Featured image with Jan Martinek

Our featured image is a spinning disk fluorescence micrograph, acquired by Jan Martinek, showing an Arabidopsis thaliana root that formed a spiral on a forgotten Petri dish lying flat on the bench. In this orientation, the root cannot grow downward gravitropically, so it keeps turning. Over time, it can close a circle and develop into a spiral. The root expresses a cell wall pH marker based on a pair of fluorescent proteins – GFP is quenched in acidic conditions, while RFP is comparatively insensitive to pH.

I originally captured the image while testing whether this spiral growth might be caused by the acid growth mechanism. The blue signal is UV-excited autofluorescence in plant tissues. The sample was imaged alive, the seedling was transferred on a small piece of agar medium onto a slide and recorded as Z-stacks on a spinning-disk microscope. The final image is a maximum-intensity projection, stitched from four tiles. Standard processing was done in Fiji/ImageJ, for subsequent non-scientific ‘artistic’ use, I additionally retouched debris and adjusted colours and tonality in a graphics editor.

You can check out more of Jan’s stunning images on Instagram.

Research career so far: During my PhD, I focused on the actin cytoskeleton, particularly the ARP2/3 complex, and how cytoskeletal organisation contributes to plant cell growth and morphogenesis. I mostly used a laser scanning confocal microscope for live-cell imaging, especially of the actin cytoskeleton and other organellar markers.

Current research: In my current postdoctoral work, I study how auxin controls directional growth, especially gravitropism and phototropism. I’m interested in the pathway from a physical stimulus to an asymmetric auxin signal, and from there to differential cell-wall expansion that drives bending. A key focus is linking subcellular processes (transport/signalling, plasma membrane H+-ATPase activity, apoplastic pH, and wall remodelling) to organ-scale growth responses.

Favourite imaging technique/microscope: My favourite approach is fluorescence imaging of living cells and plants. I started on conventional laser-scanning confocals and have recently become especially fond of spinning-disk systems for fast and gentle, as well as long-term live imaging.
For gravitropism and phototropism experiments, I use a ‘vertical stage’ setup where seedlings grow in a natural orientation (rather than lying flat on a coverslip). I enjoy prototyping customized components for my experiments, such as 3D-printed chambers for long-term plant imaging, which allow me to rotate the seedlings or treat them with lateral illumination. Recently, I’ve also been exploring SEM – a completely different way of seeing plant structure, which has been quite exciting despite the obvious limitation that samples are no longer alive.

What are you most excited about in microscopy? On the hardware side, I’m excited about progress in super-resolution and the ongoing improvements in camera sensitivity and acquisition speed. I recently had the chance to test a new STED system with Z-correction optics and FLIM, which allows high resolution deeper in tissue and (with lifetime gating) can strongly suppress autofluorescence.
On the software side, I really enjoy how AI helps me write ImageJ macros and develop analysis workflows with much less effort. It saves me a huge amount of time. In the past, I often hesitated to write my own macros because my programming experience was limited. More broadly, I expect specialised AI approaches to become increasingly valuable for image analysis and robust quantitative measurements in complex plant samples.

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