Ethylene plays a key regulatory role in carnation flower senescence. Flower senescence is associated with a significant increase in ethylene production. Continued perception of this ethylene by the flower is necessary to sustain the climacteric rise in ethylene and the expression of senescence related genes associated with senescence. In addition, increased sensitivity by the flower to ethylene during development and senescence has been observed. In order to study the perception of ethylene at the molecular level, an ethylene receptor gene was cloned from carnation petals. The clone, CARETR, shows 68% homology at the nucleic acid level with the Arabidopsis ethylene receptor gene, ETR1. Northern blot analysis revealed that CARETR is present as a low abundant transcript in petals, styles, and ovaries. Further analysis also showed that CARETR is upregulated during flower senescence. Treatment with the ethylene action inhibitor norbornadiene (NBD) resulted in decreased levels of CARETR transcripts. These data suggest that CARETR plays a role in the increased sensitivity of carnation flowers to ethylene during flower development and is involved in staging the rapid and orchestrated death of the flower.
In Dianthus caryophyllus flowers the pollinated stigma gives rise to signals that are translocated throughout the flower and ultimately result in corolla senescence. Pollination leads to a rapid increase in ethylene production by the pollinated styles followed by ethylene biosynthesis from the ovaries, the receptacle tissue, and lastly the petals. The accumulation of ACC in these floral tissues also correlates with the sequential pattern of ethylene production. Ethylene production by the pollinated style can be defined temporally by three distinct peaks, with the first peak detected as early as 1 hour after pollination. In a carnation flower with multiple styles it is also possible to detect ethylene production from an unpollinated style on a pollinated gynoecium by 1 hour after pollination. This finding provides evidence for very rapid post-pollination signaling between styles. ACC synthase expression is induced in pollinated styles as early as 1 hour after pollination, but no message is detected in pollinated ovaries. ACC synthase enzyme activity is also absent in the pollinated ovaries despite the accumulation of large amounts of ACC in the ovary after pollination. This indicates that ACC must be translocated between organs after pollination. When a pollinated styles is removed from the flower at least 12 hours after pollination the corolla will still senesce. This indicates that the pollination signal has exited the style by this time. Evidence in carnations suggests that ACC and ethylene may both be involved in aspects of post-pollination signaling.
We have investigated the patterns of ethylene biosynthesis in carnation (Dianthus caryophyllus L.) genotypes that exhibit extended vase life in comparison to flowers of White Sim'. `White Sim' flowers exhibited typical symptoms of senescence, including petal in-rolling and rapid wilting, beginning 5 days after harvest. In contrast, the other genotypes studied did not show petal in-rolling or rapid wilting associated with petal senescence. The first visible symptom of senescence in these flowers was necrosis of the petal tips, and it occurred from 3 to 7 days after the initial symptoms of senescence were seen in `White Sim' flowers. In all cases, the extended-vase-life genotypes did not exhibit the dramatic increase in ethylene production that typically accompanies petal senescence in carnation. This appeared to be the result of limited accumulation of ACC. In addition, flowers of these genotypes had limited capacity to convert ACC to ethylene. Therefore, we conclude that the low level of ethylene produced by these flowers during postharvest aging is the result of low activities of both ACC synthase and the ethylene-forming enzyme. Treatment of `White Sim' flowers at anthesis with 1.0 μl ethylene/liter resulted in the induction of increased ethylene biosynthesis and premature petal senescence. The extended-vase-life genotypes exhibited varying responses to ethylene treatment. One genotype (87-37G-2) produced elevated ethylene and senesced prematurely, as did flowers of `White Sim'. A second genotype (82-1) was induced to senesce by ethylene treatment but did not produce increased ethylene. A third genotype (799) was unaffected by ethylene treatment. The results of this study suggest these extended-vase-life genotypes are representative of genetic differences in the capacity to synthesize and respond to ethylene. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).
High-temperature treatments can be used for disinfestation of a variety of horticultural crops. Carnation flowers were subjected to a heat treatment in order to determine if it is a viable option for disinfestation of this crop. Flowers were exposed to 45°C for 24 hr in the dark, while control flowers were held at RT for 24 hr in the dark. Subsequently, the flowers were held at RT in the light and monitored for ethylene production, an indicator of imminent floral senescence. In the heat-treated flowers, the ethylene climacteric occurred at 96 hr after the heat treatment, a delay of 12 hr when compared to the control. Peak ethylene production was decreased by 25% to 30% in heat-treated flowers. Northern blot analysis of the ethylene biosynthetic pathway genes, ACC synthase, and ACC oxidase, showed that the expression of these genes is delayed by 8 to 16 hr in heat-treated flowers. This indicates that the delay and decrease in ethylene production is at least, in part, due to a delay or reduction in the expression of these genes. Further investigation revealed a decreased responsiveness of the petals to ethylene. Petals from heat-treated and control flowers were exposed to 1 ppm ethylene for 0, 0.5, 1, 2, 4, 6, 12, and 32 hr. The heat-treated petals again showed a delay and a decrease in maximum ethylene production after exposure to ethylene. A delay in expression of ACC synthase and ACC oxidase was also observed. The beneficial effects of exposing carnation flowers to high temperatures, a delay in ethylene production, and reduced responsiveness to ethylene, suggest that heat treatments could be used for disinfestation of this crop.
‘Forever Yours’ roses (Rosa Hybrid Tea) were grown in recirculating nutrient solutions at 1.0 and 10.0 meq/liter K in combination with 10.0 meq/liter NO3-N or NH4-N. Low K limited the growth and flower production, regardless of N form. Ammonium-N fertilized plants showed NH4-N toxicity symptoms as interveinal chlorosis of the lower leaflets. An increased K supply reduced NH4-N toxicity symptoms. Concentrations of Ca and Mg were lower, while P was higher, in the tissue of NH4-N fertilized plants, as compared to NO3-N fertilized plants. Total N, alcohol insoluble N, soluble organic N, and NH4-N were higher in the tissue of plants which received NH4-N, as compared to NO3-N, regardless of K level. An increased K supply from 1.0 to 10.0 meq/liter resulted in higher NO3-N in NO3-N fertilized plants and lower NH4-N in NH4-N fertilized plants.
Storage of Caladium × hortulanum L. tubers at 5°C for 1 to 3 weeks resulted in an elevation in CO2 production when transferred to 22°. A decrease in storage temperature from 22° to 1° resulted in an increase in respiratory activity following transfer of tubers to 22°. The respiratory burst associated with low temperature storage was greatest following 24 hr at 22°, after which a decline in CO2 production was seen. Electrolyte leakage from ‘Carolyn Whorton’ tuber disks increased when tubers were held for either 3 weeks at 5° or 2 weeks at 1°, as compared to shorter durations of chilling or higher temperatures. Sprouting (days to emergence) of planted tubers was delayed following low temperature storage, as compared to tubers held at 22°. Although delayed, all tubers sprouted when held a maximum of 3 weeks at 5°, or 2 weeks at 1°.
Changes in dry weights, total N, nitrate N, and reduced N in the aboveground parts of Chrysanthemum × morifolium Ramat. ‘Gt.#4 Indianapolis White’ were determined at intervals from planting of rooted cuttings until inflorescence maturity. Plant dry matter accumulation rate (mg/day) increased in the combined aboveground tissues with each successive harvest, while N accumulation rate (mg N/day) peaked early in the plants’ growth and decreased after the 6th week of growth. Continued dry matter accumulation in the leaves during inflorescence development suggested that photosynthetic capacity was in excess of the inflorescences’ needs. In contrast, a loss of N from the vegetative portions, and primarily the stems plus petioles, indicated that newly absorbed N was inadequate to meet the demands of the developing inflorescence. The partitioning of N between NO3 and reduced N indicated that enzymatic reduction of NO3 did not limit the availability of reduced N during inflorescence development.
‘Forever Yours’ roses (Rosa Hybrid Tea) were grown in recirculating nutrient solutions at 0.25, 2.5, 5.0 and 10.0 meq K/liter. Low K supply (0.25 and 2.5 meq/liter) reduced growth, flower production, and length of flowering stems. Leaf K concentration was reduced at the lowest K concentration in solution. Increasing K concentration in solution from 0.25 to 10.0 meq/liter had no antagonistic effect on the accumulation of Ca or Mg in the leaves. Plants which received 0.25 meq K/liter developed K deficiency symptoms after 5 weeks of growth in treatment solutions.
Mefluidide was applied as a foliar spray to the point of runoff to plants of Hibiscus rosa-sinensis L. ‘Pink Versicolor’ at 0, 500, 1000, 2000, 4000, and 8000 mg/liter. Mefluidide treatment increased lateral branching, but inhibited the length of lateral growth and plant height as compared to untreated controls. Tip necrosis of young, expanding leaves was seen at the lowest mefluidide concentration, and increased to the point of severe defoliation of plants at the highest concentration. Mefluidide delayed flowering, but increased the number of flower buds produced. In a 2nd experiment, single and double spray applications of 0, 100, 200, 400, and 800 mg/liter mefluidide were evaluated in comparison to hand-pinching the plants. Both pinching and mefluidide application increased the number of lateral shoots, compared to an untreated control. In contrast to pinched plants, mefluidide treatment inhibited the average length of the lateral shoots. Double applications of mefluidide inhibited plant height, lateral shoot number, and shoot length, as compared to single applications. Treatment with 10 mg/liter gibberellic acid following mefluidide applications was ineffective in reversing the effects of mefluidide on hibiscus growth. Chemical name used: N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl]amino]phenyl]acetamide (mefluidide).
Dark storage of Chinese hibiscus (Hibiscus rosa-sinensis L. cv. Brilliant Red) for 5 days to simulate shipping promoted flower bud abscission. Less developed flower buds (<30 mm) were more susceptible than developed buds to dark-storage-induced abscission. Removal of mature buds (>30 mm) before dark storage reduced subsequent abscission of younger, less developed buds. Plants grown under low irradiance conditions (500 µmol·s–1·m–2 PPF) abscised more flower buds in response to dark storage than those grown in high irradiance (980 µmol·s–1·m–2 PPF). These results indicate factors that decrease the availability and partitioning of photosynthates to immature flower buds increase the incidence of abscission.