Root and shoot gas exchange respond additively to moderate ozone and methyl jasmonate without induction of ethylene: ethylene is induced at higher O₃ concentrations

摘要

The available literature is conflicting on the potential protection of plants against ozone (O₃) injury by exogenous jasmonates, including methyl jasmonate (MeJA). Protective antagonistic interactions of O₃ and MeJA have been observed in some systems and purely additive effects in others. Here it is shown that chronic exposure to low to moderate O₃ concentrations (4–114 ppb; 12 h mean) and to MeJA induced additive reductions in carbon assimilation (A _n) and root respiration (R _r), and in calculated whole plant carbon balance. Neither this chronic O₃ regime nor MeJA induced emission of ethylene (ET) from the youngest fully expanded leaves. ET emission was induced by acute 3 h pulse exposure to much higher O₃ concentrations (685 ppb). ET emission was further enhanced in plants treated with MeJA. Responses of growth, allocation, photosynthesis, and respiration to moderate O₃ concentrations and to MeJA appear to be independent and additive, and not associated with emission of ET. These results suggest that responses of Pima cotton to environmentally relevant O₃ are not mediated by signalling pathways associated with ET and MeJA, though these pathways are inducible in this species and exhibit a synergistic O₃×MeJA interaction at very high O₃ concentrations.