PHYTOHORMONES IN NEEDLES OF HEALTHY AND DECLINING SILVER FIR (ABIES-ALBA MILL.) .1. INDOLE-3-ACETIC-ACID

Levels of indole-3-acetic acid (IAA) were determined in needles from s ilver fir (Abies alba Mill.) trees in the northern Black Forest. IAA w as quantified by gas chromatography (GC) as 1-heptafluorobutyryl-IAA-m ethylester (HFB-LAA-ME) using electron capture detection. Prior to GC analysis, extensive purification of needle extracts was performed empl oying two HPLC steps. Peak identity of HFB-IAA-ME was confirmed by com bined gas chromatography-mass spectrometry in selected samples. Levels of IAA in needles belonging to different needle age-classes exhibited a cyclic seasonal pattern with highest concentrations in winter and l owest levels in spring when bud-break occurred. Such a cyclic seasonal pattern of IAA levels was also observed in needles from declining fir trees or fir trees suffering from a strong sulfur impact (S-impact) i n the field due to a local SO2 source. Levels of IAA increased with in creasing needle age. This age dependency of IAA concentrations was mos t pronounced in late autumn when LAA levels were high and nearly disap peared in spring when IAA levels reached their minimum. In needles fro m declining fir trees or fir trees suffering from a strong S-impact in the field, LAA levels hardly increased with increasing needle age. It is suggested that in healthy trees high levels of LAA protect older n eedles from abscission and that the considerable losses of older needl es of declining fir trees or of fir trees under S-impact are a consequ ence of the low levels of IAA found in older needles of such trees.