“…(1) Rice cultivars (either Japonica or Indica) with higher concentrations of free Spd and free Spm in the grains during filling exhibited higher content of amino acids in the milled grains than those with lower PA concentrations, and the concentrations of free Spd and free Spm in the filling grains are significantly and positively correlated with the contents of total essential amino acids, total nonessential amino acids, and total amino acids in the milled grain [72]. (2) Application of Spd or Spm to rice panicles at the early grainfilling stage significantly increased the activities of enzymes involved in the biosynthesis of amino acids in the grain including GS, GOGAT, AST, AK, and AST during grain filling, and accordingly, significantly increased the content of amino acids in milled grain of rice, and applying methylglyoxal-bis (guanylhydrazone) (MGBG, an inhibitor of Spd and Spm synthesis that inhibits SAMDC activity) had the opposite effect [72]. (3) Adoption of moderate soil-drying, or alternate wetting and moderate soil-drying (AWMD), or proper application of N fertilizer significantly increased the concentrations of PAs (Spd and Spm) by enhancing the activities of enzymes in PA synthesis, such as SAMDC, Spd synthase, and Spm synthase, in the grain during the filling, and consequently significantly promoted grain filling and increased the content of amino acids in milled grain of rice [62,73].…”