| Popis: |
Sucrose has been the carbohydrate traditionally used for potato microtuber production. Added to nutrient media, sucrose can act solely as a carbon source, or as an osmoticum, or both. Preliminary tests showed that the osmolarity of sucrose solutions was increased by autoclaving, indicating some breakdown of the sugar. This was taken into consideration in experiments which involved supplementing 4% sucrose media with sucrose, maltose, glucose or fructose, while keeping the osmotic potential of the media constant. A medium concentration of about 400 mM with only sucrose was more suitable for microtuber production than media supplemented with maltose, glucose or fructose. However, a better microtuber yield was obtained when hexoses were added than with unsupplemented 4% sucrose media. When glucose was supplied at concentrations which had the same number of carbon atoms as 8% sucrose, the high osmolarity inhibited microtuberisation. Sugar movement in the tubering plantlet was followed using radio-labelled sucrose, glucose and fructose. The sucrose was translocated and used at a faster rate than the other sugars, which tended to remain in the roots of the plantlets. Furthermore, there was no difference in microtuber production on media to which the sucrose was added before or after autoclaving, indicating that levels of breakdown were not severe enough to affect the process. Therefore, it is concluded that sucrose acts primarily as a suitable carbon source for uptake and utilization by the plantlets, but, at 8%, it also provides a favourable osmolarity for the development of microtubers. |
