Responses of vegetative gametophytes of Undaria pinnatifida to high irradiance in the process of gametogenesis

The population of Undaria pinnatifida in its ecologic niche sustains itself in high temperature summer in the form of vegetative gametophytes, the haploid stage in its heteromorphic life cycle. Gametogenesis initiates when seawater temperature drops below the threshold levels in autumn in the northern hemisphere. Given that the temperature may fall into the appropriate range for gametogenesis, the level of irradiance determines the final destiny of a gametophytic cell, either undergoing vegetative cell division or initiating gametogenesis. In elucidating how vegetatively propagated gametophytes cope with changes of irradiance in gametogenesis, we carried out a series of culture experiments and found that a direct exposure to irradiance as high as 270 μmol photons m^?2 s^?1 was lethal to dim‐light (7–10 μmol photons m^?2 s^?1) adapted male and female gametophytes. This lethal effect was linearly corelated with the exposure time. However, dim‐light adapted vegetative gametophytes were shown to be able tolerate as high as 420 μmol photons m^?2 s^?1 if the irradiance was steadily increased from dim light levels (7–10 μmol photons m^?2 s^?1) to 90, 180 and finally 420 μmol photons m^?2 s^?1, respectively, at a minimum of 1–3 h intervals. Percentage of female gametophytic cells that turned into oogonia and were eventually fertilized was significantly higher if cultured at higher but not lethal irradiances. Findings of this investigation help to understand the dynamic changes of population size of sporophytic plants under different light climates at different site‐specific ecologic niches. It may help to establish specific technical details of manipulation of light during mass production of seedlings by use of vegetatively propagated gametophytes.     

Photon irradiance required to support optimal growth and interrelations between irradiance and pigment composition in the green alga Haematococcus pluvialis

The aim of the work was to find the optimal photon irradiance for the growth of green cells of Haematococcus pluvialis and to study the interrelations between changes in photochemical parameters and pigment composition in cells exposed to photon irradiances between 50 and 600?µmol?m^?2?s^?1 and a light:dark cycle of 12:12?h. Productivity of cultures increased with irradiance. However, the rate of increase was higher in the range 50–200?µmol?^?2?s^?1. The carotenoid content increased with increasing irradiance, while the chlorophyll content decreased. The maximum quantum yield of PSII (F_v/F_m) gradually declined from 0.76 at the lowest irradiance of 50?µmol?^?2?s^?1 to 0.66 at 600?µmol?^?2?s^?1. Photosynthetic activity showed a drop at the end of the light period, but recovered fully during the following dark phase. A steep increase in non-photochemical quenching was observed when cultures were grown at irradiances above 200?µmol?^?2?s^?1. A sharp increase in the content of secondary carotenoids also occurred above 200?µmol?m^?2?s^?1. According to our results, with H. pluvialis green cells grown in a 5-cm light path device, 200?µmol?^?2?s^?1 was optimal for growth, and represented a threshold above which important changes in both photochemical parameters and pigment composition occurred.     

Photosynthetic and biochemical characterization of in vitro-derived African violet (Saintpaulia ionantha H. Wendl) plants to ex vitro conditions

African violet (Saintpaulia ionantha H. Wendl) is one of the most easily and commonly tissue-cultured ornamental plants. Despite this, there are limited reports on photosynthetic capacity and its impact on the plant quality during acclimatization. Various growth, photosynthetic and biochemical parameters and activities of antioxidant enzymes and dehydrins of micropropagated plants were assessed under three light intensities (35, 70, and 100 µmol m^?2 s^?1 photosynthetic photon flux density – PPFD). Fresh and dry plant biomass, plant height, and leaf area were optimal with high irradiance (70–100 µmol m^?2 s^?1 PPFD). Chlorophyll and carotenoid contents and net photosynthesis were optimal in plants grown under 70 µmol m^?2 s^?1 PPFD. Stomatal resistance, malondialdehyde content, and F_v/F_m values were highest at low light irradiance (35 µmol m^?2 s^?1 PPFD). The activities of three antioxidant enzymes, superoxide dismutase, catalase, and glutathione peroxidase, increased as light irradiance increased, signaling that high light irradiance was an abiotic stress. The accumulation of 55, 33, and 25 kDa dehydrins was observed with all light treatments although the expression levels were highest at 35 µmol m^?2 s^?1 PPFD. Irradiance at 70 µmol m^?2 s^?1 PPFD was suitable for the acclimatization of African violet plants. Both low and high irradiance levels (35 and 100 µmol m^?2 s^?1 PPFD) induced the accumulation of antioxidants and dehydrins in plants which reveals enhanced stress levels and measures to counter it.     

Rapid, reversible alterations in spinach thylakoid appression upon changes in light intensity

Changes in light quantity and quality cause structural changes within the thylakoid membrane; long‐term responses have been described for so‐called ‘sun’ and ‘shade’ leaves. Many leaves, however, experience changes in irradiance on a time scale of minutes due to self‐shading and sun flecks. In this study, mature, attached spinach leaves were grown at 300 µmol photons m^?2 s^?1 then rapidly switched to a different light treatment. The treatment irradiances were 10, 800 or 1500 µmol m^?2 s^?1 for 10 min, or 10 or 20 min of self‐shading (about 10 µmol m^?2 s^?1). Image analysis of transmission electron micrographs revealed that a 10 min switch to a lower light intensity increased grana size and number per chloroplast profile by 10–20%. Returning the leaves to 300 µmol m^?2 s^?1 for 10 min reversed the phenomenon. Chlorophyll fluorescence measurements of detached, intact leaves at 77 K were suggestive of a transition from state 2 to state 1 upon shading. Diurnal ultrastructural measurements of granal size and number did not reveal a significant net change in ultrastructure over the time scale of hours. It is concluded that spinach chloroplasts can alter the degree of thylakoid appression in response to irradiance changes on a time scale of minutes. These ultrastructural responses are caused by biochemical and biophysical adjustments within the thylakoid membrane that serve to maximize photosynthesis and minimize photo‐inhibition under rapidly fluctuating light environments.     

Growth rates of phytoplankton under fluctuating light

• 1 The effect of light fluctuations on the growth rates of four species of freshwater phytoplankton was investigated. Experimental light regimes included constant irradiance and fluctuations of a step function form, with equal proportion of high (maximum of 240 µmol photons m^‐2 s^‐1) and low light (minimum of 5 µmol photons m^‐2 s^‐1) (or dark) in a period. Fluctuations of 1, 8 and 24‐h periods were imposed over several average irradiances (25, 50, 100 and 120 µmol photons m^‐2 s^‐1).
• 2 Growth rate responses to fluctuations were species‐specific and depended on both the average irradiance and the period of fluctuations. Fluctuations at low average irradiances slightly increased growth rate of the diatom Nitzschia sp. and depressed growth of the cyanobacterium Phormidium luridum and the green alga Sphaerocystis schroeteri compared to a constant irradiance.
• 3 Fluctuations at higher average irradiance did not have a significant effect on the growth rates of Nitzschia sp. and Sphaerocystis schroeteri (fluctuations around saturating irradiances) and slightly increased the growth rates of the cyanobacteria Anabaena flos‐aquae and Phormidium luridum (when irradiance fluctuated between limiting and inhibiting levels).
• 4 In general, the effect of fluctuations tended to be greater when irradiance fluctuated between limiting and saturating or inhibiting levels of a species growth‐irradiance curve compared to fluctuations within a single region of the curve.
• 5 The growth rates of species under fluctuating light could not always be predicted from their growth‐irradiance curves obtained under constant irradiance. When fluctuations occur between limiting and saturating or inhibiting irradiances for the alga and when the period of fluctuations is long (greater than 8 h), steady‐state growth‐irradiance curves may be insufficient to predict growth rates adequately. Consequently, additional data on physiological acclimation, such as changes in photosynthetic parameters, may be required for predictions under non‐constant light supply in comparison to constant conditions.

     

High-light damage in air-dry thalli of the old forest lichen Lobaria pulmonaria-interactions of irradiance, exposure duration and high temperature

High-light damage in air-dry thalli of Lobaria pulmonaria were measured in the laboratory as reductions in maximal PSII efficiency (Fv/Fm) after a 48 h recovery in a hydrated state at low light to account for permanent damage. Thalli treated with the lowest light dose (90 mol photons m^-2) recovered normal Fv/Fm-values with increasing irradiances (400-700 nm) up to 1000 mol photons m^-2 s^-1. Doubling this dose lowered the threshold level for damage from 1000 to 320 mol photons m^-2 s^-1, and reduced Fv/Fm at 1000 mol photons m^-2 s^-1 by more than 50%. A second doubling of the dose to 360 mol photons m^-2 caused damage at 200 mol photons m^-2 s^-1, and a nearly complete cessation of PSII efficiency occurred at 1000 mol photons m^-2 s^-1. No reciprocity of irradiance and duration of illumination for PSII function was found. The measured time-dependent decrease in Fv/Fm was remarkably similar for the naturally coupled, but artificially separated, light and temperature factors. Therefore, the damage of high light on desiccated L. pulmonaria seemed to be an additive effect of high irradiance and high temperatures. Air-dry thalli were highly heat susceptible, being affected already at temperatures around 40C. Logging operations in forests are likely to raise the solar radiation at remaining lichen sites to destructive levels.Keywords: Lichens, high-light damage, heat stress, poikilohydric organisms, reciprocity.      

Decrease of polypeptides in the PS I antenna complex with increasing growth irradiance in the red alga Porphyridium cruentum

Thylakoids isolated from cells of the red alga Porphyridium cruentum exhibit an increased PS I activity on a chlorophyll basis with increasing growth irradiance, even though the stoichiometry of Photosystems I and II in such cells shows little change (Cunningham et al. (1989) Plant Physiol 91: 1179–1187). PS I activity was 26% greater in thylakoids of cells acclimated at 280 mol photons · m^–2 · s^–1 (VHL) than in cells acclimated at 10 mol photons · m^–2 · s^–1 (LL), indicating a change in the light absorbance capacity of PS I. Upon isolating PS I holocomplexes from VHL cells it was found that they contained 132±9 Chl/P700 while those obtained from LL cells had 165±4 Chl/P700. Examination of the polypeptide composition of PS I holocomplexes on SDS-PAGE showed a notable decrease of three polypeptides (19.5, 21.0 and 22 kDa) in VHL-complexes relative to LL-complexes. These polypeptides belong to a novel LHC I complex, recently discovered in red algae (Wolfe et al. (1994a) Nature 367: 566–568), that lacks Chl b and includes at least six different polypeptides. We suggest that the decrease in PS I Chl antenna size observed with increasing irradiance is attributable to changes occurring in the LHC I-antenna complex. Evidence for a Chl-binding antenna complex associated with PS II core complexes is lacking at this point. LHC II-type polypeptides were not observed in functionally active PS II preparations (Wolfe et al. (1994b) Biochimica Biophysica Acta 1188: 357–366), nor did we detect polypeptides that showed immunocross-reactivity with LHC II specific antisera (made to Chlamydomonas and Euglena LHC II).Abbreviations Bis-Tris bis(2-hydroxyethyl)imino-tris(hydroxymethyl)methane - DCPIP 2,6-dichlorophenol indophenol - -dm dodecyl--d-maltoside - HL high light of 150 mol photons · m^–2 · s^–1 - LGB lower green band - LHC I light-harvesting complex of PS I - LHC II light-harvesting complex of PS II - LL low light of 10 mol photons · m^–2 · s^–1 - ML medium light of 50 mol photons · m^–2 · s^–1 - MES 2-(N-morpholino) ethanesulfonic acid - P700 reaction center of PS I - PFD photon flux density - Trizma tris(hydroxymethyl)aminomethane - UGB upper green band - VHL very high light of 280 mol photons · m^–2 · s^–1     

Ecophysiological and morphological comparison of two populations of Chlainomonas sp. (Chlorophyta) causing red snow on ice-covered lakes in the High Tatras and Austrian Alps

Based on analyses of multiple molecular markers (18S rDNA, ITS1, ITS2 rDNA, rbcL), an alga that causes red snow on the melting ice cover of a high-alpine lake in the High Tatras (Slovakia) was shown to be identical with Chlainomonas sp. growing in a similar habitat in the Tyrolean Alps (Austria). Both populations consisted mostly of smooth-walled quadriflagellates. They occurred in slush, and shared similar photosynthetic performances (photoinhibition above 1300 µmol photons m^–2 s^–1), very high levels of polyunsaturated fatty acids (PUFA, 64% and 74% respectively) and abundant astaxanthin accumulation, comparable to the red spores of Chlamydomonas nivalis (Bauer) Wille. Physiological differences between the Slovak and Austrian populations included higher levels of α-tocopherol and a 13Z-isomer of astaxanthin in the former. High accumulation of secondary pigments in the Slovak population probably reflected harsher environmental conditions, since the collection was made later in the growing season when cells were exposed to higher irradiance at the surface. Using a polyphasic approach, we compared Chlainomonas sp. with Chlamydomonas nivalis. The latter causes ?conventional? red snow, and shows high photophysiological plasticity, with high efficiency under low irradiance and no photoinhibition up to 2000 µmol photons m^–2 s^–1. Its PUFA content was significantly lower (50%). An annual cycle of lake-to-snow colonization by Chlainomonas sp. from slush layers deeper in the ice cover is proposed. Our results point to an ecologically highly specialized cryoflora species, whose global distribution is likely to be more widespread than previously assumed.     

Effects of salinity,light intensity and sediment on growth,pigments, agar production and reproduction in Gracilaria tenuistipitata from Songkhla Lagoon in Thailand

The effects of salinity, light intensity and sediment on Gracilaria tenuistipitata C.F. Chang & B.M. Xia on growth, pigments, agar production, and net photosynthesis rate were examined in the laboratory under varying conditions of salinity (0, 25 and 33 psu), light intensity (150, 400, 700 and 1000 µmol photons m^?2 s^?1) and sediment (0, 0.67 and 2.28 mg L^?1). These conditions simulated field conditions, to gain some understanding of the best conditions for cultivation of G. tenuistipitata. The highest growth rate was at 25 psu, 700 µmol photons m^?2 s^?1 with no sediments, that provided a 6.7% increase in weight gain. The highest agar production (24.8 ± 3.0 %DW) was at 25 psu, 150–400 µmol photons m^?2 s^?1 and no sediment. The highest pigment contents were phycoerythrin (0.8 ± 0.5 mg g^?1FW) and phycocyanin (0.34 ± 0.05 mg g^?1 FW) produced in low light conditions, at 150 µmol photons m^?2 s^?1. The highest photosynthesis rate was 161.3 ± 32.7 mg O₂ g^?1 DW h^?1 in 25 psu, 400 µmol photons m^?2 s^?1 without sediment in the short period of cultivation, (3 days) and 60.3 ± 6.7 mg O₂ g^?1 DW h^?1 in 25 psu, 700 µmol photons m^?2 s^?1 without sediment in the long period of cultivation (20 days). The results indicated that salinity was the most crucial factor affecting G. tenuistipitata growth and production. This would help to promote the cultivation of Gracilaria cultivation back into the lagoon using these now determined baseline conditions. Extrapolation of the results from the laboratory study to field conditions indicated that it was possible to obtain two crops of Gracilaria a year in the lagoon, with good yields of agar, from mid‐January to the end of April (dry season), and from mid‐July to the end of September (first rainy season) when provided sediment was restricted.     

Photosynthetic response of Nereocystis luetkeana (Phaeophyta) to high light

Photosynthetic response to high light was determined for Bull kelp, Nereocystis luetkeana (K. Mertens) Postels and Ruprecht in order to understand how this species is affected by short‐term fluctuations in irradiance. Exposure of N. luetkeana blades to high intensity photosynthetically active radiation (1000 µmol photons m^?2 s^–1) caused increased non‐photochemical quenching of fluorescence and higher de‐epoxidation ratios for xanthophyll pigments indicating that energy‐quenching xanthophylls were used to protect blades against photoinhibition. Despite initiation of these photoprotective mechanisms, maximum photochemical efficiency of photosystem II (F_v/F_m) decreased 40% in response to a 60 min exposure to 1000 µmol photons m^?2 s^–1 photosynthetically active radiation indicating that photoinhibition had occurred. Light‐saturated rates of oxygen evolution were not changed significantly by the high light treatment. Recovery of maximum photochemical efficiency of photosystem II to within 8% of initial values occurred after a 300‐min dim light period. Younger sections of the blades were slightly more susceptible to high light damage than older sections. Middle sections of the blades were more prone to light‐induced damage at water temperatures of 7°C or 18°C, as compared to 13°C. Exposure to biologically effective ultraviolet‐B radiation (UV‐B_be) (up to 4.5 kJ m^–2 day^–1) in photoinhibitory light conditions did not significantly affect light‐induced damage to photosystem II.     

Productivity of Chlorella sorokiniana in a short light‐path (SLP) panel photobioreactor under high irradiance

Maximal productivity of a 14 mm light‐path panel photobioreactor under high irradiance was determined. Under continuous illumination of 2,100 µmol photons m^?2 s^?1 with red light emitting diodes (LEDs) the effect of dilution rate on photobioreactor productivity was studied. The light intensity used in this work is similar to the maximal irradiance on a horizontal surface at latitudes lower than 37°. Chlorella sorokiniana, a fast‐growing green microalga, was used as a reference strain in this study. The dilution rate was varied from 0.06 to 0.26 h^?1. The maximal productivity was reached at a dilution rate of 0.24 h^?1, with a value of 7.7 g dw m^?2 h^?1 (m² of illuminated photobioreactor surface) and a volumetric productivity of 0.5 g dw L^?1 h^?1. At this dilution rate the biomass concentration inside the reactor was 2.1 g L^?1 and the photosynthetic efficiency was 1.0 g dw mol photons. This biomass yield on light energy is high but still lower than the theoretical maximal yield of 1.8 g mol photons^?1 which must be related to photosaturation and thermal dissipation of absorbed light energy. Biotechnol. Bioeng. 2009; 104: 352–359 © 2009 Wiley Periodicals, Inc.     

Optimization of photosynthesis,growth, and biochemical composition of the microalga <Emphasis Type="Italic">Rhodomonas salina</Emphasis>—an established diet for live feed copepods in aquaculture

The cryptophyte Rhodomonas salina is widely used as feed for copepod cultures. However, culturing conditions to obtain high-quality algae have not yet been efficiently optimized. Therefore, we aimed to develop a cultivation protocol for R. salina to optimize its nutritional value and provide technical recommendations for later large-scale production in algal photobioreactors. We studied photosynthesis, growth, pigments, fatty acid (FA) and free amino acid (FAA) composition of R. salina cultured at different irradiances (10–300 μmol photons m^?2 s^?1) and nutrient availability (deficiency and excess). The optimal range of irradiance for photosynthesis and growth was 60–100 μmol photons m^?2 s^?1. The content of chlorophylls a and c decreased with increasing irradiance while phycoerythrin peaked at irradiances of 40–100 μmol photons m^?2 s^?1. The total FA content was maximal at optimal irradiances for growth, especially under nutrient deficiency. However, highly unsaturated fatty acids, desired components for copepods, were higher under nutrient excess. The total FAA content was highest at limiting irradiances (10–40 μmol photons m^?2 s^?1) but a better composition with a higher fraction of essential amino acids was obtained at saturated irradiances (60–140 μmol photons m^?2 s^?1). These results demonstrate that quality and quantity of FA and FAA of R. salina can be optimized by manipulating the irradiance and nutrient conditions. We suggest that R. salina should be cultivated in a range of irradiance 60–100 μmol photons m^?2 s^?1 and nutrient excess to obtain algae with high production and a balanced biochemical composition as feed for copepods.     

Assessment of photosynthetic performance in the two life history stages of Alaria crassifolia (Laminariales,Phaeophyceae)

Understanding of the physiological responses of kelp to environmental parameters is crucial, especially in the context of environmental change that may have contributed to the decline of kelp forests all over the world. The current study presents the photosynthetic characteristics of the macroscopic sporophyte and microscopic gametophyte stages of the brown alga Alaria crassifolia from Hokkaido, Japan, as determined by examining their photosynthetic responses over a range of temperature and irradiance using dissolved oxygen and chlorophyll fluorescence measurements. Net photosynthetic rates of the sporophyte were consistently higher than those of gametophyte across temperature gradients and irradiance levels. Photosynthesis–irradiance curves at 8°C, 16°C, and 20°C revealed similar initial slopes (α = 0.4–0.9) on the two life history stages, but higher compensation (E _c = 4–7 μmol photons m^?2 s^?1) and saturation irradiances (E _k = 53–103 μmol photons m^?2 s^?1) for the sporophyte than for the gametophyte (E _c = 0–7 μmol photons m^?2 s^?1; E _k = 7–10 μmol photons m^?2 s^?1). Both stages exhibited chronic photoinhibition, as shown by the failure of recovery in their maximum quantum yields (F _v/F _m) following high irradiance stress, with greater possibility of photodamage at low temperature. Gametophytes were less sensitive to low temperatures than sporophytes, given their relatively stable F _v/F _m response. Nevertheless, temperature optima for photosynthesis of both stages coincide with each other at 20–23°C, which correspond to the growth and maturation periods of A. crassifolia in Japan. This species is also likely to suffer from thermal inhibition as both GP rates and F _v/F _m decreased above 24°C.     

Andreaea Hartmanii Thed.—A histological study

Abstract

Photosynthetic responses to light intensity were studied under laboratory conditions in seven bryophyte species from evergreen laurel forest, a threatened habitat, on Terceira island in the Azores. Four mosses (Andoa berthelotiana, Echinodium prolixum, Fissidens serrulatus, Myurium hochstetteri) and three liverworts (Bazzania azorica, Frullania tamarisci, Lepidozia cupressina) were selected to encompass a range of potential responses to variations in the forest light environment. Carbon dioxide exchange measurements were made, using an infra-red gas-analyser, at photosynthetic photon flux densities (PPFD) of 0-900 µmol m^-2 s^-1 and a mean temperature of 21°C in fully hydrated shoots. Most species achieved light saturation of photosynthesis below 30 µmol m^-2 s^-1, the lowest value being for A. berthelotiana (20 µmol m^-2 s^-1) and the highest for M. hochstetteri (68 µmol m^-2 s^-1). The liverwort F. tamarisci had the highest maximum photosynthetic rate (P_max, 23 µmol CO₂ g^-1 h^-1) whereas P_max was lowest in the mosses E. prolixum and M. hochstetteri (10 µmol CO₂ g^-1 h^-1). Dark respiration rate, a critical factor in toleration of shade by forest floor plants, was highest in the species with the highest values for P_max. Compensation point was extremely low (7 µmol photons m^-2 s^-1) in Fissidens serrulatus, a species found in the deep shade of forest ravines and caves, and highest in M. hochstetteri a moss restricted to better illuminated habitats within and outside the forest. No photoinhibition was detected during the relatively short exposures to high irradiances. Comparison of these responses with data on the forest light environment indicates that, despite the possession of considerable shade adaptations, during winter in the evergreen laurel forest, low light levels may often limit photosynthetic rates of the bryophytes.     

Abstracts of Papers Read at the Winter Meeting at the University of Liverpool

Previous investigations with planktonic cyanobacteria have suggested that these organisms do not form new gas vesicles in the dark. This study, on Microcystis sp., confirmed that cells that had been preincubated at low photon irradiances (< 15 μmol m^-2 s^-1) formed negligible amounts of gas vesicles in the dark. Significant gas vesicle formation occurred, however, in cells preincubated continuously at higher irradiances, and particularly within the range 65 to 105 μmol m^-2 s^-1. The results suggest that gas vesicle formation in the dark is dependent on the prior accumulation of energy reserves. The amount of gas vesicles formed in continuous light was linearly related to irradiance over the range 0 to 20 μmol m^-2 s^-1, and reached a maximum at only 30 μmol m^-2 s^-1 that was over five times the amount formed at higher irradiances. This suggests that the rate of gas vesicle formation, regulated directly in response to irradiance, has a role in the light-mediated buoyancy regulation of this cyanobacterium.     

Relative enhancement of photosynthesis and growth at elevated CO2 is greater under sunflecks than uniform irradiance in a tropical rain forest tree seedling

The survivorship of dipterocarp seedlings in the deeply shaded understorey of South‐east Asian rain forests is limited by their ability to maintain a positive carbon balance. Photosynthesis during sunflecks is an important component of carbon gain. To investigate the effect of elevated CO₂ upon photosynthesis and growth under sunflecks, seedlings of Shorealeprosula were grown in controlled environment conditions at ambient or elevated CO₂. Equal total daily photon flux density (PFD) (～7·7 mol m^?2 d^?1) was supplied as either uniform irradiance (～170 µmol m^?2 s^?1) or shade/fleck sequences (～30 µmol m^?2 s^?1/～525 µmol m^?2 s^?1). Photosynthesis and growth were enhanced by elevated CO₂ treatments but lower under flecked irradiance treatments. Acclimation of photosynthetic capacity occurred in response to elevated CO₂ but not flecked irradiance. Importantly, the relative enhancement effects of elevated CO₂ were greater under sunflecks (growth 60%, carbon gain 89%) compared with uniform irradiance (growth 25%, carbon gain 59%). This was driven by two factors: (1) greater efficiency of dynamic photosynthesis (photosynthetic induction gain and loss, post‐irradiance gas exchange); and (2) photosynthetic enhancement being greatest at very low PFD. This allowed improved carbon gain during both clusters of lightflecks (73%) and intervening periods of deep shade (99%). The relatively greater enhancement of growth and photosynthesis at elevated CO₂ under sunflecks has important potential consequences for seedling regeneration processes and hence forest structure and composition.     

Photosynthesis and growth of Ulva ohnoi and Ulva pertusa (Ulvophyceae) under high light and high temperature conditions,and implications for green tide in Japan

The macroalga Ulva ohnoi constitutes a considerable fraction of green tides in coastal areas of Japan, but little is known about the physiological characteristics of this species. To investigate the environmental factors that promote the formation of green tides, we tested the responses of U. ohnoi and another common Japanese species, Ulva pertusa, to various levels of irradiance at different water temperatures. Because the two species are morphologically similar, we identified them using the PCR‐restriction fragment length polymorphism method. Under laboratory conditions, we evaluated the photosynthetic, dark respiration, and relative growth rate at a range of water temperatures (5 to 35°C) and photosynthetically active radiation (0 to 1000 μmol photons m^?2 s^?1). The maximum gross photosynthetic rate of U. ohnoi was larger than that of U. pertusa. The dark respiration rates revealed no significant differences among the species and temperature conditions. At 500 μmol photons m^?2 s^?1, the relative growth rate of U. ohnoi was larger than that of U. pertusa in higher temperature and the difference was the largest at 20°C. The estimated compensation irradiance and estimated saturation irradiance of U. ohnoi and U. pertusa ranged from 0.709 to 5.510 and 40.530 to 58.674 μmol photons m^?2 s^?1, which were lower than those in other intertidal green macroalgae, from 6 to 11 and 50 to 82 μmol photons m^?2 s^?1, respectively. Thus, U. ohnoi which exists as free‐floating near the water surface and accumulating inside the green tide can survive extensively in the water column of the intertidal zone, furthermore, the species can maintain rapid growth in this situation. Therefore, as a result of this study, it is suggested that the ecological success of U. ohnoi in shallow waters such as the tidal flats, estuarine, and coasts of the inner bay in comparison with U. pertusa.     

Temperature and irradiance impacts on the growth,pigmentation and photosystem II quantum yields of <Emphasis Type="Italic">Haematococcus pluvialis</Emphasis> (Chlorophyceae)

The microalga Haematococcus pluvialis Flotow has been the subject of a number of studies concerned with maximizing astaxanthin production for use in animal feeds and for human consumption. Several of these studies have specifically attempted to ascertain the optimal temperature and irradiance combination for growth of H. pluvialis, but there has been a great deal of disagreement between laboratories. “Ideal” levels of temperature and irradiance have been reported to range from 14 to 28°C and 30 to 200 μmol photons m⁻² s⁻¹. The objective of the present study was to simultaneously explore temperature and irradiance effects for a single strain of H. pluvialis (UTEX 2505) across an experimental region that encompassed the reported “optimal” combinations of these factors for multiple strains. To this end, a two-dimensional experimental design based on response surface methodology (RSM) was created. Maximum growth rates for UTEX 2505 were achieved at 27°C and 260 μmol photons m⁻² s⁻¹, while maximum quantum yield for stable charge separation at PSII (F_v/F_m) was achieved at 27°C and 80 μmol photons m⁻² s⁻¹. Maximum pigment concentrations correlated closely with maximum F_v/F_m. Numeric optimization of growth rate and F_v/F_m produced an optimal combination of 27°C and 250 μmol photons m⁻² s⁻¹. Polynomial models of the various response surfaces were validated with multiple points and were found to be very useful for predicting several H. pluvialis UTEX 2505 responses across the entire two-dimensional experimental design space.     

Carpospore early development and callus-like tissue induction of <Emphasis Type="Italic">Chrysymenia wrightii</Emphasis> (Rhodymeniaceae,Rhodophyta) under laboratory conditions

Morphological and culture studies of germlings derived from carpospores of Chrysymenia wrightii (Harvey) Yamada were carried out under various treatments combining temperature and irradiance. Basal, main, and tip branches were applied for inducing callus-like tissue. Focus was on how carpospores develop into germlings, how callus-like tissues are induced from explants, and how temperature and irradiance affect carpospore germination and discoid crust growth. Results show that carpospore development can be divided into three stages: division stage, discoid crust stage, and erect juvenile germling stage. Discoid crusts, even more than ten, might coalesce into a big discoid crust, and then developed into germlings. Filamentous fronds, formed on the rims of discoid crusts, exhibited in self-existence or co-existence form with germlings, could form spherical tufts if cultured separately. Filamentous callus-like tissues appeared on the tip branches after 13 days. PES is suitable for filament induction and culture, and filaments have potential use in germplasm preservation and vegetative propagation. Temperature (10, 15, 20, 25°C) and irradiance (8 and 36 μmol photons m⁻² s⁻¹) significantly influenced carpospore germination rate and discoid crust diameter. Carpospores germinated normally under 36 μmol photons m⁻² s⁻¹, 15~25°C, and maximum growth of discoid crusts was at 25°C, 36 μmol photons m⁻² s⁻¹; 10°C and 8 μmol photons m⁻² s⁻¹ did not favor carpospore germination or discoid crust growth.     

Leaf Structure of Tobacco In Vitro Grown Plantlets as Affected by Saccharose and Irradiance

Tobacco plantlets were cultured in vitro under high (200 µmol m^–2 s^–1) or low (60 µmol m^–2 s^–1) irradiance with or without saccharose in the medium. Light microscopy and image analysis were used to evaluate the effect of these culture conditions on leaf anatomy. Addition of saccharose resulted in thicker leaves (all leaf layers) and larger mesophyll cells under both growth irradiances. Various irradiance affected leaf anatomy differently when plantlets had been cultivated in presence or absence of saccharose in the medium. While under high irradiance in presence of saccharose leaf thickness and number of chloroplasts per cell section were increased, plantlets grown under high irradiance in absence of saccharose had thinner leaves and less chloroplasts per cell section. The changes were more pronounced in palisade parenchyma layer.