The role of temperature during dormancy development is being reconsidered as more research emerges demonstrating that temperature can significantly influence growth cessation and dormancy development in woody plants. However, there are seemingly contradictory responses to warm and low temperature in the literature. This research/review paper aims to address this contradiction. The impact of temperature was examined in four poplar clones and two dogwood ecotypes with contrasting dormancy induction patterns. Under short day (SD) conditions, warm night temperature (WT) strongly accelerated timing of growth cessation leading to greater dormancy development and cold hardiness in poplar hybrids. In contrast, under long day (LD) conditions, low night temperature (LT) can completely bypass the short photoperiod requirement in northern but not southern dogwood ecotypes. These findings are in fact consistent with the literature in which both coniferous and deciduous woody plant species' growth cessation, bud set or dormancy induction are accelerated by temperature. The contradictions are addressed when photoperiod and ecotypes are taken into account in which the combination of either SD/WT (northern and southern ecotypes) or LD/LT (northern ecotypes only) are separated. Photoperiod insensitive types are driven to growth cessation by LT. Also consistent is the importance of night temperature in regulating these warm and cool temperature responses. However, the physiological basis for these temperature effects remain unclear. Changes in water content, binding and mobility are factors known to be associated with dormancy induction in woody plants. These were measured using non-destructive magnetic resonance micro-imaging (MRMI) in specific regions within lateral buds of poplar under SD/WT dormancing inducing conditions. Under SD/WT, dormancy was associated with restrictions in inter- or intracellular water movement between plant cells that reduces water mobility during dormancy development. Northern ecotypes of dogwood may be more tolerant to photoinhibition under the dormancy inducing LD/LT conditions compared to southern ecotypes. In this paper, we propose the existence of two separate, but temporally connected processes that contribute to dormancy development in some deciduous woody plant: one driven by photoperiod and influenced by moderate temperatures; the other driven by abiotic stresses, such as low temperature in combination with long photoperiods. The molecular changes corresponding to these two related but distinct responses to temperature during dormancy development in woody plants remains an investigative challenge.

1989, Free radical and freezing injury to cell membranes of winter wheat, -Physiol, Plant, 76: 86-94,The symptoms of injury in microsomal membranes isolated from crowns of seedlings of Triticum aestivum L, eultivar Fredrick after a lethal freeze-thaw stress included an increased lipid phase transition temperature, loss of lipid phosphate (lipid-P), and increased free fatty acid levels. However, minimal changes in fatty acid saturation were observed, suggesting minimal amounts of hpid peroxidation. All of these injury symptoms, including the lack of lipid peroxidation, were simulated in vitro by treatment of isolated membranes with oxygen free radicals, generated from either xanthine oxidase (EC 1,1,3,22) or paraquat (l,r-dimethyl-4,4'-bipyridinium dichloride). Further evidence indicating a relationship between free radicals and freezing injury comes from the observation that both protoplasts and microsomal membranes isolated from wheat seedhngs, that had been acclimated to induce freezing tolerance, also had increased tolerance of oxygen free radicals, and contained higher lipidsoluble antioxidant levels, than those from non-acclimated seedlings, Lipid-soluble antioxidants accumulated in the crown tissue of the wheat seedling during the aeclimation period. Freezing stress accelerated the formation of oxygen free radicals. Membranes isolated from crowns after a freeze-thaw stress tended to produce higher levels of superoxide as shown by the reduction of Tiron (l,2-dihydroxy-l,3-benzenedisulfonic acid). In protoplasts, increased superoxide production coincided with lethal freezing injury. These results are discussed in terms of the possible involvement of oxygen free radicals in mediating aspects of freezing injury to cell membranes.

No abstract