Abstract
Biogenic polyamines are involved in a wide range of plant cellular processes, including cell division, morphogenesis and stress responses. However, the exact roles of biogenic polyamines are not well understood. We recently reported that biogenic polyamines that have multiple amino groups can react with CO2 and accelerate calcium carbonate formation in seawater. The ability of biogenic polyamines to capture atmospheric CO2 prompted us to examine their roles in photosynthesis. Here, we demonstrated that atmospheric CO2 captured by biogenic polyamines is a candidate substrate for the carboxylation reaction of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), which is an enzyme involved in the first major step of carbon fixation during photosynthesis, and that biogenic polyamines can accelerate the carboxylation reaction of this enzyme because of their specific affinity for CO2. Moreover, the results of our nuclear magnetic resonance (NMR) analysis showed that putrescine, which is the most common biogenic polyamine, reacts with atmospheric CO2 and promotes the formation of carbamate derivatives and bicarbonate in aqueous environments. A sufficient amount of CO2 is well known to be produced by carbonic anhydrase from bicarbonate in vivo. The present study indicates that CO2 would be also produced by the equilibrium reaction from carbonate produced by biogenic polyamines and would be used as a substrate of Rubisco, too. Our results may suggest a new photosynthetic research strategy that involves CO2-concentrating mechanisms and also possibly constitutes a potential tool for reducing atmospheric CO2 levels and, consequently, global warming.
Highlights
The carboxylation reaction that fixes atmospheric CO2 into organic compounds during photosynthesis is the first reaction of organic synthesis
We recently reported that biogenic polyamines can capture atmospheric CO2 and accelerate bicarbonate/ carbonate formation in aqueous solutions; these findings led to the formation of extracellular bacterial CaCO3 21
The ability of biogenic polyamines to capture atmospheric CO2, reported by us for the first time, led us to examine the roles of biogenic polyamines in photosynthesis
Summary
The carboxylation reaction that fixes atmospheric CO2 into organic compounds during photosynthesis is the first reaction of organic synthesis. The CO2 used for photosynthesis in terrestrial plants diffuses from the atmosphere into the leaves through the stomata This CO2 dissolves in the liquid phase of the mesophyll cell wall surface and reaches the Rubisco in the stroma of the chloroplast via the cell membrane, cytoplasm, and chloroplast envelopes[5]. This diffusion process substantially decreases the CO2 concentration. We show that polyamines possibly contribute to CO2 diffusion and photosynthesis These findings should be useful both for elucidating novel physiological functions of polyamines and for developing new methods to reduce atmospheric CO2
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