Accumulation pattern of steviol glycosides in Stevia rebaudiana Bertoni and its stimulation by red-light

The leaves of the Paraguayan herb Stevia rebaudiana Bertoni contain at least 30 steviol glycosides (SVglys), of which ST, Reb A, Reb C and Dul A accumulate the most. The accumulation of these SVglys occurs within different plant parts and is dependent on numerous environmental, agronomic and physiological factors. It is generally known that the greatest content of SVglys is reached when the plant moves from the budding phase to an initial flowering stage with less than 10% flowers. Very large amounts are found within the upper leaves during the budding phase. As more and more buds grow into flowers, leaves contain lesser amounts of SVglys. The spatial and temporal accumulation pattern of SVglys during ontogeny of Stevia rebaudiana is discussed as it unfolds within plants grown under greenhouse conditions, both in long and short days. It is also known that Stevia rebaudiana is an obligate short-day plant with a critical day-length of about 13 hours. Growing plants under long-day conditions (16 hour photoperiod) slows the growth, delays the flowering stage and results in a greater accumulation of SVglys. A model is presented to easily simulate long-day conditions using red-light irradiation. Preliminary results are discussed. It is shown that five minutes of red LED light in the middle of each night is enough to facilitate a phytochrome-mediated response which delays flowering and results in a much greater yield of SVglys. The possibility of scaling up this method to a field is also discussed.