PLANT PHYSIOLOGY , Vol 113, Issue 3 967-973, Copyright © 1997 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Osmotic Stress Suppresses Cell Wall Stiffening and the Increase in Cell Wall-Bound Ferulic and Diferulic Acids in Wheat Coleoptiles
K. Wakabayashi, T. Hoson and S. Kamisaka
Department of Biology, Faculty of Science, Osaka City University, Sumiyoshi-ku, Osaka 558, Japan
The relationship between the mechanical properties of cell walls and the
levels of wall-bound ferulic (FA) and diferulic (DFA) acids was
investigated in wheat (Triticum aestivum L.) coleoptiles grown under
osmotic stress (60 mM polyethylene glycol [PEG] 4000) conditions. The cell
walls of stressed coleoptiles remained extensible compared with those of
the unstressed ones. The contents of wall-bound FA and DFA increased under
unstressed conditions, but the increase was substantially reduced by
osmotic stress. In response to PEG removal, these contents increased and
reached almost the same levels as those of the unstressed coleoptiles. A
close correlation was observed between the contents of FA and DFA and the
mechanical properties of cell walls. The activities of phenylalanine
ammonia-lyase and tyrosine ammonia-lyase increased rapidly under unstressed
conditions. Osmotic stress substantially reduced the increases in enzyme
activities. When PEG was removed, however, the enzyme activities increased
rapidly. There was a close correlation between the FA levels and enzyme
activities. These results suggest that in osmotically stressed wheat
coleoptiles, reduced rates of increase in phenylalanine ammonia-lyase and
tyrosine ammonia-lyase activities suppress phenylpropanoid biosynthesis,
resulting in the reduced level of wall-bound FA that, in turn, probably
causes the reduced level of DFA and thereby maintains cell wall
extensibility.
