Depicting X-ray radiation damage to in vivo plant tissues: a glance on elemental, ultrastructural, and histochemical responses

Full text: The X-ray fluorescence spectroscopy (XRF) is a powerful technique for the in vivo assessment of plant tissues. However, the potential X-ray exposure damages might affect the structure and elemental composition of living plant tissues, hence, implying on artifacts on the recorded data [3]. In this framework, we herein explored the exposure of soybean (Glycine max (L.) Merrill) leaves to several X-ray doses on a polychromatic benchtop microprobe X-ray fluorescence spectrometer. We modulated the photon flux by playing with both beam size and focus, as well as the exposure time. Besides, the structure and physiological responses of the irradiated plant tissues were further investigated by transmission electron microscopy (TEM) and histochemical analysis. Depending on the dose, the X-ray exposure induces a sharp decrease of K and the X-ray scattering intensities, whereas Ca, P, and Mn signals increase on soybean leaves. Besides, the presence of necrosis and scorching were also recorded on the irradiated spots. The transmission electron microscopy images reveal the collapse of cytoplasm and cell-wall breaking on the irradiated spots. Furthermore, the histochemical analysis detected the production of reactive oxygen species, callose, and autophagic vacuoles, as well as inhibition of chlorophyll autofluorescence in these areas. Therefore, it highlights that some X-ray exposure conditions, e.g., high photon flux and exposure time affect its structures soybean leaves elemental composition, cellular structures, and then induce programmed death cell. These results might shed light on the characterization of the radiation damage, and thus, help to assess the safety limits and strategies for in vivo for XRF analysis. (author)