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The contrasting N management of two oilseed rape genotypes reveals the mechanisms of proteolysis associated with leaf N remobilization and the respective contributions of leaves and stems to N storage and remobilization during seed filling.

Girondé A, Etienne P, Trouverie J, Bouchereau A, Le Cahérec F, Leport L, Orsel M, Niogret MF, Nesi N, Carole D, Soulay F, Masclaux-Daubresse C, Avice JC - BMC Plant Biol. (2015)

Bottom Line: Oilseed rape is the third largest oleaginous crop in the world but requires high levels of N fertilizer of which only 50% is recovered in seeds.Nitrate restriction decreased seed yield and oil quality for both genotypes but Aviso had the best seed N filling.The results confirm the importance of foliar N remobilization after bolting to satisfy seed filling and highlight that an efficient proteolysis is mainly associated with (i) cysteine proteases and proteasome activities and (ii) a fine coordination between proteolysis and export mechanisms.

View Article: PubMed Central - PubMed

ABSTRACT

Background: Oilseed rape is the third largest oleaginous crop in the world but requires high levels of N fertilizer of which only 50% is recovered in seeds. This weak N use efficiency is associated with a low foliar N remobilization, leading to a significant return of N to the soil and a risk of pollution. Contrary to what is observed during senescence in the vegetative stages, N remobilization from stems and leaves is considered efficient during monocarpic senescence. However, the contribution of stems towards N management and the cellular mechanisms involved in foliar remobilization remain largely unknown. To reach this goal, the N fluxes at the whole plant level from bolting to mature seeds and the processes involved in leaf N remobilization and proteolysis were investigated in two contrasting genotypes (Aviso and Oase) cultivated under ample or restricted nitrate supply.

Results: During seed filling in both N conditions, Oase efficiently allocated the N from uptake to seeds while Aviso favoured a better N remobilization from stems and leaves towards seeds. Nitrate restriction decreased seed yield and oil quality for both genotypes but Aviso had the best seed N filling. Under N limitation, Aviso had a better N remobilization from leaves to stems before the onset of seed filling. Afterwards, the higher N remobilization from stems and leaves of Aviso led to a higher final N amount in seeds. This high leaf N remobilization is associated with a better degradation/export of insoluble proteins, oligopeptides, nitrate and/or ammonia. By using an original method based on the determination of Rubisco degradation in the presence of inhibitors of proteases, efficient proteolysis associated with cysteine proteases and proteasome activities was identified as the mechanism of N remobilization.

Conclusion: The results confirm the importance of foliar N remobilization after bolting to satisfy seed filling and highlight that an efficient proteolysis is mainly associated with (i) cysteine proteases and proteasome activities and (ii) a fine coordination between proteolysis and export mechanisms. In addition, the stem may act as transient storage organs in the case of an asynchronism between leaf N remobilization and N demand for seed filling.

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N fluxes in Aviso (A) and Oase (B) in LN conditions between D42 and D70. The plants were supplied with a low concentration of nitrate (LN, 0.375 mM of nitrate). D42 corresponds to pod formation and D70 to the start of seed filling. Fluxes of N from remobilization or uptake in the different organs are expressed as mg of N remobilized or taken up, respectively. A shaded box means that the organ was not present during these growing stages. For fluxes of N remobilization, the N amount is indicated with a minus sign (−) when N is remobilized from a source organ, or it is indicated with a plus sign (+) when remobilized N is redistributed towards a sink organ. Data are indicated as the mean value ± standard error. Asterisks represent significant differences between treatments and hashes represent significant differences between genotypes (n = 4 plants; p < 0.05).
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Fig5: N fluxes in Aviso (A) and Oase (B) in LN conditions between D42 and D70. The plants were supplied with a low concentration of nitrate (LN, 0.375 mM of nitrate). D42 corresponds to pod formation and D70 to the start of seed filling. Fluxes of N from remobilization or uptake in the different organs are expressed as mg of N remobilized or taken up, respectively. A shaded box means that the organ was not present during these growing stages. For fluxes of N remobilization, the N amount is indicated with a minus sign (−) when N is remobilized from a source organ, or it is indicated with a plus sign (+) when remobilized N is redistributed towards a sink organ. Data are indicated as the mean value ± standard error. Asterisks represent significant differences between treatments and hashes represent significant differences between genotypes (n = 4 plants; p < 0.05).

Mentions: Between D42 and D70, no N uptake was detectable and the total remobilized N amount decreased for both genotypes under N limitation (Figure 5) contrary to HN plants (Additional file 4). This was mainly related to lower contributions of leaves and pod walls, leading to a lower N redistribution to seeds. The N remobilization was 1.2-fold higher for Aviso than Oase (Figure 5), mainly due to a 2-fold higher N remobilization from leaves. Nevertheless, the N redistribution to seeds was not significantly different between the genotypes (144.73 mg N for Aviso and 127.75 mg N for Oase). These results can be explained by the fact that flowers and stems are sink organs for Aviso contrary to Oase, and a higher N loss by dead leaves occurs for Aviso.Figure 5


The contrasting N management of two oilseed rape genotypes reveals the mechanisms of proteolysis associated with leaf N remobilization and the respective contributions of leaves and stems to N storage and remobilization during seed filling.

Girondé A, Etienne P, Trouverie J, Bouchereau A, Le Cahérec F, Leport L, Orsel M, Niogret MF, Nesi N, Carole D, Soulay F, Masclaux-Daubresse C, Avice JC - BMC Plant Biol. (2015)

N fluxes in Aviso (A) and Oase (B) in LN conditions between D42 and D70. The plants were supplied with a low concentration of nitrate (LN, 0.375 mM of nitrate). D42 corresponds to pod formation and D70 to the start of seed filling. Fluxes of N from remobilization or uptake in the different organs are expressed as mg of N remobilized or taken up, respectively. A shaded box means that the organ was not present during these growing stages. For fluxes of N remobilization, the N amount is indicated with a minus sign (−) when N is remobilized from a source organ, or it is indicated with a plus sign (+) when remobilized N is redistributed towards a sink organ. Data are indicated as the mean value ± standard error. Asterisks represent significant differences between treatments and hashes represent significant differences between genotypes (n = 4 plants; p < 0.05).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4384392&req=5

Fig5: N fluxes in Aviso (A) and Oase (B) in LN conditions between D42 and D70. The plants were supplied with a low concentration of nitrate (LN, 0.375 mM of nitrate). D42 corresponds to pod formation and D70 to the start of seed filling. Fluxes of N from remobilization or uptake in the different organs are expressed as mg of N remobilized or taken up, respectively. A shaded box means that the organ was not present during these growing stages. For fluxes of N remobilization, the N amount is indicated with a minus sign (−) when N is remobilized from a source organ, or it is indicated with a plus sign (+) when remobilized N is redistributed towards a sink organ. Data are indicated as the mean value ± standard error. Asterisks represent significant differences between treatments and hashes represent significant differences between genotypes (n = 4 plants; p < 0.05).
Mentions: Between D42 and D70, no N uptake was detectable and the total remobilized N amount decreased for both genotypes under N limitation (Figure 5) contrary to HN plants (Additional file 4). This was mainly related to lower contributions of leaves and pod walls, leading to a lower N redistribution to seeds. The N remobilization was 1.2-fold higher for Aviso than Oase (Figure 5), mainly due to a 2-fold higher N remobilization from leaves. Nevertheless, the N redistribution to seeds was not significantly different between the genotypes (144.73 mg N for Aviso and 127.75 mg N for Oase). These results can be explained by the fact that flowers and stems are sink organs for Aviso contrary to Oase, and a higher N loss by dead leaves occurs for Aviso.Figure 5

Bottom Line: Oilseed rape is the third largest oleaginous crop in the world but requires high levels of N fertilizer of which only 50% is recovered in seeds.Nitrate restriction decreased seed yield and oil quality for both genotypes but Aviso had the best seed N filling.The results confirm the importance of foliar N remobilization after bolting to satisfy seed filling and highlight that an efficient proteolysis is mainly associated with (i) cysteine proteases and proteasome activities and (ii) a fine coordination between proteolysis and export mechanisms.

View Article: PubMed Central - PubMed

ABSTRACT

Background: Oilseed rape is the third largest oleaginous crop in the world but requires high levels of N fertilizer of which only 50% is recovered in seeds. This weak N use efficiency is associated with a low foliar N remobilization, leading to a significant return of N to the soil and a risk of pollution. Contrary to what is observed during senescence in the vegetative stages, N remobilization from stems and leaves is considered efficient during monocarpic senescence. However, the contribution of stems towards N management and the cellular mechanisms involved in foliar remobilization remain largely unknown. To reach this goal, the N fluxes at the whole plant level from bolting to mature seeds and the processes involved in leaf N remobilization and proteolysis were investigated in two contrasting genotypes (Aviso and Oase) cultivated under ample or restricted nitrate supply.

Results: During seed filling in both N conditions, Oase efficiently allocated the N from uptake to seeds while Aviso favoured a better N remobilization from stems and leaves towards seeds. Nitrate restriction decreased seed yield and oil quality for both genotypes but Aviso had the best seed N filling. Under N limitation, Aviso had a better N remobilization from leaves to stems before the onset of seed filling. Afterwards, the higher N remobilization from stems and leaves of Aviso led to a higher final N amount in seeds. This high leaf N remobilization is associated with a better degradation/export of insoluble proteins, oligopeptides, nitrate and/or ammonia. By using an original method based on the determination of Rubisco degradation in the presence of inhibitors of proteases, efficient proteolysis associated with cysteine proteases and proteasome activities was identified as the mechanism of N remobilization.

Conclusion: The results confirm the importance of foliar N remobilization after bolting to satisfy seed filling and highlight that an efficient proteolysis is mainly associated with (i) cysteine proteases and proteasome activities and (ii) a fine coordination between proteolysis and export mechanisms. In addition, the stem may act as transient storage organs in the case of an asynchronism between leaf N remobilization and N demand for seed filling.

Show MeSH
Related in: MedlinePlus