The effects of photosynthetic rate on respiration in light, starch/sucrose partitioning, and other metabolic fluxes within photosynthesis.

Abstract

In the future, plants may encounter increased light and elevated CO₂ levels. How consequent alterations in photosynthetic rates will impact fluxes in photosynthetic carbon metabolism remains uncertain. Respiration in light (R_L) is pivotal in plant carbon balance and a key parameter in photosynthesis models. Understanding the dynamics of photosynthetic metabolism and R_L under varying environmental conditions is essential for optimizing plant growth and agricultural productivity. However, measuring R_L under high light and high CO₂ (HLHC) conditions poses challenges using traditional gas exchange methods. In this study, we employed isotopically nonstationary metabolic flux analysis (INST-MFA) to estimate R_L and investigate photosynthetic carbon flux, unveiling nuanced adjustments in Camelina sativa under HLHC. Despite numerous flux alterations in HLHC, R_L remained stable. HLHC affects several factors influencing R_L, such as starch and sucrose partitioning, v_o/v_c ratio, triose phosphate partitioning, and hexose kinase activity. Analysis of A/C_i curve operational points reveals that HLHC's major changes primarily stem from CO₂ suppressing photorespiration. Integration of these fluxes into a simplified model predicts changes in CBC labeling under HLHC. This study extends our prior discovery that incomplete CBC labeling is due to unlabeled carbon reimported during R_L, offering insights into manipulating labeling through adjustments in photosynthetic rates.