A mutant strain of Chlamydomonas reinhardi lacking ribulose diphosphate carboxylase activity.

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A mutant strain of the unicellular green alga, Chlamydomonas reinhardi, is unable to fix carbon dioxide by photosynthesis because it is deficient in phosphoribulokinase activity. The absence of light-dependent carbon dioxide fixation in cells of the mutant strain supports the operation of the Calvin-Benson scheme of photosynthetic carbon dioxide fixation in this organism. No deficiency other than low phosphoribulokinase activity was found which would account for the inability of cells of the mutant strain to fix carbon dioxide by photosynthesis. Activities comparable to those in the wild-type strain were found for eight other enzymes of the Calvin cycle and two enzymes associated with the C(4) dicarboxylic acid pathway. The normal rates of nicotinamide adenine dinucleotide phosphate photoreduction and of photosynthetic phosphorylation observed in chloroplast fragments prepared from cells of the mutant strain indicated that the photosynthetic electron transport chain in the mutant is intact.

Mutants with impaired photosynthesis in [formula omitted

Four mutant strains of Euglena gracilis have been isolated after treatment of wild type cells with ultraviolet light or the chemical mutagen nitrosoguanidine. None of the mutants is capable of autotrophic growth or photosynthetic carbon dioxide fixation. The mutant strains contain normal amounts of the enzymes of the reductive pentose phosphate cycle and are qualitatively similar to the wild type in pigment composition, but are unable to carry out the Hill reaction (light induced reduction of 2,6-dichlorophenol indophenol). Isolated mutant plastids cannot photoreduce NADP with water as the electron donor but can carry out this reaction when the electron donating system is ascorbate and 2,6-dichlorophenol indophenol. Whole cells of the mutants show the light induced oxidation of cytochrome f by light reaction I but are unable to bring about cytochrome f reduction by light reaction II. The mutants appear to be blocked at or near light reaction II in the photosynthetic electron transport chain. The mutants may represent alterations of the chloroplast genome since the mutation isolation was carried out under conditions where chloroplast viability was severely impaired, but cell viability was unaffected.

This book contains the proceedings of the 1991 Nobel Symposium devoted to the study of carbon dioxide (CO2) fixation and reduction in biological and model systems. With chapters authored by leading experts from around the world, the book covers subjects as diverse as photosynthetic carbon dioxide fixation and electrochemical reduction of CO2. Others topics include the organometallic chemistry of CO2 pertinent to catalysis, how enzymes deal with carbon dioxide and bicarbonate, photochemical electron transfer applied to the reduction of CO2, and the molecular biology and biochemistry of CO2, among many others. Students and researchers in biochemistry and the chemistry of CO2 fixation will welcome this timely survey of the field.

RECENTLY, Gibbs et al.1–4 emphasized the differences between whole and broken chloroplasts regarding their sensitivity against inhibitors during fixation of carbon dioxide and the distribution of carbon-14 in the sugars so formed. In our experiments an additional difference, the markedly lower pH optimum of fixation of carbon dioxide in whole chloroplasts, as compared with broken chloroplasts, was observed.

The photosynthetic electron transport chain of a mutant strain of Chlamydomonas reinhardi lacking P700 activity

The origin and evolution of photosynthesis is considered to be the key to the origin of life. This eliminates the need for a soup as the synthesis of the bioorganics are to come from the fixation of carbon dioxide and nitrogen. No soup then no RNA world or Protein world. Cyanobacteria have been formed by the horizontal transfer of green sulfur bacterial photoreaction center genes by means of a plasmid into a purple photosynthetic bacterium. The fixation of carbon dioxide is considered to have evolved from a reductive dicarboxylic acid cycle (Chloroflexus) which was then followed by a reductive tricarboxylic acid cycle (Chlorobium) and finally by the reductive pentose phosphate cycle (Calvin cycle). The origin of life is considered to have occurred in a hot spring on the outgassing early earth. The first organisms were self-replicating iron-rich clays which fixed carbon dioxide into oxalic and other dicarboxylic acids. This system of replicating clays and their metabolic phenotype then evolved into the sulfide rich region of the hotspring acquiring the ability to fix nitrogen. Finally phosphate was incorporated into the evolving system which allowed the synthesis of nucleotides and phospholipids. If biosynthesis recapitulates biopoesis, then the synthesis of amino acids preceded the synthesis of the purine and pyrimidine bases. Furthermore the polymerization of the amino acid thioesters into polypeptides preceded the directed polymerization of amino acid esters by polynucleotides. Thus the origin and evolution of the genetic code is a late development and records the takeover of the clay by RNA.

The vertical distribution of the photosynthetic fixation of carbon dioxide within a crop of corn was calculated from carbon dioxide profile data and transfer coefficients obtained by analysis of windspeed measurements. Infrared analyzers were used to measure the carbon dioxide concentration at several heights within and above the crop. The calculated total fixation for the day was approximately 60 g CO2 m−2 (equivalent to 470 pounds of sugar per acre per day). The results demonstrated the importance of the upper leaves in the fixation of carbon dioxide and showed the increased fixation by the lower leaves during periods of high light penetration. There was some indication that a coupling existed between the level of windspeed and fixation under conditions of high light and relatively low windspeed. With refinement in technique the method could be used to obtain more quantitative estimates of the distribution of photosynthesis in other crops.

2 - Photosynthesis

Every year, about 1011 tons of CO2 are incorporated into the biosphere by the photosynthetic activities of plants and microorganisms. Photosynthetic CO2 fixation proceeds through the incorporation of CO2 into ribulose bisphosphate (RuBP) which is then split into two molecules of phosphoglycerate. Part of the phosphoglycerate is used to synthesize energy-rich compounds such as starch or fatty acids. The remaining phosphoglycerate is used to regenerate RuBP, the primary acceptor of CO2, in a cyclic series of reactions, the reductive pentose phosphate or Calvin cycle.

Photosynthetic carbon dioxide fixation by isolated chloroplasts in good's buffers

Carbon dioxide fixation by leaf pieces from 12 different chloroplast mutants and wild type barley has been analysed. In the light leaf pieces from wild type seedlings fixed14CO2 at a rate of approximately 80 μmoles per gram fresh weight per hour, or 40 μmoles per mg chlorophyll per hour. Fixation of14CO2 in darkness occurred at one to four per cent of the rate in light. Five of the mutants investigated (vir-zb 63, vir-l27, vir-zd69, vir-c12 andxan-m 3) were completely blocked in light-dependent CO2 fixation. The mutantsvir-m 29, vir-u46, xan-d49, xan-c47, vir-t45, xan-t50 andvir-k 23 all yielded reduced photosynthetic rates on a gram fresh weight basis, but, with the exception ofvir-k 23, their photosynthetic rates on a chlorophyll basis differed by less than a factor of two from that of the wild type. On a chlorophyll basisvir-k 23 showed an enhanced rate of14CO2 fixation in comparison with the wild type. Barley mutants lacking light-dependent14CO2 incorporation fixed in darkness or in light similar small amounts of14CO2 into malate, aspartate, glutamate and citrate as did the wild type in darkness. Photosynthetic products in the mutants capable of light-dependent CO2 fixation were qualitatively the same as in the wild type, and the patterns of distribution of tracer carbon gave no evidence of any defects in reactions following the fixation of CO2. The gross correlation between chlorophyll contents and photosynthetic rates on a chlorophyll basis among these mutants with the exception ofvir-k 23 suggests that the reduced absorption of light by the lower amounts of chlorophyll in these mutants is the major or only factor responsible for their reduced photosynthetic rates on a gram fresh weight of leaf basis. The suggestion is made thatvir-k 23, which is characterized by a far higher photosynthetic rate in bright light than the wild type on a chlorophyll basis, contains several-fold lower amounts of light-harvesting chlorophyll per photosynthetic unit than wild type, whereas the other mutants that are capable of photosynthesis have photosynthetic units of the same size as the wild type but fewer of them.

Chronological recognition of the intermediates and mechanisms involved in photosynthetic carbon dioxide fixation is delineated. Sam Ruben and Martin Kamen's development of application of radioactive carbon for the study of carbon dioxide fixation provided impetus and techniques for following the path of carbon in photosynthesis. Discovery The identity of the primary carboxylation enzyme and its identity with the major protein of photosynthetic tissues ('Fraction 1' protein of Sam Wildman) is reviewed. Memories are dimmed by sixty years of exciting discoveries exploration in newer fields [see Benson 2002 (Annu Rev Plant Biol 53: 1-25), for research and perspectives beyond the early Berkeley days].

1. Induction periods in carbon dioxide fixation by isolated pea chloroplasts were shortened by small quantities of Calvin-cycle intermediates. The additional fixation was larger than that which would have followed direct stoicheiometric conversion into ribulose 1,5-diphosphate. 2. When chloroplasts were illuminated in the absence of added substrates (other than carbon dioxide) soluble products were formed in the medium that stimulated fixation by fresh chloroplasts. 3. The induction periods were lengthened by washing the chloroplasts. Addition of catalytic quantities of Calvin-cycle intermediates then decreased the induction periods to their previous values. 4. The induction period was extended by a decrease in temperature but was largely unaffected by a decrease in light-intensity that was sufficient to decrease the maximum rate. 5. It is concluded that the lag periods are a consequence of the loss of Calvin-cycle intermediates, such as sugar phosphates, through the intact chloroplast envelope and that these losses can be made good by new synthesis from carbon dioxide in the reactions of the Calvin cycle.