Abstract
Background and AimsThe ability to avoid drought-induced embolisms in the xylem is one of the essential traits for plants to survive periods of water shortage. Over the past three decades, hydraulic studies have been focusing on trees, which limits our ability to understand how herbs tolerate drought. Here we investigate the embolism resistance in inflorescence stems of four Arabidopsis thaliana accessions that differ in growth form and drought response. We assess functional traits underlying the variation in embolism resistance amongst the accessions studied using detailed anatomical observations.MethodsVulnerability to xylem embolism was evaluated via vulnerability curves using the centrifuge technique and linked with detailed anatomical observations in stems using light microscopy and transmission electron microscopy.Key ResultsThe data show significant differences in stem P50, varying 2-fold from −1.58 MPa in the Cape Verde Island accession to −3.07 MPa in the woody soc1 ful double mutant. Out of all the anatomical traits measured, intervessel pit membrane thickness (TPM) best explains the differences in P50, as well as P12 and P88. The association between embolism resistance and TPM can be functionally explained by the air-seeding hypothesis. There is no evidence that the correlation between increased woodiness and increased embolism resistance is directly related to functional aspects. However, we found that increased woodiness is strongly linked to other lignification characters, explaining why mechanical stem reinforcement is indirectly related to increased embolism resistance.ConclusionsThe woodier or more lignified accessions are more resistant to embolism than the herbaceous accessions, confirming the link between increased stem lignification and increased embolism resistance, as also observed in other lineages. Intervessel pit membrane thickness and, to a lesser extent, theoretical vessel implosion resistance and vessel wall thickness are the missing functional links between stem lignification and embolism resistance.
Highlights
Long-distance water transport in the xylem connecting roots to leaves is essential for plant survival and distribution (Sperry, 2003; Brodribb, 2009; Lucas et al, 2013; Lens et al, 2016; Trueba et al, 2017; Choat et al, 2018; Brodribb et al, 2020)
We found 2-fold variation in stem P50 amongst the A. thaliana accessions studied, which was significantly associated with an increase in the thickness of the intervessel pit membrane (TPM; Fig. 4) and is in line with the air-seeding hypothesis
Variation in stem P50 amongst Arabidopsis accessions agrees with other herbs and is best explained by intervessel TPM
Summary
Long-distance water transport in the xylem connecting roots to leaves is essential for plant survival and distribution (Sperry, 2003; Brodribb, 2009; Lucas et al, 2013; Lens et al, 2016; Trueba et al, 2017; Choat et al, 2018; Brodribb et al, 2020). Plants have developed an ingenious system to transport water upwards against gravity by a largely passive mechanism that is driven by a difference in negative xylem pressure created in the leaf mesophyll cell walls, known as the cohesion-tension theory (Dixon and Joly, 1895; Pickard, 1981; Brown, 2013). This negative or subatmospheric pressure inside the water-conducting xylem conduits puts water in a metastable liquid state, making it vulnerable to heterogeneous cavitation: the transition from liquid water to vapour by spontaneous destabilization of the hydrogen bonds between water molecules at nucleating sites (Steudle, 2001; Wheeler and Stroock, 2008; Brown, 2013; Venturas et al, 2017). Acquiring a sufficient level by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited
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