rebaudioside-a and gibberellic-acid

Steviol glycosides (SGs) and gibberellic acids share a part of their biosynthesis pathways. Despite the widespread studies on the effect of gibberellic acid 3 (GA

Topics: Benzyl Compounds; Cytokinins; Diterpenes, Kaurane; Gibberellins; Glucosides; Kinetin; Plant Leaves; Plant Shoots; Purines; Stevia

Stevia (Stevia rebaudiana B.) has auxiliary buds that often remain dormant for a long time and sometimes remain dormant until the plants change at the reproductive stage. This study was designed out to investigate whether decapitation and exogenous application of plant growth regulators enhance the productivity of stevia through breaking the apical dominance and increasing physiological characteristics. Experiment was carried out as a factorial in randomized complete block design with three replications. Factors were consisted two agricultural practices (Decapitation and No-decapitation) and eight foliar spray including without spray as control, water spray, GA3 (300, 600 and 900 µm) and CK (100, 200 and 400 µm). The results of the present investigation indicated a positive response on number of branches and leaves, leaves and stem fresh weight and total dry weight, in both harvests not only from the decapitation of apical buds but also from foliar application of CK (400 µM). Thus, it can be concluded that the decapitation practices in conjunction with foliar application of CK (400 µM) could be used to increase the dry-leaf yield of stevia. However, further studies are required to standardize the dose of CK (400 µM) to improve the yield and quality of stevia.

Topics: Carotenoids; Chlorophyll; Cytokinins; Gibberellins; Plant Growth Regulators; Plant Leaves; Plant Stems; Stevia; Water

The sweet steviol glycosides found in the leaves of Stevia rebaudiana Bert. are derived from the diterpene steviol which is produced from a branch of the gibberellic acid (GA) biosynthetic pathway. An understanding of the spatial organisation of the two pathways including subcellular compartmentation provides important insight for the metabolic engineering of steviol glycosides as well as other secondary metabolites in plants. The final step of GA biosynthesis, before the branch point for steviol production, is the formation of (-)-kaurenoic acid from (-)-kaurene, catalysed by kaurene oxidase (KO). Downstream of this, the first committed step in steviol glycoside synthesis is the hydroxylation of kaurenoic acid to form steviol which is then sequentially glucosylated by a series of UDP-glucosyltransferases (UGTs) to produce the variety of steviol glycosides. The subcellular location of KO and three of the UGTs involved in steviol glycoside biosynthesis was investigated by expression of GFP fusions and cell fractionation which revealed KO to be associated with the endoplasmic reticulum and the UGTs in the cytoplasm. It has also been shown by expressing the Stevia UGTs in Arabidopsis that the pathway can be partially reconstituted by recruitment of a native Arabidopsis glucosyltransferase.

Topics: Arabidopsis; Arabidopsis Proteins; Cell Fractionation; Cloning, Molecular; Cytochrome P-450 Enzyme System; Cytoplasm; Diterpenes, Kaurane; Endoplasmic Reticulum; Gibberellins; Glucosyltransferases; Glycosides; Green Fluorescent Proteins; Oxygenases; Plant Proteins; Plants, Genetically Modified; Recombinant Fusion Proteins; Stevia