thermonasty

thumb|Rhododendron (Nature's thermometers) In plant biology, thermonasty is a nondirectional response to temperature in plants. It is a form of nastic movement, not to be confused with thermotropism, which is a directional response in plants to temperature. A common example of this is in some Rhododendron species, but thermonasty has also been observed in other plants, such as Phryma leptostachya. Flower opening in certain crocus and tulip species is also known to be thermonastic. These movements are thought to be regulated by having unequal cell elongation in certain plant tissues, causing different tissues to bend. In other processes, like in the temperature regulation of flower openings, movement has instead been shown to be a result of irreversible cell growth, a growth type not typically associated with plant movement. Furthermore, thermonasty has been shown to be independent of other environmental signals, such as light and gravity.

Thermonasty is generally considered to be an adaptation for protection against colder temperatures. It is hypothesized that thermonastic movement is an adaptation for photoprotection, as harsh freezing conditions make leaves more susceptible to light damage from the sun. In flowers it may instead serve as a signal for flower opening and closing with rising and falling temperatures. Although the exact mechanism for thermonasty is still not fully understood, there has been research conducted to reveal more.