Further studies on plant-plant communication will promote our understanding of systemic defence in natural ecosystems, which in turn may provide clues to manipulate plant defences in agroecosystems.
One can argue by extension that the CMNs may induce systemic defence in ecosystems, minimizing disease occurrence and severity in plant communities.
Herbivory or addition of JA to the leaves did not have an effect on floral nectar secretion, demonstrating a functional separation of systemic defence signalling from reproductive nectar secretion.
To study whether systemic defence signalling interferes with the observed JA-mediated induction of floral nectar, we treated the leaves of B. napus with JA, mechanical damage and natural herbivores, treatments which are all known to increase endogenous JA levels [11], [12], [26].
Furthermore, the distinct metabolic profiles of intact (I) and directly damaged (D) leaves showed that local and/or systemic defence responses were induced in the plant within 32 h of herbivore feeding.
Furthermore, AcH 505 induced a systemic defence response against Microsphaera alphitoides in pedunculate oak leaves, involving both jasmonic acid (JA)/ethylene (ET) and salicylic acid (SA -dependent SA -dependent26].
Previous studies have established that Norway spruce trees resistant to necrotrophic pathogens have rapid induction of defence related genes (e.g. peroxidases, class IV chitinase and others) [ 24, 29], and also appear to have more efficient systemic defence signalling than susceptible genotypes.
In Norway spruce a host of defense related proteins are upregulated in response to pathogen attack and other stressors, and the chitinase PaChi4 has proven to be a particularly useful marker for local and systemic defence response in both Norway spruce and Sitka spruce [ 23- 25].
Pathogen-triggered immunity and effector-triggered immunity activate both local and systemic defence responses, which are mainly modulated by the signalling pathways related to the jasmonic acid (JA), generally associated to necrotrophic pathogens, chewing insects attack and salicilic acid (SA), more related to defenses triggered by biotrophic pathogenes.
In fact, MtrST6 does not undergo changes in its expression pattern during systemic defence response although it does when establishing symbiosis [ 66, 67], its transcript being strongly reduced when the formation of arbuscular mycorrhiza-induced apocarotenoids was inhibited [ 68], and increased when Myc factors were added to the medium [ 69].
