Overlapping expression of cytosolic glutamine synthetase and phenylalanine ammonia-lyase in immature leaf blades of rice

In order to estimate whether cytosolic glutamine synthetase (GSI; EC 6.3.1.2) is partly coupled to the reaction of phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) in developing organs of rice (Oryza sativa L.), we compared the expression pattern of transcripts and proteins for GSI and PAL in the tissue sections from leaf blades at various stages of development. In immature vascular bundles of unexpanded leaf blades, GSI mRNA was mainly detected in xylem parenchyma cells, mestome-sheath cells, and sclerenchyma cells. PAL transcripts were also accumulated in these cell types. Vascular bundles in midribs; of immature leaf blades contained mRNAs and proteins for both GSI and PAL abundantly in sclerenchyma cells, although distribution of these two proteins was not completely overlapped. In immature vascular bundles in midribs, lignin deposition was observed in cell walls of xylem parenchyma cells, mestome-sheath cells and sclerenchyma cells. These results implied that a part of GSI in unexpanded leaf blades is possibly involved in reassimilation of ammonia released from PAL reaction during the lignin production.