Effect of cis-Cinnamic Acid and some Isomeric Compounds on the Germination of Zygotes of Chlamydomonas

Abstract

THE effect of a number of organic acids as inhibitors of germination has been tested on the zygotes of the blastikos race of Chlamydomonas eugametos¹. It was observed that trans-cinnamic acid inhibits germination to about 50 per cent even at a dilution of 10⁻⁷ gm./c.c. The experiment has now been extended to the three different allotropic modifications of cis-cinnamic acid and a few isomeric compounds. The percentage of inhibition of germination with respect to that of control is shown in the accompanying graph. The experimental method and evaluation have been described in greater detail elsewhere². The percentage germination of the control (in. Volvox solution) is 85.92 ± 0.429 per cent (n = 1,186 zygotes). The activity of cinnamic aldehyde is very small, since at 10⁻⁵ gm./c.c. the germination remains unaffected. A similar effect is also found in the case of trans-2-oxy-cinnamic acid (o-coumaric acid). β-d-Glucosido-o-coumaric acid is less active than the aglucone. Coumarin is a hundred times more active; even at a dilution of 10⁻⁸ gm./c.c. a statistically significant promotion of germination can be definitely observed. Still more active is trans-cinnamic acid as has been already reported¹; though in very dilute solution (10⁻¹⁰ to 10⁻¹² gm./c.c.) no statistically significant promotion of germination was recorded. The range of activity of cis-cinnamic acid is fifty to eighty times more than that of the trans form, since even at a dilution of 10⁻¹¹ to 10⁻¹² gm./c.c. a significant promotion of germination could be observed. The three allotropic modifications of cis-cinnamic acid (42° C., 58° C., 68° C.) have the same activity².