Effect of photoperiod prior to cold acclimation on freezing tolerance and carbohydrate metabolism in alfalfa (Medicago sativa L.)
Bertrand, A., Bipfubusa, M., Claessens, A., Rocher, S., Castonguay, Y. (2017). Effect of photoperiod prior to cold acclimation on freezing tolerance and carbohydrate metabolism in alfalfa (Medicago sativa L.). Plant Science, [online] 264 122-128. http://dx.doi.org/10.1016/j.plantsci.2017.09.003
Plain language summary
The length of the day (photoperiod) in autumn is an important factor influencing the acclimatisation of perennial plants. We tested different growth photoperiods for 4 weeks (8, 10, 12, 12, 14, and 16 h) prior to alfalfa’s cold acclimatization on freezing tolerance and accumulation of chemical compounds typically associated with freezing tolerance. Our results showed that a short growth photoperiod (8 h) induced superior freezing tolerance in alfalfa in northern regions and that this response was related to the accumulation of cryoprotective sugars from the raffinose family.
Cold acclimation proceeds sequentially in response to decreases in photoperiod and temperature. This study aimed at assessing the impact of photoperiod prior to cold acclimation on freezing tolerance and related biochemical and molecular responses in two alfalfa cultivars. The fall dormant cultivar Evolution and semi-dormant cultivar 6010 were grown in growth chambers under different photoperiods (8, 10, 12, 14 or 16 h) prior to cold acclimation. Freezing tolerance was evaluated as well as carbohydrate concentrations, levels of transcripts encoding enzymes of carbohydrate metabolism as well as a K-3dehydrin, before and after cold acclimation. The fall dormant cultivar Evolution had a better freezing tolerance than the semi-dormant cultivar 6010. The effect of photoperiod prior to cold acclimation on the level of freezing tolerance differed between the two cultivars: an 8h-photoperiod induced the highest level of freezing tolerance in Evolution and the lowest in 6010. In Evolution, the 8h-induced superior freezing tolerance was associated with higher concentration of raffinose-family oligosaccharides (RFO). The transcript levels of sucrose synthase (SuSy) decreased whereas those of sucrose phosphatase synthase (SPS) and galactinol synthase (GaS) increased in response to cold acclimation in both cultivars. Our results indicate that RFO metabolism could be involved in short photoperiod-induced freezing tolerance in dormant alfalfa cultivars.