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

Abstract

Broccoli (Brassica oleracea L. Botrytis group 'Green Duke') seeds were cultured in vitro photoautotrophically (without sugar in the medium) or photomixotrophically (with sugar in the medium) for 3 weeks at 23°C and 150 μmol · m-2 · s-1 photosynthetic photon flux (PPF). Vessels were then stored at 5°C under 1.6, 4.1, or 8.6 μmol · m-2 · s-1 of white (400-800 nm), red (600-700 nm), or blue (400-500 nm) light. Concentrations of CO2 inside the vessels were monitored until equilibrium was reached. Light compensation point was reached at 3.5 μmol · m-2 · s-1 for photoautotrophic seedlings and at 6.5 μmol · m-2 · s-1 for photomixotrophic seedlings. Therefore, in the long-term storage experiment, seedlings were stored for 4, 8, or 12 weeks at 5°C in darkness or under 5 μmol · m-2 · s-1 (average 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 overall appearance, whereas blue light decreased chlorophyll content and increased stem elongation. The addition of 2% sucrose to media increased dry mass and leaf area and maintained overall seedling quality during illuminated storage. However, plantlets stored for more than 4 weeks did not survive poststorage greenhouse conditions, regardless of light treatment.