During the growth treatments, photosynthetic active radiation
was given for 12 h with fluorescent light tubes 165–175 lmol
m2s1 (Phillips TLD 58W/840; Eindhoven, The Netherlands). The
long photoperiod treatments were extended to 24 h with low
irradiance lamps for 12 h, 6–8 lmol m2s1 (Osram delux el
longlife 2020, Munich, Germany). The 12 h low irradiance extensions
were in combination with the reduced night temperature. Eleven
weeks after the germination period, 50% of the plants were harvested
and the remaining plants exposed to a cold acclimatised
treatment. All treatments had similar plant height except low
growth temperature/short day which were about 30% lower.
The remaining plants were kept for 2 weeks at 6 C, then two
weeks at 3 C and finally at 0.5 C for 1 week. All plants received
12 h of low intensity light (6–8 lmol m2s1). There was little or
no plant growth during the cold acclimatisation.