Abstract:Photomorphogenetic phenomena of excised roots of various plants cultured aseptically in White medium were studied. Continuous white fluorescent light (3000 lx) could generally inhibit extension growth of the primary roots and lateral roots, depress emergence of lateral roots and raise of fresh weight of roots. If greening of the roots could be induced by light, however, the light would increase the fresh weight and formation of lateral roots. Addition of 75 mg/l inositol significantly improved root development. Continuous irradiation stimulated greening of excised roots from some plants (e. g. cucumber, bird rape, India mustard and maize) depending on their hereditary potency. Chlorophyll a, chlorophyll b and carotenoids accumulated slowly. After 1 day or 5 days under the light, chlorophyll or carotenoids could be detected separately. Total amount of plastid pigments per unit of fresh weight in roots was much lower than in leaves. More sucrose applied could pro- mote synthesis of chlorophyll and growth of roots. Chloroplasts appeared in small parenchyma cells located in the stele. They did not come frorn proplastid, but were transformed from a kind of leueoplast-amyloplast. Electron microscopic photographes indicated that starch grains diminished gradually while lamella structure appeared first within enveloped and then filled inner-space of plastid. Many thylakoids stacked to form irregular-shaped gram. These chloroplasts seemed to be different from those in mesophyll. Special inhibitor of carotenoid biosynthesis (norflurazon) prevented chlorophyll synthesis with high efficiency while another photosynthetic inhibitor (motoxuron) increased chlorophyll accumulation in isolated roots.