Winter wheat leaves were used to investigate effects of Ozone(O 3) on membrane protective system in varied growth stages(jointing stage,heading stage,grain filling stage).The plants were exposed in open top chambers(OTCs)in the field conditions for five levels of O 3 concentration(ambient level,charcoal filtered air,50nl/L,100nl/L,200nl/L)from 1999 04 04～1999 06 06.Under O 3 exposure condition,chlorophyll a content and chlorophyll b content in winter wheat leaves were significantly declined:Membrane ...