Phenanthrene-triggered tricarboxylic acid cycle response in wheat leaf

Abstract

Tricarboxylic acid cycle (TCA cycle) is the most effective energy metabolism pathway in higher plants and animals. However, there is no information about its response in plants under environmental stress, especially under polycyclic aromatic hydrocarbons (PAHs) pollution. Here, this study is the first to discuss the intermediate and related enzyme changes in TCA cycle in plants. We applied high performance liquid chromatography (HPLC) and isobaric tags for relative and absolute quantitation (iTRAQ) proteomics to analyze the intermediate concentration and related protein response in wheat leaf cells, respectively. The concentrations of citrate and malate (0.37 and 0.57 mg kg−1) in the treatment with 1.0 mg L−1 phenanthrene were higher than those in the control, and the concentrations of the other five intermediates (i.e., α-ketoglutarate, fumarate, oxaloacetate, pyruvate and succinate) in the treatment were lower than those in the control. Three detected proteins (pyruvate dehydrogenase, dihydrolipoyllysine-residue succinyltransferase and fumarate hydratase) involved in TCA cycle were up-regulated when phenanthrene was accumulated in wheat leaf cells. Meanwhile, real-time PCR results of seven key TCA cycle enzymes genes further confirmed the aforementioned enzyme results. The gene expressions of ketoglutarate dehydrogenase, fumarase and pyruvate dehydrogenase were promoted when phenanthrene was accumulated, while the other four genes were suppressed. In general, pyruvate decrease is the key reason for TCA cycle inactivation under exposure to phenanthrene. Meanwhile, malate concentration increases significantly (P < 0.05), and all the three conversion enzymes turn active. Our results offer helpful information for understanding TCA cycle energy metabolism response to PAH exposure.