Problem:

If you grow a plant from seed in your nice warm house, then plant it out in your temperate garden, it will stop growing for a while, possibly die, and if not, subsequently resume growth. Standard gardening practice is to 'harden off' plants, moving them to an area of intermediate temperature for a while before planting them out.

Required:

Question 1: Why does this happen?Please express your answer.

Question 2: What is the difference between a plant adapted to a warm environment and one adapted to a cold environment?

Question 3: Expression of cold-tolerance genes? Levels of some secondary metabolite? Thickness of cell walls? Density of root hairs?

An unidentified author on the Royal Horticultural Society website states that "The effect of hardening off is to thicken and alter the plant's leaf structure and increase leaf waxiness", which is not quite detailed enough to satisfy.