Increase In Incident Light Intensity Research Articles

Effects of light intensity on soluble microbial products produced by Synechocystis sp. PCC 6803 and associated heterotrophic communities

The success of algal and cyanobacterial cultivation hinges on the robustness of the processes, and a key to this success is managing the microbial community co-existing with the algae or cyanobacteria. In this work, we grew the cyanobacterium Synechocystis sp. PCC6803 in a flat-plate photobioreactor operated as a sequencing batch reactor using two light conditions: continuous incident photosynthetically active radiation of 112 or 364 μmol m−2 s−1 (32 or 90 μmol m−2 s−1 average internal light intensity, respectively). As expected, the higher light condition supported more Synechocystis biomass, but the proportion of photosynthetically produced electrons released as soluble microbial products (SMP; cellular components released during growth and decay) also increased – ~42% compared to 20% at the lower light condition – which corresponded to an increase in heterotrophic biomass that grew by oxidizing the SMP. After the increase in incident light intensity, the co-existing community of heterotrophic bacteria showed a large taxonomical transition, with Sphingobacteriales declining and Comamonadaceae increasing. Over the course of 7 days, however, the microbial community structure stabilized, gradually moving towards the initial composition. We suggest that changes in the microbial community resulted from changes in SMP composition from Synechocystis at the different light intensities.

Effect of Mother Stem Training on Spear Quality and Yield of Asparagus (Asparagus officinalis L.) in the Greenhouse

This study examined the effects of mother stem training on spear quality and yield of asparagus (Asparagus officinalis L.) in the greenhouse. The training was performed with the “mother stem bending method” (Sakamoto et al., 2011). No significant differences were found in the diameter, soluble solid content, firmness, and index of spear tightness of asparagus spears between the untreated group and the mother stem training treatment group. However, the mother stem training method was effective in improving the spear color quality owing to the increase in incident light intensity. On the other hand, the mother stem training treatment resulted in a decrease in the fresh weight of the spear, marketable yield, and marketable yield ratio of the LL (over 33 g) spear size when compared to that of the untreated group. The cause of this decrease in summer yield in the treated group was hypothesized to be a failure in nutrient translocation and low light interception in close proximity to the other stems.

EXPERIMENTAL INVESTIGATION ON CHARACTERISTICS OF LOW-CONCENTRATING SOLAR CELLS

At room temperature, the performance of low-concentrating solar cells is investigated experimentally and discussed by theory. The results show that the short-circuit current, which is larger than that of unconcentrated radiation, linearly increases with the light intensity and is directly proportional to the concentration ratio. However, the different behavior is obtained for the open-circuit voltage. The open-circuit voltage is also larger than that at the unconcentrated light level and follows a logarithmic function of the light intensity, showing almost no dependence on the concentration ratios. The main reason is the decrease in internal resistance of solar cell with decreasing spot size, because the increase of incident light intensity leads to an increase of current density. Therefore, an advantage of the low-concentrating photovoltaic systems results from the improvement of the short-circuit current, but not from the open-circuit voltage. This work is very significant for the design of low-concentrating system.

Photocatalytic activity of AgBr/TiO2 in water under simulated sunlight irradiation

In this paper, the synthesis of AgBr/TiO2 catalyst and the photocatalytic activity in water under simulated sunlight irradiation were studied. The influence of AgBr content in catalyst and the incident light intensity on the degradation of methyl orange (MO) was investigated. It was found that the initial reaction rate constant was dependent on the relative levels of AgBr content and incident light intensity, ranging between 0.008min−1 and 0.023min−1. At higher levels of AgBr content (>9wt%), MO degradation was exclusively dependent on the incident light intensity, which implied that the excessive AgBr in catalyst had negligible effect on catalyst activity. However, at lower AgBr contents, the reaction rate increased with the increase of incident light intensity, and eventually reached a plateau level, indicating that the degradation of MO was limited by AgBr content. The results from powder X-ray diffraction (XRD) analysis showed that more than 80% of AgBr remained intact after 14h of irradiation, although metallic silver was also detected.

Localization and Role of Manganese Superoxide Dismutase in a Marine Diatom

Superoxide dismutase (SOD) catalyzes the transformation of superoxide to molecular oxygen and hydrogen peroxide. Of the four known SOD isoforms, distinguished by their metal cofactor (iron, manganese [Mn], copper/zinc, nickel), MnSOD is the dominant form in the diatom Thalassiosira pseudonana. We cloned the MnSOD gene, sodA, using the expression vector pBAD, overexpressed the product in Escherichia coli, and purified the mature protein (TpMnSOD). This recombinant enzyme was used to generate a polyclonal antibody in rabbit that recognizes MnSOD in T. pseudonana. Based on quantitative immunoblots, we calculate that in vivo concentrations of TpMnSOD are approximately 0.9 amol cell(-1) using the recombinant protein as a standard. Immunogold staining indicates that TpMnSOD is localized in the chloroplasts, which is in contrast to most other eukaryotic algae (including chlorophytes and embryophytes) where MnSOD is localized exclusively in mitochondria. Based on the photosynthetic Mn complex in photosystem II, cellular Mn budgets cannot account for 50% to 80% of measured Mn within diatom cells. Our results reveal that chloroplastic MnSOD accounts for 10% to 20% of cellular Mn, depending on incident light intensity and cellular growth rate. Indeed, our analysis indicates that TpMnSOD accounts for 1.4% (+/-0.2%) of the total protein in the cell. The TpMnSOD has a rapid turnover rate with an apparent half-life of 6 to 8 h when grown under continuous light. TpMnSOD concentrations increase relative to chlorophyll, with an increase in incident light intensity to minimize photosynthetic oxidative stress. The employment of a Mn-based SOD, linked to photosynthetic stress in T. pseudonana, may contribute to the continued success of diatoms in the low iron regions of the modern ocean.

Characterization of Chlorella Cell Cultures in Batch and Continuous Operations under a Photoautotrophic Condition.

In a microalgal culture under illuminated conditions, the production rate of cells depends on the distribution of light intensity and growth rate of cells. The relationship between light transmittance through culture liquid and cell concentration was estimated from experimental data using a green alga, Chlorella sp. UK001. In batch cultures of this alga, the optimum conditions for the growth were temperature of 30°C and pH of 5.7. Under these conditions, the value of specific growth rate of the alga increased with the increase in incident light intensity (I 0 ) up to 130 W m -2 , and it decreased when I 0 was over 130 W m -2 . Continuous cultures of the alga in a rectangular reactor were performed at I 0 =55.8 and 71.4 W m -2 . The dilution rates maximizing the production rate of cells existed for the respective values of I 0 . The production rates of cells in these cultures were calculated considering the distribution of light intensity in the reactor. The calculated results could successfully describe the experimental data at different dilution rates, and when I 0 =55.8 and 71.4 W m -2 , the production rates of cells indicated maxima at dilution rates of 0.0218 and 0.0220 h -1 , respectively.

Studies on Photosynthesis in Sugar Beet Plant : III. Photosynthesis in the community.

The effect of light on the photosynthesis in the community of sugar beet plants was studied from the view point of intensity of light received by the individual leaves of the community. The results obtained are as follows. (1) Light response curves of photosynthesis in community obtained by calculation on the basis of light intensity on the surface of individual leaves and light response curves of photosynthesis of individual leaves, showed the same tendency as those obtained by direct measurement on photosynthesis of community. (2) These light response curves are light saturation curves, having a saturation point at the horizontal light intensity of ca. 40 Klx. The similar fact is seen in the communities of different leaf area indices (LAI) ranging from 0.9 to 5.6. Light receiving coefficient (ρ) under the incident horizontal light intensity where the photosynthesis shows saturation phenomenon, is lower than 1, and the higher the LAI of community, the lower the ρ. (3) When the horizontal light intensity of incident light becomes higher, some leaves in community receive more and more intense light. However, there remain some leaves on which light intensity does not increase, regardless of the increment of incident light intensity. Even though horizontal light inetnsity gets higher than 30 or 40 Klx, the area of leaves that receive light intensity below the saturation point, does not decrease, and their mean light intensity does not increases either. Consequently photosynthetic rates of these leaves remain at low level. On the other hand, accompanying with the increase of incident light intensity, the photo synthetic intensity of another leaves will become higher untill light intensity of these leaves reaches at saturation point of single leaves. These circumstances cause the light saturation phenomenon in photosynthesis in community. (4) The percentage of leaves whose photosynthetic intensity remains at low level, increases as the LAI of community becomes higher, resulting in the lower ρ in the community of larger LAI.