Differential Protein Expression in Olive Tissues Due to Salt Treatments

In this work, differential protein expression in olive tissues after salt treatments has been investigated. Olive clones selected in vitro according to their salt tolerance were submitted, also in vitro, to high salt concentrations. After each treatment, the leaves and stems were collected and protein extracts of them subjected to polyacrilamide gel electrophoresis to analyse their band patterns. Some differences were observed referring to 2 bands of approximately 24 kD and 40 kD which appeared in the extracts after exposition to salt. It is discussed the possible implication of this polypeptide in the response of olive tree to salt stress and similarities with other proteins described in other plant species. INTRODUCTION Salt stress is a major concern in the fruit tree industry. Although olive could be considered as relatively tolerant to soil salinity, a sustanaible oliviculture would require more tolerant varieties which could, for example, be irrigated with saline waters. For the selection of these new varieties or to test the salt tolerance of other already known varieties, it would be of great help to find specific markers associated to salt stress which could assist the selection process. Such markers would enable the acceleration and increased reliability of selection for resistance among cultivars in breeding programmes. Furthermore, these markers could be instrumental in identifying relevant genes, thus helping in the efforts of introducing stress resistant by gene transfer. Up to date work on markers for different physiological situations in the olive tree has been scarce. Differential protein expression was reported for juvenile and mature olive tissues (García et al., 2000; García et al., 2002). In relation to stress resistance, Bartolini et al. (1994) found different protein patterns between tolerant and non tolerant clones of cv. Leccino when submitted to cold stress. In this work we have compared the electrophoretic protein patterns of two different clones of cv Jabaluna after cultured in vitro with different concentrations of NaCl in seeking differential protein expression due to the salt treatments. MATERIAL AND METHODS Two clones of olive cv Jabaluna were used as plant material. These 2 clones (J0 and J79) were obtained by in vitro germination of isolated embryos as described elsewhere (Acebedo et al., 1997). Clone J0 was obtained from an embryo germinated in normal medium without salt while clone J79 was obtained from an embryo grown on 120 mM of NaCl, then this was considered as tolerant. After germination, the plantlets selected were subcultured to attain enough plant material of each clone. To check the tolerance to salt of both clones, explants from them were cultivated for 7 weeks on medium OM + 15 g.l of mannitol and 1 g.l zeatine as base medium and 3 different treatments: control (no salt added), 50 mM, and 90 mM of NaCl. Single node explants of