Developmental Changes in Nuclease and other Phosphohydrolase Activities in Anthers of Nicotiana tabacum L.

Abstract

Summary Nuclease activity in maturing tobacco anthers is mainly confined to the extracellular fraction and is the lowest in pollen extract. The extracellular fraction further contains phosphodiesterase (exonuclease), 3'- and 5'-nucleotidase and phosphatase activities. The level of enzyme activities exhibits different changes during anther development from the stage of microspore to the maturity. An overall rise occurring after completion of microspore division is followed by a fall of phosphodiesterase, a relative constancy in nucleotidase and a continuous rise of nuclease activities till the stage of almost mature anthers. The nuclease is similar in electrophoretic pattern and in substrate specificity to the earlier described extracellular pollen nuclease classified as plant nuclease I (E.C. 3.1.30.x). The diffusate of mature pollen exhibits as much as 28 % of nuclease activity but less than 4 % of the other phosphohydrolytic activities, with respect to their highest levels in the extracellular anther fraction. Polynucleotide molecules present in this fraction are heterogeneous and of low molecular mass, and the RNA component has high G and low U content, corresponding to the preference of nuclease for poly(U) sequences and to its inability to hydrolyze poly(dG) homopolymers. High nuclease and nucleotidase activities in the extracellular anther fraction coincide with the earlier observed high RNA synthesis and an increase of uptake capacity for uridine in developing pollen. The function of extracellular anther phosphohydrolases is discussed in relation to anther senescence and to pollen maturation.