Variations in the Alternative Oxidase in Chlamydomonas Grown in Air or High CO₂

Abstract

Chiamydomonas in the resting phase of growth has an equal capacity of about 15 micromole 02 uptake per hour per milligram of chlorophyll for both the cytochrome c, CN-sensitive respiration, and for the altemative, salicylhydroxamic acid-sensitive respiration. Altemative respiration capacity was measured as salicylhydroxamic acid inhibited 02 uptake in the presence of CN, and cytochrome c respiration capacity as CN inhibition of 02 uptake in the presence of salicylhydroxamic acid. Measured total respiration was considerably less than the combined capacities for respiration. During the log phase of growth on high (2-5%) C02, the altemative respiration capacity decreased about 90% but retumed as the culture entered the lag phase. When the altemative oxidase capacity was low, addition of salicylic acid or cyanide induced its reappearance. When cells were grown on low (airlevel) C02, which induced a CO2 concentrating mechanism, the altemative oxidase capacity did not decrease during the growth phase. Attempts to measure in vivo distribution of respiration between the two pathways with either CN or salicylhydroxamic acid alone were inconclusive. is activated. In unicellular algae, such as Chlamydomonas, Dunaliella, Chlorella, and Euglena, the oxidation ofglycolate formed during photosynthesis is catalyzed by a mitochondrial membrane bound glycolate dehydrogenase which also oxidizes i-lactate (24). This dehydrogenase does not transfer electrons directly to oxygen as does the FMN-linked, peroxisomal glycolate oxidase. By using a cytochrome oxidasedeficient mutant of Chlamydomonas reinhardtii, Husic andTolbert (1 1) showed that glycolate and D-lactate metabolism could proceed through a SHAM-sensitive, alternative, electron transport pathway. These considerations raised the question whether there might be a difference in the cyanidesensitive (Cyt c) and cyanide-insensitive (alternative) respiration by C. reinhardtii during their growth cycle in low C02 (air) or high C02.

Cyanide-resistant respiration in diverse marine phytoplankton. Evidence for the widespread occurrence of the alternative oxidase

“…This is consistent with previous reports that, in both nutrient-sufficient and nutrient-deficient C. reinhardtii, the respiration rate is, at most, only slightly affected by SHAM or PG (Peltier & Thibault 1985, Goyal & Tolbert 1989, Weger e t al. 1990a, Weger 1996.…”

“…Early studies revealed that, in addition to cytochrome oxidase, Chlorella contain a second terminal oxidase resistant to inhibitors like KCN, CO, or H,S (Negelein 1925, Emerson 1927, Syrett 1951, Sargent & Taylor 1972. More recent studies on Chlamydomonas reinhardtii have shown that, although cyanide-resistant respiration through the AOX may exceed the total rate of respiration of cells not exposed to inhibitors, the addition of AOX inhibitors alone has little or no effect on the respiration rate (Peltier & Thibault 1985, Goyal & Tolbert 1989, Weger et al 1990a, Weger 1996. It therefore has been concluded that the AOX is present but rarely engaged in C. reinhardtii.…”

Characterization of two genes encoding the mitochondrial alternative oxidase in Chlamydomonas reinhardtii

“…A protein of 36 kDa which is recognized by a monoclonal antibody raised against S. guttatum AOX has been identified (Derzaph and Weger 1996). The alternative respiration is present under normal growth conditions but considerably decreases when the cells are cultivated at high CO 2 concentration (Goyal and Tolbert 1989).…”

Molecular and ultrastructural aspects of the adaptation of Chlamydomonas reinhardtii to limiting CO2

“…Glycolate dehydrogenase ) and the subsequent enzymes of the glycolate metabolic pathway are found in the mitochondria of both C reinhardtii and S. and Dunaliella under certain conditions (Goyal and Tolbert 1990). It also has been observed that there is a higher level of alternative oxidase activity in air-adapted cells (Goyal and Tolbert 1989). These are only correlative observations at this point, but do suggest some possible involvement of the alternative respiration pathway in adaptation to limiting COj.…”

“…It was not clear whether inorganic carbon was being transported at the plasma membrane, and concentrated within the entire cell, or at the chloroplast envelope, and concentrated within the chloroplast. Work with isolated chloroplasts of Chlamydomonas (Sultemeyer et al 1988, Moroney et al 1987 and Dunaliella (Goyal and Tolbert 1989) has indicated that chloroplasts from air-adapted, but not COj-enriched cells, have the ability to accumulate inorganic carbon and that chloroplasts from air-adapted cells have a higher affinity for inorganic carbon. This would argue for the location of a transporter at the chloroplast envelope.…”