The Physiological Response of Rough Bluegrass (Poa trivialis L.) to Red and Blue Light.

One of the identifying features of rough bluegrass (Poa trivialis L.) is the presence of purple leaf and sheath tissue.  Anthocyanins, the pigments responsible for this purple color, are in demand for their health promoting properties as well as for use as natural food colorants.  Turfgrasses, like rough bluegrass, provide an alternative source for anthocyanins and other flavonoid compounds in that their tissue can be harvested multiple times per month without damaging the entire plant.  Many environmental factors can elicit anthocyanin biosynthesis including light, water stress, temperature stress, and nutrient stress; however, the key factor(s) have still yet to be determined for this species.  Both red and blue light are known to have roles in anthocyanin biosynthesis; on the other hand, some species only respond to one or the other wavelengths or combinations of the two.  The purpose of this research was to determine what wavelength of light, red or blue, stimulates anthocyanin biosynthesis in rough bluegrass.  Historically blue light has been shown to induce anthocyanin synthesis in many species; therefore, a dose response curve for blue light was first generated to determine an appropriate quantum flux.  Results showed that blue light intensities greater than 200 µmol m^-² s^-¹ produced anthocyanin pigmentation.  LED arrays were then constructed to produce blue light gradients ranging from 0 – 100% blue light supplemented with red in order to determine if co-action existed.  Both for seedlings and mature plants, the addition of red light to blue resulted in anthocyanin production when light intensities were set below 200 µmol m^-² s^-¹; however, red light alone did not produce pigmentation.  These results indicate that blue light is sufficient for anthocyanin synthesis, red light is not sufficient, but the combination of the two may result in co-action producing pigmentation at lower light intensities.