POLLEN MATURATION - WHERE UBIQUITIN IS NOT REQUIRED

A recent paper((1)) describing the stage-specific loss of ubiquitin (U BQ) and ubiquitinated proteins (UBQ-Ps) during pollen development has raised some interesting questions regarding our understanding of the r egulation of protein turnover during cellular differentiation and the specialized development of the pollen grain. The authors, Callis and B edinger((1)), describe experiments in which the profiles of free and p rotein-conjugated ubiquitin were examined during pollen development, U BQ and UBQ-Ps were immunologically detected in extracts of microspores and maturing pollen of maize at six developmental stages. Their resul ts remarkably demonstrate that UBQ and UBQ-Ps decline to barely detect able levels during the final stages of pollen development.