O3‐induced degradation of Rubisco protein and loss of Rubisco mRNA in relation to leaf age in Solanum tuberosum L.

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Abstract
The effect of ozone (O3) 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 O3 for 6 h. Rubisco small subunit (rbcS) 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 O3 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 O3 in the mature leaves. The immature leaves sustained a similar decline in Rubisco quantity in both O2 and control treatments. O3 had a significant effect on the relative quantity of rbcS mRNA in the immature leaves (sampled immediately following the O3 exposure). Levels of rbcS mRNA in mature leaves and Rubisco large subunit (rbcL) mRNA in both leaf ages were not significantly affected by O3, There was no effect of O3, 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 O3 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 O3 caused enhanced degradation of Rubisco in mature leaves of plants induced to senesce by dark incubation following O3 exposures. The potential for O3-induced reduction in synthesis of Rubisco also exists.