Molybdenum supply increases root system growth of winter wheat by enhancing nitric oxide accumulation and expression of NRT genes

Abstract

Increasing evidence shows that root system growth is strongly affected by different nitrogen (N) signals and the available N source in the rhizosphere. Molybdenum (Mo), an essential trace element, plays a key role in N assimilation and metabolism. However, Mo efficacy may vary with different N sources. The present experiment was performed to examine the Mo role on root system growth in winter wheat under different N sources. A hydroponic experiment was conducted consisting of two winter wheat cultivars; Mo-efficient (97003) and Mo-inefficient (97014) under two Mo levels (0 and 1 μM) and three N sources (NO3−, NH4NO3 or NH4+). The results showed that Mo supply increased root dry weight and other morphological traits, nitrate reductase (NR) activities, nitric oxide (NO) contents, total N concentration and the expressions of nitrate transporter (NRT) genes under various N sources, however, such effects were in the order of NH4NO3 > NO3− > NH4+, suggesting that Mo fertilizer shows more complementary effects towards NO3− form of N than sole NH4+ in winter wheat. These findings imply that Mo plays a significant role in increasing the root system growth of wheat through NO production, efficient N uptake and assimilation, and regulation of NRT gene expressions, especially under NH4NO3 nutrition.