Über die Lichtempfindlichkeit von Auxin-a-lacton. 35. Mitteilung über pflanzliche Wachstumsstoffe

Abstract

Auxin-a shows no absorption in the u.-v.; auxin-b has a characteristic absorption band at 250 mu. Auxin-a is reversibly converted into auxin-a-lactone. When the absorption of an alcoholic or CHCl3 soln. of auxin-a-lactone is measured by the photoelectric method, the soln. shows a strong absorption band at 295 m[mu], and after the measurements are made, the auxin-a-lactone has lost about 80% of its activity as is shown by oat growth tests. The weak radiation during the measurements changes the lactone into the inactive product, lumi-auxone, m. p. 172[degree]. Solns. of the lactone stored in the dark gradually lost their activity. In this case also, the lactone was changed into the lumi-auxone. Polarimetric, spectrometric and biological methods for detg. auxin-a-lactone activity are in agreement. Tetrahydro-lumi-auxone (C18H32O3), m. p. 181[degree], is prepd. by hydrogenat-ing 10 mg. lumi-auxone in methanol with PtO-Pt black. The tetrahydro-lumi-auxone is saponified by boiling 3.7 mg. of the product in 1.5 ml. water for 15 min. The [image]-lactone is split off, and a product with a m. p. of 191[degree] obtained.