Abstract

A recent paper(1) describing the stage‐specific loss of ubiquitin (UBQ) and ubiquitinated proteins (UBQ‐Ps) during pollen development has raised some interesting questions regarding our understanding of the regulation of protein turnover during cellular differentiation and the specialized development of the pollen grain. The authors, Callis and Bedinger(1), describe experiments in which the profiles of free and protein‐conjugated ubiquitin were examined during pollen development. UBQ and UBQ‐Ps were immunologically detected in extracts of microspores and maturing pollen of maize at six developmental stages. Their results remarkably demonstrate that UBQ and UBQ‐Ps decline to barely detectable levels during the final stages of pollen development.