Figure 3.

Hypothetical model of the potential polyamines- (PAs-) based responses of citrus plants against viroid diseases. (a) Integration of PAs with ethylene in citrus response to the infection with Citrus Exocortis Viroid (CEVd), and (b) The interaction between PAs, ethylene, and salicylic acid during the CEVd infection. Solid lines with arrowhead signify positive reaction, dashed lines with blunt-heads indicate negative interaction, while round-dotted lines with arrows represent hypothetical mechanisms or uncharacterized elements. For more details and abbreviations, see the main text.