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Inorganic carbon transport across cell compartments of the halotolerant alga Dunaliella salina
Author(s) -
Ramazanov Ziyadin,
Cárdenas Jacobo
Publication year - 1992
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1992.tb04713.x
Subject(s) - dunaliella salina , halotolerance , carbonic anhydrase , photosynthesis , total inorganic carbon , chloroplast , algae , intracellular , biochemistry , chemistry , extracellular , intracellular ph , biology , biophysics , botany , carbon dioxide , enzyme , salinity , ecology , gene , organic chemistry
The inorganic carbon (C i ) accumulation and the intracellular location of carbonic anhydrase (CA, EC 4.2.1.1) in the halotolerant unicellular alga Dunaliella salina have been investigated. The rate of HCO 3 ‐dependent O 2 evolution was determined by growth conditions. Algae grown under high CO 2 conditions (5% CO 2 in air, v/v; high C i cells) had a very low affinity for HCO 3 − at pH 7.0 and 8.2, whereas algae grown under low CO 2 conditions (0.03% CO 2 in air; low C i cells) showed a high affinity for HCO 3 − at both pH values and were sensitive to Dextran‐bound sulfonamide (DBS), an inhibitor of extracellular CA. The photosynthetic rate or HCO 4 − dependent O 2 evolution was always higher at pH 7.0 than at pH 8.2. Ethoxyzolamide (EZ), an inhibitor of total (extacellular plus intracellular) CA activity, strongly inhibited photosynthesis at both pH values. During adaptation from high to low CO 2 conditions CA activity increased in chloroplasts in a process dependent on the novo protein synthesis. Carbonic anhydrase activity was found in the supernatant and pellet fractions of chloroplast homogenates. The rate of photosynthesis of chloroplasts from low C i cells was higher at pH 7.0 than at pH 8.2. The alkalinization of the growth medium, which took place only in the presence of C i , was partially inhibited by DBS and completely by EZ. We suggest that in D. salina CO 2 is the general form of C i transported across the plasma membrane and the chloroplast envelope and that bicarbonate enters the cell mainly, although not entirely, by an ‘indirect’ mechanism after dehydration to CO 2 .