The role of abscisic acid and secondary growth on embolism resistance and drought tolerance in herbaceous plants

• Ano de defesa: 2023
• Autor(a) principal: Haverroth, Eduardo José
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Fisiologia Vegetal; Plantas - Relações hídricas; Plantas - Resistência à seca; Plantas - Crescimento; Cavitação; Fisiologia de Plantas Cultivadas
• Link de acesso: https://locus.ufv.br//handle/123456789/31807; https://doi.org/10.47328/ufvbbt.2023.464

Drought resistance is crucial for plant productivity in water-limited conditions. While the role of abscisic acid (ABA) in stomatal regulation is well-studied, its influence on hydraulic function beyond stomata remains understudied. Moreover, the impacts of secondary growth on xylem resistance are still poorly understood. In the first chapter, we aimed to elucidate the impact of ABA on drought-induced dysfunction by examining genotypes with divergent ABA accumulation abilities. All genotypes exhibited similar resistance to leaf and stem embolism and similar leaf hydraulic resistance. However, pronounced differences between extreme genotypes, sitiens (sit; a strong ABA- deficient mutant) and sp12 (a transgenic line with constitutive ABA over-accumulation) were observed. The water potential inducing 50% embolism was 0.25 MPa lower in sp12 compared to sit. Notably, plants with higher ABA levels (wild type and sp12) demonstrated significantly lower maximum stomatal conductance and minimum leaf conductance than ABA-deficient mutants. These variations in gas exchange were associated with ABA levels, stomatal density, and size. The elevated ABA content in plants resulted in decreased water loss, consequently leading to a delayed onset of lethal water potentials associated with embolism during drought stress. Therefore, the primary mechanism by which ABA enhances drought tolerance is through the regulation of water loss, thereby postponing the onset of dehydration and hydraulic dysfunction. In the second chapter, we focused on exploring the embolism resistance in the leaves, basal stems, and upper stems of two herbaceous species, Solanum lycopersicum and Senecio minimus, which undergo secondary growth in their mature stems. Our findings unveiled that the basal stem region with advanced secondary growth exhibited increased embolism resistance, leading to vulnerability segmentation between the basal stem and the remaining vegetative shoot. Alongside enhanced woodiness, embolism resistance in basal stems coincided with changes in anatomy and lignin content. Decreases in the pith-to-xylem area, increases in the proportion of secondary xylem conduits, and higher lignin content were observed in the basal stems. This study highlights the role of ABA in regulating drought tolerance by reducing waterloss and delaying hydraulic dysfunction. Additionally, it elucidates how secondary growth in herbaceous plants contributes to increased embolism resistance and ensures survival during drought periods while supporting the upper canopy. Keywords: Embolism. Cavitation. ABA. Solanum lycopersicum. Senecio minimus. Stomata. Xylem. Water deficit. Secondary growth. Lignin.