Effect of Photoperiod Duration on Efficiency of Low-Temperature Hardening of Arabidopsis thaliana Heynh. (L.)

The effect of photoperiod duration on efficiency of low-temperature hardening was investigated in Arabidopsis thaliana (L.) Heynh. plants, ecotype Col-0. Six-week-old plants were exposed to cold acclimation at a temperature of 2°С during 1‒5 days at photoperiods of 0, 8, and 16 h (illuminance of 200 µmol/(m2 s)). According to survival data and leakage of electrolytes after test freezing (–6°C, 24 h), the plants exposed to cold acclimation in the dark did not show frost resistance. The plants hardened in the light (irrespective of the length of photoperiod) considerably improved their frost resistance by the end of the cold-acclimation period. Net photosynthesis/dark respiration ratio in these plants was almost two times greater than in control material (without hardening). The plants exposed to a 16-h-long photoperiod surpassed the type of treatment with 8-h-long illumination both in the highest levels of accumulation of sugars (by almost 40