Oxalate synthesis pathways that contribute to oxalate accumulation in leaves of bitter dock (Rumex obtusifolius L.) differ between day and night

Oxalate is a simple dicarboxylate that accumulates primarily in terrestrial parts of plants. Inhibition experiments of a previous study focusing on “new leaves” of Rumex obtusifolius revealed that the isocitrate pathway, one of three oxalate pathways, is the primary contributor to oxalate accumulation. However, that experiment was conducted in the dark. In the present study, we conducted inhibitor experiments to evaluate the contribution of the isocitrate pathway to oxalate accumulation in the light. Oxalate accumulation was not inhibited by itaconate in the light, but uptake of itaconate in leaves of R. obtusifolius was greater in the light than in the dark. Multivariate statistical analyses revealed that itaconate only slightly affected the metabolite content under light conditions, but itaconate significantly affected the contents of oxalate and related compounds in the dark. These data suggest that the oxalate synthesis pathways that contribute to oxalate accumulation differ between day and night.