Daily Light Integral Influences Steviol Glycoside Biosynthesis and Relative Abundance of Specific Glycosides in Stevia

Abstract

<jats:p>The biosynthesis of steviol glycosides is affected by both genetic and environmental factors. To evaluate the influence of total daily solar radiation or daily light integral (DLI) under long-day conditions on steviol glycoside concentration, we grew <jats:italic>Stevia rebaudiana</jats:italic> under ambient irradiance or varying levels of shading at different times of the year in both greenhouse and field environments, resulting in DLIs ranging from 3.55 to 20.31 mol·m<jats:sup>−2</jats:sup>·d<jats:sup>−1</jats:sup> in the greenhouse and 10.32 to 39.7 mol·m<jats:sup>−2</jats:sup>·d<jats:sup>−1</jats:sup> in the field. Total steviol glycoside concentration of selected leaves from greenhouse-grown plants increased as DLI increased up to ca. 10 mol·m<jats:sup>−2</jats:sup>·d<jats:sup>−1</jats:sup>, remaining constant with further increases in DLI, and was similar across the range of DLIs evaluated in the field. DLI influenced both the concentration and the relative proportions of specific steviol glycosides. Rebaudioside A concentration increased as DLI increased from 3.55 to 8.53 mol·m<jats:sup>−2</jats:sup>·d<jats:sup>−1</jats:sup>, remaining similar with further increases in DLI. Rebaudioside D and stevioside concentration of selected leaves from field-grown plants decreased by 22% and 13%, respectively, as DLI increased from 10.32 to 39.7 mol·m<jats:sup>−2</jats:sup>·d<jats:sup>−1</jats:sup>, while rebaudioside A and M concentrations remained similar across this DLI range. Collectively, these results indicate that the greatest influence of DLI on steviol glycoside concentration occurs under relatively low DLIs (&lt;10 mol·m<jats:sup>−2</jats:sup>·d<jats:sup>−1</jats:sup>). However, higher DLIs can significantly affect the synthesis of minor glycosides of increasing commercial importance including rebaudioside D.</jats:p>

Do Steviol Glycosides Act Either as a Carbon Storage Pool or in Osmoregulation within Leaves of Stevia rebaudiana?

“…N deficit results in reduced growth, with C diverted to storage in the carbon–nutrient balance hypothesis. A long-term increase in S. rebaudiana leaf SG content associated with increased red light ratio has been reported . A 2-fold higher leaf SG concentration was associated with a seven-week red light break during the night under natural short-day conditions that caused a developmental delay in flowering, as flowering is associated with a decrease in leaf SG concentration .…”

“…Intact plant leaf SG concentrations increased by 20% to 45% with increase in daily light integrals from 3.5 to ca. 10 mol m –2 d –1 over a 13-week period, but not at higher light integrals . An absence of diurnal fluctuation in leaf SG under either increasing or decreasing photoperiods, while leaf glucose and sucrose concentrations fluctuated diurnally by a factor of 3, has been reported .…”

“…A long-term increase in S. rebaudiana leaf SG content associated with increased red light ratio has been reported. 20 A 2-fold higher leaf SG concentration was associated with a seven-week red light break during the night under natural short-day conditions that caused a developmental delay in flowering, as flowering is associated with a decrease in leaf SG concentration. 21 In vitro, higher concentration of medium sucrose (over the range 1% to 5% w/v) led to increased expression of genes that code for steviol synthesis and glycosylation.…”

“…10 mol m −2 d −1 over a 13-week period, but not at higher light integrals. 20 An absence of diurnal fluctuation in leaf SG under either increasing or decreasing photoperiods, while leaf glucose and sucrose concentrations fluctuated diurnally by a factor of 3, has been reported. 23 Likewise, a poor correlation (r 2 < 0.2) between leaf sucrose or glucose and SG concentration across daylength treatments has been reported.…”

Influence of Environmental Parameters, Pinching, and Ethephon Application on Growth and Branching of Potted Stevia

“…Stevia vegetative growth and morphological responses to irradiance and nutrient levels are only partially understood, and information on the influence of temperature on stevia growth and development in controlled environments is lacking. Increasing daily light integral generally decreased plant height and individual leaf area (Evans et al, 2015). For field-grown plants, increasing nitrogen (N) application rate from 30 to 90 kg•ha À1 (the highest level evaluated) increased branch number, dry leaf yield, and dry stem yield (Pal et al, 2015).…”