Thermotropism

Mimosa pudica also show thermotropism by the collapsing of leaf petioles leading to the folding of leaflets, when temperature drops.

[1] The term "thermotropism" was originated by French botanist Philippe Van Tieghem in his 1884 textbook Traité de botanique.

[2] The definition of thermotropism can sometimes be confused with the term, thermotaxis, a mechanism by which temperature gradients can alter the behavior of cells, such as moving toward the cold environment.

[5] Gardening hobbyists have frequently noted the dramatic change in the shape of Rhododendron or "Rhodie" leaves during warm versus cold weather.

Research on Rhododendron leaf thermotropism suggests that the curling response might help prevent damage to cell membranes caused by rapid thawing after a freeze.

During the winter months, wild Rhododendrons in the Appalachian Mountains regularly drop to freezing temperatures at night, then thaw again in the early morning.

The exact stimulus for this output is not understood, but it is known that freezing cold temperatures causes an influx of water to the leaf petiole.

Another hypothesis for leaf rolling called the desiccation theory, circulating in recent years, is to prevent membrane and light damage.

[8] Thermotropic response in rhododendron leaves protects cells by changing leaf shape and protein levels.

[11] Para-heliotropic movements in the Phaseolus genus (beans) coincided with regulating leaf temperatures to improve photosynthesis efficiency and heat avoidance in hot, sunny, and arid environments.