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- NAA and STS effects on potted bougainvillea: early flower death allows delayed bract abscissionPublication . Gago, Custódia; Monteiro, JoséThe effects of Silver Thiosulphate (STS) and Naphtalene Acetic Acid (NAA) (0,45%NAA+1,2% NAA-amide at 500 mg.l-1) on flowering bud development, anthesis duration, bract longevity and bract photosynthetic rate were studied in Bougainvillea spectabilis ‘Killie Campbell’ plants, under interior conditions. The relationships between bract longevity and the above parameters were also investigated. NAA induced longer bract longevities, shorter flower anthesis duration and lower percentage of flowers reaching anthesis. STS alone increased duration of flower anthesis but did not affect CD (completely developed) bract abscission, as compared to the water treatment. Depending on the experiment, adding STS to NAA delayed or had no effect on bract abscission. Longer bract longevities were related to shorter flower anthesis and lower percentage of flowers reaching anthesis. Manual removal of flowers from the bract+flower unit increased bract longevity. Despite the low level of irradiance, bracts photosynthesized and plants treated with NAA (alone or with STS) had lower bract photosynthetic rates. Bract photosynthetic activity, although with relevant rates (similar to leaves and most probably capable of covering respiration expenditure) did not seem important as an energy source for bract longevity since bracts that lasted longer had lower photosynthetic rates. In the water control, percentage of flowers reaching anthesis positively correlated with bract photosynthetic rates. In potted bougainvillea under low light conditions, flower senescence and bract abscission are under different types of control. In addition to the classical effect of auxin reducing ethylene production, and/or sensitivity of the abscission zone to ethylene, NAA delays bougainvillea bract abscission via early interruption of flower development.
- Root-to-shoot ABA signaling does not contribute to genotypic variation in stomatal functioning induced by high relative air humidityPublication . Carvalho, Dália R. A.; Fanourakis, Dimitrios; Correia, Maria João; Monteiro, José; Araújo-Alves, José Pedro L.; Vasconcelos, Marta W.; Almeida, Domingos P. F.; Heuvelink, Ep.; Carvalho, Susana M. P.High relative air humidity (RH >= 85%) during leaf expansion hampers stomatal responsiveness to closing stimuli, a genotype-dependent effect. Genotypes with reduced stomatal closure in response to closing stimuli (i.e., sensitive genotypes) show low bulk leaf abscisic acid concentration ([ABA]). We hypothesized that the amount of ABA produced in the roots and delivered with the transpiration stream to the leaves is a critical step for a proper stomatal functioning in high RH-grown plants. Ten genotypes from a cut rose tetraploid population were grown at moderate (62%) or high (89%) RH. Stomatal anatomy and responsiveness to desiccation or ABA feeding were evaluated. Root and leaf petiole xylem sap [ABA] were quantified, and ABA delivery rate from root-to-shoot was estimated. High RH reduced stomatal responsiveness to both closing stimuli in the sensitive genotypes, whereas it had a nonsignificant effect in the tolerant ones. Estimates of [ABA] in root xylem sap at transpirational flow rate were not related to the genotypic differences in the sensitivity to high RH. However, high RH increased this concentration irrespective of the genotype, probably due to a reduced dilution of the [ABA] in the xylem sap as a result of a lower transpiration rate compared to moderate RH-grown plants. Leaf petiole xylem sap [ABA] was neither related to the genotypic differences in the sensitivity to high RH nor it was affected by RH. We concluded that genotypic differences in the stomatal sensitivity to high RH cannot be explained by changes in the [ABA] delivered with the transpiration stream from the roots to the leaves. (C) 2015 Elsevier B.V. All rights reserved.