A History of Commercial Plant Growth Regulators in Apple Production

Abstract

DNA breakdown (Miller et al., 1955). Kinetin was significantly more active than adenine in the tobacco tissue culture bioassay. The use of the plant cell culture bioassay was a key to the eventual isolation of zeatin from corn by Letham (1963). ETHYLENE. The growth regulating properties of ethylene were first recognized by the Russian scientist Nejebulov in 1901 (Beyer et al., 1984). His experiments showed that illuminating gas could cause leaf abscission and epinasty. The fruit physiologist Crocker developed the Alaskan pea bioassay that used the triple response of shortening and thickening of the hypocotyl, agravitropic growth, and maintained hypocotyl hook (Reid and Howell, 1995) to assess ethylene levels. He was the first to suggest that ethylene was an endogenous plant hormone. However, few scientist at the time agreed with Crocker since it was difficult to visualize that a gas could act as an endogenous regulating substance. It was not until the 1960s when gas chromatography was used to quantify endogenous ethylene that the significance of ethylene was recognized and acknowledged as an endogenous hormone. ABSCISIC ACID.While researchers had long speculated that a hormone which affected abscission, dormancy, and stress reduction existed, it was not until the 1950s that work on the isolation and identification of this compound began. In 1953 Bennet-Clark and Kefford discovered an acid fraction of plant extracts that was a potent growth inhibitor. In 1955 Osborne reported on the diffusion of a senescence factor from older leaves that could speed the abscission of bean petioles. By 1963, Addicott s group studying cotton fruit abscission in California had identified and characterized abscisin II. At the same time, Wareing s group in Wales identified the dormin as a compound that promoted dormancy in woody plants. In 1968, these groups formally redesignated abscisin II and dormin as abscisic acid (Milborrow, 1984).