Can We Use Gene Expression to Determine Nitrogen Sufficiency in Potatoes?.

A number of optical and chemical methods can be used to assess potato N sufficiency, as an aide to improved fertilizer N management. As a first step in evaluating the feasibility of using gene expression to assess potato N sufficiency, we determined potato plant response to nitrate deficiency at an early vegetative growth stage under greenhouse conditions. Three potato cultivars (Shepody, Russet Norkotah, and Red Pontiac) were grown with abundant (7.5 mM NO₃), limited (0.75 mM NO₃) or deficient (0 mM NO₃) nitrate supply in nutrient culture over a 7 d period. RNA was extracted from the last fully expanded leaf and quantified using realtime RT-qPCR. Shoot dry weight, petiole nitrate concentration and leaf chlorophyll concentration measured using a SPAD-502 meter were also determined  Reduced nitrate supply had no measurable effect on shoot dry weight or leaf chlorophyll concentration, but decreased petiole nitrate concentration. Under deficit nitrate supply, down-regulation of nitrate reductase and nitrite reductase were measured within three days for all cultivars, and down-regulation of asparagine synthetase was measured in two cultivars. Nitrate supply had no effect on expression of ammonium transporter. This experiment demonstrates the potential to use gene expression to detect reduced nitrate supply in potato plants.