Spatial coordination between leaf gradient and temperature response in barley

Authors: FERNANDEZ, EDWARD CEDRICK - North Dakota State University; TU, GAOYA - North Dakota State University; DAI, WEI - North Dakota State University; Yang, Shengming; LIU, ZHAOHUI - North Dakota State University; GRZYBOWSKI, MARCIN - University Of Warsaw; LIANG, ZHIKAI - North Dakota State University

Submitted to: The Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2026
Publication Date: 4/12/2026
Citation: Fernandez, E., Tu, G., Dai, W., Yang, S., Liu, Z., Grzybowski, M., Liang, Z. 2026. Spatial coordination between leaf gradient and temperature response in barley. The Plant Journal. 126(1). https://doi.org/10.1111/tpj.70857.
DOI: https://doi.org/10.1111/tpj.70857

Interpretive Summary: As a crop adapted to cool weather, Barley growth and productivity are significantly compromised by high temperatures. Barley leaves develop differentially along the leaf axis, with mature cells at the tip, newly formed cells at the base, and transitional cells in the middle. Despite this known pattern, how these distinct cell types within a single leaf respond to high temperature remains poorly understood. In this study, we used a specialized tool, chlorophyll fluorescence imaging, to assess how different leaf regions respond to heat stress and protect their photosynthetic capacity. Our results showed that the leaf base lost protective response the most, and the tip the least. Through a gene identification method called genome-wide association mapping, we detected several genes linked to these protective traits. We also investigated how genes were turned on or off across the leaf during heat stress, and the results showed that plant shifts energy away from growth and toward defense in response to heat stress. Therefore, our research shows that different parts of a single leaf can behave in their own way under stress, and identification of heat tolerance genes can help barley geneticists and breeders develop varieties with improved resilience to heat.

Technical Abstract: The linear-lanceolate shape of cereal leaves exhibits distinct developmental zones coordinating development and resource allocation along the longitudinal axis. Under abiotic stress such as heat, these longitudinal zones may differentially activate protective pathways, revealing hidden heterogeneity in stress perception and response. Barley (Hordeum vulgare) is a cold-adapted crop particularly sensitive to elevated temperatures, making it an ideal model for studying region-specific heat responses in leaves. Using chlorophyll fluorescence imaging, we found that NPQ-kinetics traits captured additional physiological changes beyond those detected by SPAD, highlighting the added value of fluorescence-based assessments. NPQ kinetics traits displayed a consistent spatial gradient from tip to base, with heat stress reducing the magnitude of NPQ induction across leaf gradients. A genome-wide association study of 17 NPQ-related traits across leaf gradients identified significant SNPs fallen inside 13 candidate genes, with HORVU.MOREX.r3.3HG0262630 repeatedly detected in 180 of 200 resamplings. Heat-induced transcriptional responses along the same spatial axis revealed both conserved and region-specific expression patterns. Shared expression patterns highlighted conserved heat response pathways, including the reactivation of the Arabidopsis thermomemory module FtsH6-HSP21, which was recapitulated in barley across the leaf gradient. In contrast, the region-by-temperature interaction analysis identified 40 genes with spatial responses indicative of resource reallocation from growth to defense, including those involved in growth and transport. Our results underscore how spatially resolved phenotyping and transcriptional profiling can reveal region-specific variation in response to heat along the leaf axis, guiding targeted strategies to enhance heat resilience in barley and other cereal crops.