Causes of Quality Loss of Cut Flowers - A Critical Analysis of Post-Harvest Treatments

Temperature is one of the most important factors in the postharvest phase to control quality losses, yet temperature is still poorly managed, partly because its effects are not always understood well. Temperature affects both physiological (development and senescence of flowers, wound responses at the cut stem end) and physical (water loss, condensation/drying) processes involved in quality loss. More¬over, pathogens like Botrytis (germination rate of conidia) and growth of bacteria are affected by temperature. Handling, like placing flowers in water during transport or keeping them dry, re-cutting of stems or not, will interact with some of the processes affected by temperature. A previous simulation model, based on temperature effects on the rate of senescence and on the development of Botrytis infection, was extended by including the effects of temperature and handling on the water balance of the cut flower. Some outcomes of simulations of temperature combinations and handling in hypothetical chains are demonstrated. They showed that the effects of temperature in the chain can be largely overruled by properties of the crop or by the handling of the flowers. The model is meant to find and understand the critical points in postharvest cut flower chains. Most of the parameters are based on limited available data from literature or preliminary experiments. Moreover, the model is not validated. For these reasons, in its present status the model should not be used to predict vase life of cut flowers for practical purpose

Obstruction of Water Uptake in cut Chrysanthemum Stems after Dry Storage: Role of Wound-induced Increase in Enzyme Activities and Air Emboli

Hydraulic conductance of cut chrysanthemum stems was lowered by the aspiration of air as well as by a wound-induced plant response. By measuring the hydraulic conductance of stem segments in which air could be introduced into and/or removed from the xylem vessels at various times after harvest, we showed that the two processes, air aspiration and wound-induced reactions, occur independently. The pronounced xylem occlusion after a longer period of dry storage is due to the progress of the enzymatic wound-induced reaction in time superimposed on emboli due to aspired air. The wound-induced blockage was also present when air entrance was precluded from harvest. Measurements of enzyme activities in stems at time intervals from harvest showed that the activity of L- phenylalanine ammonia-lyase (PAL) increased after wounding in contrast to the activities of peroxidase and polyphenol oxidase. This suggests a major role of PAL in the xylem occlusion caused by wounding of the flower ste

Distribution of xylem hydraulic resistance in fruiting truss of tomato influenced by water stress

In this study xylem hydraulic resistances of peduncles (truss stalk), pedicels (fruit stalk) and the future abscission zone (AZ) halfway along the pedicel of tomato (Lycopersicon esculentum L.) plants were directly measured at different stages of fruit development, in plants grown under two levels of water availability in the root environment. The xylem hydraulic connection between shoot and fruits has previously been investigated, but contradictory conclusions were drawn about the presence of a flow resistance barrier in the pedicel. These conclusions were all based on indirect functional measurements and anatomical observations of water-conducting tissue in the pedicel. In the present study, by far the largest resistances were measured in the AZ where most individual vessels ended. Plants grown at low water availability in the root environment had xylem with higher hydraulic resistances in the peduncle and pedicel segments on both sides of the AZ, while the largest increase in hydraulic resistance was measured in the AZ. During fruit development hydraulic resistances in peduncle and pedicel segments decreased on both sides of the AZ, but tended to increase in the AZ. The overall xylem hydraulic resistance between the shoot and fruit tended to increase with fruit development because of the dominating role of the hydraulic resistance in the AZ. It is discussed whether the xylem hydraulic resistance in the AZ of tomato pedicels in response to water stress and during fruit development contributes to the hydraulic isolation of fruits from diurnal cycles of water stress in the shoot

Disentangling agglomeration and network externalities : a conceptual typology

Agglomeration and network externalities are fuzzy concepts. When different meanings are (un)intentionally juxtaposed in analyses of the agglomeration/network externalities-menagerie, researchers may reach inaccurate conclusions about how they interlock. Both externality types can be analytically combined, but only when one adopts a coherent approach to their conceptualization and operationalization, to which end we provide a combinatorial typology. We illustrate the typology by applying a state-of-the-art bipartite network projection detailing the presence of globalized producer services firms in cities in 2012. This leads to two one-mode graphs that can be validly interpreted as topological renderings of agglomeration and network externalities

Short trips and central places: the home-school distances in the Flemish primary education system (Belgium)

This paper was published in the journal Applied Geography and the definitive published version is available at https://doi.org/10.1016/j.apgeog.2014.06.025.This paper examines the extent to which home-school trip length in northern Belgium is influenced by the spatial distribution of the school sites, and to what extent this distribution contemporarily functions according to propositions of central place theory. Furthermore, from a sustainable mobility perspective, it is evaluated if the primary school network's density supports a daily urban system based on short distances. The results indicate that the overall system's density meets the requirements of a non-motorized system, while the distribution confirms central place mechanisms. The majority of the pupils live within walking or cycling distance from their school, while opportunities exist to further reduce this distance by choosing an alternative school. However, depending on the structure of the concerned settlement, school accessibility varies considerably. Finally, the results suggest that recent increases in school trip length and motorization are mainly caused by non-spatial factors

Effect of (Changes in) Air Humidity on Transpiration and (Adaptation of) Stomatal Closure of Tradescantia Leaves during Water Stress

This paper summarises our recent research on the physiological effects of prolonged high RH during growth on stomatal function and we discuss possibilities that arise from this work for reducing postharvest quality problems in cut flowers. Chlorophyll fluorescence imaging was used to measure stomatal closure in response to desiccation of Tradescantia virginiana leaves grown under high (90%) and moderate (55%) relative humidities, or transferred between these humidities. Stomata of plants transferred from moderate RH conditions to high RH showed the same diminished closure in response to desiccation, as did stomata that developed at high RH. This response was found both when the leaves were either fully expanded or still actively expanding during the moderate RH pre-treatment. However, when leaves were grown in high RH prior to a moderate RH treatment, the reduced stomatal closure response to desiccation was only reversed in leaves (regions) which were still actively expanding during moderate RH treatment. This indicates that with respect to stomatal responses to desiccation, high RH leaf regions have only a limited capacity to adapt after transfer to moderate RH conditions. It is suggested that the diminished stomatal closure in high RH-grown plants is the result of changes in the signalling pathway for ABA-related closure induced by a prolonged period (several days) at a low ABA level. A short increase of VPD (by decreasing RH or increasing temperature) once every 2 or 3 days is probably sufficient to overcome vase life problems of cut flowers grown at high RH. Testing the acclimation ability of stomata to desiccation by transferring high RH grown plants to low VPD for just a few days would be a simply and effective screening procedure for genotypes with more adaptable stomat

Comparison of the physical properties of vermicompost from paper mill sludge and green compost as substitutes for peat-based potting media

The properties of vermicompost, green compost, and their mixes as substitutes for peat were evaluated regarding their recommendation for potting media. The mixes with a maximum of 50% of vermicompost or green compost had acceptable air filled porosity (AFP) and easily available water (EAW). In the vermicompost the level of organic matter (OM), dry bulk density (DBD) and shrinkage were acceptable; however, the AFP and EAW together were not at the recommended level in the different batches; as a consequence, vermicompost should not be used alone for potting media. In the green compost, the level of OM was low which increased the DBD and consequently the AFP was diminished. The particle size distribution (PSD) was different among peat, vermicompost and green compost. The coarse peat had the lower proportion of particles from 0.25 to 2.00 mm (41%) whereas the green compost had the lower coarseness index (CI: percentage by weight of particles larger than 0.5 mm in diameter), 48.4%. The direct effect of the PSD, OM and DBD in the water and air availability was confirmed. Moreover, there were high correlations between the OM, DBD, shrinkage, pore volume and PSD with the water release curve. Those properties should be considered in order to increase the level of substitution of vermicompost in peat-based potting media

Amino Acid Quenching

Alexa Fluor 594 is a fluorescent molecule commonly used to tag calmodulin, a protein that regulates a variety of cell processes. By measuring fluorescence, scientists can study calmodulin and its interactions with other proteins. However, fluorescence is not the only fate of Alexa Fluor 594. The molecule is also known to transfer energy to coupled amino acids through a mechanism called quenching. The purpose of this experiment was to study the quenching effects of Histidine, Tyrosine, and Methionine on the Alexa Fluor 594. These amino acids’ Stern-Volmer plots suggest static quenching may be occurring. Moreover, the Stern-Volmer plot of Potassium Iodide (KI), a dynamic quencher, suggested that KI quenches the excitation Alexa Fluor 594 in part through a static mechanism. We plan to replicate our experiment and complete statistical testing to determine the significance of our data. Determining if these amino acids quench AlexaFluor594 will help researchers better characterize the calmodulin protein and its interactions