Abstract - Growth responses of Betula pendula ecotypes to red and far-red light

Growth responses of Betula pendula ecotypes to red and far-red light

Berhanu A. Tsegay*
Department of Biology
Bahir Dar University, Ethiopia
Tel: 251 8 206208 (home)
Fax: 251 8 202025
E-mail: berhanutsegay@yahoo.com

Leidulf Lund
Department of Biology
Faculty of Science, University of Tromsø
N-9037 Tromsø, Norway
Tel: 47 77 64 49 04
Fax: 47 77 64 48 98
E-mail: leidulf.lund@ib.uit.no

Jarle Nilsen
Department of Biology
Faculty of Science, University of Tromsø
N-9037 Tromsø, Norway
Tel: 47 77644899
Fax: 47 77646333

Jorunn E. Olsen
Department of Plant and Environmental Sciences
Agricultural University of Norway
P.O. Box 5003
N-1432 Aas, Norway
Tel: 47 64 96 50 00
Fax: 47 64 94 75 05

Jorgen M. Molmann
Department of Biology
Faculty of Science, University of Tromsø
N-9037 Tromsø, Norway
Tel: 47 77 64 44 45
Fax: 47 77 64 63 33
E-mail: jorgen.molmann@ib.uit.no

Arild Ernsten ^†Department of Biology
Faculty of Science, University of Tromsø
N-9037 Tromsø, Norway

Olavi Juntttila
Department of Biology
Faculty of Science, University of Tromsø
N-9037 Tromsø, Norway
Tel: 47 77 64 44 30
Fax 47 77 64 63 33
E-mail: olavi.junttila@ib.uit.no

*Corresponding author

Financial support: This research was funded by the Norwegian Research Council.

Keywords: Diode, ecotype, monochromatic, photomorphogenesis, phytochrome, photosynthetically active radiation (PAR).

Abbreviations:

R: red light;
FR: far red light;
PAR: photosynthetically active radiation;
Pr: red light perceiving phytochrome;
Prf: far red light perceiving phytochrome;
SDs: short days;
LDs: long days.

The effect of Red light (R), Far-red light (FR) and R/FR combinations on shoot growth of latitudinal ecotypes of B. pendula was studied using special diodes that emit monochromatic lights. When a 12 hrs PAR (110 µmol m^-2 s^-1) was extended with R, FR or R/FR ratios, lower intensities of monochromatic lights could not prevent growth cessation. At 25 µmol m^-2 s^-1, FR compared to R enhanced stem elongation in all ecotypes. This was due to the inhibitive effect of R on internode elongation. When day-length was extended by R/FR at various ratios, there was continuous shoot elongation, but was found to be declining with increasing ratios. The more the R, the shorter were the internodes of each plant. B. pendula ecotypes produced branches when PAR light during the day was extended by incandescent light, but did not do so when the light extensions were made by monochromatic R or FR or their combination. Branching increased with decreasing latitude of the ecotype.