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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 D70 and D99. The plants were supplied with a low concentration of nitrate (LN, 0.375 mM of nitrate). D70 corresponds to the start of seed filling and D99 to mature seeds. Fluxes of N from remobilization or uptake in the different organs are expressed as mg N remobilized or taken up, respectively. 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 (vertical bars). Asterisks represent significant differences between treatments and hashes represent significant differences between genotypes (n = 4 plants; p < 0.05).
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Fig6: N fluxes in Aviso (A) and Oase (B) in LN conditions between D70 and D99. The plants were supplied with a low concentration of nitrate (LN, 0.375 mM of nitrate). D70 corresponds to the start of seed filling and D99 to mature seeds. Fluxes of N from remobilization or uptake in the different organs are expressed as mg N remobilized or taken up, respectively. 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 (vertical bars). Asterisks represent significant differences between treatments and hashes represent significant differences between genotypes (n = 4 plants; p < 0.05).

Mentions: Between D70 and D99, the N remobilization from all source organs was low for both genotypes (Figure 6), leading to a lower total N remobilization in LN compared with HN plants (−59% for Aviso and −43% for Oase; Figure 3). Consequently, a lower N amount was redistributed to seeds (−73.13 mg N for Aviso and −14.22 mg N for Oase; Figure 6). Under LN conditions, Aviso had a higher amount of total remobilized N than Oase (+27 mg N) resulting in a higher redistribution of remobilized N to seeds (+29 mg N). This was related to a higher remobilization from stems (+21.81 mg N) and source leaves (+2.42 mg N) for Aviso compared with Oase. The flowers were sink organs for remobilized N in Oase LN plants (Figure 6B) in contrast to Aviso LN plants. It is noteworthy that contrary to the HN treatment, sink leaves were present for both genotypes (Figure 6). Unlike the previous period (D42-D70, Figure 5), a significant N uptake occurred in both genotypes under LN conditions (Figure 6). The N uptake and allocation of N taken up into seeds were respectively 1.57- and 1.86-fold higher for Oase than for Aviso. Nevertheless, the total N amount distributed to the seeds of Oase LN plants (i.e. from N uptake and N remobilization, 54.8 mg N) remained lower than the total N amount distributed to seeds of Aviso LN plants (66.2 mg N, Figure 6).Figure 6


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 D70 and D99. The plants were supplied with a low concentration of nitrate (LN, 0.375 mM of nitrate). D70 corresponds to the start of seed filling and D99 to mature seeds. Fluxes of N from remobilization or uptake in the different organs are expressed as mg N remobilized or taken up, respectively. 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 (vertical bars). 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
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getmorefigures.php?uid=PMC4384392&req=5

Fig6: N fluxes in Aviso (A) and Oase (B) in LN conditions between D70 and D99. The plants were supplied with a low concentration of nitrate (LN, 0.375 mM of nitrate). D70 corresponds to the start of seed filling and D99 to mature seeds. Fluxes of N from remobilization or uptake in the different organs are expressed as mg N remobilized or taken up, respectively. 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 (vertical bars). Asterisks represent significant differences between treatments and hashes represent significant differences between genotypes (n = 4 plants; p < 0.05).
Mentions: Between D70 and D99, the N remobilization from all source organs was low for both genotypes (Figure 6), leading to a lower total N remobilization in LN compared with HN plants (−59% for Aviso and −43% for Oase; Figure 3). Consequently, a lower N amount was redistributed to seeds (−73.13 mg N for Aviso and −14.22 mg N for Oase; Figure 6). Under LN conditions, Aviso had a higher amount of total remobilized N than Oase (+27 mg N) resulting in a higher redistribution of remobilized N to seeds (+29 mg N). This was related to a higher remobilization from stems (+21.81 mg N) and source leaves (+2.42 mg N) for Aviso compared with Oase. The flowers were sink organs for remobilized N in Oase LN plants (Figure 6B) in contrast to Aviso LN plants. It is noteworthy that contrary to the HN treatment, sink leaves were present for both genotypes (Figure 6). Unlike the previous period (D42-D70, Figure 5), a significant N uptake occurred in both genotypes under LN conditions (Figure 6). The N uptake and allocation of N taken up into seeds were respectively 1.57- and 1.86-fold higher for Oase than for Aviso. Nevertheless, the total N amount distributed to the seeds of Oase LN plants (i.e. from N uptake and N remobilization, 54.8 mg N) remained lower than the total N amount distributed to seeds of Aviso LN plants (66.2 mg N, Figure 6).Figure 6

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