Leaves turn yellow naturally, in autumn, when they get old or when the plant is exposed to stresses like darkness or drought. Daria Chrobok compared in her PhD thesis different scenarios of leaf yellowing and analysed what happens on the metabolic level. She showed that mitochondria, the respiratory power stations of the cell, are crucial for a coordinated adjustment of metabolism during leaf yellowing. Mitochondria stay active until the last stages of leaf yellowing to provide the energy that is needed for recycling nutrients from the dying leaf. Daria Chrobok successfully defended her thesis on the 8th of June.
The yellowing of a leaf, also called senescence, occurs naturally in for example deciduous trees in autumn or when annual plants get old and produce seeds. However, also stresses like a lack of nutrients, drought or pathogens can induce senescence. Daria Chrobok compared naturally aging plants with plants where senescence was induced by darkening a single leaf. She showed that in both cases the mitochondria remain intact until the last stages of leaf senescence to provide the energy needed for the mobilisation and transport of nutrients.
In addition, she showed that especially the amino acid glutamate, that can be easily transported within the plant, accumulates during leaf senescence. She hypothesized that this accumulation of glutamate in the mitochondria and its conversion to glutamine in the cytosol are essential steps for the reallocation of nitrogen rich compounds to other parts of the plant.
The export of amino acids with high nitrogen content into developing parts of the plant, e.g. seeds, is of high importance to ensure that those seeds contain enough nitrogen and the survival of the next generation is guaranteed. Nitrogen is often a limiting factor for plant growth and development and therefore the reallocation of nitrogen during senescence is important for plants.
Without light, plants cannot perform photosynthesis and produce energy-rich carbon compounds like sugars. If only one leaf is darkened, the covered leaf will rapidly turn yellow. In contrast, when the whole plant is darkened, the leaves are repressing this induction of senescence, i.e. they stay green. The plant keeps all components needed for photosynthesis alive and intact so that upon sudden light exposure, the plants are ready to start photosynthesis and continue growing.
Daria Chrobok and her colleagues analysed how plants adjust their metabolism to those two darkening conditions and they compared these results with the light-dependent “stay-green” mutant. When one leaf of a stay-green plant is darkened, it stays green, whereas the same treatment in a wild type plant leads to the yellowing of the darkened leaf. This darkened stay-green leaf, as well as the whole darkened plant accumulate amino acids, especially those with high nitrogen and low carbon content.
The understanding of how “stay-green” plants manage to stay green is interesting for the food industry to keep vegetables green for longer time and for agriculture, to ensure proper grain and nutrient filling as well as other improved traits for crop plants.
The public defence took place in Lilla hörsalen at KBC, Umeå University, on Friday, 8th of June 2018. Faculty opponent was David Macherel, IRHS-MitoStress, University of Angers, France. Supervisors were Olivier Keech and Per Gardeström.
Title of Daria Chrobok’s thesis: “To “leaf” or not to “leaf” - Understanding the metabolic adjustments associated with leaf senescence”
Link to the doctoral thesis: urn:nbn:se:umu:diva-147700
Are you interested to read more? Have a look on the comic strip made by Neil E. Robbins II. He illustrated the results from the article Law et al., 2018 (Plant Physiology) that is included in Daria Chrobok’s thesis. The comic explains very nicely the metabolic adjustments during the different dark treatments:
Simon R Law, Daria Chrobok, Marta Juvany, Nicolas Delhomme, Pernilla Lindén, Bastiaan Brouwer, Abdul Ahad, Thomas Moritz, Stefan Jansson, Per Gardestrom, Olivier Keech (Plant Physiology) 2018; DOI: https://doi.org/10.1104/pp.18.00062
Title: Darkened leaves use different metabolic strategies for senescence and survival
The registration to the UPSC Days 2018 is now open! They will take place on September 6-7 at Sliperiet on the Konstnärlig Campus in Umeå.
The first day will start with a session about future visions for UPSC and continue after lunch with an update about the most recent changes of the UPSC infrastructures. We will also have a scientific session with 3 minutes flash talks and end the first day with a barbecue that will take place in front of UPSC.
On the second day, Anna-Karin Byström from DC Consulting AB will give a workshop on intercultural communications. This workshop will include seminars giving theoretical background about cultural understanding and the communication process as well as practical exercises and tools to handle and interpret actions and reactions that arise in meetings with people of different backgrounds. We will finish the second day with the lunch.
Location: White boxes, Sliperiet, Konstnärlig campus, Umeå (see on map)
|Day 1 - Thursday, 6th September 2018
|9:30 - 10:00||Registration and coffee|
|10.00 - 10.10||Welcome|
|The future UPSC|
|10.10 - 10.40||Visions for UCMR (Umeå Centre for Microbial Research)
Bernt Eric Uhlin, UCMR & MIMS, Department of Molecular Biology, Umeå University
|10.40 - 11.35||Visions for UPSC
Ove Nilsson (director of UPSC), Karin Ljung (prefect of the Department of Forest Genetics and Plant Physiology, SLU) and Stefan Jansson (prefect of the Department of Plant Physiology, Umeå University) will talk about their visions for UPSC.
|11.35 - 12.15||Podiums discussion
Chair: Catherine Bellini, Chairmen of the UPSC board
|12.15 - 13.30||Lunch|
|13.30 - 13.50||The new phenotyping platform at UPSC
Ove Nilsson (director of UPSC)
|13.50 - 14.10||News from the Bioinformatics platform
Nicolas Delhomme (Manager of the UPSC Bioinformatics platform)
|14.10 - 14.40||Coffee break|
|14.40 - 15.10||Flash-talk competition
Scientific session with 3 min flash talks (max. 1 slide)
|15.10 - 15.20||Voting and award presentation
|16.30||Barbecue at the Umeå Plant Science Centre (Please bring your own food and drinks)
|Day 2 - Friday, 7th September 2018|
|Intercultural communications workshop
Anna-Karin Byström, Ph.Lic. Organisational Communication and CEO, DC Consulting AB
|9.00 - 9.10||Brief introduction and presentations
|9.10 - 10.10||Intercultural communication - introduction to cultural understanding and the communication process
|10.10 - 10.55||Coffee and workshop|
|10.55 - 11.45||Practical tips concerning communication between people of different backgrounds including practical exercises
|11.45 - 12.00||Concluding the workshop and shorter reflection
|12.00 - 12.10||Final conclusion by the organisers
|12.10 - 13.10||Lunch|
On Friday, 18th of May, HalehHayatgheibi successfully defended her PhD thesis. She has worked on lodgepole pine (Pinus contorta), a fast-growing tree that was largely introduced into Sweden in the mid-1960s. One major problem of lodgepole pine trees is that their stems are often bending or even break and this lowers the economic value of the wood. Haleh Hayatgheibi designed breeding strategies to optimize both wood quantity and quality of lodgepole pine to reduce stem bending and breakage.
Haleh Hayatgheibi estimated genetic parameters which determine wood quality and quantity of lodgepole pine. She measured for example the diameter of the stem as parameter for wood quantity and the stiffness of the stem. A higher stiffness might prevent the breakage of the stem when it bends and decrease the economic loss. This feature is especially interesting for Northern Sweden.
Lodgepole pine trees from different origin in Canada were planted in different climatic regions in Northern Sweden, e.g. close to the coast or more inland. Haleh Hayatgheibi compared those trees with each other to see which are best suited for which region in Northern Sweden. Based on her results, she can now recommend tree breeders which lodgepole pine trees have the best prerequisites for which climatic region.
Title of the thesis: “Quantitative genetics of lodgepole pine (Pinus contorta) wood quality traits in Sweden”
Link to the doctoral thesis: http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-e-4836
The public defence took place in Björken at SLU Umeå on Friday, 18thof May 2018. Faculty opponent was Yousry A. El-Kassaby from the Forest Sciences Centre, University of British Columbia, Canada. The supervisor was Harry Xiaming Wu.
Six collaborative projects were selected by external reviewers and are now open for application. The postdoctoral fellows will be recruited at the Umeå Plant Science Centre in Sweden but will spend some time at the collaborating partner institute either in France or in Spain. The goal is to intensify the exchange between the three partners of the INUPRAG cooperation.
The INUPRAG cooperation exists since 2015 and is a collaboration between the Umeå Plant Science Centre(UPSC, Sweden), the National Institute for Agricultural Research(INRA, France) and the Centre for Research in Agricultural Genomics(CRAG, Spain). The goals are to foster joint research projects in plant science between the different partners and to train young scientists through regular exchanges between the partner laboratories.
The six granted postdoctoral projects cover different topics within plant science. All group leaders from UPSC could apply with collaborative projects for the postdoctoral fellowships. Three (?) external referees evaluated all submitted projects and selected the six best, three from Umeå University (Department of Plant Physiology) and three from SLU (Department of Forest Genetics and Plant Physiology).
The granted projects are:
Project 1: Interactions between Plastid and Light Signalling Pathways
Project leaders: Åsa Strand (UPSC) & Elena Monte (CRAG)
Project 2: Regulation of the Master Floral Regulator LEAFY by Ubiquitination through the E3 Ligases UFO and BOP2
Project leaders: Markus Schmid (UPSC), Ove Nilsson (UPSC) & François Parcy (INRA, Grenoble)
Project 3: An evo-devo approach to elucidate the role of PIRIN proteins during non-cell autonomous lignification
Project leaders: Hannele Tuominen (UPSC) and Richard Sibout (INRA, Nantes)
Postdoctoral project 4: Unravelling cluster root emergence in white lupin
Project leaders: Stéphanie Robert (UPSC) & Benjamin Péret (INRA, Montpellier)
Project 5: Cell wall mediated control of differential cell elongation in Arabidopsis hook Development
Project leaders: Rishikesh Bhalerao (UPSC) and Olivier Hamant (ENS, INRA, Lyon)
Project 6: Enabling scale-up of somatic embryogenesis (SE) plant production by physiological analysis of embryos processed in bioreactors and the R&D SE System for harvest
Project leaders: Ulrika Egertsdotter (UPSC) and Marie-Anne Lelu-Walter (INRA, Orleans)
On Friday, 20th of April, Christoffer Johnsson successfully defended his thesis titled “Elucidating the phytohormonal control of xylem development”. He could show in his thesis that the plant hormones auxin and gibberellin are important signals for normal wood development in poplar trees. The public defence took place in P-O Backströms sal at SLU Umeå. Faculty opponent was Andrea Polle from the Buesgen Institut, Georg-August University Göttingen, Germany. His academic supervisor was Urs Fischer.
Link to the doctoral thesis: http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-e-4828
You can find more background information about Christoffer Johnsson’s work here (in Swedish):
Torgny Näsholm discovered that amino acids play an important role as nitrogen source for plants. He receives now the Marcus Wallenberg Prize 2018 for his ground-breaking research.
Please have a look on the Marcus Wallenberg Foundation homepage for more information:
The plant geneticist and lecturer at the Department of Plant Physiology, Nathaniel Street, is awarded the pedagogical prize from the Faculty of Science and Technology. The prize jury motivated its decision due to his outstanding ambition, good organization and strong interest in developing new ways of teaching. Nathaniel Street will receive the prize during the Spring graduation ceremony of Umeå University on the 19th of May.
“I was on the Ski lift and checked my emails when I found out that I was awarded for the prize”, tells Nathaniel Street. “I was so surprised that I had to read the message twice to be sure that it was true. It is fantastic to know that the efforts made for teaching are acknowledged and appreciated. I really did not expect this, especially because there are so many other excellent teachers in our institute.”
Nathaniel Street came as a postdoc to Umeå University in 2007. In 2011, he became Assistant Professor and is since January 2016 Associate Professor at the Department of Plant Physiology.
During his time at Umeå University, he has fast developed his teaching skills further. He became the course leader of the department’s genomics courses in 2011 and has refined the course since then. Nathaniel Street is also teaching on the courses Bioinformatics and Genome Analysis and Microbiology and Basic Molecular Biology at Umeå University as well as the course Plant Biology for Future Forestry at the Swedish University of Agricultural Sciences (SLU).
The prize motivation emphasizes Nathaniel Street’s extremely careful preparation of his teaching. He gives well prepared and clear lectures that are greatly appreciated by the students and he is continuously improving his teaching methods. Among others, he has introduced interactive and student-led discussions, new practical classes in the lab and discussions on ethics. Several of these initiatives have subsequently been taken over by other teachers at the institution.
“He involves both his own research group and the bioinformatics platform at the Umeå Plant Science Centre in his work and successfully creates extremely smooth ways of teaching, that not only allow the students to get in contact with actual research, but are also very interesting for the research itself”, is stated in the prize motivation. “His high competence in both plant biology and genetics as well as in advanced computing has made this possible.”
Nathanial Street focuses his research on finding the genes that control natural variation and he is analysing microbial communities that are living close together with forest trees. His ambition is to combine his research interest with his educational ambition and strong willingness to develop his teaching methods further.
“My hope is to convey my own fascination and interest in my research area. It can be a challenging area to teach because it is changing very fast, but I try to keep the courses up to date. I do not want the students to just sit and listen to me. It is fun to think of new ways to motivate the students to learn together and from each other and to help them develop skills to learn independently in the future. The courses I have attended at the University Education and Teacher Support (UPL) have been a great inspiration for this.”
Link to the Swedish press release
For more information, please contact:
Umeå Plant Science Centre
Department of Plant Physiology
Phone: 090-786 54 73
For trees in boreal and temperate climates, it is important that buds do not burst precociously, but only when it's spring for real. Therefore, the buds are put in dormancy in the autumn, which means they have to go through a long cold period before they slowly become susceptible to the signals of spring. The mechanism behind this is revealed in a new study led by Rishi Bhalerao from UPSC, recently published in the journal Science.
Trees are amongst the longest-living organisms on Earth, and some species can live for thousands of years. One of the key mechanisms that enable such a long life is their synchronization of growth with change in seasons. For example, in temperate and boreal ecosystems, trees stop their growth and establish dormancy prior to the advent of winter. Growth cessation and dormancy establishment is a key adaptive mechanism for winter survival, since failure to cease growth and establish dormancy can result in fatality from extreme low temperatures in the winter.
How trees know when to stop their growth and establish dormancy is a question that has been of interest to researchers since a long time. That growth stops in response to the decrease in daylight during autumn has been well understood. The establishment of dormancy, which means that buds cannot burst before they have experienced a long cold period, and are not awakened by short warm periods during winter, has been more of a mystery. The recent article in Science, however, provides an important insight into how winter dormancy is regulated in perennial trees.
What the researchers could show is that the so-called plasmodesmata, channels that connect different cells with each other, are closed by the deposition of callose, a polysaccharide, in response to the shortening of day length in the autumn. The blockage of the plasmodesmata prevents cells from receiving growth promotive signals, thereby maintaining growth arrest and establishing dormancy in the buds.
The researchers also show that short-day induced dormancy is regulated by the plant hormone abscisic acid which activates (among others) the production of the callose that is used to block the plasmodesmata. Once blocked, a long exposure to low temperatures is needed to slowly re-open the plasmodesmata again, so that the growth-inducing signals can reach the buds and stimulate the growth in the buds in the spring.
"Interestingly, some of the facets of the dormancy regulation mechanism described in our paper have been observed in winter wheat as well as characean algae, suggesting that this mechanism is probably ancient and evolutionarily conserved", says Rishikesh Bhalerao.
The study was conducted using hybrid aspen, which is a model plant in tree research.
The study has been conducted by a research team led by Rishi Bhalerao from SLU's Department of Forest Genetics and Plant Physiology and the Umeå Plant Science Center. The colleagues come from SLU in Alnarp, Uppsala University, University of Helsinki, Cambridge University, Monash University and the University of Environmental and Life Sciences in Norway.
Link to the Swedish press release on the SLU homepage
Rishikesh P. Bhalerao, Professor
Umeå Plant Science Centre
Department of Forest Genetics and Plant Physiology
Swedish University of Agricultural Sciences, Umeå
S. Tylewicz, A. Petterle, S. Marttila, P. Miskolczi, A. Azeez, R. K. Singh, J. Immanen, N. Mähler, T. R. Hvidsten, D. M. Eklund, J. L. Bowman, Y. Helariutta, R. P. Bhalerao. 2018. Photoperiodic control of seasonal growth is mediated by ABA acting on cell-cell communication. Science 10.1126/science.aan8576 (2018).
Direct link to the article in Science
Text: David Stephansson (SLU)
If you are interested in reading more about Mateusz Majda's findings, have a look here: https://www.upsc.se/about-upsc/news/5235-the-growth-of-puzzle-piece-shaped-leaf-cells-gets-an-explanation.html
Link to the doctoral thesis: https://pub.epsilon.slu.se/15263/
For more information please contact:
Umeå Plant Science Centre
Department of Plant Physiology