Fred B. Abeles

Ethylene: An Urban Air Pollutant

Ethylene is an unusual air pollutant in that it is a plant hormone. Motor vehicle exhaust is a primary source. In the Washington, D. C, area, ethylene concentrations ranged from 700 ppb in the city center to 39 ppb in areas outside the circumferential beltway. Plants grown in these concentrations of ethylene, using controlled environment chambers, exhibited typical symptoms of ethylene toxicity: reduced growth, premature senescence, and reduced flowering and fruit production. When plants were grown in carbon-filtered ambient air, which was also filtered through KMnO4 to remove ethylene by oxidation, growth, flowering, and fruit production increased. These observations demonstrate that ethylene air pollution is a continual source of stress for plant growth and development in an urban environment.

Isolation and sequencing of cDNA clones encoding ethylene-induced putative peroxidases from cucumber cotyledons.

A cDNA library from ethephon-treated cucumber cotyledons (Cucumis sativus L. cv. Poinsett 76) was constructed. Two cDNA clones encoding putative peroxidases were isolated by means of a synthetic probe based on a partial amino acid sequence of a 33 kDa cationic peroxidase that had been previously shown to be induced by ethylene. DNA sequencing indicates that the two clones were derived from two closely related RNA species that are related to published plant peroxidase sequences. Southern analysis indicates that there are 1–5 copies in a haploid genome of a gene homologous to the cDNA clones. The deduced amino acid sequences are homologous with a tobacco (55% sequence identity), a horseradish (53%), a turnip (45%), and a potato (41%) peroxidase. The cloned sequences do not encode the 33 kDa peroxidase from which the original synthetic probe was been derived, but rather other putative peroxidases. An increase in the level of mRNA is evident by 3 hours after ethephon or ethylene treatment and plateaus by 15 hours.

Cellulase activity in developing apple fruits

Abstract Changes in cellulase, polygalacturonase and total protein were measured during the growth and ripening of three apple cultivars (Malus sylvestris Mill ‘Stark Lodi’, ‘Paulared’ and ‘Golden Delicious’) with the view of establishing the role of these cell wall-degrading enzymes in fruit development. In agreement with earlier work, no endo-polygalacturonase activity was evident at any stage of apple development. Cellulase was present in young expanding fruit and decreased in activity as the fruit reached full size and ripened. Separation of cellulase on MonoQ columns indicated the presence of three isoforms, two of which had molecular weights of 67 kDa. Electrophoresis of proteins from developing fruit indicated that proteins with molecular weights of 24, 26 and 67 kDa increased during ripening. Unlike other climacteric fruit, ripening in apples was not associated with an increase in extractable cellulase or polygalacturonase. The sodium dodecylsulfate-polyacrylamide gel electrophoresis studies suggest that a 67 kDa protein increased during ripening. The decrease in enzyme activity may be due to the inability of available extraction techniques to release this enzyme from apple cell walls.

Role of peroxidase during ethylene-induced chlorophyll breakdown inCucumis sativus cotyledons

Yellowing is a visible result of ethylene-enhanced senescence. In certain plants, such asCucumis sativus, an increase in peroxidase levels occurs during this period. Experiments described here were designed to test the hypothesis that peroxidase levels induced during senescence play a role in chloroplast degradation. Inhibitors of heme synthesis and protein glycosylation, which had no effect on chlorophyll degradation, reduced the synthesis of pI 9 peroxidase. Decapitation of seedlings, which enhanced greening of cotyledons, increased levels of peroxidase. These observations are consistent with the view that while the role of aging- or ethylene-induced peroxidases are not known, they are not involved in chlorophyll degradation.

A comparative study of ethylene oxidation inVicia faba andMycobacterium paraffinicum

Vicia faba L. ‘Herz Freya’ (fababean) cotyledons andMycobacterium paraffinicum Bardane strain (MPB) cells were studied to describe and compare physiological and biochemical factors regulating ethylene oxidation. Both organisms demonstrated a linear rate of ethylene uptake as a function of concentration from 1 ppm to 1,000 ppm. CO2 did not influence ethylene oxidation by either organism. Zero degree temperatures and CO inhibited ethylene oxidation by fababeans but not by MPB.An N2 gas phase blocked ethylene consumption by fababeans. In contrast, MPB continued to consume ethylene at a reduced rate under anaerobic conditions. Hydrocarbon oxidation was limited to alkenes. Alkanes were not oxidized by either organism. Both organisms were sensitive to diethyldithiocarbamic acid, o-phenanthroline, carbonyl cyanidem-chlorophenyl hydrazone, and CS2. The possibility that CS2 acted as a suicide substrate is discussed. Evidence is presented that hydrocarbon gas oxidation by fababeans is not a part of, or reflection of, the way ethylene acts as a hormone.