Post-flowering nitrogen uptake leads to the genotypic variation in seed nitrogen accumulation of oilseed rape

Citation

Guo, X., Nan, Y., He, H., Ma, B.L., McLaughlin, N.B., Wu, X., Chen, B., Gao, Y. (2021). Post-flowering nitrogen uptake leads to the genotypic variation in seed nitrogen accumulation of oilseed rape. Plant and Soil, [online] 461(1-2), 281-294. http://dx.doi.org/10.1007/s11104-020-04815-7

Plain language summary

During the past 40 years, plant breeding programs have resulted in dramatic increases in oilseed rape (Brassica napus L.) yield with a reduced seed nitrogen (N) or protein concentration, although both of them are the dominant determinants of the economic value of the harvested product. Due to the strong negative genetic relationship between these two traits, it is difficult to improve yield and seed N concentration simultaneously. Previous studies have demonstrated that increasing post-flowering N uptake is likely to increase seed N concentration without decreasing yield, and thus will help breeders to break the negative relationship between yield and seed N concentration. However, the relative contribution of post-flowering uptake N to grain N depends not only on growing environment, but also to some extent on the plant characteristics, such as timing of plant senescence after flowering. Plant senescence is a developmental process needed for the redistribution of plant resources, which is regulated by programmed cell death. Previous studies suggested that post-flowering N uptake was responsible for the variation in nitrogen use efficiency (NUE) of oilseed rape genotypes, which provides strong incentive for investing more effort in enhancing post-flowering related traits to improve the NUE of oilseed rape.

In this research, we hypothesized that for oilseed rape: (i) high N utilization efficient (NUtE) genotypes display distinct root traits that are responsible for N uptake at post-flowering, leading to greater grain N accumulation, (ii) root senescence is negatively affected post-flowering N uptake, and (iii) high NUtE genotypes maintain stay-green phenotype for a longer period of time after flowering providing energy to support post-flowering N uptake, resulting in greater yield and NUE. The specific objectives of the present study were to: (i) unravel the effect of post-flowering root traits on grain N accumulation, (ii) assess the relationship between root senescence and post-flowering N uptake, and (iii) elucidate the contribution of post-flowering N uptake to stay-green phenotype.

We documented the genotypic variation in grain N accumulation resulting from the differences in post-flowering root N uptake. Our results suggest that breeding genotypes with higher grain N accumulation could be achieved through increasing post-flowering root indices, such as root morphological parameters, N metabolic enzyme activity, RNA transcription level and antioxidant enzyme activity. The higher grain N accumulation led to enhanced harvest index and nitrogen harvest index, and ultimately greater seed yield and NUE. It is proposed that the high N utilization efficient genotype could be considered as the ideotype for concurrent improvements in NUE and yield to achieve the dual goals of reducing N loading to the environment and boosting seed yield to meet the increasing food demand from a predicted world population growth.

Abstract

Aims: Increasing post-flowering nitrogen (N) uptake is likely to improve seed N accumulation, ultimately leading to greater seed yield and N use efficiency (NUE). Methods: A comprehensive study on contrasting N utilization efficiency (NUtE) winter oilseed rape genotypes was conducted for three years (2017–2020) to unravel the effect of post-flowering N uptake on seed N accumulation. Results: Compared to the low NUtE genotype, the high NUtE genotype displayed respectively 31%, 28% and 70% greater root biomass, length and volume, along with 40%, 44%, 46% and 82% higher root nitrate reductase (NR), glutamine synthetase (GS), glutamate synthetase (GOGAT), and glutamate dehydrogenase (GDH) activities after flowering. These were accompanied by a significant increase (P < 0.05) in catalases (134%), peroxidase (45%), glutathione (45%) and ascorbate peroxidase (41%), leading to 27% higher seed N accumulation, 23% higher seed yield and 60% higher NUE. Conclusions: Stronger post-flowering N uptake potential for high NUtE genotype was a main contributor to the enhanced seed N accumulation, and ultimately increased seed yield and NUE.

Publication date

2021-04-01

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