Taking a closer look at perennial ryegrass vascular tissue

By Maicy Vossen

This article was originally published on the WinterTurf project blog.

Perennial ryegrass (Lolium perenne) is a turfgrass species that is quick to germinate and establish but is one of the least winter hardy cool-season species. As part of the WinterTurf project, we are trying to understand the physiologic characteristics that contribute to freeze tolerance.

Perennial ryegrass, along with other turfgrass and plant species, has vascular tissue composed of phloem for transporting organic substances and xylem for transporting water and dissolved minerals throughout the plant. Xylem vessels and freezing damage are interconnected. Water traveling through the xylem can freeze at below zero temperatures, sometimes leading to blockages in the vessel, halting water from continuing to other parts of the plant. This blockage can create embolisms in the xylem and permanently disrupt the flow of water in the vessel. Once water is frozen inside of xylem vessels, ice crystals can spread through surrounding cells and rupture cell walls. Research in winter barley shows that “freezing-tolerant genotypes consistently exhibited smaller metaxylem vessel diameters” and that this trait was heritable (Tamang et al., 2021). A similar trait was observed in bahiagrass (Paspalum notatum), with freeze tolerant genotypes exhibiting smaller xylem elements and vascular tissue bundles in the leaves of this species (Breman et al., 2009).

cross sections of plant root and stem
Figure 1. Cross sections of perennial ryegrass root (top) and leaf (bottom).  Arrows indicate xylem vessels. Images obtained through LAT at the Roots Lab at Penn State.

To understand the dynamics between vascular tissue and freeze tolerance in perennial ryegrass, we must be able to take a closer look inside of plant leaves, roots, and crowns. The way that we have done this is through a technology called Laser Ablation Tomography (LAT) developed by the Roots Lab at Penn State (2023). This technology is a “high-throughput, high-resolution phenotyping platform combines laser optics and serial imaging with 3-D image reconstruction and quantification to understand plant anatomy” (Laser Ablation Tomography, 2023). We have been able to use this technology to get images the leaves and roots of perennial ryegrass genotypes that contrast in freeze-tolerance (Figure 1). Analysis of these images will allow us to determine if xylem vessel diameter impacts freeze tolerance in perennial ryegrass. In the future, we plan to compare these images, taken of plants grown in optimal growing conditions, to images of leaves and roots that have experienced freezing temperatures. This information can be used to make progress on breeding efforts of more winter hardy cultivars of perennial ryegrass. 


Breman, J. W., Sinclair, T. R., Blount, A. R., Quesenberry, K. H., & Brennan, M. M. (2009). Leaf vascular dimensions associated with freeze tolerance in bahiagrass (Paspalum notatum). Annals of Applied Biology, 155(2009), 219–223. https://doi.org/10.1111/j.1744-7348.2009.00332.x

Laser Ablation Tomography. (2023). Roots lab: Research methodology.   


This project is supported by the U.S. Department of Agriculture, National Institute of Food and Agriculture, Specialty Crop Research Initiative under award number 2021-51181-35861.