On Ammonium Uptake in Ulva pertusa Kjellman

Algae > Volume 11(3); 1996 > Article

Algae 1996;11(3): 317-323.

Bang-Ook Jun, Sung-Won Lee, Young-Myung Kwon

Department of Biology, Kangnung National University, Department of Biology, Seoul National University

ABSTRACT

Ammonium uptake kinetics and effects of several factors influencing ammonium uptake rate in Ulva pertusa were investigated and the possible uptake mechanism was speculated. Uptake rate was calculated from ammonium depletion in a solution by multiple flask method. The uptake was not linear with time. The concentration of ammonium maximum uptake was 200 μM, and uptake rate was decreased at higher concentration. Michaelis-Menten kinetics could not be applied. The optimum temperature was 20℃ and Q sub(10) value was about 1.2, indicating that ammonium uptake can occur via passive diffusion. Active transport process using cellular eneragy might not be involved because vanadate, an ATPase inhibitor, did not inhibit ammonium uptake. Light treatment caused two times increase compared to the dark control, and DCMU, a photosynthesis inhibitor, nullified light caused uptake increase. This result suggest the possibility that ammonium can further be incorporated in the carbon skeleton made photosynthetically. The fact that caycloheximide significantly reduced uptake rate also support this possibility. But 2,4-dinitrophenol, a potent respiration inhibitor could not make any effects. The uptake was reduced as the pH of external solution was decreased, because concentration difference of uncharged ammonium between external solution and cell sap of Ulva pertusa became smaller. Membrane electrical potential calculated on the base of internal and external solution by Nernst equation did not rule out the passive transport hypothesis. In summary, ammonium uptake in Ulva pertusa is thought to be occurred thru passive transport due to concentration difference of uncharged ammonium between external solution and cell sap of Ulva pertusa rather than menbrane porter and energy consuming active process.

Key words: green alga, nitrate uptake, Ulva pertusa