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- Physiological and molecular mechanisms of stomatal functioning in plants grow at high humidityPublication . Carvalho, Dália Rosa Alves; Carvalho, Susana Maria Pinto de; Vasconcelos, Marta W.; Heuvelink, EpStomata from several plant species developed at high relative air humidity (RH ≥ 85%) may become malfunctional, leading to excessive water loss in conditions of high evaporative demand. In ornamental plants, including rose, this results in a low postharvest longevity. The factors underlying a poor stomatal functioning under high RH are not yet fully understood, but the magnitude of this effect is genotype dependent which broadens the possibilities for plant breeding. The aim of this thesis is to analyze the physiological and molecular mechanisms of stomatal malfunctioning in plants cultivated at high RH, focusing on abscisic acid (ABA) regulation and its effects on stomatal closure. The identification of genomic regions associated with the control of water loss is also a subject of this study. Rosa × hybrida was used as the model system since in this species there are cultivars with a contrasting sensitivity to high RH. Stomatal movements are to a large extent regulated by ABA concentration ([ABA]), which is determined by its metabolism within the leaf, as well as by its import from the roots. The role of root-to-shoot ABA signaling in inducing stomatal closure and its role in inducing genotypic differences in stomatal functioning was investigated in ten genotypes grown at contrasting RH conditions. It was found that xylem sap [ABA] did not explain genotypic differences in stomatal functioning, since sensitive and tolerant genotypes to high RH had a similar estimated [ABA] in the root xylem sap and a similar ABA delivery rate and [ABA] in the leaf petiole sap. Elevated air movement (MOV) and moderate salinity are two environmental stress factors known to induce stomatal closure. In two different studies, we combined a high RH level with high MOV or with a moderate salinity throughout plant growth in order to test if these physiological stresses would counteract the negative effect of high RH on stomatal functioning due to an increased [ABA]. Indeed, stomata developed at high RH with additional MOV or moderate salinity closed faster in response to leaf desiccation when compared to plants grown at high RH without either of the imposed stresses. While salinity enhanced stomatal functioning due to an increase in leaf [ABA], high MOV improved stomatal responsiveness due to a higher stomatal sensitivity to ABA. The two parents and the 108 offspring of the K5 tetraploid cut rose population grown at high RH were phenotyped for stomatal responsiveness to desiccation, showing large genotypic differences [i.e., relative water content after 4h of leaflet desiccation (RWC_4h) varied between 7 and 62%]. Three QTLs (two major and one putative minor) explained 32% of the genotypic variability and low RWC_4h proved to be a good proxy for eliminating the offspring with shorter vase life. These particular findings contribute to speeding up genotype selection using marker-assisted selection programs for breeding cultivars with more responsive stomata after cultivation at high RH, minimizing the negative impacts associated with excessive water loss during postharvest. The transcriptional analysis of nine ABA-related genes (involved in ABA biosynthesis, oxidation and conjugation) and two non-ABA related genes (involved in water stress response) in four contrasting genotypes selected from the K5 tetraploid cut rose population revealed that stomatal responsiveness to desiccation is a polygenic trait forming a highly complex regulatory network acting towards tolerance to high RH. The large majority of the studied genes had a relevant role on stomatal functioning (NCED1, AAO3, UGT75B2, BG2, OST1, ABF3 and Rh-APX) while three others showed a minor contribution (CYP707A1, CYP707A3 and BG1) and DREB1B did not contribute to the tolerance trait. Overall, this study has helped identifying major factors responsible for the reduction of potential vase life of cut roses due to uncontrolled water loss, and represents a major step forward in developing future tools to mitigate this phenomenon. In summary, it highlights that: (1) roses have a large genotypic variation in terms of stomatal functioning; (2) xylem sap [ABA] does not explain genotypic differences in stomatal functioning; (3) additional MOV or moderate salinity enhances stomatal functioning due to higher sensitivity to ABA or higher leaf [ABA], respectively; (4) three QTLs can explain 32% of the genotypic variability in stomatal functioning of the K5 tetraploid cut rose population in response to desiccation; (5) multiple genes form a highly complex regulatory network acting together towards the genotypic tolerance to high RH.
- Bioinoculants for Zea mays production in P-deficient agricultural soilsPublication . Pereira, Sofia I. A.; Castro, Paula M. L.Aims and scope: Phosphorus (P) is a limiting factor in crop growth and, due to its low availability, P-deficiency in soils is widespread, and as such the successive application of P- fertilizers to maintain crop production has occurred, leading to severe environmental problems. The development and application of environmentally friendly biotechnological approaches as alternatives to chemical fertilizers has gained considerable interest in agricultural practices worldwide. The harnessing of Phosphate Solubilizing Bacteria (PSB) seems to be of utmost importance towards the reverse of the current use of large amounts of P fertilizers, since they can stimulate plant growth in particular through the conversion of bound P in soil into bioavailable P forms. This work aimed to evaluate the ability of PSB to enhance Zea mays growth in an agricultural P-deficient soil. Methodology: P solubilizing strains Rhodococcus sp. EC35 (B1), Pseudomonas sp. EAV (B2) and Arthrobacter nicotinovorans EAPAA (B3) were inoculated in maize growing in P-deficient soils without P fertilization and amended with soluble - KH2PO4 and insoluble P - Ca3(PO4)2; Plant dry biomass and P accumulation in plant tissues were determined after 90 days; Available P in rhizosphere soils were determined at the end of experiment; The persistence of inoculated strains in soils was evaluated by Denaturing Gel Gradient Electrophoresis (DGGE). Conclusions: PSB significantly enhanced Z. mays growth and P uptake in P-deficient soils; Rhodococcus sp. EC 34, Pseudomonas sp. EAV and A. nicotinovorans EAPAA may be used as biofertilizers and constituting an interesting alternative to the application of phosphatic fertilizers in P-deficient soils, reducing costs and improving crop yields.