POTASSIUM ALLEVIATES THE INHIBITORY ACTION OF AMMONIUM UPON THE PHOTOSYNTHETIC RECOVERY OF NOSTOC FLAGELLIFORME (CYANOPHYCEAE) DURING REHYDRATION1

Abstract

Effects of ammonium on the photosynthetic recovery of Nostoc flagelliforme Berk. et M. A. Curtis were assayed when being rehydrated in low-K⁺ or high-K⁺ medium. Its photosynthetic recovery was K⁺ limited after 3 years of dry storage. The potassium absorption of N. flagelliforme reached the maximum after 3 h rehydration in low-K⁺ medium but at 5 min in high-K⁺ medium. The K⁺ content of N. flagelliforme rehydrated in high-K⁺ medium was much higher than that in low-K⁺ medium. The maximal PSII quantum yield (F_v /F_m ) value of N. flagelliforme decreased significantly when samples were rehydrated in low-K⁺ medium treated with 5 mM NH₄ Cl. However, the treatment of 20 mM NH₄ Cl had little effect on its F_v /F_m value in high-K⁺ medium. The relative F_v /F_m 24 h EC₅₀ (concentration at which 50% inhibition occurred) value of NH₄⁺ in high-K⁺ medium (64.35 mM) was much higher than that in low-K⁺ medium (22.17 mM). This finding indicated that high K⁺ could alleviate the inhibitory action of NH₄⁺ upon the photosynthetic recovery of N. flagelliforme during rehydration. In the presence of 10 mM tetraethylammonium chloride (TEACl), the relative F_v /F_m 24 h EC₅₀ value of NH₄⁺ was increased to 46.34 and 70.78 mM, respectively, in low-K⁺ and high-K⁺ media. This observation suggested that NH₄⁺ entered into N. flagelliforme cells via the K⁺ channel. Furthermore, NH₄⁺ could decrease K⁺ absorption in high-K⁺ medium.

Keywords: Nostoc flagelliforme; ammonium; cyanobacterium; photosynthesis; potassium.