genes and flower color (technical)

“These findings indicate that these genes may be involved in the flower color difference in the rose mutants, and competition between anthocyanin and flavonol biosynthesis is a primary cause of flower color variation, with its regulation
reflected by transcriptional and secondary metabolite levels.”


This is an interesting topic that needs more consideration, even by amateur breeders.

For instance, I recently came across this item:

Shisa, M. & Takano, T. The effects of temperature and light on the colour of rose flowers. J. Jap. Hort. Soc. 33: 140-146. 1964.
The formation of red pigments in the hybrid tea variety Crimson Glory was studied in plants growing in a phytotron at temperatures ranging from 10 degrees to 30 degrees C. At 10 and 20 degrees the petals were dark red and resembled velvet, the upper epidermis being much thicker than that of petals treated at 30 degrees. At a day and/or night temperature of 30 degrees, the upper epidermis was flattened and the red colour did not appear.

The point is not merely that ‘Crimson Glory’ loses its color at 30 C. Rather, it is important to recognize that an enzyme involved in synthesizing anthocyanin pigments becomes inactive at 30 C.

Then there is another note from 19th century France describing the color of the “blush” Tea-scented rose as “nankin”, which implies some yellow tint. This is noteworthy because Eugster & Märki-Fischer (1991) reported that ‘Maréchal Niel’ produces a particularly deep yellow carotene only when raised in a greenhouse. I can’t say for sure that the same pigment was involved in both cases, but this is the sort of thing that should be kept in mind.

I have observed that orange roses (the color being derived from pelargonin) are distinctly brighter in low temperatures than high. One possibility, the one that comes to mind, is that the enzyme-step between dihydrokaempferol (precursor of pelargonidin) and dihydroquercetin (precursor of cyanidin and peonidin) is weaker at low temperatures.

Each step in the chain of enzyme-controlled reactions allows variations. This is not simply presence/absence, of course. There are many degrees of alteration that allow environmental conditions (e.g., temperature, light) to alter the effectiveness of the enzyme acting at a specific point in the chain.

An interesting (I think) side note is that the “wingless” fruitflies can grow wings if the larvae are cultured at a temperature of around 75F or higher.

Oh! And sex in crocodilians is determined by ambient temperature at a critical stage of embryonic development. No sex genes or chromosomes at all.

I had a schematic of this series of reactions that lead, ultimately to anthocyanin pigments, but have misplaced it.


Historical note:
The origin of “White Margo Koster” is not at all certain. It seems that white sports have occurred in two or three (maybe more) members of the Koster Clan, and that they have not been kept separate. One obvious reason is that it is more profitable for a nursery to associate a white-flowered sport with the popular ‘Margo Koster’ rather than with the relatively obscure ‘Dick Koster’ (sport parent of Margo Koster).

The form I saw first in Hayward, CA and later at the San Jose Heritage Rose Garden frequently produce a bloom or two or several with some red pigment sectors … about the same red as ‘Mothersday’, another ‘Dick Koster’ sport.

And in my own garden, while in Hayward, I caught ‘Mothersday’ trying to sport to white, at least in part.

Here is a little more info on pigment synthesis, and a brief note on how the change of a single amino acid in an enzyme can alter its substrate specificity … in the case given, the modified enzyme worked more to making pelargonidin than cyanidin.

And the same change in substrate preference has occurred in Rosa rugosa ‘Salmon Pink’. In most roses (aside from R. moyesii and its close kin), glusose is the sugar added to the anthocyanidin skeleton to give it color. But in ‘Salmon Pink’ the glucose transferase sometimes attaches sophorose instead of glucose, and more rarely it attaches rhamnose. The sophoroside form is a bit orangey. I don’t know how the rhamnosidea look in roses, but they give a nice lilac color to an anthurium.

While thinking about the flavonoid pigments, I was reminded of an interesting tidbit about the a role of pelargonidin in human health.

Tsuda T. Mechanism for the peroxynitrite scavenging activity by anthocyanins. FEBS Lett 2000 Nov 10;484(3):207-10.
Pel can protect tyrosine from undergoing nitration through the formation of p-hydroxybenzoic acid and 4-hydroxy-3-nitrobenzoic acid.

I know precious little about brain chemistry, but the above passage suggests that nitration of tyrosine is not a good thing, considering one of the several roles of tyrosine.

According to Wikipedia:
In dopaminergic cells in the brain, tyrosine is converted to L-DOPA by the enzyme tyrosine hydroxylase (TH). TH is the rate-limiting enzyme involved in the synthesis of the neurotransmitter dopamine. Dopamine can then be converted into other catecholamines, such as norepinephrine (noradrenaline) and epinephrine (adrenaline).

So, picking just one thread, the pelargonidin in the strawberries we eat (for example) helps protect tyrosine from nitration, possibly allowing for a greater supply of dopamine. That sounds like a good thing.

A more obscurely written paper from Bertuglia et al. concluded that the anthocyanosides from the Bilberry (Vaccinium myrtillus) improved blood flow in mice overall, and particularly in the smaller vessels. That’s pretty much how Ginkgo biloba supplements are supposed to work.

There’s more, of course.