Responses of broccoli seedlings to light quality during low-temperature storage in vitro: I. Morphology and survival

Broccoli (Brassica oleracea L. Botrytis group 'Green Duke') seeds were cult ured in vitro photoautotrophically (without sugar in the medium) or photomi xotrophically (with sugar in the medium) for 3 weeks at 23 degrees C and 15 8 mu mol.m(-2).s(-1) photosynthetic photon flux (PPF), Vessels were then st ored at 5 degrees C under 1.6, 4.1, or 8.6 mu mol.m(-2).s(-1) of white (400 -800 nm), red (600-700 nm), or blue (400-500 nm) light. Concentrations of C O, inside the vessels were monitored until equilibrium was reached. Light c ompensation point was reached at 3.5 mu mol.m(-2).s(-1) for photoautotrophi c seedlings and at 6.5 mu mol.m(-2).s(-1) for photomixotrophic seedlings. T herefore, in the long-term storage experiment, seedlings were stored for 4, 8, or 12 weeks at 5 degrees C in darkness or under 5 mu mol.m(-2).s(-1) (a verage light compensation point) of white, red, or blue light. Illumination during storage was necessary to maintain dry mass, leaf area, and regrowth potentials of in vitro seedlings. All seedlings stored in darkness were of poor quality and died when transferred to the greenhouse. Red light during storage increased seedling dry mass and chlorophyll content and improved o verall appearance, whereas blue light decreased chlorophyll content and inc reased stem elongation. The addition of 2% sucrose to media increased dry m ass and leaf area and maintained overall seedling quality during illuminate d storage, However, plantlets stored for more than 4 weeks did not survive poststorage greenhouse conditions, regardless of light treatment.