2.2. SDH staining

Plant and Sol muscles were dissected and quickly frozen in isopentane (#26405-65, Nacalai Tesque) that was prechilled in liquid nitrogen. The muscles were sectioned into 10-μm slices using cryostat (CM3050S, Leica Biosystems, Hesse, Germany). SDH staining was performed as previously reported with slight modifications [22]. Sections were stained in a solution containing 0.5 mg/mL nitroblue tetrazolium (#N5514, Sigma-Aldrich) and 50 mM sodium succinate in 50 mM phosphate buffer at 37 °C for 20 min. The SDH-positive area was defined by a fixed threshold and automatically quantified at 100x magnification under optical microscopy with BZ II Analyzer software (BZ-9000 series, Keyence, Osaka, Japan).