Sugar and starch dynamics in the medium-root-leaf system indicate possibilities to optimize plant tissue culture

Sucrose is commonly provided as a carbohydrate source in a plethora of plant tissue cultures to stimulate in vitro plant growth. However, this exogenous supply might compromise photosynthetic performance and hamper the transition from in vitro to in vivo. To evaluate sucrose addition to in vitro media a novel, holistic carbohydrate approach was used in this research taking into account carbohydrate contents in the whole medium-root-leaf system. Therefore in vitro plants of Guzmania 'Hilda' were initially provided with 15, 37, 73 and 117 μmol sucrose g−1 medium. After 4 weeks of plant culture most of the sucrose had been consumed by the plants while significant concentrations of glucose and fructose were measured in the media, indicating invertase activity. Plants growing on higher sucrose enriched media showed higher gains in dry weight and a massive increase of leaf hexose sugars and starch of about 600% in comparison with physiological concentrations. However, this potential advantage was not valorized as no differences in growth were observed during acclimation and on the longer term during 12 months of growth in the greenhouse. On the contrary, the carbohydrate dynamics data indicated that plants originating from high enriched media depend on sugar and starch breakdown during the first weeks after transfer to the greenhouse to enucleate sugar mediated feedback inhibition. Plants originating from low enriched media engage easily in photosynthesis to sustain growth and maintenance. As such, lower enriched media (e.g. 15 μmol g−1 medium instead of 25 μmol g−1 medium) can effectively be used to grow healthy in vitro plants which are able to perform photosynthesis immediately when transferred to the greenhouse, without compromising plant development and growth in the entire production cycle.