Myrigalone A Inhibits Lepidium sativum Seed Germination by Interference with Gibberellin Metabolism and Apoplastic Superoxide Production Required for Embryo Extension Growth and Endosperm Rupture

Abstract

Myrica gale L. (sweet gale) fruit leachate contains myrigalone A (MyA), a rare C-methylated dihydrochalcone and putative allelochemical, which is known to be a phytotoxin impeding seedling growth. We found that MyA inhibited Lepidium sativum L. seed germination in a dose-dependent manner. MyA did not affect testa rupture, but inhibited endosperm rupture and the transition to subsequent seedling growth. MyA inhibited micropylar endosperm cap (CAP) weakening and the increase in the growth potential of the radical/hypocotyl region (RAD) of the embryo, both being key processes required for endosperm rupture. We compared the contents of abscisic acid (ABA) and gibberellins in the tissues and found that the major bioactive forms of gibberellin in L. sativum seed tissues were GA(4) and GA(6), while GA(8) and GA(13) were abundant inactive metabolites. MyA did not appreciably affect the ABA contents, but severely interfered with gibberellin metabolism and signaling by inhibiting important steps catalyzed by GA3 oxidase, as well as by interfering with the GID1-type gibberellin signaling pathway. The hormonally and developmentally regulated formation of apoplastic superoxide radicals is important for embryo growth. Specific zones within the RAD were associated with accumulation of apoplastic superoxide radicals and endoreduplication indicative of embryo cell extension. MyA negatively affected both of these processes and acted as a scavenger of apoplastic reactive oxygen species. We propose that MyA is an allelochemical with a novel mode of action on seed germination.

Dynamic "Symbionts" Linked over Two Centuries: A Tribute to Lynn Margulis (1938–2011)

“…A derivative of coumarin, 4-methylumbelliferone, inhibited germination of Arabidopsis thaliana seeds (Li et al, 2011); 6-metoxy-benzoxazolin-2(3H)-one (MBOA, a benzoxazolinone) or myrigalone A inhibited germination of cress (Lepidium sativum) seeds (Kato-Naguchi and Macias, 2006;Oracz et al, 2012). Pieper's value is one of the most useful parameters for describing seed germination rate.…”

Natural Compounds as Next-Generation Herbicides

“…Myrigalone, a natural b-triketone produced by the plant M. gale, interferes with GA metabolism and signaling by inhibiting GA 3-oxidase and by disrupting the GA signaling pathway. These processes are important for endosperm weakening and embryo growth (Oracz et al, 2012).…”

Inhibition of tomato (Solanum lycopersicumL.) root growth by cyanamide is not always accompanied with enhancement of ROS production

“…Some have even antioxidant properties, as (±)-catechin and myrigalone A. 14,15 However, radical-scavenging properties also may have serious implications in acceptor plant physiology, high value Ψs = -0.1 MPa, indicating no direct impact on passive water uptake. Therefore, maybe CA acts as inhibitor of aquaporins as it was suggested for caffeic acid in regulation of growth of leafy spurge (Euphorbia esula L.).…”

“…Some data suggest involvement of respiratory or photosynthetic electron chain 18,19 or activation of plasma membrane NADPH oxidase. 15 CA may function similarly to KCN, an inhibitor of cytochrome c oxidase, leading to transient overproduction of ROS followed by higher rates of alternative oxidase (AOX) activity, which finally act as compensatory tool that reduces ROS generation. 20 More advanced study on that aspect of CA phytotoxicity are needed.…”