Purple $cience: From Carrots to Crowns
Apparently, girls tend to like purple more than boys. I did. So much that I wore it every day. It was not until the popularization of Barney- that purple Goofus dinosaur- that I stopped wearing purple. This decision was not based on the fact that the guy who played Barney on TV became a tantric sex guru, but because it made one look like a goofus dinosaur. Wearing it is one thing, being it is another. From tea to Prince, purple is in bajillions of “inconspicuousities” of daily life.
Figure 1: Aqueous solutions of cobalt, water, and chloride shift to purple from blue and pink during heating.
Have you ever taken a cobalt hydroxyl solution and mixed it in chloride just see its violet coloring? If so, then props to you for being an uber nerdicus (Figure 1). A Pinterest favorite, the purple family can range from violet to plum, and go from adorning nails and staining bacteria to deciphering social status. In ancient Rome, purple was defined as a privileged rank. In 2018, Pantone deemed it the year of Ultra Violet. UV (ultraviolet) and IR (infrared radiation) sandwich the visible wavelength spectrum. Violet is the shortest visible wavelength, but has the highest energy as it resides at the upper extreme of the visible wavelength. The wavelengths beyond that are not visible to the human eye. So, is purple real or not?
“Am I black or white, am I straight or gay?”
Purple may increase acceptance by others, but it is not an actual color defined by a wavelength on the color spectrum. Wha, wha, what?! ROY G BIV (Figure 2) is that dude Isaac Newton created on a color wheel. Purple is definitely recognized by the visual system that Ewald Hering (1834-1918) proposed in his color opponent theory and both men’s and women’s retinal cones favor this mix of red and blue. For example, the protein expressed by the purple chromoprotein gene in some sea anemones found near Fiji has a purple color because it’s highest absorption of light is at 574nm. Scientists use this gene as a selection marker gene when verifying engineered clones because earthlings can see it.
Figure 2: Spectral wavelengths put the purple family at the far lower end. (Image: Dr. K)
The Math:
Red + Blue = Purple
You like red flowers on your birthday? Thank those healthy flavonoids called anthocyanins (Figure 3) that are stored in plant vacuoles. Similar to playing with paint colors, mixing purple anthocyanins with yellow-orange carotenoids (the C40H56 that makes tomatoes red) yields red flowers. Isn't that just the cutest thing ever?
Figure 3: Chemical structures of anthocyanin. (Image: Quina and Bastos 2018)
It’s in the Genes:
Transgenics using RNAi can produce a dark purple carnation after silencing a red color using RNAi technology. Researchers determined that an amino acid substitution determines the purple-coloring of a flower due to the mutations effect on the amounts of cyanidin anthocyanins (found in grapes and raspberries). Purple carrots have been cultivated for over 3000 years and are also possessors of cyanidin anthocyanins. Their phenols can also lessen the probability of getting breast cancer and treat colitis caused by certain inflammatory inducers (Figure 4). Also, rice bran oil from purple rice can prevent colorectal cancer (Figure 5). Anthocyanins not only impart nutrients for humans, but also protect plants from strong light, heavy metals, and pathogens. Structural genes produce anthocyanins responsible for the purple-ness of purple carrots. Candies, ice cream, and beverages are given their purple color due to the addition of anthocyanins from purple carrots due to the stability provided.
Figure 4: Purple carrots decrease inflammatory response in the colon, thus decreasing colitis. (Image: Kim Y-J et al. 2018)
Figure 5: Spectral analysis of purple rice oil bran using HPLC (high performance liquid chromatography). (Image: Sirithunyalug et al. 2018)
Have you ever been to Lake Cadagno, hung out with bacteria, or chatted with sea urchins? Neither have I, but environmentalists and OBGYN's can thank nerds in Switzerland and Canada for deciphering the genome sequence of purple sulfur bacterium, and deciphering how the XY functions, respectively [Figure 6, left (Luedin SM et al. 2018) and 7, right].
“Purple does something strange to me”
More anthocyanin-carrying purple goodness:
Spilling the tea: Kenyan-produced purple tea assists in decreasing fat accumulation. Losing the last 5 for summer may need some purple.
Happy Hour: Purple potato, a type of sweet potato, is made into a wine, which holds antioxidant activity due to increased levels of anthocyanin present after fermentation. So, drink that wine and lose those wrinkles.
Purple tells us things…
Lab life depends on documenting information from expression models. Staining with visible colors indicates what we are looking for, and importantly, what we are not. Genetic reporters produce blue-purple dye in E.coli transfected with a plasmid detection system where less purple allows indistinguishable characterization of gene expression [Figure 8, left (Tafoya-Ramírez et al.)]. The cell stain Crystal Violet not only stains Gram-positive bacteria, but also detects healthy neuronal cells during cancer treatment. Less purple pigment = cancer cell death (Figure 9, right).
Figure 10: Queen Elizabeth's crown is clad in velvet with diamonds ceded from territories occupied by the British government. (Image: The Royal Collection Trust)
Purple is symbolic for royalty, power, luxury, creativity, and magic, but is also linked with youth and amusement. Check out how excited kids got when singing along with the purple dinosaur, or Queen Elizabeth’s purple velvet Crown from 1937 (Figure 10). Oh, and The Purple One continues to rain… I mean reign (Figure 11).
Figure 11: The Purple One contemplating Purple Rain.
SCIENCE IS ART
Lab Nerds
Bakhshi S and Gilbert E (2015) Red, Purple and Pink: The Colors of Diffusion on Pinterest. PLoS ONE 10(2): e0117148.
Belak ZR et al. (2018) Conserved RNA binding activity of a Yin-Yang 1 homologue in the ova of the purple sea urchin Strongylocentrotus purpuratus. Sci. Rep. 8:8061.
Kim Y-J et al. (2018) Anti-Colitic Effect of Purple Carrot on Dextran Sulfate Sodium (DSS)-Induced Colitis in C57BL/6J Mice. Prev. Nutr. Food Sci. 23(1):77-83.
Luedin SM et al. (2018) Complete genome sequence of “Thiodictyon syntrophicum” sp. nov. strain Cad16T, a photolithoautotrophic purple sulfur bacterium isolated from the alpine meromictic Lake Cadagno. Standards in Genomic Sciences 13:14.
Neuroscience News. (2015) Brain cancer autophagy antidepressants.
Ng J and Smith SD (2016) How to make a red flower: the combinatorial effect of pigments. AoB PLANTS 8: plw013.
Quina FH and Bastos EL (2018) Chemistry inspired by the colors of fruits, flowers and wine. Ann. Braz. Acad. Sci. 90(1): 681-695.
Shih C-H et al. (2015) Purple chromoprotein gene serves as a new selection marker for transgenesis of the microalga Nannochloropsis oculata. PLoS ONE 10(3): e0120780.
Shimoda H et al. (2015) Purple tea and its extract suppress diet-induced fat accumulation in mice and human subjects by inhibiting fat absorption and enhancing hepatic carnitine palmitoyltransferase expression. Int. J. Biomed. Sci. 11(2): 67-75.
Sirithunyalug B et al. (2018) Development of colorectal-targeted dietary supplement tablets containing natural purple rice bran oil as a colorectal chemopreventive. Nutrients 10:444.
Sun H et al. (2018) Antioxidant and prebiotic activity of five peonidin-based anthocyanins extracted from purple sweet potato (Ipomoea batatas (L.) Lam.). Sci. Rep. 8: 5018.
Tafoya-Ramírez et al. (2018) Replacing standard reporters from molecular cloning plasmids with chromoproteins for positive clone selection. Molecules 23: 1328.
Tanaka Y and Brugliera F (2013) Flower colour and cytochromes P450. Phil. Trans. R. Soc. B. 368:20120432.
Xu Z-S et al. (2014) Transcript profiling of structural genes involved in cyanidin-based anthocyanin biosynthesis between purple and non-purple carrot (Daucus carota L.) cultivars reveals distinct patterns. BMC Plant Biology 14:262.
Zhong-Hua L and Jie G (2015) Preparation and antioxidant activity of purple potato wine. Open Biomed Eng J 9:282-287.
