Monitoring Plant Drought Stress Response Using Terahertz Time-Domain Spectroscopy  

Abstract

We present a novel measurement setup for monitoring changes in leaf water status using nondestructive terahertz time-domain spectroscopy (THz-TDS). Previous studies on a variety of plants showed the principal applicability of THz-TDS. In such setups, decreasing leaf water content directly correlates with increasing THz transmission. Our new system allows for continuous, nondestructive monitoring of the water status of multiple individual plants each at the same constant leaf position. It overcomes previous drawbacks, which were mainly due to the necessity of relocating the plants. Using needles of silver fir (Abies alba) seedlings as test subjects, we show that the transmission varies along the main axis of a single needle due to a variation in thickness. Therefore, the relocation of plants during the measuring period, which was necessary in the previous THz-TDS setups, should be avoided. Furthermore, we show a highly significant correlation between gravimetric water content and respective THz transmission. By monitoring the relative change in transmission, we were able to narrow down the permanent wilting point of the seedlings. Thus, we established groups of plants with well-defined levels of water stress that could not be detected visually. This opens up the possibility for a broad range of genetic and physiological experiments.

Distinguishing Gasoline Engine Oils of Different Viscosities Using Terahertz Time-Domain Spectroscopy

“…This includes gases [44][45], liquids [46], liquid crystals [47][48], and different types of solids [49][50][51][52][53]. But also artwork [54] and plants [55][56] have been investigated by THz-TDS.…”

ABA-regulation of root hydraulic conductivity and aquaporin gene- expression is crucial to the plant shoot rise caused by rhizosphere humic acids

“…The Terahertz (THz) Imaging-System Analysis has been used in medical applications (Pickwell-MacPherson and Wallace, 2009;Smith and Arnold, 2011) and more recently, water content determination in leaves (Castro-Camus et al, 2013;Born et al, 2014;Gente and Koch, 2015). Water has a typical resonance that can be measured when it is applied at a frequency between 0.14 and 0.22 THz.…”

Using Terahertz Time-Domain Spectroscopy to Discriminate among Water Contamination Levels in Diesel Engine Oil

“…THz technology is a rapidly expanding field (Jepsen et al, 2011), and several agricultural applications have been identified, including measuring plant drought stress (Born et al, 2014) and leaf dehydration (Castro-Camus et al, 2013), estimating aflatoxin in peanut oil (Chen and Xie, 2014), and other applications summarized by Mathanker et al (2013). Various methods (Tonouchi, 2007) have been developed to generate and detect THz waves, but THz timedomain spectroscopy (THz-TDS) (Vieweg et al, 2014;Withayachumnankul and Naftaly, 2014) is considered the most powerful and widely used scheme.…”

“…THz-TDS uses ultrashort laser pulses and photoconductive antennas (Hunsche et al, 1998;Moreno et al, 2014;Tani et al, 1997) or nonlinear crystals (Moreno et al, 2014). THz-TDS has been used to characterize solids (Jiang et al, 2014;LloydHughes et al, 2006;Misochko et al, 1998;Nickel et al, 2014;Wietzke et al, 2011), liquids (Wang et al, 2014), liquid crystals (Reuter et al, 2013;Vieweg et al, 2010), gases (Harde et al, 1995;Mittleman et al, 1998), and plants (Born et al, 2014;Castro-Camus et al, 2013).…”