Are nastic responses growth responses?

Question

I know they are non directional movement responses, but like tropic responses, does their movement involve growth?

Answer 1

Hello!

To answer your question in short, nastic movements are not usually growth responses.

Nastic responses are usually reversible i.e. Sensitive plants folds its leaves and can unfold them, no growth. Tropic movements i.e. phototropism, plant grow towards lights and this cannot be undone.

Here is more detail:

Tropic responses= external stimuli with a direction (i.e. light, gravity, touch) produces a directional move, which are usually not reversible

Ex. Phototropism plants stems responds to light and grows toward the direction of the light. This growth cannot be undone.

Nastic responses= external stimuli that is direction independent produces mechanic response, that are usually fast and reversible.

Ex. Sensitive plant (Mimosa pudica) closing its leaves upon sensing mechanical touch. The leaves will fold regardless from what angle you touch them. The plant can open its leaves again, so no growth

Sources

Guo, Q et al. “Fast nastic motion of plants and bioinspired structures.” Journal of the Royal Society, Interface vol. 12,110 (2015): 0598. doi:10.1098/rsif.2015.0598