SEASONAL-VARIATION OF 2 PHENOLIC AMINES IN ACACIA-BERLANDIERI

The low growing, multi-stemmed shrub Acacia berlandieri Benth. is wide ly distributed through the Rio Grande Plains of Texas, where it is an important component of the forage supply to both deer and domestic her bivores. The plant is known to contain a number of phenolic amines, in cluding tyramine and N-methyl-beta-phenethylamine (NMP). Phenolic amin es, like other secondary compounds, may be used as a defence against h erbivory, and NMP has been implicated in the occurrence of a hind-limb ataxia in animals consuming A. berlandieri forage over extended perio ds. Current hypotheses advanced to explain the effects of environmenta l changes (including herbivory) on phenotypic exhibition of secondary compound metabolism may not apply to plants adapted to semi-arid envir onments. We examined the seasonal changes in concentrations of phenoli c amines in mature and regrowth leaves of A. berlandieri during the 19 89 and 1990 growing seasons. Tyramine concentrations, as measured by h igh performance liquid chromatography, were consistently higher than N MP concentrations in both mature (4.4 +/- 0.14 us. 1.5 +/- 0.12) and r egrowth (5.4 +/- 0.35 vs. 1.8 +/- 0.31 mg.g DM(-1)) leaf. Tyramine and NMP concentration in mature leaves did not appear to be greatly influ enced by rainfall amount or distribution or by seasonal variation. Reg rowth leaf contained higher concentrations of both tyramine and NMP th an mature leaves, with tyramine and NMP concentrations increasing by 4 0 and 35% (3.7 +/- 0.15 and 1.5 +/- 0.13 to 6.2 +/- 0.33 and 2.3 +/- 0 .28 mg.g DM(-1)), respectively, with additional defoliations. The appa rent induction of both tyramine and NMP in regrowth leaf may adversely impact nutrition and reproduction of wild and domestic livestock brow sing A. berlandieri, especially under conditions of heavy utilization. (C) 1995 Academic Press Limited