Therefore, by virtue of its ability to withstand temperatures greatly below those at which its tissues freeze, D. antarctica is a true cryophile.Īll Antarctic plant species studied have been reported to exhibit ice recrystallization inhibition (RI) activity when exposed to low temperature ( Doucet et al. D. antarctica has a CA-induced freeze tolerance mechanism that involves depression of its ELT 50 from −12.0 to −26.6 ☌, well below its acclimation induced ice nucleation temperature of −10.4 ☌ ( Bravo et al. 2006), but temperatures are highly variable and plants are regularly exposed to episodes of sub-zero temperatures. During the short growing season in the Antarctic summer, mean daily temperatures range between 0 and 6 ☌ ( Cannone et al. For much of the year D. antarctica is quiescent and covered by snow. (Antarctic hair grass) provides a unique resource in which to study adaptation to extreme abiotic stresses in plants. 2004 Hannah, Heyer & Hincha 2005).Īs one of only two vascular plants to have colonized Antarctica, Deschampsia antarctica E. 2006), with many genes reported to be cold induced ( Fowler & Thomashow 2002 Maruyama et al. Most studies on the regulation of CA induced gene expression have utilized the model plant, Arabidopsis thaliana, which is moderately tolerant of sub-zero temperatures and is a freeze avoider ( Reyes-Diaz et al. The two major CA induced mechanisms that plants use to deal with sub-zero temperatures are freeze tolerance, and freeze avoidance, or supercooling.
![irip serials irip serials](https://lasopawatch715.weebly.com/uploads/1/2/7/1/127171087/184066787.jpg)
Furthermore, there is a distinct phenomenon known as sub-zero acclimation, or second-phase hardening, produced by exposure to moderate sub-zero temperatures, that can further enhance CA mediated freeze tolerance, and is associated with the induction of a transcriptome and proteome distinct from that of CA ( Herman et al.
![irip serials irip serials](https://nmac.to/wp-content/uploads/2014/08/iRip.png)
Acquired tolerance to freezing stress can also be lost through a less well characterized process known as de-acclimation, that has been reported to occur more rapidly than acclimation ( Kalberer, Wisniewski & Arora 2006). CA is associated with a range of physiological and biochemical changes, including modulation of gene expression, protein levels and protein activity ( Thomashow 1999). Tolerance to freezing temperatures can be acquired in advance by exposure to low, non-freezing temperatures, in a process known as cold acclimation (CA). Plants can enhance their capacity to withstand various abiotic and biotic stresses through acquired tolerance. Thus, D. antarctica is highly responsive to temperature fluctuations, able to rapidly deploy IRIP based RI activity and enhance its freeze tolerance. Plant survival-based testing revealed that cold acclimation enhanced freeze tolerance by 5 ☌ within 4 d, and that sub-zero acclimation conferred an additional 3 ☌ of tolerance. These data correlated with the onset and decline of RI activity in acclimated and de-acclimated leaves. Western analysis detected three major immuno-reactive bands whose pattern of accumulation mirrored that of transcript. Quantitative profiling revealed that IRIP transcript levels significantly increased and decreased within hours of cold acclimation and de-acclimation, respectively, becoming up to 1000-fold more abundant in fully acclimated plants.
![irip serials irip serials](https://static.taigame.org/image/screenshot/201304/apothecarium-renaissance-of-evil-collectors-edition-4.jpg)
We used molecular and physiological analyses to investigate temporal responses of D. antarctica to cold acclimation and de-acclimation, and sub-zero acclimation. We have previously characterized a multi-gene family in D. antarctica encoding ice recrystallization inhibition proteins (IRIPs) whose transcript levels are responsive to cold acclimation, and whose products confer ice recrystallization inhibition (RI) activity that can account for activity seen in cold acclimated plants. Desv., one of two higher plants indigenous to Antarctica, represents a unique resource for the study of freeze tolerance mechanisms. The cryophilic Antarctic hair grass, Deschampsia antarctica E.