Gene Expression in the Developing Barley Leaf Under Varying Light Conditions : The Light-harvesting Chlorophyll A/b Protein and the Small Subunit of Ribulose-1.5-bisphosphate Carboxylase

The expression of proteins within the developmental gradient in wild-type and mutant barley leaves has been studied under different light programs. The analyses have been performed both at the mRNA level by in vitro translation and by separation of proteins. It has been found that in mutant leaves under a normal light cycle, as well as in wild-type leaves under intermittent light conditions, mRNA for light-harvesting chlorophyll a/b protein (LHCP) and the small subunit of ribulose-1.5-bisphosphate carboxylase (RuBPCase) is distributed in the same manner as has been previously described for wild-type barley under a normal light-dark cycle. This observation is surprising considering that, in both cases, LHCP does not accumulate in the membranes. In dark-grown plants as well as in plants grown under intermittent light, synthesis of both LHCP mRNA and protein can be restored in the apical cells of the leaf upon continuous illumination. In such case, integration of LHCP into the membranes occurs without any delay in plants pretreated with intermittent light, in contrast to dark grown plants. For the small subunit of the major soluble protein RuBPCase, no differences in the shape of the gradients both at the level of mRNA or protein have been found under the various light programs, indicating that light exerts only modulating effects on RuBPCase in barley.