Assessing radiation dose limits for X-ray fluorescence microscopy analysis of plant specimens

Abstract

Background and Aims X-ray fluorescence microscopy (XFM) is a powerful technique to elucidate the distribution of elements within plants. However, accumulated radiation exposure during analysis can lead to structural damage and experimental artefacts including elemental redistribution. To date, acceptable dose limits have not been systematically established for hydrated plant specimens. Methods Here we systematically explore acceptable dose rate limits for investigating fresh sunflower (Helianthus annuus) leaf and root samples and investigate the time–dose damage in leaves attached to live plants. Key Results We find that dose limits in fresh roots and leaves are comparatively low (4.1 kGy), based on localized disintegration of structures and element-specific redistribution. In contrast, frozen-hydrated samples did not incur any apparent damage even at doses as high as 587 kGy. Furthermore, we find that for living plants subjected to XFM measurement in vivo and grown for a further 9 d before being reimaged with XFM, the leaves display elemental redistribution at doses as low as 0.9 kGy and they continue to develop bleaching and necrosis in the days after exposure. Conclusions The suggested radiation dose limits for studies using XFM to examine plants are important for the increasing number of plant scientists undertaking multidimensional measurements such as tomography and repeated imaging using XFM.

Soft X-ray induced radiation damage in thin freeze-dried brain samples studied by FTIR microscopy

“…The most serious effects were noted for the 8.1 kGy dose after two days, where severe blackening was observed due to cellulose carbonization by free radicals. Up from the fifth day, the K signal was no longer present, whereas Ca and Mn remained locked in place This suggests that radiation damage can impact time-wise concentration characteristics of highly diffusive elements in an irradiated hydrated sample (Jones et al, 2020). In this study, we were not able to observe such a pattern, since estimating elemental concentrations in the brain tissue is practically hindered by a strong observer effect in the soft X-ray regime (Hare et al, 2015).…”

“…This proves overall radio-resilience of Si 3 N 4 in a nearly one-month time-scale upon routine soft XRM experiments. Temporal characteristics of radiation-driven sample degradation have been recently characterized by Jones et al (2020) upon routine hard XRF microscopy measurements of fresh plant samples at the energy of 15.3 keV. Short-term effects involved substantial potassium (K) signal loss after 10 min upon 8.0 kGy exposures.…”

“…This itself is proof and evidence of increased propensity for ageing degradation effects. Recently, Jones et al (2020) concluded that post-irradiation damage ageing effects involve bleaching, necrosis and carbonization of plant tissues. The authors highlighted long-term action of reactive free radicals.…”

“…Although XRF microscopy offers the unprecedented possibility to investigate elemental distribution in a variety of (bio)samples, accumulated exposure to the microprobe can induce structural damage, and alter the elemental distribution (Jones et al, 2020). In particular, soft XRM experiments' versatility and suitability for brain tissue analysis rely on high absorption cross sections of C, N and O K-shells, especially in the so-called 'water window' (between 0.28 keV and 0.54 keV), where the radiation is strongly absorbed by carbonrich biological structures (Teramoto et al, 2018).…”

The XFM beamline at the Australian Synchrotron

“…For samples sensitive to radiation damage, a cryogenic stream environment is available (Oxford Cryostream 700 Series), where the stream is directed downwards. It typically operates at À100 C and is effective in minimizing the influence of radiation damage in organisms such as Caenorhabditis elegans (Jones et al, 2017) and hydrated plant material (Jones, Kopittke et al, 2019). A jacket flow of dried facilitycompressed air is used to avoid the inherent noise, vibration and bulk of a local compressor.…”