The effects of ultraviolet radiation-B response on the morphology,ultrastructure, and photosynthetic pigments of Laurencia catarinensis and Palisada flagellifera (Ceramiales,Rhodophyta): a comparative study

The present work aims to compare the effects of ultraviolet radiation on the morphology, ultrastructure, and photosynthetic pigments of two species of Ceramiales: Laurencia catarinensis and Palisada flagellifera. To accomplish this, plants were cultivated and exposed to photosynthetically active radiation (PAR) at 60 μmol photons m^?2 s^?1 and PAR + ultraviolet B radiation (UVBR) at 0.35 W m^?2 at 3 h per day for 7 days. Subsequently, the apical segments of L. catarinensis and P. flagellifera were analyzed under light and transmission microscopy, and both growth rates and photosynthetic pigments were studied. After exposure to PAR + UVBR, L. catarinensis exhibited a high reduction in growth rate and loss of biomass, in addition to a reduction in the concentration of chlorophyll a when compared with treated plants of P. flagellifera. However, after 7 days of exposure to PAR + UVBR, both plants showed a reduction in phycobiliprotein content. Toluidine blue reaction did not show cell wall changes in treated species with PAR + UVBR. Staining of L. catarinensis and P. flagellifera with periodic acid–Schiff (PAS) after UVBR exposure showed an increase in the number of starch grains in both species. When observed by transmission electron microscopy, treated samples of both species also showed disrupted thylakoids of the chloroplasts and an increased number of plastoglobuli. Based on this line of evidence, the present study demonstrates that ultraviolet radiation negatively affects the intertidal macroalgae L. catarinensis and P. flagellifera.     

Response of the agarophyte Gelidium floridanum after in vitro exposure to ultraviolet radiation B: changes in ultrastructure, pigments, and antioxidant systems

As a source of agar, the red macroalga Gelidium floridanum is a seaweed of great economic importance. However, it grows in a region exposed to high ultraviolet B radiation (UVBR). Therefore, to study the in vitro effect of UVBR on this plant, apical segments of G. floridanum were cultivated and exposed to photosynthetically active radiation (PAR) at 80?μmol photons m^?2?s^?1 and PAR + UVBR at 1.6?W?m^?2 at 3?h per day for 7?days. The samples were processed for electron microscopy, and agar yield, growth rates, mitochondrial activity, protein levels, chlorophyll a, phycobiliproteins, carotenoids and phenolic compounds, and photosynthetic performance were examined. After 7?days of exposure to PAR + UVBR, G. floridanum experienced ultrastructural damage that was primarily observed in the internal organization of chloroplasts, increased cell wall thickness, as well as increased volume of plastoglobuli and free ribosomes. Moreover, this exposure might have caused photodamage and photoinhibition of photosynthetic pigments (chlorophyll a and phycobiliproteins), leading to a decrease in photosynthetic efficiency, relative electron transport rate, and maximum photosynthetic rate. These phenomena were matched with a corresponding decrease in growth rates and depigmentation, combined with partial necrosis of the apical segments exposed to PAR + UVBR. Additionally, the UVBR-induced damage elicited a marked cellular antioxidant response, possibly as a consequence of free radical generation.     

Alterations in architecture and metabolism induced by ultraviolet radiation-B in the carragenophyte <Emphasis Type="Italic">Chondracanthus teedei</Emphasis> (Rhodophyta,Gigartinales)

The in vivo effect of ultraviolet radiation-B (UVBR) in apical segments of Chondracanthus teedei was examined. Over a period of 7 days, the segments were cultivated and exposed to photosynthetically active radiation (PAR) at 80 μmol photons m⁻² s⁻¹ and PAR + UVBR at 1.6 W m⁻² for 3 h per day. The samples were processed for electron microscopy and histochemistry; also was analyzed growth rates, mitochondrial activity, protein levels, content of photosynthetic pigments and photosynthetic performance. UVBR elicited increased cell wall thickness and accumulation of plastoglobuli, changes in mitochondrial organization and destruction of chloroplast internal organization. Compared to controls, algae exposed to PAR + UVBR showed a growth rate reduction of 55%. The content of photosynthetic pigments, including chlorophyll a and phycobiliproteins, decreased after exposure to PAR + UVBR. This result agrees with the decreased photosynthetic performance observed after exposing algae to PAR + UVBR. Irradiation also elicited increased activity of the antioxidant enzyme glutathione peroxidase and decreased mitochondrial NADH dehydrogenase activity, which correlated with the decreased protein content in plants exposed to PAR + UVBR. Taken together, these findings strongly indicate that UVBR negatively affects the architecture and metabolism of the carragenophyte C. teedei.     

Effects of UVB radiation on the carragenophyte <Emphasis Type="Italic">Kappaphycus alvarezii</Emphasis> (Rhodophyta,Gigartinales): changes in ultrastructure,growth, and photosynthetic pigments

Damage to the ozone layer has led to increased levels of ultraviolet radiation at the earth’s surface. Increased ultraviolet radiation can affect macroalgae in many important ways, including reduced growth rate, changes in cell biology and ultrastructure. Kappaphycus alvarezii is a red macroalga of economic interest due to its production of kappa carrageenan. In this study, we examined two strains of K. alvarezii (green and red) exposed to ultraviolet B radiation (UVBR) for 3 h per day during 28 days of cultivation in vitro. UVBR caused changes in the ultrastructure of cortical and subcortical cells, which included increased thickness of the cell wall and plastoglobuli, reduced intracellular spaces, changes in the cell contour, and destruction of chloroplast internal organization. While the green strain exposed to photosynthetically active radiation (PAR) showed growth rates of 6.75% day⁻¹, the red strain grew only 6.35% day⁻¹. Upon exposure to PAR + UV-B, a decreasing trend in growth rates was observed for both strains, with the green strain growing 3.0% day⁻¹ and the red strain growing 2.77% day⁻¹. Significant differences in growth rates between control and UV-B-exposed algae were also found in both strains. Furthermore, compared with control algae, phycobiliprotein contents (phycoerythrin, phycocyanin, and allophycocyanin) were observed to decrease in both strains after PAR + UV-B exposure. However, while the chlorophyll a levels increased in both strains, the green strain showed no significant differences in chlorophyll a levels. Taken together, these findings strongly suggested that UVBR negatively affects the ultrastructure, growth rates, and photosynthetic pigments of intertidal macroalgae and, in the long term, their economic viability.     

The effect of temperature on photosynthetic induction under fluctuating light in Chrysanthemum morifolium

The photosynthetic response was investigated on Chrysanthemum morifolium under dynamic light conditions in the 20–35 °C temperature range to evaluate the effect of climatic variables on photosynthetic induction. The plant material was grown under uniform, controlled conditions and its gas exchange was analyzed. The gas exchange measurements were used to investigate the rate of induction, momentary induction state, and the opening of stomata. At the varying temperature ranges and under dynamic light conditions, C. morifolium reached a quasi-steady-state induction equilibrium (IS_eq(PAR,T)) within 14–45 min. For the same level of photosynthetically active radiation (PAR), the equilibrated level of steady-state induction increased as the temperature increased. It was highest approximately at 30 °C. The induction state was equilibrated at a lower level as the temperature increased to 35 °C. The interaction effect of PAR and temperature on induction state was not significant. The rate of photosynthetic induction and the time required at which the induction reached its 90 % value (t ₉₀) was influenced by PAR significantly. The light history of a leaf had a significant effect on t ₉₀, indicating that the time to reach a steady-state induction is different depending on the light environment and the period at which the leaf was exposed to light. The velocity of the photosynthetic induction was not affected by the temperature. It was associated with stomatal conductance of the leaf prior to the onset of light (g _Sini).     

Sensitivity of Laminariales zoospores from Helgoland (North Sea) to ultraviolet and photosynthetically active radiation: implications for depth distribution and seasonal reproduction

Depth distribution of kelp species in Helgoland (North Sea) is characterized by occurrence of Laminaria digitata in the upper sublittoral, whereas L. saccharina and L. hyperborea dominate the mid and lower sublittoral region. Laminaria digitata is fertile in summer whereas both other species are fertile in autumn/winter. To determine the light sensitivity of the propagules, zoospores of L. digitata, L. saccharina and L. hyperborea were exposed in the laboratory to different exposure times of photosynthetically active radiation (PAR; 400–700 nm), PAR + UVA radiation (UVAR; 320–400 nm) and PAR + UVAR + UVB radiation (UVBR; 280–320 nm). Optimum quantum yield of PSII and DNA damage were measured after exposure. Subsequently, recovery of photosynthetic efficiency and DNA damage repair, as well as germination rate were measured after 2 and 3 d cultivation in dim white light. Photosynthetic efficiency of all species was photoinhibited already at 20 µmol photons m⁻² s⁻¹ PAR, whereas UV radiation (UVR) had a significant additional effect on photoinhibition. Recovery of the PSII function was observed in all species but not in spores exposed to irradiation longer than 4 h of PAR + UVA + UVB and 8 h of PAR + UVA. The amount of UVB-induced DNA damage measured as cyclobutane–pyrimidine dimers (CPDs) increased with exposure time and highest damage was detected in the spores of lower subtidal L. hyperborea relative to the other two species. Significant removal of CPDs indicating repair of DNA damage was observed in all species after 2 d in low white light especially in the spores of upper subtidal L. digitata. Therefore, efficient DNA damage repair and recovery of PSII damage contributed to the germination success but not in spores exposed to 16 h of UVBR. UV absorption of zoospore suspension in L. digitata is based both on the absorption by the zoospores itself as well as by exudates in the medium. In contrast, the absorption of the zoospore suspension in L. saccharina and L. hyperborea is based predominantly on the absorption by the exudates in the medium. This study indicates that UVR sensitivity of zoospores is related to the seasonal zoospore production as well as the vertical distribution pattern of the large sporophytes.     

Motility and photosynthetic responses of the green microalga Tetraselmis subcordiformis to visible and UV light levels

To test the effects of photosynthetic active radiation (PAR, 400–700 nm) and ultraviolet radiation (UVR, 280–400 nm) on phototaxis and photosynthesis of free swimming microalgae, experiments were performed with Tetraselmis subcordiformis (Wille) Butcher under a solar simulator. In particular, we evaluated the effects of different PAR levels and radiation regimes (i.e., PAR only and PAR+UVR) on those two processes. We found that the cells preferred to move to a particular area (e.g., receiving 100 W m^?2 PAR) with little photochemical suppression or inhibition of carbon fixation. Adding UV-A to high PAR decreased its swimming capacity and photosynthetic capability, and further adding UV-B led to more inhibition. The suppression of the moving capability of T. subcordiformis was reversible but the cells exposed to PAR combined with UVR needed longer time intervals to recover their motility as compared with those irradiated only with PAR. Based on the above results, we postulate that in nature, the motile capability and photosynthesis of free swimming the green microalga might be impaired by enhanced solar UVR. On the other hand, the cells can reduce the damage caused by high irradiances (and even get the optimum light level for photosynthesis) by a behavioral swimming response.     

CHRONIC EFFECTS OF ULTRAVIOLET-B RADIATION ON GROWTH AND CELL VOLUME OF PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

Cultures of the temperate estuarine diatom, Phaeodactylum tricornutum Bohlin (NEPCC Clone 31), were grown under ambient intensities of ultraviolet-A radiation (UVAR), photosynthetically active radiation (PAR), and various intensities of ultraviolet-B radiation (UVBR; 290–320 nm). Growth rates and cell volumes were monitored for 36 d. UVBR decreased growth rates and increased cell volumes. Sensitivity of growth to UVBR increased with time. Growth rates of P. tricornutum decreased with increasing ratios of UVBR:UVAR + PAR.     

UV RADIATION,PHOSPHORUS, AND THEIR COMBINED EFFECTS ON THE TAXONOMIC COMPOSITION OF PHYTOPLANKTON IN A BOREAL LAKE1

We examined how UV radiation and phosphorus (P) affect the taxonomic composition, abundance, and biomass of phytoplankton in an oligotrophic boreal lake. We exposed phytoplankton to three different solar radiation regimes (PAR + UV‐A radiation [UVAR]+ UV‐B radiation [UVBR], PAR + UVAR, and PAR only) and to five levels of P. The biomass of small chrysophytes was reduced by 350% after exposure to PAR + UVAR + UVBR compared with PAR only. No other taxa were found to be negatively affected by exposure to UVBR. Several taxa (e.g. Chry‐ sochromulina laurentiana Kling) were sensitive to UVAR, whereas others (e.g. Tabellaria flocculosa (Roth) Kutzing) were not affected by UV radiation exposure. Principal components analysis ordination separated phytoplankton that were negatively affected by UV radiation and/or positively affected by P treatments (e.g. small chrysophytes, Cryptomonas rostratiformis, T. flocculosa) from those that generally were unaffected by either treatment (e.g. desmids, some Cyanobacteria). Richness, Shannon‐Weaver diversity, and evenness were significantly higher in phytoplankton communities shielded from UVAR and UVBR. The relationship between diversity and richness was positive in all phytoplankton samples except in those exposed to UVBR. Thus, UVBR‐exposed phytoplankton communities were dominated by a few species even though the number of taxa remained relatively unchanged. Consequently, alterations in the UV environments of lakes resulting from climate warming (e.g. drought) and land‐use change (e.g. increased P export) will likely promote shifts in the community composition of lake phytoplankton.     

Importance of the green color,absorption gradient,and spectral absorption of chloroplasts for the radiative energy balance of leaves

Terrestrial green plants absorb photosynthetically active radiation (PAR; 400–700 nm) but do not absorb photons evenly across the PAR waveband. The spectral absorbance of photosystems and chloroplasts is lowest for green light, which occurs within the highest irradiance waveband of direct solar radiation. We demonstrate a close relationship between this phenomenon and the safe and efficient utilization of direct solar radiation in simple biophysiological models. The effects of spectral absorptance on the photon and irradiance absorption processes are evaluated using the spectra of direct and diffuse solar radiation. The radiation absorption of a leaf arises as a consequence of the absorption of chloroplasts. The photon absorption of chloroplasts is strongly dependent on the distribution of pigment concentrations and their absorbance spectra. While chloroplast movements in response to light are important mechanisms controlling PAR absorption, they are not effective for green light because chloroplasts have the lowest spectral absorptance in the waveband. With the development of palisade tissue, the incident photons per total palisade cell surface area and the absorbed photons per chloroplast decrease. The spectral absorbance of carotenoids is effective in eliminating shortwave PAR (<520 nm), which contains much of the surplus energy that is not used for photosynthesis and is dissipated as heat. The PAR absorptance of a whole leaf shows no substantial difference based on the spectra of direct or diffuse solar radiation. However, most of the near infrared radiation is unabsorbed and heat stress is greatly reduced. The incident solar radiation is too strong to be utilized for photosynthesis under the current CO₂ concentration in the terrestrial environment. Therefore, the photon absorption of a whole leaf is efficiently regulated by photosynthetic pigments with low spectral absorptance in the highest irradiance waveband and through a combination of pigment density distribution and leaf anatomical structures.     

<Emphasis Type="Italic">Terminalia arjuna</Emphasis> bark extract alleviates nickel toxicity by suppressing its uptake and modulating antioxidative defence in rice seedlings

Terminalia arjuna (Ta) bark contains various natural antioxidants and has been used to protect animal cells against oxidative stress. In the present study, we have examined alleviating effects of Ta bark aqueous extract against Ni toxicity in rice (Oryza sativa L.). When rice seedlings were raised for 8 days in hydroponics in Yoshida nutrient medium containing 200 μM NiSO₄, a decline in height, reduced biomass, increased Ni uptake, loss of root plasma membrane integrity, increase in the level of O₂˙^?, H₂O₂ and ˙OH, increased lipid peroxidation, decline in photosynthetic pigments, increase in the level of antioxidative enzymes superoxide dismutase, catalase and glutathione peroxidase and alterations in their isoenzyme profile patterns were observed. Transmission electron microscopy (TEM) showed damage to chloroplasts marked by disorganised enlarged starch granules and disrupted thylakoids under Ni toxicity. Exogenously adding Ta bark extract (3.2 mg ml^?1) to the growth medium considerably alleviated Ni toxicity in the seedlings by reducing Ni uptake, suppressing generation of reactive oxygen species, reducing lipid peroxidation, restoring level of photosynthesis pigments and ultrastructure of chloroplasts, and restoring levels of antioxidative enzymes. Results suggest that Ta bark extract considerably alleviates Ni toxicity in rice seedlings by preventing Ni uptake and reducing oxidative stress in the seedlings.     

Developmental phase-dependent photosynthetic responses to ultraviolet-B radiation: damage, defence, and adaptation of primary leaves of wheat seedlings

Alterations in photosynthetic capacity of primary leaves of wheat seedlings in response to ultraviolet-B (UV-B; 280–320 nm; 60 μmol m⁻² s⁻¹) exposure alone and in combination with photosynthetically active radiation (PAR; 400–800 nm; 200 μmol m⁻² s⁻¹) during different phases of leaf growth and development were assessed. UV-B exposure resulted in a phase-dependent differential loss in photosynthetic pigments, photochemical potential, photosystem 2 (PS2) quantum yield, and in vivo O₂ evolution. UV-B exposure induced maximum damage to the photosynthetic apparatus during senescence phase of development. The damages were partially alleviated when UV-B exposure was accompanied by PAR. UV-B induced an enhancement in accumulation of flavonoids during all phases of development while it caused a decline in anthocyanin content during senescence. The differential changes in these parameters demonstrated the adaptation ability of leaves to UV-B stress during all phases of development and the ability was modified in UV-B+ PAR exposed samples.     

Effects of ultraviolet radiation on protein content,respiratory electron transport system (ETS) activity and superoxide dismutase (SOD) activity of Antarctic plankton

Depletion of stratospheric ozone causes a significant increase in UV radiation in the Antarctic regions. Its effects include DNA damage, as well as impairment of photosynthesis, respiration, protein synthesis and other metabolic functions. Defence systems of cells are directed against free oxygen radicals liberated through UV radiation. One of their main components of defence systems are superoxide dismutases (SODs). The effects of ultraviolet radiation A and B (UVAR and UVBR) on protein synthesis, respiratory electron transfer (ETS) activity and superoxide dismutase (SOD) activity in Antarctic plankton were examined. Samples were taken in the Gerlache Strait (Antarctica). Three stations were situated in an area, which showed a Cryptomonas bloom. Two stations were located in areas having a bloom of green nanoflagellates. Samples were exposed for 3 h to photosynthetically active radiation (PAR), or to PAR + UVAR or to PAR + UVAR + UVBR, under fixed experimental irradiances. UVBR inhibited protein synthesis and ETS activity, and enhanced SOD activity. UVAR enhanced protein synthesis and ETS activity, and inhibited SOD activity. Samples, which had received more solar radiation prior to experiments showed less inhibition of protein synthesis by experimental UVBR, which suggests acclimation to ambient radiation. Cryptomonas-dominated stations showed less SOD activity than the green flagellate-dominated stations, which might be related to the protection conferred by their phycoerythrin.     

Interaction of Photoprotective and Acclimation Mechanisms in Ulva rigida (Chlorophyta) in Response to Diurnal Changes in Solar Radiation in Southern Chile

Species of the genus Ulva (Chlorophyta) are regarded as opportunistic organisms, which efficiently adjust their metabolism to the prevailing environmental conditions. In this study, changes in chlorophyll‐a fluorescence‐based photoinhibition of photosynthesis, electron transport rates, photosynthetic pigments, lipid peroxidation, total phenolic compounds, and antioxidant metabolism were investigated during a diurnal cycle of natural solar radiation in summer (for 12 h) under two treatments: photosynthetically active radiation (PAR: 400–700 nm) and PAR+ ultraviolet (UV) radiation (280–700 nm). In the presence of PAR alone, Ulva rigida showed dynamic photoinhibition, and photosynthetic parameters and pigment concentrations decreased with the intensification of the radiation. On the other hand, under PAR+UV conditions a substantial decline up to 43% was detected and an incomplete fluorescence recovery, also, P‐I curve values remained low in relation to the initial condition. The phenolic compounds increased their concentration only in UV radiation treatments without showing a correlation with the antioxidant activity. The enzimatic activity of superoxide dismutase (SOD) and ascorbate peroxidase (APX) increased over 2‐fold respect at initial values during the onset of light intensity. In contrast, catalase (CAT) increased its activity rapidly in response to the radiation stress to reach maxima at 10 a.m. and decreasing during solar. The present study suggests that U. rigida is capable of acclimating to natural radiation stress relies on a concerted action of various physiological mechanisms that act at different times of the day and under different levels of environmental stress.     

Leaf anatomy and photosynthetic efficiency of <Emphasis Type="Italic">Acrostichum danaeifolium</Emphasis> after UV radiation

This paper reports effects of ultraviolet B (UVB) radiation on leaf anatomy and contents of chlorophyll and carotenoids, as well as photosynthetic parameters, in young sporophytes of Acrostichum danaeifolium Langsd. & Fisch. (Polypodiopsida, Pteridaceae) exposed to UV radiation treatments for 1 h daily for six weeks. The leaves showed large aerenchyma and present chloroplasts in both epidermises. After cultivation under PAR + UVA + UVB, leaves showed curling and malformed stomata on the abaxial face. After the UV treatment, chloroplasts in leaves were arranged against the inner wall of the epidermal cells. Transmission electron microscopy analysis showed some dilated thylakoids and plastoglobuli in chloroplasts and vesicles containing phenolic compounds in the cytoplasm. Differences were not observed between control and UV-treated plants in their contents of chlorophylls, carotenoids, and photosynthetic parameters. A. danaeifolium grown in sunny mangrove environment seems to have mechanisms preventing photosystem damage.     

Response of chlorophyll d-containing cyanobacterium Acaryochloris marina to UV and visible irradiations

We have previously investigated the response mechanisms of photosystem II complexes from spinach to strong UV and visible irradiations (Wei et al J Photochem Photobiol B 104:118–125, 2011). In this work, we extend our study to the effects of strong light on the unusual cyanobacterium Acaryochloris marina, which is able to use chlorophyll d (Chl d) to harvest solar energy at a longer wavelength (740 nm). We found that ultraviolet (UV) or high level of visible and near-far red light is harmful to A. marina. Treatment with strong white light (1,200 μmol quanta m^?2 s^?1) caused a parallel decrease in PSII oxygen evolution of intact cells and in extracted pigments Chl d, zeaxanthin, and α-carotene analyzed by high-performance liquid chromatography, with severe loss after 6 h. When cells were irradiated with 700 nm of light (100 μmol quanta m^?2 s^?1) there was also bleaching of Chl d and loss of photosynthetic activity. Interestingly, UVB radiation (138 μmol quanta m^?2 s^?1) caused a loss of photosynthetic activity without reduction in Chl d. Excess absorption of light by Chl d (visible or 700 nm) causes a reduction in photosynthesis and loss of pigments in light harvesting and photoprotection, likely by photoinhibition and inactivation of photosystem II, while inhibition of photosynthesis by UVB radiation may occur by release of Mn ion(s) in Mn₄CaO₅ center in photosystem II.     

Physiological, biochemical, and ultrastructural responses of the green macroalga Urospora penicilliformis from Arctic Spitsbergen to UV radiation

Exposure of the filamentous turf green alga Urospora penicilliformis to ambient and artificial ultraviolet radiation (UVR) revealed a considerable resilient species. This explains the ability of this alga to thrive in the middle–upper intertidal zones of the Arctic sea where it is periodically exposed to environmental extremes. A transient UVR effect on photosynthesis under photosynthetically active radiation (PAR) + UV-A and PAR + UV-A + UV-B was found, but dynamic recovery of photoinhibition was observed immediately after reduction of the photon fluence rate of PAR in the absence or presence of background UVR under laboratory and natural solar radiation, respectively. Chlorophylls, carotenoids, and xanthophyll cycle pigments (violaxanthin, antheraxanthin, and zeaxanthin) concentrations were not significantly different between freshly collected samples and filaments exposed to additional laboratory radiation treatment. The ultrastructure of the U. penicilliformis gametophytes showed that the cells are well adapted to UVR. No significant ultrastructural alterations were observed in filaments exposed to different spectral irradiance in the laboratory compared to in situ acclimated specimen. The antioxidant α-tocopherol was detected in minute quantity while the search for flavonoid-like compounds was negative. Other UV screening strategies or certain genetically fixed physiological protective mechanism could be operating in this species responsible for their occurrence in higher shoreline and ecological success. Further molecular and biochemical studies are needed to elucidate the stress resistance in this turf alga. There is an indication that the extremely thick cell wall of U. penicilliformis gametophytes covered with mucilage sheath and dense layer of mineral depositions may provide a shield against unfavorable environmental conditions in general and against UVR in particular.     

Diminution of photosynthesis in rice (Oryza sativa L.) seedlings under elevated CO2 concentration and increased temperature

The photosynthetic responses to elevated CO₂ concentration (EC) at ambient and ambient +4°C temperature were aßsessed in the second leaf of rice (Oryza sativa L.) seedlings. The duration of different leaf developmental phases, as characterised by changes in photosynthetic pigment contents and photochemical potential, was protracted in the seedlings grown under EC. On the other hand, a temporal shift in the phases of development with an early onset of senescence was observed in the seedlings grown under EC at ambient +4°C temperature. The contents of carotenoids, ß-carotene, and xanthophyll cycle pigments revealed that EC downregulated the protective mechanism of photosynthetic apparatus against oxidative damages, whereas this mechanism assumed higher significance under EC at ambient +4°C temperature. We observed an enhancement in electron transport activity, photochemical potential, and net photosynthesis in spite of a loss in photostasis of photosynthesis under EC. On the other hand, the loss in photostasis of photosynthesis was exacerbated under EC at ambient +4°C temperature due to the decline in electron transport activity, photochemical potential, and net photosynthesis.     

Effect of ultraviolet-B radiation on growth,photosynthetic pigments,and cell biology of <Emphasis Type="Italic">Kappaphycus alvarezii</Emphasis> (Rhodophyta,Gigartinales) macroalgae brown strain

Kappaphycus alvarezii is a seaweed of great economic importance for the extraction of kappa carrageenan from its cell walls. The most common strains are dark red, brown, yellow, and different gradations of green. It is known that ultraviolet radiation (UVR) affects macroalgae in many important ways, including reduced growth rate, reduction of primary productivity, and changes in cell biology and ultrastructure. Therefore, we examined the brown strain of K. alvarezii exposed to ultraviolet-B radiaton (UVBR) for 3 h per day during 28 days of cultivation. The control plants showed growth rates of 7.27% d⁻¹, while plants exposed to UVBR grew only 4.0% d⁻¹. Significant differences in growth rates and in phycobiliproteins between control and exposed plants were also found. Compared with control plants, phycobiliprotein contents were observed to decrease after UV-B exposure. Furthermore, the chlorophyll a (Chl a) contents decreased and showed significant differences. UVBR also caused changes in the ultrastructure of cortical and subcortical cells, which included increased thickness of the cell wall and number of plastoglobuli, reduced intracellular spaces, changes in the cell contour, and destruction of chloroplast internal organization. Reaction with Toluidine Blue showed an increase in the thickness of the cell wall, and Periodic Acid-Schiff stain showed a decrease in the number of starch grains. By the significant changes in growth rates, photosynthetic contents and ultrastructual changes observed, it is clear that UVBR negatively affects intertidal macroalgae and, by extension, their economic viability.     

Comparison of power output by rice (Oryza sativa) and an associated weed (Echinochloa glabrescens) in vascular plant bio-photovoltaic (VP-BPV) systems

Vascular plant bio-photovoltaics (VP-BPV) is a recently developed technology that uses higher plants to harvest solar energy and the metabolic activity of heterotrophic microorganisms in the plant rhizosphere to generate electrical power. In the present study, electrical output and maximum power output variations were investigated in a novel VP-BPV configuration using the crop plant rice (Oryza sativa L.) or an associated weed, Echinochloa glabrescens (Munro ex Hook. f.). In order to compare directly the physiological performances of these two species in VP-BPV systems, plants were grown in the same soil and glasshouse conditions, while the bio-electrochemical systems were operated in the absence of additional energy inputs (e.g. bias potential, injection of organic substrate and/or bacterial pre-inoculum). Diurnal oscillations were clearly observed in the electrical outputs of VP-BPV systems containing the two species over an 8-day growth period. During this 8-day period, O. sativa generated charge ～6 times faster than E. glabrescens. This greater electrogenic activity generated a total charge accumulation of 6.75?±?0.87 Coulombs for O. sativa compared to 1.12?±?0.16 for E. glabrescens. The average power output observed over a period of about 30 days for O. sativa was significantly higher (0.980?±?0.059 GJ?ha^?1?year^?1) than for E. glabrescens (0.088?±?0.008 GJ?ha^?1?year^?1). This work indicates that electrical power can be generated in both VP-BPV systems (O. sativa and E. glabrescens) when bacterial populations are self-forming. Possible reasons for the differences in power outputs between the two plant species are discussed.