Answer:
cells suddenly become flaccid after stimulation because of the loss of K+
Explanation:
Nastic responses are non-directional movements of parts of plants in response to diffuse stimuli. The closinf of leaves of Mimosa pudica when touched is a type of haptonastic response. These movements are brought about by turgor pressure changes of the leaf and the petal bases. At the bases, there are pressure sensitive swellings called pulvini which through loss of turgidity cause nastic movements.
According to research, cells go through an efflux of potassium (K) which leads to the reduction of turgor. Direct quote on Reed-Guy et al. (2017)'s paper "This mechanism is initiated when a stimulus causes an efflux of potassium within the leaf, creating a loss of turgor pressure, which closes the leaves and causes them to droop."