The formation of S-aminolevulmic acid (ALA), energy-dependent steps ffom ALA to protoporphyrin IX (Proto) and from Proto to protochlorophyllide (PChlide) formation, the roles of NADPH in PChlide photoreduction and geranylgeraniol hydrogenation, the source of adenylates and reduced pyridine nucleotides for the reactions of chlorophyll biosynthesis, and the compartmentation and interrelationships of porphyrin biosynthesis pathways are reviewed.
Oxygen deficiency is a widespread stress factor. Its consequences studied with the seedlings of Triticum aesíivum, under a special consideration of their root growth and morphology, the gas exchange and pyridine nucleotide systém, and the chlorophyll biosynthesis in shoots, are reviewed here on the basis of the general stress concept.
Photosynthesis, as a fundamental element in the life process, is integrated in the evolution of living systems on the basis of hydrogen cycles on various hierarchic levels. Conversion of radiant energy enables the oxidation of water, whereby free oxygen accumulates in the atmosphere. Hydrogen is (reversibly) stored in organic materials formed under reductive CO2-fixation and by the incorporation of the other elements, which are necessary for living systems. All endergonic processes in living cells are finally driven by the energy released through the clean recombination of protons and electrons with oxygen to water. Duration of the stored energy and the complexity of the systems thus produced is correlated negatively with the conversion efficiency of the radiation energy. Entropy is a unifying principle in the evolution of living systems, inclusive human societies.
The review deals with photosynthetic H2 production by various organisms, paying a speciál attention to eukaryotes, It includes a generál characterization of the catalyzing enzymes (hydrogenase and nitrogenase), quantum efficiency, the kinetics and mechanism of H2 photoevolution, the distribution and activity of H2 photoproducers (33 genera of eukaryotes), physiological functions of this process as well as recent developments in photobiological hydrogen technology.
Etiolated oat mesophyll protoplasts and etioplasts released from etiolated protoplasts were able to perform protochlorophyliide (PChlide) reduction but showed a high amount of inactive P633/628» compared with intact leaves. In špite of this, the anabolic reduction charge (ARC, NAPDH+H+/NADP+ + NADPF1+H+) was maintained at 0.66 - 0.77 up to 30 min of irradiation with weak "white light" (10 W m‘2). This indicated a high buffering capacity of the isolated systém to provide NADPF1+H+, only at the expense of intemal reserves. A change in the redox statě of the NADP+/NADPH+H^ couple during protochlorophyliide reduction was not observed in etioplasts. The resulting redox potential was in the range of -330 mV optimal for protochlorophyliide reduction.