Tracking stone cell formation in pears with in vivo lignification imaging

For the first time, researchers have visualized in vivo the precise timing and location of active lignin deposition in developing pear cells. This allowed them to trace how isolated cells begin lignifying as early as 10 days after full bloom (DAFB), initiating a cascading process that leads to the formation of large, hard stone cell clusters.

Pear fruit is prized for its flavor and nutritional value but often suffers from gritty texture caused by hard, lignified stone cells. These sclereids, rich in lignin, are essential for structural support in plants but undesirable in fruit flesh due to their tough texture and negative impact on edibility and processing. While genetic and biochemical studies have identified some regulators of lignification in pear, a detailed understanding of how and when these cells begin to lignify—and how they form into large clusters—has been lacking. Traditional imaging methods cannot distinguish newly deposited lignin from preexisting cell wall components, leaving key questions unanswered in fruit developmental biology.

A study (DOI: 10.1016/j.plaphe.2025.100010) published in Plant Phenomics on 25 February 2025 by Shaoling Zhang’s team, Nanjing Agricultural University, provides an unprecedented cellular map of stone cell development, offering a potential roadmap for improving pear texture and quality through targeted breeding and cultivation strategies.

To investigate lignification dynamics during pear fruit development, researchers employed a bioorthogonal chemistry-based imaging technique using a synthetic lignin precursor called 3-O-propargylcaffeyl alcohol (3-O-PCA). This compound mimics natural coniferyl alcohol but includes an alkyne group that allows specific labeling via click chemistry. Upon feeding 3-O-PCA to Arabidopsis and pear seedlings, and tagging it with Alexa 594-azide through a copper-catalyzed azide-alkyne cycloaddition, strong fluorescence signals at 561 nm were observed, confirming that 3-O-PCA was successfully incorporated into newly synthesized lignin. In Arabidopsis, active lignification was most prominent in vascular bundles and interfascicular fibers. Similarly, in pear seedlings, lignification was observed in xylem, parenchyma, and phloem stone cells, validating the probe's biocompatibility and utility for tracing in vivo lignification. Using this approach, lignification trajectories in developing pear fruits were visualized across five stages (S1–S5). Initial lignification in parenchyma cells appeared at stage S2 (10 DAFB), with single cells depositing lignin. By stage S3, lignification intensified and began spreading to adjacent cells, forming small clusters. At S4, further expansion produced larger clusters. At S5, large mature stone cell clusters were observed with no new lignin formation, indicating a quiescent phase. Notably, early lignified cells—primordial stone cells (PSCs)—had larger size and distinct morphology compared to surrounding parenchyma. Over time, lignification spread radially from PSCs to neighboring cells, forming pit canals and secondary walls, eventually resulting in fully lignified clusters. Fluorescence intensity measurements confirmed progressive lignin accumulation and spatial expansion of lignified zones, with the outer cells in clusters showing stronger lignification activity than inner cells. This cascade-like process resembles a "domino effect," wherein lignification initiates randomly but spreads systematically, offering a detailed cellular model of stone cell aggregation in pear fruit.

This research offers significant potential for improving fruit quality by targeting the formation of stone cells in breeding and cultivation. By identifying the early lignification stages and understanding the cascading expansion mechanism, scientists can now develop strategies to limit stone cell proliferation in pear cultivars. The method also establishes a new standard for studying dynamic cell wall processes in other fruits and crops, offering real-time, spatially resolved insights that traditional staining or microscopy cannot provide.

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References

DOI

10.1016/j.plaphe.2025.100010

Original Source URL

https://doi.org/10.1016/j.plaphe.2025.100010

Funding information

This study was supported by the National Key Research and Development Program of China (2022YFD2001001), the Jiangsu Independent Innovation Fund Project of Agricultural Science and Technology [CX(21)1006], the Jiangsu Collaborative Innovation Center for Modern Crop Production (JCICMCP), and the 111 Project.

About Plant Phenomics

Science Partner Journal  Plant Phenomics is an online-only Open Access journal published in affiliation with the State Key Laboratory of Crop Genetics & Germplasm Enhancement, Nanjing Agricultural University (NAU) and distributed by the American Association for the Advancement of Science (AAAS). Like all partners participating in the Science Partner Journal program, Plant Phenomics is editorially independent from the Science family of journals. Editorial decisions and scientific activities pursued by the journal's Editorial Board are made independently, based on scientific merit and adhering to the highest standards for accurate and ethical promotion of science. These decisions and activities are in no way influenced by the financial support of NAU, NAU administration, or any other institutions and sponsors. The Editorial Board is solely responsible for all content published in the journal. To learn more about the Science Partner Journal program, visit the SPJ program homepage.