Migration of adult spinach chloroplasts in the S-rho space, before and after photoperiodic floral induction

Abstract

Summary The migration of adult chloroplasts isolated from spinach leaves submitted to different photoperiodic treatments was followed in time series through the S-rho space (sedimentation coefficient and density measured in zonal rotors). It was shown that a large S-rho surface is the same for plants in short days of 8 hours (vegetative state), in continuous days (fully induced and floral states) and during the mimicked inductive treatment (see Material and methods). In sharp contrast to this, the S-rho surface occupied by the chloroplasts isolated from plants transferred from short days to continuous illumination (floral inductive treatment) is quite specific and significantly different from the other light treatments. The acquisition of the induced state is characterized by a very sharp increase in the sedimentation coefficients of the two chloroplastic subpopulations differing by their densities. After a comparison of these results with the in vivo ultrastructural observations, an interpretation of the events accompanying the acquisition of the floral state in the leaf is proposed. These events can be considered as a transitory change in the regulation control systems of the chloroplasts. If it is assumed that the logics of the vegetative state (steady-state) is different from that of the floral state (another steady-state), then this transition must be accompanied by important disturbances in the system, especially in the energy transducers which are responsible for the maintenance of these steady-states. This transitory period appears as a particular moment in which some negative feedbacks become positive, permitting thus the new floral steady-state and a new equilibrium in the structuro-functional relationships to take place.