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 cultured photoautotrophically (without sugar) or photomixotrophically (with sugar) in vitro for 3 weeks at 23 degrees C and 150 mu mol.m(-2).s(-1) photosynthetic photon flux (PPF). In vitro seedlings were stored for 0, 4, 8, or 12 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 ability and soluble sugar contents were determined after removal from storage. Photomixotrophic seedlings contained approximately five times more soluble sugars than did photoautotrophic seedlings. Dark storage reduced soluble sugars in both photoautotrophic and photomixotrophic plants, but photosynthetic ability was maintained for up to 8 weeks in the latter whereas it decreased 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 higher in illuminated seedlings. Red light was more effective in increasing or maintaining leaf and stem soluble sugars than was white or blue light. Regardless of media composition or illumination, storage for more than 8 weeks resulted in dramatic losses in quality and recovery, as well as photosynthetic ability. Seedlings stored for 12 weeks completely lost their photosynthetic 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-temperature storage for up to 4 or 8 weeks.