Effects of vase solution pH and abscisic acid on the longevity of cut 'Baccara' roses

Abscisic acid (ABA) supplied in the vase solution can induce stomatal closure in the leaves of cut flowers, including roses (Rosa hybrida L.). This effect may be beneficial in reducing water deficit stress. Extracellular pH can affect active ABA concentrations in the apoplast of guard cells, with sap alkalisation enhancing the physiological activity of ABA. Accordingly, it was hypothesized that vase solution pH may affect ABA-mediated stomatal closure of cut roses. Two experiments were conducted to study the interaction of vase solution pH and ABA. In the first, cut 'Baccara' roses were held in vase solutions with +/- 10(-5) M ABA at pH 6, pH 7 and pH 8. In the second experiment, roses were held with +/- 10(-5) M ABA at pH 6 and pH 8 in the presence and absence of 1 mg l(-1) AgNO3 as a bactericide. Supply of ABA increased vase life and reduced vase solution usage of flowers held in low pH 6 solutions, indicating induction of stomatal closure. Conversely, ABA supplied at pH 8 was associated with reduced vase life. This negative result was associated with enhanced development of vase solution microbes at high pH, which overrode any potential pH-mediated ABA efficacy effects.