Effect of Triacontanol on Chlamydomonas: II. Specific Activity of Ribulose-Bisphosphate Carboxylase/Oxygenase, Ribulose-Bisphosphate Concentration, and Characteristics of Photorespiration

Increased photosynthetic CO₂ assimilation by Chlamydomonas reinhardtii cells treated with triacontanol (TRIA) was not due to changes in glycolate excretion, CO₂ compensation point, or the sensitivity of photosynthetic CO₂ assimilation to O₂. Kinetic analysis of TRIA-treated cells showed that the increase in photosynthetic CO₂ assimilation was a result of an increase in the apparent V_max for intact cells. The total activity of ribulose-P₂ carboxylase/oxygenase was higher in cell lysates from TRIA-treated cells. However quantification of this enzyme concentration by binding of ¹⁴C]carboxyarabinitol-P₂ did not show an increase in TRIA-treated cells. Thus, there was an increase in the specific activity of ribulose-P₂ carboxylase/oxygenase extracted from Chlamydomonas cells treated with TRIA. TRIA alone had no effect on the activity of the enzyme in cell lysates from Chlamydomonas or purified from spinach (Spinacia oleracea L.) leaves.

The ribulose-P₂ pool was 50 to 60% higher in cells treated with TRIA that were assayed for photosynthetic CO₂ assimilation at high- and low-CO₂. TRIA also increased ribulose-P₂ levels in the absence of CO₂ in the light with atmospheres of N₂ or N₂ with 21% O₂.