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Phosphorus nutrition of poplar

dc.contributor.advisorPolle, Andrea Prof. Dr.
dc.contributor.authorKavka, Mareike Jana
dc.date.accessioned2017-05-29T09:05:38Z
dc.date.available2017-05-29T09:05:38Z
dc.date.issued2017-05-29
dc.identifier.urihttp://hdl.handle.net/11858/00-1735-0000-0023-3E5C-3
dc.identifier.urihttp://dx.doi.org/10.53846/goediss-6316
dc.identifier.urihttp://dx.doi.org/10.53846/goediss-6316
dc.language.isoengde
dc.rights.urihttp://creativecommons.org/licenses/by-nc-nd/4.0/
dc.subject.ddc570de
dc.titlePhosphorus nutrition of poplarde
dc.typedoctoralThesisde
dc.contributor.refereePolle, Andrea Prof. Dr.
dc.date.examination2016-12-15
dc.description.abstractengPhosphorus (P) is a major plant nutrient required for the biosynthesis of nucleic acids, nucleotides, membrane lipids and metabolites such as organic esters. P further plays a role in enzyme regulation by phosphorylation. Plants take up P in its inorganic form H2PO4- (Pi). Pi is present only in low concentrations in the soil solution and therefore has to be replenished all the time to ensure sufficient plant nutrition. In plants different strategies can be distinguished in response to P starvation: (i) P conservation by re-use of P from P containing compounds e.g. membrane lipids and avoidance of P requiring metabolic pathways. This results in growth reduction. (ii) Enhanced acquisition of P from the soil. For this purpose plants secrete purple acid phosphatases (PAPs) to mobilize Pi from organic sources and increase the activity of phosphate transporters (PHTs) for enhanced uptake capacity. Only little is known for woody plants about the molecular responses to low P availability because to date most of our knowledge stems from the model plant Arabidopsis. The main aims of this thesis were to characterize molecular changes at the whole-transcriptome level in leaves and roots of Populus × canescens in response to P deprivation and to relate these changes to poplar growth, Pi acquisition and Pi uptake. The following questions were addressed: (a) How does P deficiency affect the nutrient states of the plant and which genes are involved in the response to P limitation in poplar? (b) How is the poplar Pi uptake kinetics affected by decreasing P availabilities and how are PHTs transcriptionally regulated by P deficiency? (c) How does low P availability affect the expression profile of PAPs and which members of the large PAP family are released into the medium upon P starvation? To address these questions transcriptome analyses for poplars (Populus × canescens) grown under reduced phosphorus availabilities were conducted using microarray technology. Plant nutrient concentrations were determined by inductively coupled plasma optical emission spectrometry and uptake by use of radioactive P. The secreted proteins were determined by proteome analyses using liquid-chromatography electrospray-ionization mass spectrometry. (a) Poplars exhibited strong growth reduction and increased P use efficiency in response to lower P availabilities. P starvation resulted also in changes of most other elements (S, N, K, Mg, Ca, Fe, Zn, Mn, Al) studied. A high number of genes (12068 in total) was differently expressed upon P starvation. These genes were clustered in eleven co-expression modules of which seven were correlated with distinct elements in the plant tissues. One module with 565 genes (4.7 % of all differentially expressed genes) was correlated with changes in the P concentration in the plant tissues and with the biomass. In this module, PAPs but no PHTs were identified among the highly upregulated P-related genes. The functional category “galactolipid synthesis” was enriched among the P-related genes. Galactolipids substitute phospholipids in membranes under P limitation. Two modules, one correlated with C and N and the other with biomass, S and Mg, were connected with the P-related module by co-expression. In these modules GO terms indicating DNA modification and cell division as well as defense (ethylene, respiratory burst) and RNA modification and signaling were enriched. In conclusion, most differentially expressed genes were not directly related to the tissue P concentrations and were, therefore, most likely regulated by downstream events of P starvation. (b) Whole-plant P uptake kinetics and expression profiles of members of the phosphate transporter families were studied under high, intermediate and low P availability in relation to plant performance. The maximum P uptake rate was more than 13-times higher in P-starved than in well-supplied poplars. The Km-values ranged between 20 µM and 26 µM for P starved poplars. The minimum concentration for net P uptake from the nutrient solution was 1 µM P. Among the PHT subfamilies, all PHTs of family 1 (PHT1) studied showed significant up-regulation upon P starvation and were higher expressed in roots than leaves, with the exception of PtPHT1;3. The transcript abundance of PtPHT1;3 was high in leaves under high P supply and increased further under P starvation. PtPHT1;1 and PtPHT1;2 showed root- and P-starvation specific expression. Expression profiles of distinct members of the PHT subfamilies, especially those of PHT1 were linked with changes in P uptake and allocation at whole-plant level. The regulation was tissue-specific with lower P-responsiveness in leaves than in roots. Because the Km for P uptake was higher than typical soil concentrations of Pi, non-mycorrhizal poplars are expected to suffer from P limitations in most environments. (c) To study the purple acid phosphatases, transcriptome and proteome analyses were combined with phosphatase activity assays. The family of PAPs was annotated showing 33 poplar PAPs that formed three main subfamilies. Among these PAPs, 23 had a probe set on the microarray and showed significant transcript abundances. Ten PAPs were transcriptionally upregulated in roots and leaves of P-starved poplars. The P-starved poplars further showed higher phosphatase activity on the roots than the well P-supplied plants. The protein PtaPAP4 was secreted by poplar roots under high and low P conditions, whereas PtaPAP1 was secreted only under low P conditions. These results suggest that increased P acquisition from organic P sources under low P conditions is mediated in roots by a specific PAP enzyme. Overall, the results of this thesis support that enhanced phosphate transporter and phosphatase activity can improve P uptake efficiency. Since poplar plantations for biomass production are often established on marginal sites where nutrients are limited, the present findings suggest that the selection of natural genotypes or molecular breeding can be used to improve tree P nutrition.de
dc.contributor.coRefereeHörandl, Elvira Prof. Dr.
dc.subject.engphosphorus deficiencyde
dc.subject.engtranscriptomede
dc.subject.engphosphate transporterde
dc.subject.enguptake kineticsde
dc.subject.engpurple acid phosphatasede
dc.subject.engroot secreted phosphatasede
dc.subject.engexpression profilede
dc.subject.engplant nutritionde
dc.subject.engPopulus x canescensde
dc.identifier.urnurn:nbn:de:gbv:7-11858/00-1735-0000-0023-3E5C-3-2
dc.affiliation.instituteBiologische Fakultät für Biologie und Psychologiede
dc.subject.gokfullBiologie (PPN619462639)de
dc.identifier.ppn888214782


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