POST-POLLINATION PHENOMENA IN ORCHID FLOWERS. IV. EFFECTS OF ETHYLENE

Treatment of Cymbidium (Orchidaceae) flowers with 10,ul/liter ethylene for up to 78 hr induces anthocyanin formation in both gynostemia (columns) and labella (lips). After that, pigment levels decrease. During 24-hr exposures, ethylene concentrations of 0.1, 1, and 10,ul/ liter cause increased anthocyanin levels in both lips and columns. Ethylene also brings about color changes in the calli and wilting of the perianth, but it does not cause straightening of gynostemia and stigmatic closure. Emasculation effects are similar to those of ethylene, whereas pollination and NAA induce anthocyanin formation and closing of stigmas, as well as swelling and loss of curvature in gynostemia. The effects of ethylene are correlated with its action in other systems. ETHYLENE CAUSES certain post-pollination phenomena in orchid blossoms including anthocyanin formation, fading, shortened flower life, and wilting of sepal tips known as "dry-sepal" injury (Crocker, Zimmerman, and Hitchcock, 1932; Lindner, 1946; Davidson, 1949; Fischer, 1950; Akamine and Sakamoto, 1951; Jester, 1952; Saylor, 1954; Kendrick et al., 1956; Middleton et al., 1956; Anonymous, 1960; Akamine, 1963; Burg and Dijkman, 1967; Clayton and Platt, 1967; Dijkman and Burg, 1970; Hindawi, 1970). Pollination, emasculation, and auxin treatments can all cause ethylene evolution which, at least in Vanda, is autocatalytic (Akamine, 1963; Burg and Dijkman, 1967; Dijkman and Burg, 1970). This is particularly noticeable during shipment of flowers in closed containers, where damage such as simple dislodgement of pollinia, can induce ethylene evolution from a single flower (Akamine and Sakamoto, 1951). When this happens, a blossom may evolve enough ethylene to cause either direct damage or bring about production by 1 Received for publication 11 January 1973. Supported in part by grants from the American Orchid Society Fund for Research and Education, the National Science Foundation (GB-13417), and the Orchid Digest Corporation Research Fund; as well as Office of Naval Research Contract, NR 1008-796 (to J. A.) and an NSF undergraduate summer research award (to N. M. H.) We thank Mrs. Samuel Mosher and Mr. Robert I. Norton, Dos Pueblos Orchid Co., Goleta, California for donating the flowers; Mr. C. L. Knowles, Acme Glass and Vial Co., for a gift of orchid tubes and caps; Drs. Fred B. Abeles and Stanley P. Burg for reading and commenting on the manuscript, and Ms B. Flick for technical assistance. 2 See Arditti and Knauft, 1969, for part I; Arditti, Flick, and Jeffrey, 1971, for part II; and Arditti, Jeffrey, and Flick, 1971,-for part 111. other flowers. Eventually enough ethylene may accumulate in a box to damage all blossoms. Since auxins induce ethylene formation in a number of systems, including orchids (Burg and Dijkman, 1967), some of their effects have been attributed to the gas. The same is true regarding several post-pollination phenomena in orchid flowers (Burg and Dijkman, 1967; Arditti, 1969, 1971a, b; Arditti and Knauft, 1969; Dijkman and Burg, 1970; Knauft, Arditti, and Flick, 1970; Arditti, Flick, and Jeffrey, 1971; Arditti, Jeffrey, and Flick, 1971). In addition, both abscisic acid (ABA) and gibberellin (GA) have been suggested to initiate ethylene evolution (Addicott and Lyon, 1969; Pratt and Goeschl, 1969). Therefore, their effects on orchid flowers could be due, at least in part, to ethylene evolution they may induce. Thus, to understand the causes of postpollination phenomena in Cymbidium flowers better, it was necessary to determine the exact effects of ethylene itself. MATERIALS AND METHODS-Flowers of Cymbidium 'Samarkand' (Dos Pueblos Orchid Co., Goleta, California) were selected for uniformity and freshness. Ovaries and pedicels were surface sterilized by a 5-minute immersion in saturated calcium hypochlorite (Wilson, 1915)-a treatment previously shown to have no deleterious effects. The flowers were then inserted into rubbercapped tubes (Acme Glass and Vial Co., Los Angeles, CA.) containing a modified Knudson C medium (Knudson, 1946; Ito, 1961; Arditti and Knauft, 1969). Culture vessels and media were sterilized by autoclaving several days before they were used to allow for dissipation of any ethylene