INVESTIGATIONS ON THE CONTENT OF INDOLE-3-ACETIC-ACID IN SPRUCE NEEDLES OF HEALTHY AND DAMAGED TREES OF VARIOUS SITES

Surveys were made on the concentration of indole-3-acetic acid (IAA) i n spruce trees of various sites. The concentrations of the hormone wer e specified with a radioimmunoassay after the needle extract had been purified in several steps. The content of IAA in needles of damaged tr ees was distinctly lower than the content in needles of healthy trees. Another feature was the annual rythm of the IAA content with the maxi mum of concentration in June. A distinct diurnal course with highest l evel of concentration during the early afternoon hours was also observ ed. The diurnal rhythm of the damaged trees was clearly lower. The sup position is that the lower IAA content is responsible for a premature needle abscission.