Fig. 9
From: Isocitrate lyase plays important roles in plant salt tolerance
A proposed salt-responsive regulatory mechanism of ICL that can shift energy metabolism from the TCA cycle to the glyoxylate cycle during salt stress. Salt stress in conjunction with CaM induces expression of aconitase, isocitrate lyase and malate synthase genes [10]. In the glyoxylate cycle, ICL generates one NADH from catalyzing malate to oxaloacetate and one FADH2 by catalyzing succinate to fumarate bypassing the two decarboxylation steps of the TCA cycle. Two steps of the glyoxylate cycle use the acetyl unit from acetyl-CoA, namely, conversion of glyoxylate to malate and the subsequent conversion of oxaloacetate to citrate. Under salt stress, pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase complex are inhibited [39]. The respiratory metabolism was previously proposed to be shifted to the GABA shunt pathway to provide alternative carbon source [39]. Because the pyruvate dehydrogenase complex is sensitive to salt stress, pyruvate might instead be fluxed to pyruvate carboxylase to generate oxaloacetate. Additionally, as 2-oxoglutarate dehydrogenase complex is inhibited under salt stress, the disrupted TCA cycle could lead to metabolite flux into the glyoxylate cycle to bypass the salt-inhibited enzymes