Abstract
Analyzing root exudates during drought poses a serious challenge; sampling root exudates in soil is destructive to roots and leads to biased molecular analysis, along with microbial decomposition and exudate sorption to soil components. Hydroponic approaches are useful to overcome these problems but lack the utility to induce drought. Nondestructive sampling techniques are thus needed to analyze root exudates from the same plants over time in combination with highly controlled variable water/nutrient stress. The proposed aeroponic approach demonstrated that cotton could be grown to maturity in the aeroponic system, then a progressive drought treatment applied while simultaneously collecting root exudates from the same plants over time. Treatments of varying irrigation rates consisted of well-watered cotton (control) that was compared to cotton given progressive water stress (drought) and subsequent drought recovery for two weeks. Plants were entering flowering as drought treatment was applied. Nondestructive morphological measurements of plant productivity were made. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was employed to analyze the molecular profile of exudates, whereas gas chromatography-mass spectroscopy (GC-MS) was used to quantify abscisic acid (ABA). Plant development was highly responsive to reduced irrigation intervals with decreased canopy height, number of green leaves, biomass, and water content. As revealed by FT-ICR MS, the complexity and connectivity of unique biochemical transformation networks in response to drought was greatest at 9 days after treatment, where severe visual symptoms were observed. Overall, the aeroponic approach is a promising technology to simulate drought while sampling root exudates nondestructively, advancing root system research and plant-stress response mechanisms.