Physiological and Biochemical Mechanisms Mediated by Allelochemical Isoliquiritigenin on the Growth of Lettuce Seedlings.

Shuang Zhang,Jin Wang,Hai-Lin Shi,Wei Wang,Xiao-Hong Liu,Yang Liu,Ke Zhao,Shi-Wei Sun

doi:10.3390/plants9020245

Abstract

Isoliquiritigenin, a natural chalcone-type flavonoid, has been recognized as an allelochemical with phytotoxicity to lettuce; however, not enough attention has been paid to the mechanisms of this secondary metabolite. In this work, we investigated the physiological and biochemical mechanisms of isoliquiritigenin on lettuce seedlings. The results show that isoliquiritigenin has a concentration-dependent inhibitory effect on radicle elongation of lettuce seedlings, but no significant impact on lettuce germination. Microscopy analyses suggest that the surface morphology of lettuce radicle tips was atrophied and the intracellular tissue structure deformed at high concentrations. Isoliquiritigenin induced the overproduction of reactive oxygen species (ROS), which led to loss of cell viability in the radicle cells. In addition, malondialdehyde (a product of lipid peroxidation) and free proline levels were found to have increased, while chlorophyll content in lettuce seedlings decreased. All these changes suggest that the primary allelopathic mechanism of isoliquiritigenin by which it inhibits radicle elongation in lettuce seedlings might be due to the overproduction of ROS, which causes oxidative damage to membrane lipids and cell death.

Highlights

Allelopathy was first introduced in 1937 by Molisch to indicate plant-to-plant interaction mediated by releasing signaling secondary metabolites through the donor plant
To the best of in this work, we investigated the phytotoxic action mechanism of isoliquiritigenin on experimental our knowledge, this is the first study reporting that overproduction of reactive oxygen species (ROS) and lipid peroxidation plants
We demonstrated that isoliquiritigenin induced more than 40% inhibition of radicle elongation in lettuce seedlings at a concentration of

Summary

Introduction

Allelopathy was first introduced in 1937 by Molisch to indicate plant-to-plant interaction mediated by releasing signaling secondary metabolites through the donor plant. More than half a century later, in 1996, the definition of allelopathy was broadened by the International Allelopathy Society as ‘any process involving secondary metabolites produced by plants, microorganisms, viruses, and fungi that influence the growth and development of agricultural and biological system, including positive and negative effects’ [1]. The allelopathic effect of allelochemicals can vary from that of inhibiting to stimulating seed germination and/or seedling growth and development of neighboring plants or other organisms, and can even be detrimental to their own species (autotoxic effect) [3]. Many studies have shown that allelochemicals affect many aspects of Plants 2020, 9, 245; doi:10.3390/plants9020245 www.mdpi.com/journal/plants

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