A Touch of Frost

Just as we prepare for winter, changing our habits and clothing, plants are quietly going through changes too. The most striking of these is leaves turning to lovely autumnal colours. This occurs as the chlorophyll degrades in the leaf, so we can see the other pigments that are there all year too, but masked by the green chlorophyll. These include orange carotenoids, purple-red anthocyanin, and yellow xanthophylls. Hormones then cause the leaves then abcise, (from the Latin ‘to cut off’), thereby protecting them from winter frost damage.

Evergreen plants protect their leaves from freezing by using their own ‘antifreeze’. This is just a high percentage of dissolved sugar and amino acids in the cells, which lowers the freezing point of water.
This is the reason why late spring frosts can be so devastating to fresh blossom and new leaves, as these changes have not occurred. Once the fluid contained within the cell has frozen, it expands and breaks the cell wall beyond repair.

The shortening days also induces dormancy in many plants, an example being the transformation of buds to withstand the cold days ahead with thick protective scales (as can clearly be seen on Horse Chestnuts).