Abstract: In order to understand the relationship between the ethylene receptor Nr gene and plant
resistance．the metabolism of tomato plants under stress of ethephon and abcisic acid(ABA)was studied．
The result showed that ABA induced largely the expression of the Nr gene．This expression was repressed by
silver ion，an ethylene depressor．ABA improved a triple response of tomato seedling—like efect caused by eth—
ylene．This decreased respiration and caused leaved chlorosis．The 50 ixmol／L ethephon supplied by spraying
leaves did not induce the expression of th Nr gene．Although the transpiration rate and stomatal conductance
were increased，the respiration and calculated CO2 and the plants grow did not change．Thus，overexpression
of the Nr gene was caused by environmental stress related to ABA．This stress induced the biosynthesis of
inner ethylene，which is the main reason of leaf chlorosis and plants senescence．

Key words: Tomato, Ethephon, ABA, Nr gene, Stress responses, Expression of gene