Mechanisms underlying the impacts of ozone on photosynthetic performance

The present study examined the effects of ozone on the photosynthetic capacity of two ‘Cos’ lettuce (Lactuca sativa L.) varieties grown widely in Greece. The role of Rubisco and Rubisco activase in mediating the O3-enhanced decline in carboxylation efficiency was explored. The transcript and protein abundances of Rubisco activase plus Rubisco large and small subunits were monitored over the leaf life-span in plants subject to ozone levels similar to those experienced regularly during the spring and summer time in Southern Europe (100 ppb ozone 8 h d−1). Ozone exposure led to a decline in net CO2 fixation (i.e. a decline in the maximum light- and CO2-saturated rate of assimilation, i.e. Amax), a reduction in carboxylation efficiency (Vcmax) and a decline in the maximum modelled capacity for RuBP regeneration (Jmax). The decline in carboxylation efficiency induced by ozone was linked to a decrease in the amount of Rubisco LSU and SSU protein, an effect resulting–at least in part–from a decrease in the transcript abundance of rbcS1 and to a lesser extent of rbcL. The work outlined in this paper shows that members of the rbcS gene family respond differentially to ozone-induced oxidative stress.