Abstract: Using the scanning electron microscope ( SEM) and ¹⁴C-labelling techniques, the accumulation and distribution of ¹⁴C-photosynthates in bulb development of tulip ( Tulipa gesneriana L. ‘Golden Apeldoorn’) were studied. The starch granules, which were gathering and stuffing in the cell of scales were observed during bulb development. Distribution of ¹⁴C-photosynthates among plant organs was different in various growth stages. At the growth stages before blooming, ¹⁴C-photosynthateswere mainly allocated into leaves and shoot. At the stage of leaf withering, about 66.01% of the total ¹⁴C-photosynthates were transported to bulbs and roots, which indicated that the regenerated bulbs became the main ‘sink’of ¹⁴ C-photosynthates, particularly in daughter bulbs distributed 60.85%. Sink activity of ¹⁴C-photosynthates at stage of leafwithering decreased as followed: bulbs > leaves > shoots > roots. The contents of endogenous GA and IAA in leaves decreased continuously after sprouting. Meanwhile, the ABA content in leaves increased dramatically with a
maximum value of 65.86 ng·g^{- 1} FM at the stage of blooming. Higher GA₃ /ABA ratios in the leaves at stage of frondescence and in the daughter bulbs at the stage of blooming were observed, which indicated that the balance of endogenous phytohormones may be an important factor for the regulation of leaf senescence and the initiation of daughter bulb in tulip.

Key words: Tulip (Tulipa gesneriana L. ), Carbon photosynthate, Starch granule, Endogenous phytohormone