Hideo Imanishi

Effects of gaseous compounds in smoke on dormancy release in freesia corms

Abstract Exposing corms to smoke generated from smouldering plant materials (“smoke treatment”) releases freesia corms from dormancy. The smoke was found to contain some hydrocarbons, i.e. ethane, ethylene, (C2H4), and propylene at concentrations below 130 μl 1−1, and carbon monoxide (CO) at 2000-400 μl 1−1. Exogenous C2H4 at low levels of 100-1 μl/litre air strongly stimulated dormancy-release. In contrast, propylene and acetylene were required at a concentration much higher than that in the smoke to exert the dormancy-releasing effect: the application of 100 μl/litre air had little or no effect. Air containing 1000 μ l CO litre air produced some effect, which could be masked by co-existence of 10 μ l C 2 H 4 litre air. Acetaldehyde, which may occasionally be present in smoke, showed the dormancy release at ca. 1 mM but was phytotoxic. Corms exposed to smoke or C2H4 did not show an endogenous C2H4 rise, while non-treated corms showed it distinctly before dormancy release. These results suggest that a C2H4-stimulus is dominant in smoke treatment.

Effects of exposing freesia corms to ethylene or to smoke on dormancy-breaking and flowering

Abstract Ethylene (C2H4), applied at an early stage of the high-temperature treatment for dormancy breaking, promoted sprouting. Five μl l−1 of C2H4, applied during 2 days, replaced 2 weeks of high temperatures. The promotive effect of C2H4 diminished with increasing exposure period and no difference was found between the effects of 5 and 50 μl l−1. The promotive effect of exposing corms to smoke was slightly lower than that of C2H4. Neither had an adverse effect on flowering and both resulted in shorter leaf length and rigid growth, which could be useful for solving the problems of leafiness during winter.

Effects of duration of exposure to ethylene on dormancy release in freesia corms

Abstract The exposure of freesia corms to ethylene (C2H4) at ca. 10 μl/l air for only 5 h was sufficient to promote sprouting, either under a closed system in which corms were treated in a sealed space of 3–10 1 or under a flow system in which corms were exposed to a continuous flow of air containing C2H4. Under the closed system, little change in corm response to C2H4 was found with increasing duration of exposure from 5 to 48 h, and the C02 concentration reached nearly 4% after 48 h. On the other hand, under the flow system, in which CO2 did not accumulate above 0.1%, the promotive effect of C2H4 was diminished by extended exposure from 5 to 48 h. Repeated treatment with C2H4 for 23 h daily on 4 successive days resulted in the lowering of the promotive effect as compared with a single treatment, but repeated application of C2H4 for 5 h daily showed the same effect as a single application and gave a high sprouting rate similar to smoke treatment, independent of ambient temperature ranging from 25 to 35° C. Corms exposed to C2H4 for 5 h daily, or to smoke for 4 days, exhibited a better chilling response and advanced flowering.

Respiratory and carbohydrate changes during ethylene-mediated flower induction in Dutch iris

Abstract The promotion of flowering in small Dutch iris (Iris × hollandica Hoog., cv. ‘Ideal’) bulbs by treatment for 24 h with 10 μl l−1 ethylene was associated with enhanced respiration, which continued long after the end of ethylene treatment. Shorter ethylene treatments, which were partially effective in inducing flowering, resulted in lower and shorter bursts of respiration. Changes in the soluble carbohydrate contents of the ethylene-treated bulbs were not detected until following the cold treatment. The possible mechanisms by which ethylene stimulates flowering are discussed.

Influence of storage temperature and its duration before or after ethylene exposure on the formation of flower buds in Dutch iris cultivar ‘Blue Magic’

Abstract Exposing bulbs of Dutch iris ‘Blue Magic’ to ethylene (C 2 H 4 ) immediately before subjecting them to precooling (9°C for 9 weeks) resulted in a high percentage of flower bud formation. If bulbs exposed to C 2 H 4 were stored at 15, 20 or 25°C for more than 8 weeks and at 30°C for more than 16 weeks before precooling them, the promotive effect of C 2 H 4 was gradually lost. The C 2 H 4 response could be restored by exposing the stored bulbs to C 2 H 4 . Bulbs stored at 15,20 or 30°C before exposure to C 2 H 4 showed a high percentage of flower bud formation, but those stored at 10°C did not form flower buds even after C 2 H 4 exposure. Among the storage temperatures, 30°C was the most effective. To optimize flowering of Dutch iris cultivar ‘Blue Magic’, especially when using small bulbs, bulbs should be stored at 30°C, exposed to C 2 H 4 and then precooled as soon as possible.

Changes in abscisic acid levels during dormancy release in freesia corms

A high level of free-abscisic acid (ABA) was detected when corms were still in deep dormancy. The level of free-ABA decreased as the corm dormancy disappeared and increased temporarily after complete release from dormancy. A gradual slight increase of bound-ABA was observed during dormancy release.Treatment of dormant corms with benzyladenine (BA) increased sprouting but the sprouts did not show normal growth. Ethylene treatment induced complete sprouting and subsequent normal growth. Changes in ABA levels and ethylene production are discussed in relation to dormancy release in freesia corms.