Environmental Effects on Photorespiration of C3-C4 Species

Abstract

The possibility of altering CO(2) exchange of C(3)-C(4) species by growing them under various CO(2) and O(2) concentrations was examined. Growth under CO(2) concentrations of 100, 350, and 750 micromoles per mole had no significant effect on CO(2) exchange characteristics or leaf anatomy of Flaveria pringlei (C(3)), Flaveria floridana (C(3)-C(4)), or Flaveria trinervia (C(4)). Carboxylation efficiency and CO(2) compensation concentrations in leaves of F. floridana developed under the different CO(2) concentrations were intermediate to F. pringlei and F. trinervia. When grown for 12 days at an O(2) concentration of 20 millimoles per mole, apparent photosynthesis was strongly inhibited in Panicum milioides (C(3)-C(4)) and to a lesser degree in Panicum laxum (C(3)). In P. milioides, acute starch buildup was observed microscopically in both mesophyll and bundle sheath cells. Even after only 4 days exposure to 20 millimoles per mole O(2), the presence of starch was more pronounced in leaf cross-sections of P. milioides compared to those at 100 and 210 millimoles per mole. Even though this observation suggests that P. milioides has a different response to low O(2) with respect to translocation of photosynthate or sink activity than C(3) species, the concentration of total available carbohydrate increased in shoots of all species by 33% or more when grown at low O(2). This accumulation occurred even though relative growth rates of Festuca arundinacea (C(3)) and P. milioides grown for 4 days at 210 millimoles per mole O(2), were inhibited 83 and 37%, respectively, when compared to plants grown at 20 millimoles per mole O(2).