Oxidative stress and senescence-like status in pear calli co-cultured on quince microcalli suspensions in an in vitro graft model system. Tree Physiology, 2010, 30: 450-458 (doi:10.1093/treephys/tpq006).

In this work we present a simple in vitro system to study physiological, biochemical and molecular changes occurring in a pear callus (Pyrus communis L., cv. Beurré Bosc) in relation to the presence of spatially separated undifferentiated homologous (pear) or heterologous (quince; Cydonia oblonga Mill., East Malling clone C) cells in its neighboring environment. After a 7-day co-culture period, the presence of heterologous cells produced negative effects on the pear callus, in which the relative weight increase and the adenylate energy charge decreased by 30% and 24%, respectively. Such a behavior was associated to a higher O2 consumption rate (+125%) which did not seem coupled to ATP synthesis. Analyses of alternative oxidase and enzymatic activities involved in reactive oxygen species (ROS) detoxification strongly suggested that the higher O2 consumption rate, measured in the pear callus grown in the heterologous combination, was probably ascribable to extra-respiratory activities which could contribute to generate metabolic scenarios where ROS-induced oxidative stresses may have the upper hand. The analysis of 2-thiobarbituric acid reactive metabolites, diagnostic indicators of ROS-induced lipid peroxidation, seemed to confirm this hypothesis. Moreover, RT-PCR analysis revealed that the expression levels of a few senescence associated genes resulted higher in the pear callus grown in the heterologous combination than in the homologous one. Taken as a whole, physiological and molecular data strongly suggest that undifferentiated cells belonging to a pear graft-incompatible quince clone may induce an early senescence-like status in a close co-cultured pear callus.