Abstract:It was observed in our preliminary experiments that the growth of Dunaliella salina (Dunal) Teed. cultured in medium containing 1 mol/L NaC1 was almost completely inhibited by the addition of 100 mmol/L KC1. This study was focused on elucidating the physiological mechanisms by which high K+ inhibits D. salina growth. Under the control conditions, the pH of the medium rapidly increased from 8 to 10 along with the growth of D. salina. However, addition of 100 mmol/L KCI significantly inhibited the increase of medium pH. The results suggested that the growth of D. salina may require a low environmental of H + concentration or be related to the H + transport into the D. salina cells. Interestingly, D. salina cultured in various media with different pH buffered with 40 mmol/L Tris-HC1 (or Tris-NaOH) did not show any significant difference in the growth rates. This result brings up the question on the previous hypothesis that Na+/H+ antiport plays a major role in Na + extrusion in D. salina. The photosynthetic rate of D. salina was not inhibited immediately following the addition of high K+ in the reaction medium, but it was significantly inhibited after the pretreatment of algae with high K+ for 12 hours or longer. The results from simultaneous measurements of O2 evolution of D. salina and the changes in pH of the medium revealed that the inhibitory effect of high K + on D. salina growth was somehow associated with K+ effect on pH changes in the medium. The high K+ treatment of D. salina also resulted in significant decrease of chlorophyll contents in the algae. It is concluded that the inhibitory effects of high K + on photosynthesis of D. salina may, at least partially, account for the growth-inhibition of D. salina growth by high K+; the inhibitory effects of high K+ on D. salina photosynthesis may result from the influence of K + on H + transport across the plasma membranes of D. salina cells.