of more illuminated environment and tree height mainly increased the photochemical instead of the non-photochemical energy flux. Regardless of the photochemical increase with TH, carbon assimilation only significantly improved with higher IQF. Therefore it seems that mainly acclimation to the light environment supports the phenotypic transition of N. nitida from shade to sun.

Temperature-dependent sensitivity of growth and photosynthesis of Scenedesmus obliquus, Navicula pelliculosa and two strains of Microcystis aeruginosa to the herbicide atrazine

The temperature-dependent sensitivities of two algal species and two strains of cyanobacteria to the photosynthesis-inhibiting herbicide atrazine were evaluated in order to understand how the interaction between acclimation temperature and herbicide will affect growth and photosynthesis of aquatic microorganisms. The green alga Scenedesmus obliquus, the diatom Navicula pelliculosa and a toxic and non-toxic strain of Microcystis aeruginosa were acclimated to three different temperatures (10, 15 and 25 °C) and exposed to five concentrations of the herbicide atrazine (0–0.15 μM) for 72 h. Growth, photosynthetic yields, energy fluxes within photosystem II and pigment content were then measured as potential responses to each treatment. With the exception of N. pelliculosa, the toxicity of atrazine was higher when microorganisms were acclimated to lower temperatures. N. pelliculosa was not only the most tolerant to atrazine, but also had a similar sensitivity to this herbicide at every temperature. The observed differences in growth sensitivity to atrazine at low temperature are associated with the ability of algae and cyanobacteria to cope with high excitation pressure, by increasing its protective carotenoid content and non-photochemical energy dissipation. Our results demonstrate that future guidelines for the protection of aquatic life should consider water temperature as an important factor influencing the toxicity of atrazine to aquatic microorganisms.