In situ hybridization study of the rice phloem thioredoxin h mRNA accumulation – possible involvement in the differentiation of vascular tissues

Thioredoxin (TRX) h was identified as a major protein in rice ( Oryza sativa L. cv. Kantou) phloem sap. Accumulation of TRX h mRNA in fully expanded rice leaves was detected only in the companion cells. To clarify the role of TRX h in phloem development, we performed in situ hybridization of TRX h mRNA in rice plants during the course of vascular development. TRX h mRNA was detected in all cell types at an early stage of development and became gradually confined to the companion cells in later stages. The possible roles of TRX h in vascular development are discussed.