Pit Membrane Thickness Determines Differences in Embolism Resistance Among Brassica oleracea Genotypes

As drought events become more severe, understanding drought-tolerance traits in crops is vital for food security. Brassica oleracea L., a widely consumed vegetable (including cabbage, cauliflower, and broccoli), has seen a rise in cultivation, but the response of different genotypes to drought remains poorly studied. Here, we investigated the mechanisms underlying drought resistance in seven genotypes of B. oleracea (two grandparental lines and five F2 genotypes) by examining stem anatomical and hydraulic traits, as well as stomatal characteristics, leaf dimensions, and stomatal regulation under drought conditions. Detailed measurements of stem anatomical traits were obtained using light and electron microscopy, while stem hydraulic vulnerability was assessed using the Optical Vulnerability method. The seven genotypes displayed contrasting water-use and hydraulic strategies. Under well-watered conditions, initial stomatal conductance (g_sΨ0) showed considerable variation independent of their leaf and stomata size and density, while the leaf water potential at 90% stomatal closure (Ψg_s90) was similar among genotypes. Stomatal safety margins (SSM) were positive across genotypes, confirming coordination between stomatal regulation and xylem hydraulics, and mainly driven by stem P₅₀, which was approximately 1 MPa lower in the most tolerant genotype. Embolism resistance was best explained by the thickness of the intervessel pit membrane, highlighting the importance of including anatomical traits in plant drought tolerance studies. To conclude, the intraspecific variation observed in anatomical, hydraulic and stomatal traits among our B. oleracea genotypes indicates potential adaptability to drought and suggests that more drought-tolerant genotypes could be identified within this crop species through targeted, human-mediated crosses.