Abstract: To elucidate the relationship between ethylene evolution from the grains and the appearance quality of rice, ten different
rice genotypes were used to determine the ethylene evolution rate, 1-aminocylopropane-1-carboxylic acid (ACC) concentration in
grains during grain filling and the appearance quality of rice, and the effects of chemical regulators on concentrations of ethylene and
ACC in the grains during grain filling were also investigated to verify the roles of ethylene in the rice quality formation. The ethylene
evolution rates and ACC concentrations in grains during the mid and late grain filling stages were very significantly and positively
correlated with chalky kernel percentage and chalkiness. The cultivars with a low ACC concentration in grains exhibited a close
amyloplast arrangement and small space between starch granules, whereas those with a high ACC concentration in grains showed a
loose arrangement and wide space between the granules. Application of 1 μmol/L ACC to panicles at mid and late grain filling stages
significantly loosened amyloplast arrangement and increased chalky kernel percentage, chalky area and chalkiness, and the results
were reversed when 1 μmol/L amino-ethoxyvinylglycine, an inhibitor of ACC synthesis enzyme, was applied to panicles. A practice of
moderate dry-wet alternate irrigation reduced ethylene evolution and ACC concentration in grains and thereby reduced chalkiness.
The results suggested that ethylene and ACC in grains play an important role in the endosperm structure and appearance quality of
rice, and the appearance quality would be improved by reducing ethylene evolution and ACC in grains through either variety breeding
and selection, or chemical regulations or cultivation techniques.

Key words: rice, ethylene, 1-aminocylopropane-1-carboxylic acid, amyloplast structure, appearance quality, dry-wet alternate irrigation