Partial reactions of photosynthesis in briefly sonicated chlamydomonas: I. Cell breakage and electron transport activities

The cell structure of Chlamydomonas reinhardi is disrupted by brief exposure to sonication. The extent of cell breakage can be determined quickly by cell count with the light microscope. Rates of photochemical activities of briefly sonicated cells approach those reported for higher plant chloroplasts. These activities are a sensitive function of time of sonication and sonic power used. The method of brief sonication is rapid and convenient and gives a stable preparation useful for determining photochemical activities in Chlamydomonas.     

Isolation and Characterization of a Mutant of Chlamydomonas reinhardtii Deficient in the CO(2) Concentrating Mechanism

A Chlamydomonas reinhardtii mutant has been isolated that cannot grow photoautotrophically on low CO₂ concentrations but can grow on elevated CO₂. In a test cross, the high CO₂-requirement for growth showed a 2:2 segregation. This mutant, designated CIA-5, had a phenotype similar to previously identified mutants that were defective in some aspect of CO₂ accumulation. Unlike previously isolated mutants, CIA-5 did not have detectable levels of the periplasmic carbonic anhydrase, an inducible protein that participates in the acquisition of CO₂ by C. reinhardtii. CIA-5 also did not accumulate inorganic carbon to levels higher than could be accounted for by diffusion. This mutant strain did not synthesize any of the four polypeptides preferentially made by wild type C. reinhardtii when switched from an environment containing elevated CO₂ levels to an environment low in CO₂. It is concluded that this mutant fails to induce the CO₂ concentrating system and is incapable of adapting to low CO₂ conditions.     

Multidisciplinary research in photosynthesis: A case history based on the green alga Chlamydomonas

This article examines the contribution of a unicellular green alga Chlamydomonas to progress in photosynthetic research. The objective is to focus on the aspects of Chlamydomonas that have provided an advantage over other photosynthetic organisms in investigating photosynthesis. To do this we discuss several examples that demonstrate the progress from a genetic study to a multidisciplinary approach that probes higher levels of complexity within the organism. These examples include the function and molecular regulation of electron transport components between photosystem II and photosystem I, the molecular genetics of the herbicide binding protein of photosystem II, and several different studies that have derived from a search for rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) mutants in Chlamydomonas, including chloroplast ribosome function, the regulation of the large subunit of rubisco, and the interaction between photosynthetic electron transport and carbon metabolism.     

Limitations on the Utilization of Glycolate by Chlamydomonas reinhardtii

Growth and shorter term incorporation measurements with both wild type Chlamydomonas reinhardtii and a mutant (F-60, lacking phosphori-bulokinase activity) indicate that the rate of glycolate utilization is always relatively low. Growth support with external glycolate is restricted to cells with full photosynthetic capacity. A high concentration of glycolate is required for optimal growth support and incorporation of [¹⁴C]glycolate. Glycolate incorporation is low at pH 3.8 even with the relatively free permeability. The F-60 mutant can take up only small quantities of glycolate in spite of photosynthetic electron transport and photophosphorylation competencies. This requirement for photosynthetic carbon metabolism indicates a significant difference in the glycolate pathway of this alga. No growth condition significantly increases glycolate incorporation rates. There is no evidence that one of the primary enzymes, glycolate dehydrogenase, is limiting utilization; measurements of glycolate uptake and excretion do not always correlate with its activity. Since the maximal utilization rate of glycolate is low, control of glycolate formation is important in preventing the loss of this fixed carbon from the algal cell.     

Evidence for Inorganic Carbon Transport by Intact Chloroplasts of Chlamydomonas reinhardtii

Isolated intact chloroplasts from wall-less mutants of Chlamydomonas reinhardtii accumulate inorganic carbon (C_i) from the medium provided the cells had been adapted to low CO₂ photoautotrophic growth conditions. Chloroplasts from cultures grown on high (5%) CO₂ or photoheterotrophically with acetate did not accumulate inorganic carbon. Chloroplast C_i accumulation from low CO₂ grown cells was light dependent and was inhibited by uncouplers and inhibitors of electron transport. In a model for C_i accumulation by Chlamydomonas, it is proposed that CO₂ diffuses into the cell and C_i accumulation occurs in the chloroplast.     

A new species of Scorzonera L. (Asteraceae) from south Anatolia, Turkey

A new species Scorzonera gokcheoglui O. Ünal & R. S. Göktürk sp. nov. from south Anatolia is described and illustrated. Its relationships with S. argyria and S. pisidica are discussed. A map showing the distribution of the species and other related species is given.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 465–468.     

Tyrosine phosphorylation of myosin heavy chain during skeletal muscle differentiation: an integrated bioinformatics approach

Previously it has been shown that insulin-mediated tyrosine phosphorylation of myosin heavy chain is concomitant with enhanced association of C-terminal SRC kinase during skeletal muscle differentiation. We sought to identify putative site(s) for this phosphorylation event. A combined bioinformatics approach of motif prediction and evolutionary and structural analyses identified tyrosines163 and 1856 of the skeletal muscle heavy chain as the leading candidate for the sites of insulin-mediated tyrosine phosphorylation. Our work is suggestive that tyrosine phosphorylation of myosin heavy chain, whether in skeletal muscle or in platelets, is a significant event that may initiate cytoskeletal reorganization of muscle cells and platelets. Our studies provide a good starting point for further functional analysis of MHC phosphor-signalling events within different cells.