Carbohydrate status and transplant quality of micropropagated broccoli plantlets stored under different light environments

Broccoli (Brassica oleracea L. Botrytis Group 'Green Duke') plantlets, which were ready for transplanting after photoautotrophic (sugar-free) culture, were stored for 6 weeks at 5°C under white, red or blue light or under darkness. Storage light intensity was 2 μmol m^-2 s^-1 photosynthetic photon flux (PPF). Regardless of light quality, shoot dry weight remained unchanged when light was present during storage. Light quality affected transplant quality of the plantlets but did not affect CO₂ exchange rate during storage. Stem elongation was observed for plantlets stored in red or blue light. Chlorophyll degradation was more pronounced in red or blue light than in white light or in darkness. The levels of soluble sugars (sucrose, glucose, and fructose) and starch were reduced significantly in dark-stored plantlets, while they were maintained at high levels in light-stored plantlets. Red and blue light enhanced hexose (glucose and fructose) accumulation in stems during storage, which may have caused stem elongation. All plantlets stored in darkness died early during the following acclimatization stage. The plantlets stored in light, however, were acclimatized successfully. Regardless of light quality, illumination during storage maintained dry weight, carbohydrate levels, and therefore, regrowth potential of micropropagated plantlets during storage.