Comparative effects of light during growth on the photosynthetic properties of NADP-ME type C4 grasses from open and shaded habitats. II. Photosynthetic enzyme activities and metabolism*

Abstract The influences of shading during growth upon the activities of several photosynthetic enzymes were examined in NADP-ME type C₄ grasses from open (Zea mays L.) and shaded (Paspalum conjugation Berg.) habitats. The substantial species-difference in maximum photosynthetic rate observed under a high light regime was correlated with large differences in both enzyme activities and leaf protein contents. With the exception of RuBP carboxylase activity, other photosynthetic enzyme activities in Z. mays were reduced by shading to a similar extent as maximum photosynthetic rate. In contrast, only PEP carboxylase and pyruvate, P_i dikinase activities were decreased by shading in P. conjugatum. As with maximum photosynthetic rate, other photosynthetic enzyme activities in P. conjugatum were relatively insensitive to irradiance during growth. Under a low photon flux density of photosynthetically active radiation (50 μmol m^?2 s^?1), the flow of ¹⁴C] label through photosynthetic intermediates in intact, shade-grown leaves of P. conjugatum was typical of C₄ metabolism. This provides incontrovertible proof for the occurrence of C₄ photosynthesis in shaded habitats.