Ethylene air pollution: effects of ambient levels of ethylene on the glucanase content of bean leaves.

Abstract

We reported earlier that ethylene increased the levels of glucanase (endo-/3-1, 3-glucan-3-glucanohydrolase, EC 3 .2. 1 .6) in bean (Phaseolus vulgaris L. cv. Red Kidney) leaves (1, 2) at Frederick, Maryland. While the function for glucanase has not been firmly established, a number of roles have been proposed and include digestion of storage glucans in seeds, control of cell elongation, regulation of pollen tube growth, yeast cell expansion, fertilization, removal of phloem callose, and an antibiotic role of attacking the cell walls of invading fungi and bacteria (1, 2). When we attempted to repeat the experiment in Beltsville, Maryland, we found the addition of ethylene failed to increase enzyme activity (see Table I). Though care was taken to use similar extraction and assay procedures, we observed considerable variation between the base levels of glucanase from one experiment to another. The reasons for these fluctuations are unknown at this time. We examined but rejected differences in cultural practices and seed stock as explanations for the inability of ethylene to increase glucanase activity and turned our attention to the possibility that the air at Beltsxille contained sufficient levels of ethylene to cause the observed effects. Ethylene levels at Frederick vary in amounts not measurable by gas chromatography (less than 1 nl/l, which is equal to 1.2 ,tg/m') to 5 nl/l. The Plant Industry Station at Beltsville is located on Route 1 and a few hundred feet north of the exit to the Washington, D.C., Beltway. Levels there vary from undetectable, on windy or rainy days, to 40 nl/l during the morning rush hour on calm days. Average values during the day are between 10 and 20 nl/l. Since glucanase induction is ethylene-sensitive, we examined the possibility that growing plants in chronic low levels of ethylene disrupted the ability of additional quantities of ethylene to induce glucanase activity. Bean plants were grown in 0.6 m' plastic chambers located in a greenhouse equipped with carbon filters to remove ozone. The 2-liter per min air supply for the chambers was passed through a 6X 30-cm column of KMnO4 absorbed on alumina pellets (Purafil, Marbon Division, Borg Warner, Washington, W. Va. 26181)1. The data in Table II show that there was less glucanase in plants grown in KMnO,-filtered air com-

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