How could Christmas trees remain evergreen? : photosynthetic acclimation of Scots pine and Norway spruce needles during winter

• Main Author: Bag, Pushan
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Umeå universitet, Institutionen för fysiologisk botanik 2022
• Subjects: Scots Pine; Norway spruce; Photosynthesis; Winter adaptation; Biochemistry and Molecular Biology; Biokemi och molekylärbiologi; Bioinformatics and Systems Biology; Bioinformatik och systembiologi; Botany; Botanik; Biophysics; Biofysik; Evolutionary Biology; Evolutionsbiologi; Norway; Psi; Tundra
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-194032

Plants and other green organisms harvest sunlight by green chlorophyll pigments and covertit to chemical energy (sugars) and oxygen in a process called photosynthesis providing the foundation for life on Earth. Although it is unanimously believed that oceanic phytoplanktons are the main contributors to the global photosynthesis, the contribution of coniferous boreal forests distributed across vast regions of the northern hemisphere cannot be undermined. Hence boreal forests account signifificantly for social, economical and environmental sustainability. Not only do conifers thrive in the tundra regions with extreme climate, but they also maintain their needles green over the boreal winter. A question remains; what makes them so resilient? In this respect, we aimed to understand the remarkable winter adaptation strategies in two dominant boreal coniferous species,i.e., Pinus sylvestris and Picea abies. First, we mapped the transcriptional landscape in Norway spruce (Picea abies) needles over the annual cycle. Transcriptional changes in the nascent needles reflflected a sequence of developmental processes and active vegetative growth during early summer and summer. Later after maturation, transcriptome reflflected activated defense against biotic factors and acclimationin response to abiotic environmental cues such as freezing temperatures during winter. Secondly, by monitoring the photosynthetic performance of Scot pine needles, we found that the trees face extreme stress during the early spring (Feb-Mar) when sub-zero temperatures are accompanied by high solar radiation. At this time, drastic changes occur in the thylakoid membranes of the chloroplast that allows the mixing of photosystem I and photosystem II that typically remain laterally segregated. This triggers direct energy transfer from PSII to PSI and thus protects PSII from damage. Furthermore, we found that this loss of lateral segregation may be a consequence of triple phosphorylationof Lhcb1 (Light harvesting complex1 of photosystem II). The ...