Progress 05/01/07 to 04/30/12
Outputs
OUTPUTS: (1) Developed methods for studying the occurrence, type, and distribution of calcium oxalate crystals (COC) in aroids. (2) Identified that raphides and druses occurred in stems, leaves, roots, and spadices, and crystal sands in stems of Dieffenbachia. (3) Quantified the density of raphides and druses in leaves of 37 Dieffenbachia cultivars and found that more druses occurred than raphides regardless of the location in the leaf. The druse densities were 7- to 76-fold greater than those of raphides depending on the cultivar. In addition, two lines of evidence indicate that COC density is under genetic control. (a) The COC densities in tetraploid cultivars were at least 34% less than their corresponding diploid cultivars. (b) Cultivar Star White, a triploid hybrid developed from a cross between 39301 and tetraploid Memoria Corsii, had one of the lowest densities of COC, partially due to the fact that Memoria Corsii had low COC density. We also identified a cultivar having a total druse and raphide density of 137 per mm2 compared to some cultivars having over 481 per mm2. (4) Surveyed 10 other aroid genera to compare similarities and differences of their COC types, quantities, and distribution patterns. Results suggested (a) only druses and raphides were found in the leaves of these aroids and (b) the density of druses was higher than raphides, which are the similar results found in Dieffenbachia. However, (c) the COC density in the other aroids studied was generally lower than that of Dieffenbachia. (5) Studied the effects of different concentrations and combinations of Ca and Mg on COC formation. Significantly less COCs were formed when plants were cultured in solutions containing zero Ca and Mg, or zero Ca with increased Mg. In addition, the formation of raphides and druses varied with Ca and Mg concentrations. Plants cultured with zero Ca had no druse idioblasts, while plants cultured with 1.0 mM Ca or higher had 4-8 druses per mm2, indicating that druses did not form until Ca in the culture attained a level of 1 mM. Thus, druses may serve as storage for Ca. (6) Determined light effects on COC formation. Results showed that raphide densities of Exotic Perfection and Snowflake produced indoors decreased by 58% and 64%, respectively, compared to those of plants produced in the shaded greenhouse. (7) Studied the type, density, and distribution of COC in three types of philodendrons: vining type, self-heading type, and tree type. Results showed that (a) only druses and raphides occurred in the studied philodendrons; (b) druses were the dominant type of COCs in philodendrons with the ratio of druses to raphides ranging from 12:1 to 300:1 in leaves, 3:1 to 30:1 in petioles, and 2:1 to 12:1 in stems; and (c) the type of philodendrons or cultivars differed significantly in the density and distribution of COCs. In leaf tissue, the vining type philodendron had the highest the density of COCs (both druses and raphides), followed by the self-heading type, and then the tree type. PARTICIPANTS: Not relevant to this project TARGET AUDIENCES: Foliage plant growers, interior plantscapers, and homeowners PROJECT MODIFICATIONS: Nothing significant to report during this reporting period
Impacts
Aroids are important ornamental foliage plants produced in Florida and used widely for interiorscaping. However, all aroids produce COCs, which are associated with mammalian toxicity, such as dermal and gastric irritations, varying from mild to severe. Reports in medical journals document that several children have had to have tracheotomies to breathe after ingesting a small part of a leaf. Nursery workers frequently report rashes after handling these plants, particularly if the sap makes contact with their skin as commonly occurs when they are taking cuttings from stock plants. Additionally, aroids are produced for use inside homes and other building interiors, people, particularly children and pets may inadvertently make dermal contact with the plants or ingest parts of them. This study was the first attempt to determine the occurrence, types, and distribution of COCs in aroids. The results showed that more druses in leaves, which may suggest that it could be druses not raphides that act as vehicles to carry proteolytic enzymes to mammalian skin. We have identified significant genetic differences among cultivars of Dieffenbachia and Philodendron in the distribution, type, and density of COCs. The density of druses varied from 126 to 481 per mm2; and the density of raphides differed from 5 to 45 per mm2 among cultivars. We also found that environmental and cultural factors, such as light levels, fertilizer regimes particularly Ca and Mg, also affect the density of COC in aroids. Our findings strongly suggest that the reduction of COC densities is possible through breeding using cultivars with low COC density as parents or chromosomal doubling to develop polyploid cultivars.
Publications
- Cao, H., J. Chen, and D.B. McConnell. 2005. Dieffenbachia calcium oxalate crystal formation affected by cultivars, nitrogen rates, light intensity. HortScience 40:1086 (abstract).
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Progress 10/01/08 to 09/30/09
Outputs
OUTPUTS: Research effort on this project in 2009 has been focused on Philodendron cultivars. The type, density, and distribution of calcium oxalate crystals (COC) in three types of philodendrons were studied. Vining type: Philodendron scandens and P. micans; self-heading type: P. x Imperial Red and P. x Imperial Green; and tree type: and P. Selloum (Yellow Selloum) were grown in the same shaded greenhouse with an identical fertilization and irrigation management program. After three months of plant growth, leaf samples were prepared using the clear leaf method, and sections were prepared from leaf, petiole, and stem samples using a microtome. The type, density, and distribution of COCs were determined using a Nikon OPTIPHOT microscope. Results from this study are as follows: (1) only druses and raphides occurred in the studied philodendrons. Most raphides were distributed in the upper epidermal cells or the Palisade parenchyma adjacent to the epidermal layer. Druses were located mainly in both the palisade parenchyma adjacent to upper epidermal layer and the spongy parenchyma next to the lower epidermal layer. In both petioles and stems, the cortex area has more druses and raphides than the central ground tissue where the vascular bundles were scattered. (2) Druses were the dominant type of COCs in philodendrons with the ratio of druses to raphides ranging from 12:1 to 300:1 in leaves, 3:1 to 30:1 in petioles, and 2:1 to 12:1 in stems. (3) The type of philodendrons or cultivars differed significantly in the density and distribution of COCs. In leaf tissue, the vining type philodendron had the highest the density of COCs (both druses and raphides), followed by the self-heading type, and then the tree type. The density of COCs in the petioles of vining types of philodendron was one fourth of that both in self-heading and tree types of philodendron. In stem tissue, COC density differed significantly between the two self-heading cultivars. On the other hand, the ree type of philodendron had significantly higher density than the vining type. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Foliage plant growers, interior plantscapers, homeowners PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The genus Philodendron has more than 700 species, which makes it the second largest genus in the family Araceae. Philodendrons differ widely in growth habits from climbing to arborescent, leaf sizes vary from small (10 cm long and 6 cm wide) to gigantic (120 cm long and 40 cm wide), leaf shapes differ from heartleaf to palm-like, and leaf colors vary from light yellow to burgundy. Thus, many philodendrons have been produced as ornamental foliage plants. Although the ornamental value of Philodendron is widely recognized, an important issue concerning their mammalian toxicity has not been. Philodendron, like Dieffenbachia, produces COCs, which cause dermal and gastric irritations, varying from mild to severe. The general public has considered Dieffenbachia the most toxic aroid. However, the American Association of Poison Control Centers ranked Philodendron number one among the top 20 most frequently ingested poisonous plants in 1989 (www.kidsource.com/kidsource/content/Ingested.html). Reports in medical journals document that several children have had to have tracheotomies to breathe after ingesting a small part of a leaf. Nursery workers frequently report rashes after handling these plants, particularly if the sap makes contact with their skin as commonly occurs when they are taking cuttings from stock plants. Additionally, philodendrons are produced for use inside homes and other building interiors, people, particularly children and pets may inadvertently make dermal contact with the plants or ingest parts of them. This study was the first attempt to determine the occurrence, types, and distribution of COCs in philodendrons. The identified differences among cultivars in the distribution, type, and density of COCs in philodendron organs may suggest that the reduction of COC densities is possible through breeding.
Publications
- No publications reported this period
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Progress 10/01/07 to 09/30/08
Outputs
OUTPUTS: Research accomplishments 2008: (1) Studied the effects of different concentrations and combinations of Ca and Mg on calcium oxalate crystal (COC) formation. Dieffenbachia Rebecca were grown in hydroponic culture and Vergo Container Mix A. Nutrient solutions containing 3.0 mM KNO, 0.25 mM NH4H2PO4, 20 micromole FeSO4, 12.5 micromole H3BO3, 2.5 micromole MnSO4, 1.0 micromole ZnSO4, 0.25 micromole CuSO4, 0.0075 micromole (NH4) Mo7O24, and 40 micromole free-acid EDTA-chelated FeSO4 with variable concentrations and combinations of Ca and Mg were used for hydroponic production of the plants and for irrigating the plants grown in the container substrate. Leaf transections of 2 mm by 5 mm from leaf margin in the middle of lamina were taken from the first unfurled leaf 10 weeks after transplanting and examined for COC density. Results from hydroponic culture showed that plant growth was stunted when cultured in solutions containing either Ca or Mg only or zero Ca and Mg. There was no difference in dry weights among plants cultured in solutions containing 1 mM Ca and 4 mM Mg, 2.5 mM Ca and 2.5 mM Mg, or 4 mM Ca and 1 mM Mg. Raphide and druse idioblasts were two predominant types of COCs in leaves. Significantly less COCs were formed when plants were cultured in solutions containing zero Ca and Mg, or zero Ca with increased Mg. In addition, the formation of raphids and druses varied with Ca and Mg concentrations. Plants cultured with zero Ca had no druse idioblasts, while plants cultured with 1.0 mM Ca or higher had 4-8 druses/mm2, indicating that druses did not form until Ca in the culture attained a level of 1 mM. Thus, druses may serve as storage for Ca. Furthermore, both raphide and druse densities in leaves of plants cultured in solution containing 1 mM Ca and 4 mM Mg were significantly lower than those cultured in solutions containing 2.5 mM Ca and 2.5 mM Mg or 4 mM Ca and 1 mM Mg, indicating that lowering Ca and increasing Mg concentrations can reduce COC density. However, plants grown in the container substrate irrigated with the same solutions did not show apparent changes in density of raphides and druses, suggesting that the container substrate had enough Ca and Mg initially, and fertigation with different concentrations of Ca and Mg had little effect on COC densities. (2) Determined light effects on COC formation. Dieffenbachia Exotic Perfection, and Snowflake were grown in Vergo Container Mix A and fertilized with N at 200 mg/L using an ebb-and-flow system in a shaded greenhouse under the maximum photosynthetic radiation of 285 micromole/m2/s. Eight months after planting, leaf sections were taken from the first unfurled leaf. The same plants were then moved to interior evaluation rooms and grown under a light intensity of 8 micromole/m2/s for eight months. Leaf sections were taken from the first unfurled leaf as well. COC types and densities were determined from the leaves produced under two light intensities. Results showed that raphide densities of Exotic Perfection and Snowflake produced indoors decreased by 58% and 64%, respectively, compared to those of plants produced in the shaded greenhouse. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Foliage plant growers, interior plantscapers, homeowners PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Results from the hydroponic culture showed that lowering Ca and increasing Mg concentrations can significantly reduce COC density without detrimental effects on plant growth. However, such effects became diminished when Dieffenbachia were produced in container substrate. This finding suggests that COC density in Dieffenbachia would not be reduced in commercial production unless plants are produced in hydroponic system. Results from the light intensity experiments showed that high quality plants produced under the optimal light level contained high COC density, but COC density was significantly reduced after plants were placed indoors. Both nutritional and light experiments showed that the manipulation of environmental and cultural factors may have a limited opportunity for reducing COC densities in commercial Dieffenbachia production. As documented in our previous reports, COC formation is under genetic control, and genetic manipulation may be the ultimate solution to the COC reduction. Dieffenbachia is an important ornamental foliage plant used widely as a living specimen for interior decoration, but it contains some proteolytic enzymes contributing to the irritant effects to mammalians. COCs have been blamed as vehicles for delivering the enzymes. The identified differences among cultivars in distribution of the type and density of COCs in Dieffenbachia organs in our previous studies as well as the cultural practices altering COC density may suggest that reduction of COC densities is possible through breeding in combination with proper cultural practices, which may result in cultivars with less skin irritation.
Publications
- No publications reported this period
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