Study of the physiological, metabolomic and transcriptional changes mediated by rootstocks to explain the water stress tolerance of grafted pepper plants

• Autores: Yaiza Gara Padilla Herrero
• Directores de la Tesis: Salvador López Galarza (dir. tes.), Ángeles Calatayud Chover (dir. tes.)
• Lectura: En la Universitat Politècnica de València ( España ) en 2023
• Idioma: inglés
• Tribunal Calificador de la Tesis: Aurelio Gómez Cadenas (presid.), Ana Adoracion Pina Sobrino (secret.), Marco Landi (voc.)
• Programa de doctorado: Programa de Doctorado en Recursos y Tecnologías Agrícolas por la Universitat Politècnica de València
• Materias:
  • Ciencias agrarias
    • Agronomía
    • Horticultura
      • Producción de cultivos
      • Técnicas de cultivo
• Enlaces
  • Tesis en acceso abierto en: RiuNet
• Resumen

  • Previously, research groups at the Valencian Institute of Agricultural Research (IVIA) and the Polytechnic University of Valencia (UPV) evaluated the water stress responses in grafted pepper plants to obtain tolerant pepper rootstocks that make the grafted variety able to overcome water stress. The best rootstocks are studied in the field under long-term water stress conditions. In this way, the NIBER® pepper hybrid rootstock was obtained and patented as water stress-tolerant rootstock, because plants grafted onto NIBER® had a lower impact on biomass and yield under long-term deficit irrigation conditions. NIBER® tolerance response was attributed to sustained photosynthetic activity and improved root biomass distribution under long-term water stress. However, the sustained tolerance response observed in plants grafted onto NIBER® may be linked to prompt responses in the early phase of water stress conditions, but the short-term modulation and behavior of NIBER® water stress response has not been studied. Hence, studying the contribution of the NIBER® short-term water stress responses to tolerance in the grafted variety would shed light into tolerance mechanisms in grafted pepper plants. Moreover, understanding the modulation of the gene expression, phytohormones balance and metabolic profile will also broad the knowledge on the molecular mechanisms implicated in water stress response. In the present doctoral thesis, we stated that the constitutive mechanisms taking place under non-water stress conditions dispose the response to water stress in grafted pepper plants, and NIBER® constitutive strategies include an enhanced ROS detoxification system and maintained ABA induction. When the water stress comes into play, its impact was minor in NIBER® roots in relation to A10 roots, which is reflected in lesser GSSG content from lower oxidative damage. NIBER® promotes the synthesis of osmolytes in roots and vitamin B6 in the grafted variety leaves to protect the plants from the oxidative damage resulting from water stress. Moreover, proline has a role in photosynthetic apparatus protection, because it is accumulated in plants grafted onto pepper hybrid H92, which showed sustained photosynthetic activity under long-term water stress conditions. The proline role in water stress tolerance is not observed under short-term water stress and may constitute a late strategy in grafted pepper plants. Short-term responses to water stress include stomatal movements in NIBER® during early phases (5h) of water stress, starting with the avoidance of stomatal closure up to 48 h by gene expression changes in ABA negative regulators and aquaporins, and followed by stomatal closure at 48 h associated with previous ABA synthesis in roots and transport to leaves. JA is also increased in the leaves of the variety grafted onto NIBER® at 48 h under water stress, and is regulated by long-distance signals from roots that promote its synthesis on leaves and transport to roots and resynthesis. JA is involved in stomatal closure and stress signaling, which leads to dehydration-responsive transcription factors activation. The auxins/cytokinins ratio is also fine-tuned by NIBER® roots during the early water stress response, beginning with promotion of root over shoot growth at 5 h, then increases the cytokinins and reduces the auxins content at 24 h, and finally increases the auxins and reduces the cytokinins content to obtain higher root biomass and greater water exploring ability. In the leaves of the grafted variety, NIBER® increases protective metabolites as chlorophyll a, stearic acid, anthocyanins and suberin and cutin biosynthesis-related metabolites, being the latter also increased in the roots. The mentioned metabolites have an antioxidant role or act as cellular barrier constituents that can control fluxes of water, gases and solutes. Lastly, siroheme increases in roots and it is possibly linked to a more effective nitrogen assimilation.