2.9 Metabolic activity assay
Triphenyl tetrazolium chloride (TTC) solution was used to determine rice cell metabolic activity as described elsewhere (Macharoen et al., 2020). In brief, the TTC solution was added to fresh rice cells and incubated at room temperature for 24 h in the dark. The red formazan stain in active rice cells was extracted, the absorbance was measured at 485 nm, and then the absorbance was normalized by g FW.