Plaut, Z., Besor Exp. Station, Southern R and D Network, M P 4, Negev 85400, Israel
Dayan, E., Inst. of Soils, Water and Environ. Sci., ARO, Bet-Dagan 50250, Israel
Grava, A., Inst. of Soils, Water and Environ. Sci., ARO, Bet-Dagan 50250, Israel
Matan, E., Besor Exp. Station, Southern R and D Network, M P 4, Negev 85400, Israel
Dori, I., Besor Exp. Station, Southern R and D Network, M P 4, Negev 85400, Israel
Presnov, Y., Besor Exp. Station, Southern R and D Network, M P 4, Negev 85400, Israel
Ben-Yunes, L., Besor Exp. Station, Southern R and D Network, M P 4, Negev 85400, Israel
Mujeira, Y., Ministry of Agriculture Israel, Israel
Pines, N., Ministry of Agriculture Israel, Israel

Water potential of rose flower leaves, stems and buds and leaves of bent stems were determined on plants grown in a greenhouse at different environmental control. A gradual decrease in organ water potential was found in the following order: flower bud, stem, leaf of the flower stem and leaf of bent stems. This change was not affected by greenhouse climatic conditions. There was no relationship between water potential of rose organs and number of picked flowers per unit area. The size of the flowering bud was, however, related to its water potential, lower water potentials of the bud resulted in larger buds. Striking results were obtained analyzing the pressure: volume curves, of flower buds. A significant increase in modulus of elasticity and a decrease in the relative volume of the cell symplast were found in roses grown under lowered night temperatures. Relative cell water content was lower and osmotic potential at zero turgor pressure was higher in flowering buds of rose plants grown under natural ventilation using no cooling or shading devices. The rate of photosynthesis and leaf conductance during summer was increased under evaporative cooling and was decreased under shading.