Gravity sensing and signal conversion in plant gravitropism

Abstract

Plant organs control their growth orientation in response to gravity. Within gravity-sensing cells, the input (gravity sensing) and signal conversion (gravity signalling) progress sequentially. The cells contain a number of high-density, starch-accumulating amyloplasts, which sense gravity when they reposition themselves by sedimentation to the bottom of the cell when the plant organ is re-orientated. This triggers the next step of gravity signalling, when the physical signal generated by the sedimentation of the amyloplasts is converted into a biochemical signal, which redirects auxin transport towards the lower flank of the plant organ. This review focuses on recent advances in our knowledge of the regulatory mechanisms that underlie amyloplast sedimentation and the system by which this is perceived, and on recent progress in characterising the factors that play significant roles in gravity signalling by which the sedimentation is linked to the regulation of directional auxin transport. Finally, we discuss the contribution of gravity signalling factors to the mechanisms that control the gravitropic set-point angle.

Antagonistic Inhibitory Circuits Integrate Visual and Gravitactic Behaviors

“…Mechanisms to detect and respond to Earth's gravitational field are found widely throughout the kingdoms of life, both in unicellular and multicellular organisms [1][2][3]. In most animals, detection of gravity involves an organ with a dense mineralized mass and accompanying sensory cells.…”

Root Tropisms: Investigations on Earth and in Space to Unravel Plant Growth Direction

“…However, the exact role of the cytoskeleton deserves more attention, as pharmacological experiments gave contradictory results, showing both inhibition and promotion of gravitropism (Ma and Hasenstein, 2006;Blancaflor, 2013). A detailed overview of studies of early gravitropic signaling is summarized in Nakamura et al (2019).…”

Nutations in plant shoots: endogenous and exogenous factors in the presence of mechanical deformations

“…We use equations (2.17) to describe a response of a material cross section to a stimulus sensed at the very same location. However, they might be adapted to the case of nonlocal responses, as it occurs for gravitropic reactions of roots [27]. Moreover, these expressions allow to include memory and delay effects, as done in recent studies [9,25], and the instantaneous models are recovered as special cases by choosing the Dirac delta as response function.…”

“…On the contrary, a more accurate choice is to consider the stimulus as perceived by the gravity sensing apparatus. In particular, it is widely accepted that plant organs sense gravity through the sedimentation of starch-filled plastids, called statoliths, into specialized cells, called statocytes, which are found along the shoot growing zone and in the root caps [9,27]. In this case, we can assume the stimulus s to be given by the average outer normal to the free surface of the pile of statoliths, as shown in Fig.…”