Physiological Responses of Maize Leaves Exposed to Ethylene and Infected by Exserohilum turcicum

Abstract

The hormone ethylene (ET) plays multiple roles in plant growth and development. However, its involvement in the maize–Exserohilum turcicum interaction must be better elucidated. This study investigated the role of ET in the infection process of E. turcicum on maize leaves at the physiological (leaf gas exchange and chlorophyll a fluorescence parameters and concentrations of photosynthetic pigments) and biochemical [concentrations of malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and superoxide anion radical] levels. Plants were sprayed with water (control), ET or aminooxyacetic acid (AOA) (an inhibitor of ET production) and challenged or not with E. turcicum. ET was not detected in the infected leaves of ET- or AOA-sprayed plants compared to noninfected leaves exposed to ET. The symptoms of northern corn leaf blight were very well developed in the leaves of ET-sprayed plants. Moreover, the greatest disease severity was closely associated with higher concentrations of MDA and H₂O₂ in the leaf tissues, indicating intense lipid peroxidation. On top of that, the photosynthetic apparatus was significantly impaired considering the lower values for net carbon assimilation rate, stomatal conductance, transpiration rate and maximal photosystem II quantum yield. In conclusion, the exogenous supply of ET to maize leaves was of pivotal importance in favouring the infection process of E. turcicum in maize leaves.