Relationships between chemical structure and inhibitory activity of C6 through C9 volatiles emitted by plant residues

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Abstract
Leaf, stem, flower, fruit, and root residues of a wide variety of plants have been reported to emit bioactive n -alkanes, 2-alkanols, n -alkanals, 2-alkenals, 2-alkanones, and n -alkanoic acids containing from six to nine carbon atoms. During a 72-hr exposure to the vapor phase of these compounds (6.9, 20.8 or 34.4 μ M/liter), germination of onion, carrot, and tomato seeds was inhibited to varying degrees. The extent of inhibition caused by these plant residue volatiles depended upon the compound type and concentration, carbon-chain length, and the seed species tested. Tomato seeds recovered more fully from exposure to these volatile inhibitors than did those of carrot and onion. Degree of recovery in all three species depended on the type and concentration of volatile present. The C_7 and C_8 compounds were the most inhibitory among these 24 volatiles. Of the six classes of chemicals examined, the 2-alkenals were the most inhibitory, followed by the 2-alkanols, n -alkanals, and 2-alkanones, which were equally effective as seed germination inhibitors. The straight-chain alkanes and alkanoic acids were relatively noninhibitory. Tests of a C_7 and C_9 alkadienal indicated that the C_7 compound was the more inhibitory.