An Electron Spin Resonance Investigation of Internal Rust Spot, A Physiological Disorder of the Potato Tuber

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Abstract
ESR spectroscopy has been used to investigate the formation of paramagnetic species during the development of internal rust spot (IRS) in the potato tuber. Production of free radicals and oxidation of metal ions such as Fe(II) and Mn(II) occur when necrotic tissue is formed. However. since IRS develops in periods of calcium stress (low calcium supply). it is suggested that the principal cause of the disorder is a loss of cell membrane integrity tvhich is brought ahout by a lack of calcium. Cell senescence and the formation of necrotic tissue may then result either from increased oxygen radical production within the cell or from oxidation of metal complexes in the extracellular regions of the tissue.