Abscisic acid suppresses the increases in cell wall-bound ferulic and diferulic acid levels in dark-grown wheat (Triticum aestivum L.) coleoptiles

Abstract

Application of abscisic acid (ABA) to dark-grown wheat (Triticum aestivum L.) roots interfered the cell wall hardening of coleoptiles during several days of the treatment. Although the amounts of wall-bound diferulic (DFA) and ferulic (FA) acids in coleoptiles increased as the coleoptiles grew, ABA substantially reduced their increases. When ABA was removed, however, these contents increased and reached levels near those of control coleoptiles. A close correlation was observed between the levels of DFA and FA and the mechanical properties of cell walls. The ratio of the amount of DFA to FA was almost constant irrespective of growth conditions. The activities of phenylalanine- (PAL) and tyrosine-ammonia-lyase (TAL) increased rapidly in the control coleoptiles. ABA greatly reduced the increases in these enzyme activities. In response to ABA removal, the enzyme activities increased rapidly. There was a close correlation between the increase in FA level and the changes in enzyme activities. These results suggest that ABA suppresses the increases in PAL and TAL activities in wheat coleoptiles, resulting in the reduced level of wall-bound FA, which, in turn, may cause the reduced DFA level and thereby maintain cell wall extensibility.