Plants can and do move! Aside from growth, some plants can move in response to the environment around them. One of the coolest movements, in my opinion, is nyctinastic movements. By definition: Nyctinasty – (Nic-ti -nasty), is a type of movement where plants close their leaves at night and open them during the day (1,2).
Defining It All
Let’s take a step back, and simply define nastic. Nastic is a plant that responds to something in the environment by moving, but how the plant actually moves is not directed by the environment (1). That’s kind of a mouthful so to help, I am going to give you an example. Say you touched a plant and its response was to uproot itself and start dancing around while singing with a little top hat and cane. Not only would this be a nastic movement it would also be absolutely mind blowing to see and improbable to actually ever happen. On the other hand, if you touched a plant and it responded by pulling away in the exact opposite direction that you touched it, that is called a tropic movement and not a nastic movement. This is a tropic movement because the plant’s movement is directed by the environmental cue (i.e. your touch).
By adding the prefix “nyc” to the front of “nastic” the environmental cue causing the plant’s movement is specific to dusk and dawn. Nyctinastic has also been called the “sleep movement” because some historical scientists thought this was a plant’s version of going to sleep at night. Sleep movement is easier to remember and say for most people too. However, since plants do not actually sleep like we humans or animals do, nystinasty is the preferred term among scientists (1,2).
Who, What, How?
There are several types of plants that take part in nyctinasty, including those of the genus Mimosa (1,2). This is not where orange juice or champagne comes from. But why does it happen and how does it happen? Yeah, those are both pretty good questions and there isn’t one easy single answer to either of them. The majority of plants around the world do not perform nyctinastic movements. However, nyctinasty does occur in tropical and temperate plants; in large trees to small flowers; to plants that live in the desert to plants that live in the water. Could there really be one answer to why or how all of these plants take part in nyctinasty (1)?
Why?
Scientists have not actually agreed on one answer on why some plants have nyctinastic movements. Here are 3 of the most commonly shared hypotheses. 1. Darwin first proposed that by closing their leaves the plants may stay a little warmer at night because they have less surface area exposed to the air.. 2. By closing at night there would be less accumulation of water from dew and rain on the leaves. 3. By closing their leaves they become less noticeable and thus less appealing to nocturnal plant-eating animals (1). This third one seems to be the most widely accepted.
How?
Generally speaking, nyctinasty occurs through the movement of water within a plant. In some plants a hinge-like structure forms at the base of the leaf called a pulvinus (2). The movement of water between cells and across this hinge causes the movement of the leaves to open and close (1,2). Depending on the species and how the water moves, leaves will close in a couple of different ways. Either they will close so the top of the leaves are facing each other, so the bottom of the leaves are facing each other, or so the leaves twist toward the plant stem (1). Mimosa sp. (the plant shown in the video) closes with the top of the leaves (leaflets actually) facing each other.
Citations:
- Minorsky, P.V. (2019). The Functions of Foliar Nyctinasty: A Review and Hypothesis. Biological Reviews 94: 216-229.
- Mano, H. and M. Hasebe (2021). Rapid movements in plants. Journal of Plant Research 134: 3-17.
Courtney The Frogologist 