© 2005 Heron Publishing—Victoria, Canada
Expression of senescence-associated genes in the leaves of silver birch (Betula pendula)
Maarit Sillanpää (1, 2, 3), Sari Kontunen-Soppela (2), Eeva-Maria Luomala (4), Sirkka Sutinen (4, 5), Jaakko Kangasjärvi (1, 6), Hely Häggman (2, 7) and Elina Vapaavuori (4, 8)
1. Institute of Biotechnology, The Viikki Biocenter, University of Helsinki, P.O. Box 56, FIN-00014 Helsinki, Finland / 2. Finnish Forest Research Institute, Punkaharju Research Station, FIN-58450 Punkaharju, Finland / 3. National Public Health Institute, Mannerheimintie 166, 00300 Helsinki, Finland / 4. Finnish Forest Research Institute, Suonenjoki Research Station, FIN-77600 Suonenjoki, Finland / 5. Finnish Forest Research Institute, Joensuu Research Centre, PL 68, 80101 Joensuu, Finland / 6. Department of Biosciences, Plant Physiology, University of Helsinki, FIN-00014 Helsinki, Finland / 7. Department of Biology, University of Oulu, P.O. Box 3000, FIN-90014 Oulu, Finland / 8. Corresponding author (elina.vapaavuori@metla.fi) / Received April 19, 2004; accepted January 15, 2005; published online July 4th, 2005
Summary
Development was monitored throughout the entire life span of silver birch (Betula pendula Roth.) leaves. The focus was on senescence-related changes in photosynthesis and gene expression. The youngest fully developed
leaves were compared with older senescing leaves in two silver birch lines: the wild-type line R and a late-senescing line
R3.1. Line R3.1 was found among transgenic lines produced with a plasmid containing sense-RbcS and nptII under the control of the 35S CaMV promoter. Compared with the wild type, line R3.1 showed no general change in the mRNA levels
of RbcS or Rubisco protein; therefore, it can be considered a line whose phenotype is due to insertional mutagenesis. Leaf senescence
started earlier in line R than in line R3.1. Senescence was characterized by declining photosynthesis as indicated by decreases
in chlorophyll fluorescence, the amount and activity of Rubisco, and the level of the ribulose-1,5-bisphosphate carboxylase/oxygenase
small subunit (RbcS1) mRNA. Some well-known senescence-associated genes (SAGs) encoding cysteine proteinases (Cyp1, Cyp2) and a pathogenesis-related gene (Pr1) were associated with leaf senescence. The expression pattern of Cyp1 indicated that it could serve as a molecular marker of leaf senescence in silver birch. Several genes related to energy metabolism,
antioxidants and phenylpropanoid biosynthesis showed enhanced expression during leaf senescence. A distinct pattern in transcript
abundance during leaf development was revealed for some of the identified SAGs.
Keywords:
antioxidants, cysteine proteinases, energy metabolism, pathogenesis-related genes, late senescing mutant, phenylpropanoid
biosynthesis, photosynthesis, Rubisco.
