Up-regulation by phytochrome A of the active protochlorophyllide, Pchlide655, biosynthesis in dicots under far-red light

It is well-documented that phytochrome A (phyA) down-regulates the synthesis of NADPH:protochlorophyllide (Pchlide) oxidoreductase and active Pchlide655 under far-red light (FR). In this work, we demonstrate that phyA can up-regulate the synthesis of Pchlide655 under FR as well and that its sign and extent depend on plant species and tissue. With the use of fluorescence spectroscopy, it was found that [Pchlide655] in the upper stems of FR-grown seedlings of pea and tobacco increased ⩾10-fold and much lower in cotyledons or leaves as compared with the dark-grown. In the upper stems of Arabidopsis and tomato, the positive effect of FR was low, 1.2- to 1.5-fold, and the negative effect of FR was seen in cotyledons. In stems of wild-type (WT) tobacco and its line overexpressing full-length oat phyA (FL), we observed gross stimulating effect of FR while in its line overexpressing N-terminally truncated (Δ7–69) oat phyA (NA) it was low. Because WT and FL comprise both native phyA forms, phyA′ and phyA″, while NA, only phyA″, the regulation under FR can be associated with phyA′, while phyA″ inhibits the action of phyA′. In etiolated seedlings of the NA line, [Pchlide655] was much higher than in those of WT and FL suggesting that phyA″ may have relation to this enhancement. The regulation of Pchlide633 in contrast to Pchlide655 was positive independent of the plant species and tissue.