Genes coding for a putative cell-wall invertase and two putative monosaccharide/H+ transporters are expressed in roots of etiolated Glycine max seedlings

Sink tissues depend on the supply of sugars produced by source tissues. Cell-wall invertases (EC 3.2.1.26) are considered to have a pivotal role in supplying sink tissues with carbohydrates via an apoplasmic pathway, while associated monosaccharide/H+ transporters take up the produced hexoses. In this study, we characterized genes coding for a putative cell-wall invertase (GmCWINV1) and two putative monosaccharide/H+ transporters (GmMST1 and GmMST2) of Glycine max. Semi-quantitative RT-PCR analysis revealed that GmMST1 and GmMST2 are expressed in various plant organs. In situ hybridization revealed that they are expressed in different root tissues. These results propose that different monosaccharide/H+ transporters may play different roles in source and sink organs. In addition, the temporal and spatial expression of GmCWINV1, as was determined by semi-quantitative RT-PCR and in situ hybridization analyses, was detected in tissues where GmMST1 and GmMST2 were also expressed, indicating that, at least part of the sucrose unloaded from soybean phloem may be hydrolyzed into hexoses before being transported from the apoplasmic space into the respective sink cells.