Characterization of the photoreceptor(s) responsible for the regulation ofthe intracellular polyamine level and the putative participation of heterotrimeric G-proteins in the signal transduction chain

In previous publications we have demonstrated a photoregulation of the intr acellular polyamine content during chloroplast development. In the present paper action spectra of the changes in the intracellular polyamine levels o f putrescine (Put),spermidine (Spd) and spermine (Spm) are presented, givin g first evidence for the existence of three photoreceptor systems: a protoc hlorophyllide photoreceptor is possibly responsible for the inhibition of P ut and Spd formation during chloroplast development; a blue-light photorece ptor that probably mediates in general the formation of polyamines, possibl y in the semiquinone form in the case of Spm; and, finally, a red-light (po ssibly the PSII reaction centre) photoreceptor that could be responsible fo r the induction of the polyamine increase. The function and the physiologic al role of these three photoreceptor systems are discussed. Although chloro plast photodevelopment and the inhibition of polyamine biosynthesis have th e same photoreceptor, it seems that this inhibition is not directly linked to the signal transduction chain of chlorophyll biosynthesis. However, ther e are hints that a separate transduction chain, in which heterotrimeric G-p roteins are involved, leads to the inhibition of polyamine biosynthesis. Da rk-grown cultures, supplemented with a non-hydrolysable GTP analogue, GTP-g amma-S, as well as cells treated with cholera (CTX) and pertussis (PTX) tox ins, simulate polyamine changes similar to those of cells grown under light qualities that do not significantly influence chlorophyll biosynthesis. A possible hypothesis for the mode of interaction of polyamine regulation and chloroplast development is presented. (C) 1999 Elsevier Science S.A. All r ights reserved.