© 2002 Heron Publishing—Victoria, Canada
Ethylene metabolism in Scots pine (Pinus sylvestris) shoots during the year
Alla Klintborg (1), Leif Eklund (1, 3) and C. H. Anthony Little (2)
1. School of Biosciences and Process Technology, Växjö University, S-351 95 Växjö, Sweden / 2. Natural Resources Canada, Canadian Forest Service - Atlantic Forestry Centre, P.O. Box 4000, Fredericton, New Brunswick, E3B
5P7, Canada / 3. Author to whom correspondence should be addressed (leif.eklund@ibp.vxu.se) / Received October 31, 2000; accepted June 17, 2001; published online December 1, 2001
Summary
Ethylene evolution, concentrations of 1-aminocyclopropane-1-carboxylic acid (ACC) and ACC conjugates, activities of ACC synthase
and ACC oxidase, and cambial growth as measured by tracheid production were monitored from November to July in 1-year-old
shoots, and between July and September in current-year shoots, of Scots pine (Pinus sylvestris L.). Needles, buds and four stem parts (cortex, phloem, cambial region and mature xylem) were surveyed. Ethylene evolution
was quantified by gas chromatography. Free ACC and bound ACC (after acidic hydrolysis of ACC conjugates) were quantified by
combined gas chromatography–mass spectrometry, with [2H]ACC as an internal standard. Activities of ACC synthase and ACC oxidase were measured in crude protein extracts.
We detected high activities of ACC synthase in needles and buds, but not in stem fractions except the phloem. In July, during
the period of intensive shoot growth, we found ACC only in buds and needles. In contrast, ACC oxidase activity was high in
stem tissues, particularly in the cambial region during the period of rapid tracheid production, but no ACC oxidase activity
was detected in needles and buds. Nevertheless, needles evolved large amounts of ethylene. Ethylene was produced by all stem
fractions, and the peak rate of ethylene evolution in the cambial region coincided with the period of maximal tracheid production.
Conjugated ACC was present in every fraction except mature xylem. The concentration of conjugated ACC decreased when rates
of tracheid production and ethylene evolution were high, suggesting that conjugated ACC may serve as a source for ACC in the
cambial region. The regulation of ethylene biosynthesis in Scots pine shoots is discussed.
Keywords:
ACC, ACC conjugates, ACC oxidase, ACC synthase, cambial activity, tracheid production.
