Who do the leaves fall off in the autumn? Part I

OK it is summer on the norhern hemisphere and one should maybe not think so much about autumn and winter, but newertheless her comes some thoughts:

With water-filled leaves left on the tree, would first of all the cells burst as the water expands when it freezes. The trees could protect themselves by producing/store lots of sugar in the leaves during the early fall to get a high sugar content in the cells.

This would work like glycol in the coolant/antifreeze and provide some protection. To produce this sugar is obviously more dangerous and energy consuming than to simply turn off all cell functions in the leaves and let them fall off.