Factors affecting the photosynthetic capacity of laboratory cultures of the diatom Phaeodactylum tricornutum
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Phaeodactylum tricornutum
Photosynthetic capacity
Photosynthetic efficiency
Photosynthetic pigment
Darkness
Phaeodactylum tricornutum
Photosynthetic efficiency
Strain (injury)
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Photosynthetic diatoms are exposed to rapid and unpredictable changes in irradiance and spectral quality, and must be able to acclimate their light harvesting systems to varying light conditions. Molecular mechanisms behind light acclimation in diatoms are largely unknown. We set out to investigate the mechanisms of high light acclimation in Phaeodactylum tricornutum using an integrated approach involving global transcriptional profiling, metabolite profiling and variable fluorescence technique. Algae cultures were acclimated to low light (LL), after which the cultures were transferred to high light (HL). Molecular, metabolic and physiological responses were studied at time points 0.5 h, 3 h, 6 h, 12 h, 24 h and 48 h after transfer to HL conditions. The integrated results indicate that the acclimation mechanisms in diatoms can be divided into an initial response phase (0-0.5 h), an intermediate acclimation phase (3-12 h) and a late acclimation phase (12-48 h). The initial phase is recognized by strong and rapid regulation of genes encoding proteins involved in photosynthesis, pigment metabolism and reactive oxygen species (ROS) scavenging systems. A significant increase in light protecting metabolites occur together with the induction of transcriptional processes involved in protection of cellular structures at this early phase. During the following phases, the metabolite profiling display a pronounced decrease in light harvesting pigments, whereas the variable fluorescence measurements show that the photosynthetic capacity increases strongly during the late acclimation phase. We show that P. tricornutum is capable of swift and efficient execution of photoprotective mechanisms, followed by changes in the composition of the photosynthetic machinery that enable the diatoms to utilize the excess energy available in HL. Central molecular players in light protection and acclimation to high irradiance have been identified.
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Photosynthetic efficiency of seven strains of Porphyra yezoensis was tested under different light intensities,different temperatures by mini-PAM,the content of the photosynthetic pigments and the recover time after photoinhibiting were also measured in the experiment.Results showed that from 20 μmol·m-2·s-1 to 1 200 μmol·m-2·s-1,the efficiency decreased gradually with increasing light intensity,however,the degree of decrease varied among strains of Porphyra yezoensis: the photosynthetic efficiency of Yjs when it suffered from the highest light intensity decreased by 27% compared with the photosynthetic efficiency at the lowest light intensity,while Yw by 33%,Gm by 53%,and Yqd by 50%.Within the temperature range from 5 ℃ to 20 ℃,all the samples obtained the highest efficiency under the condition of 15~20 ℃ and 120 μmol·m-2·s-1,and most of them reached the peak at the 15 ℃,except Yh2 and Wjs,which reached the peak at 20 ℃.After the photoinhibiting(200 μmol·m-2·s-1),the strains could recover in 30～60 min,under the condition of 60 μmol·m-2·s-1 and 12 ℃.No direct relationship was found between the photosynthetic efficiency and the content of photosynthetic pigments.The relationship between the photosynthetic efficiency and ecological conditions was discussed in this paper as well.
Photosynthetic efficiency
Light intensity
Photosynthetic pigment
Porphyra
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Phaeodactylum tricornutum
Photobioreactor
Photosynthetic efficiency
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Phaeodactylum tricornutum
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Phaeodactylum tricornutum
Photosynthetic efficiency
Metabolic pathway
Carbon fixation
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The effects of UV B radiation enhancement on photosynthetic pigments (chlorophyll a and carotenoid) are studied in Dicrateria inornata and Phaeodactylum tricornutum by means of batch culture method. Results show that lower dosage of UV B radiation has slight effects on the content of photosynthetic pigments; and higher dosage causes their decrease in Dicrateria inornata.The content of photosynthetic pigments in Phaeodactylum tricornutum decreases gradually with increasing dosage of UV B radiation. This indicated that UV B radiation enhancement could damage photosynthetic pigments of marine microalgae.
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In the present study,Phaeodactylum tricornutum was grown in laboratory under darkness condition for 12 days in order to investigate its growth and some chemical compositions in response to the darkness environment and to evaluate the adaptation of this economic microalga to darkness stress.The results indicated that Phaeodactylum tricornutum could still survive in the darkness condition,while darkness stress imposed significantly inhibitory influence on the growth of Phaeodactylum tricornutum during the course of the experiment.Algal cell density and biomass in the darkness treatment were reduced to 2.93 ⅹ1 05 cells.ml-1 and 0.011 g.ml-1 on the day of termination of the experiment,only 8.0% and 37.3% of the control.Moreover,some chemical compositions including chlorophyll a,soluble sugar and protein were also apparently limited in the darkness condition,the contents of which were approximately 89%,87% and 85% lower than those in the control on the 12th day.Our results have provided supportive evidence that Phaeodactylum tricornutum tended to exhibit the capacity of sustaining in the darkness stress,which might be due to its pronounced ability in the biosynthesis and metabolism of protein,soluble sugar and chlorophyll a,but its growth performance was remarkably restricted over time.The findings presented here suggested that the adaptive ability of Phaeodactylum tricornutum to darkness stress should be considered into the core collection and screening,as well as comprehensive exploiture of microalgal resources.
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Darkness
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:Little is known about the combined impacts of temperature increases and fluctuating radiation regimes on the photosynthetic capability of marine diatoms. We incubated Phaeodactylum tricornutum cells under normal (18°C) vs elevated temperature (+6°C) in semicontinuous cultures and exposed them to fixed and fluctuating radiation conditions. Photosynthetic performance was determined based on the effective quantum yield of open photosystem II (PSII; F′V/F′M), the maximum relative electron transport rate (rETRmax), the light saturation parameter (Ek) and the photosynthetic efficiency parameter (α). These photophysiological parameters were affected more by irradiance than by the increase of temperature when P. tricornutum cells were exposed to fixed light regimes, and there was no significant difference between temperature treatments. In contrast, under fluctuating radiation regimes, the impact of temperature was clearly evident. Cells incubated at high temperature showed higher F′V/F′M, rETRmax and α but lower Ek when exposed to fast cycling in irradiance (20 min per cycle). In addition, cells grown at high temperature possessed a smaller value of effective target size for photoinactivation of PSII (σi), particularly for cells exposed to fast cycling in irradiance. This indicated that they were more resistant to PSII photoinactivation. These results showed that the photosynthetic capacity of P. tricornutum cells could be favoured by the increase of temperature, and fast cycling in irradiance increased the ability of cells to use the light and provoked much less photoinactivation.
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Ocean acidification (OA) due to atmospheric CO2 rise is expected to influence marine primary productivity. In order to investigate the interactive effects of OA and light changes on diatoms, we grew Phaeodactylum tricornutum, under ambient (390 ppmv; LC) and elevated CO2 (1000 ppmv; HC) conditions for 80 generations, and measured its physiological performance under different light levels (60 µmol m(-2) s(-1), LL; 200 µmol m(-2) s(-1), ML; 460 µmol m(-2) s(-1), HL) for another 25 generations. The specific growth rate of the HC-grown cells was higher (about 12-18%) than that of the LC-grown ones, with the highest under the ML level. With increasing light levels, the effective photochemical yield of PSII (Fv'/Fm') decreased, but was enhanced by the elevated CO2, especially under the HL level. The cells acclimated to the HC condition showed a higher recovery rate of their photochemical yield of PSII compared to the LC-grown cells. For the HC-grown cells, dissolved inorganic carbon or CO2 levels for half saturation of photosynthesis (K1/2 DIC or K1/2 CO2) increased by 11, 55 and 32%, under the LL, ML and HL levels, reflecting a light dependent down-regulation of carbon concentrating mechanisms (CCMs). The linkage between higher level of the CCMs down-regulation and higher growth rate at ML under OA supports the theory that the saved energy from CCMs down-regulation adds on to enhance the growth of the diatom.
Phaeodactylum tricornutum
Photosynthetic efficiency
Ocean Acidification
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