Identification and characterization of improved nitrogen efficiency in interspecific hybridized new-type Brassica napus

Abstract

Background and aims: Oilseed rape (Brassica napus) is an important oil crop worldwide. The aim of this study was to identify the variation in nitrogen (N) efficiency of new-type B. napus (genome A(r)A(r)C(c)C(c)) genotypes, and to characterize some critical physiological and molecular mechanisms in response to N limitation.

Methods: Two genotypes with contrasting N efficiency (D4-15 and D1-1) were identified from 150 new-type B. napus lines, and hydroponic and pot experiments were conducted. Root morphology, plant biomass, N uptake parameters and seed yield of D4-15 and D1-1 were investigated. Two traditional B. napus (genome A(n)A(n)C(n)C(n)) genotypes, QY10 and NY7, were also cultivated. Introgression of exotic genomic components in D4-15 and D1-1 was evaluated with molecular markers.

Key results: Large genetic variation existed among traits contributing to the N efficiency of new-type B. napus. Under low N levels at the seedling stage, the N-efficient new-type D4-15 showed higher values than the N-inefficient D1-1 line and the traditional B. napus QY10 and NY7 genotypes with respect to several traits, including root and shoot biomass, root morphology, N accumulation, N utilization efficiency (NutE), N uptake efficiency (NupE), activities of nitrate reductase (NR) and glutamine synthetase (GS), and expression levels of N transporter genes and genes that are involved in N assimilation. Higher yield was produced by the N-efficient D4-15 line compared with the N-inefficient D1-1 at maturity. More exotic genome components were introgressed into the genome of D4-15 (64·97 %) compared with D1-1 (32·23 %).

Conclusions: The N-efficient new-type B. napus identified in this research had higher N efficiency (and tolerance to low-N stress) than traditional B. napus cultivars, and thus could have important potential for use in breeding N-efficient B. napus cultivars in the field.

Keywords: 15NH4+; 15NO3− uptake; Brassica napus; New-type; character traits; gene expression; genetic variation; glutamine synthetase; interspecific hybridization; nitrate reductase; nitrogen efficiency; nitrogen transporter.

Fig. 1.

(A) Shoot dry weight, (B) root dry weight and (C) relative shoot or root dry weight of D4-15, D1-1 and NY7 under two N conditions. High-N: plants were grown in 3·0 mm NH₄NO₃ solution for 23 d. Low-N: plants were grown in 3·0 mm NH₄NO₃ solution for 15 d and then were transferred to 0·15 mm NH₄NO₃ solution for 8 d. Different letters indicate significant differences (P < 0·05).

Fig. 2.

¹⁵N (¹⁵NH₄⁺ and ¹⁵NO₃⁻) accumulation in the two genotypes. Plants were grown in HN solution (3·0 mm NH₄NO₃) for 15 d, followed by growth in LN solution (0·15 mm NH₄NO₃) for 8 d, and then transferred to stable isotope ¹⁵N solution with 3·0 mm ¹⁵NH₄NO₃ or 3·0 mm NH₄¹⁵NO₃. Shoots (A, C) and roots (B, D) were harvested at 3, 11 and 24 h after being grown in the ¹⁵N solution. *P < 0·05, **P < 0·01.

Fig. 3.

Activities of nitrate reductase (NR; A, B) and glutamine synthetase (GS; C, D) of leaf (A, C) and root (B, D) of D4-15 and D1-1 under both levels of N supply. High-N: plants were grown in 3·0 mM NH₄NO₃ solution for 23 d. Low-N: plants were grown in 3·0 mm NH₄NO₃ solution for 15 d and then were transferred to 0·15 mm NH₄NO₃ solution for 8 d. *P < 0·05, **P < 0·01.

Fig. 4.

Expression of BnAMT1;1 and NRT family member genes (BnNRT1;1, BnNRT2;2, BnNRT2;5, BnNRT2;6 and BnNRT2;7) in leaves and roots of D4-15 and D1-1 under both levels of N supply. High-N: plants were grown in 3·0 mm NH₄NO₃ solution for 23 d. Low-N: plants were grown in 3·0 mm NH₄NO₃ solution for 15 d and then were transferred to 0·15 mm NH₄NO₃ solution for 8 d. *P < 0·05, **P < 0·01.

Fig. 5.

Expression of glutamine synthetase (GS) family member genes (BnGln1;1, BnGln1;2, BnGln1;3, BnGln1;4, BnGln1;5 and BnGln2) in leaves and roots of D4-15 and D1-1 under both levels of N supply. High-N: plants were grown in 3·0 mm NH₄NO₃ solution for 23 d. Low-N: plants were grown in 3·0 mm NH₄NO₃ solution for 15 d and then were transferred to 0·15 mm NH₄NO₃ solution for 8 d. *P < 0·05, **P < 0·01.

Fig. 6.

Expression of nitrate reductase (NR) family member genes (BnNR1 and BnNR2) in leaves and roots of D4-15 and D1-1 under both levels of N supply. High-N: plants were grown in 3·0 mm NH₄NO₃ solution for 23 d. Low-N: plants were grown in 3·0 mm NH₄NO₃ solution for 15 d and then were transferred to 0·15 mm NH₄NO₃ solution for 8 d. *P < 0·05, **P < 0·01.