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Thesis (Ph. D.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains xii, 108 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 97-108).

M.Sc. (Botany) / Please refer to full text to view abstract

M.Sc. / The commercial value of cut flowers, whether for ornamental use or as an export product, has increased significantly over the years. Much attention is given to flower quality and flower longevity. These two factors are influenced by preharvest and postharvest treatments. The major postharvest loss reduction techniques in carnation flowers include regulation of preharvest growing, use of improved harvesting techniques, use of various storage techniques, use of growth regulators and use of floral preservatives. Senescence of carnation flowers (Dianthus caryophyllus L. cv. White Candy), is accompanied by a climacteric rise in ethylene synthesis and an increased sensitivity of the flowers to ethylene. A pulse treatment with sucrose caused a delay and suppression of the climacteric rise in ethylene synthesis. The action of sucrose, with reference to ethylene, was similar to that of cytolcinins. Dry storage also caused an increase in flower longevity. This is due to the flower's ability to maintain water balance by lowering the cells osmotic potential. Dry storage is of importance, as transportation of the flowers occurs under these conditions. Although sucrose increased the longevity of freshly cut carnations, it caused a decrease in longevity of flowers that were subjected to water stress. With the lowering of the tissue water potential through treatment with sucrose and thereafter by dry storage, the flowers are subjected to stress, and are not able to recover even after rehydration. Applied sucrose increased the carbohydrate pool, thereby resulting in a gradual decline of starch. Administering both sucrose and water stress to the carnation flowers resulted in an early peak in the sugar content, as well as an early depletion of sugar in the flower petals. Cytokinin activity in untreated carnation flowers appeared to be higher compared to flowers treated with sucrose. Water stress have the effect of decreasing cytokinin levels and activity. It is thus clear from the results of this study, that carnations subjected to water stress through dry storage, should not be pretreated with any preservative containing sucrose, as it leads to a reduction in vase life.

A review of the literature pertaining to cut carnation flower senescence and the regulatory role of plant hormones in this process revealed the value of this system in physiological studies. Carnation flower senescence is a good example of correlative senescence and therefore this final development stage involves an interaction between flower parts dying at the expense of the development of others. Due to the survival value of the seed, ovary growth occurs to the detriment of the surrounding flower parts especially the petals, the flower part that determines vaselife. This senescence strategy occurs, although at a later stage, even when pollination is unsuccessful. Additional ethylene applied using 2-chloroethyl phosphonic acid, which when incorporated into plant tissue produces ethylene, accelerated carnation flower senescence. If the carnation flowers are treated with silver thiosulphate,which prevents ethylene action,and ethanol,which inhibits ethylene biosynthesis,petal longevity is extended to the detriment of ovary growth. Correlating the physical appearance of the flowers in the presence and absence of ethylene with dry mass and labelled sucrose analyses, carbohydrate movement appeared to be a major event during the senescence of this cut flower. Such a conclusion could not be reached on dry mass analyses alone as the photosynthetic organs of the carnation flower contribute to the carbohydrate pool in the first days following harvest. Furthermore the respiratory pattern of the flower is not a steady decline. Concomitant with the natural ethylene emanation as the petals irreversibly wilt, so the respiratory rate increases. On the other hand, the respiratory rate is greatly reduced with silver thiosulphate and ethanol treatment. In the presence of ethylene, together with the growth of the ovary there is an influx of carbohydrates from all the flower parts including the petals into the ovary. With silver thiosulphate and ethanol treatment the petals become the dominant carbohydrate sink. It thus appears that insufficient carbohydrates moving to the ovary may be the cause of the lack of ovary development. However , an experiment with isolated cultured ovaries on a modified MILLER'S (1965) medium lacking in plant hormones but with a range of sucrose concentrations showed that sucrose alone cannot stimulate ovary growth. The mechanism by which this source-sink relationship is determined appears to be controlled from the sink. The source organs contribute carbohydrates that are in excess of their metabolic needs. Acid invertase activity, maintaining the sucrose gradient into the sink, was considered as a mechanism by which sink strength could be controlled due to the parallel in other plant systems between the activity of this enzyme and sink strength. On investigation the levels of acid invertase activity are higher in the ovaries of senescing carnations than in the petals. This balance of invertase activity was reached mainly due to a decline in petal invertase activity. However, as silver thiosulphate treatment lowered the level of acid invertase activity in the ovary and this flower part was not the dominant sink with this treatment, acid invertase activity appears to contribute to sink activity in the senescing carnation flower. Nevertheless due to the immobility of sucrose through membranes, for the passive movement of sucrose down a concentration gradient, membrane permeability to sucrose would have to be altered. This is a possible role of the plant hormones and specific ions. Furthermore, this ovary growth was correlated with chloroplast development in the ovary wall. In the presence of ethylene 'greening' or an increase in chlorophyll content during flower senescence was measured. This increase in the chlorophyll content did not occur in the silver thiosulphate and ethanol treated carnations. Relating this to chloroplast development, an electron microscope study showed that in the presence of ethylene the original amyloplast present at harvest developed into a chloroplast with thylakoids stacked into grana. With the ethylene inhibitory treatments, although thylakoids developed in the ovary wall chloroplasts, grana did not form. As chlorophyll is synthesised in the thylakoids, this chloroplast structure correlated with the chlorophyll measurements. The results of the parameters measured during the senescence of the cut carnation flower suggested that the other plant hormones besides ethylene were involved in this process. Endogenous cytokinin measurements showed that, overall, the level within the cut flower declined as the flower senesced. The ovary cytokinin levels did not steadily decline but increased as the petals irreversibly wilted. This peak of cytokinin activity was common to ovaries of flowers treated with 2-chloroethyl phosphonic acid and naphthalene acetic acid, treatments that accelerated senescence. Previous workers showed that a silver thiosulphate treatment prevented this increase in cytokinin activity in the ovary. This, together with the lack of ovary development, suggests that the ovary cytokinin activity may be a crucial event in the regulation of carnation flower senescence. To confirm such a hypothesis zeatin was injected into the ovary but was found ineffective in mobilising sucrose and accelerating petal senescence. It was only when both zeatin and indoleacetic acid were applied to the ovary that sucrose mobilisation and accelerated petal senescence occurred. Thus auxins together with cytokinins appear important in ovary development. The importance of the presence of auxin in ovary development was further recognised by a naphthalene acetic acid treatment being far more effective in ~timulating the growth of isolated cultured ovaries than kinetin. Auxin treatment increased the size of the cells within the ovary wall and the development of the chloroplasts within these cells to a greater extent compared to control and kinetintreated ovaries. It was thus hypothesised that the auxin levels in the ovary were protected against conjugation by the presence of adequate levels of cytokinins. When the cytokinin levels dropped, as in the petals, ethylene could then accelerate auxin conjugation resulting in a retardation of growth. Sink tissues, such as the ovary, with a higher cytokinin and hence auxin content, may utilise mobilised assimilates from the petals thus contributing to petal senescence. To further prove this hypothesis an investigation into the site of ethylene action using the silver ion as a tool was initiated. A review of the histochemical and histological literature revealed that common silver binding sites in plants included sulphydryl groups, chloride ions, ascorbic acid and invertase. Each was considered as potential channels via which ethylene could effect its physiological response but no conclusion was reached. Because of this a decision on the importance of the translocatory path of a ten minute silver thiosul phate pulse within the flowerhead and its accumulation within the receptacle could not be reached. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1985.

M.Sc. / The senescence of climacteric flowers such as carnations is accompanied by an increase in ethylene synthesis during the later stages. This increase in ethylene synthesis is preceded by an increase in the sensitivity of the flowers to ethylene. The increase in ethylene sensitivity is accompanied by a concomitant increase in the levels of short-chain saturated fatty acids (SCSFAs). Treatment of carnation flowers with SCSFA results in an increase in ethylene sensitivity. It appears that these acids act by increasing membrane fluidity, causing slight conformational changes in membrane associated proteins and thereby increasing the ability of the tissue to bind ethylene to its membrane associated receptor molecules. The levels of SCSFAs in senescing carnation petals is controlled by the activity of the enzyme acetyl-coenzyme A carboxylase (ACCase). A decrease in the activity of this enzyme results in an increase in the levels of the SCSFAs and vice versa. During the senescence of carnation flowers, ACCase activity fluctuated from day to day. This fluctuation can be correlated to the fluctuations in the ethylene sensitivity of the flowers on a daily basis. In carnation petals, ACCase is located mainly in the plastids. ACCase activity could be controlled via feedback inhibition by long-chain fatty acids such as oleic acid. Treatment of carnation flowers with oleic acid resulted in a concomitant inhibition of ACCase activity, an increase in SCSFA-levels and an increase in ethylene sensitivity. Oleic acid is a competitive inhibitor of ACCase activity, and changes in the levels of oleic acid will affect the activity of the enzyme. An increase in oleic acid concentration resulted in a decrease in enzyme activity. However, in carnations it appears that ACCase activity is not controlled via feedback inhibition by long chain saturated fatty acids. The results of this study clearly show that ACCase activity is controlled directly by the expression of at least the biotinylated (BCCP) subunit of the enzyme. A decrease in the expression of the gene during the early stages of senescence coincided with a decrease in ACCase activity and was accompanied by a concomitant increase in ethylene sensitivity. These results indicate that the increase in ethylene sensitivity caused by an increase in SCSFA levels is directly controlled by the expression of the ACCase genes.

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The vase life of cut flowers is determined by various physiological factors that determine the rate of their senescence. A thorough understanding of these factors is required in order to design treatments that will extend the vase life and delay senescence of cut flowers. Senescence of climacteric flowers such as carnations (Dianthus caryophyllus L. cv. Nordika and cv. Snow White) and freesias (Freesia refracta cv. Athena) is characterized by a climacteric rise in respiration rate and ethylene synthesis during the late stages. The increase in ethylene production is preceded by an increase in the sensitivity of the flowers to ethylene. Pulse treatments with sucrose caused a delay and suppression of the climacteric rise in ethylene synthesis and a delay in the climacteric maximum of the respiration rate. A pulse treatment for 24 hours with a 20% sucrose solution was most effective in extending the longevity of both carnations and freesias. The ability of the receptor molecules to bind ethylene is greatly reduced when flowers are pulse-treated with sucrose. In freesias, the ability to bind ethylene is reduced even further when flowers are treated with STS or 1-MCP. Ethylene synthesis in freesias is suppressed and inhibited when treated with STS or 1-MCP but longevity of the freesias and number of open florets on the stem is not increased. The uptake and distribution of sucrose in the buds of freesias is seen by the distribution of sucrose from the first bud on the stem to the next bud after the bud opens. The distribution of sucrose from one bud to the next results in more buds opening on the stem than that on the stems of STS or 1-MCP treated freesias. It is thus clear from the results of the study, that pulsing senescing climacteric flowers with sucrose increases the vase life of the flowers and suppresses ethylene sensitivity of the flowers, thus delaying the autocatalytic process of ethylene production. It is also evident from the results that the osmolality in the flowers has a direct influence on the metabolic processes of the flowers. In freesias, pulse treatment with sucrose increases the number of open buds on the stem and delays senescence of the florets. / Mr. C.S. Whitehead