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| Author(s): |
Simone Cespedes Vitor
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia |
| Defense date: | 2017-07-26 |
| Examining board members: |
Ladaslav Sodek;
Marina Câmara Mattos Martins;
Paulo Mazzafera;
Halley Caixeta de Oliveira;
Luciano do Amarante
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| Advisor: | Ladaslav Sodek |
| Abstract | |
In the present work we studied the translocation of organic acids and amino acids in the xylem sap of soybean plants under N deficiency and root hypoxia. We observed an important amount of malate transported in xylem sap of non-nodulated soybean plants under N depletion. Nodulated plants whose sole N source is provided by N2 fixation in nodules also showed a higher content of malate in the xylem. When roots are supplied with nitrate or ammonium the amount of malate decreased. In non-nodulated plants under hypoxia we also found a higher amount of malate together with succinate. The same was seen in nodulated plants. Our aim was then to elucidate the origin of the elevated quantities of malate transported. The amino acid Asp is the main compound transported in phloem sap from shoot to roots in N suficient nutrition or normal conditions of O2 availability, as well as in both of the stress conditions: N-free medium or root hypoxia. Thus this amino acid is a candidate to provide the C skeleton for malate formation in roots. Incubation of roots with 13C-Asp demonstrated that malate was readily labeled in the xylem sap of plants deprived of nitrate, as well as in root pieces under hypoxia. Plants cultivated with sufficient N levels in the nutrient solution transport substantial amounts of Asn, that is strongly reduced in plants deficient in N or under hypoxia. Our hypothesis is that Asp supplied by the phloem would be converted to Asn in roots when N uptake and assimilation in roots are active and this Asn transport N from the root to the shoot. However if N metabolism in roots is impaired, Asp would provide N to the root by transamination reactions thereby forming other amino acids demanded for root maintenance during the period of stress. Malate is a by-product of transamination with Asp. Thus, according to the N status of the plant, the xylem contains elevated levels of either asparagine or malate. Under root hypoxia the impairment of oxidative metabolism leads Asp to supply N for Ala production, and malate and succinate are formed in roots. The transport of these organic acids to the shoot would allow the oxidation of these molecules in leaves where oxidative metabolism is normal (AU) | |
| FAPESP's process: | 13/03325-8 - Role of organic acids in the metabolism and recycling of N in the roots of soybean |
| Grantee: | Simone Cespedes Vitor |
| Support Opportunities: | Scholarships in Brazil - Doctorate |