O 3 ‐induced degradation of Rubisco protein and loss of Rubisco mRNA in relation to leaf age in Solanum tuberosum L.

SUMMARY The effect of ozone (O 3 ) on Rubisco degradation was investigated by dark incubation of potato plants ( Solanum tuberosum L. cv. Norland) following exposure to charcoal‐filtered air or 0.30μl l −1 O 3 for 6 h. Rubisco small subunit ( rbc S) mRNA levels declined dramatically in control foliage within 10.16 h of dark incubation; thus declines in Rubisco protein following a 48‐h dark period were ascribed to proteolytic degradation. Foliage sampled from the 4th and 6th leaves from the apex, designated immature and mature, respectively, showed no effect of O 3 on Rubisco protein content immediately following the exposure. However, the decline in Rubisco quantity during the dark incubation was significantly enhanced by prior treatment with O 3 in the mature leaves. The immature leaves sustained a similar decline in Rubisco quantity in both O 2 and control treatments. O 3 had a significant effect on the relative quantity of rbc S mRNA in the immature leaves (sampled immediately following the O 3 exposure). Levels of rbc S mRNA in mature leaves and Rubisco large subunit ( rbc L) mRNA in both leaf ages were not significantly affected by O 3 , There was no effect of O 3 , on Rubisco quantity in immature or mature leave's of plants maintained in the greenhouse under a 16 h photoperiod far 48 h following the exposure. Thus the effect of short‐term O 3 exposure on processes affecting Rubisco synthesis and degradation may have been transient, and a more prolonged exposure would he necessary to effect a decline in Rubisco protein quantity in plants grown under a 16 h photoperiod. We concluded that O 3 caused enhanced degradation of Rubisco in mature leaves of plants induced to senesce by dark incubation following O 3 exposures. The potential for O 3 ‐induced reduction in synthesis of Rubisco also exists.