Release of Ammonia by Plant Tissues treated with Indole-3-Acetic Acid

Abstract

IN a previous investigation¹, the uptake of amino-acids by plant tissues was followed by means of radioisotopic techniques. When colorimetric techniques were employed in their stead it was found that uptake was masked by the movement of ninhydrin-positive substances from the tissue into the external solution. This observation led to a study of the release of these substances by plant segments. It was observed that when segments of etiolated hypocotyls of Helianthus annuus were floated in water or a solution of indole-3-acetic acid (the range tested was 1.1 × 10⁻⁵ − 1.1 × 10⁻⁴ M) ninnydrin-positive substances rapidly made their appearance in the external medium. The concentration of these substances appeared to reach a maximum value within 2 hr.: continued immersion led to no increase in the ninhydrin colour of the medium but, on the contrary, to its gradual diminution. It was further observed that, while indole-3-acetic acid had no clear-cut influence on the initial loss from the tissue, it had a remarkable effect on the amount of ninhydrin-positive material detectable in the medium after about 20 hr. At this stage the concentration in the media containing the auxin was 2–6 times higher than that in the controls (see Table 1).