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

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