Defense elicitation activity of the ellagitannin HeT depends on its redox state

Abstract

It was previously reported that the ellagitannin HeT obtained from strawberry leaves can elicit a defense response in strawberry and lemon plants, and exhibits antibacterial properties. It was also shown that the antibacterial activity was due to a strong interaction with bacterial membrane affecting the electron flux involved in the oxygen consumption, and as result of this interaction HeT becomes irreversibly oxidized. The aim of this paper was to investigate whether HeT is oxidized in contact with plant cells, and the influence of the redox state of HeT on the activation of a defense response; consequently, on the capacity of HeT to protect strawberry plants against a virulent pathogen. Results showed that HeT is rapidly oxidized by contact with the mesophilic cells of the strawberry, as previously reported with the bacterial cells, and only the reduced species of HeT (HeT-red) induce a defense response that protects plants against the virulent isolate M11 of Colletotrichum acutatum. Also, strawberry plants treated with the HeT-red exhibits a biphasic ROS accumulation. By contrary the oxidized species (HeT-ox) had no effect on plants. Evaluation of genes associated to the activation of a defense response depending on the salicylic acid (e.g. FaPR1, FaChi2-2) and ethylene pathways (e.g. FaERS1 and FaETR1) showed that HeT-red, but not HeT-ox, caused the upregulation of all of them 48 hpt. These findings indicate that only the reduced species of HeT is capable to induce a defense response which provides the plant protection against a virulent isolated of C. acutatum.