| Treatment of Chlamydomonas reinhardtii Dangeard cells (-, strain N. 90), cultured at 5% CO(,2), with 1 to 1000 ug/L triacontanol (TRIA) resulted in a 21% to 35% increase in cell density, 7% to 31% increase in total chlorophyll, and 20% to 100% increase in photosynthetic CO(,2) assimilation. Chlamydomonas cells responded to a broad range of TRIA concentrations that were at least 10-fold above the optimum concentration for higher plants. The necessity for higher concentrations of TRIA may be due to destabilizing effects of Ca('++) and K('+) present in the Chlamydomonas growth medium on the TRIA formulation. Octacosanol inhibited the effect of TRIA on photosynthetic CO(,2) assimilation.; TRIA did not alter glycolate excretion, the CO(,2) compensation point or sensitivity of photosynthetic CO(,2) assimilation to O(,2) in Chlamydomonas. Kinetic analysis of TRIA-treated cells showed that the increase in photosynthetic CO(,2) assimilation was a result of an increase in the whole-cell apparent Vmax. The activity of RuBP carboxylase/oxygenase was significantly higher in cell lysates from TRIA-treated cells than those from control cells. However, quantification of RuBP carboxylase/oxygenase levels by ('14)CABP binding did not show increased enzyme levels in TRIA-treated cells. Therefore, there was an increase in the specific activity of RuBP carboxylase/oxygenase extracted from Chlamydomonas cells treated with TRIA. TRIA alone had no effect in vitro on the activity of RuBPcarboxylase/oxygenase purified from spinach (Spinacia oleracea) leaves or from cell lysates of Chlamydomonas.; ; RuBP levels were significantly higher in TRIA-treated cells at high and low CO(,2). Increased RuBP levels in TRIA-treated Chlamydomonas cells were also observed in the absence of CO(,2) with atmospheres of N(,2) and 21% O(,2). |
