Accumulation of a Glycoprotein That is Homologous to a Seed Storage Protein in Mung Bean Hypocotyls at the Late Stage of Tissue Elongation

Physiological changes were examined in the amount of a 50-kDaglycoprotein (gp50) that was recovered in a nuclear fractionfrom hypocotyls of mung bean (Vigna radiata) seedlings. Immunoblotanalysis indicated that the glycoprotein was present in hypocotylsand epicotyls from 4- and 5-day-old seedlings but not in hypocotylsfrom 2-day-old seedlings. The glycoprotein was not detectedin leaves or roots. When we divided hypocotyls of 3-day-oldseedlings into the elongating region (0 to 1.5 cm below thecotyledon) and the mature region, we found gp50 in the matureregion only. The results suggest that the 50-kDa glycoproteinis synthesized de novo and accumulates at the late stage duringelongation of cells in the hypocotyl. Furthermore, an antibodyspecific to gp50 reacted with a major 50-kDa protein in cotyledons,which is known as a storage protein in mung bean cotyledon.Eighteen amino acid residues among 22 amino-terminal residuesof gp50 were identical to those of the storage protein fromcotyledon. A peptide map of the glycoprotein after digestionwith V8 protease was similar to that of the storage protein.Overall, our findings suggest that the glycoprotein recoveredin the nuclear fraction is an isoform of the seed storage proteinthat is expressed only in the mature cells of hypocotyls andepicotyls. ⁴ Present address: Bioscience and Chemistry Division, HokkaidoNational Industrial Research Institute, Agency of IndustrialScience and Technology, Sapporo, 062 Japan