Surviving A Frosty Reception

Many herbaceous plants, such as California poppy, broad beans and winter lettuce, survive repeated light frost freeze/thaw cycles throughout winter, collapsing and freezing at night then recovering as the day warms up.

While scientists know that some plants have specially adapted cell membranes that survive repeated light freezing and thawing, a group of Canberra researchers wondered how the fragile leaves coped with the build-up of ice deposits outside the cells.

By using liquid nitrogen to snap-freeze frost-frozen leaves and recovered leaves, and examining them using a cryo-scanning electron microscope, they saw that the living plant cells in the frost-frozen leaves were reduced to a third of their normal volume, as water was drawn out of them to form huge ice deposits outside the cell.

The plant accommodated the ice by forming fault regions between cells, which opened up to enclose the ice. When the ice melts in the morning sun the water returns to the wilted cells, the faults close up, and the leaf returns to normal.

The team is now investigating exactly how this newly-discovered phenomenon of repeated separation and rejoining of living cells is accomplished. Further research into the effects of frost on other plants, including wheat and canola, is also being planned.

Professor McCully, and collaborators MJ Canny and CX Huang from the Australian National University's Research School of Biological Sciences, have published their observations in the Annals of Botany.

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