Factors affecting the water relations of cut roses placed in different vapor pressures

'Bridal Pink' roses (Rosa hybrida L.), with their cut stems in deionized wa ter, were held at 20 degrees C in a glass tank in which the vapor pressure was maintained at 2.3 kPa thigh vapor pressure: HVP) or 1.4 kPa (intermedia te vapor pressure: IVP). Large, heavy cut roses with high initial water pot entials retained water longer in HVP than in IVP. Transpiration and water u ptake rates of cut roses placed in HVP were markedly lower than those in IV P. Transpiration and water uptake rates of individual organs, and defoliate d, disbudded, and intact cut roses revealed that water losses from leaves a nd/or flower buds were closely correlated to water uptake by intact cut ros es. The low water potential of flower buds, which occurred earlier and seve rer in IVP than in HVP, is attributed to: 1) the initial increase in petal volume; 2) the following decrease in water uptake capacity of leaves and fl ower buds, and 3) competition for water between leaves and a flower bud.