Effect of pinene isomers on germination and growth of maize

Terpenes, secondary metabolites that are present in the essential oils of aromatic plants, are responsible for the biochemical interaction between plants, known as allelopathy. Monoterpenes are a major component of essential oils. Pinene is a monoterpene well-known for its phytotoxic action, but little is known about the allelopathic effect of its isomers. The aim of this study is to determine the effect of pinene's structural isomers and enantioisomers [(−)-α-pinene; (+)-α-pinene; (−)-β-pinene and (+)-β-pinene] at 0.16 mM, on certain physiological parameters (growth, dry weight, phenol, photosynthetic pigments and abscisic acid content) in both the germination and growth of maize (Zea mays L.). In germination bioassays, neither of the α-pinene stereoisomers showed change when compared to the control with respect to seed vigour; but root growth was increased, while β-pinene (racemic mixture) inhibited germination and plant length. In the growth bioassay, all of the pinene isomers decreased the plant length. In general, β-pinene terpene was more phytotoxic than α-pinene in both bioassays. Differences in germination and growth of maize treated with the pinene isomers can be attributed to different action mechanisms which depends both on the growth phases of maize and on the particular pinene isomers.