Browsing by Subject "Apple"

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Changes in the concentration of particular hormones and carbohydrates in apple shoots after "bending" respectively chemical treatments and relationship to the flower induction process
(2005) Boonplod, Nopporn; Bangerth, Fritz
SUMMARY Apples are cultivated commercially throughout the temperate zone. A regular production however does not seem possible because of irregular yields from year to year. Main causes for this are the so called "alternate bearing" behavior which is the result of profuse flowering in one year but few or no flowers in the following year. It is reported that too vigorously growing shoots are part of the reasons for alternate bearing in apple trees. Applications of chemicals or conventional cultural practices, such as bending shoots have been widely used to restrict shoot growth and promote flower induction. However, the physiological mode of action of these methods in FI is still unknown. Phytohormones are thought to be involved in the process of flower induction (FI). In the above experiments, we investigated changes in endogenous hormones, starch and sugar contents after bending upright shoots into a horizontal position and spraying apple trees with the growth regulators Alar plus Ethrel to improve FI. The experiments were carried out during the years 2001 to 2003 at the Experiment Station, of the University of Hohenheim, Germany, whereby the apple cvs. ?Golden Delicious?, ?Boskoop?, ?Elstar? and ?Idared? were used. The apical part of growing shoots and non-growing bourse shoots, beside bark, wood and shoot diffusates were collected. Plant samples were frozen immediately in liquid nitrogen and freeze dried. Phosphate buffer 0.1M, pH 6.2 was used for collecting auxin in the shoot diffusates. All samples were stored at ?20C until extraction and purified, identified and quantified by Radio Immuno Assay (RIA). The results revealed, in general, that shoot bending and spraying with Alar plus Ethrel changed the endogenous hormone concentrations in the apical part of shoots, as well as in wood, bark and shoot exudates of apple trees. The ?Golden Delicious? cultivar and vigorously growing shoots showed clearer tendencies of hormonal changes than the other cvs. and non-growing bourse shoots. Cytokinin concentrations in the apical part of shoots, and in wood and bark increased after both treatments. Contrary to that, GAs and IAA concentrations in the apical part of shoots and in shoot exudates showed the opposite results. Both treatments had no effect on the concentration of ABA. Ethylene production in shoot tips was considerably stimulated by the combined treatment of Ethrel plus Alar probably due to Ethrel being a "synthetic precursor" of ethylene. Considerable variation existed in the mentioned hormonal changes in respect to the year of examination and the cv. under investigation. Time of treatments and in particular climatic conditions were probably the most influential variables. In spite of all this and on the basis of the above results the conclusion can be drawn that higher concentrations of cytokinins and lower concentrations of gibberellins and auxin are favorable for FI. Spraying with Alar plus Ethrel and bending of shoots seemed to decrease the reducing-sugars, as well as sucrose and starch concentrations in growing shoots and their leaves. In non-growing shoots, spraying seemed to reduce starch but to increase reducing-sugars and sucrose concentrations. A correlation between changes in carbohydrate contents (reducing sugar, sucrose and starch) caused by the spraying treatments and FI does not seem to exist. All the observed changes in the carbohydrate concentrations caused by spraying treatments were not particular impressive and did not really support the often published claim that the effect of spraying growth regulators, bending shoots or other cultural practices may mediate their stimulatory effect on FI via a change in carbohydrates. In contrast to that the above observed experimental results rather suggest that hormones are more effectively involved in the flower induction process of fruit trees.
Effects of a two-factorial dynamic storage system on apple fruit metabolism, quality attributes, disorder incidences and biochemical properties
(2024) Büchele, Felix; Vögele, Ralf; Kittemann, Dominikus
Dynamic Controlled Atmosphere (DCA) technologies are designed to monitor the metabolism of fruit as a function of time and the oxygen partial pressure (pO2) in the storage atmosphere. By identifying signals sent by the fruit in response to low oxygen stress, this concept allows defining the lowest oxygen level tolerated by the fruit material and the specific and transient pO2, which is proposed to slow down the aerobic respiration of the fruit to a minimum and accordingly the ripening-related loss of fruit quality. This work examines a novel storage technology for pome fruit referred to as DCA-CD+, which can be considered the first generation of a two-factorial dynamic storage system. DCA-CD+ aims to define both a transient optimum pO2 and storage temperature in real-time, based on monitoring the carbon dioxide (CO2) production rate of the stored product. The CO2-release rate is proposed as a dependable indicator of low oxygen stress and an accurate depiction of the metabolic intensity of the fruit in response to temperature variations. The idea behind dynamic temperature adjustments is based on the assumption, that increased storage temperatures can reduce the energy usage of the refrigeration systems during long-term storage substantially, while also mitigating oxidative stress in the fruit, thus contributing to reducing the occurrence of storage disorders. The extremely low pO2 levels established in the storage atmosphere are suggested to counteract the ripening-inducing effects of this dynamic temperature approach. The assessment of DCA-CD+ in this work is based on a comparison to other postharvest conditions such as cold storage (RA) or static controlled atmosphere (CA). Furthermore, the interactions between storage atmosphere, temperature, and applications of the ethylene-inhibitor product 1-methylcyclopropene (1-MCP) are investigated. The conducted biochemical analyses highlight that apples stored under DCA-CD+ undergo repeated periods of hypoxia. Fruit adapt to the energy crisis induced by low oxygen stress by increasing their glycolytic flux, which is coupled to the activation of the fermentative pathway. Importantly, none of the examined apple cultivars in any of the experimental seasons exceeded critical thresholds for volatile fermentative products acetaldehyde (AA) and ethanol (EtOH), which could potentially be associated with the development of off-flavors or internal disorder symptoms. Consequently, the atmospheric conditions implemented did not result in any fruit damage associated with low oxygen stress in any of the tested scenarios. These findings suggest that DCA-CD+, specifically the use of carbon dioxide as an input value, is effective in identifying low oxygen stress in stored fruit and defining the pO2 for optimum quality conservation. pO2 setpoint calculation by the DCA-CD+ algorithm showed an interaction effect with the respective storage temperatures. Furthermore, the sensitivity of the stored fruit to temperature variation was found to be cultivar-dependent and transient during the storage period. Depending on the stored apple cultivar and season, DCA-CD+ calculated temperature setpoints reaching up to 3°C to 4°C, from the baseline temperature of 1°C. Temperature peaks were generally followed by a significant decrease in the calculated temperature setpoints, as an increased CO2 production rate signaled an intensifying fruit metabolism due to elevated storage temperature. The analysis of quality-defining parameters and disorder symptoms support the conclusion that DCA-CD+ allows for dynamic temperature adjustments without accelerating fruit ripening and the associated loss of quality. Preliminary findings indicate that this approach can reduce the energy usage of the cooling system in commercial storage rooms, without requiring cost-intensive additional installation of technology or renovations of room structural components. Lower pO2 setpoints were calculated at higher temperatures, suggesting that increasing the storage temperature can contribute to alleviating low oxygen stress in apples. Improved conservation of fruit quality attributes and a reduction in storage disorder incidences of DCA-CD+ in comparison to CA could be demonstrated in some instances, contingent on experimental season and apple cultivar. These benefits presumably become more pronounced with extended storage durations exceeding eight months. Ultimately, it can be argued that the complementary and interactive effects of dynamic temperature and oxygen in DCA-CD+ with 1-MCP application provide the highest potential for fruit quality conservation, limiting storage disorder, and reducing cooling-related energy usage. DCA-CD+ was demonstrated to potentially counteract detrimental effects of 1-MCP applications, e.g. an increased risk of carbon dioxide injuries. This work aimed to contribute to understanding the mechanisms behind the interference of the established temperature and atmospheric conditions in the DCA-CD+ system with the volatile aroma profile of apples. It was demonstrated that the synthesis capacity of volatile organic compounds (VOC) is primarily suppressed on a principal substrate level, and less in the later conversion of aldehydes to alcohols and esters. The pathways for the synthesis of linear volatiles originating from fatty acids were determined more responsive to low oxygen environments, in comparison to the pathways of branched volatiles derived from amino acids. Further insights were gained into the physiological mechanisms underlying the activation of the fermentative pathway, suggesting it functions as an adaptation mechanism not exclusively linked to low oxygen stress. Moreover, efforts were made to establish a connection between ripening and disorder-related modifications in cell structural components and associated alterations in the volatile profile, primarily highlighting the role of the lipoxygenase pathway. Statistical classification demonstrated that the repeated induction of low oxygen stress in DCA-CD+ storage resulted in a distinct volatile profile and a higher association with aroma defining compounds compared to CA storage. The observed increased EtOH accumulation is discussed to mitigate the ripening-inducing effects of the hormone ethylene, while also providing additional substrate for the synthesis of ethyl esters. Preliminary findings of this work indicate that storage temperatures can play a role in the aroma development of stored apples, even when low pO2 conditions are established. In summary, this study created a comprehensive documentation of the commercial viability of two-factorial dynamic storage systems for pome fruit and provided insights into the metabolomic responses of apples to extremely low oxygen levels, particularly in interaction with dynamic storage temperature adjustments.
Physiological, metabolic and molecular basis of biennial bearing in apple
(2023) Kofler, Julian; Zörb, Christian
Alternate or biennial bearing in apple (Malus ×domestica Borkh.) is characterized by ‘On’ years with high crop load and inhibited floral bud initiation and ‘Off’ years with little crop load and promoted formation of floral buds, respectively. Apple cultivars differ in their degree of biennial bearing behavior. The cropping irregularity has severe effects on quality and yield of apple harvests in commercial orchards and thereby directly poses an economic risk to apple growers. The aim of this study was to contribute to the understanding of the underlying mechanisms of biennial bearing in apple by analyzing the physiological processes in bud meristems during the time of flower bud induction. A field experiment was conducted during the growing seasons 2015 and 2016 and provided bud meristems of various developmental stages for a variety of analyses. The regular bearing cultivar ‘Royal Gala’ and the biennial bearing cultivar ‘Fuji’ allowed the comparison of two different developmental responses to high and low crop load treatments. Buds from 2-year-old spurs were sampled starting approximately four weeks after full bloom. Histological analysis of bud meristems successfully identified the time point of flower bud initiation in both cultivars at the experimental site. The onset of flower bud initiation was affected by crop load, cultivar and heat accumulation. While heavy cropping delayed the onset in ‘Royal Gala’ trees for 20 days compared to ‘Royal Gala’ trees with no crop load, bud initiation in heavy cropping ‘Fuji’ trees was negligible. ‘Fuji’ trees with no crop load started initiating buds 19 days earlier than ‘Royal Gala’ trees with the same cropping status. Proteomic profiling of the buds sampled during flower bud induction and during flower bud initiation revealed distinct differences in specific protein abundances depending on the cropping status. Buds from trees with a high crop load, where the flower bud initiation was inhibited and the buds primarily remained in a vegetative state, showed a decreased abundance of enzymes belonging to the phenylpropanoid and flavonoid pathways. Specifically, PAL was reduced, which could lead to less active auxin due to the reduced production of chlorogenic acid and thereby inhibiting flower bud formation. Furthermore, increased abundances of histone deacetylase and ferritins were also found in buds from high cropping trees, indicating that histone modification and building up enough iron storage capacities are involved in the vegetative bud development. Buds growing on non-cropping trees with a high rate of flower bud initiation, showed significantly higher concentrations of proteins involved in histone and DNA methylation. Metabolomic profiling and next-generation RNA sequencing showed that thiamine, chlorogenic acid, and an adenine derivative play a role in metabolic pathways promoting early flower bud development in apple, and that tryptophan was more abundant in buds collected from high-cropping trees compared to non-cropping trees. The selection of proteins, metabolites, and genes that the current work produced through its broad, non-targeted approach provides a comprehensive data base for future, more targeted analyses. The results of this study lay a thorough baseline to contribute to the identification of biological markers that are linked to a certain bearing behavior. Such markers can accelerate and facilitate breeding programs aimed at selecting apple cultivars, that are less prone to biennial bearing.
Sortenspezifische Veränderung der Fruchtfleischfestigkeit bei Apfel während der Lagerung unter Berücksichtigung des Signalmoleküls Ethylen
(2019) Zimmermann, Telse; Wünsche, Jens Norbert
Ripening of apples is initialized by ethylene, a ripening hormone, and the start of ripening is marked by an increase of ethylene production. During ripening fruit firmness is one of the changing processes and it is one of the major quality parameters for consumer and trade. After harvest the decline of apple fruit firmness consist of three distinct phase, in which the first phase, where no significant firmness reduce is observed, is the main part. The length of the first phase is different between the cultivars, so rapid softening cultivars have a short and cultivars, which obtain firmness over long time, have a long first phase. Application of ethylene will shorten this phase depending on the ethylene sensivity of the cultivars. The decline of fruit firmness is affected by changes in the cell wall. The aim of this study is to investigate this cultivar specific firmness decline by measuring gene expression of cell wall modifying enzymes and the activity of the cell wall modifying enzyme β galactosidase (GAL), and to find out the reason for the ethylene sensivity of the cultivars by recording ethylene production, gene expression and activity of ethylene biosynthesis enzymes also gene expression of the ethylene receptors and ethylene signal transduction proteins. To reach that goals three cultivars with different firmness and ethylene production are used and stored up to 4 month in a cool storage with 10 °C. The used cultivars are ‘Pinova’, which maintain firmness, ‘Elstar’ and ‘Golden Delicious’, which soften rapidly. ‘Pinova’ and ‘Elstar’ have a low ethylene production compared to ‘Golden Delicious’. Additional the ripening process is influenced by an inhibiting action of 1 Methylcyclopropen (1 MCP) and a promoting effect of ethylene. The main results are that correlation between ethylene production and fruit firmness persist just in softening cultivars although there are no difference between ‘Elstar’ and ‘Pinova’ in gene expression of ethylene biosynthesis enzymes. Also there are no differences between them in gene expression of ethylene receptors and ethylene signal transduction proteins while ‘Elstar’ shows an ethylene sensivity in contrast to ‘Pinova’. By comparison of the literature it is hypothesized that the amount of the ethylene receptors ERS1 and ERS2 is related to fruit firmness and the ethylene receptor ETR2 could be the sensor of ethylene sensivity. Furthermore the results about the changes/shifting of the cell wall refer to a difference between the cultivars in the gene expression of MdPG, MdAF, MdXTH2 und MdXYL with higher values for ‘Elstar’, but neither the expected inhibition of 1 MCP nor the promotion of ethylene in this genes happened. The activity of GAL shows indeed a cultivar specific pattern but it doesn´t correlate to fruit firmness. Also for other cell wall modifying enzyme activity or cell wall content exist no reference for a relationship to fruit firmness. So it is hypothesized that the interlinkage of the single cell wall components causes the fruit firmness on the one hand and limits the substrate availability of the respective cell wall modifying enzyme on the other hand.