Ozone effects on carbon metabolism in sensitive and insensitive Phaseolus cultivars

An ozone treatment of 165 nL L−1 for 3 h evoked differential responses in the primary leaves of two bean cultivars of the common bean (Phaseolus vulgaris L.). While cv ‘Cannellino’ showed visible symptoms of injury within 24 h of exposure, no visible symptoms at all were evident in the cv ‘Top Crop’. In primary leaves of the sensitive cultivar Cannellino, we observed an increase in carbon breakdown (an increase in PFK and Fumarase) and a reduction in CO2 photoassimilation, linked also to the diminished synthesis of sucrose (a decrease in SPS activity) and to the stimulation of the degradation of this sugar (an increase in SuSy and Invertase activities). A strong stimulation of PEPcase activity indicates both an increased synthesis of OAA and an enhanced replenishment of the tricarboxylic acid cycle. Finally, in Cannellino leaves the activity of NADP-malic enzyme increased indicating a stimulation of enzymes delivering NADPH. The findings of this research suggest that the visible symptoms in Cannellino represent an active response that this cultivar initiates to cope with excess oxidative load. The pattern in Top Crop was different. This cultivar did not show visible symptoms of injury, nor any responsive changes at the physiological and biochemical levels. Oxidative pathways are partially enhanced, e.g., increases in Invertase, PFK and IDH. There were also increases in some enzyme linked to the production of cytosolic NADPH as G6PD, probably caused by the slight increase in activity of the enzymes SKDH and PAL involved in synthesis of phenolic compounds. However, the absence of visible injury in Top Crop leaves is confirmation that, in this cultivar, the need to produce carbon skeleton and NADPH used in detoxification and repair process is lower.