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PSII Activity (psii + activity)
Selected AbstractsTEMPERATURE INDUCED PHOTOINHIBITION IN OUTDOOR CULTURES OF MONODUS SUBTERRANEUSJOURNAL OF PHYCOLOGY, Issue 2000A. Vonshak Outdoor algal cultures are continuously exposed to changes in environmental conditions, particularly irradiance and temperature. While the changes in light intensity take place in a range of one to two hours, the increase in temperature is a slower process and takes about four to five hours. This de-synchronization between the two important environmental factors governing photosynthesis and growth of algae results in a unique stress condition where photoinhibition can be induced at relatively low light intensity. Outdoors the early morning culture temperature was found to be about 12 to 14° C, and reaches 25 to 28° C at mid-day. In an experiment, such a natural temperature regime was compared to another one in which the morning temperature of the culture was increased to 20° C by using a heating system. A fast decline in the maximal photochemical efficiency of PSII (Fv/Fm) was observed starting as soon as sunrise. The decline was faster in the non-heated culture and was to a lower value. The diurnal changes in the electron transfer rate (ETR) and in the non-photochemical quenching (NPQ) of the cultures, indicated that the early morning exposure of cells to sub-optimal temperature results in a fast inactivation of PSII activity which was reflected in an inhibition of the photosynthetic activity even when the two cultures finally reached the same temperature at mid-day. Thus, under the same light and temperature mid-day conditions the ETR was higher and the NPQ was significantly lower in the heated culture. Significant changes in productivity of the cultures also were observed. [source] Impact of nitrate supply in C and N assimilation in the parasitic plant Striga hermonthica (Del.) Benth (Scrophulariaceae) and its host Sorghum bicolor L.PLANT CELL & ENVIRONMENT, Issue 4 2006P. SIMIER ABSTRACT The threshold of tolerance for nitrate of the parasitic weed Striga hermonthica (Del.) Benth and the host plant Sorghum bicolor L. was determined by estimating the impact of increasing nitrate loads on plant growth and various parameters of C and N assimilation. Nitrate supply improved chlorophyll (Chl) content and photosystem II (PSII) photochemistry of infected S. bicolor that, in comparison to S. hermonthica, displayed a low imbalance between C and N assimilation when nitrate was supplied up to 1500 mg N per plant. Indeed, nitrate supplies increased strongly the leaf N:C ratio of the parasite. The higher nitrate load induced strong accumulation of nitrate, nitrite and ammonium, and consequently the death of S. hermonthica. Nevertheless, lower nitrate loads (up to 500 mg N per S. bicolor in this study) promoted leaf expansion, PSII photochemistry and N metabolism of S. hermonthica mature (M) plants, as attested by the significant rise in soluble protein and free amino-acid contents. Following these N supplies, the nitrate tolerance of S. hermonthica was correlated with an increase in PSII activity and a high incorporation of N excess into asparagine. This confirmed the central role of asparagine in the N metabolism of S. hermonthica, although this detoxification pathway was insufficient to limit ammonium accumulation under higher nitrate loads. [source] Hydrogen production by photoautotrophic sulfur-deprived Chlamydomonas reinhardtii pre-grown and incubated under high lightBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2009Irina V. Tolstygina Abstract We have previously demonstrated that Chlamydomonas reinhardtii can produce hydrogen under strictly photoautotrophic conditions during sulfur deprivation [Tsygankov et al. (2006); Int J Hydrogen Energy 3:1574,1584]. The maximum hydrogen photoproduction was achieved by photoautotrophic cultures pre-grown under a low light regime (25 µE,m,2,s,1). We failed to establish sustained hydrogen production from cultures pre-grown under high light (100 µE,m,2,s,1). A new approach for sustained hydrogen production by these cultures is presented here. Assuming that stable and reproducible transition to anerobiosis as well as high starch accumulation are important for hydrogen production, the influence of light intensity and dissolved oxygen concentration during the oxygen evolving stage of sulfur deprivation were investigated in cultures pre-grown under high light. Results showed that light higher than 175 µE,m,2,s,1 during sulfur deprivation induced reproducible transition to anerobiosis, although the total amount of starch accumulation and hydrogen production were insignificant. The potential PSII activity measured in the presence of an artificial electron acceptor (DCBQ) and an inhibitor of electron transport (DBMIB) did not change in cultures pre-grown under 20 µE,m,2,s,1 and incubated under 150 µE,m,2,s,1 during sulfur deprivation. In contrast, the potential PSII activity decreased in cultures pre-grown under 100 µE,m,2,s,1 and incubated under 420 µE,m,2,s,1. This indicates that cultures grown under higher light experience irreversible inhibition of PSII in addition to reversible down regulation. High dissolved O2 content during the oxygen evolving stage of sulfur deprivation has a negative regulatory role on PSII activity. To increase hydrogen production by C. reinhardtii pre-grown under 100 µE,m,2,s,1, cultures were incubated under elevated PFD and decreased oxygen pressure during the oxygen evolving stage. These cultures reproducibly reached anaerobic stage, accumulated significant quantities of starch and produced significant quantities of H2. It was found that elevation of pH from 7.4 to 7.7 during the oxygen producing stage of sulfur deprivation led to a significant increase of accumulated starch. Thus, control of pH during sulfur deprivation is a possible way to further optimize hydrogen production by photoautotrophic cultures. Biotechnol. Bioeng. 2009;102: 1055,1061. © 2008 Wiley Periodicals, Inc. [source] Kinetic modeling of light limitation and sulfur deprivation effects in the induction of hydrogen production with Chlamydomonas reinhardtii: Part I. Model development and parameter identificationBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2009Swanny Fouchard Abstract Chlamydomonas reinhardtii is a green microalga capable of turning its metabolism towards H2 production under specific conditions. However this H2 production, narrowly linked to the photosynthetic process, results from complex metabolic reactions highly dependent on the environmental conditions of the cells. A kinetic model has been developed to relate culture evolution from standard photosynthetic growth to H2 producing cells. It represents transition in sulfur-deprived conditions, known to lead to H2 production in Chlamydomonas reinhardtii, and the two main processes then induced which are an over-accumulation of intracellular starch and a progressive reduction of PSII activity for anoxia achievement. Because these phenomena are directly linked to the photosynthetic growth, two kinetic models were associated, the first (one) introducing light dependency (Haldane type model associated to a radiative light transfer model), the second (one) making growth a function of available sulfur amount under extracellular and intracellular forms (Droop formulation). The model parameters identification was realized from experimental data obtained with especially designed experiments and a sensitivity analysis of the model to its parameters was also conducted. Model behavior was finally studied showing interdependency between light transfer conditions, photosynthetic growth, sulfate uptake, photosynthetic activity and O2 release, during transition from oxygenic growth to anoxic H2 production conditions. Biotechnol. Bioeng. 2009;102: 232,245. © 2008 Wiley Periodicals, Inc. [source] | ||||||||||