Responses of broccoli seedlings to light quality during low-temperature storage in vitro: II. Sugar content and photosynthetic efficiency

Broccoli (Brassica oleracea L. Botrytis group 'Green Duke') seeds were cult ured photoautotrophically (without sugar) or photomixotrophically (with sug ar) in vitro for 3 weeks at 23 degrees C and 150 mu mol.m(-2).s(-1) photosy nthetic photon flux (PPF). In vitro seedlings were stored for 0, 4, 8, or 1 2 weeks at 5 degrees C in darkness or under 5 mu mol.m(-2).s(-1) of white ( 400-800 nm), blue (400-500 nm), or red (600-700 nm) light. Photosynthetic a bility and soluble sugar contents were determined after removal from storag e. Photomixotrophic seedlings contained approximately five times more solub le sugars than did photoautotrophic seedlings. Dark storage reduced soluble sugars in both photoautotrophic and photomixotrophic plants, but photosynt hetic ability was maintained for up to 8 weeks in the latter whereas it dec reased in the former. Illumination in storage increased leaf soluble sugars in both photoautotrophic and photomixotrophic seedlings. Soluble sugars in stems decreased during storage regardless of illumination, but remained hi gher in illuminated seedlings. Red light was more effective in increasing o r maintaining leaf and stem soluble sugars than was white or blue light. Re gardless of media composition or illumination, storage for more than 8 week s resulted in dramatic losses in quality and recovery, as well as photosynt hetic ability. Seedlings stored for 12 weeks completely lost their photosyn thetic ability regardless of media composition or illumination. The results suggest that carbohydrate, supplied in the media or through illumination, is essential for maintenance of photosynthetic ability during low-temperatu re storage for up to 4 or 8 weeks.