Abstract
Cold atmospheric plasma has recently emerged as a simple, low-cost and efficient physical method for inducing significant biological responses in seeds and plants without the use of traditional, potentially environmentally-hazardous chemicals, fungicides or hormones. While the beneficial effects of plasma treatment on seed germination, disease resistance and agricultural output have been reported, the mechanisms that underpin the observed biological responses are yet to be fully described. This study employs Fourier Transform Infrared (FTIR) spectroscopy and emission spectroscopy to capture chemical interactions between plasmas and seed surfaces with the aim to provide a more comprehensive account of plasma−seed interactions. FTIR spectroscopy of the seed surface confirms plasma-induced chemical etching of the surface. The etching facilitates permeation of water into the seed, which is confirmed by water uptake measurements. FTIR of exhaust and emission spectra of discharges show oxygen-containing species known for their ability to stimulate biochemical processes and deactivate pathogenic microorganisms. In addition, water gas, CO2, CO and molecules containing −C(CH3)3− moieties observed in FTIR spectra of the exhaust gas during plasma treatment may be partly responsible for the plasma chemical etching of seed surface through oxidizing the organic components of the seed coat.
Highlights
Crop yield is highly dependent on three aspects of seed quality, namely seed germination, vigour and size, which affect crop yield through indirect effects, e.g. percentage and time from sowing to emergence, and plant population density, spatial arrangement, and crop duration, as well as direct effects, such as subsequent plant performance[1]
Despite a rich assortment of experimental evidence that shows improved seed germination and effective deactivation and removal of surface-residing pathogenic fungi and bacteria, further investigation into the mechanisms of plasma–seed surface interactions is warranted to enable the translation of these advances into agricultural practice
Using Fourier Transform Infrared (FTIR) spectroscopy of seed surfaces and plasma exhaust and emission spectroscopy of discharges, this study provides an insight into the nature of chemical interactions that take place in plasmas generated in the presence of seeds, including the evolution of species as a result of plasma–surface interactions
Summary
Crop yield is highly dependent on three aspects of seed quality, namely seed germination, vigour and size, which affect crop yield through indirect effects, e.g. percentage and time from sowing to emergence, and plant population density, spatial arrangement, and crop duration, as well as direct effects, such as subsequent plant performance[1]. Significant effort has gone into the development of physical and chemical methods to break seed dormancy, enhance seed germination parameters, and improve disease resistance in seeds and the plants they produce Chemical methods, such as those that rely on the use of fungicides or hormones, have been shown to be highly effective, yet they carry significant environmental risks. Species (ROS) and reactive nitrogen species (RNS) noted for their catalytic activity and biological significance, highly-energetic electrons, electromagnetic radiation and thermal effects, which individually and synergistically affect the treated target[24, 25] In agriculture, these effects have been exploited to induce stress and selectively stimulate seed germination[22, 26], decontaminate seed surfaces[3], improve seed disease resistance[27], and enhance biochemical processes associated with higher crop yields[5]. High-performance cotton seeds were treated with dielectric barrier discharge (DBD) plasma in a needle−plate configuration at atmospheric pressure
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