Rubisco from two ecotypes ofPlantago lanceolataL. that are native to sites differing in atmospheric CO2levels

Abstract

AbstractRubisco, the most prevalent protein on the planet, initiates the conversion of CO2into carbohydrates during photosynthesis. Responses of this process to atmospheric CO2fluctuations daily, seasonally, and over millennia is still poorly understood. We have hypothesized that higher plants maintain carbon-to-nitrogen homeostasis by adjusting the balance of magnesium and manganese in chloroplasts to alter their relative carbon fixation and nitrogen assimilation rates. The following study examined the influence of magnesium and manganese on rubisco carboxylation and oxygenation in protein purified from two ecotypes ofPlantago lanceolata: one adapted to the high atmospheric CO2that occurs near a natural CO2spring and the other adapted to more typical CO2atmospheres that occur nearby. The plastid DNA coding for the large unit of rubisco were similar in both ecotypes. The kinetics of rubiscos from the two ecotypes differed more when they were associated with manganese than magnesium. Specificity for CO2over O2(Sc/o) for rubiscos from both ecotypes were higher when the enzymes were bound to magnesium than manganese. This disparity may account for the adaptation of this species to different CO2environments.