Features of carthamin synthesis in inflorescences of safflower Carthamus tinctorius L.

Safflower Carthamus tinctorius L., a member of the Asteraceae family, is an important oilseed crop; its seeds are rich in fatty acids, particularly oleic and linoleic. Safflower is also used for ornamental purposes and has been extensively cultivated in many countries for centuries. In recent years, secondary metabolites obtained from safflower inflorescences, particularly flavonoids, have attracted particular interest. Safflower flavonoids can be divided into two groups: specialized flavonoids, represented by quinochalcones, and general ones. Many of these substances significantly influence the color of safflower inflorescences, which changes depending on the flowering stage (from yellow to orange and red at fading). Safflower flavonoids are widely used in medicine and as natural dyes in the manufacture of fabrics, cosmetics, and in the food industry. The process of pigment biosynthesis in inflorescences is still being studied; many stages remain unexplored, and the mechanical aspects of their formation are unknown. Of particular interest is the synthesis of the red pigment, carthamin, a unique dimeric quinochalcone extracted only from orange and red safflower inflorescences. When properly purified, this pigment acquires a metallic golden sheen. A 2021 study used safflower inflorescences for extracting carthamin synthase (CarS) proteins responsible for the final step in converting precarthamin to carthamin. The CarS genes ( CtPOD1 , CtPOD2 , and CtPOD3 ) are expressed in safflower tissues regardless of flower color. Presumably, precarthamin accumulates in corolla cellular structures that are physically separated from the cellular compartment containing CarS. During floral senescence, cells degrade, allowing CarS to interact with precarthamin and form carthamin, which is adsorbed by the corolla cell wall, thereby stabilizing the red pigmentation. This review summarizes data on the specifics of carthamin synthesis, particularly the final step – the conversion of precarthamin to carthamin and its accumulation in inflorescences.