What Pigments Give Roses Their Color?
The color of roses is primarily determined by two types of pigments: anthocyanins and carotenoids.
What Are Anthocyanins?
Anthocyanins are responsible for the red, pink, purple, and blue colors in roses. These pigments belong to the flavonoid family and are water-soluble, residing in the cell vacuoles. The color expressed by anthocyanins is highly pH-dependent:
– In acidic conditions, anthocyanins appear red or orange.
– In neutral to weakly acidic conditions, they appear purple or violet.
– In alkaline conditions, they appear blue.
The biosynthesis of anthocyanins involves several key enzymes, including chalcone synthase (CHS), dihydroflavonol 4-reductase (DFR), and anthocyanidin synthase (ANS). These enzymes catalyze the conversion of flavonoids into anthocyanidins, which are then glycosylated by specific glycosyltransferases, such as UDP glucose:flavonoid 3-O-glucosyltransferase (3GT) and UDP-glucose:anthocyanidin 5,3-O-glycosyltransferase (RhGT1).
What Are Carotenoids?
Carotenoids are responsible for the yellow and orange colors in roses. These pigments are hydrophobic and located in the chromoplasts. The main carotenoids in roses include lycopene, antheraxanthin, and violaxanthin. The structure and breeding history of the rose influence the types of carotenoids present, with different varieties having distinct carotenoid profiles.
How Do Genetic Factors Influence Rose Color?
The color expression in roses is influenced by genetic variations that affect the anthocyanin and carotenoid biosynthetic pathways.
What Genes Are Involved in Anthocyanin Biosynthesis?
Key genes involved in the anthocyanin biosynthesis include:
– CHS (Chalcone Synthase): Initiates the flavonoid pathway.
– DFR (Dihydroflavonol 4-Reductase): Converts dihydroflavonols to leucoanthocyanidins.
– ANS (Anthocyanidin Synthase): Converts leucoanthocyanidins to anthocyanidins.
– 3GT and RhGT1: Glycosylate anthocyanidins to form stable anthocyanins.
How Does Inheritance Affect Rose Color?
The inheritance of flower color in roses is complex and involves multiple genes. For example, the presence and combination of different anthocyanins and their glycosylation patterns determine the final flower color. Studies on miniature roses have shown that the coordinated upregulation of genes such as CHS, DFR, FLS, and specific glycosyltransferases is crucial for anthocyanin synthesis and accumulation.
How Do Environmental Factors Influence Rose Color?
Environmental factors significantly influence the color of roses.
How Does Soil pH Affect Rose Color?
Soil pH affects the availability of nutrients and can influence the pH of the cell sap in rose petals. Higher pH levels in the cell sap can cause structural modifications in anthocyanins, leading to a shift from red to blue colors. This is because higher pH levels increase the formation of complexes between anthocyanins and other flavonoids, resulting in bluish hues.
How Does Light Exposure Affect Rose Color?
Light exposure can influence the synthesis and degradation of pigments. For instance, high light intensity can increase the production of anthocyanins as a protective mechanism against excessive light. However, prolonged exposure to high light can also lead to the degradation of these pigments, affecting the flower color.
How Does Temperature Affect Rose Color?
Temperature affects the rate of biochemical reactions involved in pigment synthesis. Optimal temperatures for anthocyanin production vary among rose cultivars, but generally, moderate temperatures support the best color development. Extreme temperatures can disrupt pigment synthesis and stability, leading to color changes or fading.
How Do Rose Cultivars Differ in Color?
Examples of Rose Cultivars
- ‘Mercedes’ Rose: This red rose cultivar exhibits a significant change in color during senescence, with the petals fading to a bluish color due to an increase in cell sap pH and the formation of ammonia.
- ‘Neptune King’ and ‘Queen’ Roses: These miniature rose cultivars have different color traits due to variations in the anthocyanin biosynthetic pathway. ‘Neptune King’ has light pink petals, while ‘Queen’ has deep pink petals, resulting from differences in the expression levels of key genes such as CHS, DFR, and specific glycosyltransferases.
How Do Growth Conditions Affect Color Stability?
The growth conditions, including soil quality, light exposure, and temperature, can affect the color stability of rose cultivars. Roses grown in conditions with optimal light and temperature tend to have more vibrant and stable colors. Postharvest care, such as maintaining the right pH and nutrient levels in the water, can also influence the color stability of cut roses.
Reference:
1. Schmitzer, V., Veberic, R., Osterc, G., & Stampar, F. (2010). Color and phenolic content changes during flower development in rose (Rosa hybrida L.). Journal of the American Society for Horticultural Science, 135(3), 195-202.
2. Forkmann, G., & Heller, W. (1999). Biosynthesis of flavonoids. In Comprehensive natural products chemistry (Vol. 1, pp. 713-748). Elsevier.
3. Harborne, J. B. (1967). Comparative biochemistry of the flavonoids-I. Distribution of chalcone and aurone pigments in plants. Phytochemistry, 6(9), 1107-1113.
4. Grotewold, E. (2006). The genetics and biochemistry of floral pigments. Annu. Rev. Plant Biol., 57, 761-780.
5. Katsumoto, Y., Fukuchi-Mizutani, M., Fukui, Y., Brugliera, F., Holton, T. A., Karan, M., … & Tanaka, Y. (2007). Engineering of the rose flavonoid biosynthetic pathway successfully generated blue-hued flowers accumulating delphinidin. Plant and Cell Physiology, 48(11), 1589-1600.
