Biophysical evidence that frostbite is triggered on nanocrystals of biogenic magnetite in garlic cloves (Allium sativum)

Creators: Kobayashi, Atsuko^{1, 2, 3}; Tanaka, Daisuke^{4, 5}; Hidaka, Hironori¹; Sakurai, Kasumi¹; Kawai, Kotaro¹; Kato, Toyohiro¹; Kihara, Kumiko⁶; Kirschvink, Joseph L.^{1, 2, 3}

1. Tokyo Institute of Technology
2. California Institute of Technology
3. Kōchi University
4. National Agriculture and Food Research Organization
5. University of Tsukuba
6. Kumamoto University

Abstract

Trace levels of biologically precipitated magnetite (Fe₃O₄) nanocrystals are present in the tissues of many living organisms, including those of plants. Recent work has also shown that magnetite nanoparticles are powerful ice nucleation particles (INPs) that can initiate heterogeneous freezing in supercooled water just below the normal melting temperature. Hence there is a strong possibility that magnetite in plant tissues might be an agent responsible for triggering frost damage, even though the biological role of magnetite in plants is not understood. To test this hypothesis, we investigated supercooling and freezing mortality in cloves of garlic (Allium sativum), a species which is known to have moderate frost resistance. Using superconducting magnetometry, we detected large numbers of magnetite INPs within individual cloves. Oscillating magnetic fields designed to torque magnetite crystals in situ and disturb the ice nucleating process produced significant effects on the temperature distribution of supercooling, thereby confirming magnetite’s role as an INP in vivo. However, weak oscillating fields increased the probability of freezing, whereas stronger fields decreased it, a result that predicts the presence of magnetite binding agents that are loosely attached to the ice nucleating sites on the magnetite crystals.

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Acknowledgement

We thank Dr. Chisato Anai of the Marine Core Research Institute of Kochi University for help with the MPMS. Support for this research was provided by the Japan Society for the Promotion of Science (JSPS) Kakenhi Grants JP20K04304 and JP23K03693 to A.K., and the Environment Research and Technology Development Fund of the Environmental Restoration and Conservation Agency Grant JPMEERF20231M05 (K. Kihara).

Contributions

Conceptualization: A.K. Methodology: A.K., J.L.K., K.S., D.T., H.H., and T.K. Investigation: D.T., A.K., H.H., K. Kawai, T.K., J.L.K. Visualization: K.S., J.L.K., A.K. Supervision: A.K. Writing—original draft: A.K., J.L.K., K. Kihara. Writing—review & editing: A.K., J.L.K., K. Kihara, and K.S.

Data Availability

The first tab of the appended Excel file (Supplementary Data 1) gives the cooling, freezing, and viability data for all garlic bulbs and cloves from this study. Subsequent tabs show the data organization for Tables 1–3, the associated statistical tests, and source data for charts presented in the main figures. This file is available online or from the senior author.

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