In-vivo femtonewton-sensing nanotribology of Tradescantia zebrina leaf cell inner surface using roll rotation detection

TL;DR

This work addresses non-invasive in vivo probing of plant cell interior mechanics by using native calcium oxalate crystals in Tradescantia zebrina as optically trapped probes. The authors exploit roll (out-of-plane) rotation detected via cross-polarized forward scattering to perform nanoscale tribology measurements of the inner leaf surface, supported by FDTD-based stability analysis and Maxwell stress tensor torques. Experimental PSD fits to a generalized Maxwell model yield a frictional force of $18.5\ \mathrm{pN}$ with sensitivity around $200\ \mathrm{fN}$, revealing viscous-dominated interior dynamics and increased surface friction near the membrane. This approach provides a new in vivo microrheology tool for plant cells and offers a path to study physiological responses under stress, chemical treatment, or developmental changes.

Abstract

Accessing the properties of a plant cell interior non-invasively is difficult due to the presence of a cell wall. Nanoparticles larger than 5 nm cannot be readily phagocytosed inside the cell like animal cells. It is here that we realise that Tradescantia zebrina plant cells have prismatic forms of calcium oxalate crystals present inside them naturally. These crystals make a ready choice to study properties of the inner cell surface with the application of optical tweezers. Moreover, out-of-plane rotations in optical tweezers have begun to be explored only recently. The pitch rotation has been detected with high resolution and several applications are explored. In this work, we first study the stable configuration while trapped in linearly polarized optical tweezers and then explore the other out-of-plane configurations to detect the roll rotation at high resolution. Then a micro-rheological analysis is performed to obtain the frictional properties of the inner surface of the plasma membrane of the leaf cell. The size of the particle is about 5 $μ$m along the diagonal, so that the contact length with the surface is about 200 nm. We measure a frictional force of 18.5 pN at a sensitivity of about 200 fN without averaging.

Figures (8)

• Figure 1: Possible configurations of a Calcium Oxalate crystal when trapped in linearly polarized optical tweezers
• Figure 2: Stability analysis of a calcium oxalate crystal based on rotational torque calculations:(a) Torque as a function of pitch rotation; the stable orientation is observed at $\Theta$=0°.(b) Torque as a function of roll rotation; stable orientations are found at $\Phi$=±45°(c) Torque as a function of yaw rotation; the stable orientation occurs at $\Psi$=0°
• Figure 3: This figure shows the roll detection system with photonic force microscopy (a) The simulated scatter patterns for such a particle exhibiting pitch rotation detected with photonics force microscopy is shown (b) Simulated scatter patterns for such a particle exhibiting roll rotation detected with photonics force microscopy (c) The transfer function for detected signal as a function of pitch angle (d) The transfer function for detected signal as a function of the corresponding roll angle turn
• Figure 4: (a) Roll rotation of CaOx particle inside plant cell using stage oscillation. The particle rotates clockwise when the stage moves left from equilibrium (b) and counterclockwise when the stage moves right (d). The equilibrium position, with no stage motion, is shown in (c)
• Figure 5: Time series for the roll rotation of CaOx particle (a) when the orientation of the crystal is mainly about $\phi$ = 45° and the crystal tilts small amounts about this orientation (b) When the general orientation of the crystal has been turned slightly off from the $\phi$= 45°, and then turned small extents about the mean (c) A typical image of a particle placed on the plasma membrane surface, and subsequent estimation of roll rotation using an alternative strategy of image processing. (d) The obtained estimates of the roll angle from the alternative strategy. The time series matches well with estimates from photonic force microscopy. The corresponding theoretical plot is shown in FIG. \ref{['fig:FOUR LOBE']}.