Each year over 250 million roses are grown for Valentine's Day. Most of us are either excited to gift one or looking forward to receiving a beautiful rose in full bloom. Roses belong to the Rosaceae family and have about 360 species. They come in a variety of colours from white to red to yellow and blue. The famous red rose is scientifically called Rosa rubiginosa.
According to Greek mythology, the name of this flower emerged when the goddess of beauty, Aphrodite, gave the rose its name in honour of her son, Erose, by rearranging just one letter in his name. Eros then gave the rose to Harpocrates, the god of silence, as a bribe to unveil the weaknesses of the gods. Consequently, the rose not only symbolises love but also secrecy and silence. Another belief is that as Aphrodite's lover, Adonis, died in her arms after a hunting trip, the first red roses were said to have sprung up from the earth as his blood soaked the ground, staining the nearby white roses a deep crimson. This gives reason as to why red roses are inextricably linked to love. On the other hand, white roses symbolise purity, innocence and eternity while yellow roses convey happiness and warmth. Naturally, different colours differ in their symbolism and the stories revolving around them can vary from culture to culture. However, one thing is consistent - their chemistry.
The phytochemicals in roses are responsible for their pigmentation. The yellow colours are produced by carotenoids, the reds by anthocyanins and the orange roses are a mixture of both. Carotenoids produce shades of yellow and orange in roses and at least 75 different carotenoids across 40 different yellow rose species have been identified. Furthermore, a clear relationship between the structure and the breeding partners in roses has been observed. For instance, old yellow roses, which arose from crosses with Chinese varieties, mainly contain carotenoids from the early stages of biosynthesis while in modern yellow roses, which are descended from Central Asian foetida types, hydroxylations, epoxidations and epoxide transformations readily occur, giving the rose its particular shade of yellow. One must note that carotenoids are found in plastids which are like small "compartments" in the plant cells' cytoplasm. Consequently, this makes them stable, making them only slightly affected by environmental factors or plant health.
On the other hand, with respect to red roses, the variety of anthocyanin compounds recorded is limited. In addition, co-pigmentation - this is the interaction of different rose compounds with each other - influences the exact shade of red produced. Unlike carotenoids, anthocyanin is water soluble and found in the plant's sap making them less stable and subject to environmental factors. Anthocyanins have a greater role than carotenoids in the colours of roses since their light absorption extends over a greater part of the spectrum. This means that at short wavelengths, the orange almost coincides with that of the carotenoids, while at long wavelengths the colour extends to a pale lilac. Thus, depending on the amount of light absorbed by this compound and at which wavelength, the rose's shade will vary.
Furthermore, studies have shown that the concentration of anthocyanins in roses varies throughout the plant's maturity together with the sap's pH. As the flower ages from bud to bloom, the sap becomes more alkaline while the anthocyanins concentration decreases. Thus, as the rose ages, the colour deepens. This occurs since high alkaline levels favour blue colourations whereas more acidic conditions lead to a pink/red shade. In saying this, one can now understand why that beautiful red rose in full bloom, darkens to a deep maroon after a few days in the vase.
Additionally, apart from the plant's genetic makeup influencing its colour, anthocyanin levels naturally impact the colour intensity of the rose. It has been observed that in sunlight the levels increase and the colour intensifies. However, overexposure to heat will lead to the degradation of anthocyanins causing the red colour to fade. Furthermore, it is known that anthocyanins interact with metals, making them natural chelating agents. When this compound binds with a metal, it reduces its positive electrically charged ions to a neutral state making it easier to be absorbed by the plant. In layman's terms, metals like zinc and iron, help stabilise the colour of roses. This is why certain rose exhibitors apply zinc to roses to intensify their bloom colour.
However, the beautiful colour of roses is not what entices the occasional buyer to purchase one for their loved ones only. The rose's scent plays a role too leading it to be used commercially to make perfumes, oils and more. The aroma of roses comes from a variety of compounds which are normally present in low concentrations but at thresholds that are high enough to be detected by our olfactory (nasal) receptors. Cis-rose oxide is the compound that gives the rose its characteristic floral fragrance and is surprisingly present at very low concentrations in the air - as little as five parts per billion which is equivalent to 2.5 teaspoons of water in an Olympic-sized swimming pool. The other compounds beta-damascenone, beta-damascone and beta-ionone which are all ketones together with some terpenes like geraniol, nerol, citronellol and farnesol also contribute to the typical aroma of roses, even though they are found in other floral species.
Lastly, just like most flora, roses have important medicinal attributes. Its phytochemicals, including but not limited to flavonoids, glycosides, terpenes, carboxylic acid, myrcene, quercetin, kaempferol and vitamin C contribute to its health benefits ranging from anti-oxidative to sedative to glucose-lowering properties. In herbal medicine, both the petals and fruit (rosehips) of the rose are used. Rose petals are particularly known for their sedative, antiseptic, anti-inflammatory, laxative and anti-parasitic properties while the rosehips which are popularly used in tea, are rich in vitamins C, A, B3, D and E making them a great nutritive supplement. In saying this, they help maintain healthy respiratory function. In fact, a study had shown that this plant was able to reduce the number of coughs induced by citric acid, in guinea pigs. It is believed that this was achievable since the roses' extract and essential oil have a potent relaxant effect which is comparable to that of theophylline on tracheal smooth muscle. This result may also be due to its possible tachykinin inhibitory substance content mediating both bronchodilation and antitussive effects.
Unsurprisingly, R. damascene is known to help with dementia as studies have observed that the chloroformic extract obtained from this species can induce neurite outgrowth activity and inhibit beta-amyloid, which is one of the major contributors to Alzheimer's. The flavonoids in roses are also known to protect against epileptic seizures while its water and methanol extract which are particularly rich in kaempferol 1 and 3-O-beta-D-glucopyranosides 3 and 6 have shown promising activities against HIV.
In conclusion, like most things in nature, the colour, scent and health benefits of roses are heavily determined by their chemistry and thanks to science we can unlock its secrets and understand the how to our why. Hopefully, after reading today's article, the next time you see a rose you can appreciate its beauty and complexity a bit more.
Finally, our final message to you, dear reader, is that we would like to wish you a happy and joyful Valentine's day and whether you received a rose or not, you are still special and loved by someone out there!
Renald Blundell is a biochemist and biotechnologist with a special interest in Natural and Alternative Medicine. He is a professor at the Faculty of Medicine and Surgery, University of Malta.
Emma Camilleri is currently a medical student at the University of Malta.