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- Avoiding high relative air humidity during critical stages of leaf ontogeny is decisive for stomatal functioningPublication . Fanourakis, Dimitrios; Carvalho, Susana M. P.; Almeida, Domingos M. P.; Domingos, P.F.; Heuvelink, EpPlants of several species, if grown at high relative air humidity (RH >= 85%), develop stomata that fail to close fully in case of low leaf water potential. We studied the effect of a reciprocal change in RH, at different stages of leaf expansion of Rosa hybrida grown at moderate (60%) or high (95%) RH, on the stomatal closing ability. This was assessed by measuring the leaf transpiration rate in response to desiccation once the leaves had fully expanded. For leaves that started expanding at high RH but completed their expansion after transfer to moderate RH, the earlier this switch took place the better the stomatal functioning. Leaves initially expanding at moderate RH and transferred to high RH exhibited poor stomatal functioning, even when this transfer occurred very late during leaf expansion. Applying a daily abscisic acid (ABA) solution to the leaves of plants grown at continuous high RH was effective in inducing stomatal closure at low water potential, if done before full leaf expansion (FLE). After FLE, stomatal functioning was no longer affected either by the RH or ABA level. The results indicate that the degree of stomatal adaptation depends on both the timing and duration of exposure to high RH. It is concluded that stomatal functionality is strongly dependent on the humidity at which the leaf completed its expansion. The data also show that the effect of ambient RH and the alleviating role of ABA are restricted to the period of leaf expansion.
- QTL analysis for stomatal functioning in tetraploid Rosa × hybrida grown at high relative air humidity and its implications on postharvest longevityPublication . Carvalho, Dália R. A.; Koning-Boucoiran, Carole F. S.; Fanourakis, Dimitrios; Vasconcelos, Marta W.; Carvalho, Susana M. P.; Heuvelink, Ep; Krens, Frans A.; Maliepaard, ChrisHigh relative air humidity (RH >= 85 %) during leaf development disturbs stomatal functioning leading to excessive water loss in conditions of high evaporative demand, resulting in severe reduction in postharvest longevity. In roses, this effect depends on the genotype, opening the possibility for breeding cultivars with more responsive stomata. In this study, we aim at identifying genomic regions associated with the control of water loss following growth at high RH. The F1 generation (108 offspring) and the two parents (P540 and P867) of a tetraploid cut rose population grown at high (85 %) RH were phenotyped for stomatal control to water loss by assessing the relative water content after 4 h of leaflet desiccation (RWC_4 h). The RWC_4 h varied between 7 and 62 % across the 110 studied individuals, with parents P540 and P867 showing 51 and 20 % RWC_4 h, respectively. Based on these data, a quantitative trait locus (QTL) analysis was performed. The impact of the identified QTLs on postharvest longevity of ten selected offspring was further evaluated. Three QTLs were identified: two major [positioned on linkage group 5 of the integrated consensus map (ICM 5) of both parents and on ICM 2 of the parent P867] and one putative minor (mapped to ICM 6 of both parents), explaining 32 % of the variability in the RWC_4 h. Low RWC_4 h was found to be a good proxy for eliminating the offspring with short vase life. This study constitutes a first step toward identifying the most likely regions for genes of interest controlling stomatal functioning in high RH-grown plants.
- Genotypic variation in the stomatal characteristics of cut roses grown under high relative air humidityPublication . Fanourakis, Dimitrios; Tapia, Alejandra; Heuvelink, Ep; Carvalho, Susana M. P.
- Effect of high relative air humidity on the cuticular water permeability, and its significance on the leaf water balancePublication . Fanourakis, Dimitrios; Carvalho, Susana M. P.; Tapia, Alejandra; Heuvelink, Ep
- Dynamics of stomatal adaptation in rose leaves exposed to long-term high relative air humidityPublication . Fanourakis, Dimitrios; Carvalho, Susana; Heuvelink, Ep
- Postharvest water relations in cut rose cultivars with contrasting sensitivity to high relative air humidity during growthPublication . Fanourakis, Dimitrios; Carvalho, Susana M.P.; Almeida, Domingos P.F.; Kooten, Olaf van; Doorn, Wouter G. van; Heuvelink, EpA constant highrelativeairhumidity (RH) during cultivation can strongly reduce the vase life in some cutrosecultivars. We studied three contrastingcultivars in their tolerance to high RH in order to analyse in detail the waterrelations during postharvest and better understand this genotypic variation. Plants were grown at moderate (60%) and high (95%) RH, and cut flowers were placed in water immediately after cutting. Flowers of cv. Pink Prophyta grown at high RH did not open throughout vase life, while flower opening of cvs. Frisco and Dream was not affected by preharvest RH. Cultivation at high RH resulted in about 80% shorter vase life in Pink Prophyta, whereas in Dream and Frisco the negative effect was considerably smaller (15 and 9% shorter vase life, respectively). The shorter vase life and reduced flower opening of cutroses grown at high RH was due to a higher rate of transpiration both in the light and dark periods. It was found that the leaves of Pink Prophyta grown at high RH could partly close their stomata upon lowering of the water potential or when flower stalks were fed with abscisic acid, but stomata remained far more open than in leaves grown at moderate RH. The RH during cultivation did not affect stem hydraulic conductivity and its recovery after air emboli induction. Preventing vascular occlusion largely alleviated the high-cultivation-RH effect on vase life and flower opening, showing that the effect of high-cultivation-RH becomes only important if water uptake is limited.
- Effect of high relative air humidity on the water uptake components of cut rosesPublication . Fanourakis, Dimitrios; Carvalho, Susana M. P.; Gebraeqziabher, Habtamu; Leperen, Wim van; Heuvelink, Ep
- 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 J.; Monteiro, José A.; 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