Plant Tropism: Cue Detection and Control Over Growth Direction – The Many Ways for Plants to Explore and Exploit the Environment

Abstract Movement promotes organismal survival. To move, one needs to interact with the environment—detect light (sight), sense surfaces (touch), recognize chemicals (taste), and distinguish sounds (hearing). Therefore, environmental sensing is critical for life. Due to their sessile nature, plants have developed alternative ways to explore the world using growth and/or shape changes of their organs. The main drivers of such exploration are meristems, the continuously dividing tips of the plant body, and elastic, modular plant cell walls. These mechanisms enable plants to adapt to their surroundings by modifying growth patterns and responding to environmental cues. Tropisms, the key mechanisms by which plants sense their environment and adjust growth direction, have been broadly studied. Plants rely on a complex interplay of hormonal signaling, gene expression, and cellular processes to perceive and respond to various stimuli. Key hormones such as auxins, cytokinins, and ethylene play crucial roles in regulating these responses. Additionally, specialized cells and structures, such as statocytes and statoliths, contribute to the plant’s ability to detect and react to changes in their environment. This review focuses on gravi-, hydro- and chemotropism, with particular emphasis on nutritropism - the directional growth response to gradients of essential micro- and macro-elements. Understanding how plants perceive and respond to uneven distributions of water and nutrients in the soil could inform strategies to enhance biofortification, improve root adaptation to changing moisture conditions under climate stress, and promote more efficient and sustainable fertilization practices. By integrating recent insights into how roots sense environmental cues, coordinate hormonal signaling, and adapt their architecture, we underscore the potential of tropism research to advance crop improvement and sustainable resource use.