ACTIVITY OF RIBULOSE BISPHOSPHATE CARBOXYLASE OXYGENASE FROM POTATO CULTIVARS WITH DIFFERENTIAL RESPONSE TO OZONE STRESS

The effect of ozone (O3) on the carboxylation activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from the fifth youngest leaf of four cultivars of Solanum tuberosum L. (potato) was investigated. Ozone-tolerant cultivars 'Superior' (SP) and 'Norgold Russet' (NR), and O3-sensitive cultivars 'Cherokee' (CK) and 'Norland' (NL) were exposed to O3 for five consecutive days in controlled-environment chambers. Leaf samples were obtained during the O3-exposure period and at 1, 5, and 10 d post-exposure. For both charcoal-filtered air (control) and O3-treated foliage, total activity of Rubisco declined with increasing leaf age. Ozone induced an accelerated decline in the carboxylation activity of Rubisco in leaves obtained from CK and NL by the third day of O3 exposure. In contrast, O3 had no impact on the Rubisco activity from leaves of SP and NR as compared to non-treated foliage. Differential foliar conductance could not account for the response of the sensitive and tolerant cultivars. Rubisco was purified from cultivars SP and CK to determine whether protein sulphydryl content correlated with foliar O3 sensitivity. The number of SH groups did not differ between the two cultivars, either in chemically denatured or non-denatured Rubisco. Consequently, neither number nor availability of SH groups appear to be factors controlling sensitivity of Rubisco to oxidative damage by O3.