Growth regulation, plastid differentiation and the development of a photosynthetic system in cultured carrot root explants as influenced by exogenous sucrose and various phytohormones

Chromoplasts, which exist in the cells of freshly isolated carrot root explants, seemed to be transformed in thylakoid containing plastids, and chlorophyll formation was initiated if the explants were cultured in a liquid medium containing inositol and IAA as a hormonal supplement. This process was intensified when kinetin was also added, but no dependence on a sucrose supply could be found.A sucrose supply of 2% in conjunction with the combination of all three hormones, however, was needed to achieve maximal thylakoid formation including stacking in individual chloroplasts and for the very extensive chloroplast multiplication in explants growing with high cell division activity. It should be noted that the number of plastids per cell is strongly increased by the sucrose supplement which leads also to starch accumulation. However, no transformation into chloroplasts occurred without the hormonal stimulus.