Effects of arbuscular mycorrhizal fungi on herbivory defense in two Solanum (Solanaceae) species
Arbuscular mycorrhizal fungi (AMF) are abundant soil organisms that have wide ranging impacts on plants and ecosystems. About 80% of land plants form symbiotic relationships with AMF (Schussler et al. 2001) and these associations can affect plant growth, fitness, and community diversity (Klironomos et al. 2000, Smith Read 2008, Jung et al. 2012) AMF hyphal networks reach parts of the surrounding soil that plant roots cannot and transfer nutrients, such as phosphate and nitrogen, to the plant in exchange for carbohydrates synthesized during photosynthesis (Smith Smith 2011) The general increase in plant fitness due to AMF was historically attributed solely to the improved nutrition AMF provide (Pfleger Linderman 1994) but more recent studies have found that plants colonized by AMF undergo physiological changes that alter their resistance to aboveand belowground antagonists (Pozo et al. 2002, Koricheva et al. 2009, Song et al. 2013, Vannette et al. 2013, Cameron et al. 2013) AMF may influence plant defenses by interacting with the jasmonic acid (JA) pathway (Pozo Azcon Aguilar 2007) Jasmonic acid is an essential hormone in the immune system of plants (Bari Jones 2009, Pieterse et al. 2009) and when a plant is attacked by an insect herbivore, JA is produced, signaling cells to begin production of defensive compounds (Pozo et al. 2004) In many plants, this induced resistance includes the general defensive chemicals peroxidase (POD) polyphenol oxidase (PPO) and protease inhibitors (PI) (Farmer Ryan 1992, Constabel Ryan 1998, Moore et al. 2003) enzymes that have been shown to have inhibitory effects on insect herbivores. In Populus spp. POD inhibits herbivore growth by oxidizing phenols in the guts of caterpillars, damaging amino acids and denaturing proteins