Oxalate contents in leaves of two rice cultivars grown at a free-air CO2 enrichment (FACE) site

ABSTRACT Rice straw can be used as a feed for livestock. It accumulates soluble oxalate, which is harmful to livestock as it can cause mineral deficiency. It is therefore necessary to reduce the oxalate content in rice leaves so that the usage of rice straw for a livestock feed can be increased. Several oxalate synthesis pathways have been reported in various plants. However, the oxalate synthesis pathway in rice has not yet been elucidated. In the present study, we found that the oxalate content of the leaves of two rice cultivars, Koshihikari and Takanari, was different. The differences in the oxalate contents in the leaves of two cultivars were also maintained under the elevated CO2 concentration and/or temperature conditions. These findings suggest that oxalate accumulation has a genetic basis and does not depend on CO2 and temperature conditions. Abbreviations: A-[CO2]: ambient CO2 concentration; CE-QQQ-MS: capillary electrophoresis-triple quadrupole-mass spectrometry; E-[CO2]: elevated CO2 concentration; E-T: elevated soil/water temperature; FACE: free-air CO2 enrichment; TCA: tricarboxylic acid; N-T: normal soil/water temperatur