Morphological and physiological effects of trans-cinnamic acid and its hydroxylated derivatives on maize root types

Roots encounter cinnamic acid and its hydroxylated derivatives that are commonly found in soils. However, root systems consist of different root types with different morphological and physiological characteristics. Very little is known about the responses and adaptation mechanisms of the root types to cinnamic acid and its hydroxylated derivatives. In this study, the morphological and physiological responses of different maize root types exposed to different concentrations of t-cinnamic, ferulic, caffeic or p-coumaric acids were investigated. The results showed that the effects of allelochemicals were dependent on concentration, chemical structure, root type and process considered. In particular, t-cinnamic acid was characterized by higher allelopathic activity when compared with its derivatives, where a hydroxyl or methyl groups were present in aromatic ring. Among root types it was possible to delineate the following tolerance hierarchy: primary > seminal > nodal > lateral of the primary = lateral of the seminal roots. Moreover, primary and seminal roots showed a different strategy to cope the chemical stress by either increasing or decreasing specific root length. Finally, an electrophysiological approach identified an involvement of proton pump activity and consequently a decrease in nitrate uptake.