title: Rubisco activation state decreases with increasing nitrogen content in apple leaves.
abstract: Based on the curvilinear relationship between leaf nitrogen content and the initial slope of the response of CO(2) assimilation (A:) to intercellular CO(2) concentrations (C:(i)) in apple, it is hypothesized that Rubisco activation state decreases with increasing leaf N content and this decreased activation state accounts for the curvilinear relationship between leaf N and CO(2) assimilation. A range of leaf N content (1.0-5.0 g m(-2)) was achieved by fertilizing bench-grafted Fuji/M.26 apple (Malus domestica Borkh.) trees for 45 d with different N concentrations, using a modified Hoagland's solution. Analysis of A:/C:(i) curves under saturating light indicated that CO(2) assimilation at ambient CO(2) fell within the Rubisco limitation region of the A:/C:(i) curves, regardless of leaf N status. Initial Rubisco activity showed a curvilinear response to leaf N. In contrast, total Rubisco activity increased linearly with increasing leaf N throughout the leaf N range. As a result, Rubisco activation state decreased with increasing leaf N. Both light-saturated CO(2) assimilation at ambient CO(2) and the initial slope of the A:/C:(i) curves were linearly related to initial Rubisco activity, but curvilinearly related to total Rubisco activity. The curvatures in the relationships of both light-saturated CO(2) assimilation at ambient CO(2) and the initial slope of the A:/C:(i) curves with total Rubisco activity were more pronounced than in their relationships with leaf N. This was because the ratio of total Rubisco activity to leaf N increased with increasing leaf N. As leaf N increased, photosynthetic N use efficiency declined with decreasing Rubisco activation state.
authors.affiliation: Department of Horticulture, Oregon State University, Corvallis, OR 97331, USA. LC89@Cornell.edu
authors.forename: L
authors.initials: L
authors.lastname: Cheng
authors.forename: L H
authors.initials: LH
authors.lastname: Fuchigami
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D004789:Enzyme Activation; D005638:Fruit / Q000201:enzymology / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D010788:Photosynthesis; D018515:Plant Leaves / Q000201:enzymology / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism*
chemical_list: D002245:Carbon Dioxide; D012273:Ribulose-Bisphosphate Carboxylase; D009584:Nitrogen