Environmental regulation of CO2 concentrating mechanisms in C4 grasses with different biochemical subtypes

摘要: The CO2 concentrating mechanism (CCM) endows C4 plants with high CO2 assimilation rate and high light saturation which in turn leads to an agricultural and ecological importance that is disproportionately high relative to their small taxonomic representation. The CCM is achieved by a series of anatomical and biochemical adaptations which allow the collaborative operation of two photosynthetic cycles, C4 and C3, across the outer mesophyll (MC) and inner bundle-sheath cells (BSC) to saturate Rubisco by CO2 in BSC. The BSC membrane is not completely impermeable to CO2, and some CO2 leaks out into the surrounding MC which increases the energetic cost of C4 photosynthesis. Therefore, leakiness (ϕ), defined as the rate of CO2 leakage out of BSC into the MC as a fraction of the rate of PEP carboxylation (Vp) is an important measure of CCM efficiency and coordination. Leakiness is determined by the …