Comparing nitrate storage and remobilization in two rice cultivars that differ in their nitrogen use efficiency

Abstract

Soil nitrogen (N) is available to rice crops as either nitrate or ammonium, but only nitrate can be accrued in cells and so factors that influence its storage and remobilization are important for N use efficiency (NUE). The hypothesis that the ability of rice crops to remobilize N storage pools is an indicator of NUE was tested. When two commonly grown Chinese rice cultivars, Nong Ken (NK) and Yang Dao (YD), were compared in soil and hydroponics, YD had significantly greater NUE for biomass production. The ability of each cultivar to remobilize nitrate storage pools 24 h after N supply withdrawal was compared. Although microelectrode measurements of the epidermal subcellular nitrate pools in leaves and roots showed similar patterns of vacuolar remobilization in both cultivars, whole-tissue analysis showed very little depletion of storage pools after 24 h. However, leaf epidermal cell cytosolic nitrate activities were significantly higher in YD when compared with NK. Before N starvation and growing in 10 mM nitrate, the xylem nitrate activity in YD was lower than that of NK. After 24 h of N starvation the xylem nitrate had decreased more in YD than in NK. Tissue analysis of stems showed that YD had accumulated significantly more nitrate than NK, and the remobilization pattern suggested that this store is important for both cultivars. Changes in nitrate reductase activity (NRA) and expression were measured. Growing in 10 mM nitrate, NRA was undetectable in roots of both cultivars, and the leaf total NRA of equivalent leaves was similar in NK and YD. When the N supply was withdrawn, after 24 h NRA in NK was reduced to 80% but no decrease was found in YD. The proportion of NRA in an active form in YD was significantly higher than that in NK under both nitrate supply and deprivation conditions. Checking NR gene expression showed that leaf expression of OsNia1 was faster to respond to nitrate deprivation than OsNia2 in both cultivars. These measurements are discussed in relation to cultivar differences and physiological markers for NUE in rice.

Nitrogen Use Efficiency Is Mediated by Vacuolar Nitrate Sequestration Capacity in Roots of Brassica napus

“…NR activity was measured by the modified method of Fan et al (2007). Fresh samples (0.5 g) were frozen in liquid N 2 , ground into powder in the presence of acid-washed sand and homogenized with 4 mL of extraction buffer (0.025mol L -1 phosphate buffer, pH 8.7, 1.211g L 21 Cys, 0.372g L 21 EDTA).…”

“…Fresh samples (0.5 g) were frozen in liquid N 2 , ground into powder in the presence of acid-washed sand and homogenized with 4 mL of extraction buffer (0.025mol L -1 phosphate buffer, pH 8.7, 1.211g L 21 Cys, 0.372g L 21 EDTA). Homogenates were centrifuged at 30,000 g for 15 min at 4°C, and the supernatants were treated with sulfanilamide and a-naphthylamine reagents for colorimetric (540 nm) determination of nitrite as described by Fan et al (2007).…”

“…Although vacuoles compartment excess NO 3 2 that accumulates in plant cells (Granstedt and Huffaker, 1982;Krebs et al, 2010), neither NO 3 2 inducible NR genes (NIA1 and NIA2; Fan et al, 2007;Han et al, 2015a) nor the NO 3 2 long-distance transport gene NRT1.5 (Lin et al, 2008) are regulated by vacuolar NO 3 2 , even though they are essential for NO 3 2 assimilation. Only NO 3 2 transported from the vacuole to the cytosol can play a role in regulating NO 3 2 inducible genes.…”

Towards an understanding of the high productivity of rice with System of Rice Intensification (SRI) management from the perspectives of soil and plant physiological processes

“…This suggested that once taken up, NO 3 in the vegetative stage could contribute to the photosynthesis of the following growth stage. Recently, some supporting results for this phenomenon have been reported by Fan et al (2007). They measured leaf nitrate reductase activity (NRA) by nitrate withdrawal from the culture solution by using rice varieties with different NUE.…”

“…Varietal differences exist in NO 3 uptake (Luo et al 1993;Yang et al 1999;Duan et al 2006Duan et al , 2007aDuan et al , 2007bFan et al 2007;Senoo et al 2007). Similarly, there is a varietal difference in NRA, e.g., indica has higher activity than japonica (Barlaan and Ichii 1996).…”