Nitrate induction of root hydraulic conductivity in maize is not correlated with aquaporin expression

Abstract

Some plant species can increase the mass flow of water from the soil to the root surface in response to the appearance of nitrate in the rhizosphere by increasing root hydraulic conductivity. Such behavior can be seen as a powerful strategy to facilitate the uptake of nitrate in the patchy and dynamically changing soil environment. Despite the significance of such behavior, little is known about the dynamics and mechanism of this phenomenon. Here we examine root hydraulic response of nitrate starved Zea mays (L.) plants after a sudden exposure to 5 mM NO(3)(-) solution. In all cases the treatment resulted in a significant increase in pressure-induced (pressure gradient approximately 0.2 MPa) flow across the root system by approximately 50% within 4 h. Changes in osmotic gradient across the root were approximately 0.016 MPa (or 8.5%) and thus the results could only be explained by a true change in root hydraulic conductance. Anoxia treatment significantly reduced the effect of nitrate on xylem root hydraulic conductivity indicating an important role for aquaporins in this process. Despite a 1 h delay in the hydraulic response to nitrate treatment, we did not detect any change in the expression of six ZmPIP1 and seven ZmPIP2 genes, strongly suggesting that NO(3)(-) ions regulate root hydraulics at the protein level. Treatments with sodium tungstate (nitrate reductase inhibitor) aimed at resolving the information pathway regulating root hydraulic properties resulted in unexpected findings. Although this treatment blocked nitrate reductase activity and eliminated the nitrate-induced hydraulic response, it also produced changes in gene expression and nitrate uptake levels, precluding us from suggesting that nitrate acts on root hydraulic properties via the products of nitrate reductase.

Effect of Nitrogen and Irrigation Application on Water Movement and Nitrogen Transport for a Wheat Crop under Drip Irrigation in the North China Plain

“…In our study, deep percolation increased with increasing irrigation level, but decreased with increasing N application level under drip irrigation (Tables 4 and 5), which was similar to the results of Behera and Panda (2009) [42]. The reason for this may be because the soil water and N level affected the growth and amount of roots [47,48]. However, in our study, it was still found that the deep percolation for winter wheat in the NCP was stable at the range of water level from 0.5 E to 0.8 E for drip irrigation.…”

“…Additionally, for the W1 and W2 irrigation schedules, no significant decrease in deep percolation losses were found between N application rates of N120-N140 or N190-N290. This was mainly because root growth rate was mainly affected by soil water level and water flow could be enhanced only to roots exposed to high NO3-levels [48]. The deep percolation was noticeably higher in 2012 than in 2013 under all treatments, possibly because of the higher precipitation in early growing season of 2012 (Table 1), when the roots of winter wheat were still fewer.…”

Nitrate Control of Root Hydraulic Properties in Plants: Translating Local Information to Whole Plant Response

“…It is worth noting that the response is nitrate specific because treatment with different salts (Fig. 1) or other forms of nitrogen (Gorska et al, 2008) did not elicit a hydraulic response.…”

Plant Hydraulic Conductivity: The Aquaporins Contribution

“…Concerning nutrient supply or excess, Adler et al (1996) were among the first to suggest that lower Lp r under NH 4+ supply was due to an effect on aquaporin activity. In addition, the excess of nutrients such as of K + and Ca + produced a toxic effect on L 0 in agreement with aquaporin functionality in pepper plants (Capsicum annuum L.) (Cabañero & Carvajal, 2007) while NO 3 -induction of root Lp r in maize was not correlated with aquaporin expression (Gorska et al, 2008).…”