Synergistic inhibitory effects ofp-coumaric and ferulic acids on germination and growth of grain sorghum

Abstract

The data support the hypothesis that there is a synergistic phytotoxic effect whenp-coumaric and ferulic acids are found together. Equimolar mixtures of both acids showed greater reduction in sorghum seed germination, shoot elongation, and total seedling growth than either phytotoxin caused when alone. Repeated experiments showed mixtures containing 5×10⁻³ Mp-coumaric and 5×10⁻³ M ferulic acids reduced germination to 34% of controls after 24 hr and 59% by 48 hr. The same concentration of either phenol-treated seeds alone showed 69 and 92% germination at comparable times. The phytotoxic action of the combination approximated the inhibitory effect on germination of 10⁻² M ferulic acid and was a greater reduction than caused by 10⁻² Mp-coumaric treatments. Sorghum seedling growth was more sensitive than germination, with an equimolar mixture of 2.5×10⁻⁴ Mp-coumaric and 2.5×10⁻⁴ M ferulic acids reducing seedling dry weight significantly below weights of seedlings treated separately with 2.5×10⁻⁴ Mp-coumaric or ferulic acids. Further dilutions showed a 1.25×10⁻⁴ M concentration of either phenol was stimulatory to seedling growth, whereas a mixture of these two produced inhibition.