XVI International Botanical Congess

The Mehler-Absorbate-Peroxidase cycle (MAPC) is an enzymatic protection system against reactive oxygen species (ROS) occuring during over-excitation of the photosynthetic apparatus. In tomato Lycopersicon esculentum (LE), long-term chilling under moderate light leads to the oxidation of rubisco, presumably by generation of ROS. In contrast, high-altitude lines o the wild species L. peruvianum (LP) are tolerant against the same chilling stress. While antioxidant levels (absorbate, glutathione) and activities of chloroplast superoxide dismutase and absorbate Peroxidase, both inducible by chilling stress, were similar in both species, chilled LE showed lower glutathione reductase (GR) activities than LP. We constructed transgenic LE plants highly overexpressing an E. Coli GR in the chloroplast. However, these plants resembled identical chilling sensitivity a wild-type. We conclude that the MAPC is not he limiting factor for the sensitivity of the photosynthetic apparatus of LE towards long-term chilling under moderate light. We suggest that a possible cause for the higher chilling tolerance of LP is prevention of ROS formation by better conversion of light energy to photochemistry at suboptimal temperatures.