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 un der blue or red light. Unlike blue light-grown plants, no tuber develo pment 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 flu x density (170 mu mol m(-2) s(-1)), similar rates of photosynthetic CO 2 fixation were found under red and blue light. Higher leaf starch acc umulation was observed in red light-grown radish plants, whereas the l evel of soluble carbohydrates was lower than in blue light-grown plant s. The absolute contents of several Calvin cycle metabolites were high er in blue light-grown plants,:but the diurnal changes in their levels were similar in leaves of both variants examined. The portion of phot osynthetically fixed carbon accumulated in roots was quantified as 0.5 0 and 0.31 for blue light-grown and red light-grown plants, respective ly. 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 i n blue light-grown plants, which facilitate the development of under-g round storage tissues. Petioles, not roots, were assumed to act as a m ain sink organ in red light-grown radish plants. A less strong sink de mand probably also accounts for reduced assimilatory leaf matter in re d light-grown plants.