Polyethylene Glycol (PEG) Application Triggers Plant Dehydration but Does Not Accurately Simulate Drought.

Polyethylene glycol (PEG), especially at high molecular weights, is highly soluble in water, and these solutions have reduced water potential. It is convenient to use PEG in hydroponics (liquid nutrient solution) for experiments with plants. However, some authors have been found to describe the application of PEG to plants incorrectly, such as drought, dehydration, osmotic, or water stresses, which can mislead readers. The presented opinion paper shows our arguments for a terminology in such experiments that is strictly limited to 'PEG-induced' or 'simulated' or 'mimicked' dehydration, and osmotic or water stresses, with the best option being 'PEG-induced dehydration'. The most popular term, 'drought', is inappropriate to be used for hydroponics at all, with or without PEG. Traditionally, drought stress study was related to only plants in soil or other substrates mixed with soil. Based on 139 published papers, the examples presented in our opinion paper can demonstrate differences in gene expression between plants grown in containers with soil and under PEG-induced stress in hydroponics. Researchers can carry out any type of experiments suitable for the purposes of their study. However, clear and correct description of experiments and careful interpretation of the results are strongly required, especially with PEG, to avoid incorrect information. In all cases, at the final stage, results of experiments in controlled conditions have to be verified in field trials with naturally occurring drought.