How to survive freezing: Ice management strategies of a nival plant species
In the nival zone the snow free time period is short (2–3 months). During this time, Ranunculus glacialis grows and reproduces successfully. We investigated how the challenging environmental conditions are survived from plant to cellular level at a natural growing site at Mount “Kleiner Isidor” in the Central Alps of Tyrol.
We found that atmospheric temperatures did not mirror leaf temperatures. Daily leaf temperatures dropped below zero at a rate of 56%, whereas air frosts occurred only at 17%. Leaf freezing occurred even when air temperature was above 0 °C. Ice nucleation was observed at average at −2.6 °C and started usually independently in each leaf. As the shoot is deep-seated in unfrozen soil we suggest it to act as an efficient ice barrier between leaves. Upon tissue ice formation all mesophyll cells were immediately subjected to freezing cytorrhysis; below −3 °C the cell area was reduced at an average of 48%. Huge ice masses formed in intercellular spaces of the spongy parenchyma. After thawing, photosynthesis was unaffected regardless if ice had formed. Cell walls were pectin rich and triglycerides occurred particularly in the spongy parenchyma.
Ranunculus glacialis defies unfazed recurrent freezing events during the active growing and reproduction phase. Many lowland and crop species are sensitive to freezing throughout development. As due to climate change, devastating spring frost events are anticipated to increase, alpine plants with a high frost survival capability may come into focus of research interest, as they can serve as perfect model organisms for freezing tolerance during active growth.
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| Figure 1 - Ranunculus glacialis at a natural growing site on 3185 m a.s.l (a). Huge ice masses (some are indicated by red arrows) are accommodated at sublethal freezing temperatures in the intercellular spaces and cells respond to the presence of ice by severe freezing cytorrhysis (b). Bar width: 100 µm. |
Stegner M, Lackner B, Schäfernolte T, Buchner O, Xiao N, Gierlinger N, Holzinger A, Neuner G (2020) Winter nights during summer time: stress physiological response to ice and the facilitation of freezing cytorrhysis by elastic cell wall components in the leaves of a nival species. International Journal of Molecular Sciences 21:18. https://doi.org/10.3390/ijms21197042