Evidence for Inorganic Carbon Transport by Intact Chloroplasts of Chlamydomonas reinhardtii

Abstract

Isolated intact chloroplasts from wall-less mutants of Chlamydomoias reinhardtii accumulate inorganic carbon (C1) 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, accumulation from low CO2 grown cells was light dependent and was inhibited by uncouplers and inhibitors of electron transport. In a model for C, accumulation by Chiamydomonas, it is proposed that CO2 diffuses into the cell and Ci accumulation occurs in the chloroplast.

Cellular Cycling, Carbon Utilization, and Photosynthetic Oxygen Production during Bicarbonate-Induced Triacylglycerol Accumulation in a Scenedesmus sp.

“…Another possible explanation is the onset of the operation of carbon concentrating mechanisms (CCMs) which employ carbonic anhydrase and bicarbonate transport proteins to effectively shuttle bicarbonate to the ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) enzyme located in the pyrenoid of the chloroplast [24][25][26][27]. Besides the fundamental importance of increasing the carbon flux into microalgae, many studies have been done on the induction of algae's CCM by shifting from high CO 2 (typically 1%-5% v/v) to atmospheric levels (0.04%) and they report 2-10 light hours are needed to synthesize the metabolic machinery necessary to concentrate inorganic carbon [29][30][31][39][40][41][42][43]. Further experimentation is needed to elucidate definitively the observed increase in photosynthetic oxygen production over time in the cultures which received additional bicarbonate.…”

The Low CO2-Inducible 36-Kilodalton Protein Is Localized to the Chloroplast Envelope of Chlamydomonas reinhardtii

“…Transport of Ci across the chloroplast envelope of algae has been proposed by severa1 researchers (Beardall, 1981;Moroney et al, 1987;Palmqvist et al, 1990). Accumulation of Ci has been observed in intact chloroplasts isolated from low C02-grown C. reinhardtii (Moroney et al, 1987;Moroney and Mason, 1991) and Dunaliella (Goyal and Tolbert, 1989;Ramazanov and Cárdenas, 1992). Both C. reinhardtii and Dunaliella (Thielmann et al, 1992) have chloroplast envelope proteins that are specifically present in low C02-grown cells.…”

“…There have been reports that d transport might take place at the plasma membrane, chloroplast envelope (Beardall, 1981;Moroney et al, 1987;Goyal and Tolbert, 1989), or both membranes (Thielmann et al, 1990;Ramazanov and Cardenas, 1992) in unicellular algae. Therefore, we isolated plasma membranes from C. reinhardtii to determine whether the plasma membranes were contaminating the chloroplast envelope preparation.…”

Isolation and Characterization of a Mutant of Chlamydomonas reinhardtii Deficient in the CO2 Concentrating Mechanism

“…It is presently thought to involve a C, transporter (14,20) and one or more isozymes of carbonic anhydrase (10,14,21). A carbonic anhydrase located in the periplasmic space of the alga has been identified as part of the CO2 concentrating system (6, 1 1, 31).…”