Figure 7.

Model for the progression of the FR block of greening response. FR block of greening is comprised of two separate phytochrome A-dependent responses that can be separated based on their dependence on WL intensity and their effects on greening and nuclear gene expression. The transcriptionally uncoupled response is WL intensity dependent, results in a partial loss of greening following transfer to WL, and is inhibited by cytokinin, the phyA mutation, and POR overexpression. The transcriptionally coupled response is WL intensity independent, and results in a complete loss of greening ability and an inhibition of HEMA1 and Lhcb gene expression in WL. This response is inhibited by Suc, the phyA mutation, and POR overexpression and requires high fluence rate FRc. ¹Sperling et al. (1997).