Ratio of intercellular CO2 concentration to stomatal conductance is a reflection of mesophyll efficiency

Carbon assimilation rates (A) have been shown to be substrate limited associated with the stomatal conductance (G(s)). However, a significant species as well as genotypic variation in intercellular CO2 concentration (C-i) in the present study implies that mesophyll factors also play an important role in regulating A through its effect in determining the CO2 concentration gradient, Efficiency of the mesophyll factors is often estimated by measuring the initial slope of CO2 response curve (dA/dC(i)). In this paper we provide experimental evidences to show that C-i at a given G(s) is also a reflection of mesophyll efficiency, Steady state C-i levels are maintained by both G(s) and the efficiency of the mesophyll to utilize the substrate CO2. Therefore, at a given stomatal conductance, lower C-i should indicate a better mesophyll efficiency, The C-i/G(s) ratio also showed an inverse relationship with dA/dC(i). Therefore, C-i/G(s) ratio can be considered as a novel approach to estimate the mesophyll efficiency, We also noticed that the C-i/G(s) ratios showed a significant inverse relationship with assimilation rate, suggesting the role of mesophyll factors in the regulation of photosynthesis, The implications of the C-i/G(s) ratio are discussed in this paper.