An Electron Paramagnetic Resonance Spin-Probe Study of Membrane-Permeability Changes with Seed Aging

Area of Science:

• Plant Physiology
• Biophysics
• Biochemistry

Background:

• Seed aging under dry storage leads to loss of viability.
• Plasma membrane integrity is crucial for seed viability.
• Assessing membrane barrier properties in aged seeds is challenging.

Purpose of the Study:

• To develop and apply an electron paramagnetic resonance (EPR) spin-probe technique to quantify plasma membrane barrier property changes in aging wheat seeds.
• To correlate changes in membrane permeability with seed germinability loss during dry storage.

Main Methods:

• Utilized a stable free radical (4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy) and ferricyanide as a spin probe and broadening agent, respectively.
• Employed EPR spectroscopy to measure the line-height ratio (R value) of the spin probe, reflecting plasma membrane permeability.
• Analyzed permeability in distinct wheat seed tissues: embryo axis, scutellum, aleurone layer, and starchy endosperm.

Main Results:

• The R value quantitatively assessed plasma membrane permeability, with high R indicating low permeability.
• Starchy endosperm cells maintained highly permeable membranes even in viable seeds.
• Loss of germinability correlated with significantly increased plasma membrane permeability in embryo axis cells.
• A threshold R value of 5-6 for individual axes indicated loss of viability.

Conclusions:

• The EPR spin-probe technique provides a sensitive method to evaluate plasma membrane barrier properties in wheat seeds during aging.
• Increased plasma membrane permeability of embryo axis cells is a key indicator of viability loss in aging wheat seeds.
• Seed viability loss is associated with an accumulation of cells with critical plasma membrane permeability levels.