## 2 Materials and Methods
### AsA Content Measurement  
Samples (approximately 50 mg fresh weight) were homogenized using a Qiagen TissueLyser with two 3-mm steel beads for 30 s at 30 Hz, turned the blocks around and ground for another 30 s. Samples were added with 1 mL of cold 3% metaphosphoric acid (\(w/v\)) and centrifuged at 12,000\(\times\)\(g\), 4 \({}^{\circ}\)C for 10 min; 20 \(\mu\)L of supernatants and AsA standards (0.1-1.0 mM) were transferred to a 96-well UV-transparent microplate and added 2 \(\mu\)L of 10 mM Tris (2-carboxyethyl) phosphine. The microplate was incubated at room temperature for 10 min. Then, 100 \(\mu\)L of 0.2 M pH 7.0 phosphate buffer was added to the microplate, and the absorbance at 265 or 280 nm was recorded. After that, 5 \(\mu\)L ascorbate oxidase (40 units mL\({}^{-1}\)) was added to the microplate and incubated at room temperature for 10 min. Finally, the absorbance was recorded again. The AsA concentration was calculated from the standard curve. Each experiment was repeated three times.  
Another method to measure AsA in Thai rice varieties is described as follows. AsA content measurement was performed as previously described [34]. Samples were ground in liquid nitrogen into a fine powder of approximately 40 mg; 500 \(\mu\)L of 6% Trichloroacetic acid (TCA) (\(w/v\)) was added to a 1.5 mL microcentrifuge tube. Samples were centrifuged at 13,000\(\times\)\(g\), 4 \({}^{\circ}\)C for 10 min; 100 \(\mu\)L of supernatants were transferred to new microcentrifuge tubes and kept on ice. Then, 50 \(\mu\)L of 75 mM pH 7.0 phosphate buffer was added to 6% TCA (\(w/v\)) (blank), AsA standards (0.1-1.0 mM) and samples; 50 \(\mu\)L of 10 mM DTT was added to all assay tubes and incubated at room temperature for 15 min, and 50 \(\mu\)L of 0.5% NEM (\(w/v\)) was added to remove excess dithiothreitol (DTT) and incubated at room temperature for at least 30 s. Then, 250 \(\mu\)L of 10% TCA (\(w/v\)), 200 \(\mu\)L of 43% H\({}_{3}\)PO\({}_{4}\) (\(v/v\)), 200 \(\mu\)L of 4% 2,2\({}^{\prime}\)-bipyridyl (\(w/v\)) and 100 \(\mu\)L of 3% FeCl\({}_{3}\) (\(w/v\)) were added to all assay tubes and incubated at 37 \({}^{\circ}\)C for 1 h. Finally, all assay tubes were measured for absorbance by spectrophotometer at 525 nm. AsA concentration was calculated from the standard curve.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Genes** & **Primer Sequence (5’-3’)** & **Product Size (bp)** & **Reference** \\ \hline \multirow{2}{*}{_OsVTC1-1_} & Forward: GTCATGTGAACTGAACCCTCC & \multirow{2}{*}{229} & [8] \\  & Reverse: GAGTTTCTTCGGTCCTCTG & & \\ \hline \multirow{2}{*}{_OsVTC1-3_} & Forward: CATCTCCCAGCAGTCATC & \multirow{2}{*}{239} & [8] \\  & Reverse: CATCCTCACACCATGAAAC & & \\ \hline \multirow{2}{*}{_OsVTC1-8_} & Forward: GATTGTCATGTGAAAATAC & \multirow{2}{*}{144} & [8] \\  & Reverse: CTCATTGAGAAGCAGTTATG & & \\ \hline \multirow{2}{*}{_OsGME1_} & Forward: AGACTTCCACTGACAGGTTTG & \multirow{2}{*}{132} & [15] \\  & Reverse: TTCCAATGTCAC & & \\ \hline \multirow{2}{*}{_OsGME2_} & Forward: GATGCCTAGGCTTGGAAA & \multirow{2}{*}{187} & [31] \\  & Reverse: CAAAACGGCTGAGGTT & & \\ \hline \multirow{2}{*}{_OsVTC2_} & Forward: GCAAACCATAACCACCCTCCA & \multirow{2}{*}{109} & [15] \\  & Reverse: CACTATTGTGCCCTCAC & & \\ \hline \multirow{2}{*}{_OsVTC4_} & Forward: GTTGCCTGAACATGATG & \multirow{2}{*}{106} & \multirow{2}{*}{This study} \\  & Reverse: CCGAAGAATCAGAGCTCCG & & \\ \hline \multirow{2}{*}{_OsGDH_} & Forward: AAGGGGAAAACATTACAAG & \multirow{2}{*}{146} & [15] \\  & Reverse: TTATCAATAGCGGAAGTAGACA & & \\ \hline \multirow{2}{*}{_OsGPX1_} & Forward: GCTTACTGCATCACTTTGCC & \multirow{2}{*}{76} & [32] \\  & Reverse: GCAGTCGCAGGTCTCAATAA & & \\ \hline \multirow{2}{*}{_OsActin_} & Forward: TCCACTTTGGCATCTCTCA & \multirow{2}{*}{337} & [33] \\  & Reverse: GTACCCCTCATCAGGCATCTG & & \\ \hline \end{tabular}
\end{table}
Table 1: Primer sequences used for qPCR analysis.