Year: 2003
Type: dissertation
Abstract: Leaf development from young expanding leaves to advanced senescence was followed in silver birch seedlings (Betula pendula Roth) during the first growing season and in young trees, representing clones V5952 and K1659, during the sixth growing season.In addition, leaf ontogeny was studied in a late senescing line, R3.1, which was found among transgenic lines produced in the present study.The leaves of line R3.1 were compared to leaves of wildtype clone R. Leaf developmental stages, young, mature and senescing, were determined by changes in photosynthetic activity based on maximal and actual efficiency of PSII, and the amount and activity of Rubisco enzyme.Photosynthetic activity increased with leaf expansion and started to decrease in fully expanded leaves.New information was gained on leaf senescence-related changes in silver birch; downregulation of photosynthesis and remobilization-related changes such as protein degradation and changes in gene expression level were well coordinated.Characteristic genes of leaf senescence such as cysteine protease (Cyp) and pathogenesis-related (PR) protein genes (PR1, PR3a, Ypr10) were also identified, and a few novel senescence-associated genes such as mitochondrial phosphate translocator (Mpt) and leucine aminopeptidase (Lap) were also found.Senescence-related changes were detected soon after leaves were fully expanded in silver birch seedlings, and also clone R, which were propagated for their first growing season under greenhouse conditions, whereas no senescence-related changes were observed in the insertion mutant line R3.1.The fully expanded leaves of field-grown 6 year-old silver birches maintained active photosynthesis for several weeks before they started to senesce.A genetic transformation method was developed for silver birch in order to study regulation of carbon metabolism in transgenic lines containing reduced Rubisco enzyme, which is the key enzyme of carbon metabolism.For further studies, several sense-RbcS lines were produced from two silver birch clones, R and E5396, by a biolistic transformation method.As a long-term solution for maintenance of transgenic silver birch lines, a cryopreservation method was applied to cold-hardened buds of transgenic silver birch plants.After cryostorage, buds were thawed and regenerated plants were used to study the effect of freezing to neomycin phosphotransferase (nptII) transgenes.Cryopreservation treatment affected neither the stability nor the expression of nptII genes, and it is therefore a suitable maintenance method for transgenic silver birch lines.
Source: Työväentutkimus Vuosikirja
Author: Maarit Sillanpää
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2211557879