A simple method for the evaluation of respiration activity of root cells of intact plants grown hydroponically and/or in agar medium was developed. The novelty of the present method is based on visual detection of dehydrogenase activity of plant roots by use of tetrazolium violet dye without destructive steps, allowing follow up of living and photosynthetically active growing plants and the impact of inhibitors such as sodium azide and cycloheximide. The results of this approach demonstrated that root tip cells comprise the highest dehydrogenase activity compared to other root parts. The non-expensive assay is easy to perform and allows to experiment a large variety of chemical compounds with potential inhibitory characteristics for plants.