Transition between seed reserve use and photosynthetic supply during development of maize seedlings

Using the carbon isotope ratio ${}^{13}\text{C}{}^{12}\text{C}$ we have determined the relative importance of carbon flow from the seed reserves and the carbon provided by leaf photosynthetic fixation during the course of development of maize seedlings. The transition from the heterotrophic stage to the autotrophic one corresponds to a growth crisis which occurs on the 10th day in our conditions. During the first 7 days after germination δ ¹³C in leaves and roots is the same as that of the reserve tissues, then a rapid isotropic dilution by incorporation of photosynthetic carbon is observed. The balance between heterotropic and autotrophic carbon is obtained on the 10th day in the leaves but only on the 13th or 14th day in the roots. No autotropic carbon occurs in the roots before the 10th day. It seems that the growth crisis would be due or corresponds, at least partially, to the setting up of translocative function of products from the leaves to the roots.