[[alternative]]Effect s of environmental factors on the photosynthesis of Synechococcus RF-1

[[abstract]]The aim of this study was (1) to identify the circadian rhythm of photosynthesis, (2) to compare the circadian rhythm between photosynthesis and membrane protein COP23 (circadian oscillating polypeptide), and (3) to investigate the effect of environmental factors such as temperature, light intensity, pH value, on the photosynthesis of Synechococcus RF-1, which is an unicellular N2-fixing cyanobacterium isolated at Taiwan. The rate of oxygen evolution in Synechococcus RF-1 exhibited circadian rhythm, which could be established by 12h white light/12h dark (12L/12D) or 12h red light/12h dark (12R/12D) entrainment, but not by 12h blue light/12h dark (12B/12D). The rhythm disappeared if the entrainment of 12R/12D was disturbed by far-red light. In addition, the rhythm could be established by 12h air/12h 5 ﹪CO2 –enriched air conduction as well. There were two different characteristics between photosynthetic and COP23 rhythms. Firstly, the peaks of photosynthetic and COP23 rhythms were in the light and dark periods respectively. Secondly, the rhythm of COP23 could be established by 12B/12D as well as 12L/12D or 12R/12D photoperiods. When Synechococcus RF-1 was cultured in the presence of nitrate, the expression of photosynthetic rhythm established by 12L/12D was inhibited, the content of chlorophyll a and carotenoids and the rate of growth were increased; in the aeration of 5 ﹪CO2 and the irradiation of 50-70 mmol photons m-2 s-1, the rates of photosynthesis and growth, and the content of chlorophyll a declined. The optimal pH for the rates of photosynthesis and growth was pH8. The glucose and the fructose might be used as the carbon source if Synechococcus RF-1 was cultured in the dark.