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Abstract By regulating carbon uptake and water loss by plants, stomata are not only responsible for productivity but also survival during drought. The timing of the onset of stomatal closure is crucial for preventing excessive water loss during drought, but is poorly explained by plant hydraulics alone and what triggers stomatal closure remains disputed. We investigated whether the hormone abscisic acid (ABA) was this trigger in a highly embolism‐resistant tree speciesUmbellularia californica. We tracked leaf ABA levels, determined the leaf water potential and gravimetric soil water content (gSWC) thresholds for stomatal closure and transpiration decline during a progressive drought. We found thatU. californicaplants have a peaking‐type ABA dynamic, where ABA levels rise early in drought and then decline under prolonged drought conditions. The early increase in ABA levels correlated with the closing of stomata and reduced transpiration. Furthermore, we found that transpiration declined before any large decreases in predawn plant water status and could best be explained by transient drops in midday water potentials triggering increased ABA levels. Our results indicate that ABA‐mediated stomatal regulation may be an integral mechanism for reducing transpiration during drought before major drops in bulk soil and plant water status.
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Abscisic acid acts essentially on stomata, not on the xylem, to improve drought resistance in tomato
Abstract Drought resistance is essential for plant production under water‐limiting environments. Abscisic acid (ABA) plays a critical role in stomata but its impact on hydraulic function beyond the stomata is far less studied. We selected genotypes differing in their ability to accumulate ABA to investigate its role in drought‐induced dysfunction. All genotypes exhibited similar leaf and stem embolism resistance regardless of differences in ABA levels. Their leaf hydraulic resistance was also similar. Differences were only observed between the two extreme genotypes:sitiens(sit; a strong ABA‐deficient mutant) andsp12(a transgenic line that constitutively overaccumulates ABA), where the water potential inducing 50% embolism was 0.25 MPa lower insp12than insit. Maximum stomatal and minimum leaf conductances were considerably lower in plants with higher ABA (wild type [WT] andsp12) than in ABA‐deficient mutants. Variations in gas exchange across genotypes were associated with ABA levels and differences in stomatal density and size. The lower water loss in plants with higher ABA meant that lethal water potentials associated with embolism occurred later during drought insp12plants, followed by WT, and then by the ABA‐deficient mutants. Therefore, the primary pathway by which ABA enhances drought resistance is via declines in water loss, which delays dehydration and hydraulic dysfunction.
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- Award ID(s):
- 2140119
- PAR ID:
- 10441543
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Plant, Cell & Environment
- ISSN:
- 0140-7791
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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