With 8901 11 and 4185, two field grown winter wheat varieties, the cha nging regulation of the effect of different zinc fertilization levels on the act ivity of carbonic anhydrase (CA) in leaves of winter wheat was determined. The activ ity of CA in top function leaves continually increased after double ridge stage and reached the maximum at flowering stage, then decreased. The activity of CA i n flag leaf and the 3rd leaf from top all reached the maximum values at the 7th o r 14th day after full expan...