Ozone reduces the mutualism effectiveness of fungal endophyte in grasses.

UENO A; GUNDEL, P.E.; OMACINI M; GHERSA CM; BUSH L; MARTINEZ-GHERSA, M.A.

Buenos Aires

Simposio; New Phytologist Symposium; 2014

Acute ozone exposure may reduce plant fitness under low levels of herbivoy. However, it may also enhance gene expression and synthesis of molecules related to defense mechanisms, which could improve plant fitness when herbivory increases. In ryegrass-endophyte symbiotic plants fitness improvements are caused by augmenting tolerance to abiotic stress factors and by increasing alkaloid-mediated defense against hebivores. Apart from the negative effect of ozone on plant fitness, acute ozone exposures have been indicated as to elicit plant defenses. These presumed effects have never been explored in plants where the anti-herbivory defense mechanism is provided by fungal endophytes. We subjected exposed ryegrass plants (symbiotic/non-symbiotic with endophyte) to short-term ozone exposure (with/without) for two hours in two days, and then, infested half of the plants were infested (with/without) by with aphids (Rhopalosiphum padi). We evaluated the growth and structure of aphid populations. Without ozone, symbiotic plants showed increased defenses againsta smaller aphid population size than non-symbiotic plants s as shown by the lower aphid population size. With ozone, however, this protective effectdifference disappeared. The population structure of aphids feeding on endophyte-symbiotic plants was characterized by a low number of nymphs and a higher of winged, and the opposite when aphids fed on non-symbiotic plants; a pattern that was reverted by ozone. On the other hand , Since there was not a negative effect of ozone on the alkaloid content of plants was not affected by ozone. , our These results suggest that while ozone stimulated defenses in non-symbiotic plants, it affected negatively the anti-herbivore mechanism provided by the endophyte and that changes in molecules related to the oxidative balance of plants were involved in this effect . We proposed that ozone is affecting negatively the endophyte by activating the salicylic acid pathway which is effective defense against biotrophic fungi.