Growth light substantially affects both primary and secondary metabolic processes in plants.

Common periwinkle ( L.) is an important medicinal plant used by the pharmaceutical industry. The present work aimed to determine the effect of low light intensity on the primary and secondary metabolic processes, using various photosynthesis and targeted and untargeted analytical techniques. Growth light had only limited effects on the photosynthetic electron transport processes, although membrane stability seemed slightly higher in plants growing under higher light conditions. The reduced growth light caused a reduction in certain primary metabolites, including amino acids and sugars, and it also reduced the contents of most of the phenolic compounds investigated in the present experiments. Interestingly, the differences in the growth light caused a much less pronounced difference in the alkaloid contents than that found in the flavonoid contents. However, besides the growth light, genotypic differences, most evident in flower colour, also affected some metabolic processes, including primary and secondary processes.