KELCH F-BOX protein positively influences Arabidopsis seed germination by targeting PHYTOCHROME-INTERACTING FACTOR1.

Seeds employ sensory systems that assess various environmental cues over time to maximize the successful transition from embryo to seedling. Here we show that the Arabidopsis F-BOX protein COLD TEMPERATURE-GERMINATING (CTG)-10, identified by activation tagging, is a positive regulator of this process. When overexpressed (OE), CTG10 hastens aspects of seed germination. CTG10 is expressed predominantly in the hypocotyl, and the protein is localized to the nucleus. CTG10 interacts with PHYTOCHROME-INTERACTING FACTOR 1 (PIF1) and helps regulate its abundance in plantaCTG10-OE accelerates the loss of PIF1 in light, increasing germination efficiency, while PIF1-OE lines fail to complete germination in darkness, which is reversed by concurrent CTG10-OE Double-mutant (pif1 ctg10) lines demonstrated that PIF1 is epistatic to CTG10. Both CTG10 and PIF1 amounts decline during seed germination in the light but reaccumulate in the dark. PIF1 in turn down-regulates CTG10 transcription, suggesting a feedback loop of CTG10/PIF1 control. The genetic, physiological, and biochemical evidence, when taken together, leads us to propose that PIF1 and CTG10 coexist, and even accumulate, in the nucleus in darkness, but that, following illumination, CTG10 assists in reducing PIF1 amounts, thus promoting the completion of seed germination and subsequent seedling development.

Strain analysis of 9 different abutments for cement-retained crowns on an internal hexagonal implant.

STATEMENT OF PROBLEM: Many aftermarket abutments for cement-retained crowns are available for the tapered screw-vent implant. Aftermarket abutments vary widely, from stock to custom abutments and in materials such as zirconia, titanium, or a combination of the two. How these aftermarket abutments perform under occlusal loads with regard to strain distribution is not clear. PURPOSE: The purpose of this in vitro study was to measure and compare the different strains placed upon the bone around implants by 9 different abutments for cement-retained crowns on an implant with an internal hexagonal platform. MATERIAL AND METHODS: Nine 4.1×11.5-mm tapered screw-vent implants were placed into a 305×51×8-mm resin block for strain measurements. Five abutment specimens of each of the 9 different abutments (N=45) were evaluated with 1 of the 9 implants. Monolithic zirconia crowns were then fabricated for each of the 9 different abutments, the crowns were cyclically loaded (maximum force 225 N) at 30 degrees, twice at a frequency of 2 Hz, and the strain was measured and recorded. The strain to the resin block was determined using a 3-dimensional digital image correlation (3D DIC) technique. Commercial image correlation software was used to analyze the strain around the implants. Data for maximal and minimal principal strains were compared using analysis of variance with a Tukey-Kramer post hoc test (α=.05). RESULTS: Strain measurements showed no significant differences among any of the abutments for minimal (compression) principal strains (P>.05). For maximal (tensile) principal strains, the zirconia abutment showed the highest, and the patient-specific abutment showed the second-highest strain around the implant, with the zirconia being significantly greater than all abutments, with the exception of the patient-specific abutment, and the patient-specific abutment being significantly greater than the straight contoured abutment in titanium and also zirconia (P<.05). CONCLUSIONS: The name brand patient specific titanium and Atlantis zirconia abutments conferred the most tensile strain to the implants. When selecting an abutment for a cement-retained crown on a tapered screw-vent implant, practitioners should consider the abutment material and the manufacturer of the abutment because not all abutments that fit in an individual implant transmit the strains in the same way.

Load to failure of different titanium abutments for an internal hexagon implant.

STATEMENT OF PROBLEM: Several aftermarket abutments are available for a commonly used internal hexagonal connection implant. However, their load to failure performance is unknown when compared with the manufacturer's abutment. PURPOSE: The purpose of this in vitro study was to conduct a load to failure comparison of 5 different titanium abutments (manufacturer's and aftermarket) for cement-retained restorations used on an implant with an internal hexagon connection. MATERIAL AND METHODS: Five implants (Tapered Screw-Vent, 4.1×11.5 mm; Zimmer Dental) were individually secured in a loading apparatus, and 3 abutment specimens of each of the 5 different titanium abutments (Atlantis, AstraTech TiDesign, Legacy Straight Contoured, Inclusive Custom, and Zimmer PSA) (n=15 total) were loaded at a 30-degree angle until fracture of the implant abutment complex. Data for load to fracture were compared with analysis of variance and a Tukey-Kramer post hoc test (α=.05). RESULTS: Significant differences were noted between the fracture loads of some abutment pairs; Atlantis-AstraTech TiDesign, Atlantis-Legacy Straight Contoured, AstraTech TiDesign-Legacy Straight Contoured, Inclusive Custom-AstraTech TiDesign, and Inclusive Custom-Legacy Straight Contoured (P<.05). The highest overall resistance to fracture was achieved by the Legacy Straight Contoured Abutment, which was significantly greater than all other aftermarket abutments (P<.05). Tested abutments fractured at an average of 649.17 N. The Zimmer PSA abutment was the only abutment that showed no fracture of any of the components before implant failure. CONCLUSION: When comparing manufacturer's versus aftermarket brands, the manufacturer's abutment (Zimmer PSA) was the only abutment without fracture of any of the components. Aftermarket brands experienced screw fractures, which could result in further clinical prosthetic complications. The clinical implications of these findings need further investigation.

Load to failure of different zirconia abutments for an internal hexagon implant.

STATEMENT OF PROBLEM: Various zirconia abutment designs are available to restore implant systems. Fracture resistance is one of the criteria involved in selecting among these options. PURPOSE: The purpose of this in vitro study was to measure and compare load to failure for 5 zirconia abutments for an internally hexagon implant. MATERIAL AND METHODS: Five 4.1×11.5-mm Zimmer tapered screw-vent implants were individually secured in a loading apparatus, and 3 specimens of each of the 5 different abutments (Zimmer Contour with a Ti ring, anatomic-contour Atlantis-Zr, anatomic-contour Inclusive-Zr, anatomic-contour Astra Tech ZirDesign, Legacy Straight Contoured abutment with Ti core) (N=15) were loaded at a 30-degree angle until the implant abutment complex failed. Data for load to failure were compared with analysis of variance and a Tukey-Kramer post hoc test (α=.05). RESULTS: The custom anatomic-contour abutment (Inclusive) showed the lowest load to fracture, and the stock anatomic-contour (AstraTech ZirDesign) the second lowest load to fracture. These were significantly lower than all other abutments (P<.05). The highest overall fracture strength was of a zirconia abutment with a titanium core-hexagon (Legacy Straight Contoured), which was significantly greater than all other abutments (P<.05). Anatomic-contour zirconia abutments fractured at an average of 275 N compared with the average fracture load of 842 N for zirconia abutments with titanium component (P<.05). CONCLUSION: The stock zirconia abutment with a titanium ring and the zirconia abutment with a titanium core-hexagon (Legacy Straight Contoured) had significantly greater fracture resistance than that of any of the 1-piece anatomic-contour zirconia abutments tested.

Identification and characterization of mutants capable of rapid seed germination at 10 degrees C from activation-tagged lines of Arabidopsis thaliana.

Five cold temperature germinating (ctg) mutants, completing germination at 10 degrees C faster than wild type, have been recovered from activation-tagged populations of Arabidopsis thaliana. Three (ctg10-D, 41-D, and 144-D) were tagged and segregated 3:1 for BASTA resistance in the F2 when crossed with wild type. None of the tagged ctg mutants was disturbed in sensitivity to abscisic acid or glucose but all were less sensitive to GA4+7 and osmoticum. The other two mutants (ctg156 and ctg225) were recessive, BASTA sensitive, and exhibited a transparent testa (tt) phenotype. They were more sensitive to abscisic acid, paclobutrazol, and GA4+7 than wild type but had similar sensitivity to osmoticum. Dimethylaminocinnamaldehyde staining of seeds from the two tt mutants, compared with stained seeds from the publicly available tt lines 1-10, suggested that ctg156 was a new allele of tt1, while ctg225 was similar to tt7-1. However, reciprocal crosses determined that ctg156 was not allelic to tt1 while ctg225 was a new allele of tt7. When the gene was sequenced from ctg225 it was missing 10 bp in the second exon, resulting in the incorporation of two spurious amino acids (G282E and D283A) followed by a stop. The screen successfully recovered mutants completing germination faster than wild type at 10 degrees C.