Synchrotron macro‐<scp>ATR</scp>‐<scp>FTIR</scp>: a powerful technique for analyzing changes in plant cell chemical composition after surfactant exposure

Surfactants, as foliar sprays, are widely used to increase the uptake of agrichemicals through plant leaf surfaces. Study of the effects of surfactants on plants has mainly focused on investigation of the mechanisms that underlie changes in droplet behavior on leaf surfaces. However, how surfactants may affect leaf chemical composition is largely unknown. The standard analysis techniques that have been widely used for leaf chemical analyses such as mass spectroscopy require complex and extensive sample preparation and leaf tissue destruction. Here, we have used an advanced technique, synchrotron macro-Attenuated Total Reflectance-Fourier Transformed InfraRed spectroscopy (synchrotron macro-ATR-FTIR), which provides a fast, non-destructive and in vivo method to capture the leaf surface and enable the chemical mapping of essential functional groups. The development of two Quasar workflows for analyzing complex FTIR data in this study highlights and strengthens the advantages of synchrotron macro-ATR-FTIR for plant research. We found that the treatment of 5-week-old maize (Zea mays L.) leaves with a commercial surfactant, Silwet-L-77, resulted in alterations in the FTIR spectral signatures associated with lipids, proteins and carbohydrates commencing 1 h after treatment. The effects of the surfactant on maize leaf water droplet behavior and photosynthetic performance were concentration-dependent. Synchrotron macro-ATR-FTIR is thus a newly emerging and powerful analytical technique for quantitative studies in plant physiology and biochemistry, especially for plant responses to external environmental factors including both abiotic and biotic stresses.