Biogenesis of ethylene

Ethylene-promoted adventitious rooting and development of cortical air spaces (aerenchyma) in roots may be adaptive responses to flooding in Zea mays L

The roots and stem base of intact, 10 day old maize (Zea mays L. cv. LG11) plants, grown in nutrient solution, were continuously aerated either with ethylene (5 μl l(-1)) in air or with air alone. Ethylene treatment hastened the emergence of adventitious (nodal) roots from the base of the shoot, but slowed their subsequent extension. Ethylene also promoted the collapse of cells in the cortex of these roots, with lysigenous development of prominent air spaces (aerenchyma). Non-aeration of the nutrient solution caused endogenously produced ethylene to accumulate in the roots, and stimulated both the emergence of adventitious roots and the formation of cortical air spaces in them. With non-aeration the concentration of oxygen did not fall below 1% in the equilibrium gas phase (air=20.8%). Complete deoxygenation of the nutrient solution, produced by passing oxygen-free nitrogen gas, prevented both air space formation and the evolution of ethylene by root segments.These results suggest that adventitious rooting and cortical air space formation in nodal roots in Zea mays may be stimulated by enhanced concentrations of endogenous ethylene arising either from entrapment of the gas by unstirred water layers around the roots and/or by increased biosynthesis. These responses are considered conducive to survival in waterlogged soil.

Studies of ethylene-forming system in rat liver extract

Evidence of enzymatic formation of ethylene from methionine by rat liver extracts is presented. The ethylene production is closely associated with growth of the animal. The conversion of L-methionine to ehtylene is oxygen dependent. Substrate analogue studies show that the ethylene-forming system is structurally specific and requires in the center of the molecule alpha-CH2-CH2- with one end attached to an unencumbered sulfur atom from a thioether moiety and the other end attached to a carboxyl group. Sylfhydryl agents are found to be very effective inhibitors of the ethylene-forming system. The finding of alpha-keto-4-methylthiobutyric acid to be a more efficient precursor of ethylene production suggests the possibility that alpha-keto-4-methylthiobutyric acid may be an intermediate in the biosynthesis of ethylene from methionine in mammalian tissues.

Investigations on the role of ethylene in phytochrome-mediated photomorphogenesis : I. Anthocyanin Synthesis

The etiolating, intact mustard (Sinapis alba L.) seedling exhibits a distinct temporal pattern of ethylene production. Light, operating through phytochrome, increases the rate of ethylene production without changing the pattern. Ethylene production of the isolated plant parts (segments), added together, exceed the production of the intact system even if the wound effect is taken into account. There is no significant light effect on ethylene production of the segments. Phytochrome-mediated anthocyanin synthesis in the cotyledons is inhibited by ethylene. The responsiveness towards ethylene of the anthocyanin producing metabolic chain is decreased by phytochrome. As anthocyanin synthesis is only partly inhibited under saturating ethylene concentrations in the atmosphere around the seedlings (100 μl l(-1)), a twofactor analysis becomes feasible. This analysis leads to the result that phytochrome and ethylene show multiplicative behavior, meaning that phytochrome and ethylene act on the same metabolic sequence (leading to anthocyanin) but independently of each other, and at different sites. Therefore, the hypothesis that ethylene mediates the action of phytochrome in anthocyanin synthesis and photomorphogenesis in general appears to be inapplicable.

The stimulation of cell extension by ethylene and auxin in aquatic plants

Elongation of the shoots of three aquatic plants (Hydrocharis morsus-ranae, Regnellidium diphyllum and Ranunculus sceleratus) is stimulated by treatment with ethylene or IAA. The effects of the two hormones are additive, and experiments with an ethylene biosynthesis inhibitor and silver ions indicate that the mechanisms by which ethylene and IAA stimulate growth may be different. Hydrocharis and Ranunculus leaf discs synthesize [(14)C]ethylene from [(14)C]methionine, but no [(14)C]ethylene is formed by Regnellidium, suggesting the existence of an alternative pathway of ethylene biosynthesis in the fern.

Production of ethylene by excised segments of plant tissue prior to the effect of wounding

A delay of 20 to 30 min precedes a rapid increase in the production of ethylene when segments are excised from the petioles of tomato plants. Measurements made during this early phase may be better estimates of production by petioles on the intact plant than those made at later times.

Ethane evolution: a new index of lipid peroxidation

Homogenates of mouse liver and brain at 37 degrees C spontaneously formed lipid peroxides and simultaneously evolved ethane. alpha-Tocopherol, a lipid antioxidant, blocked ethane formation. When mice were injected with carbon tetrachloride (a liquid prooxidant for liver), the animals produced ethane. Ethane evolution in vivo was stimulated by prior administration of phenobarbital and it was diminished by prior injection of alpha-tocopherol. These data suggest that ethane production may be a useful index of lipid peroxidation in tissue homogenates and in intact animals.