Patterns of protein synthesis in dividing and auxin-starved soybean cell suspensions. Differential expression of a major group of Mr-17000 peptides.

Auxin starvation of soybean cell suspensions results in the arrest of cell growth after about 4 days. The addition of 4 μM 2,4-D enables cells to divide again after a lag phase of 1 day. By comparing the patterns of in vivo and in vitro protein synthesis, we have identified two sets of polypeptides whose synthesis is positively or negatively regulated by auxin. Several major peptide bands (17, 26, 31, 35, 38 kD) are characteristic of auxin-starved cells. The 17 kD peptide group, containing one major (75%) component, accounts for 6% and 25% of the radiolabeling in vivo of proteins from respectively dividing and auxin-starved cells. Our results suggest the 17 kD major component to be a direct translation product whose synthesis is regulated by the abundance or the activity of the relevant mRNA. The soybean suspension culture system here described provides a model to study auxin-mediated control of gene expression.