Phytochrome Properties and Biological Action

Genes encoding the small subunit of ribulose-l/5-bisphosphate carboxylase-oxygenase (rbcs) and the chlorophyll a/b binding proteins (cab) have been the focus of many studies on the organization and regulation of plant nuclear genes, rbcs and cab genes are typically light-responsive. In etiolated and dark-adapted tissue transcript abundance is low; following illumination of the plant rbcs and cab transcript abundance increases dramatically (see Tobin & Silverthorne 1985; Kuhlemeier et al., 1987a; Jenkins, 1988). There are however exceptions to this rule in which the transcripts of specific rbcs or cab genes are also present in the dark (Manzara & Gruissem, 1988; Sullivan et al., 1989). Light-responsive genes that exhibit a reciprocal pattern of expression, namely, high transcript levels in the dark and low levels in the light, have also been characterized (Batschauer & Apel, 1984; Lissemore & Quail, 1988; kay et al., 1989; Darrah et al., 1990; Tsai & Coruzzi, 1990; Kay, this volume).