INFLUENCE OF NITROGEN SUPPLY ON OSMOREGULATION IN TOMATO (LYCOPERSICON-ESCULENTUM MILL) PLANTS UNDER MODERATE WATER-STRESS

The influence of three levels of nitrogen fertilization on the osmotic adjustment of tomato plants (Lycopersicon esculentum Mill.) grown in individual pots on a sandy soil and subjected to water deficit was est ablished. The plants were maintained at soil field capacity by daily t rickle watering until the start of stress. In each irrigation 100 ml o f Hoagland's solution (NO treatment), Hoagland's solution plus 60 mM N O3- (N1 treatment) or Hoagland's solution plus 110 mM NO3- (N2 treatme nt) were added through the emitters. After withholding water for 3 day s, the percentage of leaf osmotic adjustment (% of the diminution of a ctual leaf osmotic potential refers to the value at the well-watered s tate) was 44% for NO plants, 63% for N1 and 29% for N2 plants. After 8 days of withholding water these percentages were similar. After withh olding water for 3 days, some plants were irrigated daily. At the end of this period of stress relief(8 days of watering), leaf osmotic pote ntial was lower (-1.86 MPa) and the osmotically adjusted state persist ed (39%) in N1, which was associated with the maintenance of turgor du ring decreasing water potential conditions. This demonstrated the poss ibility of a synergistic effect of the N1 dose in increasing avoidance and tolerance of dehydration in tomato plants.