The modulation of the conversion of l-aminocyclopropane-l-carboxylic acid to ethylene by light

Abstract

Endogenous ethylene production of tobacco leaves was similar in light and in darkness. However, the rate of conversion of exogenously applied l-aminocyclopropane-l-carboxylic acid (ACC) to ethylene was reversibly inhibited by light. Virus-stimulated ethylene production, during the hypersensitive reaction of tobacco leaves to tobacco mosaic virus, was likewise inhibited by light. Under such circumstances ethylene production is limited at the level of the conversion of ACC to ethylene. Inhibition of the increase in ACC-stimulated ethylene production by cycloheximide and 2-(4-methyl-2,6-dinitroanilino)-N-methyl-propionamide after shifting leaf discs from light to darkness indicated that de novo protein synthsis was involved. Regulation of ACC-dependent ethylene production by reversible oxidation/reduction of essential SH groups, as suggested by Gepstein and Thimann (1980, Planta 149, 196-199) could be excluded. Instead, regulation of the ACC-converting enzyme at the level of both synthesis/degradation and activation/inactivation is suggested. Phytochrome was not involved in light inhibition, but low intensities of either red or blue light decreased the rate of ACC conversion. Dichlorophenyldimethylurea counteracted the inhibitory effect of light, indicating that (part of) the photosynthetic system is involved in the light inhibition. The ethylene production of Pharbitis cotyledons grown in darkness or light, either in the presence of absence of the inhibitor of carotenoid synthesis, SAN 9789 (norflurazon), supported this view.

Does Light Inhibit Ethylene Production in Leaves?

“…These findings are in accord with the results obtained by earlier workers (3,(6)(7)(8) (2,4), when measured in a continuous flow system. The problem is further compounded by possible differences in ACC deposition and uptake under different experimental conditions.…”

“…There have been a number of reports that suggest that white light inhibits ethylene production (3,(6)(7)(8)(9). This inhibitory effect of light was first reported by Gepstein and Thimann (6) in tobacco and oat leaf segments.…”

“…These workers used ACC2 in the incubation medium to increase the basal rate of ethylene production. De Laat et al (3) reported that endogenous ethylene production oftobacco leafdiscs was similar in light and darkness but the conversion of ACC to ethylene was reversibly inhibited by light. Grodzinski et al (7) have recently published a paper indicating that light inhibits ethylene production from Xanthium leaf discs both in the presence and absence of ACC, although the effect was much more pronounced in the presence of ACC.…”

The Effect of Light and Phytochrome on 1-Aminocyclopropane-1-Carboxylic Acid Metabolism in Etiolated Wheat Seedling Leaves

“…Depending on the tissues and conditions employed, light promoted (16,18) and inhibited (2)(3)(4)(5)(6)(7)(8)(9)(10)20) ethylene production. Since the plant tissues used in these earlier studies normally contained low level of endogenous ACC,3 the effects of light on the changes in ACC levels in relation to ethylene production were not examined.…”

Bicarbonate/CO2-Facilitated Conversion of 1-Amino-cyclopropane-1-carboxylic Acid to Ethylene in Model Systems and Intact Tissues

“…White light also affects ethylene production by leaf tissue, presumably through modulation of endogenous CO2 levels. For example, exposure of leaf tissue to white light has been found to inhibit ethylene production relative to controls maintained in darkness ( 11,14,15,18). Moreover, light inhibition of ethylene production can be overcome by the addition of NaHCO3 or CO2 (15,18).…”