The differential effectiveness of two synthetic Auxins in delaying floret abscission in red cestrum cut flowers depends on their transport and metabolism.

ABSTRACT Floret abscission in Red Cestrum ( Cestrum elegans Schlecht) cut flower shoots was significantly delayed by a pulse treatment of 2,4-dichlorophenoxyacetic acid (2,4-D) while 1-naphthaleneacetic acid (NAA) was less effective. This phenomenon is attributed to the findings showing that significant amount of 2,4-D moved acropetally and accumulated in florets, leaves, and upper parts of the stem, while NAA remained in the lower parts of the stem. In addition, a significant amount of the accumulated 2,4-D remained in the active free form for a relatively longer period of time during vase life, while NAA was quickly metabolized. 2,4-D induced higher rates of ethylene evolution and increased expression levels of Aux/IAA homologous genes, cloned from the floret abscission zone, compared to those observed in response to NAA. This suggests that ethylene evolution and expression of Aux/IAA homologous genes may serve as markers for the activity of these two synthetic auxins. INTRODUCTION It is well accepted that both the natural auxin, indole-3-acetic acid (IAA), and the synthetic auxins exhibit polar transport (Lomax et al., 1995). This is also true for the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D), which has transport characteristics similar to those of IAA, except for a slower transport rate (McCready, 1963; McCready and Jacobs, 1963). When 2,4-D was combined with silver thiosulfate (STS) for pulsing ‘Red Cestrum’ (