Drivers of apoplastic freezing in gymnosperm and angiosperm branches (original) (raw)
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The interaction between freezing tolerance and phenology in temperate deciduous trees
Frontiers in plant science, 2014
Temperate climates are defined by distinct temperature seasonality with large and often unpredictable weather during any of the four seasons. To thrive in such climates, trees have to withstand a cold winter and the stochastic occurrence of freeze events during any time of the year. The physiological mechanisms trees adopt to escape, avoid, and tolerate freezing temperatures include a cold acclimation in autumn, a dormancy period during winter (leafless in deciduous trees), and the maintenance of a certain freezing tolerance during dehardening in early spring. The change from one phase to the next is mediated by complex interactions between temperature and photoperiod. This review aims at providing an overview of the interplay between phenology of leaves and species-specific freezing resistance. First, we address the long-term evolutionary responses that enabled temperate trees to tolerate certain low temperature extremes. We provide evidence that short term acclimation of freezing ...
PLANT PHYSIOLOGY, 2014
Freeze-thaw events can affect plant hydraulics by inducing embolism. This study analyzed the effect of temperature during the freezing process on hydraulic conductivity and ultrasonic emissions (UE). Stems of 10 angiosperms were dehydrated to a water potential at 12% percentage loss of hydraulic conductivity (PLC) and exposed to freeze-thaw cycles. The minimal temperature of the frost cycle correlated positively with induced PLC, whereby species with wider conduits (hydraulic diameter) showed higher freezethaw-induced PLC. Ultrasonic activity started with the onset of freezing and increased with decreasing subzero temperatures, whereas no UE were recorded during thawing. The temperature at which 50% of UE were reached varied between 29.1°C and 231.0°C across species. These findings indicate that temperatures during freezing are of relevance for bubble formation and air seeding. We suggest that species-specific cavitation thresholds are reached during freezing due to the temperature-dependent decrease of water potential in the ice, while bubble expansion and the resulting PLC occur during thawing. UE analysis can be used to monitor the cavitation process and estimate freeze-thaw-induced PLC. Ball MC, Canny MJ, Huang CX, Egerton JJG, Wolfe J (2006) Freeze/thawinduced embolism depends on nadir temperature: the heterogeneous hydration hypothesis. Plant Cell Environ 29: 729-745
American Journal of Botany, 2005
The response to freeze-thaw stress was examined for two co-occurring evergreen species, Malosma laurina and Rhus ovata. Laboratory and field experiments on adults and seedlings were made in the spring and winter in 1996 and again on adults in 2003 and 2004. Laboratory and field results indicated that the stem xylem for adults of M. laurina and R. ovata were similarly susceptible to freezing-induced cavitation (percentage loss of conductivity ϭ 92 Ϯ 2.6% for R. ovata and 90 Ϯ 4.2% for M. laurina at Յ Ϫ6ЊC). In contrast, leaves of M. laurina were more susceptible to freezing injury than leaves of R. ovata. Among seedlings in the field, leaves of M. laurina exhibited freezing injury at Ϫ4ЊC and total shoot mortality at Ϫ7.2ЊC, whereas co-occurring seedlings of R. ovata were uninjured. Surprisingly, R. ovata tolerates high levels of freezing-induced xylem embolism in the field, an apparently rare condition among evergreen plants. Rhus ovata avoids desiccation when xylem embolism is high by exhibiting low minimum leaf conductance compared to M. laurina. These results suggest a link between minimum leaf conductance and stem hydraulics as a mechanism permitting the persistence of an evergreen leaf habit in freezing environments.
Structural changes in acclimated and unacclimated leaves during freezing and thawing
Functional Plant Biology, 2004
Freeze-induced damage to leaf tissues was studied at different states of acclimation to low temperatures in snow gum, Eucalyptus pauciflora Sieber ex Sprengel. Intact, attached leaves of plants grown under glasshouse or field conditions were frozen at natural rates (frost-freezing) and thawed under laboratory conditions. Leaves were cryo-fixed unfrozen, during frost-freezing or after thawing for observation in a cryo-scanning electron microscope. Frost-freezing in unacclimated tissues caused irreversible tissue damage consistent with tissue death. Intracellular ice formed in the cambium and phloem, killing the cells and leaving persistent gaps between xylem and phloem. Many other cells were damaged by frost-freeze-induced dehydration and failed to resorb water from thawed extracellular ice, leaving substantial amounts of liquid water in intercellular spaces. In contrast, acclimated leaves showed reversible tissue displacements consistent with leaf survival. In these leaves during fr...
HortScience
It is not well known how cold-hardy new buds and emerging leaves or flowers are during spring. Extreme temperature fluctuations that sometimes bring early frost in spring (April–May) are very common in northern latitudes and cause severe damage to emerging leaves and flowers. Even though most woody plants can tolerate frost in spring, others show early tissue damage and can fully recover. There are some trees, e.g., Japanese maples (Acer palmatum) that when leaves are damaged due to spring frost, the results include severe dieback and eventual death. We tested new flowers and leaves of four crabapples: Malus ×micromalus, M. sargentii, `Mary Potter', and M. hupehensis, after budbreak for 3 years using electrical conductivity (EC) and differential thermal analysis (DTA) in spring: May 1997, Apr. 1998, and Apr. 2000, at The Morton Arboretum. Both flowers and leaves can tolerate from –6 to –12 °C and we observed higher ion leakage in leaves than flowers. The high temperature exother...
Effect of apoplastic proteins on freezing tolerance in leaves
Phytochemistry, 1999
Freezing tolerance was determined in cabbage (Brassica oleracea cv Acephala) and winter wheat (Triticum aestivum cv DogAE u-88) leaves growing under control and cold conditions. Freezing injury was less in cold-acclimated leaves than in control leaves. In cold-acclimated leaves, the freezing injury increased when apoplastic solution is extracted. In addition, ice nucleation activity was lower with apoplastic proteins extracted from cold-acclimated leaves than from control leaves. These results suggest that the proteins present in the apoplast during cold acclimation are an important component of the mechanism by which cabbage and winter wheat leaves inhibit extracellular ice formation. Winter wheat has greater freezing tolerance than cabbage because winter wheat leaves have lower freezing injury and apoplastic proteins in winter wheat leaves have lower ice nucleation activity.