The role of leaf senescence in relation to nitrogen uptake and translocation to the reproductive plant organs for genotypic differences in nitrogen efficiency of rapeseed
Final Report Abstract
Decreasing the high nitrogen (N) balance surpluses in winter oilseed-rape production requires the breeding and cultivation of N-efficient cultivars. The overall objective of the project was the clarification of the role of leaf senescence and of N mobilization from leaves in grain yield formation of rapeseed genotypes at limited N supply (N efficiency). We hypothesized as follows: (i) Genotypic differences in N deficiency-induced leaf senescence at early vegetative stages are representative for stay-green during the reproductive growth stage. (ii) Delayed leaf senescence is mainly governed by root growth and activity, particularly an enhanced cytokinin production as the main root signal. (iii) Genotypic differences in initiation of leaf senescence are N deficiency-specific and due to leaf-inherent factors such as differences in the sensing of the plant N status in the leaf and/or inhibition of the degradation of N compounds. (iv) The main effects of delayed leaf senescence on reproductive yield are higher photosynthetic productivity of the leaves and longer duration of N translocation to the reproductive organs. The main conclusions drawn from the results of different experimental approaches in close cooperation with members of FOR948 and published in peer-reviewed scientific journals are: (i) N efficiency of oilseed rape line, but not of hybrid cultivars was related to higher N uptake during reproductive growth and delayed leaf senescence (functional stay-green); SPAD of individual leaves, percentage of green leaves and canopy light interception were suitable to characterize the senescence status of the plant under field conditions; the cultivar-specific early or late senescence trait can be mimicked by N starvation in hydroponics; the superior N efficiency of hybrids compared to line cultivars was not related to stay-green but rather to a high biomass production and thus higher N uptake during vegetative growth and a high N utilization efficiency. (ii) A reciprocal grafting of early and late senescing line cultivars showed that the cultivar differences in N starvation-induced leaf senescence are governed by leaf-inherent factors; phytohormone analysis and the expression of genes suggest that during the progression of N starvation-induced leaf senescence the homeostasis of biologically active cytokinins (CKs) in the leaf tissue is of major importance. (iii) Micro-array profiling of the transcriptome of N starvation-, shading- and detaching-induced leaf senescence revealed that the cysteine protease SAG12-1 is not a very sensitive and specific marker for N starvation-induced leaf senescence; N starvation induced a specific leaf-senescence programme after four days of stress; the genes ANAC029, ANS, DRL1, UPS5, AMT1;4 and SPSA1 were specific for N starvation-induced leaf senescence and suitable for the detection of cultivar differences shortly after induction. (iv) Remobilization of N particularly from stems and leaves was more important for pod N accumulation than N uptake after full flowering; not leaves (low N concentrations and biomass) but pod walls (high N concentrations) and stems (high biomass) mainly contributed to the crop-residue N at maturity; in-vitro culture of pods suggested a high nitrate-N requirement for growth of individual pods; however, in-situ (pot and field experiments) growth of individual pods and seed development appeared not to be N-limited under N deficiency. Taken together, it is concluded that genotypic N efficiency may contribute to reduce the crop-inherent high N budget surplus of winter oilseed-rape. This requires in particular increasing the low N remobilization efficiency of pod-wall N to the grains by increasing the protein content of seeds without compromising the oil yield by plant breeding.
Publications
- (2011): Agronomic traits contributing to nitrogen efficiency of winter oilseed rape cultivars. Field Crops Res. 124: 114–123
Schulte auf’m Erley G., Behrens T., Ulas A., Wiesler F., Horst W.J.
(See online at https://doi.org/10.1016/j.fcr.2011.06.009) - (2012) Root-growth characteristics contributing to genotypic variation in nitrogen efficiency of oilseed rape (Brassica napus L.). J. Plant Nutr. Soil Sci. 175: 489-498
Ulas A., Schulte auf´m Erley G., Kahm M., Wiesler F., Horst W.J.
(See online at https://doi.org/10.1002/jpln.201100301) - (2013): Does genotypic variation in nitrogen remobilisation efficiency contribute to nitrogen efficiency of winter oilseed-rape cultivars (Brassica napus L.)? Plant Soil 371: 463-471
Ulas A., Behrens T., Wiesler F., Horst, W.J., Schulte auf’m Erley G.
(See online at https://doi.org/10.1007/s11104-013-1688-y) - (2014): The superior nitrogen efficiency of winter oilseed rape (Brassica napus L.) hybrids is not related to delayed nitrogen starvation-induced leaf senescence. Plant Soil 384: 347-362
Koeslin-Findeklee F., Meyer A., Girke A., Beckmann K., Horst W.J.
(See online at https://doi.org/10.1007/s11104-014-2212-) - (2015) Transcriptomic analysis of nitrogen starvation and cultivar-specific leaf senescence in winter oilseed rape (Brassica napus L.). Plant Sci. 233: 174-185
Koeslin-Findeklee F., Rizi V.S., Becker M.A., Parra-Londono S., Arif M., Balazadeh S., Mueller- Roeber, S., Kunze, R., Horst, W.J.
(See online at https://doi.org/10.1016/j.plantsci.2014.11.018) - (2015): Contribution of nitrogen uptake and retranslocation during reproductive growth to the nitrogen efficiency of winter oilseed-rape cultivars (Brassica napus L.) differing in leaf senescence. Agronomy
Koeslin-Findeklee F., Horst W.J.
(See online at https://doi.org/10.3390/agronomy6010001) - (2015): Defoliation affects seed yield but not N uptake and growth rate in two oilseed rape cultivars differing in post-flowering N uptake. Field Crops Res. 179: 1-5
Ulas A, Behrens T., Wiesler F., Horst W.J., Schulte auf’m Erley G.
(See online at https://doi.org/10.1016/j.fcr.2015.04.005) - (2015): Differences between winter oilseed-rape (Brassica napus L.) cultivars in nitrogen starvation-induced leaf senescence are governed by leaf-inherent rather than root-derived signals. J. Exp. Bot. 66: 3669–3681
Koeslin-Findeklee F., Becker M.A., Van der Graaff E., Roitsch T., Horst W.J.
(See online at https://doi.org/10.1093/jxb/erv170)
