THz and Agronomy

The Multilayer Structure of Sunflower Leaves Revealed by Terahertz Waves

To explore the multilayer structure of leaves, a new non-contact, non-invasive analytical method based on pulsed terahertz spectroscopy was developed. This innovative technique allows, for the first time, in-depth observation of the multilayer structure of the leaf blade (the sunflower in this study). Combined with computational codes, it makes it possible to determine, for a given genotype, the number of layers comprising the leaf blade, as well as their respective thicknesses, refractive indices, and absorption coefficients—with the refractive index and absorption coefficient being associated with the layer’s composition. This technique also makes it possible to track changes in these parameters over time, particularly when plants are subjected to controlled environmental conditions.

Sunflower leaves analyzed using pulsed terahertz spectroscopy.		Parameters obtained for the 8-layer structure of a sunflower leaf: thicknesses, real (n) and complex (k) indices

Y. Abautret, D. Coquillat, M. Zerrad, et al. Terahertz probing of the multilayer organization of sunflower leaves. OPTICS EXPRESS 28, 35018–35037 (2020).
 

Monitoring a Plant's Response to Water Stress Using Imaging and Terahertz Spectroscopy

Environmental stresses (drought, salinity, and possibly low temperatures) affect plant growth and yield, and southern France is among the regions of the world where, for example, there is a risk of severe drought with adverse consequences for agriculture. Plants respond to stress at the cellular and molecular levels; for example, they experience significant water loss at the cellular level. Current methods for studying these responses have various drawbacks, particularly because they are destructive or alter plant organs. The THz frequency range can be used for non-contact monitoring of stress at the cellular and morphological levels and holds promise for yielding interesting results at the molecular level.

Visible images (left) and 300 GHz images (right)		Fig Leaf in Transmission at 0.65 THz

      To improve plants’ tolerance to environmental stresses, transgenic plants have been developed around the world. However, the potential risks associated with transgenic plants remain unclear. To detect the presence and quantities of transgenic plants, reliable, sensitive, and ideally non-destructive methods are urgently needed. Very recent studies using THz spectroscopy, combined with chemometric analysis techniques (most of which were published in 2016), have demonstrated the ability to distinguish transgenic plants using these new techniques (seeds, proteins, etc.). Furthermore, these new techniques are expected to provide information on differences in chemical composition between transgenic and conventional plants.