Development of storage roots in radish (Raphanus sativus) plants as affected by light quality

The development of storage roots was studied in radish plants grown under blue or red light. Unlike blue light-grown plants, no tuber development was found in red light-grown plants. Instead of the storage root formation, a larger development of petioles was observed in red light-grown plants. Reduced leaf matter was found in red light-grown plants compared with blue light-grown ones. At the growth chamber photon flux density (170 mu mol m(-2) s(-1)), similar rates of photosynthetic CO2 fixation were found under red and blue light. Higher leaf starch accumulation was observed in red light-grown radish plants, whereas the level of soluble carbohydrates was lower than in blue light-grown plants. The absolute contents of several Calvin cycle metabolites were higher in blue light-grown plants,:but the diurnal changes in their levels were similar in leaves of both variants examined. The portion of photosynthetically fixed carbon accumulated in roots was quantified as 0.50 and 0.31 for blue light-grown and red light-grown plants, respectively. The levels of two phytohormones, indole-3-acetate and zeatin plus zeatin riboside were found to be several-fold higher in roots of blue light-grown plants compared with red light-grown ones. Thus, the above hormones obviously create a higher sink demand from roots to leaves in blue light-grown plants, which facilitate the development of under-ground storage tissues. Petioles, not roots, were assumed to act as a main sink organ in red light-grown radish plants. A less strong sink demand probably also accounts for reduced assimilatory leaf matter in red light-grown plants.