Induction of Cold Acclimation in Cornus stolonifera Michx.
A warm (20 to 15 Celsius day or night) preconditioning treatment enhanced cold acclimation of Cornus stolonifera bark under short-day conditions when plants were preconditioned for at least 4 weeks. Warm preconditioning inhibited the acclimation of plants subjected to long photoperiods. Removing leaves from plants exposed to low temperatures and short days inhibited acclimation. Removal of buds did not affect acclimation. Plants did not acclimate unless they were exposed to at least 4 weeks of short photoperiods prior to defoliation. Plants began to acclimate to cold at the time of growth cessation but not before. When half of the leaves were removed from plants, the defoliated and foliated branches both acclimated as well as branches on completely foliated plants. Girdling the phloem between foliated and defoliated branches prevented acclimation of the latter regardless of the position of the girdle in relation to the root system and the defoliated branch. When all of the leaves of plants were covered with aluminum foil to exclude light after 0 or 4 weeks of exposure to short days, the results resembled a defoliation study, i.e., plants with leaves covered at the start of the experiment failed to acclimate, and those covered after 4 weeks acclimated to some extent but less than uncovered control plants. Under longday conditions plants with all leaves covered failed to acclimate, and plants with none or half of their leaves covered acclimated equally and to a limited extent. Under short-day conditions, however, the covered branches of partially covered plants acclimated more than their uncovered counterparts or branches of totally uncovered plants.