Water relations and abscissic acid content in tomato as affected by osmotic stress

We investigated the effects of increasing EC of the nutrient solution on water status and ABA levels of tomato grown in hydroponics. Plants were grown in a greenhouse in pots filled with aerated nutrient solution replaced every week. Two weeks after transplanting the plants were divided into 8 treatments which were fertigated with nutrient solution containing NaCl and CaCl2 (2:1 molar ratio) to reach 2.5 (control), 4.2, 6.0, 7.8, 9.6, 11.4, 13.2 and 15.0 dS m(-1) respectively. At 54 days after transplanting, stomatal conductance, leaf water potentials and relative water content of leaves were measured at dawn, at midday, in the afternoon and at sunset. At the end of the measurement day, plant samples were collected for measuring leaf area. and dry mass yield. ABA measurements were performed in leaves by enzyme immunoassays. Salinity caused a reduction of leaf area development, which turned out to be correlated to a decrease of shoot dry matter accumulation. Photosynthates possibly underwent to a functional redistribution within different organs to optimise adaptation and growth in saline environment. Consistent with this assumption, we found an increased root/shoot ratio in salinized tomato plants. Due to increasing osmotic adjustment leaf turgor potential increased with the EC of the nutrient solution. We observed a salt-induced increase of the free ABA in tomato leaves that was associated with reduced stomatal conductance, suggesting that under osmotic stress conditions, the ABA acts as a stress messenger from the roots to the shoots.