Carbonic anhydrase is induced prior to arylsulfatase under the simultaneous deprivation of inorganic carbon and sulfate in Chlamydomonas reinhardtii (Volvocales, Chlorophyta)

SUMMARY The activity of periplasmic arylsulfatase (Ars), which catalyzes the cleavage of sulfate from aromatic sulfur compounds, was detected in cells acclimated to the sulfate‐deficient conditions in a unicellular green alga Chlamydomonas reinhardtii Dangeard, but not in Chlorella, Scenedesmus, Dunaliella and Porphyridium. Upon the transfer of cells to sulfate‐deficient autotrophic media under high‐CO2 conditions, the induction of Ars was observed only in the light, but not in the light with dichlorophenyldimethylurea (DCMU) nor in the dark. However, Ars was induced in the light with DCMU or in the dark when acetate was present as an organic carbon source, but not citrate. Under similar high‐CO2 conditions, high‐CO2 requiring mutants of cia‐3 and cia‐5, whose photosynthetic activities are greatly limited under low CO2, showed much lower level of Ars activities than wild type cells. Under Iow‐CO2 conditions the induction of Ars was greatly suppressed even in wild type and no induction was observed in both mutants. These results suggest that the stimulation of photosynthetic or respiratory carbon metabolism are necessary for the induction of Ars. In contrast, the induction of periplasmic carbonic anhydrase (CA) which was synthesized de novo specifically under CO2‐limited conditions was strongly suppressed by the addition of organic carbon sources, such as acetate and citrate. When cells are subjected to CO2‐limitation and sulfate‐deficiency simultaneously, the induction of CA was initiated immediately, while that of Ars was initiated following the completion of CA induction with an about 4‐h lag. When the concentration of CO2 was suddenly lowered during the induction of Ars, the induction of Ars ceased quickly, and the induction of CA was initiated instead. From these results the induction of CA was suggested to have priority over that of Ars under the dual stress of CO2, and sulfate‐deprivation.