Dyakia bioluminescence—1. Bioluminescence and fluorescence spectra of the land snail,D. striata

The luminescent land snail Dyakia striata displayed a bioluminescence spectrum with a maximum wavelength of 515 nm. A green fluorescent substance extracted from the photogenic organ of an adult snail had a similar wavelength maximum but its fluorescence spectrum differed from that of flavin chromophore substances involved in light emission in some other luminescent organisms.     

Studies on Polyoxins,Antifungal Antibiotics

Seven additional components, polyoxins C, D, E, F, G, H and I were isolated from polyoxin complex. They have molecular formulae corresponding to C₁₁H₁₅N₃O₈, C₁₇H₂₃N₅O₁₄, C₁₇H₂₃N₅O₁₃, C₂₃H₃₀N₆O₁₅, C₁₇H₂₅N₅O₁₂, C₂₃H₃₂N₆O₁₃ and C₁₉H₂₄N₄O₁₂, respectively. These polyoxins except inactive polyoxins C and I were highly active against various kinds of phytopathogenic fungi. The close structural similarity among them including polyoxins A and B is also discussed.     

Filiation biochimique des acides phénoliques produits parPenicillium brevi-compactum

Résumé LeP. brevi-compactum produit onze substances phénoliques différentes: l'acide mycophénolique, les acides phénoliques C₁₀H₁₀O₅, C₁₀H₁₀O₆, C₁₀H₁₀O₇ et C₈H₆O₆ et les substances phénoliques non identifiées désignées par les chiffres VI, VII, VIII, IX, X et XI. L'acide mycophénolique et les substances X et XI qui en dérivent, sont synthétisés par la moisissure suivant un processus plus complexe que les autres substances phénoliques et sans rapport direct avec lui. Ces dernières dérivent les unes des autres par une série de transformations dont certaines sont réversibles. Il semble que les substances VI et VII soient des intermédiaires entre C₁₀H₁₀O₇ et C₈H₆O₆, tandis que les substances VIII et IX seraient des produits de réduction de C₁₀H₁₀O₅.

---

Summary P. brevi-compactum produces eleven phenolic different substances, mycophenolic acid, phenolic acids C₁₀H₁₀O₅, C₁₀H₁₀O₆, C₁₀H₁₀O₇ and C₈H₆O₆, and the non-identified substances designed by the numbers VI, VII, VIII, IX, X and XI. Mycophenolic acid and its derivates X and XI are synthesized by the mould according to a process more complex than the other phenolic substances and have no direct connection with them. The latter derive the one from the other, in a succession of transformations some of which are reversible. It seems that the substances VI and III are intermediaries between C₁₀H₁₀O₇ and C₈H₆O₆, the substances VIII and IX being produced by reduction of C₁₀H₁₀O₅.

     

A solvothermal method to synthesize fluorescent carbon nanoparticles and application to photocatalysis and electrocatalysis

A novel solvothermal approach to synthesize fluorescent carbon nanoparticles (CNPs) was developed using glucose and ammonium oxalate as the carbon source, and glycol as the solvent. The solution of as‐prepared CNPs emitted blue‐green fluorescence under ultraviolet (UV) light at 365 nm, and the carbon nanoparticle formation was investigated through XRD, TEM, DLS, FT‐IR, UV, PL, XPS. The particle was well dispersed with an average diameter of about 10–30 nm. In contrast with previous methods, in this synthesis process neither strong acid treatment nor further surface modification was necessary. The solution of as‐prepared CNPs were applied to photocatalytic degradation of mountain green in the present H₂O₂, and the decolorization rate was over 97% when the reaction time was more than 7 h under visible light. The as‐prepared CNPs were also applied to electrocatalysis and showed excellent electrocatalytic activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Leaf‐Mosaic‐Inspired Vine‐Like Graphitic Carbon Nitride Showing High Light Absorption and Efficient Photocatalytic Hydrogen Evolution

Green plants use solar energy efficiently in nature. Simulating the exquisite structure of a natural photosynthesis system may open a new approach for the construction of desirable photocatalysts with high light harvesting efficiency and performance. Herein, inspired by the excellent light utilization of “leaf mosaic” in plants, a novel vine‐like g‐C₃N₄ (V‐CN) is synthesized for the first time by copolymerizing urea with dicyandiamide‐formaldehyde (DF) resin. The as‐prepared V‐CN exhibits ultrahigh photocatalytic hydrogen production of 13.6 mmol g^?1 h^?1 under visible light and an apparent quantum yield of 12.7% at 420 nm, which is ≈38 times higher than that of traditional g‐C₃N₄, representing one of the highest‐activity g‐C₃N₄‐based photocatalysts. This super photocatalytic performance is derived from the unique leaf mosaic structure of V‐CN, which effectively improves its light utilization and affords a larger specific surface area. In addition, the introduction of DF resin further optimizes the energy band of V‐CN, extends its light absorption, and improves its crystallinity and interfacial charge transport, resulting in high performance. It is an easy and green strategy for the preparation of broad‐spectrum, high‐performance g‐C₃N₄, which presents significant advancement for the design of other nanophotocatalysts by simulating the fine structure of natural photosynthesis.     

Characterization of the non-photochemical quenching of chlorophyll fluorescence that occurs during the active accumulation of inorganic carbon in the cyanobacterium Synechococcus PCC 7942

Previous work has shown that the maximum fluorescence yield from PS 2 of Synechococcus PCC 7942 occurs when the cells are at the CO₂ compensation point. The addition of inorganic carbon (C_i), as CO₂ or HCO₃ ^–, causes a lowering of the fluorescence yield due to both photochemical (q_p) and non-photochemical (q_N) quenching. In this paper, we characterize the q_N that is induced by C_i addition to cells grown at high light intensities (500 mol photons m^–2 s^–1). The C_i-induced q_N was considerably greater in these cells than in cells grown at low light intensities (50 mol photons m^–2 s^–1), when assayed at a white light (WL) intensity of 250 mol photons m^–2 s^–1. In high-light grown cells we measured q_N values as high as 70%, while in low-light grown cells the q_N was about 16%. The q_N was relieved when cells regained the CO₂ compensation point, when cells were illuminated by supplemental far-red light (FRL) absorbed mainly by PS 1, or when cells were illuminated with increased WL intensities. These characteristics indicate that the q_N was not a form of energy quenching (q_E). Supplemental FRL illumination caused significant enhancement of photosynthetic O₂ evolution that could be correlated with the changes in q_p and q_N. The increases in q_p induced by C_i addition represent increases in the effective quantum yield of PS 2 due to increased levels of oxidized Q_A. The increase in q_N induced by C_i represents a decrease in PS 2 activity related to decreases in the potential quantum yield. The lack of diagnostic changes in the 77 K fluorescence emission spectrum argue against q_N being related to classical state transitions, in which the decrease in potential quantum yield of PS 2 is due either to a decrease in absorption cross-section or by increased spill-over of excitation energy to PS 1. Both the C_i-induced q_p (t _0.5<0.5 s) and q_N (t _0.51.6 s) were rapidly relieved by the addition of DCMU. The two time constants give further support for two separate quenching mechanisms. We have thus characterized a novel form of q_N in cyanobacteria, not related to state transitions or energy quenching, which is induced by the addition of C_i to cells at the CO₂-compensation point.Abbreviations BTP- 1,3-bis[tris(hydroxymethyl)-methylaminopropane] - Chl- chlorophyll - C_i- inorganic carbon (CO₂+HCO₃ ^–+CO₃ ^2–) - DCMU- 3-(3,4-dichlorophenyl)-, 1-dimethylurea) - F- chlorophyll fluorescence measured at any time in the absence of a saturating flash - F_o- chlorophyll fluorescence with only the weak modulated measuring beam on - F_M'- chlorophyll fluorescence during a saturating flash - F_M- maximum chlorophyll fluorescence, measured in the presence of WL and FRL at the CO₂-compensation point or in the presence of DCMU - F_V- variable fluorescence (= F_M'–F₀) - FRL- supplemental illumination with far red light - MB- modulated measuring beam of the PAM fluorometer - MV- methyl viologen - PAM- pulse amplitude modulation - PFD- incident photon flux density - PS 1, 2- Photosystems 1 and 2 - Q_A- primary electron-accepting plastoquinione of PS 2 - q_N- non-photochemical quenching of chlorophyll fluorescence - q_p- photochemical quenching of chlorophyll fluorescence; rubisco-ribulose bisphosphate carboxylase/oxygenase - SF- saturating flash (600 ms duration) - WL- white light illumination     

Chemiluminescence in Wounded Root Tissue : EVIDENCE FOR PEROXIDASE INVOLVEMENT

Root and stem segments from soybean (Merrill cv. `Bragg') showed an enhanced chemiluminescence upon mechanical injury. Roots emitted more light than did stems. Light emission was diminished by CN⁻ and N₃⁻ but was not affected by rotenone and antimycin A. Catalase quenched chemiluminescence in wounded root segments as did ascorbic acid and hydroquinone. Superoxide dismutase addition resulted in a small diminution in light emission, but mannitol, an OH· scavenger, was without effect. The addition of H₂O₂ to wounded root segments markedly elevated chemiluminescence in the presence of air as well as under N₂. It is concluded that peroxidases, found abundantly in roots, predominantly contribute to light emission in wounded plant tissue.     

Studies on the Chlorosis-inducing Substances Produced by a Fungus

Viridominic acids A, C₃₃H₄₈O₉, B, C₃₃H₄₈O₁₀, C, C₃₃H₅₀O₉ and cephalosporin P₁ were isolated as chlorosis-inducing substances against higher plants. The isolation, physicochemical properties and biological activities of these compounds are described in detail.     

Studies on Mitomycins,Carcinostatic Antibiotics

Mitomycin A (C₁₆H₁₉O₆N₃) and mitomycin C (C₁₅H₁₈O₅N₄) are pigments which have the quinoid structure. When treated with aqueous ammonia, mitomycin A is converted to mitomycin C. Acid hydrolysis of mitomycin C gave three degradation products, namely, C₁₄H₁₅O₅N₄, C₁₄H₁₅O₆N₃ and C₁₃H₁₄O₅N₂. Acetylation with acetic anhydride and pyridine and methylation with methyl iodide gave monoacetyl and monomethyl derivatives of mitomycin C respectively, though diacetate of demethyl derivatives were obtained when boiled with acetic anhydride.     

Eu3+‐tetrakis β‐diketonate complexes for solid‐state lighting application

Eu³⁺–β‐diketonate complexes are used, for example, in solid‐state lighting (SSL) or light‐converting molecular devices. However, their low emission quantum efficiency due to water molecules coordinated to Eu³⁺ and low photostability are still problems to be addressed. To overcome such challenges, we synthesized Eu³⁺ tetrakis complexes based on [Q][Eu(tfaa)₄] and [Q][Eu(dbm)₄] (Q1 = C₂₆H₅₆N⁺, Q2 = C₁₉H₄₂N⁺, and Q3 = C₁₇H₃₈N⁺), replacing the water molecules in the tris stoichiometry. The tetrakis β‐diketonates showed desirable thermal stability for SSL and, under excitation at 390 nm, they displayed the characteristic Eu³⁺ emission in the red spectral region. The quantum efficiencies of the dbm complexes achieved values as high as 51%, while the tfaa complexes exhibited lower quantum efficiencies (28–33%), but which were superior to those reported for the tris complexes. The structures were evaluated using the Sparkle/PM7 model and comparing the theoretical and the experimental Judd–Ofelt parameters. [Q1][Eu(dbm)₄] was used to coat a near‐UV light‐emitting diode (LED), producing a red‐emitting LED prototype that featured the characteristic emission spectrum of [Q1][Eu(dbm)₄]. The emission intensity of this prototype decreased only 7% after 30 h, confirming its high photostability, which is a notable result considering Eu³⁺ complexes, making it a potential candidate for SSL.     

Chemically shifted singlet oxygen spectrum

The estimated light emission spectrum was determined for a singlet oxygen (¹O₂)-producing system, NaOCl + H₂O₂, alone and in the presence of tryptophan and bovine serum albumin. Tryptophan and bovine serum albumin caused a decrease in the red emission of ¹O₂ and an increase in the amount of shorter wavelength light. This effect was due to chemiluminescence rather than fluorescence. Arachidonic acid caused a similar spectral shift, while guanosine demonstrated a late chemiluminescent reaction of predominantly short wavelength light in the presence of ¹O₂.     

Role of Microorganisms in Emission of Nitrous Oxide and Methane in Pulse Cultivated Soil Under Laboratory Incubation Condition

Soil from a pulse cultivated farmers land of Odisha, India, have been subjected to incubation studies for 40 consecutive days, to establish the impact of various nitrogenous fertilizers and water filled pore space (WFPS) on green house gas emission (N₂O & CH₄). C₂H₂ inhibition technique was followed to have a comprehensive understanding about the individual contribution of nitrifiers and denitrifiers towards the emission of N₂O. Nevertheless, low concentration of C₂H₂ (5 ml: flow rate 0.1 kg/cm²) is hypothesized to partially impede the metabolic pathways of denitrifying bacterial population, thus reducing the overall N₂O emission rate. Different soil parameters of the experimental soil such as moisture, total organic carbon, ammonium content and nitrate–nitrogen contents were measured at regular intervals. Application of external N-sources under different WFPS conditions revealed the diverse role played by the indigenous soil microorganism towards green house gas emission. Isolation of heterotrophic microorganisms (Pseudomonas) from the soil samples, further supported the fact that denitrification might be prevailing during specific conditions thus contributing to N₂O emission. Statistical analysis showed that WFPS was the most influential parameter affecting N₂O formation in soil in absence of an inhibitor like C₂H₂.     

Selective effects of H<Subscript>2</Subscript>O<Subscript>2</Subscript> on cyanobacterial photosynthesis

The sensitivity of phytoplankton species for hydrogen peroxide (H₂O₂) was analyzed by pulse amplitude modulated (PAM) fluorometry. The inhibition of photosynthesis was more severe in five tested cyanobacterial species than in three green algal species and one diatom species. Hence the inhibitory effect of H₂O₂ is especially pronounced for cyanobacteria. A specific damage of the photosynthetic apparatus was demonstrated by changes in 77 K fluorescence emission spectra. Different handling of oxidative stress and different cell structure are responsible for the different susceptibility to H₂O₂ between cyanobacteria and other phytoplankton species. This principle may be potentially employed in the development of new agents to combat cyanobacterial bloom formation in water reservoirs.     

Dramatic Enhancement of CO2 Photoreduction by Biodegradable Light‐Management Paper

Photocatalytic reduction of CO₂ with H₂O vapor is gaining increased interest because it is a promising “green chemistry” route for the direct conversion of CO₂ to value‐added chemicals driven by solar energy. To increase the efficiency of photocatalytic conversion, most efforts are made by exploring various photocatalysts while little effort on advanced light management. For the first time, it is demonstrated that bio‐degradable transparent paper with excellent light diffusivity can effectively enhance the light utilization of photocatalytic reactions when attached on the device surface, and thus greatly increase the conversion efficiency. As a proof‐of‐concept, a graphitic carbon nitride (g‐C₃N₄) photocatalyst with transparent paper attached, exhibited 1.5 times higher photocatalytic activity than bare g‐C₃N₄ in the reduction of CO₂ under visible light irradiation. The improved catalytic performance can be ascribed to the (1) refractive index matching and (2) enhanced light absorption via prolonged light traveling path in transparent paper, which decreases the light reflection at surface and traps the absorbed light inside, leading to an increased light absorption at the active layer of the device. The transparent paper with a controllable light management behavior has an unprecedented potential for applications in photocatalysis as a general method for improved light utilization.     

Luminescence investigation of novel MgPbAl10O17:Tb3+ green‐emitting phosphor for solid‐state lighting

In this work, we studied the luminescence properties of Tb³⁺‐doped MgPbAl₁₀O₁₇ green phosphor. To understand the excitation mechanism and corresponding emission of the prepared phosphor, its structural, morphological and photoluminescence properties were investigated. In general, for green emission, Tb³ is used as an activator and the obtained excitation and emission spectra indicated that this phosphor can be effectively excited by a wavelength of 380 nm, and exhibits bright green emission centered at 545 nm corresponding to the f → f transition of trivalent terbium ions. The chromaticity coordinates were (C_x = 0.263, C_y = 0.723). The impact of Tb³⁺ concentration on the relative emission intensity was investigated, and the best doping concentration was found to be 2 mol%. This study suggests that Tb³⁺‐doped MgPbAl₁₀O₁₇ phosphor is a strong candidate for a green component in phosphor‐converted white light‐emitting diodes. Copyright © 2015 John Wiley & Sons, Ltd.     

Treatment with NaHSO3 greatly enhances photobiological H2 production in the green alga Chlamydomonas reinhardtii

Treatment with NaHSO₃ induces a 10-fold increase in H₂ photoproduction in the filamentous N₂-fixing cyanobacterium Anabaena sp. strain PCC 7120. However, it is unclear whether this treatment also increases H₂ photoproduction in green alga. In this study, treatment with 13 mM NaHSO₃ resulted in about a 200-fold increase in H₂ production in Chlamydomonas reinhardtii, and this increase was most probably the result of reduced O₂ content and enhanced hydrogenase activity. Compared to the conventional strategy of sulfur deprivation, NaHSO₃ treatment results in a higher maximum rate of H₂ photoproduction, greater efficiency of conversion of light energy into H₂, shorter half-time to produce the maximum accumulated H₂ levels, and reduced costs because no centrifugation is involved. We therefore conclude that NaHSO₃ treatment is an efficient, rapid, and economic strategy for improving photobiological H₂ production in the green alga C. reinhardtii.     

Co-regulation of dark and light reactions in three biochemical subtypes of C<Subscript>4</Subscript> species

Regulation of light harvesting in response to changes in light intensity, CO₂ and O₂ concentration was studied in C₄ species representing three different metabolic subtypes: Sorghum bicolor (NADP-malic enzyme), Amaranthus edulis (NAD-malic enzyme), and Panicum texanum (PEP-carboxykinase). Several photosynthetic parameters were measured on the intact leaf level including CO₂ assimilation rates, O₂ evolution, photosystem II activities, thylakoid proton circuit and dissipation of excitation energy. Gross rates of O₂ evolution ( J_\textO2 J_{{{\text{O}}_{2} }} , measured by analysis of chlorophyll fluorescence), net rates of O₂ evolution and CO₂ assimilation responded in parallel to changes in light and CO₂ levels. The C₄ subtypes had similar energy requirements for photosynthesis since there were no significant differences in maximal quantum efficiencies for gross rates of O₂ evolution (average value = 0.072 O₂/quanta absorbed, ~14 quanta per O₂ evolved). At saturating actinic light intensities, when photosynthesis was suppressed by decreasing CO₂, ATP synthase proton conductivity (g _H ⁺) responded strongly to changes in electron flow, decreasing linearly with J_\textO2 J_{{{\text{O}}_{2} }} , which was previously observed in C₃ plants. It is proposed that g _H ⁺ is controlled at the substrate level by inorganic phosphate availability. The results suggest development of nonphotochemical quenching in C₄ plants is controlled by a decrease in g _H ⁺, which causes an increase in proton motive force by restricting proton efflux from the lumen, rather than by cyclic or pseudocyclic electron flow.     

On the relationship between the quantum yield of Photosystem II electron transport,as determined by chlorophyll fluorescence and the quantum yield of CO2-dependent O2 evolution

We tested the two empirical models of the relationship between chlorophyll fluorescence and photosynthesis, previously published by Weis E and Berry JA 1987 (Biochim Biophys Acta 894: 198–208) and Genty B et al. 1989 (Biochim Biophys Acta 990: 87–92). These were applied to data from different species representing different states of light acclimation, to species with C₃ or C₄ photosynthesis, and to wild-type and a chlorophyll b-less chlorina mutant of barley. Photosynthesis measured as CO₂-saturated O₂ evolution and modulated fluorescence were simultaneously monitored over a range of photon flux densities. The quantum yields of O₂ evolution (ØO₂) were based on absorbed photons, and the fluorescence parameters for photochemical (q_p) and non-photochemical (q_N) quenching, as well as the ratio of variable fluorescence to maximum fluorescence during steady-state illumination (F'_v/F'_m), were determined. In accordance with the Weis and Berry model, most plants studied exhibited an approximately linear relationship between ØO₂/q_p (i.e., the yield of O₂ evolution by open Photosystem II reaction centres) and q_N, except for wild-type barley that showed a non-linear relationship. In contrast to the linear relationship reported by Genty et al. for q_p×F'_v/F'_m (i.e., the quantum yield of Photosystem II electron transport) and ØCO₂, we found a non-linear relationship between q_p×F'_v/F'_m and ØO₂ for all plants, except for the chlorina mutant of barley, which showed a largely linear relationship. The curvilinearity of wild-type barley deviated somewhat from that of other species tested. The non-linear part of the relationship was confined to low, limiting photon flux densities, whereas at higher light levels the relationship was linear. Photoinhibition did not change the overall shape of the relationship between q_p×F'_v/F'_m and ØO₂ except that the maximum values of the quantum yields of Photosystem II electron transport and photosynthetic O₂ evolution decreased in proportion to the degree of photoinhibition. This implies that the quantum yield of Photosystem II electron transport under high light conditions may be similar for photoinhibited and non-inhibited plants. Based on our experimental results and theoretical analyses of photochemical and non-photochemical fluoresce quenching processes, we conclude that both models, although not universal for all plants, provide useful means for the prediction of photosynthesis from fluorescence parameters. However, we also discuss that conditions which alter one or more of the rate constants that determine the various fluorescence parameters, as well as differential light penetration in assays for oxygen evolution and fluorescence emission, may have direct effect on the relationships of the two models.Abbreviations F₀ and F'₀ fluorescence when all Photosystem II reaction centres are open in dark- and light-acclimated leaves, respectively - F_m and F'_m fluorescence when all Photosystem II reaction centres are closed in dark and light, respectively - F_v variable fluorescence equal to F_m-F₀ - F_s steady state level of fluorescence in light - F'_v and F'_m variable (F'_m-F'₀) and maximum fluorescence under steady state light conditions - HEPES N-2-hydroxyethylpiperazine-N-2-ethane-sulphonic acid - Q_A the primary, stabile quinone acceptor of Photosystem II - q_N non-photochemical quenching of fluorescence - q_p photochemical quenching of fluorescence - ØO₂ quantum yield of CO₂-saturated O₂ evolution based on absorbed photons     

Effect of anaerobiosis on photosynthetic reactions and nitrogen metabolism of algae with and without hydrogenase

Summary The effect of anaerobic (N₂+CO₂) pre-incubation in the dark on photosynthetic reactions (O₂ evolution, measured manometrically and with the oxygraph; fluorescence; and photoproduction of H₂, measured with the mass spectrometer) was studied in algae with hydrogenase (strains of Chlorella fusca, C. kessleri, C. vulgaris f. tertia, and Ankistrodesmus braunii) and in algae without hydrogenase (strains of Chlorella vulgaris, C. saccharophila, and C. minutissima).The inhibition by anaerobic incubation of photosynthetic O₂ evolution is much stronger in algae without hydrogenase than it is in algae with hydrogenase. The effect of anaerobiosis is most pronounced at rather low light intensity (about 1000 lux), in acid medium (pH 4), and after prolonged anaerobic incubation in the dark (about 20 h). These results indicate that the presence of hydrogenase might be ecologically advantageous for algae under certain conditions.Chlorophyll fluorescence showed the fastest response to anaerobic incubation, and the most pronounced difference between algae with and without hydrogenase. After only 30 min under N₂+CO₂, fluorescence in algae with hydrogenase starts with a peak and decreases within 10 to 20 sec to a rather low steady-state level which is only slightly higher than that found under aerobic conditions. In algae without hydrogenase, fluorescence is rather low during the first 1 to 2 sec and then rises to a higher steady-state level which is much higher than that of the aerobic controls. This indicates an inhibition due to anaerobiosis of photosystem II in algae without hydrogenase.Algae with hydrogenase can react in different ways during the first minutes of illumination. In some cases there is an immediate photoproduction of H₂, which is followed after a few minutes by photosynthetic O₂ evolution; in other algae there is a simultaneous production of H₂ and O₂ from the very beginning; in a few experiments there was no photoproduction of H₂ at all, and in this case there was no photosynthetic O₂ evolution either. Thus, photoproduction of H₂ seems to be the process which normally enables algae with hydrogenase to oxidise and thereby activate their photosynthetic electron transport system after anaerobic incubation.A mass spectrometric search for nitrogen fixation (using N₂ and acetylene) in eucaryotic green algae gave negative results, even with species containing hydrogenase and under anaerobic conditions.     

Photosynthetic H<Subscript>2</Subscript> metabolism in <Emphasis Type="Italic">Chlamydomonas reinhardtii</Emphasis> (unicellular green algae)

Unicellular green algae have the ability to operate in two distinctly different environments (aerobic and anaerobic), and to photosynthetically generate molecular hydrogen (H₂). A recently developed metabolic protocol in the green alga Chlamydomonas reinhardtii permitted separation of photosynthetic O₂-evolution and carbon accumulation from anaerobic consumption of cellular metabolites and concomitant photosynthetic H₂-evolution. The H₂ evolution process was induced upon sulfate nutrient deprivation of the cells, which reversibly inhibits photosystem-II and O₂-evolution in their chloroplast. In the absence of O₂, and in order to generate ATP, green algae resorted to anaerobic photosynthetic metabolism, evolved H₂ in the light and consumed endogenous substrate. This study summarizes recent advances on green algal hydrogen metabolism and discusses avenues of research for the further development of this method. Included is the mechanism of a substantial tenfold starch accumulation in the cells, observed promptly upon S-deprivation, and the regulated starch and protein catabolism during the subsequent H₂-evolution. Also discussed is the function of a chloroplast envelope-localized sulfate permease, and the photosynthesis–respiration relationship in green algae as potential tools by which to stabilize and enhance H₂ metabolism. In addition to potential practical applications of H₂, approaches discussed in this work are beginning to address the biochemistry of anaerobic H₂ photoproduction, its genes, proteins, regulation, and communication with other metabolic pathways in microalgae. Photosynthetic H₂ production by green algae may hold the promise of generating a renewable fuel from nature’s most plentiful resources, sunlight and water. The process potentially concerns global warming and the question of energy supply and demand.