EFFECTS OF ANAEROBIOSIS ON ETHYLENE PRODUCTION, RESPIRATION AND FLOWERING IN IRIS BULBS

Ethylene production of iris bulbs (Iris hollandica cv. Ideal) was very low. When stored at 30-degrees-C, production was 12-20 pmol C2H4 (kg fresh weight)-1 h-1. Higher temperatures (35-degrees-C, 40-degrees-C) enhanced the ethylene production; a treatment with 40-degrees-C for ca 7 days caused a 3 times higher ethylene production than at 30-degrees-C. During anaerobic storage (in 100% N2) ethylene production was equal to that of control bulbs. When after a 7 day period of anaerobiosis the N2 was replaced by air, a burstlike ethylene production was observed. Twenty-four h after the replacement, ethylene production was equal to control values again. The effects of this production of ethylene on mitochondrial respiration and flowering were investigated. When mitochondria were isolated immediately after the anaerobic treatment (before the enhanced ethylene production) alternative pathway capacity was not detectable, a situation also occurring in control bulbs. When mitochondria were isolated 24 h after the end of the anaerobiosis (after the ethylene burst) uninhibited respiration did not change significantly, but a capacity of the alternative pathway was observed. The increase in alternative pathway capacity after anaerobiosis was partly inhibited by 2,5-norbornadiene (NBD), an ethylene antagonist. Fermentation occurred during anaerobiosis: ethanol concentrations increased during the treatment and decreased when air was supplied. When bulbs were exposed to ethanol vapour the alternative pathway was induced but only when very high ethanol levels in the bulbs were reached. The amount of ethanol accumulated in the bulbs during a 7 day anaerobic treatment was far too low to explain the observed induction of alternative pathway capacity. Flowering percentages were enhanced after a 24 h treatment with ethylene and after a 7 day anaerobic treatment. NBD significantly inhibited the effect of exogenous ethylene and of anaerobiosis on flowering. Ethanol was not able to induce flowering. The burst-like production of ethylene after anaerobiosis probably is responsible for the effects on respiration and flowering.