Photosynthetic Energy Conversion: Hydrogen Photoproduction by Natural and Biomimetic Means

The main function of the photosynthetic process is to capture solar energy and to store it in the form of chemical fuels. Many fuel forms such as coal, oil and gas have been intensively used and are becoming limited. Hydrogen could become an important clean fuel for the future. Among different technologies for hydrogen production, oxygenic natural and artificial photosynthesis using direct photochemistry in synthetic complexes have a great potential to produce hydrogen as both use clean and cheap sources - water and solar energy. Photosynthetic organisms capture sunlight very efficiently and convert it into organic molecules. Artificial photosynthesis is one way to produce hydrogen from water using sunlight by employing biomimetic complexes. However, splitting of water into protons and oxygen is energetically demanding and chemically difficult. In oxygenic photosynthetic microorganisms water is splitted into electrons and protons during primary photosynthetic processes. The electrons and protons are redirected through the photosynthetic electron transport chain to the hydrogen-producing enzymes-hydrogenase or nitrogenase. By these enzymes, e- and H+ recombine and form gaseous hydrogen. Biohydrogen activity of hydrogenase can be very high but it is extremely sensitive to photosynthetic O2. At the moment, the efficiency of biohydrogen production is low. However, theoretical expectations suggest that the rates of photon conversion efficiency for H2 bioproduction can be high enough (> 10%). Our review examines the main pathways of H2 photoproduction using photosynthetic organisms and biomimetic photosynthetic systems and focuses on developing new technologies based on the effective principles of photosynthesis

Effect of cryptochrome 1 deficiency and spectral composition of light on photosynthetic processes in A. thaliana under high-intensity light exposure

The role of cryptochrome 1 in photosynthetic processes and pro-/antioxidant balance in the Arabidopsis thaliana plants was studied. Wild type (WT) and hy4 mutant deficient in cryptochrome 1 grown for 20 d under red (RL, 660 nm) and blue (BL, 460 nm) light at an RL:BL = 4:1 ratio were kept for 3 d in different lights: RL:BL = 4:1, RL:BL:GL = 4:1:0.3 (GL - green light, 550 nm), and BL, then were exposed to high irradiance (4 h). Activity of PSII and the rate of photosynthesis in WT and hy4 decreased under the high irradiance in all spectral variants but under BL stronger decrease in the activity was found in the hy4 mutant than in WT. We assumed that lowered resistance of photosynthetic apparatus in the hy4 mutant may be associated with the low activity of the main antioxidant enzymes and reduced content of low-molecular-mass antioxidants in the mutant compared to the WT

Hydrogen photoproduction by use of photosynthetic organisms and biomimetic systems

10.1039/b814932aPhotochemical and Photobiological Sciences82148-156PPSH

Impact of weak water deficit on growth, photosynthetic primary processes and storage processes in pine and spruce seedlings

We investigated the influence of 40 days of drought on growth, storage processes and primary photosynthetic processes in 3-month-old Scots pine and Norway spruce seedlings growing in perlite culture. Water stress significantly affected seedling water status, whereas absolute dry biomass growth was not substantially influenced. Water stress induced an increase in non-structural carbohydrate content (sugars, sugar alcohols, starch) in the aboveground part of pine seedlings in contrast to spruce seedlings. Due to the relatively low content of sugars and sugar alcohols in seedling organs, their expected contribution to osmotic potential changes was quite low. In contrast to biomass accumulation and storage, photosynthetic primary processes were substantially influenced by water shortage. In spruce seedlings, PSII was more sensitive to water stress than PSI. In particular, electron transport in PSI was stable under water stress despite the substantial decrease of electron transport in PSII. The increase in thermal energy dissipation due to enhancement of non-photochemical quenching (NPQ) was evident in both species under water stress. Simultaneously, the yields of non-regulated energy dissipation in PSII were decreased in pine seedlings under drought. A relationship between growth, photosynthetic activities and storage processes is analysed under weak water deficit

EFFECT OF ADDITIONAL LOW INTENSITY LUMINESCENCE RADIATION 625nm ON PLANT GROWTH AND PHOTOSYNTHESIS

Tomato (Licopersicon esculentum Mill.) and cabbage (Brassica oleracea L. var. Cymosa) plants were grown in a glass greenhouse under natural radiation in summer. A half of pots with plants were placed under an ordinary (control) and the other part under the \u22Redlight\u22 (experimental variant) polyethylene films, both 100μm thick. The Redlight film had the same transmittance but transformed 3.5% of ultraviolet light falling on a plant into fluorescent radiation with a main maximum of 625nm. Plants grown under modified solar radiation exhibited high intensity of photosynthesis at light saturation, a shift of saturation region to the higher level of radiation, as well as high efficiency of photosynthesis under low light intensity. An appreciable increase in the CO_2 assimilation rate and biological productivity under modified light irradiation of plants allows recommending the method of additional plant irradiation under controlled conditions. Under natural irradiation of plants this can be achieved by the use of Redlight film

EFFECT OF ADDITIONAL LOW INTENSITY LUMINESCENCE RADIATION 625nm ON PLANT GROWTH AND PHOTOSYNTHESIS

Tomato (Licopersicon esculentum Mill.) and cabbage (Brassica oleracea L. var. Cymosa) plants were grown in a glass greenhouse under natural radiation in summer. A half of pots with plants were placed under an ordinary (control) and the other part under the "Redlight" (experimental variant) polyethylene films, both 100μm thick. The Redlight film had the same transmittance but transformed 3.5% of ultraviolet light falling on a plant into fluorescent radiation with a main maximum of 625nm. Plants grown under modified solar radiation exhibited high intensity of photosynthesis at light saturation, a shift of saturation region to the higher level of radiation, as well as high efficiency of photosynthesis under low light intensity. An appreciable increase in the CO_2 assimilation rate and biological productivity under modified light irradiation of plants allows recommending the method of additional plant irradiation under controlled conditions. Under natural irradiation of plants this can be achieved by the use of Redlight film