Plant Growth Regulatory Substances Exudation of Hairy Roots of Malus domestica and Chenopodium murale - a Contribution to Their Allelopathic Profiling

Abstract

Root-exuded compounds play a key role in the regulation of plant allelopathic interactions. In contrast to numerous studies showing that many secondary metabolites have an allelopathic function, evidence of exudation of phytohormones into the rhizosphere and their involvement in allelopathic interactions is scarce. We postulated that phytohormones secreted by roots into the environment may act as allelochemicals that affect the growth performance of neighboring plants. Hairy root culture media of two distinct species, the fruit tree species Malus domestica cv. Golden delicious[1] and the herbaceous weed species Chenopodium murale [2,3] were collected and analyzed by ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS). We found that most of plant growth substances exuded by the hairy roots of C. murale and M. domestica were assorted from fraction A (96.8% and even 98.9%, respectively) including OxIAA, PAA, SA, BzA, and ABA, with SA and BzA being the most abundant, whereas those from fraction B, including cytokinins and the ethylene precursor ACC, accounted for only 1% of the regulatory substances detected in both species. Exogenous application of SA at concentrations released by the hairy roots of the respective plant species and accumulated in the culture media for four weeks significantly affected the hairy root growth of the other species and also the shoot and root growth of the Arabidopsis seedlings. The disruptive effect of SA in the exuded concentration on the membrane potential of Arabidopsis root cells was determined. The data obtained would be useful for designing further studies aimed at elucidating the contribution and role of exuded phytohormones to overall allelopathic potential of these two plant species. OxIAA = 2-oxindole-3-acetic acid, PAA = phenylacetic acid, SA = salicylic acid, BzA = benzoic acid, ABA = abscisic acid, ACC = 1-aminocyclopropane-1-carboxylic acid