Study of electron-dense thylakoids in chloroplasts of Stevia rebaudiana Bertoni in relation to the biosynthesis of diterpenoids

Abstract

Using transmission electronic microscopy and mass spectrometry electron-dense thylakoids of chloroplasts of Stevia rebaudiana leaves during active vegetable growth of this plant were studied in relation to the biosynthesis of diterpenoid glycosides (DGs). It was found that these compounds are absent in these thylakoids, but they contain a water-insoluble weakly polar ent-kauren, a known biosynthetic precursor of DGs as well as gibberellins. This finding provides a base for the suggestion that similar, electron-dense, thylakoids were observed earlier by other authors in other plant species. These data allowed us to conclude that an intensive biosynthesis of ent-kauren is likely related to adaptation of the short-day plants including Stevia rebaudiana to vegetable growth under the long day conditions.

Impact of cultivation factors in vitro on the growth and the biosynthesis of steviol glycosides in Stevia rebaudiana cell cultures

“…SGs production in mixotrophic callus lines as compared to heterotrophic cultures is significantly activated. This confirms the suggestion on participation of chloroplasts in the biosynthesis of these compounds (Bondarev et al 2001(Bondarev et al , 2014Ladygin et al 2008). However, these organelles in cells of callus tissue have weakly developed membrane structure and by this reason low functional activity.…”

“…Light is an essential cultivating factor as well influencing SGs biosynthesis since its intensity depends, as revealed, on development and the activity of chloroplasts (Ladygin et al 2008). This circumstance is to be quite expected because SGs biosynthesis is initiated in plastids on alternative 1-deoxy-D-xyluloso-5-phosphate pathway of isoprenoids synthesis (Bondarev et al 2014). In our earlier studies, an impact of nutrient medium components (Bondarev et al 2003) and also of the parameters of light irradiation on development of S. rebaudiana shoots in vitro as well as SGs biosynthesis were investigated Bondarev et al 2008Bondarev et al , 2010.…”