After stratification of the seeds at 2°C for 5 days or vernalization at 2°C for 6 weeks on wet filter paper and in darkness, plants of Arabidopsis (Columbia) were grown in 8-h SDs or 16-h LDs. The photon flux density was 120 (HL) or 50 μmol.m-2.s-1 (LL) PAR (Very High Output fluorescent tubes; Sylvania, Zaventem, Belgium) and the temperature was 20°C. Relative humidity – which is critical for the success of germination and seedling establishment – was set optimally at 70%.