Cold resistance in Antarctic angiosperms

Deschampsia antarctica Desv, (Poaceae) and Colobanthus quitensis (Kunth) Ba rtl, (Cariophyllaceae) are the only two vascular plants that have colonized the Maritime Antarctic, The primary purpose of the present work was to det ermine cold resistance mechanisms in these two Antarctic plants. This was a chieved by comparing thermal properties of leaves and the lethal freezing t emperature to 50% of the tissue (LT50), The grass D, antarctica was able to tolerate freezing to a lower temperature than C, quitensis. The main freez ing resistance 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 lit tle 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. antarc tica growing in the laboratory under cold-acclimation conditions was studie d. During the cold-acclimation treatment, the LT50 was lowered more effecti vely 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 v alues). Oligo and polyfructans accumulated significantly during cold acclim ation only with the medium day length treatment. Oligofructans accounted fo r more than 80%, of total fructans, The degrees of polymerization were most ly between 3 and 10, C, quitensis under cold acclimation accumulated a simi lar amount of sucrose than D, antarctica, but no fructans were detected. Th e suggestion that survival of Antarctic plants in the Antarctic could be at least partially explained by accumulation of these substances is discussed .