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David Gopaulchan, Adrian M. Lennon and Pathmanathan Umaharan

Anthurium (Anthurium andraeanum) is a tropical ornamental valued for its colorful spathe (modified bract) that subtends the inflorescence. The present genetic model for spathe color inheritance in anthurium does not account for differences among the red- and pink-spathed cultivars or for differences in the shades of pink among pink cultivars. To identify the mechanisms responsible for the variation in color and intensity, five genetically defined pink-spathed cultivars, with respect to the O, R, and M loci, with varying shade intensities, along with a genetically defined red-spathed cultivar (control), were analyzed at the mRNA, protein, chemical, and phenotypic levels at different spathe development stages. Spathe color values were recorded based on CIE L*a*b* system. Intensity of color (L*, which represents lightness) correlated with the anthocyanin content, with L* showing a strong negative relationship with anthocyanin abundance. Additionally, the red spathe accumulated anthocyanin throughout the spathe developmental stages, whereas the pinks either produced anthocyanin at early stages of development, which decreased as the spathe matured or showed a marked delay in anthocyanin accumulation. The level of anthocyanin closely mirrored flavonoid 3′-hydroxylase (F3H) expression but did not correspond with the expression of any of the other genes assayed, chalcone synthase (CHS), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), and anthocyanidin synthase (ANS). It was found that earlier the expression and higher the rate of expression of F3H during spathe development, the greater the accumulation of anthocyanin in the spathe. Differences in the a* color space parameter among cultivars also suggests that qualitative differences in color could be mediated through F3H. Other ancillary mechanisms that down regulate F3H, ANS, and DFR expression levels, evident in some pink cultivars, are discussed.

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Aidan D. Farrell, Sarah Evelyn, Adrian M. Lennon and Pathmanathan Umaharan

The role of water status in determining vase life was investigated in three Anthurium andraeanum Hort. cultivars: Spirit, Success, and Honduras. The cultivars were selected based on their vase life in previous studies and designated as ‘Vshort’, ‘Vmed’ and ‘Vlong’ respectively. A timeline experiment observing spadix necrosis (bloom degradation) under controlled conditions determined end of vase life as 15, 18, and 36 days for Vshort, Vmed and Vlong respectively. Spathe relative water content (RWC) was closely associated with bloom degradation with all three cultivars reaching end of vase life at ≈75% spathe RWC. Membrane integrity of the spathe showed no association with bloom degradation before the end of vase life with increased ion leakage found only after spadix necrosis was visible, indicating that bloom degradation was driven by spathe water status rather than senescence induced by other factors. RWC of the peduncle base and apex showed no association with bloom degradation in any of the cultivars. In fact, base and apex RWC remained high throughout the experiment despite the consistent loss of spathe RWC. This suggests that the reduced water content of the spathe was not induced by reduced hydraulic conductance of the peduncle. Stomatal conductance (g S) was highest in Vshort (approximately twice that of Vlong) and likely contributed to the rapid loss of spathe RWC in this cultivar. However, Vmed and Vlong had similar g S rates and water uptake rates despite large differences in spathe RWC. Thus, the two cultivars differed in their ability to retain water within the spathe tissue. In all three cultivars, end of vase life was determined by spathe water status. Genotypic variation in vase life was not driven by differences in the hydraulic conductance of the peduncle as previously thought. Differences in spathe water status were partially explained by differences in g S but other factors were also involved.

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Omaira Avila-Rostant, Adrian M. Lennon and Pathmanathan Umaharan

The relationship between vacuolar pH in Anthurium andraeanum (Hort.) and spathe color, cultivar, developmental stage, spathe location, spathe surface differences, and time after harvest was investigated with the overall long-term objective of developing a methodology for engineering blue-colored spathes. Chromospectral analysis of the pigmentation was also studied. Six experiments were conducted involving 23 cultivars of anthurium with each experiment arranged in a randomized complete block design with five replications. Spathe color was associated with vacuolar pH with the whites and greens having the highest pH (average 5.65) followed by corals (5.38), pinks (5.20), reds (5.10), and oranges (4.5). In general, there was correspondence between the lightness of the pigmentation (L*) and the pH values with the lighter colors having higher pH values. There were, however, significant differences among cultivars within the color groups. Whereas spathe pH decreased with aging, there was no difference in the spectral data, suggesting that factors other than anthocyanin content may be contributing to the pH difference. There were no differences in pH between locations sampled on the spathe nor between the spathe surfaces provided there were no differences in color intensity (L*). The pH increased with vase life in two of three cultivars tested with pH values showing an association with increases in a* and b* (chromospectral data) reflecting a bluing effect. The importance of the results to engineering blue-colored spathes in anthurium is discussed.

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Fazeeda N. Hosein, Adrian M. Lennon and Pathmanathan Umaharan

Gene function studies in anthurium (Anthurium andraeanum) have been hindered by the low efficiency of stable transformation, the long regeneration time required as well as the genotype-dependent nature of Agrobacterium (Agrobacterium tumemaciens)-mediated transformation protocols. Agrobacterium-mediated transient expression assays can serve as an attractive alternative for investigating gene function once such assays are optimized. The effects of host factors (genotype, explant type, and developmental maturity of explants), Agrobacterium factors (strain, growth phase, and its concentration), media conditions (infiltration medium used, acetosyringone concentration, type of surfactant, and its concentration), and other experimental factors (infiltration time, cocultivation time, and vacuum infiltration) were investigated on the efficiency of Agrobacterium transient transformation, with replications, using transient expression of β-glucuronidase as an indicator. Although the efficiency of transient transformation was initially found to be highly host genotype-dependent, the genotypic differences in transient transformation efficiency diminished as the protocol was optimized. Agrobacterium strain GV3101 grown to an optical density at 600 nM (OD600) of 1.5 and resuspended to a final OD600 of 0.8 in infiltration medium [0.5% glucose, 10 mm 2-(N-morpholino) ethanesulfonic acid] supplemented with 100 μM acetosyringone and 0.05% of a non-ionic surfactant (S240), for an infiltration period of 16 hours and a cocultivation timeframe of 2 days yielded transient transformation efficiencies as high as 100%.