Addition of 2,4-D Enhances Excretion of Barley Lectin in Transgenic Tobacco Cells of Vacuole Targeting Signal Deleted Mutant

A suspension culture of tobacco cells was transformed with a gene encoding barley lectin to obtain an efficient production system of lectin. Lectin excreting transgenic tobacco was constructed by transformation with barley lectin deleted of the C-terminal vacuole targeting peptide (CTPP). 2, 4-Dichlorophenoxyacetic acid (2, 4-D) was examined for its effect on the excretion of lectin at different concentrations from 0 to 5mgl-1. 2, 4-D addition increased excretion efficiency, defined as the amount of excreted lectin per cell, but reduced the growth rate. Microscopic observations showed loosening of the cell wall, which is assumed to be one of the causes of the enhanced excretion. Decrease in extracellular lectin was observed in spite of the growth of cells, which was confirmed to be caused by a degradation process in the culture medium. These results suggest that an efficient production process of lectin would include a process of simultaneously removing culture medium with high lectin content before degradation occurs and maintaining the cells at high excretion efficiency.