Plasma glows and shifting water flows: Measuring the changes to water transport phenomena in seeds after plasma treatment

Abstract

Plasma discharges have been used as a treatment for seeds for a variety of food, horticultural and agricultural applications. It has generally been reported that plasma exposure increases the seed's water wettability, with some studies reporting increased water imbibition by seeds. It is speculated that increased water imbibition after plasma treatment is related to increased germination especially for food crops, yet there is little mechanistic understanding of why this may be so. Moreover, it is not well understood why plasma affects different plant species' seed in different ways. In this study, the objective was to develop a mechanistic understanding of how plasma exposure influences water transport in seeds/grains from different plant species. We exposed seeds to plasma and then analysed water absorption curves using modelling to extract thermodynamic constants related to the kinetics of water transport. The resulting quantitative data provided a clear understanding how plasma treatments increased the rate and amount of water uptake. We also discovered that with increasing plasma exposure, the rates at which water enters the seed changes depending on diffusional and capillary pathways. These insights help to explain why different seeds respond to plasma exposure in a variety of ways. Conclusions from water modelling studies were consistent with observed changes from microscopy and dye imbibition assays. This approach to analysing quantitative water transport phenomena after plasma exposure provides a method to mechanistically understand how plasma affects water imbibition in seeds with differing physiology. We discuss the relevance to food applications, and we believe results will be relevant to future studies of how to best apply plasma treatments to increase germination for food crops.