Ultrastructure changes in grapevine chloroplasts caused by increased tropospheric ozone concentrations

The ultrastructure of chloroplasts in the leaves of grapevine plants (Vitis vinifera L.) exposed to different ozone concentrations was investigated. O zone fumigations were performed in open-top chambers at four different ozon e levels (charcoal-filtered air (F), ambient air (N), ambient air + 25 mm(3 )m(-3) ozone (O-25) and ambient air + 50 mm(3)m(-3) ozone (O-50)). Under sl ightly elevated ozone concentrations chloroplasts showed an increase in num ber and size of plastoglobuli. The thylakoid system appeared to be relative ly well preserved even under elevated ozone concentration (O-25). The O-50 leaves showed a decrease in the content of chlorophyll a + b and in the rat io chl a + b/carotenoids as well as disintegration of some chloroplasts, wh ile others - sometimes within the same cell - appeared still intact. We conclude that low concentrations of ozone lead to an accelerated senesce nce of leaves, and that the thylakoid membrane is damaged only under higher ozone concentrations and prolonged ozone exposure.