STRESS RESPONSES OF TOMATO FRUIT TISSUE SUBMITTED TO MASSIVE DOSES OFIONIZING-RADIATION

In plant tissue, massive doses of ionising radiation (0.5-3 kGy) induc e an oxidative burst due to the overproduction of oxygen-centred free radicals. Changes in the protein metabolism of cherry tomato fruits we re investigated in response to this peculiar stress. Although DNA dama ge definitively arrested cell division, the changes observed on a shor t-term basis were attributed to genetic regulation. Changes in protein metabolism were also maintained long term. Gamma-induced proteins (GI Ps) were classified according to their induction kinetics. Group 1 pro teins were induced immediately after the treatment and their synthesis was stopped within 24 h. During the same time period, global protein synthesis was restored and a new set of GIPs was induced. The function of these proteins is not yet known; but they may be involved in physi ological disorders triggered by irradiation or in repair processes. Sh ort-term typical changes involve the synthesis of ACC synthase - the e thylene pathway regulating enzyme - and most probably of some LMW-HSPs . A non-relevant response to irradiation has also been discovered, nam ely the long-term accumulation of chitinases. Irradiation induces both specific and non-specific responses which can be analysed by comparis on with other types of oxidative stress and some GIPs seem to be speci fic to the treatment. The ability of irradiation to induce such differ ent responses might be profitably applied for a better understanding o f the oxidative mechanisms involved in signal transduction during envi ronmental stress situations.