Cells accumulate sugars and amino acids that act as antifreeze to lower the freezing point of the water in the protoplasm. The buds that remain following leaf drop become enclosed in thick, protective scales so they can function as the meristems for spring growth. The lipids or oils that make up the plasma membrane are altered to become more fluid , so they are less like a solid and more like an oil at lower temperatures. These changes take place over several weeks and contribute to the process of cold-hardening . The ability to cold-harden determines the distribution of plant species into zones of low minimum annual temperatures.
Many plants grown in temperate climates have a negative response to high temperatures .
These plants are most efficient at temperatures of 100 F or higher .