THE RELATIONSHIP OF ETHYLENE TO SENESCENCE
With Hibiscus Rosa-sinensis abscission zone explants, ethylene and abscisic acid (ABA) levels were found to be related. Ethylene production increased with time both prior to and during abscission and usually reached a peak after abscission was completed. Free ABA was greater than the bound ABA prior to flower anthesis. In the acropetal section of the abscission zone, free ABA increased from petal abscission to a peak at calyx abscission.
In an attempt to examine endogenous biosynthesis of ethylene a pathogenic bacterium (Pseudomonas solanacearum No.25) was used. Twenty other bacteria species were investigated to show their possible contribution to ethylene - induced senescence of diseased plants.
The discovery that ethylene gas acted as a growth regulator and altered plant growth and development can be traced to Girardin (1864) when he reported that illuminating gas from broken gas mains in German cities defoliated street trees. However, Neljubov (1901) showed that ethylene was the active compound in illuminating gas. This Russian worker was perhaps the first to aid in the later development of the pea seedling bioassay for ethylene detection, as he noted that germinating pea seedlings grew horizontally when exposed to illuminating gas and he systematically eliminated the various constituents of illuminating gas and stated that ethylene was the most active at only 0.06 ppm which caused horizontal growth (Neljubov, 1913). Knight et al., (1910) described the triple etiolated seedling pea response of inhibited elongation, with subsequent swelling and horizontal growth (Knight et al., 1910). These observations lead the pea to be used as a diagnostic tool for ethylene detection. Crocker and Knight between 1908–1913, (Krocker and Knight, 1908; Knight and Crocker, 1913) and Harvey (1915) confirmed Neljubov's work and in addition stated that ethylene