Staining with 0.05% neutral red reduces nutrient uptake by wheat roots

Abstract

A number of studies have used a 0.05% solution of neutral red to stain live roots so that short term root growth could be measured. These studies, which used a 5 or 10 min staining time, report no effects of the stain on plant properties such as growth, respiration, or nitrate uptake. This paper reports on two experiments conducted to determine whether this staining technique, with a 15 min stain time, affected macronutrient uptake of 6- and 7-week-old wheat (Triticum aestivum L.) plants grown in solution culture. The results showed that, compared with unstained controls, staining plants with 0.05% neutral red halted or halved nitrate uptake measured over a 4 h period the following day. Potassium uptake was also significantly reduced by staining. In the experiment with smaller plants nutrient uptake rate recovered 5 days after staining, but not in the second experiment with larger plants. Stained roots were 19% narrower than unstained roots, suggesting that the stain affected the root structure. We do not recommend the use of 0.05% neutral red staining, for wheat at least, in experiments where accurate measurement of nutrient uptake rate is important.

Keywords: 3-Amino-7-dimethylamino-2-methylphenazine hydrochloride; Dye; Nitrate uptake; Potassium uptake; Root diameter; Vital stain.