# Response of Plants to Touch Stress at Morphological, Physiological and Molecular Levels

## TL;DR

Plants respond to touch stress with changes in shape, growth, and internal processes, which are influenced by hormones and genetic activity.

## Contribution

The study integrates new findings on how mechanical stress affects hormonal balance and plant development.

## Key findings

- Prolonged mechanical stress suppresses auxin biosynthesis but does not affect auxin transport.
- Thigmostimulation is linked to gibberellin biosynthesis, flowering intensity, and other phytohormone signaling pathways.
- Calmodulin isoforms and GH3.1 gene expression correlate, suggesting a mechanistic link between mechanosensing and hormone regulation.

## Abstract

Thigmomorphogenesis denotes a suite of anatomical, physiological, biochemical, biophysical, and molecular responses of plants to mechanical stimulation. This phenomenon is evolutionarily conserved among diverse plant lineages; however, the magnitude and character of the response are strongly determined by both the frequency and intensity of the applied stimulus. In angiosperms, thigmomorphogenetic reactions typically occur gradually, reflecting a complex interplay of morphological alterations, biochemical adjustments, and genetic reprogramming. In dicotyledonous plants, thigmomorphogenesis is commonly expressed as a reduction in leaf blade surface area, shortening of petioles, decreased plant height, radial thickening of stems, and modifications in root system architecture. In monocotyledons, in turn, mechanical stress frequently results in stem rupture below the inflorescence, with concomitant shortening and increased flexibility of younger internodes. These specific traits can be explained by structural features of monocot secondary walls as well as by the absence of vascular cambium and lateral meristems. Mechanical stimulation has been shown to initiate a cascade of responses across multiple levels of plant organization. The earliest events involve activation of mechanoresponsive genes (e.g., TCH family), followed by enzymatic activation, biochemical shifts, and downstream physiological and molecular adjustments. Importantly, recent findings indicate that prolonged mechanical stress may significantly suppress auxin biosynthesis, while leaving auxin transport processes unaffected. Moreover, strong interdependencies have been identified between thigmostimulation, gibberellin biosynthesis, and flowering intensity, as well as between mechanical stress and signaling pathways of other phytohormones, including abscisic acid, jasmonic acid, and ethylene. At the molecular scale, studies have demonstrated a robust correlation between the expression of specific calmodulin isoforms and the GH3.1 gene, suggesting a mechanistic link between mechanosensing, hormone homeostasis, and regulatory feedback loops. The present study consolidates current knowledge and integrates novel findings, emphasizing both morphological and cellular dimensions of thigmomorphogenesis. In particular, it provides evidence that mechanical stress constitutes a critical modulator of hormonal balance, thereby shaping plant growth, development, and adaptive potential.