Cuttings of Ficus benjamina L. and Chrysanthemum × morifolium(Dendranthema grandiflora tzvelev.) were rooted in aero-hydroponics to study the effect of dissolved oxygen concentrations in the range of 8 mg·liter. (ambient saturation) to 0 mg·liter−1. The results of this study indicate that dissolved oxygen is essential to root formation and root growth. Woody (Ficus) and herbaceous (Chrysanthemum) cuttings responded similarly. Lowering the dissolved oxygen concentration increased the time required to form adventitious roots, reduced rooting percentages, reduced numbers of roots formed per cutting, and reduced average root lengths. Comparisons between stirred and unstirred water suggested the development of an area of depleted oxygen concentration (boundary layer) at the stem-water interface on cuttings immersed in unstirred water. Cuttings in water stirred constantly rooted sooner and formed more roots than did those in unstirred water. Maximum rooting occurred in misted (high dissolved oxygen concentrations) sections of cuttings suspended in the aero-hydroponics chambers. Chemical name used: potassium salt of lH-indole-3-butyric acid (K-IBA).
A 60-fold increase in ethylene content was observed in stem cuttings of chrysanthemum (Chrysanthemum x morifolium Ramat.) held in aero-hydroponics under anoxic conditions during the 8 to 12 days necessary for adventitious root formation. Ethylene, 1-aminocyclopropane-1-carboxylic acid, and 1-(malonylamino) cyclopropane-1-carboxylic acid contents were highest in the immersed portion of the cuttings, but there was substantial ethylene produced by the anoxic, misted portions of the cutting above the liquid. Application of ethylene (10 microliters per liter) to chrysanthemum cuttings stimulated root development in cuttings held in high dissolved oxygen concentrations (8.0 milligrams per liter). Since the application of ethylene did not inhibit rooting in cuttings held at low dissolved oxygen concentrations (2.0 milligrams per liter), the inhibition of rooting under low oxygen concentrations is not mediated by the observed increase in endogenous ethylene content.The effectiveness of the aero-hydroponic system for propagation and production of plants has been attributed to the superior oxygenation of the medium achieved using this technique (13 the growth of roots is very sensitive to ethylene (6), being first stimulated, and then inhibited, as the concentration of ethylene in the medium increases. It has recently been shown that high concentrations of ACC inhibit root production (8). It could be that increased ethylene and ACC concentrations in hypoxic cuttings inhibit the formation of adventitious roots, thereby explaining the marked reduction of rooting under such conditions. We report here an examination of the role of ethylene in the inhibition of rooting by hypoxia. MATERIALS AND METHODSChrysanthemum x morifolium Ramat. cuttings of three cultivars, 'Bright Golden Anne,' 'Intrepid White,' and 'Intrepid Gold,' were harvested from mother plants maintained under 16-h photoperiods by supplemental incandescent lighting at the end of the day. Cuttings (20-25 cm long with 3-4 leaves) were harvested, dipped for 5 s in a 0.3% (w/v) solution of KIBA, and placed immediately in Ein Gedi system (EGS), aero-hydroponic, propagation units held in a growth chamber (24°C, 60-70% RH, 14-h photoperiod with photosynthetic photon flux [PPF] of 400 uE m-2-sec' from metal halide lamps). Rooting TechniqueCuttings were rooted in propagation units containing 10 L of deionized water. The water was continuously agitated, and the 8 L air space above the water was continuously misted (14). The cuttings were held so that the basal 5 cm were immersed in the water, the middle 5 cm were exposed to the mist, and the upper 5 cm were surrounded by the holder used to insert the cuttings in the propagation unit and thus unmisted. The remaining, leafy portion of the cuttings was exposed to the air in the growth chamber. Four concentrations of dissolved oxygen were established, each in two propagation units: 0 (anoxic), 2.5, 5.0, and about 8.0 mg.L-'. We define anoxic cuttings as those that have the basal portion of stem immersed in water with 0...
Hydroponic and aeroponic methods have been used to study the propagation and growth of plants (1, 2, 4). A combination of these two methods of liquid culture, aero-hydroponics, has been developed (3). Known as the Ein Gedi System (EGS), this aerohydroponics method incorporates the advantages (buffered nutrient capacity of hydroponics and water oxygenation of aeroponics) of both types of liquid culture. The objective of this study was to compare aero-hydroponics (EGS) and solid media for cutting propagation with and without overhead mist.
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