PLANT PHYSIOLOGY , Vol 111, Issue 2 569-576, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Differential Expression of Lipoxygenase Isoenzymes in Embryos of Germinating Barley
W. L. Holtman, G. van Duijn, NJA. Sedee and A. C. Douma
Center for Phytotechnology, Leiden University-Netherlands Organization for Applied Scientific Research, Department of Plant Biotechnology, Netherlands Organization for Applied Scientific Research, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands
Expression of lipoxygenase was studied in barley (Hordeum distichum L.)
embryos during germination. Total lipoxygenase activity was high in
quiescent grains, dropped during the 1st d of germination, and subsequently
increased to a level similar to that in quiescent grains. The contribution
of two isoenzymes, lipoxygenases 1 (LOX-1) and 2 (LOX-2), was studied at
the activity, protein, and mRNA levels. Activity ratios of the two isoforms
were determined via the ratio of 9- and 13-hydroperoxides, which are formed
from linoleic acid. Isoenzyme protein levels were determined using specific
monoclonal antibodies. mRNA levels were studied using the specific cDNA
probes LoxA and LoxC, which correspond to LOX-1 and LOX-2, respectively.
The major difference in temporal expression of LOX-1 and LOX-2 was observed
in quiescent grains. At this stage, LOX-1 contributed almost exclusively to
total lipoxygenase activity. LOX-2 activity rapidly increased until d 2 of
germination. From this time point onward, LOX-1 and LOX-2 showed similar
patterns at both activity and protein levels. The tissue distribution of
the two isoenzymes in the germinating embryo was closely similar, with the
highest expression levels in leaves and roots. The levels of LOX-1 and
LOX-2 may be regulated mainly pretranslationally, as suggested by the
similarity of the protein and mRNA patterns corresponding to the two
isoforms.
