Hormetic effects of low-dose gamma rays in soybean seeds and seedlings: A detection technique using optical sensors

The use of radiation technology in agriculture has increased remarkably in recent years. The stimulating effect of low-dose gamma rays, known as hormesis, improves the adaptive response of living organisms to more severe challenges. Different areas of agriculture such as plant physiology, crop breeding and seed biology demand accurate methods for real-time diagnosis of the ionizing radiation effect on biological systems. However, traditional measures are still calculated from slow, laborious and destructive techniques, which depend on human vision. Here, we present two robust optical sensors based on multispectral and fluorescence imaging approaches for rapid and non-destructive detection of the hormetic effects of low-dose gamma radiation in soybean seeds and seedings. Multispectral images were acquired from seeds treated with gamma radiation (0, 12, 16 and 20 Gy), and the reflectance, autofluorescence, texture and color features were extracted from images. Next, a chlorophyll fluorescence-based technique was applied to measure the minimal level of fluorescence (F-0), maximum fluorescence (F-M), average chlorophyll a fluorescence and quantum yield of photosystem II (F-V/F-M) in seedlings grown from irradiated and non-irradiated seeds. Using a reflectance technology, the seedlings were also evaluated for anthocyanin, chlorophyll a and normalized difference vegetation index (NDVI). Results showed that multispectral and fluorescence-based techniques provide useful information on the hormetic effects of gamma rays in soybean seeds and seedlings, which are invisible to the naked eye. Our findings provide a better understanding of the link between spectral and fluorescence parameters and the hormetic effect of low-dose gamma rays. From a practical point of view, such optical sensors can provide markers for fast, non-destructive and reliable identification of the best gamma-ray doses to stimulate soybean growth parameters. However, we strongly support in-depth studies of the dose-response relationship in seeds with different initial physiological potential from different soybean genotypes. (AU)