%0 Journal Article %1 Bravoetal_01 %A Bravo, L. A. %A Ulloa, N. %A Zuniga, G. E. %A Casanova, A. %A Corcuera, L. J. %A Alberdi, M. %D 2001 %J Physiologia Plantarum %K antarctic, bibtex-import, cellular, citeulikeExport freezing, solutes, tolerance %P 55--65 %T Cold resistance in antarctic angiosperms %V 111 %X Deschampsia antarctica Desv. (Poaceae) and Colobanthus treatquitensis (Kunth) Bartl. (Cariophyllaceae) are the only two vascular plants that have colonized the Maritime Antarctic. The primary purpose of the present work was to determine cold resistance mechanisms in these two Antarctic plants. This was achieved by comparing thermal properties of leaves and the lethal freezing temperature to 50\% of the tissue (LT50). The grass D. antarctica was able to tolerate freezing to a lower temperature than C. quitensis. The main freezing resis- tance mechanism for C. quitensis is supercooling. Thus, the grass is mainly a freezing-tolerant species, while C. quitensis avoids freezing. D. antarctica cold acclimated by reducing its LT50. C. quitensis showed little cold-acclimation capacity. Because day length is highly variable in the Antarctic, the effect of day length on freezing tolerance, growth, various soluble carbohydrates, starch, and proline contents in leaves of D. antarctica growing in the laboratory under cold-acclima-tion conditions was studied. During the cold-acclimation treatquitensis ment, the LT50 was lowered more effectively under long day (21:3 h light:dark) and medium day (16:8) light periods than under a short day period (8:16). The longer the day length treatment, the faster the growth rate for both acclimated and non-acclimated plants. Similarly, the longer the day treatment during cold acclimation, the higher the sucrose content (up to 7-fold with respect to non-acclimated control values). Oligo and polyfructans accumulated significantly during cold acclimation only with the medium day length treatment. Oligofruc- tans accounted for more than 80\% of total fructans. The degrees of polymerization were mostly between 3 and 10. C. quitensis under cold acclimation accumulated a similar amount of sucrose than D. antarctica, but no fructans were detected. The suggestion that survival of Antarctic plants in the Antarctic could be at least partially explained by accumu- lation of these substances is discussed.

@article{Bravoetal_01, abstract = {{Deschampsia antarctica Desv. (Poaceae) and Colobanthus treatquitensis (Kunth) Bartl. (Cariophyllaceae) are the only two vascular plants that have colonized the Maritime Antarctic. The primary purpose of the present work was to determine cold resistance mechanisms in these two Antarctic plants. This was achieved by comparing thermal properties of leaves and the lethal freezing temperature to 50\% of the tissue (LT50). The grass D. antarctica was able to tolerate freezing to a lower temperature than C. quitensis. The main freezing resis- tance mechanism for C. quitensis is supercooling. Thus, the grass is mainly a freezing-tolerant species, while C. quitensis avoids freezing. D. antarctica cold acclimated by reducing its LT50. C. quitensis showed little cold-acclimation capacity. Because day length is highly variable in the Antarctic, the effect of day length on freezing tolerance, growth, various soluble carbohydrates, starch, and proline contents in leaves of D. antarctica growing in the laboratory under cold-acclima-tion conditions was studied. During the cold-acclimation treatquitensis ment, the LT50 was lowered more effectively under long day (21:3 h light:dark) and medium day (16:8) light periods than under a short day period (8:16). The longer the day length treatment, the faster the growth rate for both acclimated and non-acclimated plants. Similarly, the longer the day treatment during cold acclimation, the higher the sucrose content (up to 7-fold with respect to non-acclimated control values). Oligo and polyfructans accumulated significantly during cold acclimation only with the medium day length treatment. Oligofruc- tans accounted for more than 80\% of total fructans. The degrees of polymerization were mostly between 3 and 10. C. quitensis under cold acclimation accumulated a similar amount of sucrose than D. antarctica, but no fructans were detected. The suggestion that survival of Antarctic plants in the Antarctic could be at least partially explained by accumu- lation of these substances is discussed.}}, added-at = {2019-03-31T01:14:40.000+0100}, author = {Bravo, L. A. and Ulloa, N. and Zuniga, G. E. and Casanova, A. and Corcuera, L. J. and Alberdi, M.}, biburl = {https://www.bibsonomy.org/bibtex/279f39365e9a79f1ece652847dcf6bd3a/dianella}, citeulike-article-id = {1523626}, comment = {(private-note)references therein on costs and benefits of supercooling Supercooling is less safe than cold-hardeningn In high tropical Andean habitats, ground-level plants showed freezing tolerance, while arborescent forms showed supercooling as the main mechanism of cold resistance (Goldstein et al. 1985, Squeo et al. 1991). They suggested that a combination of freezing tolerance and avoidance by insulation is less expensive and a more secure mechanism than supercooling alone. There is no evidence of direct involvement of fructans in cryoprotection. However, they have a well-established osmotic activity, which could indicate a possible function as volume regulators of vacuoles (Pontis 1989). Further research is necessary to clarify if fructans are involved in cold resistance. * how about osmotic to keep vessels full?* detached leaves cooled at 2oC/h to -17, thermocouple attached, enclosed in cryo-tube (to keep humidity constant) Freezing tolerance- used AgI as a nucleating agent temperature lowered at a rate of 1C h 1. The vials were maintained for 90 min at each test temperature and then removed and thawed at 3C in a refrigerator. LT50- 50\% leakage- "a good index of freezing injury for herbaceous plant tissues". Total soluble sugars were determined spectrophotometrically by the phenol-sulfuric method (Dubois et al. 1956), at a wavelength of 485 nm, using glucose as standard. Carbohydrates were separated by HPLC with a Partisil 10 carbohydrate column (Whatman, Maidstone, UK) at room temperature. The mobile phase was a mixture of acetonitrile: water (75:25 v:v) with a flow of 1 ml min 1. A differential refractometer (Knauer, Berlin, Germany) was used for detection and quantification of sucrose, glucose and fructose using pure standards (Merck KGaA, Darmstadt, Germany). TLC for fructan and starch analysis Results: D. antarctica LT50 was -26.6 (21 days of acclimation) nucleation temperatures and LT50 decreased following cold-acclimation (nucleation at -5.3 non-acclimated, -10.4 acclimated) C. quitensis acclimation didn't cause such}, interhash = {9f17b485eb9f8ee2b6378d52e7dde7b3}, intrahash = {79f39365e9a79f1ece652847dcf6bd3a}, journal = {Physiologia Plantarum}, keywords = {antarctic, bibtex-import, cellular, citeulikeExport freezing, solutes, tolerance}, pages = {55--65}, posted-at = {2007-07-31 06:08:16}, priority = {2}, timestamp = {2019-03-31T01:16:26.000+0100}, title = {{Cold resistance in antarctic angiosperms}}, volume = 111, year = 2001 }